We enter the topic: the basic principles of the paper machine. paper machine

A paper machine is a combination of continuous production sections, as a result of which paper and cardboard are obtained from a fibrous suspension. There are two types of this...

The paper machine is the combination of continuous production sections, as a result of which paper and cardboard are obtained from a fibrous suspension. There are two types of this unit: canteen (with a flat mesh) and cylinder (with a round mesh).

More common table paper machine, with which the main types of paper are made.

The main sections of this design are: mesh, press, drying and finishing parts.

Grid part

The grid part is an endless grid made of synthetic materials or various copper alloys. In this section, a paper web is formed from a highly diluted slurry and the first part of the excess water is removed. These stages occur due to the free flow of the suspension and the suction effect of the register rollers. Further dehydration is carried out using special vacuum pumps.

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press part

After passing through the wire section, the paper web with a dryness percentage of approximately 18-22% enters the press section. Here, excess water is removed by mechanical extraction. The paper is passed through 2-3 roller presses arranged in series under the simultaneous action of vacuum and pressure. At the same time, its bulk density and strength increase, while the absorbency and porosity, on the contrary, decrease. The pressing process takes place between wool felts, which absorb moisture and transport the web, and also perform an important function of protecting the weak paper web from destruction. In order to achieve an increase in the density and smoothness of the paper, additional smoothing presses are often installed.

Drying part

The paper web enters the drying section with a dryness of about 45%. This section of the paper machine consists of rotating cylinders staggered and heated by steam. At this stage of production, the paper web is pressed against heated cylinders with the help of felts, which prevents its wrinkling and warping. Its movement occurs from the lower cylinder to the upper one, then again to the lower one located nearby, etc. The paper in the drying section is dried to a moisture content of 5–7%.

Finishing part

In the finishing section there are 5-10 cast iron chilled rollers located one above the other. The paper, pre-moistened with cold water, moves from top to bottom between the rollers. After passing through this stage, the paper web acquires a flat, smooth surface and uniform thickness. To prevent wrinkling, the canvas is wound into rolls on the reel. If it is necessary to release paper of increased smoothness, additional moisturizing equipment is installed above the reel. The resulting rolls are then fed to a slitting machine, where they are cut into pieces with the required parameters.

Special equipment

The paper machine is also equipped with a large number of automatic devices that ensure its continuous operation. The task of this additional equipment control the technological parameters of the entire process. For the manufacture of various types of paper web, their technically justified parameters are set, namely the operating speed and width of the machine. The paper machine can be narrow or wide.

Narrow machines with a web width of 1.6 to 4.2 m are mainly intended for the production of special technical, high-quality bond papers. Wide machines with a web width of more than 6 m are used for the production of sack and newsprint. The operating speed of the paper machine in the production of newsprint and tissue paper is much higher than the speed in the manufacture of high-quality papers. The presence of special equipment and automatic devices contributes to the accuracy of the paper machine and reduces the number of workers serving it to 3–8 people.

Manufacturing Process Improvement

To further improve the paper production process, it is necessary to change the production technology, increase the productivity of the machine due to the width and speed, and modernize the device of the machine and its components.

To increase the productivity of the paper machine due to speed and width will help:

special high-speed flow distributors that release the fibrous suspension onto the mesh at the speed that is necessary with the increased speed of the mesh;
hydroplanki and register rollers, increasing the removal of moisture;
different kinds presses such as hot and multi-shaft presses, presses with wide suction chambers;
suction rolls fixed in the middle, grooved corrugated rolls, suction vacuum cloth washers;
reels of peripheral type with pneumatic paper web clamp, used for winding a roll of 2200–2500 mm in diameter.

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For the drying section of a paper machine, the following can also be successfully used: siphon removal of condensate, new layouts of steam distributors, higher steam pressure, replacement of dryer felts with dryer nets. Currently, there is an active search for new types of drying, in order to replace the traditional type with a more advanced one, which would increase the uniformity of the drying process and significantly reduce the working area of the drying section. New types of drying such as infrared irradiation, hot air drying, dielectric drying and vacuum drying have good prospects for the future.

The principle of operation of the paper machine

The paper machine is used to make paper from fibrous mass by casting a layer of fibers, followed by dewatering, pressing and winding into a roll. In tsarist Russia, such units began to be used from the second half of the 19th century. They were distinguished by low productivity, poor water separation, and manual control. Repairs required stopping the machines, but they were highly reliable and simple in design. At the Slavuta paper mill, such a unit was installed in 1864 and worked until the end of the 20th century.

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The principle of the machine

There are 2 types of paper machine: canteen - the pulp is distributed on a flat endless grid and cylinder - with a round grid. Table units are mainly used, cardboard and some types of paper are made on cylinder units. The machine is made according to the principle of sequentially installed continuously operating sections:

grid;
press;
drying room;
finishing.

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In addition, there are many auxiliary systems and mechanisms that provide and control a continuous cycle of paper production. The speed of the paper web varies from 40 m/min in the production of thin capacitor paper, up to 1000 m/min in newsprint. This is a very energy-intensive unit that consumes up to 30 MW of electricity and 45 tons of steam. A process control system is used to control the technological process. At such speeds, manual control and adjustment of parameters is impossible.

The paper manufacturing process begins with the preparation of raw materials. For this, a mixing chamber is used, into which the crushed and previously cleaned of foreign objects that are not involved in the process (metal, stones, adhesive tape, etc.) are fed paper components - waste paper, rags. If wood is used, then pre-prepared chips are boiled in a solution of caustic substances until completely dissolved.

The finished stock is pumped from the mixing section to the paper machine pool. The concentration of the incoming medium is 3-4%. In the tank there is a constant mixing of the solution to maintain a homogeneous state of the paper pulp throughout the volume. By supplying recycled water containing cellulose inclusions, the concentration of the prepared solution is adjusted to 0.15-1.5%, it is sent to the treatment equipment. For this, knot catchers, centrifuges and others are used. After that, the paper mass through the inlet device enters the grid.

The quality of the material produced depends on the synchronism of the speeds of the mesh and the outflow of the suspension. The lag of mass movement from the grid should not exceed 5-10%. The deviation of the parameters in one direction or another leads to an uneven distribution of the fibers over the grid area and their orientation in the direction of the web movement. This is reflected in the density, uniformity and strength of the manufactured products.

Paper forming

Sheet shedding is a filtration process in which, as water is removed, a fibrous layer is formed. After passing through the register part of the grid table, a sheet with a mass concentration of about 3% is formed. When such values are reached, the “mirror of the bay” ends and the concepts of “paper, paper web” and its dryness are introduced. The ebb process is most intensive in the register part, located in the first third of the table. Errors made at this stage can no longer be corrected during paper manufacture and will be considered a product defect.

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The quality of the paper ebb and the position of the fibers relative to the direction of flow depend on the nature and concentration of the mass, the speed of the mesh and the outflow of the colloidal solution, and the intensity of water filtration. In turn, these parameters depend and are determined by the purpose of the manufactured products.

In some cases, it becomes necessary to increase the rate of dewatering of the web, for example, to prevent flocculation, that is, the formation of clumps of fibers. The course of this process is largely influenced by the concentration of the mass. At low values, active water filtration occurs, which greatly reduces the likelihood of flocculation.

On the other hand, too much water separation leads to the washing out of fibers, especially fine fractions. Intensively this process occurs in the initial stage of leaf formation. Ultimately, this leads to a decrease in the content of the filler in the lower (grid) side of the sheet. This defect is eliminated by reducing the filtration rate.

The change in the intensity of water separation occurs with an increase in sheet thickness and filtration resistance. This leads to the need to use forced methods of dehydration of the fibrous layer. For this, suction boxes are used. A vacuum is created in them with special pumps, which allows removing moisture that did not have time to drain in the initial stage of paper formation.

The mesh table ends with a device called a suction couch roll. A vacuum of 30-70 kPa is maintained in its chamber, which makes it possible to effectively suck out moisture. Under the couch-shaft there is a bath, into which water is drained and the so-called wet waste is discharged. These are the cut-off edges of the paper web, breaks from the press part, the contents of the mesh table when the paper breaks. An agitator located in the bath transfers the mixture to transfer pumps, which return the solution to the receiving tank for recycling.

press part

After the couch roll, the paper web with a dryness of 15-20% is transferred by a vacuum transfer device to the press section of the paper machine for further mechanical dehydration. It usually consists of 2-3 twin-shaft presses. The upper shaft is made of granite, the lower one is metal lined with rubber. Between them, together with the paper web, the cloth moves, protecting the surface of the wet paper from damage.

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The design of the press mechanism allows the use of sequential passage of different sides of the web between the shafts. This ensures that both sides of the paper are smoothed evenly. A cloth washer is used to remove fibers adhering to the fabric. After successive passage of the press section, the dryness of the paper is 30-40%.

In this section of the machine, not only dewatering takes place, but also the web is compacted. This increases the area of contact and adhesion between the fibers. In addition, paper properties change: strength increases, porosity decreases, transparency increases, etc. The press part must operate at full load, since an increase in dryness by 1% reduces the steam consumption for heating the drying cylinder by 5%. The intensification of these processes can significantly reduce the overall energy consumption, which ultimately affects the cost of products.

Drying the paper web in the press section is 10 times cheaper than in the dryer. Of the total volume of removed water, about 95% falls on the wire part, 3-4% on the press part, and the rest on the drying part. Therefore, the first 2 parts are called wet. To remove the remaining 1-2% of moisture, most of the energy intended for dehydrating the paper web is expended.

Drying part

This section of the machine consists of 2 rows of successively staggered cylinders covered by a drying cloth. The device of the drying cylinder is a hollow cylindrical container, heated from the inside with steam. The pressure of the working environment is 0.35 MPa. The diameter of the drying cylinder is 1500 or 1800 mm, depending on the type of paper being produced.

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The number of cylinders depends on the product type and machine speed. For the manufacture of capacitor paper, 5-8 drums are installed, and for newsprint and bag paper - 50-80. Drying cylinders are combined into 3-5 independent groups, which allows for separate regulation and maintenance of temperature in separate blocks. The scheme of movement of paper and felts provides heating and evaporation of moisture not only when it comes into contact with the heating surface of the drying cylinder, but also during freewheel. The use of an individual drive for each of the groups allows you to synchronize the speeds of neighboring blocks to ensure the smooth movement of the paper web.

Each group provides for the installation of a drying cylinder for felts designed not only to absorb moisture, but also to transport the paper web through this part of the unit. In machines with high paper speeds, the dryer section is completely covered with a hood, allowing heat to be retained without additional use of energy. It is equipped with a forced ventilation system and heat exchangers-recuperators. Heated moist air, before being released into the atmosphere, with its heat heats the supplied medium, which is heated up on the heat exchanger and enters to blow the web.

Depending on the type of paper produced, the temperature of the cylinders is 80-115 °C. During the drying process, up to 2.5 liters of moisture is removed from 1 kg of paper, which is 60-80 times less than on the wire and press parts of the machine. An increase in the heating rate of the drums speeds up the drying process, so it should be carried out at the maximum values of this parameter, which does not affect the quality of the finished product. In drying hoods of high-speed machines, nozzle blowing of the web with heated air is used. This speeds up the dehydration process and reduces energy costs.

The finishing part consists of a calender and reel. It is installed between the drying part and reel and consists of 5-8 horizontally arranged shafts. The lower ones are driven and provide the passage of paper between them. At the same time, it is additionally compacted and smoothed. On the reel, the paper is formed into rolls by weight or diameter and then sent for cutting.

This completes the papermaking process. The use of advanced technologies and automation of the manufacturing process, at web speeds of 1000 m/min or more, made it possible to reduce the maintenance of the unit to 5-8 people.

I bring to your attention my debut article in a new way. It gives the general principles of the paper machine for a more comfortable entry of the translator into the topic.
I ask you to express your wishes on the format for presenting such material.

paper machine(paper machine) - multi-section unit continuous (continuous) of the action on which of strongly diluted (diluted) water fibrous suspension (fibrous suspension) get paper and some kinds cardboard (board).
There are 2 main types of paper machines: flat mesh / table (four-drinier machine) used to make the main types of paper, and circular/cylinder (vat machine), which produce a limited range of paper and cardboard. These types have various devices for release paper pulp (paper/papermaking pulp or stock) on the grid (wire) paper machine and low tide (formation) paper web, the design of the remaining nodes, as well as technological process paper making are similar.
The finished paper pulp with a concentration of about 3-4% is fed with a pump ( feed) from mass preparation department (stock preparation department) in machine pool (machine chest), from where it enters the paper machine. Permanent mixing (agitation) the masses in the engine pool achieve alignment degree of grinding (beating/refining degree) and mass concentration throughout the volume. It is pre-diluted recycled water (white/back water) received from dehydration (dehydration) paper pulp on the grid of the paper machine, to a concentration of 0.1-1.5% and passed through treatment (screening) equipment - knotters ( screen/strainer), centriccleaners (centricleaner), centriscreens (centriscreen), etc., where various foreign inclusions and coarse particles of mineral and fibrous origin are removed. From the cleaning equipment, the paper pulp enters the headbox (headbox), which provides expiration (discharge) mass with a certain speed (rate) and the same thickness jets (jet) over the entire width of the grid.

The paper machine consists of the following main parts:

grid (wire section), where a dilute suspension is continuously molded paper canvas (paper web ) and the first part is removed from it excess water (excess water );
press (press section), where dehydration is performed and seal (compacting) paper webs:
drying room (dryer section), in which the moisture remaining in the paper web is removed:
finishing (finishing section), where the canvas is subjected to the necessary processing to give gloss (glaze), density (density), smoothness (smoothness) and wound in rolls (wind to rails ).

Grid part - an endless mesh woven from threads of various copper alloys or synthetic materials. The grid drive is carried out from couch shaft (couch roll). On new machines with vacuum transfer devices (vacuum pick-up arrangement), the drive shaft is also the main shaft of the grid. To prevent the paper pulp from flowing, the edges of the grid are installed restrictive rulers (guides). The dehydration of the paper pulp and the formation of the paper web occur due to the free flow and suction action (suction) register rollers ( table roll). For a more uniform web of paper in longitudinal (machine/grain direction) and transverse directions (c ross direction ), when the machine speed is not more than 300 m/min, the register part is sometimes subjected to shaking (shake) in the transverse direction. Further dehydration occurs over suction boxes (suction box) under the action of a vacuum created by special vacuum pumps (suction pump). When developing high-grade papers (fine paper) above them are often installed easy comparative roller (Dandy roll). Leveling roller for application watermarks (water marks) is called egutere (egoutteur). After that, the paper web still contains a relatively large amount of moisture (88-90%), to remove which the mesh, together with the paper web, passes over the couch shaft, which has from one to three suction chambers (vacuum chamber). Couch-shaft - perforated hollow cylinder (drum) of bronze alloy or stainless steel (perforation area is about 25% of the shaft surface). Inside the body is a stationary vacuum chamber with graphite seals, which are pneumatically pressed against the inner surface of the cylinder. The vacuum chamber is connected to a continuously operating vacuum pump. The couch roll completes the shaping and dewatering (to a dryness of 18-22%) of the paper web on the wire of the paper machine.

Further dehydration occurs in the press section mechanical extraction under pressure and vacuum by passing the web through several (2-3, less often 4-5) roller presses (roll press) arranged in series (often the first and second presses are combined into double press - two-roll press). At the same time, they increase bulk density (specific density), strength properties (strength properties), transparency (transparency), decrease porosity (porosity) and absorbency (absorption) paper. Pressing is carried out between woolen cloths (felt), which protect the still weak paper from destruction, absorb the squeezed moisture and at the same time transport the web. Each press has its own cloth. On all new high-speed paper machines, the lower press rolls are made perforated (perforated) (like couch shafts). They are covered special rubber (rubber cover), which improves dehydration and increases service life. On some paper machines, instead of lower suction shafts (bottom roll) are set shafts with special grooved corrugation (grooved roll). On powerful paper machines, the lower rolls of the first and second presses are made suction (similar to the couch shaft). Often, in addition to presses with felts, they also install smoothing (or offset) presses (second nip) without felt to compact the paper and make it smooth. Then the paper web with a dryness of up to 45% enters the drying section.

Finishing part is a calender calendar), consisting of 5-10 located one above the other chilled cast iron shafts (cast chilled iron roll). In order to make it more elastic and soft, the paper is preliminarily cooled and slightly moistened on a refrigerating cylinder (through the hollow necks of which cold water). When moving between the shafts from top to bottom, the web becomes smoother, compacted and leveled in thickness. Then the paper is wound with an endless tape into rolls on a forcibly rotated cylinder, against which the roller with the paper wound on it is pressed - reel. To moisten the paper when additional finishing it on supercalenders (supercalender) (to obtain paper with increased smoothness, gloss and bulk) is installed above the reel humidifier (rewetting device). Next, the roll is cut into slitting machine (longitudinal cutter) to the required formats. At the same time, the paper is sorted cliffs (break) that have arisen during its development are glued together. When releasing paper in sheets, the rolls for cutting are fed to the paper web cutting machine - self-tapping screw (sheeter/sheet cutter).

paper machine

a multi-sectional unit of continuous operation, on which paper and some types of cardboard are obtained from a fibrous suspension highly diluted with water ( rice. one ).

Two main types of paper are distinguished: flat-grid (table) paper, which is used to produce the main types of paper, and round-grid (cylinder) paper, which is used to produce a limited assortment of paper and cardboard. These types have different devices for discharging paper pulp onto the paper web and for casting the paper web, while the design of the remaining units, as well as the technological process of making paper, are similar (with the exception of the “dry forming” machine).

On fig. Figure 2 shows a diagram of a flat-grid paper machine, which, along with the machine itself, includes auxiliary equipment designed to prepare paper pulp before feeding it to the wire. The types of auxiliary equipment and their design are extremely diverse.

The finished paper pulp with a concentration of about 3-4% is pumped from the pulp preparation department to the machine pool, from where it enters the paper mill. By constantly stirring the stock in the machine pool, the degree of grinding and mass concentration throughout the entire volume are equalized. It is preliminarily diluted with recycled water (from dehydration of the paper pulp on the B. m. grid to a concentration of 0.1-1.5%) and passed through the cleaning equipment (knotters, centric cleaners, centric screens, etc.), where various foreign inclusions are removed and coarse particles of mineral and fibrous origin. From the cleaning equipment, the paper pulp enters the headbox, which ensures the outflow of the pulp at a certain speed and the same thickness of the jet over the entire width of the grid.

B. m. consists of the following main parts: mesh, where a sheet of paper is continuously formed from a diluted suspension and the first part of excess water is removed from it; press, where the paper web is dehydrated and compacted; dryer, where the moisture remaining in the paper web is removed; finishing, where the web is subjected to the necessary processing to give gloss, density, smoothness and is wound into rolls.

Grid part- endless mesh (woven from threads of various copper alloys or synthetic materials). The mesh drive is carried out from the couch-shaft. On new machines with vacuum transfer devices, the driving shaft of the mesh is also driven. To prevent the paper mass from flowing, restrictive rulers are installed along the edges of the grid. The dehydration of the paper stock and the formation of the web of paper occur due to the free flow and suction action of the register rollers. To obtain a more uniform web of paper in the longitudinal and transverse directions, at a machine speed of not more than 300 m/min, the register part is sometimes subjected to shaking in the transverse direction. Further dehydration takes place above the suction boxes under the action of a vacuum created by special vacuum pumps. When producing high-grade papers, a light leveling roller (eguter) is often installed above them. It also serves to apply watermarks to paper (See Watermark). After that, the paper web still contains a relatively large amount of moisture (88-90%), to remove which the mesh, together with the paper web, passes over the couch shaft (on low-speed couch press machines), which has from one to three suction chambers. Couch-shaft - a perforated hollow cylinder made of bronze alloy or stainless steel (perforation area is about 25% of the shaft surface). Inside the body is a stationary vacuum chamber with graphite seals, which are pneumatically pressed against the inner surface of the cylinder. The vacuum chamber is connected to a continuously operating vacuum pump. The couch-shaft completes the formation and dehydration (to dryness of 18-22%) of the paper web on the B. m grid.

Further dehydration occurs in the press section mechanical extraction under the action of pressure and vacuum by passing the web through several (2-3, less often 4-5) roller presses arranged in series (often the first and second presses are combined into a double press). At the same time, the volumetric mass, strength properties, transparency increase, the porosity and absorbency of the paper decrease. Pressing is carried out between woolen felts, which protect the still weak paper from destruction, absorb the squeezed moisture and at the same time transport the web. Each press has its own cloth. On all new high-speed B. m., the lower rolls of the presses are made perforated (like couch rolls). They are covered with special rubber, which improves dehydration and increases the service life. On some B. m., shafts with special grooved corrugations (grooves) are installed instead of the lower suction shafts. On powerful B. m., the lower shafts of the first and second presses are made suction (similar to the couch shaft). Often, in addition to presses with felts, smoothing (or offset) presses without felts are also installed to compact the paper and make it smooth. Then the paper web with a dryness of up to 45% enters the drying section.

Drying part(largest in length) consists of rotating cylinders heated from the inside by steam and usually arranged in 2 rows in a checkerboard pattern. The web is pressed against the heated surface of the cylinders with the help of felts, which improve heat transfer and prevent warping and wrinkling of the paper surface during drying. The upper and lower rows of drying cylinders have separate felts, and one cloth covers several cylinders at once (a group of drying cylinders). The paper web moves from the upper cylinder to the lower one, then to the neighboring upper one, and so on. The paper is then dried to a residual moisture content of 5-7%. On modern paper machines, a two-shaft gluing press is usually placed in the second half of the drying section for surface sizing of the paper and applying a surface layer. The drying section of some paper machines is equipped with automatic regulators for supplying steam to the cylinders, devices for automatically threading the web of paper onto the drying cylinders, and so on. The steam is collected under a hood located above the entire drying part of the B. m., and then it is removed by exhaust fans to the outside. Heat is used in heaters and heat exchangers.

Finishing part is a calender consisting of 5-10 chilled cast iron shafts arranged one above the other. In order to make it more elastic and soft, the paper is preliminarily cooled and somewhat moistened on a refrigerating cylinder (cold water is supplied and removed through the hollow necks of which). When moving between the shafts from top to bottom, the web becomes smoother, compacted and leveled in thickness. Then the paper is wound with an endless tape into rolls on the reel (a forcedly rotated cylinder, against which the roller with the paper wound on it is pressed). To moisten the paper during its additional finishing on supercalenders (to obtain paper with increased smoothness, gloss and bulk density), a humidifier is installed above the reel. Next, the roll is cut on a slitting machine into the required formats. At the same time, the paper is sorted, the breaks that have arisen during its development are glued together. When releasing paper in sheets, the rolls for cutting are fed to the self-cutting machine.

BM also has a large number of various equipment necessary to ensure its continuous operation, and automatic devices that regulate technological parameters. For each type of paper, technically and economically justified paper width and working speed are established. The narrowest paper paper (with a paper web width of 1.6-4. m) are designed for the production of the thinnest capacitor papers, special technical, high-quality photographic and document papers. Wide B. m. (over 6 m) are used to produce newsprint and sack paper. The working speed of B. m. in the production of capacitor paper is 40-150 m/min, newsprint - up to 850 m/min, sanitary papers - about 1000 m/min and more. Productivity B. m., manufacturing capacitor paper with a thickness of 4-12 micron, is 1-4 t/day, newsprint - 330-500 t/day and more. The length of the B. m. for the production of newsprint reaches 115 m, weight about 3500 t, height of individual parts up to 15 m, power of all electric motors (including paper stock preparation equipment) about 30,000 kW. The drive of individual sections of the B. m. is carried out by DC motors. Within 1 hour, such B. m. consumes up to 45 t pair. Automatic devices regulate the processes of casting and drying paper at high speeds. The high level of equipment with automatic devices and the accuracy of adjustment and execution of the BM make it possible to reduce the number of workers directly servicing it to 3-8 people.

Many new designs of paper materials are being developed, differing mainly in the methods of forming the web of paper. In inverform-type paper (England), a sheet of paper is cast and molded between two grids - the lower and the upper ( rice. 3 ). The pulp from the headbox is fed into the gripper between the lower and upper screens, which creates pressure on the fluid flow. Some of the water passes down through the deposited layer of fiber on the bottom wire and the rest is removed through the top wire. From the inner surface of the mesh, water is removed by a scraper equipped with a knife made of plastic material and a tray for draining water. Further dehydration is carried out on conventional and "inverted" suction boxes with a vacuum not exceeding 12 kn/m 2 (0,12 kgf / cm 2). A press is installed behind the suction boxes, and the squeezed water is sucked off through the upper grid with a scraper. When producing multilayer paper, there are several upper grids (according to the number of layers). Water is practically removed only through the upper screens along the scrapers and into the “inverted” suction boxes.

In B. m. of the vertiform type ( rice. four ) the paper web is dehydrated on both sides between two vertically moving grids using scrapers and suction boxes, which ensures that fibers of the same fraction are deposited on both sides of the paper web. In this case, short and thin fibers are deposited first, as a result of which a surface is formed that is most suitable for printing, and large fibers appear in the middle of the sheet, which increases the strength of the paper web.

There is a trend towards the use of circular wire machines for paper casting, where the formation of the paper web is carried out on cylinders covered with a net and located in a bath or without a bath, where the paper pulp is fed. In a rotoformer machine ( rice. 5 ) the headbox and the mesh part are made in one compact unit, and dehydration is carried out using a suction chamber located inside the rotating shaft. The speed of such machines is up to 300 m/min. They can work with low concentrations, which is important when making papers from artificial fibers.

In the production of long-staple papers made from cotton, asbestos and synthetic materials, “dry forming” of the paper web is used, based on the principle of deposition on the grid of fibers dispersed in the air stream. It is possible that such molding will be widely used for the production of technical and special types of paper.

A further increase in the efficiency of papermaking is associated with a change in the technology of paper production, an improvement in the design of the machine and individual components, and an increase in productivity due to speed and width. Sharp increase the speed and width of the machine will be provided by: flow distributors and closed-type headboxes, allowing the mass to be discharged onto the mesh at a speed corresponding to the increased speed of the mesh; register rolls of grooved and mesh type, hydroplanks, two- and three-chamber suction couch-rolls that intensify dehydration; new types of presses (reverse suction presses, presses with a wide suction chamber, multi-shaft and hot presses); rubberized suction rolls and rolls fixed in the middle, rolls with grooved corrugation, presses with underlay mesh, vacuum suction cloth washers, rolls, calender-mounted open bed with articulated arms, fixed in the middle (lower and upper), floating, not needing bombing to compensate for deflection; peripheral type reels for winding rolls with a diameter of up to 2200-2500 mm with pneumatic clamping of the roll and automatic transfer of it from filling to working supports, etc. In the drying part of the B. m., it is planned to use a higher steam pressure, new schemes of steam distributors with steam circulation, siphon removal of condensate, completely closed hoods over the drying part, installation of drying nets instead of drying felts, and so on. In addition to the widespread and relatively cheap drying through the contact of the surface of the drying cylinders of the machine with the paper web, new types are being sought that would significantly reduce the working area of the drying part and increase the uniformity of drying. New types of drying are promising: dielectric (due to high-frequency current passed through the paper web); irradiation with infrared rays; hot air blowing; under vacuum.

Lit.: IvanovS. N., Technology of paper, M.-L., 1960; Eidlin I. Ya., Paper-making and finishing machines, 2nd ed., M., 1962; Jahn K., Arbeit an der Papiermaschine, 4 Aufl., Darmstadt, 1958; Hardman H. and Cole E. I., Papermaking practice, Manch., 1960.

V. A. SMIRNOV

§ 5. Press part of paper machines

General characteristics of the press part of the paper machine

After the wire part of the machine, for most types of paper, the dryness of the paper web is about 20%. Thus, in front of the press part of the machine, the paper web retains a significant amount of water, of which a part is loosely bound to the polymer. The task of the press part of the machine is the maximum possible removal of water from the paper web without disturbing its structure and with minimal energy consumption.

The press part of the machine consists of sequentially installed wet presses, the number of which can vary from two to five, depending on the type of paper being produced and the mode of operation of the paper machine. The distribution of energy consumption and the proportion of water removed in a modern paper machine, shown in fig. 91 illustrates the role of the press part in this process.

Rice. 91. Distribution of energy consumption on a paper machine (L.12. p.163. Fig. 1.126)

As can be seen from the diagram in the press part of the machine, on average, 2.1% of the total water present in the original paper pulp is removed. As a result of pressing, the dryness, strength and density of the paper web increase. The cost of paper drying and the productivity of the machine depend on the efficiency of the press part. In order to reduce the consumption of steam for drying, they strive to achieve maximum dryness of the paper web after the presses. Calculations show that five times more energy is spent on evaporating water in the drying part of the machine than in the press part when removing the same amount of water mechanically (squeezing and suction). However, in order to achieve optimal technical and economic performance of the paper machine as a whole, it must be taken into account that an excessive increase in dryness due to an increase in pressure between the press shafts leads to an increase in energy costs for driving the shafts, which may not be compensated by a decrease in drying costs.

Double Shaft Press

Twin-shaft and multi-shaft presses have been widely used in production until recently. The appearance of multi-shaft presses is associated with the desire to make the design of the press compact and provide closed paper web wiring, which reduces the number of breaks and increases the efficiency of the paper machine.

Twin-shaft presses are divided into ordinary, with smooth shafts, suction, grooved and blind-drilled.

A conventional twin-shaft press consists of a body (skeleton) and two smooth shafts installed in it. A general view of this press is shown in Fig. 92.

Rice. 92. Conventional twin-shaft press

1 - paper web; 2 - scraper; 3 - upper shaft (granite); 4 - paper roller; 5 - felt roller; 6 - press cloth; 7 - lower shaft (rubberized); 8 - skeleton of the press; 9 - high pressure spray; 10 - low pressure spray; 11 - cloth washer; 12 - cloth tension roller; 13 – shaft clamping mechanism; 14 - felting roller.

To move and feed the paper web into the wringing zone, a press cloth 6 is used. It moves endlessly along the felt rollers 5. The outer side of the cloth in contact with the paper web is cleaned with the help of sprays 9, 10 and a cloth washer 11.

The lower shaft 7 has a rubber coating, if there are several presses in the machine, then the hardness rubber coating rises from the first press to the last. This, taking into account the increase in the strength of the paper web, increases the efficiency of water extraction. The upper shaft 3 is most often made of granite, this is due to the low adhesion of the paper web of various compositions to granite, which reduces the possibility of winding the paper web to the shaft. Other useful property granite is its high hardness and, as a result, wear resistance

Felt rollers 5 are made of steel pipes with anti-corrosion coating, and some of the rollers are equipped with a drive, which ensures the normal running of the felt. In order to ensure a constant tension of the cloth (to compensate for the drawing of the cloth), felt tension rollers 12 are used, which have movable bearing supports.

During the operation of the press, due to the non-parallelism of the axes of the shafts and rollers, the operation of the cloth washer and improper bombardment of the wringer rolls, the cloth may shift relative to its normal position and wrinkles may form on it. To eliminate these problems, on the way of the cloth, the felt rollers 14 and the felt rollers are installed. The most widely known are accelerating rollers, on the surface of which there are protrusions in the form of spirals. In this case, the left spiral is applied to one half of the roller, and the right spiral is applied to the other, so that when the roller rotates, the spirals stretch the paper web from the middle to the edges. Thus, the folds on the surface of the canvas are straightened out.

When using screw spreaders, the felt is subject to increased wear. Arc spreaders, which are also widely used in fabric finishing equipment, have a softer effect on the felt. An accelerating roller of this type is called the Mount Hope roller, its design is shown in fig. 93.

The arc expander consists of a non-rotating curved axis 3, along the entire length of which bearings 5 are installed. A rubber jacket 1 is put on the support bushings 2. Due to the curvature of the axis, during rotation, the generatrix of the rubber shirt (it receives rotation from the cloth) stretches on one half of the circle, and on the other half of the circle is compressed. The cloth must be in contact with the surface of the roller at the line of the beginning of the stretching of the generatrix of the rubber jacket, then the cloth is stretched in width along with the rubber jacket and the folds on its surface are straightened. The degree of impact of the arc spreader can be changed by changing the position of the curved axis of the shaft in relation to the direction of movement of the cloth.

Fig.93. Arc accelerating roller (arc spreader) (L.12. see 172. fig. 1.136)

1 - shaft shirt; 2 - support sleeve; 3 - shaft axis; 4 - bushing; 5 - bearing.

The cloth washer 11 and the high and low pressure showers 9 and 11 are used to remove small fibers, filler and sizing agents from the cloth pores that have passed during the extraction from the paper web, which restores the properties of the cloth to its original level. This process is called cloth conditioning.

The press shafts are pressed against each other by a pressing mechanism. Distinguish lever, pneumatic and hydraulic mechanisms of a clip of shaft. Pneumatic and hydraulic mechanisms are used in modern presses, as they allow you to adjust the degree of roller pressure during machine operation and ensure accurate setting of its value. Linkage mechanisms create pressure with the help of a load (or spring) and increase the overall dimensions of the machine.

Granite shaft. The hard surface wringer roll is made from a single piece of granite with a hole drilled for the steel core. The design of the granite shaft is shown in fig. 94.

Rice. 94. Granite shaft. (L.12. p. 173. fig. 1.137)

1 – left nut; 2.7 - oblique washers; 3 - gasket; 4 - core; 5 – granite shirt; 6 - bushing; 7 - shield; 9 - right nut; 10 - concrete or polyurethane foam.

A granite shirt 5 is put on the steel core 4 and the gap between them is filled with concrete or polyurethane foam 10. On the core, the granite shirt is fixed with bushings 6 screwed onto the core. In case of damage to the surface of the granite shaft due to the ingress of foreign particles into the pressing zone, it is restored by grinding.

Rubberized shaft. The surface of the shaft is formed by a rubber jacket. During the operation of the press, the surface of this shaft heats up and the surface temperature can reach 100 - 120 0 C, which leads to premature failure of the rubber coating of the shaft. To create constant operating conditions for the press, its surface is cooled: an external and or internal cooling system is used. The most effective is the internal cooling system of the shaft surface. Figure 95 shows the design of a shaft with internal water cooling.

Rice. 95. Press roller with internal water cooling (L.12. p. 174. fig. 1.138)

1 - pin left; 2 - rubber coating; 3 - shaft shirt; 4 - pin right; 5 - screw.

The shaft structure is formed by a shirt 3 and the left and right trunnions 2.4 screwed to it. A water-air mixture is fed into the shirt through the left trunnion at a temperature of 21-27 0 C. For normal heat transfer, the water-air mixture should flow along the inner surface of the shirt in a thin layer, flooding the inner volume of the shirt with water should not be allowed. It is important to ensure that the coating temperature is evenly distributed along the length of the roll. Why is it necessary to control the temperature range of the water falling inside the shaft and the water drained from it. This difference, as the researchers found, should not exceed 6 - 8 0 C.

On fig. 96 is a diagram explaining the mechanism of squeezing water in a conventional press.

Rice. 96. The work of a conventional, two-shaft press (L.12. p. 175. Fig. 1.139)

1 - paper web; 2 - upper shaft; 3 - lower shaft; 4 - press cloth.

In order to ensure a gradual increase in pressure on the paper web and facilitate the removal of water, the upper roll 2 is slightly shifted in relation to the position of the lower roll 3. The amount of displacement depends on the diameter of the rolls, the speed of the machine, the position of the press in the machine, and other factors and is 50 - 250 mm. As you can see from the diagram. The paper web 1 and the cloth 4 enter the wringing zone, the wrung out water moves opposite to the movement of the cloth, in the wringing zone the cloth and paper web are compressed and water is removed from them. After leaving the squeezing zone, the water from the felt tends to fill the pores of the paper web. The surface of the upper shaft is cleaned of adhering fibers, filler, etc. with a scraper.

Press with suction roller. The suction roll press is used as the first press of the paper machine. Normally the suction roll is in the lower position. On fig. 97 shows a diagram of the operation of a press with a suction roll and the design of the surface of the suction roll.

Rice. 97. Pressing a paper web in a suction press (L.12. p. 177. fig. 1.142)

1 - rubber coating; 2 - steel shirt; 3 - rear seal; 4 - front seal; 5 - cloth; 6 - upper shaft; 7 - suction chamber..

The suction roller is paired with a granite or cast iron roller. As can be seen from the diagram, the suction shaft consists of a perforated steel jacket 3 with a rubber coating 1. A suction chamber 7 is installed inside the steel jacket, connected to a vacuum pump. The vacuum chamber is installed under the pressing zone and is shifted towards the movement of the paper web. For the vacuum chamber to work effectively, it must be completely covered with cloth and paper. Vacuum in chamber (width 100 – 150 mm) is maintained at 50–65 kPa. Hole diameter in steel jacket 3.7 - 4 mm, covered with rubber – 4 to 5 mm.

Distinguish between opening and closing suction presses. In open presses, part of the suction chamber after the pressing zone is open (see Fig. 97). In closed presses, the chamber is located so that its rear wall is inside the pressing zone. In suction presses, the formation of air bubbles between the felt and the paper web before they enter the pressing zone is eliminated, which prevents the web from being crushed. This reduces the risk of paper web breakage. The disadvantage of the suction shaft is the complexity of the design, as a result of the high cost of operation and low durability.

Grooved press. It differs in that grooves 0.5 wide are cut on the surface of the rubberized shaft. mm. When wringing out the water from the cloth is displaced into these grooves and discharged through the end surfaces of the shaft. These rolls are often used to replace suction rolls. Grooves are sometimes applied to the surface of the suction rolls to help remove water from the felt more easily, reduce the risk of web crushing, and reduce shadow marking even with increasing pressure. Usually presses with grooved shafts are installed in the last positions.

On fig. 98 shows a diagram of a double compact press

The compact press consists of three pressure rollers, of which the middle one has a hard surface, and the other two have a rubber coating and a moisture suction chamber. The paper web from the surface of the long mesh 3, together with the plastic mesh, enters the pressing zone of the first rubber-coated roll 7 and the granite roll 6. Then, after passing the surface of the granite roll, it enters the pressing and suction zone of the second rubber-coated roll and the granite roll. After the presses, the paper web 4 is sent for drying to the drying drums 4.

Rice. 98. Scheme of arrangement of double presses of compact type (L. 5. p. 328. fig. 3.91.)

1 - cloth; 2 - grid; 3 - long grid; 4 - paper; 5 - cloth press; 6 – granite rampart; 7 - rubberized shaft; 8 - dryer drum..

Press parts of modern paper and board machines

For the purpose of production High Quality paper and board machines specialize in the production of a certain type of product. Based on this, press machines containing a combination of suction, grooved and smooth-surfaced rollers are used to complete them. For example, for the production of sanitary and hygienic types of paper, high-quality paper with a weight of up to 100 g / m 2, presses with a relatively rigid contact zone are used: a granite shaft and a grooved shaft with a stainless steel jacket without rubber coating. When producing paper and cardboard with a large mass of 1 m 2, it is recommended to use presses with an extended pressing zone.

Many modern paper machines have compact multi-shaft presses with three or four press zones. As an example, consider the principle of operation of the Twinver press, the flow diagram of which is shown in fig. 99.

Rice. 99. Scheme Twinver press (L 12. p. 200. fig. 1.165)

1 - couch-shaft; 2 - cloth pickup; 3 - transfer shaft; 4 - upper grooved shaft; 5 - cloth; 6 - paper web; 7 – granite rampart; 8 - suction shaft.

The working bodies of the Twinver press are suction 3, suction 8, granite 7 and grooved 4 shafts. The wet paper web is separated from the mesh of the machine by the suction roller 3 and, accompanied by the felt 2, is transferred to the suction roller 8, where moisture is removed from it by suction vacuum. In this zone, the strength of the paper web increases and this allows the web to continue to be pressed between the granite roller 7 and the grooved roller 4. Due to the contact of the wire side of the paper web in two zones of pressing with the smooth surface of the granite roller, a reduction in the net marking is achieved. The disadvantages of this design of the press are: the possibility of the formation of air bubbles in front of the pressing zone between the granite shaft and the grooved shaft and the danger of breaking the web in the area between the second and third pressing zones.

On high-speed machines that produce newsprint, the Tri-Vent press has proven itself well, the technological scheme of which is shown in fig. 100. This press also includes rolls with a grooved surface.

Rice. 100. Tri scheme - Vent press (L.12. p.201, fig. 1.167)

1 - paper web; 2 - transfer shaft; 3 - cloth pickup; 4 - suction shaft; 5, 8 - upper cloths; 6,7,12 - grooved shafts; 9 - paper roller; 10 – granite rampart; 11 - bottom cloth; 13 - grid.

In the diagram, the paper web is marked with a dotted line. Wet paper web 1 is separated from the mesh 13 of the machine by a suction roller 2 and, accompanied by a felt 3, is transferred to the pressing zone between the granite roller 4 and the grooved roller 12. Then the canvas passes between the granite roller and the suction roller 4, the granite roller and two grooved rollers 6 and 7 .

The design of this press differs from other presses in that it includes a third grooved shaft 7 with its own felt. The first free passage of the paper web occurs after four pressing zones (the fourth pressing zone is the pressing between the granite roll 10 and the grooved roll 7). Therefore, the risk of paper web breaks, even when working at high speeds, is small.

§ 6. Drying part of paper machines

The dryer section of the paper machine removes approximately 1.5% of all moisture to be removed from the paper web on the paper machine (see Figure 91, page ...). This means that 1.5 - 2.5 kg moisture per 1 kg paper. Dehumidification by drying is 10 to 12 times more expensive than in a press and 60 to 70 times more expensive than dewatering on a wire bed. If we take into account that an increase in the relative dryness of the paper web in front of the drying part by 1% corresponds to a 5% saving in steam consumed for drying, then the importance of the correct organization of the operation of the wire and press parts of the machine becomes clear. The dryer part of the machine consumes approximately 25 - 33% of all electricity consumed to drive the paper machine. Therefore, an appeal is required special attention on the condition of bearings, lubrication units, the quality of daily inspection and repair of all kinds. At the same time, the drying part of the machine is the most expensive part of the machine, which is confirmed by the data below:

In the process of drying the paper web, physical and chemical processes take place, leading to the achievement of equilibrium (conditional) humidity, a decrease in the size of the web in all three directions.

In the production of paper, contact, convective, combined and radiation drying methods are used. The radiation method of drying, although effective, has not yet found wide application due to its high cost. The most widely used combined method, which combines the contact method of drying with convective. The advantage of the contact drying process over other drying methods is that the hot surface of the drying cylinders acts like an iron and gives the paper a smooth surface on one or both sides.

This drying method is implemented on multi-cylinder dryers. On fig. 101 shows a diagram of the dryer part of the paper machine.

The drying part of the paper machine is a complex unit, consisting of the actual drying cylinders, arranged in two rows, cloth drying and cooling cylinders, drying clothes, a system of shafts providing uniform movement of the cloth in the straightened state. All structural elements of the dryer are mounted on a frame, which must be sufficiently rigid to reduce vibration during operation of the machine. Depending on the type of manufactured products, the drying part of the machine may include additional elements, such as: infrared emitters, devices for activating air exchange in the intercylinder spaces, high-frequency current generators, etc.

Rice. 101. circuit diagram drying part of paper machine (L.12.str.215. Fig.1.176)
vacuum shaft; 2 - paper drying cylinder; 3 - paper web; 4 - drying grid; 5 - ventilation hood; 6 - drying air; 7 - air supply to general ventilation; 8 - scrubber; 9 - air intake shaft; 10 - heat trap of the 2nd stage; 11 - heat trap of the 1st stage; 12 - upper drying grid with a traditional paper web wiring scheme; 13 - calender; 14 - reel; 15 - lower drying grid; 16 - air distribution channels.

Drying cylinders are usually arranged in two rows in a checkerboard pattern, so the paper web alternately comes into contact first with one side of the cylinders of the upper row, and then the opposite side with the cylinders of the lower row.

Principle of operation

The wet paper web, guided from the press part of the paper machine, is filled between the heated surface of the first drying cylinder 2 and the drying mesh (cloth) 4. At the initial stage of movement, the drying mesh (cloth) accompanies the dried web in the free area between the upper drying cylinders and the lower vacuum rollers. This is a feature of this paper web filling scheme. This refilling reduces the risk of paper web breakage. In the following drying sections, the felt accompanies the paper web only on the contact surface with the heated surface of the drying cylinders. In the area of contact of the fabric with the heated surface of the drying cylinder, there is an intense heat transfer to the paper web, due to which moisture evaporates, part of which impregnates the cloth. In the free section of the movement of the web from cylinder to cylinder, the evaporation of moisture continues, due to which the temperature of the web decreases. The drying cylinders are hermetically sealed with a ventilation hood 5, from which exhaust moist air is removed. Part of the exhaust air in the heat trap 11 is mixed with fresh shop air, heated in the heater and through the drying air duct 6 is fed into the drying chamber through the air distribution channels 16. Part of the exhaust air, mixing with the shop air in the heat trap 10 and water drops coming from the scrubber 8, after conditioning, it is sent to the general ventilation of the workshop. After processing in the 13 calender, the paper web dried to the standard humidity is wound into a roll on the reel 14.

Drying felts or nets press the paper web tightly against the heated surface of the cylinders, thereby ensuring good contact between them. This prevents the formation of wrinkles and folds on the surface of the paper web.

The paper web guiding scheme under consideration is called “breakless”, which is achieved by guiding the web in the initial section of movement with a net or felt in the free drying section between the upper drying cylinders. On the bottom row, instead of two drying cylinders, mesh-guiding vacuum rollers are installed, which serve to prevent the formation of bubbles and “bags”.

Drying cylinder

The main working element of the dryer, which supplies heat to the paper web and ensures its movement inside the dryer, is the drying cylinder. On fig. 102 shows a longitudinal section of the drying cylinder.

Rice. 102. Drying cylinder (L. 12. p. 219. fig. 1.179)

1 - front pin; 2 - front end cover; 3 - inspection hatch; 4 - grooves of filling cords; 5 - recess for the tip of the siphon; 6 - wired end cap; 7 - drive pin; 8 - cylindrical body (shell).

The drying cylinder consists of a cylindrical body (shell) 8 to which spherical end caps 2 and 6 are bolted. Spherical end caps can be monolithic or prefabricated, with pressed pins. To give a high surface smoothness and obtain a higher heat transfer coefficient to the paper web, the outer surface of the cylindrical body is carefully ground and polished, high hardness is imparted, which ensures a long service life of the cylinder. The material of the cylindrical body is high-quality fine-grained cast iron. Per recent times some use was made of steel cylinders.

The inner surface of the cylinders is machined to obtain a wall of the same thickness, which ensures uniform distribution cylinder surface temperature. The cylinders of high speed paper machines are dynamically balanced. The width of the cylinders is somewhat greater than the width of the paper web. The most widely used cylinders with a diameter of 1500 mm, for high-speed machines, the cylinder diameter is 1812 mm, and in last years cylinders with a diameter of 2200 are used mm.

Spherical caps are made from high quality pre-annealed cast iron. On the cover there is an employee's hatch for internal inspection and maintenance. The mating surfaces of the body 8 of the cylinder and end caps 2 and 6 are sealed with an asbestos cord with sealant applied.

Drying cylinders are internally heated by high pressure steam (more than 0.07 MPa), therefore they fall into the category of high pressure apparatus and therefore they are subject to the rules Gosgortekhnadzor. In accordance with these rules, the manufacture of cylinders is allowed only to enterprises that are equipped with technical means that ensure their high-quality manufacture in accordance with the rules of GOST.

At the end of the drying part of the machine, refrigerating cylinders are installed, which serve to cool the paper web from 85 ÷ 90 0 С to 50 ÷ 55 0 С and increase the moisture content of the web by 1.5 ÷ 2.5%, due to the condensation of water vapor on the cold surface of the cylinders . To do this, these cylinders are cooled from the inside with cold water. Cooling and moistening the paper contributes to its better compaction on the calenders, reducing the difference in the smoothness of the mesh and front sides of the paper web. The surface temperature of the refrigerating cylinders is recommended to be maintained within 35 ÷ 40 0 С.

Steam supply unit for removing condensate from the drying cylinder

As explained above, the paper web is dried by contacting the hot surface of the drying cylinder. The surface of the drying cylinder is heated by the condensation heat of the water vapor supplied inside the cylinder. The resulting condensate, depending on the speed of rotation of the cylinder, may have the location shown in Fig. 103.

Rice. 103. Location of condensate in the cavity of the drying cylinder (L.12. p.224, fig.1.183). a - with settling condensate formation; b - with ring formation of condensate; c - in the transition mode.

1 - paper web; 2 – drying cylinder; 3 - condensate; 4 - condensate ring.

Inside the drying cylinder, the condensate can have two modes of stable location: settling and annular, as well as an intermediate state - a transitional mode.

Settling mode is observed at a low speed of the paper machine (350 ÷ 400 m/min), while the resulting condensate flows down and is located in the lower part of the cylinder in the form of a segment. As the cylinder rotates, the condensate segment shifts slightly in the direction of cylinder rotation. The energy used to drive the dryer depends on the speed of the machine, on the diameter of the cylinders, and also on the location of the condensate inside the cylinders. In settling mode, as the speed increases, the energy consumed by the machine increases. As soon as a condensate ring forms in the cylinder (the annular mode of condensate location), the power consumption decreases sharply due to the reduction in power consumption for friction between the condensate and the inner surface of the cylinder.

The choice of scheme and design of the condensate removal unit from the cylinder depends mainly on the location of the condensate, i.e., on the speed of the paper machine. In high-speed machines, where the annular mode of condensate location is implemented, rotating or stationary siphons are used. On fig. 104 shows the design of the steam supply and condensate removal unit of a high-speed machine.

Rice. 104. Rotating siphon and steam head of the drying cylinder.

(L. 12. p. 225. fig. 1.185)

1 – drying cylinder; 2 - graphite sealing rings; 3 - spacer spring; 4 - rod; 5 - siphon tube; 6 - nozzle; 7 - spring; 8 - pipe; 9 - steam head.

Steam is supplied to the cylinder through the annular gap between the rotating siphon tube 5 and tube 8. Graphite sealing rings 2 and spring 7 ensure the tightness of the steam head 9. The rotating siphon consists of a siphon tube 5, one end of which ends with a nozzle 6, and the other end passes through the center hollow trunnion of the drying cylinder and ends in the steam head 9. The rotating siphon is fastened with an adjustable support rod 4, ending with a conical spring 3. Nozzle 6 fits snugly against the inner surface of the cylinder, and the gap for condensate inflow can be adjusted using special bolts. The advantages of siphons of this type are their reliable fastening in the cylinder and the possibility of installing several siphons along the length of the cylinder. The disadvantage can be considered the need for a pressure drop to remove condensate.

Another important element of multi-cylinder dryers are nets and felts, which serve to transport the paper web and create tight contact between the wet paper web and the heated surface of the cylinder. Previously, woolen and cotton cloths were used, now synthetic drying nets are widely used. When using felts, the machine must have felt-drying cylinders. On fig. 105 shows a diagram of filling the cloth on the top row of drying cylinders.

Rice. 105. Scheme of dressing cloth on drying cylinders (L.12.p. 228, Fig. 1.187)

1
7
- paper canvas; 2 - paper drying cylinder; 3 - felt rollers; 4 - tension roller; 5 - correct roller; 6 - cloth-drying roller; 7 - cloth ..

As can be seen, the cloth 7 passes through the surfaces of the drying cylinders and the dried paper web 1 is pressed against the surface of the cylinders 2 by the cloth, providing a tight contact between them. During the drying process, part of the moisture is absorbed by the cloth, so there is a need to dry it in the drying cylinder 6. Auxiliary rollers 3, 4 and 5 ensure that the cloth passes at constant tension and straightened out in the center of the machine.

The advantages of synthetic nets over woolen and cotton cloths are their long service life, lightness and higher vapor permeability, breathability, no need for drying, high strength, etc. An important factor is that the use of synthetic nets releases natural fibers from technical application. The table shows the characteristics of drying nets and felts manufactured by Russian enterprises.

Table Characteristics of drying nets and felts

From the above data, it is clear that synthetic meshes have a much lower mass and higher air permeability, which positively affects the efficiency of the dryers.

§ 7. Other types of paper machines

1. Selfie machines

Self-shooting machines, also called Yankee machines, were invented in 1827. They are designed to form thin absorbent sanitary papers weighing 1 m 2 8  20 g, as well as to produce denser paper of one-sided smoothness weighing 1 m 2 30  55 g (ticket, etiquette, poster, match, etc.). If the first designs of these machines worked at speeds not exceeding 100  150 m/min, then the operating speeds of modern machines reach 1500 m/min, with a width reaching up to 7 m. 106 shows a schematic diagram of a self-shooting machine.

Rice. 106. Scheme of a self-recording paper machine (L. 13. str. 613. fig. 231)

1 - mesh table; 2 - couch press; 3 - removable cloth; 4 - wet press; 5 - roller cloth washer; 6 - large drying cylinder; 7 - ironing press; 8 - reel; 9 - ventilation hood; 10 - cloth.

A distinctive design feature of this type of paper machine from a long wire machine is that the wire part is shortened (6  8 m) and has one large diameter drying cylinder (3.6  6 m). Five or six register rollers and two or three suction boxes are usually installed in the wire part of the machine. Machines designed for the production of thin absorbent tissue papers have a chest roll with suction chambers. These types of paper are produced from highly diluted pulp (0.10.2%).

The paper web from the grid of the mesh table 1 is removed by a removable cloth 3, which is put on the upper shaft of the couch press 2. Then the canvas located between the removable cloth 3 and the cloth 10 is spun in a wet press 4 to a dryness of 3235%, after which the paper web is transferred to a large drying cylinder 6, working without a cloth. The paper web is pressed against the drying cylinder by ironing 7 (or pressure) rollers. On the surface of the cylinder, the canvas is dried by the contact-convective method. A ventilation hood 9 is put on the drying cylinder, which houses the heating - ventilation system air, where the air is heated and blown onto the surface of the paper web with the help of nozzles. The dried paper web is taken up by the reel 8.

On fig. 107 shows a diagram of the initial section of the machine.

Rice. 107. Scheme of the pressure device and the chest shaft of the self-shooting machine. (L.13 p.614 fig. 232)

1 - suction chest shaft; 2 - the first vacuum chamber; 3 – second vacuum chamber; 4 – head box of closed type; 5 - grid.

From the headbox 4, the paper pulp is fed to the surface of the breast roll 1 with suction chambers 2, 3. The outlet slot is formed from two plates (lips), the upper of which reaches the center of the breast roll, and the lower one is shorter than the upper one by 150  200 mm. With this design of the outlet slot, the stock exits the headbox directly above the first suction chamber of the breast roll.

Two wire table machines

Two-grid cutlery machines are designed to produce technical paper with an increased weight of 1 m 2, which is difficult to form on a conventional single-grid paper machine. The difficulty lies in reducing the rate of dehydration of the paper pulp, which leads to a decrease in paper quality and machine productivity. The production of two-layer paper on two-wire machines makes it possible to overcome these difficulties and obtain paper with good clearance and uniform physical and mechanical properties. On fig. 108 shows a flow diagram of a two-wire paper machine.

Fig.108. Two-grid table machine (L.13 p.619 fig. 235)

1 - upper grid table; 2 - lower grid table; 3 - the first press.

As can be seen from the above flow diagram, a two-wire machine differs from a conventional paper machine only in the presence of a second mesh table, which is located above the lower mesh table of the machine. The upper mesh table 1 is located in a slightly shifted position to the left compared to the lower table, and the paper web is transferred to the suction boxes or to the couch - press of the lower mesh table with a special conveying cloth or mesh of the upper table. Next, the doubled paper web is transferred to the first wet press 3. These machines are relatively slow-moving, the maximum operating speed is 250 m / min with a machine width of 2.5 - 3.5 m.

The presence of cleaning equipment for each wire table is a design feature of two wire paper machines. Thus, each wire table is a self-acting element of the paper machine.

3 . Cylinder paper machines

Cylinder paper machines are widely used for the production of multi-layer rolled cardboard weighing 1 m 2 up to 800 G. On fig. 109 shows a flow diagram of a three-cylinder paper machine

Rice. 109. Scheme of a three-cylinder paper machine (L.13 str.6239 Fig. 238)

1 - grid cylinders; 2 - pressure rollers; 3 - suction shaft; 4 - pre-cooking press; 5 - couch press; 6 - upper removable cloth; 7 - bottom cloth; 8 - roller cloth washer; 9 - suction boxes; 10 - the first wet press; 11 - Frank's cloth washer.

The composition of the paper machine, in addition to the elements indicated in the diagram, includes a press, a drying part and a reel. On machines of this type, some types of document, money, drawing, drawing, and other papers are produced,

The number of mesh cylinders, depending on the type of products produced, can reach 7 - 8, the working width is 4 - 5 m, the working speed is 250 m / min.

As can be seen from the above diagram, mesh cylinders 1 are installed in series and interconnected by one removable cloth 6. Such a machine allows you to produce multilayer paper or a folder in the form of an endless web.

The principle of operation of the machine is as follows: the mesh cylinder 1 is immersed in a metal bath, into which the diluted paper stock is fed according to the principle of co-current or counter-current. A vacuum chamber is placed inside the cylinder, connected to a vacuum pump. Due to the suction of water, a paper web is formed on the surface of the mesh cylinder, which is removed from the surface of the cylinder with woolen cloth 6. The pressure roller 2, the surface of which forms a layer of soft rubber, presses the cloth and paper web to the mesh cylinder. The suction roller 3 installed after the mesh cylinders is used for preliminary dehydration of the paper web. Preliminary presses 4 and couch press 5 further dehydration of the paper web occurs. The upper removable cloth 6 passes through the entire mesh part of the machine and carries with it a web of raw paper. In order to avoid crushing the raw paper web during squeezing, a second removable cloth 7 is brought under the paper web after the mesh cylinders from below. After the couch press, the paper web enters the press part of the machine. The top and bottom removable felts are washed on the way back by cloth washers 8 and 11. Tubular suction boxes 9 prevent separation of the wet paper web from the top cloth.

The main forming structural element of the machine is the mesh cylinder.

SAINT PETERSBURG STATE TECHNOLOGICAL UNIVERSITY OF PLANT POLYMERS

CORRESPONDENCE FACULTY

course design

By discipline: "APCS"

On the topic: Development of process control systems for the dry part of the paper machine

Head: Surikov V.N.

abstract

Drying part of the paper machine No. 1 At JSC PZBF. automation project, temperature control and steam supply.

The object of automation is the Drying part of PM No. 1 of JSC PZBF.

The purpose of the work is to modernize the process control system with a detailed development of a live steam supply control system.

The structure of the process control system was proposed, and the technical means included in the system were selected. The structure and composition of the PLC APCS has been developed

PTK MITSUBISHI Series FX was chosen as the technical means of automation.

Implementation is expected at the Drying section of PM No. 1 of JSC PZBF.

Introduction

This course project considers the automation of the drying part of PM#1. JSC "PZBF"

ACS for controlling the supply of steam to the dryer

ACS for collecting and pumping condensate into the deaerator.

Thus, it is necessary to create an automated control system for choosing the structure of the control system, its functioning and a set of technical means.

Improving product quality indicators can be achieved through the use of microprocessor controllers. The use of controllers also simplifies the performance of diagnostic and protection functions.

1.Purpose and goals of creating automated process control systems

The purpose of the introduction of the Automated Control System based on programmable controllers is to optimize the process of drying the paper web on the drying part of PM No. 1.

To do this, the system of government must solve the following tasks

· control of steam supply to the dryer

· level control in dehumidifiers.

· collection and pumping of condensate to the deaerator

· warning and emergency signaling.

To perform these tasks, regulation, control and registration of process parameters is carried out.

All parameters of the drying process are displayed on the operator's console, including the operation of protections and alarms.

Automatic regulation

temperature and pressure of incoming steam;

surface temperature of the drying cylinders;

paper machine speed;

properties of the surrounding air;

the presence of air and condensate in the cylinder;

tension of drying nets and their condition;

dryness of the paper web after presses;

Signaling

Operation of the ventilation system;

Deviation of parameters from the norm;

Operation of emergency protection;

2.Analysis of the existing automation system (APCS)

The enterprise does not yet have a centralized control system for the automation of the drying section on the PM. It is still local.

The existing automation system includes the following automation systems;

ACS for controlling the supply of steam to the dryer section.

ACS for level control in dehumidifiers.

ACS for collecting and pumping condensate to the deaerator.

The drying process is controlled by the dryer in a semi-manual mode, using simple TRM210 regulators. The automation system has a very low speed, which does not provide a good dynamic process. This system does not give the slightest idea about the characteristics of the change in the dynamic drying process. Constant monitoring of the operation of regulators by service personnel is required. The system does not have the ability to inform the operator about the state of operation of the actuators. There is no possibility for the operator to quickly influence the drying processes when switching to different types of products.

As measuring instruments are used:

· Gauge pressure transducer. Measurement range 0-10Mpa. Output 4-20mA Metran 100-DI Model 1152PG "Metran" Russia, Chelyabinsk.

· Measuring transducer of hydrostatic pressure (level). Measurement range 0-25kPa. Overpressure 0.4 MPa. Output 4-20 mAMetran-100-DG, model 1541PG "Metran" Russia, Chelyabinsk.

· Pressure difference transducer. Measuring range 0-0.2 MPa Output 4-20 mA Metran 100-DD Model 1152PG "Metran" Russia, Chelyabinsk.

· Flow converter. Measuring range 20.45 - 613.48 m 3 . Output 4-20mA. Metran331PG "Metran" Russia, Chelyabinsk.

as an executing mechanism

Globe valve with electro-pneumatic positioner. DN 150, DN 80, DN 50, 4-20 mA input ES3241EN-JL1040, Samson.

3.Requirements for APCS

The developed process control system must comply with the requirements of GOST34.602-89. The complex of software and hardware tools for automated process control systems should be built on the basis of information technologies and products that meet generally accepted international standards, and also have an open scalable architecture, with the expectation of increasing functionality and modernization.

3.1Requirements for ACS in general

The commissioning of an automated control system should lead to useful technical, economic, social or other results, for example:

*reduction in the number of management personnel;

*improving the quality of the functioning of the control object;

*improving the quality of management.

The ACS must ensure compatibility between its parts, as well as with automated systems(AS) interconnected with this ACS. In cases where an automated control system or a set of automated control systems (AS) is created on the basis of a computer network, to ensure compatibility between the elements of such a network, systems of protocols for multilevel interaction should be applied.

The automated control system as a whole and all types of its support must be adapted to modernization, development and expansion within the requirements specified in the TOR for the automated control system.

The reliability of the automated control system as a whole and each of its automated functions should be sufficient to achieve the established goals of the system functioning under the given conditions of use.

The adaptability of the automated control system should be sufficient to achieve the established goals of its operation in a given range of changes in the conditions of use.

The automated control system should provide for monitoring the correctness of the implementation of automated functions and diagnosing, indicating the place, type and cause of violations, the correct functioning of the automated control system.

In automated control systems with measuring channels, it should be possible to control the metrological characteristics of the measuring channels.

The automated control system must provide for measures to protect against incorrect actions of personnel leading to an emergency state of an object or control system, from accidental changes and destruction of information and programs, as well as from unauthorized interference.

Any information entering the ACS is entered into the system once using one input channel, if this does not lead to non-fulfillment of the requirements. Installed in the TOR for the automated control system (in terms of reliability, reliability, etc.)

Output information of the same semantic content should be generated in the ACS once, regardless of the number of recipients.

The information contained in the ACS databases must be updated in accordance with the frequency of its use in the performance of system functions.

The automated control system must be protected from information leakage if it is stated in the TOR for the automated control system. 3.1.13. The name of the automated control system should include the name of the type of automated control system and the control object.

3.2 Requirements for ACS functions

ACS in the required volumes should automatically perform: collection, processing and analysis of information (signals, messages, documents, etc.) about the state of the control object;

development of control actions (programs, plans, etc.);

transfer of control actions (signals, instructions, documents) for execution and its control;

implementation and control of the implementation of control actions;

The composition of automated functions (tasks, task complexes - hereinafter referred to as functions) of the ACS should provide the ability to control the corresponding object in accordance with any of the goals established in the TOR for the ACS.

The composition of the automated functions of the automated control system and the degree of their automation must be technically, economically and (or) socially justified, taking into account the need to free personnel from performing repetitive actions and create conditions for using their creative abilities in the process of work.

3 Requirements for the technical support of automated control systems

The complex of technical means of the automated control system should be sufficient to perform all automated functions of the automated control system.

In the complex of technical means of automated control systems, technical means of mass production should be mainly used. If necessary, the use of technical means of single production is allowed.

Replicated automated control systems and their parts should be built on the basis of unified technical means.

The technical means of the automated control system must be placed in compliance with the requirements contained in the technical, including operational, documentation for them, and so that it is convenient to use them during the operation of the automated control system and perform maintenance.