Modern paper production in brief. All about paper: production basics. Requirements for the quality of printed paper.
Paper
Ministry of Education of the Russian Federation
Ussuri State Pedagogical Institute
Essay
Theme “Paper”
Completed by: student of group 521 Yastrebkova S. Yu.
Checked:
Ussuriysk 2001
- (page 19)
Sheet of paper (page 3)
How it happened (page 4)
How paper is made these days (page 5)
Another method is to immerse the entire sheet in colored water, and on both sides it becomes tinted, papers prepared in this way, today, in most cases of Pisanello's studies, the scale of which is known to the Codex Vallardi of the Louvre, manipulation of the drawings and changes that could have place for centuries, it is often prevented from determining with the naked eye whether the artist used a dry preparation or a wet preparation, as in the case of the mystical marriage of St. Catherine of Parmesan.
Ready paper. One of Kennini's tips is chalk, bone powder or lead white with skin glue, keeping the proportions: too little glue, the preparation collapses under the tip; Too much glue, the paper becomes hard and glossy and the clue slides around without registering. He gives a recipe for his glue: Take a piece of apothecary's glue, not fish glue, put it in a small pot to melt into two glasses clean water for six hours, then place this pot on low temperature and smoke when it boils.
Making paper on a paper making machine (stru10)
Basic technological processes for making paper on a paper-making machine, their purpose and characteristics (page 14)
Paper classification (page 18)
Properties of paper and their connection with the properties of fibrous semi-finished products.
1.References (page 21)
Paper
When it has simmered a little and the glue has been well extended, pass it through twice. The glue is then mixed with chalk or bone powder, then spread on a piece of paper with a large soft brush, lightly, in one direction and the other. Bone powder, calcium phosphate or calcium carbonate is obtained from the burnt bones of various animals. The bones should be baked until they are white and crumbly. They are then reduced to powder by grinding them with a small amount of water. This operation is long and tedious. According to Cennini, it takes a good two hours to spray one burned bone.
We all, to one degree or another, come across paper and products made from it on a daily basis. This, so to speak, communication with paper begins in early childhood, when the child reaches for a bright book, a white sheet of paper, to leave traces of his first pencil exercises on it. Paper accompanies a person throughout his life. She reminds of herself every time he turns to documents - a passport, diploma, certificate, when we pick up a book, takes correspondence out of the mailbox. Many of our actions are related to paper. It is needed for business writing, for creative work, and for everyday needs.
This powder, to which lead may be added, is then diluted in resinous water or gum arabic solution. Be that as it may, bone powder gives a rough and uneven surface and should be sanded, but not to a satin point, which would render it unable to take on a style feature.
Perhaps because even though it is brown, this surface remains imperfect, Cennini advises adding a layer of white lead to make it more receptive. The number of coats of primer applied by brush varies from one to nine, according to the authors. Each layer, which is very thin, must be completely dry before it receives the next layer, and all layers must be of a minimum thickness, but sufficient to hide the structure of the substrate. It is clear that just one coat of primer does not provide sufficient coverage.
But what do we know about paper? We can say that paper is a material for printing books, magazines and newspapers. Paper occupies an exceptional place in people's lives. Its discovery, like the invention of the wheel, is a miracle, one of the greatest achievements of the human mind. Having appeared once, paper firmly established itself on Earth and, without knowing any competitors, continues victoriously through the centuries.
Laptops give us good examples. Skill is not always carefully studied: in Chapter St. Should artists be accused of neglect? Probably not, for two reasons. Firstly, these ugly brush strokes that today define these drawings were, of course, less noticeable from the very beginning; Oxidation will remove them.
Moreover, it should be borne in mind that all the drawings that we preserve as precious relics were often for the artists only “drafts” of work or exercises, which most often were added to this At that time the workshop breaks down. In general, at the beginning of the Renaissance, artists tended to use more layers, while in the second half of the fifteenth century they increasingly illuminated them, to the limit of the necessary minimum. And Meder is right to write: The thicker the finish, the oldest drawing. But no matter the thickness of the layer, the leaves remain very fragile and can be scattered without careful handling.
Paper had many predecessors. Stone and clay, wood and bone, leather and birch bark, wax and metal, papyrus and parchment - all of them served people as writing materials in different historical eras. But each of them was not entirely suitable for this. Some materials were heavy, others were fragile, and others were expensive. Their processing required a lot of effort, which, however, was not always justified.
There is no doubt that artists who spend a lot of time preparing their documents handle them with care and take care to complete the drawings they want to preserve, either for teaching or as examples of the repertoire. On the other hand, when these small drawings, finished products are used in the design of a painting, their survival is greatly endangered: managed by assistants, not always very respectful, during handover, manipulated by artists during their work, these structures are often crumpled, torn or painted over.
And then paper appeared - a simple material, accessible for writing, made from raw materials of plant origin. The birth of paper brought about profound changes in human society. Having received the paper, people began to actively engage in knowledge. This was largely facilitated by the rapid development of the book business.
The friendship that began with paper in childhood does not end throughout life. At home, on the street, in the store, at work, we are glad to meet you. In the morning, paper enters our apartment with a fresh newspaper, a new issue of a magazine, a letter. Most of the home furnishings are paper related.
Perugino's study for Saint San Sebastian escaped this fate, but has reached us in a state of mediocrity. The amount of color broken by bone powder, chalk, or lead white varies in proportion to the desired tone: a little color for a pale finish, a lot of color for a more or less obscure primer, and proportionately less white. The addition of lead white reduces the intensity of the colors but increases the opacity of the dyes, thus their coverage power. The artist can also obtain certain shades by grinding several different pigments with the main ingredient.
2. How it happened
There is Baoqiao Cave in the northern Shaanxi province of China. In 1957, a tomb was discovered in it , where scraps of sheets of paper were found. The paper was examined and it was established that it was made in the 2nd century BC. This discovery shed light on the history of paper. It was believed. That paper appeared in China in the year 105 of the new calendar. The Baoqiang find pushes this date forward by two centuries. It can therefore be assumed that paper, this, as the poet puts it, priceless spiritual bread, appeared more than 2 thousand years ago.
Cennini demonstrates six other dyeing recipes that are difficult to put together today. However, Maeder notes that most of these pigments are of mineral origin, including terrao verde, hematite, sinopria, ocher, and cinnabar, the only indigo vegetable color. However, it is difficult to say how far apart Cennini's recipes were from the artists, especially since we do not know whether he is offering commonly used recipes, his own invention, or a little of both. Undoubtedly, seminars compete with each other to improve known practices without revealing their secrets.
The raw materials for paper in China were silk scraps, waste from silkworm cocoons, and scraps of old nets. They were soaked and manually ground between stones. The pulp obtained in this way was poured onto some smooth surface and pressed with another polished stone. The gruel was allowed to sit, dry, and turn into a flat cake like felt.
The fact remains that Cennini's mixed recipes point to a point that has hitherto been ignored, namely: the remarkable tonalities of the primers of conservative designs lead either to mixtures of pigments or not; it is likely that only chemical analysis can answer this question.
In the late 14th and early 15th centuries, according to Cennini, there was an outright predilection for green soil: Green soil is the most common and the one we use the most. But the 15th century also has relatively strong tones such as violet and embodied, or delicate like roses, light yellows, light blues and pearl greys. At the same time, and often among the same artists, there are preparations of soft colors: Filippo Lippi, Benozzo Gozzoli and Leonardo da Vinci, for example. Among the known designs, preparations based on pure and darker pigments are found in smaller quantities, of course, because artists know that they are harmful to the delicate shades of the tips.
At the turn of the 2nd and 3rd centuries AD, paper made from plant fibers was not considered a rare material in China. In the 3rd century, it completely replaced wooden tablets used for writing. The paper was made of a certain format, color, weight, and impregnated with special substances. Which repel harmful insects. Chinese paper was stored for a very long time. Since time immemorial, China has had a method of reproducing texts using signets. Initially, impressions were made on clay and bamboo tablets; later, paper was used for these purposes. Paper made it possible to expand the copying of manuscripts of sacred books. All kinds of decorations, umbrellas, fans were made from paper, food was wrapped in it, and it was inserted into windows. At the beginning of the 9th century, “flying coins” - paper money - appeared in China. For many centuries, the Chinese alone owned the secrets of paper making, jealously guarding the secrets of the craft.
While their lines receive relief and harmony in the midtones, dark backgrounds weaken them, suffocating them. These undertones play on a wide range of shades in Italian designs. But the beauty of these colors, which attract attention from the very beginning, should not make us forget that their main function is to provide the middle tone that a three-dimensional drawing requires.
Colored paper. The first difference between writing paper and drawing paper, according to Maeder, is in the 16th century, when colored papers appear in the grain. In the last quarter of the fifteenth century, the Venetian papermakers have the happy idea of coloring the paper in an attempt to eliminate the yellowish or rough color of the paper and thus obtain card tercina or azzura by adding indigo during the refining of the paste and its collage. On the other hand, the idea could also have come from the thriving local dyeing industry, which would have allowed the Venetians to transfer this technique to the dyeing of paper pulp.
The appearance of paper in Russia dates back to the 12th-13th centuries. The first paper mills appeared in the 17th century. A technical revolution in paper production in Russia was made by a paper-making machine, which began operating in 1816 in St. Petersburg. In 1916, 55 pulp and paper enterprises were already operating in Russia. The average width of papermaking machines did not reach 2 m, and their speed did not exceed 100 m/min.
All the artists of Venice, including Carpaccio, Bellini, Titian, Tintoretto, Pordodon, etc. Also associated with the Venetian school, but there are also green papers, gray-green, gray-blue, Veronese and Bassani, make good use of it for different reasons: firstly, colored paper ideal for the vision of these artists, for whom the form is a spot of color before the outline. goes very well with the dynamism of their features with black stone, charcoal or rich coal, as well as with velvety shadows, as is often the case with Titian.
The soft but stable tones of the sheets also facilitate the impression of Looking bright and wonderfully illuminating, but they are not completely unaware of this, and an artist like Signorelli proves this to us. Treatises and other art publications recommend that artists obtain copies different colors for sale everywhere. For example, gray paper is recognized as having absorbent properties and is especially used for extensive research on charcoal or blackstone. It's also easy to add lighting effects in white.
3. How paper is made these days
The initial link in the technological chain of paper production is an open warehouse of wood raw materials, called a timber exchange. Every pulp and paper enterprise has such warehouses. They are located in vast areas behind production buildings, often on the banks of reservoirs where ports or berths are built for receiving fused wood. To make some types of paper, softwood and hardwood raw materials are used. Newsprint is produced only from spruce, since spruce wood has the largest number of thin and long fibers and the lowest content of resinous substances. Hardwood pulp can be mixed with softwood pulp. Short and hard fibers of deciduous wood and long and elastic softwood form a mass from which paper with good properties is obtained. The technological scheme for paper (cardboard) production consists of the following processes:
Several artists use one color of paper or another indifferently. A little later the brown paper appears, finer and less grainy, varying in color from flesh to flesh in a range of shades of very pale dark. These half-tone papers are very favorable to the "two crayons" and "three crayons" techniques highly prized in France in the 17th century.
From Vasari we describe this method of drawing as creating figures with clear values on a dark background, as opposed to the usual method of artists of drawing dark lines on a white surface. Most of these designs are done with a pen or brush. During the Renaissance, artists who work with this type of drawing especially seek new aesthetic effects. The paper they use comes in three varieties: thin, textured, dark wash-dyed paper, heavier, grain-dyed, or drug-dyed paper.
preparation of paper pulp, including operations for mass grinding of fibers, sizing, filling and dyeing of the pulp;
accumulation of paper pulp;
diluting the mass with water to the required concentration;
cleaning from foreign inclusions and nodules;
making paper (cardboard) on a paper (cardboard) machine, including casting a paper (cardboard) sheet, pressing it, drying, finishing and winding into a roll;
Even if the papers used for charcoal are also available in different colors, they are too light for ink, watercolor or gouache. It should be noted that Italian papers are very stable and flexible at the same time. If they "survive" to this day, it is due to the quality of their workmanship, reflecting the institutions and materials used. Of course, various elements can make the sheet imperfect, such as stains on the threads on which it is dried, small fine accumulations of fibers in places, hairs, hairs or other dust found in the paste.
finishing and processing of paper (cardboard), including supercalendering, rewinding, cutting and packaging.
Mass grinding of fibrous semi-finished products. Grinding is the process of special mechanical processing of plant fibers in the presence of water, carried out in grinding mill machines. Milling is one of the most important processes in paper production, allowing many properties of paper to be changed over a wide range of values. Fibers are ground in continuous machines (conical, cylindrical and disk mills). What is common to grinding devices is that their operation is based on the principle of crossing knives and rubbing surfaces.
Passing between the knives of grinding machines, the fibers are exposed to mechanical and hydrodynamic forces, leading to the occurrence of complex physicochemical and colloidal processes in the structure of the fibers. As a result, some shortening of the fibers (cutting), surface splitting and combing in the longitudinal direction of the fibrillar structure of the cell wall into fibrils (surface fibrillation), swelling and hydration of the fibers occur. The fibers become softer, their elasticity and ductility increase. During the process of fibrillation, the bonds between individual fibrils of the cell wall of the fibers are weakened and destroyed. On the surface of the fibrils, a “puff” of thin fluffy material consisting of cellulose molecules is formed. As a result, the specific surface area of the fibers and the number of free hydroxyl groups increase, facilitating better contact and connection of individual fibers into a paper sheet. Increasing the specific surface area of the fibers and releasing hydroxyl groups increases the ability of the fibers to retain water.
Depending on the grinding mode, it is possible to obtain paper pulp of varying degrees of grinding: from low (sad pulp) to high (fat pulp). To obtain a free mass, grinding is carried out in a mode that primarily ensures fiber chopping over surface fibrillation. During the process of forming a sheet of paper, a mass of low degree of grinding (crude) quickly settles on the mesh, is easily dehydrated and forms a loose and porous structure of the sheet. A high degree of grinding of the mass (fat mass) is characterized by a predominance of fibrillated fibers with a well-developed surface, which are more difficult to dewater on the mesh of the papermaking machine and form a dense, closed and durable sheet structure. The nature of grinding of the mass is chosen depending on the type and quality of the paper and cardboard produced.
The strength of paper is characterized by a number of indicators: resistance to tearing, breaking, punching, tearing and tearing, which has a certain value for each type and grade of paper, and generally depends on the strength of the fibers, their length, the strength of the bond between the fibers and the structure of the paper sheet.
When tested, a sheet of paper is torn at its weakest point. In most cases, this weak point is not the fibers themselves, but the connections between them. When the sheet is torn on both sides V At the point of rupture, a predominant pulling out of fibers from the thickness of the sheet is observed, which indicates a break in the bond between them. And only part of the fibers breaks in the transverse direction.
The main factors influencing the quality of cellulose grinding are: grinding duration, specific pressure between mill knives, mass concentration, type of grinding accessory, peripheral speed of the rotor or drum, temperature of the mass during grinding. Controlled factors include duration, specific pressure, concentration and temperature of the mass.
To grind semi-finished fibrous products at enterprises that produce mass-produced types of paper and have high productivity, disc mills are used. Mass grinding is carried out in single-disc and twin closed-chamber mills, which provide a throughput of up to 650 t/day.
The widespread use of disc mills is due to the rapid development of the production of high-yield fibrous semi-finished products. They replace other types of grinding equipment (conical mills, rolls) due to the following advantages: the possibility of grinding at high mass concentrations (up to 40%); lower specific energy consumption; large unit power and productivity, compactness, simplicity of design; wider scope of application (grinding cellulose, high-yield semi-finished products, wood chips, sorting waste from wood-pulp and pulp production); the possibility of obtaining a more homogeneous mass in structure.
The main working elements of the mill – the stator (housing) and the rotor – are made in the form of cones. The inner surface of the stator and the outer surface of the rotor are formed by replaceable blade jackets. The gap between the stator and rotor blades is adjusted by moving (additive or lightening) the rotor along its axis using an adder mechanism. When the mill is operating, the mass moves in the direction from the small diameter of the rotor to the larger one. The productivity of the mill for air-dried fiber is 4-16 tons/day, the rotor speed is 1000 min-1, the contact surface area of the rotor headset and the stator is 0.40 m 2.
Sizing. The purpose of sizing is to give paper or cardboard limited absorbent properties in relation to water, ink, printing ink and other liquids and improve many other physical and mechanical properties. With unlimited absorption (in non-glued paper), for example, ink, they will be absorbed into the thickness of the sheet of paper, diverge and pass to its reverse side. A complete lack of absorbent properties will cause ink to run off the surface of the paper. The first and second phenomena make the paper unsuitable for writing and printing. Therefore, the sizing process is designed to provide each specific type of paper and cardboard with its own strictly defined absorbency, which is assessed by the degree of sizing .
A distinction is made between surface sizing and bulk sizing. Surface sizing is carried out by applying starch or animal glue to the surface of the finished paper. It is used for the production of some special high-grade types of paper - document, drawing, cartographic, etc. The vast majority of types of paper and cardboard are sized by introducing sizing agents into the paper pulp before casting the paper sheet, i.e., they are sized in the mass. For sizing, hydrophobic (water-repellent) substances are used in the mass, and the sizing process is increasingly called hydrophobization of paper or cardboard. The main hydrophobic substance is rosin, extracted from the resin of coniferous trees. Rosin or resin sizing of paper was invented in 1807. Illig.
Many enterprises supply sizing agents in the form of ready-made glue - glue-paste (this is welded glue, but not yet diluted with water). After diluting with water to the required concentration, it is ready for use. This eliminates the need to have a glue department on site, and, more importantly, the glue is always stable and of high quality. In the future, it is planned to transfer all enterprises to the use of glue paste, supplied centrally from several glue factories.
Filling. Paper filling refers to the introduction of mineral filler substances into the paper composition to improve its quality and economic performance. By introducing fillers into the paper composition, the following goals are achieved: the cost of paper production is reduced, since the cost of filler is lower than the cost of fibers, some of which are replaced by filler; the whiteness of the paper increases, since almost all fillers have a higher degree of whiteness than the fibers; the smoothness of the paper surface significantly increases due to filler particles filling the pores and irregularities between the fibers on the rough surface of the sheet; the opacity of the paper is reduced, which makes it possible to write and print on both sides of the sheet; lumen uniformity improves; softness and plasticity increases - the paper makes less noise when flipped; the bulk density, porosity and, consequently, the absorption of printing inks, etc. are reduced.
Based on ash content, paper is divided into four groups: paper with natural ash content - filter paper, electrical insulating paper, base for fiber and parchment, greaseproof; no fillers are introduced;
low ash paper (with ash content up to 5%) - newspaper, mouthpiece, wallpaper, etc.;
in these types of paper it is important to maintain mechanical strength, therefore increasing the content of fillers, which significantly reduce the mechanical properties of paper, is impractical; medium ash paper
-writing paper with ash content up to 6-8%, some types of printing paper with ash content up to 15%; filler is added to these types of paper in limited quantities;
high ash paper
(ash content over 15%) - this is for printing, for intaglio printing, etc.; For these papers it is important to have good printing properties and high opacity, so their filler content is high.
A common disadvantage of introducing fillers is a noticeable decrease in the mechanical strength and degree of paper sizing. In addition, with an increase in the content of fillers, paper dustiness is detected to a greater extent - the phenomenon of separation of small fibers, filler particles, and sizing agents from the surface of the paper. This effect dramatically worsens the print quality - paper dust sticks to the printing plate, clogging the type and cliche.
4. Dyeing and tinting.
For the production of paper and cardboard, two types of papermaking machines are used: flat mesh and round mesh. The former are used to produce paper, the latter - cardboard. The main difference between the machines is that in flat mesh machines the paper web is formed on a moving horizontal mesh, while in round mesh machines the web is formed on a rotating cylindrical mesh.
Paper making machine structure . The paper making machine consists of wire, press, drying and finishing parts and drive. In addition, it includes a machine pool for accumulating paper pulp before feeding it to the machine, equipment for refining, grinding and cleaning the pulp, pumps for supplying water and pulp, vacuum pumps, devices for processing scrap, circulating water pools, supply and exhaust ventilation system , regulating and control instruments. Let's look at a more detailed structure of the main parts of a flat mesh machine and their purpose using the example of a modern domestic wide-format high-speed paper-making machine B-15 for the production of newsprint.
Mesh part designed for forming and dewatering paper webs and includes a headbox and a wire table. The headbox is designed to uniformly and continuously inject mass onto the mesh over its entire width. Closed head boxes are now widely used, in which the required mass pressure is created by the pressure of the air cushion. The paper pulp is poured onto the mesh using an inlet device, which ensures its release at the same speed and in the same quantity over the entire width of the mesh, supplying the mass in a calm flow, without crossing streams, turbulence and flocculation.
Grid table is a horizontal plane formed by a mesh stretched between the chest shaft and the suction couch shaft. The reverse (lower) branch of the mesh is supported by mesh guide, mesh straightening and mesh tension rollers. The tension of the mesh is carried out by mesh tension rollers, and the mesh straightening rollers serve to prevent the mesh from sliding to the sides from the longitudinal axis of the table. The mesh is driven by a rotating mesh (mesh driving) shaft (it is located under the suction shaft) or simultaneously by a rotating mesh and a caching shaft.
The grid is the main element of the grid table. On it, a paper web is formed from paper pulp. Using the mesh, the chest shaft and all other rollers of the mesh table are driven. When performing technological functions, the mesh is subjected to intense mechanical and chemical influence, so it must have sufficient tensile strength, bending, abrasion and be acid-resistant. It must have good water throughput and high density, so that as few small fibers as possible escape with the circulating water and the paper marking (the mesh imprint on the side of the paper web in contact with the mesh during molding) is less noticeable.
Under the upper branch of the mesh, in the direction of its stroke successively from the chest to the couch shaft, there are located: a forming board or box, hydroplanes or register rollers, suction boxes. The main purpose of these elements is to form the paper web by creating a mode of dehydration of the paper pulp on the mesh of the required intensity, as well as maintaining the mesh from sagging between the chest and couch shafts.
In modern high-speed paper machines, register rollers have given way to hydroplanes and wet suction boxes. This ensures high-quality formation of the structure of the paper web with a more intensive process of dehydration.
Press part serves for further mechanical dewatering of the paper web after the grid table. In most papermaking machines, the press section consists of 2-3 twin-shaft presses. Machines designed for producing paper from a mass of fatty grinding have 4-5 presses. A conventional press has 2 shafts: an upper one, granite or stonite, and a lower one, metal, lined with rubber. The intensity of dewatering in the press is regulated by the pressure between the rollers, created by the clamp, or by lightening one of the rollers (usually the upper one). Each press has a cloth covering one of the shafts. The cloth is installed and maintained in working position with the help of cloth guides, cloth tensioners, cloth spreaders and cloth straightening rollers. The main purpose of felts is to protect the structure of the paper web from crushing during pressing, absorb moisture, transport weak raw paper in the press and transfer it to the next press. As the press passes, one side of the paper lies on the felt and receives markings from it, and the other is in contact with the upper smooth shaft. As a result, one side of the paper is smoothed, but the other is not. To smooth its surface, a reverse press is often installed, in which the side of the paper that came into contact with the felt in the previous press is in contact with the smooth shaft of the press. The development of the press part of machines to intensify the paper pressing process, instead of conventional presses, is the installation of suction and dual presses. Each of these presses is driven strictly by an individual drive.
Drying part serves for the final dehydration of the paper web by evaporation of moisture. The drying part consists of drying cylinders arranged in two tiers in a checkerboard pattern. The drying cylinder is a hollow steel cylinder with a diameter of 1500 or 1800 mm, heated from the inside by steam. The surface of the cylinders, like the press rolls, has a high degree of processing - it is ground and polished. The cylinders are designed for a working pressure of 0.35 MPa. The number of cylinders depends on the type of paper being produced and the speed of the machine.
Finishing part consists of a machine calender and reeling. A machine calender installed between the drying section and the reel serves to increase the gloss, smoothness and bulk of most types of paper. The calender consists of 5-8 horizontally located shafts one above the other, driven from the lower shaft. The surface of the shafts is ground and polished. Linear pressure between the shafts is controlled by a pressing and lifting mechanism. During operation, the rolls become very hot due to friction, so a cooling system is provided to cool the calender rolls. Sometimes, for surface treatment of paper and cardboard (sizing, painting, impregnation, etc.) during its production, a size press is installed on a paper-making machine in the drying section.
After machine calendering, the paper goes to the reel, where it is wound into a roll. Currently, almost all modern machines use peripheral drum-type rollers. Their main part is a cast iron drum with a diameter of 1200 mm, which rotates from the drive of the papermaking machine. The peripheral speed of the drum is equal to the speed of production of the paper web. The paper roll is wound onto a tambour roller, which is pressed against the drum by a special device, ensuring uniform and tight winding of the paper.
The paper machine drive is designed to drive all parts of the paper machine. It ensures a smooth change in the speed of individual parts within certain limits, and strict constancy of the speed of the driven parts under steady state operating conditions of the machine. The limits for changing speed control depend on the type of paper being produced.
5. Basic technological processes for making paper on a paper-making machine, their purpose and characteristics.
The technological process of manufacturing paper (cardboard) includes the following main operations:
accumulation of paper pulp; diluting it with water to the required concentration and cleaning it from foreign inclusions and nodules; adding mass onto the mesh; forming the paper web on the machine mesh; pressing the wet sheet and removing excess water: drying; machine finishing and winding of paper (cardboard) into rolls. In the technological flow of paper production, a paper-making machine is an independent unit, the main components of which are installed strictly sequentially along the mounting axis.
Storage. The preparation of paper pulp is carried out in the grinding and preparation department. Flows of fibrous, filling, sizing, coloring and other materials that make up a composition of this type future paper, are sent to a dispenser or composition compiler, where they are continuously and strictly dosed in a given ratio, and then enter the mixing basin. In this pool, the mass is thoroughly mixed and accumulated (accumulated).
Refining. Refining of the paper pulp is carried out before it is fed to the machine in continuous machines - conical and disk mills. In the process of refining paper pulp, the degree of grinding of the pulp is leveled, fiber bundles are eliminated, and some grinding of the pulp occurs. For this purpose, the mills are installed after the machine basin directly in front of the paper machine.
Feeding stock to the paper machine. Upon exiting the machine pools, the mass at a concentration of 2.5-3.5% is dosed and sent to the papermaking machine. Before entering the machine, it is diluted with recycled water, cleaned of foreign contaminants, as well as nodules and lumps. To maintain a constant mass of 1 m 2 of produced paper, it is necessary that the same amount of mass enters the machine grid per unit time, and the speed of the machine must be constant. The speed of the machine is changed when switching to the production of another type of paper.
On modern paper-making machines, the mass of 1 m 2 of paper produced is kept constant by automatic regulators. The pulp is fed to the paper machine using a pump and a constant pressure box. The pulp entering the paper machine is diluted with water in the mixing pump. Dilution is necessary, firstly, for subsequent purification of the mass, since it is difficult to remove contaminants from a thick mass, and, secondly, for better shaping of the paper on the mesh of the papermaking machine.
Forming a paper sheet on the mesh of a paper making machine. The paper pulp, diluted to the required concentration and cleared of foreign matter, enters the headbox of the papermaking machine. The required degree of dilution of the mass for casting paper on the mesh of a paper-making machine depends on the mass of 1 m 2 of paper, the type of fiber and the degree of grinding of the mass. Forming a paper sheet on the mesh of a paper making machine. The paper pulp, diluted to the required concentration and cleared of foreign matter, enters the headbox of the papermaking machine. The required degree of dilution of the mass for casting paper on the mesh of a paper-making machine depends on the mass of 1 m 2 of paper, the type of fiber and the degree of grinding of the mass
Adding mass onto the mesh. This operation is carried out using an inlet device - a headbox. For normal operation of machines at speeds of 450-500 m/min, a mass pressure in the head box of 2.5-3 m is required, at a speed of 600 m/min - about 4.2 m, etc. The filling device ensures the supply of paper pulp to an infinite a mesh moving in the direction from the chest to the couch shaft, at the same speed and in the same quantity across the entire width of the mesh. The mass is injected almost parallel to the grid without splashes. The speed of mass inflow onto the mesh should be 5-10% lower than the speed of the mesh. If the mass speed lags significantly behind the mesh speed, the longitudinal orientation of the fibers (orientation in the machine direction) and the strength of the paper in the longitudinal direction increase.
F formation paper sheet (low tide) . Forming, or casting, a paper sheet is the process of combining fibers into a sheet form to create a defined three-dimensional capillary-porous structure. This process is carried out on the wire part of the papermaking machine by gradual and consistent removal of water from the paper pulp (dewatering). The dewatering regime, starting at the beginning of the wire table and ending with drying the paper in the drying section, at all stages of the technological process has a significant impact on the quality of the paper and the productivity of the machine.
Pressing. After the mesh part, the paper web enters the press room, which usually consists of several presses, in which it is sequentially dehydrated to a dryness of 30-42%. To intensify the dewatering of the web, presses with grooved shafts and increased linear pressure between them are used in the press section. Proper selection of felts and their conditioning are important for dewatering the fabric. The paper web, formed in the mesh part, is automatically transferred by a vacuum-suction device to the felt of the press part. Modern designs of combined multi-shaft presses ensure the passage of paper without free areas (areas where the paper web is not supported by the felt), which allows for uninterrupted passage of paper in the press section.
Drying. In the drying section of the paper machine, the paper web is dewatered to a final dryness of 92-95%. During the drying process, 1.5-2.5 kg of water is removed per 1 kg of paper, which is approximately 50-100 times less than in the mesh and press parts of the machine. During drying, further compaction and convergence of the fibers occurs at the same time. The result is increased mechanical strength and smoothness of the paper. The drying mode determines the bulk density, absorbency, air permeability, transparency, shrinkage, moisture strength, degree of sizing and coloring of the paper.
The paper web, passing through the drying cylinders, alternately comes into contact with the lower and upper cylinders with one or the other surface. For better contact between the cylinders and the paper and to facilitate loading, drying felts (grids) are used, covering the drying cylinders by approximately 180°.
Drying paper on a drying cylinder consists of two phases: on the heated surface of the cylinder under the felt and in the free-running section, that is, when the paper web moves from one cylinder to another. In the first phase, under the cloth, the main amount of moisture evaporates: on low-speed machines up to 80-85%, on high-speed machines up to 60-75% of all moisture evaporated in the drying part of the machine. In the second phase, in the free-running areas, moisture evaporates from both sides of the paper due to the heat absorbed by the paper in the first drying phase. In this case, the paper, depending on the speed of the machine, undergoes a temperature drop of 4-15°. As the temperature drops, the drying speed decreases, especially on low-speed machines, since the drop in temperature of the paper web is greater on them than on high-speed ones. As the speed of the machine increases, the amount of evaporated water in the free-running area of the paper increases. As the amount of water in the paper web decreases, the drying intensity in the free area decreases.
The temperature of the drying cylinders is increased gradually, which helps to improve the quality of the paper and complete the sizing process. At the end of the drying part, the surface temperature of the cylinders is reduced, since high temperatures with low paper humidity have a destructive effect on the fibers.
Finishing. After drying, the paper web passes through a machine calender, consisting of 2-8 shafts located one above the other, in order to compact and increase smoothness. The canvas, alternately bending around the calender shafts, passes between them under increasing pressure. Modern machine calenders are equipped with mechanisms for pressing, lifting and lightening the shafts. The lower shaft and one of the intermediate ones are made with adjustable deflection,
Similar abstracts:
Fibers obtained from organic natural and synthetic polymers are called chemical fibers. Depending on the type of feedstock, chemical fibers are divided into
The ability of cellulose to swell and dissolve in sodium hydroxide solutions, its features, technical significance, methods for determining the degree of its swelling and solubility, as well as analysis of the mass fraction in alkali. Determination of alpha cellulose content.
General concept about polyvinyl acetate. Basic physical and chemical properties. Alcoholysis, hydrolysis, aminolysis, ammonolysis of PVA. Production of polyvinyl acetate in industry. Basic curing methods. Common types of PVA glue. Application of PVA dispersion.
Chemical transformations of wood components under sulphate cooking conditions. Quality indicators of technical celluloses. Determination of uniformity of pulp bleaching and cooking method. Chemical and physical-chemical analyses. Identification of cellulose fibers.
Acrylamide: physical and chemical properties, solubility. Preparation and determination, toxicity of acrylamide. Features of the use of acrylamide and derivatives. Application and production of acrylamide polymers. Characteristic chemical properties polyacrylamide.
Rosin: chemical composition and properties of its various types. Preparation and study of the physicochemical properties of synthesized salt samples. Optimization of the process of obtaining the amido-ammonium salt of maleopimaric acid based on maleinated rosin.
The use of plastics in industries and Agriculture as materials for structural, protective, electrical, decorative, friction and antifriction purposes. Basic properties of thermoplastics and thermosets.
Representatives of cellulose ethers: alkylcellulose, benzylcellulose, methylcellulose, ethylcellulose, carboxymethylcellulose, hydroxyethylcellulose. Methods of preparation, application, production of cellulose ethers. Environmental aspect of production.
Stability and protection of textiles from microorganisms. Natural stability of textiles, microorganisms that cause their deterioration. Fungicides for textiles, chemical modification of cellulose. Stability of paper and its protection from microbiological corrosion.
Ministry of Education Russian Federation Report on Chemistry on the topic Starch Completed by: 10th grade student. B Nechin Evgeniy Krasnoyarsk, 1998 Starch Starch consists of 2 polysaccharides - amylose and amylopectin, formed by glucose residues. It has been experimentally proven that the chemical formula of starch...
Moscow State Textile University named after. A.N. Kosygina Report on educational practice at UPM Passed by: student htf gr 26-99 Belaya Victoria Checked by: professor Safonov V.V.
Latest developments in the field of synthetic fiber chemistry. Recent advances in chemical technology allow us to hope for the production of hollow chemical fibers in the very near future. This technology is already being mastered for the use of new materials in membrane technologies.
Abstract on chemistry on the topic: St. Petersburg 2003. What is fiberglass? Fiberglass is a composite material consisting of a glass filler and a synthetic polymer binder. The filler is mainly glass fibers in the form of threads, strands (rovings), fabrics, mats, rub...
Features of the technology for manufacturing polymer materials, the main parameters of processing processes. Methods for molding products from unfilled and filled polymer materials. Methods for processing reinforced polymers. Aspects of their application.
Making paper is a complex physical and chemical process. Simple sheet - result large quantity stages of the production process. Now we will look at the step-by-step process of creating paper.
Paper production consists of the following steps. First, the logs are delivered to the mill. There they are crushed using production equipment and then boiled with special substances. After this, the mixture is filtered, resulting in the formation of paper pulp. It is placed in machines where it is turned into canvas and then into paper. Each stage contains many nuances, so let’s look at them in more detail.
Understanding all the stages of paper creation will help you accept correct solution when choosing the appropriate type for printing. This way, you can choose the paper with the best image quality, which will reduce jams and other inconveniences.
