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Packing generally refers to the material filled in other objects. In chemical engineering, packing refers to the inert solid materials installed in the filling tower, such as Bauer ring and RASI ring, whose function is to increase the contact surface between atmosphere and liquid, so that they are strongly mixed with each other. In chemical products, fillers, also known as fillers, refer to solid materials used to improve processing performance, mechanical properties of products and (or) reduce costs. In the field of sewage treatment, it is mainly used in contact oxidation process. Microorganisms will accumulate on the surface of the filler to increase the contact with the sewage surface and degrade the sewage.
Fillers are also known as fillers, extenders. Some fillers are also body pigments. The filler of micro button has good covering power and is often used in coating industry.
Fillers can be used in a variety of polyurethane products, such as polyurethane coatings, sealants: Polyurethane paste, special elastomer polyurethane foam. Melamine plant fiber polymerization, soap ginseng polyol, organic filler can be used for polyurethane foam; calcium carbonate kaolin (clay, clay), molecular sieve powder talcum powder, wollastonite, titanium dioxide, barite powder (barium sulfate) and other micro inorganic powder can be used as two polyurethane sealant, polyurethane flexible polyurethane elastomers, adhesives, polyurethane coatings and other filler.
Generally speaking, it refers to materials filled in other objects. In chemical engineering, packing refers to the inert solid materials installed in the filling tower, such as Bauer ring and RASI ring, whose function is to increase the contact surface between atmosphere and liquid, so that they are strongly mixed with each other. In chemical products, fillers, also known as fillers, refer to solid materials used to improve processing performance, mechanical properties of products and (or) reduce costs. Among them, fillers that can significantly improve the strength of products, such as long fibers and whiskers, are often called reinforced materials, and carbon black is called reinforcing fillers. Solid materials and calcium carbonate are often added to pharmaceutical tablets, cosmetics and detergents as fillers, but their purpose is to adjust the dosage and concentration rather than improve the performance, so they should be called diluents. Plastic plasticizer, rubber oil filling agent and spinning oil agent can improve the performance and affect the cost, but they are usually regarded as processing aids.
In polymer chemical industry, fillers (fillers) are additives with the largest amount. Almost all plastics (including thermoplastic and thermosetting plastics), rubber and coatings use a large number of fillers. For example, adding wood powder, clay or calcium carbonate to plastics can not only improve the mechanical properties of products, increase the hardness, but also reduce the cost; using graphite, magnetic powder or mica as fillers can improve the conductivity, magnetic flux and heat resistance of plastics; adding carbon black or silicon dioxide (silica) to rubber can significantly improve the physical properties of products; adding titanium dioxide (dioxygen) to spinning solution Titanium) can block light and dye. In the coating industry, white or colored fillers (such as titanium dioxide, talcum powder, calcium carbonate, barium sulfate, etc.) are often added to improve the optical, physical and chemical properties of the coating. Fillers (fillers) for such purposes are called physical pigments or color extenders.
Mainly depends on:
① There is a large specific surface area (m2 / m3 packing layer);
② The liquid has a good uniform distribution on the surface of the packing;
③ The air flow can be evenly distributed in the packing layer;
④ The seasoning has a large void ratio (m3 / m3 filling layer).
In addition, the mechanical strength, source, manufacture and price should also be considered when selecting fillers.
The packing makes the material viscosity increase, especially the fiber packing makes the viscosity increase obviously. The fillers before addition need to be dehydrated to avoid consumption of some isocyanates. It should be noted that the formation of carbon dioxide will cause foaming of the resin and affect the physical properties of polyurethane resin.
In order to speed up the wetting speed of the filler, reduce the viscosity of the system or add more fillers to the polyurethane resin, it is sometimes necessary to add wetting and wetting dispersing agent to the resin in advance.
The interior paint is a kind of assistant with three functions of paint, color paste and mold release agent. It is evenly sprayed in the mold, and after drying, the molded polyurethane soles, self formed foam plastics, polyurethane soft foams and hard foam products can be moulded, and the colored paints are attached to the molded products.
Mechanism of fillers: fillers, as additives, mainly play a role by occupying volume. Due to the existence of fillers, the molecular chains of matrix materials can no longer occupy all the original space, so that the connected segments are fixed to some extent, and may cause the orientation of matrix polymers. Due to the size stability of fillers, the movement of molecular chain in the polymer interface area is limited, which leads to the increase of glass transition temperature, the increase of thermal deformation temperature, the decrease of shrinkage, and the increase of elastic modulus, hardness, rigidity and impact strength.
Function of packing:
① Reduce the shrinkage rate of the molded parts, improve the dimensional stability, surface finish, smoothness and flatness or matte of the products, etc;
② Resin viscosity effective regulator;
③ Most fillers can improve the impact strength and compression strength, but not the tensile strength;
④ It can improve the coloring effect of pigment;
⑤ Some fillers have good light stability and chemical corrosion resistance;
⑥ It can increase capacity, reduce cost and improve the competitiveness of products in the market.
Purpose of filler in epoxy floor paint
Filler in epoxy floor paint is also known as filler, generally refers to the material added to the epoxy resin liquid as a component of the epoxy floor paint to change the performance of the epoxy resin glue and reduce the cost.
The purpose of using filler in epoxy floor paint is as follows:
1. Reduce the cost, inhibit the reaction heat and brilliant color.
2. Extend the application period of resin mixture.
Reduce the shrinkage of the cured resin.
Improve the heat resistance of the cured resin.
5. Reduce the thermal expansion coefficient of the cured resin, reduce the water absorption of the cured resin, and improve the aging resistance and chemical resistance of the cured resin.
6. Increase the compressive strength of the cured resin, but decrease the tensile strength and impact toughness.
Improve the arc resistance and other electrical properties of the cured resin.
8. Improve the wear resistance of the cured resin.
Filler selection criteria
For a particular application, the best standard for packing is based on the desired properties of the composite, but the following basic principles must be taken into account.
1. In the process of packing processing, the original structure should be maintained, and the inert, insoluble, heat stable, non-volatile, non catalytic and low adsorption properties should be maintained.
2. The filler shall be compatible with the base material and be non corrosive.
3. Easy to handle, high bulk density, low moisture content, low dust.
4. It should be easy to obtain, with sufficient supply, moderate price and stable quality.
Type of filler
There are many kinds of filler, aluminum powder, zinc powder, copper powder, silver powder and other metal powder can be used as conductive filler. Cement and fly ash can also be used as fillers. Wood powder, starch and other plant powders can also be used as fillers. Calcium fluoride can be used as a small amount of polyurethane adhesive and sealant system, and has the function of carbon dioxide absorbent.
Generally speaking, the micro powder filler or modified micro filler, as well as fibrous and flaky filler, can improve its overall performance with a small amount of use, for example, it has a certain reinforcing effect on the elastic polymer (such as rubber and polyurethane elastomer), increases the modulus, strength, wear resistance and heat resistance, improves its dimensional stability, and can also appropriately improve the strength and aging resistance of hard products 。 However, if the amount of filler is too large, the physical properties will be reduced, and it is difficult to operate when the amount of filler is large. There are several kinds of fillers: according to the different ways of filling, they can be divided into bulk fillers and regular fillers.
It is a kind of particle with a certain geometry and size, which is usually stacked in the tower in a random way, also known as random packing or particle packing. According to different structural characteristics, bulk packing can be divided into ring packing, saddle packing, ring saddle packing and spherical packing.
Several typical bulk fillers are introduced
LacI ring, Bauer ring, step ring, arc saddle packing, rectangular saddle packing, metal ring rectangular saddle packing, spherical packing
La Xi Huan
(1) Rassier ring packing
Invented by F. rashching in 1914, it is a ring with the same outer diameter and height. The packing of lacI ring has poor gas-liquid distribution, low mass transfer efficiency, large resistance and small flux, which has been rarely used in industry.
(2) Bauer ring packing
It is an improvement of rassier ring. Two rows of rectangular window holes are opened on the side wall of rassier ring. One side of the ring wall that is cut is still connected with the wall surface, and the other side is bent to the inner ring to form an extended tongue leaf. The sides of the tongue leaves are overlapped in the center of the ring. Because of the holes in the wall of the ball ring, the utilization of the inner space and the inner surface of the ring is greatly improved. The air flow resistance is small and the liquid distribution is uniform. Compared with lacI ring, the gas flux of Bauer ring can be increased by more than 50%, and the mass transfer efficiency can be increased by about 30%. Bauer ring is a widely used packing .
(3) Step ring packing
It is an improvement of Bauer ring. Compared with Bauer ring, the height of step ring is reduced by half and a taper flanging is added at one end. Due to the reduction of the ratio of height to diameter, the average path of gas around the outer wall of the packing is greatly shortened, and the resistance of gas passing through the packing layer is reduced. The tapered flanging not only increases the mechanical strength of the packing, but also makes the packing change from linear contact to point contact, which not only increases the gap between the packing, but also becomes the collection and dispersion point of the liquid flowing along the packing surface, which can promote the surface renewal of the liquid film and improve the mass transfer efficiency. The comprehensive performance of step ring is better than that of ball ring, and it is one of the best ring packing.
(4) Saddle packing
The utility model belongs to a saddle shaped filler, which has the shape of a saddle and is generally made of porcelain materials. The characteristics of saddle fillers are that the surface is all open, both inside and outside, the liquid flows evenly on both sides of the surface, the surface utilization rate is high, the flow channel is arc-shaped, and the flow resistance is small. The disadvantage of this method is that it is easy to overlap, resulting in a part of the packing surface being overlapped, which reduces the mass transfer efficiency. The strength of saddle fillers is poor, and the capacity of them is broken.
Rectangular saddle packing
(5) Saddle packing
The arc surface of the two ends of the saddle packing is changed into a rectangular surface, and the sizes of the two sides are not the same, that is to say, the saddle packing is rectangular. When the saddle packing is piled up, it will not be jacketed, and the liquid distribution is relatively uniform. Rectangular saddle packing is generally made of porcelain material, and its performance is better than that of lacI ring. Most of the occasions in which ceramic lacing ring is used in China have been replaced by ceramic saddle packing
Metal ring saddle packing
(6) Metal ring saddle packing
Ring moment saddle packing (called Intalox in foreign countries) is a new type of packing designed with consideration of ring and saddle structure characteristics. The packing is generally made of metal material, so it is also called metal ring moment saddle packing. The ring moment saddle packing combines the advantages of both ring packing and saddle packing, and its comprehensive performance is better than that of Bauer ring and step ring. It is widely used in bulk packing.
(7) Spherical packing
Generally, it is made of plastic injection, with various structures. The spherical packing is characterized by the hollow sphere, which allows gas and liquid to pass through it. Due to the symmetry of the sphere structure, the packing density is uniform, and it is not easy to produce holes and bridge, so the gas-liquid dispersion performance is good. Generally, spherical packing is only suitable for some special occasions, and it is seldom used in engineering.
In addition to the above several typical bulk packing, new packing with unique configuration has been developed, such as conjugate ring packing, Haier ring packing, natt ring packing, etc.
Regular packing is a kind of packing arranged in a certain geometric configuration and stacked orderly. There are many kinds of structured packing, which can be divided into grid packing, corrugated packing, pulse packing and so on.
(1) Grid packing
It is formed by the regular combination of strip units and has many structural forms. In industry, the earliest grid packing is wood grid packing. The application of more common grid filler are grid filler, mesh grid filler, honeycomb grid filler, among which grid filler is representative.
The specific surface area of the grid packing is relatively low, which is mainly used in occasions requiring small pressure drop, large load and anti blocking.
(2) Corrugated packing
Most of the structured packing used in industry is corrugated packing, which is a disc type packing composed of many corrugated sheets. There are two obliquity angles between the corrugated sheet and the tower shaft: 30 ° and 45 °. During assembly, the two adjacent corrugated sheets are overlapped reversely. The packing of each tray is vertically installed in the tower, and the adjacent two trays are staggered 90 °.
Corrugated packing can be divided into mesh corrugated packing and plate corrugated packing according to its structure, and its material is divided into metal, plastic and ceramics.
Wire mesh corrugated packing is the main form of wire mesh corrugated packing, which is made of wire mesh. The pressure of corrugated metal wire mesh packing is reduced and the separation efficiency is very high. It is especially suitable for accurate distillation and vacuum distillation devices. It provides an effective means for distillation of difficult separation and heat sensitive systems. Despite its high cost, it has been widely used because of its excellent performance.
Corrugated metal sheet packing is a main form of corrugated metal sheet packing. There are many f5mm holes punched on the corrugated plate of the packing, which can distribute the liquid on the plate roughly and strengthen the transverse mixing. The corrugated plate is rolled into small grooves, which can subdivide the liquid on the plate and enhance the wettability of the surface. Metal orifice corrugated packing has high strength and strong corrosion resistance, which is especially suitable for large diameter tower and occasions with large gas-liquid load.
The corrugated packing of metal calendered orifice plate is another kind of representative corrugated packing. The main difference between it and corrugated metal plate packing is that the surface of the plate is not a punching hole, but a pricking hole. A very dense small pricking hole with a diameter of 0.4-0.5mm is rolled on the plate by rolling. Its separation ability is similar to that of mesh corrugated packing, but its anti blocking ability is stronger than that of mesh corrugated packing, and its price is cheaper, so it is widely used.
The advantages of corrugated packing are compact structure, small resistance, high mass transfer efficiency, large processing capacity and large specific surface area (commonly used are 125, 150, 250, 350, 500, 700, etc.). The disadvantage of corrugated packing is that it is not suitable to deal with materials with high viscosity, easy polymerization or suspended solids, and it is difficult to load, unload and clean, with high cost.
(3) Pulse packing
It is a kind of regular packing which is assembled by hollow prismatic individuals with necks in a certain way. After the assembly of pulse packing, a porous channel with necking will be formed, and its longitudinal channel will contract and expand alternately, resulting in strong turbulence when gas-liquid two phases pass through. In the necking section, the gas velocity is high and the turbulence is violent, so the mass transfer is strengthened. In the expansion section, the gas velocity is reduced to a minimum to realize the separation of two phases. The process of "pulse" mass transfer is realized by the alternate repetition of channel contraction and expansion.
Pulse packing is characterized by large capacity and small pressure drop, which is an ideal packing for vacuum distillation. Due to its excellent liquid distribution performance, the amplification effect is reduced, so it is especially suitable for large tower diameter occasions.
Polytetrafluoroethylene stem packing is a kind of soft product, which is made of polytetrafluoroethylene powder and processed by a new technology. White, continuous rope, round section. It has high flexibility, good filling, self-lubricating, low friction coefficient, corrosion resistance and other properties.
Operating temperature - 260 to + 260
Service pressure < 20MPa
Applicable to all chemicals except Fluorine and molten alkali metal.
Loading is convenient and fast. In general, it is not necessary to disassemble the valve during filling, just wrap the rope packing around the valve stem, push it into the packing box, tighten the cover cap of the box, and the packing will be pressed into a dense whole.
Excellent sealing performance. The unique microstructure of expanded polytetrafluoroethylene gives the product good flexibility and plasticity, which makes it easy to fill the internal space of the stuffing box, even all the pits and grooves on the valve rod and the box body, which also prevents the old valve from being replaced or repaired due to corrosion and wear.
Long service life. Because of its long-term soft plasticity, the leakage gap is filled at any time, but also because it is not corroded, not aging, can be used for a long time.
The valve can be opened and closed flexibly and easily. Because polytetrafluoroethylene has low friction coefficient and excellent self-lubricating property.
Do not contaminate the fluid in the pipe. Because it is white and clean, and will not fall off due to corrosion and aging, it is especially suitable for pharmaceutical, fine chemical, food and other industries.
The specification has good universality, reduces the packing storage quantity, saves the expense. Only a few sizes of stem packing are needed to meet the needs of most valves. Generally, large-sized packing which can be inserted by hand is selected, but the finer packing can also be used in large-sized valves. After compaction, it will also be molded to obtain a dense packing body.
Plastic packing is a kind of packing which is pressed by mould. It does not need to be cut off like braided packing to form a ring, and it is made into a ring according to the size of the journal. There are two types of plastic fillers: cotton like and laminated.
(1) Spongy filler
The soft filler is a mixture of fiber, graphite, mica, metal powder (or metal flake), grease and elastic binder, which is molded into a ring, and then a layer of asbestos yarn is weaved on the outer layer (metal wire can also be used as required). Another way of use is to put the mixture directly into the packing chamber and use it directly after being pressed by the gland. Because the packing has no fixed size, improper packing will easily affect the sealing performance, so this method is rarely used. According to the working conditions, the types and proportions of various mixtures in the soft packing can be adjusted, such as adding copper powder to the high-pressure steam seal, adding lead particles or pieces to the acid medium seal, adding more elastic and good adhesive to the shaft when there is vibration, etc. Because the packing does not contain lubricant, its volume changes little under high pressure, and it can be used for sealing high-speed pumps and high-pressure valves. If solid lubricant is added, good self-lubricating performance can be guaranteed, and the structure is compact, which is helpful to improve the sealing performance. In addition, the soft packing has plastic fluidity and can be combined with metal packing.
(2) Laminated packing
This kind of packing is made by coating rubber on the surface of asbestos cloth or canvas, laminating or winding and then hot pressing and vulcanizing. It can also be sandwiched with soft packing such as rubber core or embedded with spring and several kinds of laminated packing structures. The laminated packing has good sealing performance, which can be used for low-pressure steam, water and ammonia liquid below 120 ℃, mainly used for reciprocating shaft seal and valve rod seal, ring packing without interface can also be used as reciprocating pump piston ring. Due to the lack of lubricant in the packing, it is necessary to add lubricant during the use.
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