Regardless of the method used to foam, the basic process is: Foaming 1 introduces a gas into a liquid or molten plastic to produce micropores; 2 to make the micropores grow to a certain volume; 3 Fix the microporous structure by physical or chemical means. According to the manner in which the gas is introduced, the foaming methods are mechanical, physical, and chemical. Mechanical method: Introduce large amounts of air or other gases into the liquid plastic with strong agitation. This method is mainly used in the industry to produce urea-formaldehyde foam, which can be used as a thermal insulation material or a set material in a movie (such as artificial snowflake). Physical method: Low-boiling hydrocarbons or halogenated hydrocarbons are often dissolved in plastics, and the plastic softens when heated, while the dissolved liquid volatilizes and expands. For example, in the case of polystyrene foam, in the suspension polymerization of styrene, pentane is first dissolved in the monomer, or the polystyrene resin which has been polymerized into beads is treated with pentane under heat and pressure to obtain a so-called polystyrene foam. Expandable polystyrene beads. The beads are pre-expanded in hot water or steam, and then placed in a mold to pass steam, so that the pre-expanded particles are secondarily expanded and sintered to each other, and after cooling, a product having the same shape as that of the mold cavity is obtained. They are widely used as shock-proof materials in insulation and packaging. An extrusion molding method may also be employed. In this case, the expandable beads may be used to be foamed and extruded into a sheet at one time; or ordinary polystyrene pellets may be used, and halogenated at the appropriate portion of the extruder. The hydrocarbon is mixed evenly with the plastic melt, and expands and foams as the material leaves the machine head. The extrusion method is commonly used for making sheets or sheets, and the sheets can be formed into food packaging boxes and trays by vacuum forming. Polyethylene can also be obtained in a similar manner to produce an extruded foamed article. Physical methods for introducing a gas include a dissolution method, a hollow microsphere method, and the like. In the dissolution method, a soluble substance such as salt, starch or the like is mixed with a resin to form a product, and then the product is repeatedly treated in water to dissolve the soluble substance, thereby obtaining an open-cell type foam product, which is often used as a filter material. The hollow microsphere method is to mix the hollow glass microspheres with high melting temperature with the plastic melt, and a special closed-cell foam can be obtained under the molding conditions that the glass beads are not broken. Chemical methods: can be divided into two categories: 1 using chemical blowing agents, which liberate gases when heated. Commonly used chemical blowing agents, such as azodicarbonamide, azobisisobutyronitrile, N,N'-dinitrosopentamethylenetetramine, sodium hydrogencarbonate and the like. Many thermoplastics can be made into foams by this method. For example, PVC foam shoes are made of resin, plasticizer, foaming agent and other additives into the injection molding machine. The foaming agent is decomposed in the barrel and the material is foamed in the mold. . The foamed artificial leather is mixed with the foaming agent into the polyvinyl chloride paste, scraped or calendered on the fabric, continuously passed through the tunnel heating furnace, the material is plasticized and melted, the foaming agent is decomposed and foamed, cooled and surface-finished, ie Made of foam artificial leather. The rigid polyvinyl chloride low foaming sheet, pipe or profile is formed by extrusion. The foaming agent is decomposed in the barrel. When the material leaves the machine head, the pressure drops to normal pressure, and the dissolved gas expands and foams. The foaming process is properly matched with the cooling and setting process to obtain a structural foam article. 2 Using a by-product gas in the polymerization process, a typical example is a polyurethane foam. When the isocyanate and the polyester or polyether are subjected to a polycondensation reaction, a part of the isocyanate reacts with water, a hydroxyl group or a carboxyl group to form carbon dioxide. As long as the gas evolution rate and the polycondensation reaction rate are properly adjusted, it is possible to produce a highly foamed product in which the cells are very uniform. There are two types of polyurethane foams. Soft open-hole shapes are like sponges. They are widely used as cushions for various seats and sofas, as well as sound absorbing and filtering materials. Hard closed-cell type is ideal for insulation, insulation and shock absorption. And floating materials. Ball Valve ,Steel Ball Valve,Stainless Steel Ball Valve,1 Inch Ball Valve Zhejiang Chenxiang import and export trade Co., Ltd , https://www.chenxiang-valve.com