Also known as plastic molding processing. It is a general term for various processes for converting synthetic resins or plastics into plastic products and is a large production part of the plastics industry. Plastic processing generally includes the formulation, molding, machining, joining, modification and assembly of plastics. The latter four processes are carried out after the plastic has been formed into a product or a semi-finished product, also known as plastic secondary processing.
Plastic processing is developed with the development of synthetic resins, which promotes the development of plastic machinery. Many plastic processing techniques are based on rubber, metal and ceramic processing. The history of plastic processing can be traced back to the 1890s. After the birth of celluloid, because of its flammability, it can only be formed into a block by molding, and then mechanically processed into a sheet, which can be processed by thermoforming.
This is the earliest plastic processing. Casting was successfully developed with the advent of phenolic resin; injection molding began in the 1920s for processing cellulose acetate and polystyrene; in the mid-1930s, soft polyvinyl chloride extrusion was successfully developed, plastic-specific A single-screw extruder was introduced; in 1938, the twin-screw extruder was also put into production. In the early 1940s, polyurethane foam was produced and blow molding technology was used to produce polyethylene hollow products. In 1952, the reciprocating screw injection machine was introduced, which made the injection molding technology enter a new stage. In the 1960s and 1970s, the newly developed plastic processing technologies were: various new reinforced plastic molding methods, such as winding, pultrusion, sheet molding, reaction injection molding, structural foam molding, profile extrusion, sheet Solid phase molding and co-extrusion, co-injection, and the like. In the 1980s, plastic processing was moving toward high efficiency, high speed, high precision, energy saving, large-scale or ultra-small, ultra-thin, etc. Computer technology entered this field and advanced the entire plastic processing technology to a new level.
Ingredients used in plastic processing of ingredients, in addition to polymers, generally add various plastic additives (such as stabilizers, plasticizers, colorants, lubricants, reinforcing agents and fillers) to improve the molding process and products. Use performance or reduce the cost of the product. The additive and the polymer are mixed and uniformly dispersed into a powder, which is also referred to as a dry blend. Sometimes the powder needs to be processed into pellets by mastication. Such powders and pellets are collectively referred to as batch or molding compound.
The key link in the processing of shaped plastics. Various forms of plastic (powder, pellets, solution or dispersion) are made into articles or blanks of the desired shape. There are more than thirty methods of forming. Its choice depends mainly on the type of plastic (thermoplastic or thermoset), the starting form, and the shape and size of the product. Commonly used methods for processing thermoplastics include extrusion, injection molding, calendering, blow molding, and thermoforming. The thermosetting plastics are generally molded, transferred, and injection molded. Lamination, molding, and thermoforming are the shaping of plastic on a flat surface. The above plastic processing methods can be used for rubber processing. In addition, there are castings using liquid monomers or polymers as raw materials. Among these methods, extrusion and injection molding are used most and are the most basic molding methods. Machining uses plastic and wood processing methods to produce plastic products of very precise or small quantities. It can also be used as an auxiliary process for forming, such as sawing of extruded profiles. Because the properties of plastic are different from those of metal and wood, the thermal conductivity of plastic is poor, the coefficient of thermal expansion and the modulus of elasticity are low. When the clamp or tool is too pressurized, it is easy to cause deformation, it is easily melted by heat during cutting, and it is easy to adhere to the tool. on. Therefore, when the plastic is machined, the tools used and the corresponding cutting speeds must be adapted to the plastic characteristics. Commonly used machining methods include sawing, shearing, punching, turning, planing, drilling, grinding, polishing, and threading. In addition, plastic can also be cut, punched and welded with a laser. The method of joining the plastic parts is welding and bonding. The welding method is hot air welding using electrodes, hot melt welding using hot poles, and high frequency welding, friction welding, induction welding, ultrasonic welding, and the like.
The bonding method can be divided into a flux, a resin solution and a hot melt adhesive according to the adhesive used. The purpose of surface modification is to beautify the surface of plastic products, usually including: mechanical modification, that is, using enamel, grinding, polishing, etc., to remove burrs, burrs, and resizing of parts, etc.; finishing, including coating the surface of the parts with paint, Use a solvent to brighten the surface, apply a patterned film to the surface of the product, etc.; apply color, including painting, printing and hot stamping; metal plating, including vacuum coating, electroplating, and chemical silver plating. The hot stamping is to transfer the colored aluminum foil layer (or other film layer) on the hot stamping film to the workpiece under heating and pressure. Many household appliances, building products, daily necessities, etc., use this method to obtain patterns such as metallic luster or wood grain. The assembly uses the methods of bonding, welding, and mechanical joining to assemble the finished plastic parts into a complete product. For example: plastic profiles are assembled into plastic window frames and plastic doors through steps such as sawing, welding and drilling.
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