Injection of polymers under pressure is a technological process of plastics processing by injection of polymer melt under pressure into an injection mold with its subsequent cooling. The term "injection molding" reflects the peculiarity of the molding process when significant melt pressures are used to compensate for volumetric and linear shrinkage when filling and cooling in the forming cavity (injection mold).
Content
Plastic Injection
More than one third of the total volume of products from polymeric materials is produced by injection molding. Due to the high productivity and relatively high cost of equipment, it is mainly used in large-scale and mass production of plastic products. Raw materials for casting are granules of thermoplastics, thermoplastic elastomers and thermosetting powders with a wide range of mechanical and physical properties. Thermoplastic materials retain the ability to be recycled after molding, and thermosets during processing undergo irreversible chemical changes, leading to the formation of a non-meltable and insoluble material.
During the casting process, specially prepared material enters the zone of the auger of the machine, where it melts and homogenizes, and then is injected into the mold through the sprue channels under high pressure, filling its cavity with high speed and then cooling, forming a casting. The curing of the material occurs first at the cold walls of the mold cavity, and then spreads deep into the body of the casting.
Plastic Injection Molding Equipment
Plastic injection is carried out on special injection molding machines - injection molding machines (TPA). There are many types of TPA that can be classified according to various criteria.
By the location of the injection unit:
- Vertical, in which the material is injected vertically downward, and the main plane of the mold connector is located horizontally. Vertical machines are usually used for the manufacture of products with embedded elements.
- Horizontal, with horizontal injection of material and a vertically arranged plane of the mold connector.
By the number of types of material used:
- For single component casting
- For multi-component casting
By type of locking system:
- Hydraulic
- Crank lever
By type of drives:
- Electric
- Hydraulic
- Hybrid
There are also many other types of classifications.
Special plastics casting methods
- Gas casting
When using this method, the polymer is densified by supplying an inert gas under high pressure directly to or near the product area, therefore, the compaction process is easier than in conventional injection molding. Gas casting allows you to get products with good surface quality, without tightening and warping, with a minimum level of residual stresses, with high dimensional stability. [one]
- Water casting
When casting with steam at the beginning of each cycle, superheated water vapor is fed into the mold channels. The injection of molten plastic takes place in a hot mold, and then coolant is supplied to the same channels. Despite the increase in the casting cycle time, this method is gaining more and more popularity since it allows to obtain a better surface of the product: without junction lines, perfectly smooth and glossy.
- Component casting
- Water casting
- Mold Decorating ( IMD )
- Mold Assembly Casting (IMA)
Notes
Literature
- Becker M.B. Zaslavsky M.L. Injection molding
- Bihler Plastic parts - cast without defects
- Bichler Injection molding process parameters
- Braginsky. Precise casting of plastic products. 1977
- Vidgof N.B. Basics of the design of injection molds for thermoplastics
- Kalinchev Reference Manual for Effective Injection Molding
- Lapshin, Basics of Thermoplastics Processing by Injection Molding. 1974
See also
- Injection molding machine