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Introduction to Plastic Cap Moulding
Edit:Taizhou Huangyan Yige Machinery Co., Ltd.   UpDate:2018-10-17


Introduction to the plasticity of plastic bottle caps


1. The flowability of thermoplastics can be generally analyzed from a series of indexes such as molecular weight, melt index, Archimedes spiral length, performance viscosity and flow ratio (flow length / wall thickness of plastic parts). Small molecular weight, wide molecular weight distribution, poor molecular structure regularity, high melt index, long helix length, low apparent viscosity, and high flow ratio are good for fluidity. For the plastic with the same product name, its manual must be checked to determine whether its fluidity Suitable for injection molding. According to the design requirements of bottle cap molds, we can roughly divide the fluidity of commonly used plastics into three categories:

(1) Good fluidity nylon, polyethylene, polystyrene, polypropylene, cellulose acetate, poly (4) methylpinene;

(2) Poor fluidity polycarbonate, rigid polyvinyl chloride, polyphenylene ether, polysulfone, polyarylsulfone, fluoroplastic.
(3) Medium-flow modified polystyrene (eg ABS · AS), plexiglass, polyformaldehyde, polychloroether;

2. The fluidity of various plastics also changes due to various forming factors. The main influencing factors are as follows:

(1) When the temperature of the material is high, the fluidity increases, but different plastics also have different differences. Polystyrene (especially those with high impact resistance and high MI value), polypropylene nylon, organic glass, modified polystyrene ( Example ABS · AS), polycarbonate, acetate and other plastics have a greater fluidity with temperature. For polyethylene and polyformaldehyde, the influence of temperature increase and decrease on its fluidity is small. Therefore, the former should adjust the temperature to control the fluidity during forming.
(2) Mold structure The form, size, layout, cooling system design, melt flow resistance (such as profile finish, section thickness of the runner, cavity shape, exhaust system) and other factors directly affect the melt. For the actual fluidity in the cavity, the fluidity will decrease if it promotes the melt to lower the temperature and increase the fluidity resistance. (3) Pressure The injection pressure increases, the melt will be affected by shearing, and the fluidity will increase, especially polyethylene and polyformaldehyde are more sensitive, so it is advisable to adjust the injection pressure to control the fluidity during forming.
When designing the mold, a reasonable structure should be selected according to the fluidity of the plastic used. During forming, the material temperature, mold temperature, injection pressure, injection speed and other factors can also be controlled to appropriately adjust the filling situation to meet the needs of forming.