The mold design is based on the shrinkage range of various plastics, the wall thickness and shape of the plastic parts, the size and distribution of the feed ports, and the shrinkage rate of each part of the plastic parts is determined empirically, and then the size of the cavity is calculated. For high-precision plastic parts and difficult to control the shrinkage rate, it is generally advisable to use the following method to design the mold:
(1) Take a small shrinkage rate for the outer diameter of the plastic part, and take a larger shrinkage rate for the inner diameter so that there is room for correction after leaving the trial mold.
(2) The test mold determines the form, size and forming conditions of the gating system.
(3) Post-processed plastic parts shall be post-processed to determine dimensional changes (measurement shall be made 24 hours after demoulding).
(4) Correct the mold according to the actual shrinkage.
(5) Retest the mold and change the process conditions appropriately. Slightly modify the shrinkage value to meet the plastic parts requirements.
(II) Liquidity
1. The fluidity of thermoplastics can be analyzed by a series of indices such as the size of the molecular weight, the melt index, the length of the Archimedean spiral, the apparent viscosity and the flow ratio (process length/plastic wall thickness). Small molecular weight, wide molecular weight distribution, poor regularity of the molecular structure, high melt index, long length of the helix, low viscosity, and good flowability when the flow ratio is large. It is necessary to check the specification of the same product plastic to determine whether its liquidity is applicable. In injection molding. According to the mold design requirements, we can roughly divide the fluidity of commonly used plastics into three categories:
(1) good fluidity nylon, polyethylene, polystyrene, polypropylene, cellulose acetate, poly (4) methyl decene;
(2) Medium-modified polystyrene (example ABS·AS), plexiglass, polyoxymethylene, polychloroether;
(3) poor fluidity of polycarbonate, PVC, polyphenylene oxide, polysulfone, polyaryl sulfone, fluorine plastic.
2. The fluidity of various plastics also changes due to various forming factors. The main influence factors are as follows:
(1) When the temperature of the material is high, the fluidity increases, but different plastics also have different, polystyrene (especially impact resistance and high MI value), polypropylene nylon, organic glass, modified polystyrene ( The fluidity of plastics such as ABS-AS), polycarbonate and acetate fibers varies greatly with temperature. For polyethylene and polyoxymethylene, the increase or decrease in temperature has little effect on its fluidity. Therefore, the former should adjust the temperature during forming to control the fluidity.
(2) The increase in pressure injection pressure increases the shear resistance of the melt and increases the fluidity. In particular, polyethylene and polyoxymethylene are more sensitive. Therefore, injection pressure should be adjusted during molding to control fluidity.
(3) Mold structure The form, size, layout, cooling system design, melt flow resistance (such as profile finish, channel section thickness, cavity shape, exhaust system) and other factors have a direct impact on the The actual fluidity in the cavity reduces the fluidity if the melt is reduced in temperature and the flow resistance is increased. (To be continued)
(1) Take a small shrinkage rate for the outer diameter of the plastic part, and take a larger shrinkage rate for the inner diameter so that there is room for correction after leaving the trial mold.
(2) The test mold determines the form, size and forming conditions of the gating system.
(3) Post-processed plastic parts shall be post-processed to determine dimensional changes (measurement shall be made 24 hours after demoulding).
(4) Correct the mold according to the actual shrinkage.
(5) Retest the mold and change the process conditions appropriately. Slightly modify the shrinkage value to meet the plastic parts requirements.
(II) Liquidity
1. The fluidity of thermoplastics can be analyzed by a series of indices such as the size of the molecular weight, the melt index, the length of the Archimedean spiral, the apparent viscosity and the flow ratio (process length/plastic wall thickness). Small molecular weight, wide molecular weight distribution, poor regularity of the molecular structure, high melt index, long length of the helix, low viscosity, and good flowability when the flow ratio is large. It is necessary to check the specification of the same product plastic to determine whether its liquidity is applicable. In injection molding. According to the mold design requirements, we can roughly divide the fluidity of commonly used plastics into three categories:
(1) good fluidity nylon, polyethylene, polystyrene, polypropylene, cellulose acetate, poly (4) methyl decene;
(2) Medium-modified polystyrene (example ABS·AS), plexiglass, polyoxymethylene, polychloroether;
(3) poor fluidity of polycarbonate, PVC, polyphenylene oxide, polysulfone, polyaryl sulfone, fluorine plastic.
2. The fluidity of various plastics also changes due to various forming factors. The main influence factors are as follows:
(1) When the temperature of the material is high, the fluidity increases, but different plastics also have different, polystyrene (especially impact resistance and high MI value), polypropylene nylon, organic glass, modified polystyrene ( The fluidity of plastics such as ABS-AS), polycarbonate and acetate fibers varies greatly with temperature. For polyethylene and polyoxymethylene, the increase or decrease in temperature has little effect on its fluidity. Therefore, the former should adjust the temperature during forming to control the fluidity.
(2) The increase in pressure injection pressure increases the shear resistance of the melt and increases the fluidity. In particular, polyethylene and polyoxymethylene are more sensitive. Therefore, injection pressure should be adjusted during molding to control fluidity.
(3) Mold structure The form, size, layout, cooling system design, melt flow resistance (such as profile finish, channel section thickness, cavity shape, exhaust system) and other factors have a direct impact on the The actual fluidity in the cavity reduces the fluidity if the melt is reduced in temperature and the flow resistance is increased. (To be continued)
Cookware Set,Enamel Cookware Set,Cast Iron Cookware Set
Casserole&Dutch Oven,Griddle&Grill Pan Co., Ltd. , http://www.chironcookware.com