Process guidelines for injection molding pvc foam shoe material
1. Mixing ratio of plastic and foaming:
The proportion of the blowing agent to be added is generally from 0.3% to 0.5% (depending on the degree of foaming required for injection molding or the surface condition after foaming of the product).
Second, the setting of the injection molding machine:
1. Setting of barrel temperature of injection molding machine:
1) The temperature of the barrel of the injection molding machine is parabolic, that is, the temperature distribution of the barrel is low at the middle and high ends. As shown below:
2) The screw feed section temperature setting is low (mainly the foaming agent and plastic begin to melt).
3) The temperature of the screw compression section is set high, generally 15 ° C -25 ° C higher than the feeding section (mainly the foaming agent gets more heat, so that the foaming agent decomposes to generate a large amount of gas and is evenly distributed in the plastic melt).
4) The temperature setting of the screw metering section is generally 10 °C - 15 °C lower than the temperature of the compression section (the pressure of the melt and gas is increased when the temperature is low-sprayed and melted, and the ability to force the gas to melt in the melt is higher).
5) The temperature setting of the nozzle should be as low as possible to just shoot out the glue (the flow rate in the melt nozzle is also lowered when the temperature is low, so that the pressure is increased and the gas is more effectively melted in the melt).
2, the speed of injection:
The speed of the shot is as fast as possible without causing defects in the product (so that the melt has sufficient time to swell before the mold is set in the mold). The shot glue is usually divided into two sections of the rate of fire, the first section is as fast as possible (usually 85% or more of the fastest speed, the shot stroke is set to 80%-95% of the total weight of the product), and the second section can be slower (generally The fastest speed is 20%-30%, so that the air in the mold has enough time to discharge).
When the melt foams and swells in the mold, its swelling pressure is smaller than the holding pressure. If the pressure is used, the melt foaming will not increase, so it is not necessary to hold the pressure during foam injection molding. Or use a relatively small pressure.
4, the melt glue termination:
When the styrofoam is injected into the cavity, it will expand in an instant, so the amount of glue to be injected needs to be reduced, so that the foaming compound has a space to rise. At the same time, the shrinkage problem of the rubber can be solved and the weight of the product is also Can be reduced.
Third, the control of the process in injection molding:
1. Bubble volume and nucleation density control:
The volume and density of the bubble are controlled by the following factors (↑ increase ↓ decrease - no effect)
Bubble volume nucleation density
(1) Barrel temperature ↑ ↑ ↑
(2) Mold temperature ↑ ↑ ↑
(3) Thickness of plastic parts ↑ ↑ ↓
2, surface smoothness:
The blowing agent contains a special tension agent to help keep the bubble in the center of the rubber part, greatly reducing the phenomenon of the floating surface of the bubble. However, if you encounter the floating surface of the bubble in special cases and affect the surface gloss, you can adjust the machine by referring to the following relationship, and eliminate the floating surface problem as much as possible (↑ increase ↓ decrease)
(1) Injection rate of fire injection ↑ ↓
(2) Barrel temperature ↓ ↓
(3) Mold temperature ↓ ↓
(4) Thickness of rubber parts ↑ ↓
(5) Die exhaust speed ↓ ↓
If the effect of the foam is not satisfactory after trying to adjust all the above parameters, then the amount of foaming agent should be adjusted to achieve a satisfactory foaming effect. The following information lists that when the injection molding parameters and the thickness of the rubber parts are constant, the amount of the blowing agent used has the following effects on the effect of the foam.
3. The effect of the amount of foaming agent on the rubber parts:
Foaming agent usage, volume, nucleation density, degree of bubble surface
Note:Due to the different design and performance of each injection molding machine and mold, the above instructions for the injection molding process are for reference only.