In the process of molding and filling the mold cavity, if the filling performance of the product is not good, the pressure drop is too large, the filling time is too long, the filling is not satisfied, etc., so that the product has quality problems.
In order to improve the filling performance of the product during molding and improve the quality of the molded product, the following aspects can generally be considered:
1. Change another series of Keyue products;
2. Change the gate position;
3. Change the injection pressure;
4. Change the geometry of the part.
The control of the injection pressure is usually divided into the control of the primary injection pressure, the secondary injection pressure (holding pressure), or the control of the injection pressure of three or more times. Whether the pressure switching timing is appropriate is very important to prevent the pressure in the mold from being too high, to prevent overflow or lack of material, etc. The specific volume of the thermoplastic rubbers injection molding process mold molding depends on the melt pressure and temperature when the gate is closed during the pressure holding stage.
If the pressure and temperature are the same every time the pressure is switched from the holding pressure to the cooling stage of the product, the specific volume of the product will not change. At a constant molding temperature, the most important parameter that determines the size of the product is the holding pressure, and the most important variables that affect the dimensional tolerance of the product are the holding pressure and temperature.
For example, after the mold filling is completed, the holding pressure decreases immediately, and when the surface layer forms a certain thickness, the holding pressure rises again, so that large products with thick walls can be formed with low clamping force, and the collapse pits and flashes can be eliminated.
The holding pressure and speed are usually 50%~65% of the maximum pressure and speed when the plastic fills the cavity, that is, the holding pressure is about 0.6~0.8mpa lower than the injection pressure. Since the holding pressure is lower than the injection pressure, the load of the oil pump is low during the considerable holding time, so the service life of the oil pump is prolonged, and the power consumption of the oil pump motor is also reduced.
A certain metering is pre-adjusted, so that there is still a small amount of melt (buffer) at the end of the screw near the end of the injection stroke, and the injection pressure (secondary or third) is further applied according to the filling of the thermoplastic rubber injection mold. injection pressure), add a little melt. In this way, the product can be prevented from sinking or the shrinkage of the product can be adjusted.
The cooling time mainly depends on the melt temperature, the wall thickness of the product and the cooling efficiency. In addition, the hardness of the material is also a factor.
Harder varieties will set faster in the mold than very soft varieties. If cooling is done from both sides, the cooling time required will typically be about 10 to 15 seconds per 0.100' of wall thickness. Encapsulated articles will require longer cooling times because they can be cooled efficiently with less surface area. The cooling time required per 0.0100' of wall thickness will be approximately 15 to 25 seconds.
