1, pressure Determination of holding pressure: T […]
Determination of holding pressure: The ideal holding pressure is usually between low holding pressure and high holding pressure. A lower holding pressure refers to a specific holding pressure based on an accurate speed-pressure turning point and holding pressure when the injection molded article appears insufficient. Higher holding pressure refers to the holding pressure at a certain speed pressure switching point, and the holding pressure when the product overflows.
In fact, different plastic types (specific holding pressure values) are usually used to describe the percentage of injection pressure.
2, holding time
The determination of the holding time, which is usually based on the gate condensation determined by the product measurement.
If the holding time is too long, it will affect the injection cycle. If the holding time is too short, the plastic parts are not heavy enough, and the interior of the product is small and empty. Holding pressure will affect the length of holding time. The higher the holding pressure, the longer the holding time.
3, screw speed
The purpose of screw rotation during injection molding is to pre-plasticize the plastic. The purpose of pre-plasticizing is to obtain uniform temperature, that is, melt, cold material, decomposition, excess gas without uniform plasticizing.
的 Determination of screw speed: The general principle of screw injection molding is to make the screw's preplasticizing time, the suction time and shrinkage time of the injection sheet slightly shorter than the cooling time of the product.
The screw speed is too fast, uneven plasticization will cause the product material to cool, insufficient filling and cracking, and plastic decomposition (caused by defects, such as focus, color difference and cracking). If the screw speed is too slow, the injection cycle will be long and production efficiency will be reduced.
4, cooling time
The general principle is that the shorter the cooling time of the product, the better, but the basic requirements are that the product does not deform, does not stick to the mold, and does not have excessive traces of demolding.
After determining the molding material, the theoretical cooling time can be calculated according to the wall thickness of the product and the temperature of the plastic, the temperature of the mold, and the temperature of the product taken out. The temperature at which the product is removed is often referred to as the thermal transition temperature.
Of course, in actual operation, the cooling time depends on the molding conditions, the type of molding material and the shape of the molded product, so the molding is performed according to the calculated cooling time, and the cooling time depends on the quality of the product.
In the molding cycle, the cooling time accounts for about 50% of the entire cycle. Therefore, in order to shorten the molding cycle, it is very effective to improve the cooling time efficiency of the mold.
In addition, the purpose of awakening the cooling mold is to smoothly demold the plastic parts without deformation, so determining a reasonable demolding temperature is essentially a reasonable cooling time. Different plastics have different emission temperatures.