The first mock exam is short shot, insufficient filling and dissatisfactory parts. It is commonly known as underinjection, which means that some incomplete phenomena at the end of the material flow, or a part of the cavity filled with a few dissatisfied parts, especially the end area of the thin wall area or the flow path. It shows that the melt condenses without filling the mold cavity, and the molten material does not fill completely after entering the mold receiving cavity, resulting in the lack of material in the product.The main reason for short injection is that the flow resistance is too large, which makes the melt unable to continue to flow. The factors influencing the melt flow length include: the wall thickness of the part, mold temperature, injection pressure, melt temperature and material composition. If these factors are not handled well, it will cause short injection.1. Improper equipment selectionWhen using the equipment, the maximum injection volume of the injection molding machine must be greater than the total weight of the plastic part and nozzle, and the total injection weight cannot exceed 85% of the plastic volume of the injection molding machine.
2. Insufficient supplyAt present, the commonly used method to control the feeding is the constant volume feeding method. Whether the roller material quantity is uniform with the fruit grain diameter of the raw material, and whether there is a "bridge" phenomenon at the bottom of the feeding port. If the temperature at the feeding port is too high, it will also cause poor blanking. In this regard, the feeding port should be dredged and cooled.
3. Poor material fluidityWhen the fluidity of raw materials is poor, the structure parameters of the die are the main reason for the under injection. Therefore, it is necessary to improve the stagnant flow defects of the mold pouring system, such as setting the sprue position reasonably, enlarging the sprue, the runner and the size of the sprue, and using a larger nozzle.At the same time, some additives can be added to the raw material formula to improve the flow performance of the resin. In addition, it is also necessary to check whether the amount of raw material is excessive and reduce the amount properly.
4. Excessive lubricantIf there is too much lubricant in the raw material formula, and the wear clearance between the feed screw check ring and the barrel is large, the refluxing of the melt in the barrel will cause the shortage of feed and the lack of injection. Therefore, it is necessary to reduce the amount of lubricant, adjust the gap between the barrel and the injection screw and the check ring, and repair the equipment.
5. Cold material impurities block the material channelWhen the impurities in the molten material block the nozzle or the cold material blockWhen gate and runner, the nozzle should be folded down to clean or expand the cold cavity and runner section of the mold.6. Unreasonable design of pouring systemWhen the first mock exam is multi chamber, the appearance defects of plastic parts often result from unreasonable design of gate and runner balance. When designing the gating system, we should pay attention to the balance of the gates. The weight of the plastic parts in each cavity should be proportional to the size of the gates, so that the cavities can be filled at the same time. The gate location should be at the thick wall, or the design scheme of balanced layout of the shunt channel can be adopted.
