What to do if air bubbles appear in injection molded products

Bubbles in injection molded products are a problem that many people encounter in production and processing. Generally speaking, there are many reasons for such problems, but if they are not handled in a timely manner, not only will plastic molding be defective, but more Defects, so when there are bubbles in the injection molded products, it must be resolved in a timely manner. The appearance of air bubbles will make the product unsatisfactory and the surface uneven. Vacuum bubbles, which are mainly caused by the shrinkage of plastic products. When the plastic products with thick walls are cooled, the surface cooling rate is faster than the middle cooling rate, which will cause a lack of glue at the center of the plastic products. Vacuum. Solving such vacuum bubbles can be improved by reducing the injection speed, increasing the injection pressure, increasing the feed, and using a material with a high melt viscosity grade.

1. Improper control of molding conditions  

Many process parameters have a direct impact on the generation of bubbles and vacuum bubbles. Setting the injection pressure too low, the injection speed is too fast, the injection time and cycle are too short, too much or too little feed, insufficient holding pressure, uneven or insufficient cooling, and improper control of the material temperature and mold temperature will cause plastic Bubbles were generated inside the piece. Especially during high-speed injection, the gas in the mold is too late to exhaust, resulting in too much residual gas in the melt. Therefore, the injection speed should be appropriately reduced. If the speed drops too much and the injection pressure is small, it is difficult to exhaust the gas in the melt, and it is easy to generate bubbles and dents and under-injection. Therefore, special care should be taken when adjusting the injection speed and pressure. In addition, air bubbles and vacuum bubbles can be avoided by adjusting the injection and dwell time, improving cooling conditions, and controlling the amount of feed. If the cooling conditions of the plastic parts are poor, the plastic parts can be slowly cooled in hot water immediately after demolding, so that the internal and external cooling rates tend to be consistent. When controlling the temperature of the mold and the temperature of the melt, it should be noted that the temperature should not be too high, otherwise it will cause the melt to degrade and decompose, generate a large amount of gas or excessive shrinkage, and form bubbles or shrinkage holes; if the temperature is too low, it will cause the filling and compaction Insufficient, voids are easily generated inside the plastic parts, and air bubbles are formed. In general, the melt temperature should be controlled slightly lower, and the mold temperature should be controlled slightly higher. Under such process conditions, it is not easy to generate a large amount of gas, and it is not easy to generate shrinkage. When controlling the temperature of the barrel, the temperature of the feeding section should not be too high, otherwise it will cause backflow and backflow and cause bubbles.

2. Mould defect  

If the gate position of the mold is incorrect or the cross-section of the gate is too small, the main flow channel and the shunt channel are long and narrow, and there is air storage in the flow channel or poor mold exhaust, which will cause bubbles or vacuum. Therefore, you should first determine whether the main cause of mold defects and air bubbles. Then, according to the specific situation, adjust the structural parameters of the mold, especially the gate position should be set at the thick wall of the plastic part. When selecting the gate type, the vacuum hole produced by the direct gate is more prominent, so it should be avoided as much as possible. This is because the pressure in the cavity is higher than the pressure in front of the gate after the holding pressure is maintained. The molten material at the place has not been frozen, and the phenomenon of reverse flow of the molten material will occur, so that holes are formed inside the plastic part. In the case where the gate form cannot be changed, it can be adjusted by extending the pressure holding time, increasing the supply amount, and reducing the taper of the gate. The cross section of the gate should not be too small, especially when forming several plastic parts with different shapes at the same time, it must be noted that the size of each gate must be proportional to the weight of the plastic part, otherwise, large plastic parts are prone to air bubbles. In addition, the slender and narrow flow channel should be shortened and widened to eliminate the air storage in the flow channel and eliminate the failure of poor mold exhaust. When designing the mold, try to avoid having extra thick parts on the shape of the plastic part or too much thickness.    

3. The raw materials do not meet the requirements for use  

If the moisture or volatile matter content in the molding raw material exceeds the standard, the pellets are too small or the size is not uniform, resulting in too much air mixed in the feeding process, the shrinkage of the raw material is too large, and the melt index of the melt is too large or too small Too much content of recycled materials will affect the production of air bubbles and vacuum bubbles. In this regard, methods such as pre-drying raw materials, sieving fines, replacing resins, and reducing the amount of recycled materials should be used to solve them.
Air bubbles often occur at seams or thicker parts of plastic products. The surface of the product is first cooled in the model. When the outer surface has cooled, the central part is still hot. The central part shrinks as it cools, and the plastic surface has cooled, so it can only shrink by itself to form air bubbles. Many thick parts have no bubbles when they are ejected, but after tens of seconds, bubbles appear in the center.
There are many reasons for air bubbles in injection molded products. When this happens, you must eliminate them one by one. In addition, you must find ways to solve them. When you use methods to solve the air bubbles in injection products, you can't be careless. Master operation.