How does the injection product bubble?
Publisher：Manager Release time：2017-03-23
In the injection molding products, there are a lot of people in the production and processing of the problem, in general, there are many reasons for this problem, but if not timely processing, not only will make plastic molding bad, but also may produce more Of the defects, so when there is injection of plastic products, we must promptly resolved. The appearance of bubbles will make the product filled with dissatisfaction, uneven surface. Vacuum bubbles, this bubble is mainly due to shrinkage caused by plastic products, wall thickness of plastic products in the cooling, because the surface cooling rate faster than the middle of the cooling rate, which will lead to plastic products at the center of the lack of glue, the formation of 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.
, Often bubble defects, bubbles can be divided into two kinds of bubbles and vacuum bubble. In general, the bubbles that occur on the transparent article can be observed directly, and the bubbles that occur on the opaque article are sometimes visible from the outside and can only be found by cutting or using other means. Bubble is generally due to the injection speed is too fast, the plastic flow can not force the air inside the cavity all discharged from the exhaust tank, the air mixed into the plastic bubble. Vacuum bubble is due to the slow wall of the product due to the slow cooling, rapid cooling and shrinkage of the surface will often pull the material over the volume shrinkage caused by uneven volume caused by the thickness of the part of the hollow; raw materials have cold and heat when the water And contains the air, the speed becomes bubbles.
1. improper control of molding conditions
Many process parameters have a direct impact on the generation of bubbles and vacuum bubbles. Set the injection pressure is too low, the injection speed is too fast, injection time and cycle is too short, too much or too little feeding, insufficient packing, uneven cooling or cooling, and the material temperature and mold temperature control properly, Pieces produce bubbles. In particular, high-speed injection, the mold of the gas too late to discharge, resulting in too much residual gas within the melt, which should be appropriate to reduce the injection speed. If the speed drops too much and the injection pressure is small, it is difficult to exhaust the gas in the melt, it is easy to produce bubbles and depression and omission, so adjust the injection speed and pressure should be particularly careful. In addition, by adjusting the injection and holding time, to improve the cooling conditions, control the amount of feeding and other methods to avoid the bubble and vacuum bubble. If the plastic parts of the cooling conditions are poor, the plastic parts can be released immediately after the hot water in the slow cooling, so that the cooling rate inside and outside the line tends to be consistent. In the control of mold temperature and melt temperature, it should be noted that the temperature can not be too high, otherwise it will cause the melt degradation of decomposition, resulting in a large number of gas or excessive contraction, the formation of bubbles or shrinkage; if the temperature is too low, Lack of plastic parts within the easy to produce gaps, the formation of bubbles. Under normal circumstances, the melt temperature control should be slightly lower, the mold temperature control was slightly higher. In such a process conditions, it is not easy to produce a lot of gas, not easy to produce shrinkage. In the control of the cylinder temperature, the temperature of the supply section can not be too high, otherwise it will produce back to the air caused by the return.
2. Mold defects
If the gate position of the mold is not correct or the gate section is too small, the main channel and the diversion channel are long and narrow, there are gas dead ends or poor mold exhaust, which can cause bubbles or vacuum. Therefore, we should first determine whether the mold defects are the main cause of bubbles and vacuum bubbles. Then, for the specific circumstances, adjust the mold structure parameters, especially the gate position should be set in the thick wall of plastic parts. Select the gate form, because the direct gate to produce a vacuum hole is more prominent, should try to avoid the selection, which is due to the end of the pressure, the pressure in the cavity than the gate in front of the high pressure, if the direct gate Where the melt has not yet frozen, it will melt back phenomenon, so that the formation of hollow cavities. In the case of the gate can not be changed, can be extended by the holding time, increase the amount of feed, reduce the taper of the gate and other methods to adjust. Gate section can not be too small, especially at the same time forming several different shapes of plastic parts, we must pay attention to the size of the gate to be proportional to the weight of plastic parts, otherwise, the larger plastic parts prone to bubbles. In addition, it should be shortened and widened slender and narrow flow path, eliminating the gas in the runner dead ends, excluding mold exhaust failure. Design mold, should try to avoid the plastic parts of the body with a thick part of the thickness or so great.
3. Raw materials do not meet the requirements
If the raw material in the raw material or volatile content of excessive, the material is too small or uneven size, resulting in the feed process mixed with too much air, the shrinkage of raw materials is too large, melt melt index is too large or too small, Recycled material too much, will affect the plastic parts of the bubble and vacuum bubble. In this regard, should be used respectively pre-drying raw materials, screening out the fine material, replace the resin, reduce the amount of recycled materials and other methods to be resolved.
Bubbles often occur at the last seam of the plastic or the thick part of the product. The product is first surface cooled in the mold, and when the outer surface is cooled, the central portion is still in a hot state. The central part of the cooling to shrink, while the plastic surface has been cooled, so only by the internal shrinkage and the formation of bubbles. There are many thick pieces in the mold when there is no bubbles, but after tens of seconds, there are bubbles in the central part of the emergence.
There are many reasons for the injection of plastic products, when there is such a situation, to one by one to exclude, in addition, but also to find a way to solve the use of methods to solve the injection products have bubbles, can not care, do not know can also please professional The master operation.
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