Generally, during the injection process of plastic gears, one or more defects may occur. These defects affect the strength of plastic gears and the performance of NVH, and may even cause the entire system to fail. Therefore, we must be able to distinguish the gear Common defects of injection molding, let's take a look at Shenzhen Huanke Precision Manufacturing Co., Ltd. below!
The defects of plastic gears are similar to the defects of other common plastic products:
(1) Scorch defects
Scorching often occurs in mold products where the injection speed is fast and the venting is insufficient.
Most people can't achieve such an effect.
Scorching has a relatively large impact on the performance of the product, especially on the specifications filled with glass fiber, which has a huge impact on performance.
(2) Internal shrinkage
Due to design / manufacturing reasons, there are defects such as shrinkage holes (bubbles) inside the gear. Such defects are difficult to completely avoid when molding larger POM gears. Therefore, for POM gears, designers should pay special attention to wall thickness. The distribution should be uniform. For the mold engineer, pay special attention to the position of the mold inlet. The process engineer should pay special attention to the setting of the process, and use special process parameters if necessary.
(3) Surface bubbles / silver wire
Air bubbles appear on the surface, which is usually easy to occur when injection molding nylon products. This is because nylon materials have a high water absorption rate, and some manufacturers have insufficient dehumidifying and drying equipment capabilities, resulting in the moisture content of the injection molding raw materials exceeding the regulations, resulting in a surface. The generation of air bubbles.
Another reason for the bubbles / silver wires is that the higher melting temperature and longer residence time lead to degradation of the material. (The process instruction is extremely important !!!)
In fact, injection molding defects are much more than the above, and it is difficult to detect with the naked eye, but the actual impact may be greater:
A. There are cold and miscellaneous materials in the product
There are cold materials and miscellaneous materials in the product. At this time, the other parts of the product are not fused with the cold materials and miscellaneous materials, and there is no connection strength. The degree of influence is even higher than the same size pore defects. In black products, cold materials and miscellaneous materials are difficult to find, which is one of the reasons why high strength products are required to be natural.
Delamination of product B
The cooling process of plastic injection leads to the emergence of laminar flow, and the longer injection time is the main factor for the occurrence of laminar flow. Once the product has a delamination phenomenon, its strength drop will be extremely drastic, such as 50% or even 80% strength drop. occur.
I have seen three quality accidents of internal stratification of plastic products due to laminar flow, the intensity of which has dropped by more than 50%, and those three major quality accidents have caused direct economic losses of millions.