What to do if PPS products have burrs during injection molding

As a cheap and high-performance engineering plastic, PPS is increasingly widely used in custom plastic injection molding. However, its molding characteristics have always been a constraint on its widespread use, and how to improve its burrs is also a problem explored by various molding departments.
1. Introduction to the characteristics of PPS engineering materials PPS, whose chemical name is polyphenylene sulfide, has good rigidity and dimensional stability, and high temperature performance, making it the preferred plastic for electronic components. It has an extremely high glass transition temperature of about 210 degrees, so a high temperature mold temperature of 130 to 150 degrees is required to improve its crystallinity, thereby producing good strength and beautiful appearance. Because its crystallization speed is too slow, it is easy to produce burrs in production, and its limit gap is 0.01mm. At the same time, because the molecular chain contains benzene rings, it produces a large π chain, which makes its structure stable and not easy to produce hydrogen chains, so it has a very low water absorption rate. Due to its extremely small burr gap, it is a great trouble in production. Of course, it is best to fundamentally improve the crystallization rate of PPS, but improving from the source of the mold is also a good method.
2. Basic principles in mold design Generally speaking, there is such a principle in mold design: use plug-in where plug-in can be used, and use backing when plug-in is really not possible, but backing must take positive tolerance to prevent the growth of burrs. Plug-in means plug-in. It is a good way to prevent burrs: from a closer look, if the flow direction of the molten material is to drill into the plug-in gap to become a burr, its flow direction will be changed vertically, and then its pressure and momentum will become smaller. Therefore, the possibility of burrs growing in the plug-in gap is very small, this is one. Secondly, its single-side gap is generally 0.005mm, which is lower than its burr limit gap. Butt-to-butt means two surfaces are close together. However, due to various reasons, after the mold is closed, the two surfaces cannot be completely close together, and burrs may grow. If it is a functional area, especially an electronic component, no burrs are allowed. Therefore, taking the positive tolerance in the butt-to-butt direction can relatively improve the burrs. For PPS, the exhaust groove in the mold, the author recommends that it should not be too large. The author once did an experiment: when the depth is 0.01mm, the exhaust groove has a slight burr, and when the depth is 0.008mm, the burr can be basically eliminated.

3. Problems and solutions in PPS mold design If the above three principles are applied, the burrs of PPS can also be effectively controlled, but how to improve the burrs of the parting surface, the author has also had such troubles. From all aspects of analysis, according to the above three principles, to improve the burrs, the best way is the first one: butt-to-butt. If we consider this aspect, we can raise the molding surface of the product and lower the parting surface, so as to form butt-to-butt. .However, due to the assembly error, this design may scratch the male and female molds on both sides of the insertion, which not only fails to achieve the improvement effect, but also wastes costs. However, we can use the principle of inclined surface insertion to improve this design, so that we can form the insertion form, and use the inclined surface to prevent the male and female molds (movable mold and fixed mold) from being scratched, thereby effectively controlling the growth of burrs. The inclined surface only needs to be 0.05mm, and in order to make the inclined surface close, a certain gap of about 0.05~0.10mm can be left on the parting surface. This aspect is an improvement case that the author has personally experienced, and the effect is obvious.
IV. Conclusion The burr problem of PPS in production is a big problem, which is also determined by its crystallization characteristics. Improving from the mold section is a good way to improve production efficiency and quality. Based on this improved design, it has shown obvious improvement effects in production.