PC / ABS injection moulding often appear 7 kinds of problems and solutions

1. Silver wire problem

Silver wire is the most common problem of PC/ABS material, silver wire is also known as silver grain, water flower, material flower, etc. It is a silver whitish filament stripe phenomenon that appears on the surface of the product along the flow direction.

The main reason is because of the interference of gases, which are divided into three main components:

Air: air involved in the melting and injection stages; and

Moisture: moisture contained in the material itself; and

Cracking gas: gas produced by high temperature hydrolysis/thermal decomposition.

Solution: Firstly, check whether the material is dried sufficiently, after confirming that the material is dried sufficiently, then improve the silver wire defect by adjusting the injection moulding process. At the same time, the defective silver wire is also related to the mould exhaust.

2.Flow marks problem

Flow marks are produced when the material is injected due to poor material flow. Flow marks are different from silver streaks in that they are not caused by moisture or material decomposition and have a different appearance.

3. Problems of shrinkage holes and dents

Shrinkage is caused by insufficient filling of material in the mould cavity.

Solution: Increase the mould temperature and material temperature to improve the fluidity of the material, prolong the holding time of the injection, increase the injection pressure, increase the injection speed to improve the mould filling, you can also increase the size of the gate, heat the gate runner to reduce and eliminate the shrinkage of the product.

Product design is not proper cause, when the material temperature is too low, it will not only produce shrinkage holes, but also the dent problem, the material temperature is too high, the mould temperature is too high, it will make the molten material shrink too much when cooling, so as to produce the dent.

Solution: Adopt suitable processing problem, improve injection speed and measures.

4 Warpage and deformation problem

The warping and deformation of injection moulded parts is due to the irrational design of the parts, improper location of the gate and irrational conditions of the injection moulding process, resulting in internal stresses, uneven or excessive shrinkage, high or uneven mould temperatures, causing the parts to stick to the film and difficult to release the mould, or uneven cooling, which will also produce warping and deformation.

Processing technology: lengthen the injection moulding cycle, reduce the injection temperature, adjust the injection pressure and injection speed appropriately, and at the same time slow down the ejector speed, increase the ejector area, and keep the ejector force balanced.

Product design: increase the wall thickness, add reinforcement and rounded corners of the reinforcement can reduce warping deformation.

5.Mottling problem

Usually caused by ‘melt breakage’ due to expansion of the melt into the mould cavity at high injection speeds.

Solution:

Moulding process: increase the material temperature, increase the nozzle temperature, slow down the injection speed, etc. to reduce the appearance of mottling.

Mould: Increase the temperature of the mould, increase the overflow groove, increase the size of the gate, modify the shape of the gate.

6.The problem of pockmarks

Solution:

Poor dispersion, add dispersant or oil, raise temperature, add back pressure.

Keep an eye on whether there is a mould problem. Try with other ingredients.

Whether the baking temperature and time are enough.

Adjust the mould temperature.

7.Product ‘Peeling’ Problems

Plastic product peeling problem and high shear caused by the rupture of the fluid has a great deal to do with, in the low shear stress or rate, caused by a variety of factors, small perturbations by the melt to inhibit; and in the high shear stress or rate, the perturbations in the fluid is difficult to inhibit, and develop into an unsteady flow; when it reaches a critical shear force, will cause the rupture of the fluid.

Solution:

Material: The PC and ABS components are partially compatible with each other, so it must be necessary to add appropriate compatibiliser in the modification process to improve its compatibility. Of course, because of the mixing of materials caused by the peeling of bad is we need to step to exclude;; step to exclude; ** step to exclude.

Mould: The principle of mould design should follow the direction of minimizing shear. Generally speaking, the dense skin surface of the product is more likely to produce skinning phenomenon (high-speed filling of the melt in the cavity and the cavity wall friction caused by shear); at the same time, the gate design, the gate size is too small, will lead to excessive shear when the melt through the gate, which leads to the skinning of the surface of the product.

Injection moulding process: the main direction is to avoid excessive shear. When the product is difficult to fill, high speed and high pressure can be used to improve the way, so in the actual injection moulding process, can also be considered to improve the injection temperature / mould temperature, as well as to improve the fluidity of the material in order to reduce the flow resistance in the actual filling process, so as to avoid high speed and high pressure caused by excessive shear.