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Process conditions for PC/ABS injection molds

update:19-10-2019
abstract:

1. Process conditions of PC/ABS injection mold: Drying […]

1. Process conditions of PC/ABS injection mold:

Drying must be done before processing. The humidity should be less than 0.04%, and the recommended drying condition is 90~110 °C, 2~4 h;

The melting temperature is 230~300 °C;

Mold temperature: 50~100 °C.

The injection pressure depends on the plastic part.

The injection speed should be as high as possible.

Chemical and physical properties: PC/ABS has the combined properties of both PC and ABS. For example, the easy processing characteristics of ABS and the excellent mechanical properties and thermal stability of PC. The ratio of the two will affect the thermal stability of the PC/ABS material. The mixed material of PC/ABS also shows excellent fluidity. The shrinkage rate is around 0.5%.

2, injection PC / ABS products often appear problems and solutions

2.1. Silver wire problem Silver wire is the most common problem of PC/ABS material. Silver wire, also known as silver grain, water flower, flower flower, etc., is a silvery white silky stripe phenomenon appearing along the flow direction on the surface of the product.

The main reason is the interference of gas. The gas produced is mainly divided into three components: air: molten rubber and air entrapped in the injection stage; moisture: moisture contained in the material itself; pyrolysis gas: gas generated by high temperature hydrolysis/thermal decomposition .

Solution: First check if the material is dry enough. After confirming that the material is dry enough, adjust the injection molding process to improve the silver wire defect. At the same time, poor injection molding silver wire is also related to mold exhaust.

2.2. Flow marks The flow marks are generated when the material is injected. The reason is that the material has poor fluidity, the flow marks are different from the silver lines, and the appearance is different.

Solution: It can be avoided by increasing the temperature of the material to improve the fluidity, properly improving the fluidity of the material in the mold and reducing the injection speed.

2.3. Shrinkage and dent problems Shrinkage is caused by insufficient filling of the material in the cavity.

Solution: Appropriately increase mold temperature and material temperature to improve material flow, prolong injection pressure retention time, increase injection pressure, increase injection speed to improve mold filling, increase gate size, and heat gate flow To reduce and eliminate shrinkage of the product;

The dent is caused by improper temperature of the material and improper design of the product. When the temperature of the material is too low, not only shrinkage holes but also dent problems will occur. The temperature of the material is too high, and the temperature of the mold is too high, which will cause the melt to cool. The time is excessively contracted, resulting in dents.

Solution: Increase the injection speed.

2.4. Warpage deformation problem The warpage deformation of the injection molded part is due to the unreasonable design of the part, the improper position of the gate and the unreasonable processing conditions of the injection molding, resulting in internal internal stress, uneven shrinkage or excessive, and the mold temperature is too high or The mold temperature is not uniform, which causes the mold release of the injection molded part to be difficult to release, or the cooling is uneven, and warp deformation also occurs;

Solution:

Processing technology: lengthen the injection molding cycle, reduce the injection temperature, adjust the injection pressure and injection speed, reduce the ejection speed, increase the ejection area, and maintain the balance of the ejection force;

Product design: increase the wall thickness, add reinforcement and reinforcement at the rounded corners;

2.5, the problem of marking is usually caused by the "melt fracture" caused by the expansion of the melt into the cavity during high-speed injection.

Solution:

In terms of molding process: reduce the temperature of the material, the temperature of the nozzle, slow down the injection speed, etc. to reduce the appearance of markings;

Mold: Improve the mold temperature, add overflow tank, increase the gate size, and modify the gate shape.

2.6, pitting problem solution: poor dispersion, add dispersant or oil, increase the temperature, plus back pressure. Also see if it is a mold problem. Use other materials.

Whether the baking temperature time is sufficient. Adjust the mold temperature appropriately.

2.7. The problem of “skinning” of products There is a great relationship between the peeling problem of plastic products and the cracking of fluids caused by high shear forces. Under low shear stress or rate, small disturbances caused by various factors are melted. Inhibition; at high shear stresses or rates, disturbances in the fluid are difficult to suppress and develop into unstable flow; when a critical shear force is reached, the fluid will be broken.

Solution:

In terms of materials: the poor skinning caused by the mixing is the first step to be excluded. The PC and ABS components are partially compatible. Therefore, it is necessary to add appropriate compatibilizer during the modification process. To improve their compatibility;

Mold: The principle of mold design is to follow the direction of cutting as much as possible. In general, products with dense dermatoglyphics are more prone to skinning (diffuse shearing of the melt in the cavity and the inner wall of the cavity during high-speed filling); at the same time, the gate size is too small. Will cause excessive shearing when the melt passes through the gate, which in turn causes the product surface to peel;

Injection molding process: The main direction is to avoid excessive shearing. When the product is difficult to fill, it can be improved by high-speed and high-pressure method. Therefore, in the actual injection molding process, the injection temperature/die temperature and the fluidity of the material can be considered to reduce the flow resistance during the actual filling process, thereby Avoid excessive shear caused by high speed and high pressure