In the process of NC machining, there are various problems, such as NC machining defects, color balance, cracks and so on. Today, I'd like to talk about the factors that cause color irregularity in the process of CNC hand board processing, as well as other problems of CNC hand board, which will be mentioned in the next article.
The handboards produced before are normal, but the color of the handboards suddenly appears, which is unacceptable. Therefore, the factors that cause the color of CNC handboards can start from the following reasons:
I. die reason
1. The mold is not clean, and dust or other dust is deposited on the material, causing the material to be polluted and discolored.
2. Imbalance of thermocouple, temperature controller or heating system leads to temperature control failure, high temperature leads to chemical change of plastic or pigment composition, decomposition and discoloration, especially PVC, which is very sensitive to temperature.
3. There are obstacles in the cylinder, which is easy to promote plastic degradation; there are metal foreign matters stuck in the cylinder or spiral groove, and the plastic discoloration is caused by continuous grinding.
II. Reasons for the process
1. The screw speed of CNC lathe is too high, the screw shear force is too large, the back pressure of preform is too large, and the plastic melting process and the cylinder friction temperature cause discoloration.
2. The temperature of cylinder and nozzle is too high, especially for materials sensitive to temperature.
3. The injection pressure is too high, the storage time is too long, and the shutdown time is too long. Plastic materials will decompose and change color.
III. reasons for raw materials
1. The material is contaminated, mixed with other colors or mixed with mixed materials.
2. Raw materials with high moisture and volatility shall be dried as required.
3. If the colorant and additive are not properly selected, and the pigment is resistant to high temperature decomposition, resulting in discoloration, a reasonable pigment formula shall be selected for adjustment.