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Complete Interpretation of ABS Injection Molding Process

1. Drying treatment of ABS injection molding

ABS plastic is hygroscopic and sensitive to moisture. It needs to be fully dried and preheated before processing to avoid silver threads and fog spots caused by water vapor. The moisture content of ABS raw materials should be controlled below 0.13%. When drying, it should be dried for 2 to 3 hours in winter below 75 to 80 °C; in summer, it should be dried at 80 to 90 °C for 4 to 8 hours; if the production process is complicated, it can be dried for longer, about 8 to 16 hours. If conditions permit, the hopper of the machine can also be converted into a hot air hopper dryer to avoid secondary moisture absorption of ABS material in the hopper.

2. ABS injection molding injection temperature

The relationship between the temperature and melt viscosity of ABS injection molding is different from that of other amorphous plastics. When the temperature increases during the melting process, the melt viscosity actually decreases very little, but when the temperature reaches between 220 and 250 ℃, the temperature continues to increase blindly. It will make the ABS material thermally degrade, but it will increase the melt viscosity, make injection molding more difficult, and reduce the mechanical properties of the parts.

The heating range of ABS injection temperature is smaller than that of polystyrene and other materials. On some injection molding machines with poor temperature control, when the number of production parts reaches a certain number, yellow or brown coking particles will be produced. The fundamental reason is that plastic particles will stick to some surfaces in the screw groove that are not easy to scour under high temperature, and long-term high temperature will degrade and carbonize them. Therefore, the operation of excessively high temperature may adversely affect the ABS material, and it is necessary to limit the furnace temperature of each section of the barrel.

3. ABS injection molding injection pressure

A higher injection pressure is used when ABS molten parts are injected, but a lower injection pressure can be used for parts with small size, simple structure and large thickness. During the injection process, the pressure in the cavity determines the surface quality and the degree of silver filiform defects. If the pressure is too small, the plastic shrinks greatly, and there is a great chance of getting out of contact with the surface of the cavity, and it is easy to cause the surface of the workpiece to be atomized. Excessive pressure will increase the friction between the plastic and the surface of the cavity, resulting in sticking.

4. ABS injection molding injection speed

ABS injection molding materials generally use a medium injection speed for better results, but use a slow speed for fire-resistant grades and fast for heat-resistant grades. At the same time, if the surface requirements are high, it is necessary to use high-speed and multi-stage injection rate control.

5. ABS injection molding mold temperature

Because the ABS molding temperature is relatively high, the mold temperature is also relatively high. Generally, the mold temperature is adjusted to 75-85 °C. When producing parts with a large projected area, the fixed mold temperature is required to be 70 to 80 °C, and the movable mold temperature is required to be 50 to 60 °C. In order to shorten the production cycle and maintain the stability of the mold temperature, after the parts are taken out, cold water bath, hot water bath or other mechanical setting methods can be used to supplement the time of cold fixing.

6. ABS injection molding back pressure

In general, the lower the back pressure, the better, usually the back pressure is 5bar, and the dyeing material needs a higher back pressure to make the color mixing uniform.

7. ABS injection molding material quantity control

In order to achieve stable quality and size of the parts, uniform surface gloss and color tone, it is necessary to control the injection volume to 50% of the nominal injection volume.

8. ABS injection molding residence time

At a temperature of 265°C, ABS can stay in the melt cylinder for up to 5 to 6 minutes. The flame retardant time is shorter. When the machine needs to be shut down, the set temperature should be lowered to 100 °C, and then the melt tube should be cleaned with general-purpose ABS. The cleaned mix needs to be placed in cold water to prevent further decomposition. If you need to change from other plastics to ABS, you need to clean the melt tube with PS, PMMA or PE first. Overheating or the long dwell time of the melt tube will cause discoloration of the part.

9. Post-processing of ABS injection molding products

Usually ABS injection molding parts do not need post-processing, only electroplating grade products need to be baked at 70~80℃ for 2~4 hours to passivate the traces on the surface, and no mold release agent can be used. Pack immediately.

10. Precautions for ABS injection molding

After the flame retardant ABS is plasticized, its melt has a strong adhesion to the screw surface, which will cause decomposition after a long time. At this time, it is necessary to pull out and wipe the screw homogenization section and compression, and regularly clean the screw with PS, etc.

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