Injection Molding Process Of ABS Plastic

ABS commonly known as Acrylonitrile Butadiene Styrene, AcrylonitrileButadieneStyrenecopolymers are made by copolymerizing three monomers, acrylonitrile-butadiene-styrene. The different ratios of the three copolymer monomers, then blended with other plastics and additives, will produce different properties, while greatly expanding the uses and properties of ABS materials. For example, heat resistant grade, transparent grade, flame retardant grade, plating grade, impact resistant grade, reinforced grade, etc.


1、ABS plastic drying treatment

ABS plastic is hygroscopic and sensitive to moisture. Before processing, it must be fully dried and preheated to avoid water vapor caused by the silver line, fogging. ABS raw material moisture should be controlled at 0.13% or less.

Drying in winter is below 75?80°C for 2?3 hours; in summer rainy days at 80?90°C for 4?8 hours; if the process itself is complex, it can be dried for a longer time, about 8?16 hours. This condition allows the machine hopper to be converted to a hot air hopper dryer to prevent the ABS material from reabsorbing the moisture in the hopper.

2. Injection Temperature

The relationship between temperature and melt viscosity of ABS plastics is different from that of other amorphous plastics. When the temperature of the melting process increases, the melt viscosity actually barely decreases, but when the temperature reaches 220-250°C, blind heating will continue. thermal degradation of ABS material, which in turn increases the melt viscosity,. Injection molding is more difficult. , the mechanical properties of the part are reduced.

The temperature rise range of ABS injection temperature is less than that of polystyrene. On some temperature-controlled injection molding machines, when a certain amount of parts are produced, embedded yellow or brown scorched particles are produced. The root cause is that plastic particles adhere to groove surfaces that are not easily cleaned at high temperatures and degrade and carbonize at high temperatures over time.

Therefore, operation at too high a temperature may adversely affect the ABS material, so it is necessary to limit the temperature of all parts of the barrel.

3、Injection pressure

ABS melt injection uses higher injection pressure, but for small, simple structures, thicker parts can use lower injection pressure. During the injection process, the pressure in the mold cavity determines the surface quality and the degree of silver-like defects.

If the pressure is too low, the plastic will shrink considerably and there is a high chance of detachment from the surface of the cavity and the surface of the part will tend to fog up. Too much pressure will increase the friction between the plastic and the surface of the cavity, which will lead to the mold sticky.

4、Injection speed

ABS material usually uses medium injection speed, but slower speed is used in fireproof grade and higher heat resistance grade. At the same time, if the requirements for the surface are high, it is necessary to use high-speed multi-stage injection rate control.

5、Mold temperature

Since ABS molding temperature is higher, the mold temperature is also higher. Typically, the mold temperature is regulated to 75-85°C. When producing parts with large projection areas, the mold temperature is 70-80°C and the mold temperature is 50-60°C. To shorten production cycles and maintain mold temperature stability, cold water baths, hot water baths or other mechanical curing methods can be used to supplement the cold curing time after the part is removed.

6、Backpressure

As a rule, the lower the back pressure the better, usually 5 bar, and the dyed material needs higher back pressure to make the mixing uniform.

7、Stock control

In order to obtain consistent part quality and dimensional stability, surface gloss for, uniform tone, the injection volume needs to be controlled at 50% of the nominal injection volume.

8、Dwell time

At 265°C, ABS can be retained in the melt cylinder for a maximum of 5 to 6 minutes. The flame retardation time is shorter. When it is necessary to shut down the machine, the set temperature should be as low as 100°C. The melting barrel should then be cleaned with Universal ABS. The cleaned mixture needs to be placed in cold water to prevent further decomposition. If the ABS material needs to be replaced from another plastic, the melt cartridge needs to be cleaned with PS, PMMA or PE.

Overheating of the melt cartridge or excessive dwell time can cause discoloration of the part.

9、Post-processing of the product

Normally, ABS parts do not require post-treatment. Only plating grade products need to be baked at 70?80°C for 2?4 hours to passivate surface marks and no release agents can be used. Package.

10、Molding Precautions

After plasticizer ABS plasticization, the melt adhesion to the surface of the screw is great. Prolonged placement will lead to decomposition. At this point, the screw homogenization section and compression pull-out wipe test is required, and regular cleaning of the screw with PS, etc.

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