Learn about ABS injection molding

- Mar 30, 2019-

ABS plastic, due to its great mechanical strength and good comprehensive performance, occupies an important position in the electronic industry, mechanical industry, transportation, building materials, toy manufacturing and other industries. Especially for the slightly large box structure and stressed components, the decorative parts requiring electroplating are inseparable from this plastic.Based on years of practical experience, the ABS plastic injection molding process is analyzed as follows.


(1)ABS plastic drying ABS plastic hygroscopicity and greater sensitivity to water, before the processing of sufficient drying and preheating, not only can eliminate the moisture caused by the surface of the workpiece fireworks bubble belt, silver wire, but also contribute to the plasticization of plastic, reduce the workpiece surface spots and moistening.ABS raw material should control moisture below 013%.Injection before drying condition is: dry winter day in 75 ~ 80 ℃ below, 2 ~ 3 h, dry summer rain days under 80 ~ 90 ℃, 4 ~ 8 h dry, such as parts to achieve special excellent gloss or itself complex parts, the drying time is longer, up to 8 to 16 h.It is often neglected that the mist spot on the surface of products is caused by the existence of trace water vapor.* refit the hopper of the machine into a hot air hopper dryer, so as to avoid the dry ABS in the hopper again moisture absorption, but this kind of hopper to strengthen the humidity monitoring, in the production of accidental interruption, to prevent the overheating of the material.


(2) the relationship between ABS plastic injection temperature and melt viscosity is different from that of other amorphous plastics.At higher temperatures the melting process, the molten actually reduce is very small, but once the plasticizing temperature (temperature range is suitable for processing, such as 220 ~ 250 ℃), if it continues to heat up, blindly without too much will cause the heat resistance of thermal degradation of ABS makes melt viscosity increases, injection more difficult, also fell on the mechanical properties of the parts.Therefore, the ABS injection temperature is higher than that of polystyrene and other plastics, but it can't have a wider heating range like the latter.Some bad temperature control injection molding machine, when the production of ABS parts to a certain number, often more or less in the parts found embedded with yellow or brown coking particles, and it is difficult to use new materials to empty injection method to remove its discharge.

The reason is that ABS plastic contains butadiene. When a plastic particle adheres to some surface which is not easy to be washed out in the screw groove at a high temperature, it will cause degradation and carbonization under the action of high temperature for a long time.Since the operation at high temperature may cause problems to ABS, it is necessary to limit the temperature of each section of the charging barrel.Of course, different types and composition of ABS are suitable for different furnace temperature.Such as plunger type machine, furnace temperature at 180 ~ 230 ℃;Screw machine, furnace temperature at 160 ~ 220 ℃.It is particularly worth mentioning that ABS is sensitive to changes of various technological factors due to its high processing temperature.Therefore, the temperature control of the front end of the cylinder and the nozzle is very important.Practice has proved that any small changes in these two parts will be reflected in the workpiece.The greater the temperature change, will bring welding seams, poor luster, flash, sticky mold, discoloration and other defects.


(3) injection pressure: the viscosity of ABS melt is higher than that of polystyrene or modified polystyrene, so higher injection pressure is used for injection.Of course, not all ABS parts to apply high pressure, small, simple structure, large thickness of the parts can be used with lower injection pressure.In the process of injection, the pressure in the instantaneous cavity of gate closure often determines the surface quality and the degree of silver filamentous defects.Pressure is too small, plastic shrinkage, and the cavity surface out of contact with the opportunity to large parts of the surface atomization.Too much pressure, plastic and cavity surface friction, easy to cause sticky mold.


(4) ABS material with medium injection speed has better effect.When the injection speed is too fast, plastic is easy to scorch or decompose out of gasification, resulting in the production of molten joints, poor luster and red near the gate plastic defects.But in the production of thin wall and complex parts, or to ensure a high enough injection rate, or difficult to fill.


(5) mold temperature ABS molding temperature is relatively high, mold temperature is relatively high.Generally adjust the mold temperature is 75 ~ 85 ℃, when the production has a large projection area of parts, mold temperature requirements of 70 ~ 80 ℃, 50 ~ 60 ℃ dynamic mold temperature requirements.In the injection of large, complex, thin - walled parts, it should be considered to heat the mold.In order to shorten the production cycle and maintain the relative stability of the mold temperature, after the parts are taken out, the cold water bath, hot water bath or other mechanical shaping method can be used to compensate the original time of cold fixation in the mold cavity.


(6) when ABS plastic is injected into the general injection molding machine for material control, the injection volume only reaches 75% of the standard injection volume.In order to improve the product quality and size stability, surface gloss, color uniformity, the injection volume is required to be 50% of the nominal injection volume is appropriate.

It is also very clear that good metal cutting performance and excellent overall cutting solutions are important to the economic production of molds.


4) what are the cutting characteristics of cast iron?

In general, it is:

The higher the hardness and strength of cast iron, the lower the metal cutting performance, and the lower the life expectancy from the blade and cutter.