Highlight, highlight products for injection molding enterprises is indeed a more difficult product, because it can not hide the external defects, even the dust in the workshop will cause different degrees of product defects, such as trachoma, pitting, staining, etc., so the environment is also one of the key factors affecting such products.

First, phenomenon

Figure 1 before the improvement of

Figure 2 after the improvement of

product surface white fog, from a visual point of view, it presents a white shape, so it is not obvious in white products, black highlights are the most obvious, as shown in Figure 1, the product is PP material production, The surrounding surface shows large and small white markings, like a cloud of symptoms, which are classified as white fog.

Two, theory

According to the above theoretical basis is: There is a certain gap between the plastic and the plastic in the unloading stage, after the screw shear is taken into the barrel, in the screw shear process, the material will undergo physical changes, from the glass state to the high elastic state, from the high elastic state to the viscous flow state, the change process may only be a few seconds - tens of seconds between, (according to the machine or product size) in such a short period of time to change a complex process, injection defects are also generated, the gap between plastics is compressed into the melt inside the gas, if the gas is not discharged to the outside of the cylinder during plasticization, the existing gas is wrapped into the melt is injected into the mold cavity, Whether the mold can be successfully discharged depends on whether the exhaust of the mold is good, and the phenomenon of fogging trapped gas or burning is generated.

Obviously, white fog is also a phenomenon of trapped gas, many people engaged in injection molding technology mistakenly believe that only burnt is trapped gas, or trapped gas to open the exhaust tank, which is unscientific, burnt because the trapped gas is too serious, the gas is compressed under high pressure, high speed state can not release the local combustion, The combustion temperature can instantly reach 600-800 бу C, which belongs to the highest state of trapped gas.

Three, the solution

How to let the gas best discharge without producing white fog phenomenon?

1 mold

exhaust is not completely by the mold to solve, for PP material characteristics, the temperature range is very wide, its flow performance is superior, if the mold exhaust groove opened too large or the wrong position, can not be correctly exhaust, but also easy to produce bad flash, so the correct exhaust is useful.

2. Process

Master the correct adjustment skills in the actual work is very effective.

1) such as reducing the rotation speed of the screw, can make the melting temperature uniform, the opportunity of the entrain air is small, such as the screw rotation speed is too fast, the opportunity of the entrain air is more; The molten material by the screw shear force is large, friction heat resulting in the temperature of the molten material is not uniform, the molten material decomposition gas.

2) Increase the mold temperature, can be conducive to high pressure, slow filling to win time, if the mold temperature is too low, the product surface is easy to freeze prematurely, slow filling can not be realized, may lead to lack of glue.

3) Reduce the injection speed, the faster the speed, the faster the gas compression, the higher the temperature. The slower the speed, the slower the gas compression, the more conducive to the discharge of gas.

4) clamping force, the greater the clamping force, the worse the exhaust effect on the surface of the cavity, the smaller the clamping force, the better the exhaust effect on the surface of the cavity.

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