Injection mold exhaust - Encyclopedia of injection mold opening technology for injection mold factory

The gas in the injection mold factory not only includes the air in the cavity, but also includes the air in the flow channel and the decomposition gas produced by the plastic melt, as well as the water in the plastic turned into water vapor at high temperature. In injection mold processing, these gases should be generated in a timely manner small storage will produce the following hazards.

(1) The formation of flow marks, spray, weld marks and other defects on the surface of the plastic parts.

(2) In the plastic parts of the internal bubble, loose tissue and other defects, serious will lead to filling.

(3) It is difficult to fill the melt, or local flaking occurs.

(4) the gas produces high temperature under high temperature and high pressure, so that the products appear local carbonization and scorch marks.

(5) Reduce the filling speed of melt. A drop in injection speed, not only prolong the molding cycle, and the melt temperature is quickly reduced, then if the injection pressure is increased, the residual stress will be increased, plastic parts after demoulding caused by the possibility of deformation increased. In order to reduce the injection pressure and increase the material temperature, it will cause plastic cracking.

Properly opening the exhaust groove can greatly reduce the injection pressure, reduce the injection time and pressure holding time and reduce the clamping pressure, so as to improve the production efficiency, reduce the production cost and reduce the consumption of the machine. For transparent plastic parts or strict surface requirements of plastic parts, special attention should be paid to the design of injection mold processing exhaust system.

1. The position of trapped air in the cavity

Trapped gas in the cavity is usually located at the following locations.

Thin wall structure cavity, end of melt flow.

② The junction of two or more melt strands.

③ In the cavity, the place where the melt arrives.

(4) The bottom of the blind hole of the injection mold cavity, and the end of the solid column in the product.

The bottom of the formed products stiffener and screw column.

Complex injection mold cavity dead Angle.

In particular, the exact position of the exhaust groove should be determined after the mold test, and it should not be taken for granted that the exhaust groove will be opened before the mold test.

2. Injection mold exhaust mode

Exhaust in this chapter refers to exhaust from cavities and gating systems. Injection mold exhaust modes include the following.

(1) Parting surface (including opening exhaust groove).

② Insert matching surface.

The matching surface of push rod or push tube and inner mold insert.

(4) Side core pulling mechanism exhaust.

⑤ Exhaust needle or insert exhaust in the trapped air.

⑥ Breathable steel exhaust.

⑦ Air valve exhaust.

3. Exhaust system design principle

(1) The exhaust groove can only let the gas out, but can not let the plastic melt out.

(2) Different plastics, because of their different viscosity, the depth of the exhaust groove is different. Cavity to design the exhaust groove, the flow passage and cold cavity also to design the exhaust groove, so that the gas in the pouring system as little as possible into the injection mold cavity.

(3) Exhaust groove must be through the mold frame, especially through the insert, exhaust pin or exhaust insert exhaust, must pay attention to.

(4) The exhaust groove should be processed with milling machine as far as possible, and polished with no.320 sandpaper after processing to remove the knife marks; Exhaust groove to avoid the use of grinding machine processing, grinding machine processing plane is too flat and smooth, exhaust effect is often not good.

(5) The exhaust groove on the parting surface should be arranged on the side of the cavity, generally on the fixed die insert.

(6) Both sides of the exhaust groove should be chamfered at 45°.