The importance of the exhaust tank in the mold design

- Nov 28, 2017-

In the injection molding process, when molten plastic into the cavity of a mold needs a moment of drain cavity air, including cavity and pouring system in the presence of air, plastic raw materials containing water evaporation at high temperature and water vapor generated, high temperature decomposition of plastic produced gas and some additives in plastics volatilization or chemical reaction produced gas and other parts. Reasonable opening of the exhaust tank can greatly reduce the injection pressure, injection time, holding time and clamping pressure and other parameters, so as to improve production efficiency, reduce production costs and reduce energy consumption of the machine.

The exhaust of the injection mold is very important in the mold injection molding, but it is often ignored or ignored by many people. The mold has a large amount of air in the middle cavity of the injection molding process, and the plastic material is heated and melting, there will be a small molecule cracking gas and other volatiles. The injection speed of the injection machine can reach the speed of the bullet. In such a rapid filling process, the air in the cavity must be quickly discharged. Otherwise, it will cause various problems of the product. The main problems are as follows:

The slow filling speed of 1. products causes the filling speed to cause material cooling, especially thin wall parts, which is not conducive to the rapid filling of the products, and it is easy to produce the material.

2. the pressure in the mold is large and the internal stress is formed on the product. It is the factor that causes the product to be deformed and the surface is not bright.

3. the temperature of the air at the end of the product increases sharply at the end of the high pressure, which causes the burning of the products and the vulnerability of the welding connection.

4. causes the material temperature to rise, carbonization, the product surface forms the glue powder, the product is bad and so on.

5. the continuous high temperature of the mold forming surface has a great influence on the service life of the die.

In order to prevent and solve the above problems, only the mould exhaust is strengthened, and the exhaust of the mould is also the work of technical content. We must not take it lightly and pay attention to it. So how should we design the processing exhaust slot?

1. a lot of mold factory exhaust is by the fitter according to their own processing experience, in fact, is not the correct approach to mold venting by mold mold flow analysis, according to the results of material spill boundary value and experience to design, the processing sector is the right way to accurately processed;

2. the selection of the location and depth of the exhaust tank is also important:

A. does not design the exhaust slot at a certain distance near the gate according to the size of the product and the thickness of the wall, because the pressure is large near the gate and the pressure time is long, so it is easy to form the cloak.

The design of B. exhaust groove depth do not like to gate as mobile end center until the material should be gradually deepened, such as material spill boundary value is 0.05MM, can be designed into the area near the gate to flow at the end of 0.015, gradually was 0.01, 0.025, 0.03, the end product flow can even design to 0.05MM or more, can be used to design the exhaust slot according to the thickness of the product and the injection pressure.  Many die factories are often troublesome to design the same depth, and the wrong idea.

The exhaust slot spacing of C. should also be based on the gate as the center gradually encrypted, and even some design circle includes vent groove, the parting surface exhaust, but should pay attention to the whole circle of the exhaust must have the same depth of different depth, or will cause the gate near the end of a cloak, but poor exhaust flow;

D. must design the exhaust tank at the end of the runner and be deep enough.

As for the E. mold insert, we should make exhaust grooves as far as possible, and design the insert as far as possible under the deep ribs and deep grooves, and design the exhaust slot, otherwise, it will also cause problems such as poor filling, product trapped gas and scorching.

The 3. slider and other structures are also designed to exhaust the same type as the mold kernel, and the design rules are the same as the kernel.

4. the exhaust slot must be designed in the position of the product fuse connection, and the depth of the exhaust tank should be larger.

5. for some thin-walled parts, because the filling speed should be very fast, it is necessary to do the whole discharge plate on the surface, and the depth of the exhaust should be well grasped.

6. some molds clearly do the exhaust or the exhaust is bad, what's the matter? Please check whether the exhaust you made is not connected to the atmosphere. If the exhaust slot can not connect with the atmosphere, it will become deaf ears. Especially the inlay exhaust is ignored by many people. This is worth noticing.

7., the exhaust section at the front part of the exhaust slot is better than the product 0.8~1.5. For special plastics, it can achieve 0.3~0.5, and it must not be too far away, and the rear end is increased to more than 0.5, and it communicates with the atmosphere.

8. to do the proper polishing treatment, is not a lot of people doing it at all? Why does the exhaust slot need polishing? Because hot air is often discharged with some plastic dust. The exhaust groove is too rough, which prevents the dust from discharging. The glue powder is stuck in the exhaust slot, which will block the exhaust and is not easy to clean up.

9. the exhaust tank must be cleaned regularly, not the product problems and re cleaning, mold maintenance to clean up, even every class to clean up.