Exhaust of injection mold

In mold manufacturing, mold exhaust is a very important link. Mold exhaust can represent the overall structure of the mold to the greatest extent. Even if excellent molds do not have good exhaust, it is impossible to produce products with stable quality. Good molds should have good tightness and can ensure the free exhaust of gas, rather than the high compression of gas. So what are the standards for mold exhaust?

First of all, understand that unreasonable exhaust will produce the following adverse effects:

1. Gas accumulation will etch the die surface and parting line;

2. Color problem: color difference occurs, making the color black or bright; Different bright fog on the flower biting surface

3. To increase mold polishing: waste time, money and, and make steel easy to corrode;

4. It is impossible to make the product meet the standards required by the guests;

5. There will be too many bonding lines (the bonding is not firm and unsightly);

6. It will waste too much injection pressure and increase the difficulty of injection molding machine;

7. It is necessary to use too high barrel temperature (increase the working difficulty of injection molding machine, abnormal temperature control, deviation of material performance, and increase the cycle time);

8. Will reduce the level of materials;

9. It will reduce the true roundness of the product and cause product deformation;

10. The struggling force of high-pressure gas in the mold cavity will increase the cycle instability and often need to adjust the machine to solve the quality problems;

11. Make the work of technicians, QA, operators and mold room personnel more difficult.

Finally, let's understand the reasonable exhaust technical requirements:

The full cycle exhaust structure shall be made as far as possible, and the depth shall be within the plastic overflow boundary value. The full cycle exhaust is the best, but 1 / 2 of the steel shall be left to compensate the pressure on the clamping line.

If the PL surface is irregular and it is impossible to exhaust all around, the better method is to use a 12mm wide exhaust slot to the master mold, and the gas must be finally discharged into the atmosphere. The exhaust slot shall be processed with a milling cutter with chamfer at the flat bottom as far as possible. If a spherical milling cutter must be used, the processing depth shall be calculated to be consistent with the depth processed at the flat bottom, The length of exhaust sealing glue is one of the most easily ignored by most people and related to the appropriate exhaust problem;

There are many different size regulations on this issue. The specification of the material supplier ranges from 3 ~ 5mm, and experience has proved that if the length is greater than 3mm, it will no longer play a good role. Therefore, for the sake of safety, we stipulate that the standard is 3mm, and the exhaust depth depends on the forming material. If in doubt, you can refer to the processing specification.

One of the most common misconceptions is that too much exhaust leads to flapping. In fact, the opposite direction is right. Unreasonable exhaust requires excessive pressure. When the gas is allowed to be discharged, the rubber will go out with the gas, and the only cause of excessive exhaust is that the depth of the gas groove is too deep.

Generally, exhaust with all thimbles as much as possible, which is particularly important for large plastic parts. Of course, this also depends on the diameter of the thimble. If this is impossible, grind the plane for exhaust, use the appropriate length and depth, and slow down the thimble matching gap. The flow channel, especially the large or long flow channel, must be opened for exhaust.

Another common problem is that when the parts cannot exhaust all around, the last glue filling position and the second last glue filling position must be considered, and these two positions must be vented. Exhaust shall be specially considered for deep bone position, column position, small needle dispensing position or thin glue position, or flat thimble, semi needle structure, exhaust steel, or even vacuum exhaust installation.

So what should we pay attention to?

A part cannot exhaust too much. Although the clamping line can do so, this will bring the following problems related to exhaust: there is not enough steel to bear pressure on the clamping line, and the exhaust on the parting surface is pressed;

The best exhaust will eventually disappear. After a certain material circulation, if there is not enough steel to compensate the pressure on the clamping line, the die will bite together, and the air groove will wear. The clamping line should avoid the reduction of the clamping part of the die, which is the biggest problem encountered by the large die. For the mold of front and rear mold inserts, the front and rear mold kernel materials cannot be closed before the mold opening surface of the mold embryo. The correct way is to close the mold at the same time with pressure block between the mold base and ab plate.