During Injection Molding, there will not be much molten material in the vent hole, because the molten material will cool and solidify at the place to block the channel. The opening position of the exhaust port should not be facing the operator to prevent accidental spraying of molten material and hurting people. The clearance between the ejector rod and the ejector hole, the clearance between the ejector block and the stripper plate and the core can also be used for exhaust.

1. The Role of the Exhaust Slot

There are two main functions of the exhaust slot:

When injecting molten material, remove the air in the mold cavity;

Eliminate all kinds of gases produced during the heating process.

The thinner the product, the farther away from the gate, the opening of the exhaust groove becomes particularly important.

For small parts or precision parts, attention should also be paid to the opening of the exhaust groove. In addition to avoiding surface burns and insufficient injection volume, it can also eliminate various defects of the product and reduce mold contamination.

Generally speaking, if the melt is injected at the highest injection rate without leaving a focal spot on the product, it can be considered that the exhaust in the cavity is sufficient.

2. Exhaust Method

There are many ways to vent the mold cavity, but each method must be guaranteed: the size of the vent groove should be designed to prevent the material from overflowing into the groove while venting; secondly, it must prevent blockage.

Measure from the inner surface of the mold cavity to the outer edge of the mold cavity, and the height of the vent groove should be about 0.25-0.4mm for the length of 6-12mm or more. In addition, too many exhaust slots are harmful. Because, if the clamping pressure acting on the parting surface of the mold cavity without opening the vent groove is very large, it is easy to cause cold flow or cracking of the mold cavity material, which is very dangerous.

In addition to venting the mold cavity on the parting surface, it can also achieve the purpose of venting by arranging venting grooves at the end of the material flow of the pouring system and leaving gaps around the ejector rods, because the venting grooves If the selection of the depth, width and position of the opening is not appropriate, the flash burrs produced will affect the appearance and accuracy of the product. Therefore, the size of the above gap is limited to prevent flash around the ejector rod.

Special attention should be paid here: when parts such as gears are exhausted, even the smallest flash may be undesirable. This type of parts should preferably be exhausted in the following ways:

Completely remove the gas in the flow channel;

The matching surface of the parting surface is shot peened with silicon carbide abrasive with a particle size of 200#.

In addition, the opening of the exhaust groove at the end of the material flow of the pouring system mainly refers to the exhaust groove at the end of the runner. Its width should be equal to the width of the runner, and the height varies depending on the material.

3. Injection Mold Design Method

For product molds with complex geometric shapes, it is best to determine the opening of the vent slot after several mold trials. The biggest disadvantage of the overall structure in the mold structure design is poor exhaust.

For the integral cavity core, there are the following exhaust methods:

Use the groove or insert installation position of the cavity;

Use side insert seams;

Partially made into a spiral shape;

Install a slotted slat core and open a craft hole in the longitudinal position;

When the exhaust is extremely difficult, the inlay structure is adopted; if the dead corners of some molds are not easy to open the exhaust groove, first of all, the mold should be appropriately changed to inlay processing without affecting the appearance and accuracy of the product, which is not only beneficial to processing The exhaust groove can sometimes improve the original processing difficulty and facilitate maintenance.

Properly opening the exhaust groove can greatly reduce the injection pressure, injection time, holding time and clamping pressure, making the molding of plastic parts easy, thereby improving production efficiency, reducing production costs, and reducing machine energy consumption.