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How To Design Injection Mold Air Vent?
Original: Original | Author: DGMF Mold Clamps | Publish Time: 2020-07-11 | 8175 Views | Share:
Appropriate opening of the injection mold air vent can greatly reduce the injection molding pressure, injection molding time, holding time, and injection mold clamping pressure, making the plastic parts from difficult to easy, thereby improving production efficiency, reducing production costs, and reducing the energy consumption of the machine.

The air vent of injection mold 
How To Design Injection Mold Air Vent - DGMF Mold Clamps Co., Ltd


It is a kind of groove-shaped air outlet opened in the injection mold to discharge the original gas brought by the melt. When the molten material is injected into the cavity, the air originally in the cavity and the gas brought by the melt must be discharged out of the injection mold through the exhaust port at the end of the flow, otherwise, the product will have air holes, poor connection, Dissatisfaction with mold filling, even accumulating air burns the product due to high temperature caused by compression.

Under normal circumstances, the vent hole can be placed either at the end of the melt flow in the cavity or on the parting surface of the injection mold. The latter is a shallow groove with a depth of 0.03-0. 2mm and a width of 1.5-6mm.

During injection molding, there will not be a lot of molten material leaking from the vent hole, because the molten material will cool and solidify at this place, blocking the channel. The opening of the exhaust port must not face the operator to prevent accidental injection molding of molten material and injury. In addition, the matching gap between the ejector pin and the ejector hole, the matching gap between the top block and the stripper plate, and the core can also be used for air vent.

1. The role of the air vent of the injection mold

The function of the air vent is mainly two points: one is to exclude the air in the injection mold cavity when the molten material is injected; the second is to exclude all kinds of gases generated by the material during the heating process. The more thin-walled products, the farther away from the gate, the opening of the exhaust slot is particularly important.

In addition, for small parts or precision parts, we must pay attention to the opening of the air vent, because it can avoid product surface burns and insufficient injection volume, it can also eliminate various defects of products and reduce mold pollution.

So, what is the exhaust of the mold cavity? 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 injection mold cavity is sufficient.

2. Air vent method of injection mold

There are many ways to evacuate the mold cavity, but each method must ensure that: the air vent is exhausted at the same time, its size should be designed to prevent the material from overflowing into the groove; secondly, it must prevent blockage. Therefore, from the inner surface of the injection mold cavity to the outer edge of the mold cavity, the length of the exhaust groove of 6-12 mm or more, the groove height should be placed about 0.25-0.4 mm.

In addition, too many exhaust slots are harmful. This is because, if the injection mold clamping pressure acting on the part of the injection mold cavity parting surface without the air vent is too large, it is easy to cause cold flow or cracking of the injection mold cavity material, which is very dangerous.

In addition to vent the injection mold cavity on the parting surface, you can also achieve the purpose of vent by providing a vent groove at the end of the flow of the die casting system and leaving a gap around the ejector rod, because the vent groove The selection of the depth, width, and location of the opening, if not appropriate, will produce flash burrs that will affect the aesthetics and accuracy of the product. Therefore, the size of the gap is limited to prevent flashing around the ejector rod.

Special attention should be paid here: when exhausting parts such as gears, even the smallest flash may be undesirable. Such parts are best exhausted in the following ways:

Completely remove the gas in the flow channel;

Shot-blasting the matching surface of the parting surface with silicon carbide abrasive with a particle size of 200#;

The air vent is set at the end of the flow of the pouring system, which 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. The design method of injection mold air vent

Based on many years of experience in injection mold design and product trial mold, this article briefly introduces the design of several injection mold air vent.

For product molds with complex geometries, the opening of the exhaust groove is best determined after several trial molds. The overall shortcoming of the overall structural form in mold structure design is the poor exhaust.

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

Use the groove or insert installation part of the cavity

Use the side insert seams

Partially made into a spiral shape

Install slotted slat core in longitudinal position and open process holes

When exhausting is extremely difficult, use mosaic structure, etc.

If the dead corners of some injection molds are not easy to open the air vent, first of all, the injection mold should be appropriately changed to inlay processing without affecting the appearance and accuracy of the product. This is not only conducive to processing the air vent but also sometimes improves the original Processing difficulty and easy maintenance.

4. Air vent design of injection mold during thermosetting plastic molding

The vent of thermosetting materials in injection molds is more important than thermoplastic materials. First, all the runners in front of the gate should be vented. The width of the air vent should be equal to the width of the shunt, and the height is 0.12mm. All sides of the mold cavity should be exhausted, and the exhaust slots should be separated by 25mm, the width is 6.5mm, and the height is 0.075-0.16mm, depending on the fluidity of the material.

Softer materials should take lower values. The ejector pin should be enlarged as much as possible, and in most cases, 3-4 planes with a height of 0.05 mm should be ground on the cylindrical surface of the ejector pin, and the direction of the wear scar should be along the length of the ejector rod. Grinding should be carried out with a fine-grained grinding wheel. The end face of the ejector rod should be ground with a chamfer of 0.12mm so that if flash is formed, it will adhere to the workpiece.

5. Conclusion

Appropriate opening of the injection mold air vent can greatly reduce the injection molding pressure, injection molding time, holding time, and injection mold clamping pressure, making the plastic parts from difficult to easy, thereby improving production efficiency, reducing production costs, and reducing the energy consumption of the machine.