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What are the methods for the position of the mold to open the exhaust groove in the injection molding process?

by:Vowin Rapid Prototyping     2023-02-13
Injection molding is a method for the production of industrial products. Rubber injection molding and plastic injection molding are commonly used for products. Injection molding can also be divided into injection molding molding method and die casting method. What methods are there for the position of the mold to open the exhaust groove during the injection molding process?

1. Exhaust slot exhaust
The amount of gas discharged from the mold for forming large and medium-sized plastic parts is relatively large, and the exhaust groove is usually set on one side of the die on the parting surface. The position of the exhaust groove is preferably at the end of the melt flow, and the size of the exhaust groove is based on the principle that the gas can be discharged smoothly without overflowing. The width of the exhaust groove is generally about 3-5mm, the depth is less than 0.05mm, and the length is generally 0.7-1.0mm.

2. Parting surface exhaust

Small molds can be vented through the parting surface gap, but the parting surface must be located at the end of the melt flow.

3. Stitching gap exhaust

The combined die or cavity can be exhausted by splicing gaps.

4. Push rod clearance exhaust

Use the fit gap between the push rod and the template or core to vent, or deliberately increase the gap between the push rod and the template.

5. Powder and unsintered gold block exhaust

Powdered unsintered alloy is a material sintered with spherical particle alloy, which has poor strength but loose texture and allows gas to pass through. Placing such alloys in the parts that need to be vented can meet the venting requirements, but the diameter of the vent hole at the bottom should not be too large to prevent the cavity from being squeezed and deformed.

6. Exhaust well exhaust

On the outside of the plastic melt, a hole is set to allow the gas to be discharged into it, and a good exhaust effect can also be obtained.

7. Forced exhaust
In the part where the gas is enclosed, setting the exhaust rod has a good exhaust effect, but it will leave rod marks on the plastic parts, so the exhaust rod should be installed in a hidden place of the plastic parts.

There are many ways to exhaust the mold cavity, but each method must ensure that the dimension design of the exhaust groove can prevent the material from overflowing the groove; secondly, it must prevent clogging. Therefore, measuring from the inner surface of the mold cavity to the outer edge of the mold cavity, the length is 6~12mm, and the height of the above exhaust groove should be enlarged by about 0.25-0.4mm. Also, an excessive number of vent slots is detrimental.

Because if the clamping pressure acting on the parting surface of the cavity is too high, it is easy to cause cold flow or cracking of the cavity material, which is very dangerous. In addition to the cavity exhaust on the parting surface, an exhaust groove can also be set at the end of the material flow of the gating system, and a gap can be left around the ejector rod to achieve the purpose of exhaust. Because of the selection of the depth, width and position of the exhaust groove; if it is not suitable, the flash and burrs will affect the beauty and precision of the product.

Therefore, the size of the above-mentioned gap is limited to prevent flashing around the ejector pin. It's important to note here that parts such as gears may not even want the tiniest flash when venting. It is best to exhaust these parts in the following ways: ① Thoroughly remove the gas in the flow channel; ② Shot peen the parting surface with silicon carbide abrasives with a particle size of 200#. In addition, the exhaust groove at the end of the material flow of the gating system mainly refers to the exhaust groove at the end of the runner, and its width should be equal to the width of the runner, and the height varies depending on the material.

The exhaust slot has two main functions. One is to remove the air in the mold cavity when injecting the molten material; the other is to remove various gases generated by the material during the heating process. The thinner the thin-walled product is, the farther it is from the gate, and the opening of the vent groove is particularly important. In addition, for small parts or precision parts, pay attention to the opening of the exhaust groove, because it can not only avoid product surface burns and insufficient injection, but also eliminate various defects of the product and reduce mold pollution.

So, how can the exhaust volume of the mold cavity be sufficient? Generally speaking, if the melt is injected at the highest injection rate, but there is no focus on the product, it can be considered that there is sufficient venting in the cavity.
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