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How to design the exhaust system of injection mold?

How to design the exhaust system of injection mold?

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  • Time of issue:2022-04-28
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(Summary description)The injection mold is a process of injecting the melt into the mold core by pressure. There is air in the mold core, so after the melt enters the mold cavity, the air must be discharged. In fact, the air in the mold is not limited to the cavity, especially in the three-plate injection mold, the air existing in the runner cannot be ignored. In addition, the plastic melt will generate a small amount of decomposition gas. These gases must be discharged in time.

How to design the exhaust system of injection mold?

(Summary description)The injection mold is a process of injecting the melt into the mold core by pressure. There is air in the mold core, so after the melt enters the mold cavity, the air must be discharged. In fact, the air in the mold is not limited to the cavity, especially in the three-plate injection mold, the air existing in the runner cannot be ignored. In addition, the plastic melt will generate a small amount of decomposition gas. These gases must be discharged in time.

  • Categories:News
  • Author:
  • Origin:
  • Time of issue:2022-04-28
  • Views:0
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The injection mold is a process of injecting the melt into the mold core by pressure. There is air in the mold core, so after the melt enters the mold cavity, the air must be discharged. In fact, the air in the mold is not limited to the cavity, especially in the three-plate injection mold, the air existing in the runner cannot be ignored. In addition, the plastic melt will generate a small amount of decomposition gas. These gases must be discharged in time.

If the exhaust performance of the mold is poor, it is easy to produce air bubbles, silver streaks, clouds, unsatisfactory filling, surface scorch marks, intermittent injection and other defects. Therefore, a reasonable exhaust structure should be provided on the mold to avoid poor products caused by poor exhaust.

Several common exhaust methods

1. Exhaust slot exhaust

For the molds for forming large and medium-sized plastic parts, the amount of gas to be excluded is large, and an exhaust groove should be opened usually on the 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 of the front end of the exhaust groove is less than 0.05mm, and the length is generally 0.7-1.0mm.

2. Parting surface exhaust

For small molds, the parting surface gap can be used to exhaust, but the parting surface must be at the end of the melt flow.

3. Exhaust the gap of the inserts

For the combined die or cavity, the combined gap can be used to exhaust.

4. Push rod clearance exhaust

Use the clearance between the push rod and the template or core to exhaust, or intentionally increase the clearance between the push rod and the template.

5. Powder unsintered alloy block exhaust

Powder unsintered alloy is a material sintered with spherical particle alloy, which has poor strength but loose texture and allows gas to pass through. Placing a piece of this alloy in the part to be vented can meet the requirements of venting, but the diameter of the vent hole at the bottom should not be too large to prevent the cavity pressure from squeezing and deforming it.

6. Exhaust well exhaust

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

7. Mandatory exhaust

In the part where the gas is closed, set the exhaust rod. This method has a good exhaust effect but will leave traces of the rod on the plastic part, so the exhaust rod should be set in the hidden place of the plastic part.

Matters needing attention in exhaust design

1. When the exhaust is extremely difficult, the inlaid structure is adopted. If some dead corners of the mold are not easy to open the exhaust groove, first of all, the mold should be appropriately changed to inlaid processing without affecting the appearance and accuracy of the product, which is not only conducive to processing Exhaust can also improve the original processing difficulty and facilitate maintenance.

2. At the closed shape of the plastic product, be sure to add a thimble to ventilate and prevent burns and fusion marks.

3. For product molds with complex geometric shapes, it is best to determine the opening of exhaust grooves after several mold trials.

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

5. For small parts or precision parts, attention should also be paid to the opening of the exhaust groove, because it can not only avoid the surface burn of the product and the insufficient injection volume, but also eliminate various defects of the product.

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