Injection mold structure: exhaust hole

author: Universe plastic

2024-08-26

Injection mold vents are critical to final product quality. During injection molding, if the gas inside the mold cannot be effectively discharged, defects such as bubbles, burns, and shrinkage holes will appear on the product surface.

The exhaust structure of the mold depends on the shape, size, material properties, etc. of the product. It is particularly important to note that the injection filling speed is the most important factor that determines the exhaust volume within the same time. Good exhaust design can improve product quality, reduce scrap rates, and improve production efficiency.

Effects of poor mold exhaust

1. Bubbles and vacuum holes

Failure to discharge the gas will result in bubbles or cavities inside or on the surface of the product.

2. Burnt and discolored

The high temperatures of gases trapped within the mold cavity may cause the material to burn or discolor under high pressure.

3. Incomplete filling

Gas entrapment can hinder the flow of plastic melt, resulting in incomplete filling of the product or surface defects.

4. Reduced mechanical properties

Due to the presence of pores, the strength and other mechanical properties of the article may be affected.

Methods for venting injection molds

1. Parting surface exhaust

Design a small gap on the parting surface of the mold, usually 0.01-0.03 mm. These gaps can allow the gas in the mold cavity to escape without affecting the flow of the plastic material.

2. Exhaust slot

Create an exhaust groove on the parting surface of the mold, at the end of the runner or at an appropriate location in the mold cavity. These grooves are typically 0.02-0.05 mm deep and 1-3 mm wide. The exhaust groove can effectively discharge the gas generated when the plastic material is filled and prevent the gas from being retained in the mold cavity.

3. Insert exhaust

The exhaust is exhausted through the mold inserts, sliders, push rods and other structures. These components have small movable gaps in the mold, which can achieve the purpose of exhaust.

4. Ejector exhaust

The gap between the ejector pin and the mold is used to exhaust air. A special exhaust structure is usually designed at the end of the ejector pin to enhance the exhaust effect.

5. Vacuum exhaust

In some special cases, a vacuum exhaust system will be used to extract the gas from the mold cavity to ensure the integrity and uniformity of plastic filling.

6. Ventilation plug

Ventilation plugs are provided in the mold, usually in places where it is difficult to vent air through the parting surface. The vent plug is made of a specially made porous material that is breathable but not plastic.

How to exhaust air more effectively

1. Increase the exhaust gap

Depending on the material, the exhaust gap of the mold can be adjusted appropriately. Generally, hard plastics are suitable for smaller gaps, while soft plastics can have slightly larger gaps.

2. Expand the exhaust area

Increase the number and area of vent holes on the mold, especially in areas with larger product thickness.

3. Use vacuum exhaust

In the extremely demanding precision injection molding process, a vacuum system is used to extract the air from the mold cavity. This not only exhausts gas, but also prevents outside air from entering, improving the density and surface quality of the product.

4. Select ventilation materials

Use porous metal materials: Use porous metal in strategic locations on the mold to create inserts or vent plugs. These materials are breathable without affecting the flow of the plastic.

5. Regularly maintain the mold

Regularly check and clean the exhaust structure on the mold to prevent residue from clogging the exhaust channel, and replace or repair it in time to ensure normal exhaust function.

6. Adjust injection molding process parameters

Appropriately reducing the injection speed and adjusting the injection pressure can reduce the chance of air being entrained when the material enters the mold, thereby reducing the exhaust burden and ensuring that the material can be filled in place.

Summarize

The exhaust structure of the injection mold is crucial to product quality. If the gas in the mold cannot be effectively discharged, defects such as bubbles, burns, and shrinkage holes will appear on the product surface.

Dongguan Universe Plastic Factory has more than 15 years of experience in injection mold design. It has a professional team, processing equipment and a high-quality mold material supply chain, and can provide high-quality injection mold manufacturing services.

If you are looking for high-quality injection mold manufacturers, please contact us to get the latest service prices.

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