Injection Mold Hot Runner VS Cold Runner

Injection mold hot runner vs cold runner

Injection mold is a tooling for manufacturing plastic parts. There are many types of injection

moulds. In this article, the injection molds are divided into hot runner and cold runner mold.

The hot runner ensures that the plastic in the runner and gate remain molten by heating.

Because there are heating rods and heating rings near or in the center of the runner, the entire  runner from the nozzle outlet of the injection molding machine to the gate is in a high temperature state, so that the plastic in the runner remains molten. 

Generally, it is not necessary to open the runner to take out the condensate after shutdown, and it is only necessary to heat the runner to the required temperature when restarting.

After cooling in the mold, the plastic in cold runner is taken out with the product, and the injection part can be obtained only after the cold runner gate is removed.

Comparison of advantages between hot runner and cold runner

 Plastic injection mold of cold runner

1) In the process of injection molding and filling, due to the constant loss of heat at the front end of the material flow, the material flow surface will solidify, and the injection pressure loss is large.

2) In the process of injection molding and filling, due to the constant loss of heat at the front end of the material flow, the surface of the material flow will solidify, resulting in the uneven temperature of the plastic injected into the mold, which may directly lead to a series of problems such as splay mark, welding mark, deformation, warpage, depression, and insufficient filling of the molded plastic products, making the plastic injection molded parts unable to meet the requirements.

3) Due to the generation of cold runner, the injection mould factory has to set up special waste secondary processing equipment, resulting in the waste of manpower, material resources.

4) Some injection mold structures have the problem that the gate and plastic products are not able to be automatically separated, so the gate trimming process needs to be added, and increases the labor cost and prolongs the production time.

5) The mold cooling time and filling time are long, resulting in low production efficiency

Plastic injection mold of hot runner

1) The temperature of the hot runner after heating is almost equal to the temperature of the barrel and nozzle of the injection molding machine, which avoids the condensation of molten plastic on the inner surface of the runner and reduces the injection pressure loss.

2) After plastic injection molding, the quality of plastic molded parts is high. Because the temperature, pressure and density of the plastic after injection into the mold cavity are uniform, the internal stress of the plastic injection molded part after molding is small, the deformation is also small, and the size is stable.

3) No waste, save materials, save resources and costs.

4) Mold cooling is fast, filling is fast, forming cycle is short, and injection molding production efficiency is high.

Characteristics of hot runner injection mold

1) The melting temperature range of plastics is wide. It has good fluidity at low temperature and good thermal stability at high temperature.

2) Sensitive to pressure. It does not flow without pressure, but flows immediately after pressure is applied.

3) Good thermal conductivity, fast heating and cooling.

Shortcomings of hot runner mold

1) Because the hot runner system has heating mechanism and splitter plate mechanism, it needs to occupy a large space. Therefore, the overall height of the mold needs to be increased, which directly leads to the increase of injection mold cost.

2) The heat loss is serious and difficult to control.

3) Serious thermal expansion will occur after heating.

4) The high price of hot runner system leads to the increase of injection mold manufacturing cost.

Type of hot runner

According to the structure, the hot runner can be divided into open hot runner and valve hot runner. The open hot runner can also be divided into edge gate hot runner and point gate hot runner.

The valve hot runner controls the opening and closing of the discharge hole through the valve, which can achieve a completely closed sealing. It is the most beautiful gate type, without any waste. Generally, the valve type is used for injection molding of products with high requirements.

Point gate hot runner, as the name implies, the gate of point gate is very small, and the product surface is very beautiful. It is suitable for injection molding of small products. The gate of edge gate hot runner is relatively large and the injection volume is large. It is suitable for injection molding of large products.

Hot runner or cold runner, how to choose?

We recommend manufacturing cold runner plastic injection mold for producing small and low volume plastic parts.

Cold runner is recommended for non-appearance large plastic parts but small output.

Hot runner is recommended for large volume plastic injection molded products.

The gate position of the hot runner can make the parts more functional and have a better surface finish. So hot runner is recommended for plastic parts with high appearance requirements.

Summary

The cost of cold runner mold is lower than that of hot runner injection mold, but the cost of injection molding plastic parts with hot runner mold is lower than that with cold runner injection mold. HanKing Mould can give you the most professional advice on whether a plastic part injection mold needs to use a hot runner, and we can propose more information on how to move on your projects, contact us for a free quotation procedure, we can quote in one day.