Hot Runner vs Cold Runner Injection Mold

Injection molding is widely used to manufacture plastic parts for high production volumes. Various types of Injection mold can be manufactured depending on part geometry, expected molded part quality, and production volume requirements. Hot Runner and Cold Runner Injection molds are injection molds with different types of the runner system.

In this article, we will discuss What is the difference between a hot runner and a cold runner injection mold? their advantages, limitations, and applications. We suggest you also read this article on factors affecting injection mold price.

A Runner is a channel inside the injection mold that guides the molten plastic from the injection molding machine barrel to the mold cavity.0

 Depending on the type of runner system, the runner keeps in a molten state or gets solidified along with injection molded parts. Here are the two types of injection molds according to the feeding system:

  • Cold runner Injection mold.
  • Hot runner Injection mold.

Cold Runner injection Mold System

In Cold runner injection molds, the runner system is not heated up and after the injection cycle, the sprue runner and gate are cooled with injection molded parts. Therefore runners and gates are ejected along with molded parts. Tunnel gates are preferred in cold runner injection mold systems and they can be two-plate or three-plate injection molds.

Cold runner molds are two plate or three plate molds. In this, runners are not heated up.
Cold Runner Injection Mold

In a two plate cold runner injection mold sprue, runner and gates are ejected with the molded component. Whereas in three plate injection molds, during mold opening runner automatically separates from injection molded plastic parts.

Advantages of cold runner Molds

Cold runner injection mold systems have the following advantages.

  • Simple mold design and construction.
  • Low cost.
  • Low maintenance cost.
  • Fewer skills are required for setup and operation.
  • Change of material and color of injection molded parts is easy.
Disadvantage of cold runner Molds

A cold runner injection mold system has the following disadvantages.

  • In cold runner mold, the runner is attached to the molded part. Therefore additional runner cutting operation is required.
  • Runner material is wasted if the runner is not recycled.

Hot Runner Injection Mold

Hot runner injection mold consists of two plates that are heated using a manifold system. In this system, runners are heated to keep injected thermoplastic in a molten state. Therefore runners are not ejected with molded parts. 

Hot runner injection mold consists of two plates that are heated using manifold system. In this system, runners are heated to keep injected thermoplastic in molten state.
Hot Runner System

The heated runner system remains stationary during the injection cycle and molten thermoplastic is kept at the barrel temperature. Heated runner delivers molten plastic to nozzles. You can check various hot runner system components here.

Types of Hot Runner Injection Molds

Hot runner molds are two plate molds with a heated runner system inside one half of the mold. They consist of two parts: Manifold and Drops

  1. The Manifold: It consists of channels that convey the molten plastic on a single plane, parallel to the parting line, to a point above the cavity.
  2. The Drops: It is situated perpendicular to the manifold, conveying the plastic from the manifold to the part.

Following are the two different types of hot runner systems.

a) Insulated Hot Runner mold

In the insulated hot runner system, heat near the runner section is insulated in such a way that runner plastic keeps in molten condition during continuous cycling. 

Insulated runner requires an extremely thick runner channel. These molds have extra-large passages formed in the mold plate. Insulated Hot runner mold system does not require manifolds and drops. Therefore an insulated runner system is less expensive.

b) Heated Hot Runners Injection Mold

In a heated hot runner system, the runner system is heated to keep the plastic in molten condition during continuous cycling. 

Following are the two types of heated hot runner systems.

  1. Externally heated hot runner mold
  2. Internally heated hot runner mold
Advantages of hot runner Injection Mold System

A hot runner injection mold system has the following advantages.

  • The runner is not attached to the molded part. Therefore the material cost is reduced.
  • Reduced Cycle time.
  • More control over the injection process. Therefore part quality improves.
  • Low pressure is required to push molten plastic.
  • Recommended for larger parts.
Disadvantages of hot runner injection mold System

Following are the limitations of the hot runner injection mold system:

  • High Injection mold cost.
  • Higher maintenance cost.
  • Complete mold cleaning is required to change material.
  • Not recommended for thermally sensitive materials.

Hot Runner vs Cold Runner Injection Mold

Here is the summary of the difference between a hot runner and cold runner injection molds:

Hot Runner Injection MoldCold Runner Injection Mold
The runner system is heated up.Runner System is not heated-up.
Two plate injection mold.Can be two plate or three plate Injection mold.
Only injection molded plastic part is ejected.Runner system is ejected with the injection molded part.
High mold manufacturing cost.Low mold manufacturing cost
High maintenance cost.Low maintenance cost.
Low part manufacturing cost.High part manufacturing cost.
Low cycle time.Relatively large cycle time.

We will keep adding more updates to hot runner vs cold runner injection molds Please add your comments or questions on the hot runner vs cold runner system in the comment box.

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