Injection mold selection depends on component design, budget and production volumes. During new product development, manufacturer always ask this question. What type of injection mold is required? According to customer requirements manufacturer provides tool estimate. In this article we will discuss about Hot runner and cold runner mold.
What is a runner?
A runner is a channel in the mold that guides the molten plastic from injection molding machine barrel to the mold Cavity.
Based on feeding system injection molds are classified into two categories:
- Cold runner mold.
- Hot runner mold
Cold Runner injection Mold System
How Two Plate Cold Runner Injection Molds are Different from Three Plate Injection Molds?
In two plate cold runner mold sprue, runner and gate are ejected with the molded component. Whereas in three plate injection molds, during mold opening runner automatically separates from molded part. For more details read this article on Two plate and Three plate injection mold.
Advantages of cold runner Molds
- Simple mold Design and Construction.
- Cold runner injection molds are Inexpensive compared to hot runner molds.
- Low maintenance cost.
- Less skills required for set up and operation.
- Change of material and color of injection molded part is easy.
Disadvantage of cold runner Molds
- In cold runner mold, runner is attached to molded part. Therefore additional runner cutting operation is required.
- Runner material is wasted if runner is not recycled.
Hot Runner Injection Mold
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.
Heated runner system remains stationary during 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.
In hot runner mold, runner is situated internally in the mold. Therefore runner is not ejected with molded part.
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
- The Manifold : It consist of channels that convey the molten plastic on a single plane, parallel to the parting line, to a point above the cavity.
- The Drops : It is situated perpendicular to the manifold, convey the plastic from the manifold to the part.
According to how runner is kept in molten state. Hot runner systems are divided in two categories.
a) Insulated Hot Runner mold
In this runner system is heat insulated in such a way that plastic stays in molten condition during continuous cycling. This type of runner requires extremely thick runner channel. These molds have extra-large passages formed in the mold plate.
Insulated Hot runner mold system does not require manifold and drops. Therefore this system is less expensive.
b) Heated Hot Runners Injection Mold
In this, runner system is heated to keep the plastic in molten condition during continuous cycling. They are classified in two categories:
- Externally Heated Hot Runner Mold
- Internally Heated Hot Runner Mold
Advantages of hot runner Injection Mold System
- Runner is not attached with molded part. Therefore material cost is reduced.
- Reduced Cycle time.
- More control over 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
- High Injection mold cost.
- Higher maintenance cost.
- Complete mold cleaning is required to change material.
- Not recommended for thermal sensitive materials.
To sum up, In cold runner system, runners are not heated. Therefore after injection cycle, sprue, runner and gate are cooled along with part. Whereas in hot runner systems, runners are heated up continuously. Therefore sprue, runner and gate are not part of injected part.
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