What is runner?
A runner is a channel in the mold that guides the molten plastic from the barrel of the injection molding machine to the cavity of mould.
In this article we will discuss hot runner and cold runner systems
Based on feeding system molds are divided in two categories:
- Cold Runner mold system
- Hot runner mold system
Cold Runner Injection Mould System
Cold runners are unheated physical channel that is used to direct molten plastic into a injection mould tool cavity after it leaves the nozzle. In cold runner injection mold, runner is cooled and ejected with the part.
Each half of the injection mould contains one-half of the runner diameter and round runner may be the best design option for a cold runner system.
Tunnel-gates are preferred with cold runner system
Advantages of cold runner Injection Moulds
- Injection mold design is very simple.
- Cold runner system is cheaper than a hot runner system.
- Mold requires less maintenance and skills for set up and operation.Change in material and colour of injection molded part is very easy task
Disadvantage of cold runner Injection Moulds
- In Cold runner injection mould runner is a part of injection moulded piece, after the completion of operation runner need to be cut and reused.
- Cycle time of cold runner injection mould is higher as compared to hot runner system.
- Rework is required on finish part (runner need to be removed from finished part)
Hot Runner Injection Mold System
Hot runners systems are heated physical channel that is used to direct molten plastic into injection mould after it leaves the nozzle. In a hot runner mold, the runner is situated internally in the mold and kept at a temperature above the melting point of the plastic. As a result runner scrap is reduced or eliminated.
Advantages of hot runner injection Molds
- Hot runner system can completely eliminate runner scrap, so there are no runners to sort from the parts, and no runners to throw away or regrind and remix into the original material.
- Injection moulding process can be controlled more precisely to Improve part quality because hot hot runner system has more control over the temperature of molten plastic.
- To manufacture very large injection molded parts hot runner system is a good choice.
- Cycle time of a injection moulded part is less as compared to cold runner system.
- Higher production rate can be achieved
Disadvantages of hot runner injection molds
- Hot runner systems are expensive as compared to cold runner injection molds.
- Higher maintenance cost.
- Complete cleaning of mould is required for changing material.
- Not good for thermally sensitive materials
Types of hot runner injection molds
Hot runner injection molds are two plate molds with a heated runner system inside one half of the mold.
A hot runner system can be divided into two parts:
- The Manifold : It has channels that convey the 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.
Hot runner systems are divided in two categories based on how the plastic is heated inside mold :
- Insulated runners mold
- Heated runners mold
1. Insulated runners mold
Runner system is 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. Cost of this system is low as this system eliminates the requirement of manifold and drops.
2. Heated runners mold
Runner system is heated to keep the plastic in molten condition during continuous cycling. Heated runner molds can be further classified in two categories :
- Externally Heated Injection Molds
- Internally Heated injection Molds