There are several benefits to using a hot runner mold as opposed to a cold runner mold. When designed and built correctly, hot runners are easy to use and allow an injection molding company to save costs and increase productivity.
Not having to deal with a cold runner saves money in a number of ways:
A hot runner makes it easier for a molding machine to inject plastic into a mould cavity. A hot runner increases the capability of a molding machine. It reduces the plastic flow length so a molder can save material by making thinner and lighter parts.
A shorter opening stroke can be used as there is no runner to eject saving cycle time.
Injection fill times are shorter because the plastic flow length is shorter which also saves cycle time.
What’s more, for high cavitation moulds runners need to be thick and cold runners will need a long cooling time before being solid enough to eject from a mold.
There are more than 20 hot runner manufacturers making high quality hot runners around the world today. Each one can custom make a hot runner to fit a new mold design.
The high number of manufacturers means competition keeps prices under control. Good support is also available from most of them.
Some injection mold makers are capable of making their own hot runners. The advantage is that one company can take full responsibility of the entire mold and it reduces the hot runner price.
To make a hot runner requires standard tool making equipment such as a radial drill, cnc machining center, a surface grinder, a cylindrical grinder and a cnc lathe. All heater elements can be bought and a person qualified in electrical wiring can connect them to the temperature controller.
The materials required to make a hot tip hot runner are P20 for the manifold and H13 for the nozzles and insulators. The nozzle tips are usually made from a copper alloy but can also be made from H13 and thru hardened for long life.
Other benefits of hot runners:
Hot runner molds involve the use of electricity so some training will be required for die setters and process technicians so that safety procedures are followed.
A hot runner mold will have a bigger mold height compared to a cold runner mold so this may limit which molding machines can be used due to the larger physical size of the mold.
The decision to use a hot runner or cold runner must be taken on a case by case basis but the fact is that a molder having a medium to high annual quantity requirement for any particular part will benefit from a hot runner mold.
The extra cost of a hot runner will be recovered through faster cycle times, better quality parts and material savings.