Cold Runner Molding

Cold Runner Molding: Efficient and Economical

Significant advantages to using a cold runner system include:

• Simple mold design
• Considerably less expensive than hot runner system
• Less skill required to set up and operate
• Mold requires less maintenance
• Color changes are easy – all plastic in the mold is ejected with each cycle

With a cold runner mold, the runner (excess material retained in the feed channels) is cooled and ejected with the part. Every cycle, a part and a runner are produced.

Cold Runner Molding: A Few Disadvantages to Consider

While it is a less expensive process than hot runner systems, there are a few disadvantages to cold runner systems to consider, including:

• Waste plastic generated
• Runner material must be either disposed of or reground and reprocessed
• Additional steps in the manufacturing process
• Regrind will increase variations in the injection molding process
• Regrinding could decrease the plastic’s strength and mechanical properties

Cold Runner Molding: Get the Right Mold for Your Project

Cold runner molds are the least expensive to build for parts of simple design. Depending on part complexity,  one of two types of cold runner molds may be used:

• A two plate cold runner mold is the easiest and least expensive type of mold to produce.
  • Two plate molds have a single parting plane, and the mold splits into two halves at the plane
  • Because the runner system must be in line with the parting plane, the part can only be gated on its perimeter
• A three plate cold runner mold differs from a two plate in that it has two parting planes, and the mold splits into three sections each time a part is ejected
  • This feature provides greater flexibility of design, which allows gating to be placed in the most efficient locations
  • Since the mold has two parting planes, the runner system can be located on one, and the part on the other, which allows for easier plate separation