Hot Runner Systems In Plastic Molding

The use of hot runner systems is increasing due to the fact that they provide a more efficient method of molding plastic parts. The cost savings can be substantial, and the part quality is very often much better than a cold runner system.

With the increasing sophistication of today's plastic injection molds, the use of a hot runner system is becoming an industry standard. Many applications simply are not possible with the old standard sprue and cold runner system, and hot runners offer a great way to maintain uniform wall thickness and eliminate knit lines and flow lines.

What are some advantages of hot runner systems?
Ability to minimize gate vestige
Uniform wall thickness
Lower cycle times
Less waste
Reduction or elimination of knit lines
Great for high cavitation molding
Often the only method for micro-molding. The center to center distance of the hot runner tips is as little as 17 mm.
Standardization of components can mean significant savings in material and manufacturing.
Many large molds rely exclusively on hot runners. Cold runners cannot meet the demands.

What about the maintenance of hot runner systems?

Hot runners systems require a new level of expertise on the part of the mold maker. However, this does not mean that it is overly complicated or highly specialized. A well designed system is relatively free from maintenance, once it is properly installed.

It can, and does happen, that mold makers become frustrated with hot runner systems and swear that they are too much trouble. This is usually due to the fact that the system is not properly installed or incorrectly operated in the molding process.

The leading hot runner system manufacturers have a well-trained team of specialists on hand to assist in the proper installation and operation of the systems. The time spent listening to these specialists is time well spent!

Are there different types of hot runner systems?

There are almost as many types of hot runner systems as there are suppliers! Most share some common features, however. There are sprue gated systems, valve gates, tip gates (the most common), and edge gates. Any of the major suppliers can describe in great detail why their system is the best for your application.

Long term benefits

Even though there is an initial investment with hot runner systems, it is easy to justify the long-term benefits. Without increasing the complexity of the design of the mold, a hot runner equipped mold can significantly reduce costs. Because the hot runner is designed and manufactured independently, yet concurrently, the lead times are not affected.

Mold makers should always suggest methods for his customer to reduce molding costs and increase the output of the mold. Being knowledgeable with hot runner systems is a good way to demonstrate an active role in helping the molders bottom line. This in turn makes the likelihood of increased business even greater for the mold maker.

Randy Hough lives and works in the Upper Valley of Vermont. His eight lively children and work experience have taught him more than he ever imagined. He has a site dedicated to helping with family stress and one about plastic injection mold making.