Key Advantages of Hot Runner Systems
Plastic injection molding is one of the most common manufacturing processes around, offering economical production for high-volume projects. If you are shopping around for a plastic injection mold manufacturer, one thing you might want to consider is using one that employs hot runner systems.
In traditional cold-runner systems, the plastic solidifies in the runner. When the finished part is ejected, this runner scrap is ejected with it. In hot runner systems, all parts of the system outside of the mold itself are kept warm so that only the plastic in the mold solidifies.
The benefits of hot runner systems
Without the runner scrap, less material is wasted and less post-molding processing is required, saving money and time on the manufacturing process.
Not all of the scrap in cold runner systems comes away with the part, requiring cleaning the mold each cycle. Since less material is wasted in hot runner systems, less material must be injected each cycle, which speeds up processing further.
Lower injection pressure
By keeping temperature of the molten plastic high, viscosity remains low and a lower injection pressure is required. This makes for easier filling of the cavities and less deflection the mold, meaning less flash and less waste. It also reduced the stress on the part and yields greater structural integrity in the finished product.
When the plastic flows through cold runners, it loses heat to the walls and runs more slowly. This can lead to under-filled molds and useless pieces. Hot runner systems maintain a steady flow throughout the entire system and give fewer failed fills.
In injection systems with multiple cavities, hot runner systems provide balanced flow to every cavity regardless of its distance from the source of plastic. In the event a given cavity becomes damaged, heat to that particular runner can be eliminated to deliberately create a blockage and prevent wasted material from being fed to the damaged cavity.
With the increased precision of hot runner systems and the lack of runner scrap, greater automation becomes possible. This leads to higher production speeds and reduced costs.
Cold runner systems aren't obsolete
There are many cases where hot runner systems aren't appropriate. Some materials are heat sensitive and may suffer chemical changes in hot runner systems. In situations where parts of different colors are produced, cold runners allow quick color changes since all of the plastic is ejected with each cycle.
The cost of hot runner systems must be balanced against the savings of faster processing and less waste. Some applications, particularly involving small parts, don't warrant the cost of hot runner systems.
Hot runner systems have become increasingly common in recent years due to improvements in the technology involved, so many manufacturers offer both hot and cold runners. Talk to your manufacturer about your needs so that you can decide on the most appropriate manufacturing process for your product.