HOT RUNNER MOLD
One of the more important enhancements you can incorporate into your mold to improve molded part quality, reduce production times, and remain price competitive is to equip it with a quality hot runner system. A hot runner-equipped mold can :
• Materials cost savings - no runner to regrind or reprocess
Least expensive cost / piece
Reduction of energy costs
Shorter, faster cycle times - no runners to cool
• Smaller machines - reduced shot volume into runners
Automated processing – runners do not need to be separated from the parts
Gates at the best position for economical design
• No runners to remove or regrind
• Reduces the possibility of contamination
Lower injection pressures
Lower clamping pressure
• Shorter cooling time
Shot size reduced
Cleaner molding process
Eliminates nozzle freeze
Consistent heat within the cavity
There are, however, a few disadvantages to hot runner systems that need to be considered
• Hot runner molds are more complex and expensive to build than cold runner molds
• Higher initial start-up costs than for cold runner systems
• Complex initial setup prior to running the mold
• Risk of thermal damage to sensitive materials
• Elaborate temperature control required
• Higher maintenance costs – more susceptible to:
o Heating element failure
o Wear caused by filled materials
Although a more expensive capital investment upfront, a hot runner system is a significantly more cost-efficient means to keep production costs to a minimum over the long run.
Since there is no cold runner to discard or recycle, resin consumption is reduced. Depending upon the molding application (i.e., medical components or parts requiring FDA approval), the product may require 100 percent virgin material—increasing overall consumption.
Energy is wasted plasticizing, cooling and regrinding each cold runner that is produced. Increased energy consumption also is a direct result of extended cycle times.
Secondary operations—such as manual part de-gating and trimming—are eliminated entirely with a hot runner system.
Mold Cost Savings
A smaller cavitation hot runner equipped mold may be able to satisfy production quotas using a smaller number of cavities since it runs at a faster cycle. The smaller mold frame size may enable installation into a smaller press.
Injection Press Costs
Hot runners allow reduced injection pressures during packing, as the system does not have to deal with injecting resin through a cooled runner. Melt in the cold runner may lose heat en route to the gate, possibly requiring higher heats and/or pressures from the injection molding machine. By reducing the injection pressure and clamp tonnage required, it is often possible to run the same part in a smaller tonnage machine as the clamp tonnage required is not as great.