When the decision has been made to incorporate a hot runner system into a mold, the question arises of what to look for. With the many independent suppliers out there, the types and choices of systems are obviously numerous and often the only resemblance of one system to another is the common term "hot runner."
Hot runner technology comes with many options and the driver of selection - in order to obtain all the molding efficiencies and part quality benefits - must be the application. There are cases where price, for instance, has taken preference over the application with the consequence of lower than expected mold efficiency and sacrificed part performance.
- Service - In addition to sales, does the supplier offer product service, training and start-up assistance?
- Complete hot runner assemblies - Are fully assembled and tested "bolt-on systems" available or just components only, leaving the moldmaker to design and machine the surrounding hot runner plates, assemble the complete system and then test it himself?
- Product range - To achieve the optimum system for the molding application, does the supplier offer an extensive nozzle range of hot tips, valve gates, edge gates, hot sprues, multi-tips, etc. for maximum design flexibility?
- Experience - Look for a wide background in mold and molding applications. The supplier should be able to offer guidance in gate location and possible part orientation for optimum filling and packing, gate/nozzle type, gate strength and gate cooling, etc. An understanding of the relationship between the mold and the hot runner system is a critical supplier strength.
- Resin testing - Is a fully equipped resin testing or R&D facility available to assist the OEM or moldmaker in choosing the best hot runner system type, nozzles and other parameters for a new hot runner application or resin?
- Balanced resin flow - Does the supplier offer flow analysis, channel sizing and other design capabilities to produce a mechanically and thermally balanced hot runner system - a system where the runners are large enough to give a relatively small pressure drop through the system without causing too much residence time?
- Melt channels - Are the channels designed and manufactured to be smooth with rounded corners, and to have no sharp corners or "dead" spots? Can the manifold be cleaned should an incident occur which leaves the system full of degraded resin?
- Insulation - The hot runner manifold and nozzle assemblies must be insulated from the mold plates to avoid heat loss and its resulting excessive power consumption.
- Plates - Are the hot runner plates machined from solid blocks of pre-hardened stainless steel to ensure ruggedness; maximum support around the manifold; minimum deflection under high clamp tonnage and injection pressures; minimum maintenance; and hot runner longevity?
- Ease of Maintenance - Can the gates be cleaned in the machine? Can wear items such as nozzle tips, thermocouples and heater bands be replaced without removing the mold from the machine? Can the valve stems in valve-gated systems be adjusted or replaced in the molding machine?
As can be seen, the use of a hot runner system can increase overall molding efficiency by reducing cycle time, energy costs and some labor and material costs - there are no runners to regrind, store and/or scrap. Its use also adds greatly to part quality and consistency, and allows more flexibility for molding automation.
Author: John Thirlwell, VP of Sales and Marketing, Caco Pacific Corp.
Source: MoldMaking Technology