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Tooling Corner: Integrated hot runner systems improve efficiences, reduce costs
May 7, 2003
4 Min Read
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Editor?s note: John Blundy is vice president of business development at Incoe Corp.
For some time now, hot runner manufacturers have provided injection half (hot half) systems that reduce the overall assembly time of a mold by building the hot runner system as a completely self-contained unit. The systems also tend to reduce errors in wiring. An extension of this concept are unitized systems?complete drop-in, preassembled units, including electrical connections as well as either the pneumatic or hydraulic plumbing required for valve-gate systems. Unitized systems provide the advantages of a complete injection half at a reduced cost.
With minor modification to the mold and use of a unitized hot runner design, integrated hot runner systems can reduce hot runner installation time, eliminate wiring errors, and reduce costs compared to conventional injection-half systems.
Design and Benefits
The heart of the integrated system lies in the unitized manifold design. Nozzles are threaded directly into the manifold, eliminating the need for a retainer plate. A uniform heat profile is ensured because the junction of nozzle and manifold is inside the manifold, eliminating any transitional heat loss that can occur with conventional bushing-type systems. Bushing-type systems often require a separate heater band on the flange to provide heat to this area, thus increasing operating costs.
An integrated design also reduces power use because the manifold system has very little contact with the mold. This minimal contact reduces heat loss from the manifold and allows the mold to maintain a more consistent temperature level. Threaded nozzles eliminate the tendency for plastic leaks between the nozzles and manifold, which can occur during heat expansion of bushing-type system designs, halting production for repairs.
Since the integrated system is based on using the unitized prewired design for installation in the mold, the chance for pinched or severed heater and thermocouple wires during assembly is eliminated. All wiring from heater to junction box is encased within a specially designed conduit. This is a benefit whenever the mold/hot runner system is disassembled. Also, since the unitized manifold system is fully functional before installation in the mold, full testing of electrical and thermal functions can be performed at the factory before shipment.
An integrated hot runner system provides further benefits:
Routine maintenance can be performed without removing the hot runner system from the molding machine. Conventional injection halves allow some maintenance to be performed while in the molding machine, but it is limited to the very front of the nozzle area because of the retainer plate. Servicing beyond this point requires removal of the hot runner manifold system from the machine to expose the manifold system.
A simple hot runner system and mold?inserts can be easily swapped without mold removal.
Valve-gate operational plumbing can be serviced without disassembly.
Putting the System to Work
Incorporating the integrated design involves preliminary review with the mold manufacturer to ensure proper operation. The unitized hot runner manifold is mounted directly to the top plate of the mold. Also added to the cavity plate are straps that can be placed in two positions: one on the cavity side of the mold, the other placed to capture both the cavity and core side of the mold joined at the parting line.
The integrated system doesn?t compromise normal production function in injection molding. When routine maintenance is required, use the following procedure:1. Open the mold using the setup mode of the molding machine.
2. Remove the socket head screw used to fix the cavity plate to the top plate.
3. Close the mold using the setup mode of the molding machine.
4. Move the strap from the cavity plate and place it over the parting line, so that the core and cavity plates are joined.
5. Slowly actuate the opening stroke, again using the setup mode of the molding machine. This action pulls both the mold core and cavity plate from the top plate and exposes the entire hot runner system.
Any of the following operations can now be performed without removing the integrated system from the injection molding machine:
Gate-tip exchange
End-cap exchange
Nozzle-heater exchange
Nozzle-thermocouple exchange
Manifold-thermocouple exchange
Complete hot runner inspection
The integrated design substantially reduces the downtime normally required compared with a conventional hot runner design?from up to a full shift to an hour or two, since the entire hot runner system is now completely exposed and easily accessible. If complete removal of the hot runner system is required, a lifting hook can be placed on the top plate, the mold clamps can be removed, and the assembly can be moved to a workbench. The unitized hot runner system can then be completely removed by unscrewing the socket head screws used to fix the system to the top plate.
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