Using a Hot Runner Manifold for Epoxy Molding

Lot of valuable Epoxy(a thermoSet) will be lost in Runners and Risers.

So depends what is important:

• Epoxy Continuity and No-Voids OR
• Economics of material wastage

Hot runner molds are used in thermoplastics because heat keeps the plastic molten in the enclosed runner. Only the plastic that goes into the cavity is cooled and solidified. In a conventional thermoplastic mold (cold runner), the runner is also cooled and solidified each shot. The plastic in the runner is either reground, or disposed of as scrap. This can be a big waste of material and energy. Epoxy is different in that heat accelerates the cure, and once it hardens, no amount of heat will melt it again. A hot runner will possibly give you a faster cycle, because the epoxy will start to cure in the runner. But if the cycle is interrupted for any length of time, the epoxy will harden in the hot runner and you will have a real mess. You may be able to use an enclosed runner that is insulated or cooled to keep the epoxy from hardening while it cures in the heated cavity. The problem will be in the gate area, where it transitions from heated cavity to cold runner. The epoxy could cure in the gate and break off, plugging the gate. Or there could be a string or blob of uncured epoxy on the part at the gate. It would take some experimenting to see if this is feasible. Another possibility would be to have the resin and hardener flow into the mold in two different enclosed channels and flow into a disposable static mixing tube installed into the mold. The nozzle of the mixing tube would form the gate into the part. Then the entire mold and runner system could be heated, which would help the epoxy cure faster. If the cycle is interrupted, the epoxy might harden in the mixing tube, but that could be pulled out and easily replaced.

Are you thinking of using a temperature activated catalyst?

If so, you can keep the hot runner manifold slightly cooler than the activation temperature. This will drop the viscosity of the epoxy mixture for better mould fill, however, you will need to have the cavities moulding surface above the activation temperature.

Gives a high production rate but the parameters need to be very tightly controlled.

So, what have you found out so far? The other comments were right on the mark. The mixing tube as a hot runner is an excellent idea as well as the info that the heating of the resin as its being injected will reduce the viscosity and make filling and more importantly completely saturating any fibers that are in a preform in the mold. In the systems I've worked with the usual methods have pre mixed the resin, run it through a heater then injected it into the mold. Sometimes the mold has vacuum sometimes it just uses the pressure of the injection system. I've also seen one part resin systems that were directly injecteded into a hot mold where the runners were the same temp as the rest of the mold they worked well.

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