Custom Designed vs. General Purpose
Today, in injection molding, molders are faced with many difficult challenges. Screw design is one such challenge that most processors have little or no experience. Since the development of the Reciprocating Screw, most molders have purchased or been provided so called "General Purpose" screw designs or designs with marginal improvements. The technology that "General Purpose" designs incorporate was developed in the early 1950's. Many new resins have been developed to accommodate ever growing molded part requirements. Molders have compensated for inadequate screw designs by utilizing "band-aids" such as backpressure, pullback, and elevated barrel temperatures. G.P. designs that require backpressure increase recovery time and melt temperature, that in turn, increases mold-cooling requirements. The damage to the resin that occurs with excessive backpressure and barrel temperatures causes many molded part failures. Properly designed mixing screws can decrease recovery time, improve melt quality, remove splay, and reduce cycle times by lowering melt temperature. Our mixing screw designs combine the most recent technological advances coupled with thirty-seven years of experience in screw design. A properly designed mixing screw, normally will enable the molder to change colors on the run while using less concentrate. There are two types of mixing devices, distributive and dispersive. One example of a distributive mixer is patented under the name "Dray Mixer". Dray mixers divert lower temperature resin from the downstream side of the channel into a groove on the upstream side of the channel, merging the lower temperature resin with the higher temperature resin, bringing the resin temperature to unity. The Spiral "W" mixer is an example of a dispersive type mixer. Mixing is accomplished by resin flowing through the inlet grooves, over the under cut flight and into the outlet groove. Shear stress is added to any particles smaller than the flight clearance allowing their temperature to come to unity with the surrounding resin. Distributive mixers are designed for high viscosity and filled resins, dispersive mixers are designed for low viscosity resins. R. Dray Mfg. was the first to guarantee screw performance and still does. Designs by Dray have been utilized in virtually every application and resin. We have six different mixer designs that cover the required viscosity ranges. To see what advanced Mixing Screw design can do for you,please contact us.
Dray Mixers	Sprial "W" Mixer
R.Dray Mfg. is committed to providing a total injection molding package from screw to nozzle tip Please give us a call and see how we can improve your process for less. Return to main page