Dray Mixer "triangle mixer"
The Dray Mixing design was created to have a screw design that was a self-cleaning, low shear, distributive mixing device. The Dray Mixer was developed primarily for high viscosity polymers, filled polymers, and color mixing in both injection molding and extrusion applications.
How it Works
The triangular diverters cause the lower temperature polymer on the trailing side of the channel to converge with the higher temperature polymer on the forwarding side of the channel. This tends to bring the melt temperature to unity. As the polymer enters the groove on the forwarding side of the flight it causes rotation and turbulence. As the polymer diverges from the groove further mixing is encouraged. The process repeats itself into the next groove along the length of the mixing section.
The surface of the triangle is cleared to allow the melted polymer to cross the triangle land but not great enough clearance to allow any unmelted particles to cross the land. The Dray Mixing design may be the only true distributive mixer design that is self-cleaning and low shear. This is accomplished as the cross-sectional area in the triangle is the same as the groove cross-sectional area. As the polymer converges and diverges thru the groove, there is minimal shear. With glass filled polymers the groove aligns the glass strands without breaking the strands - this alignment provides maximum strength in the polymer.
In wave type designs the valley in the trailing channel has less flow, this can cause material to hang up and degrade. The Dray mixing design is used routinely in rigid PVC applications that must have flow without areas of low flow that can cause material to hang up and degrade. This design has been used in hundreds of applications in both extrusion and injection molding in virtually every sector.
True Distributive Mixing
The Dray Mixer is ideal for higher viscosity, shear sensitive materials and filled materials (PC, GF Nylon, PVC, PMMA, etc.) The triangular diverters cause the resin to converge and diverge along the length of the mixing section, promoting a high quality isothermal melt.
The block clearance is not great enough to allow any unmelted solids to cross the land. This self cleaning mixing design ensures adequate melting and a high quality extrudate at lower melt temperatures. Our customers have achieved high clarity, good surface finish, and increased molded part physical properties in both extrusion and injection molding in virtually every industry sector.