Nordson Corp. has developed a complete injection-unit package for liquid silicone rubber (LSR) molding that reportedly meets the special mixing and metering requirements of low-viscosity thermoset ingredients and can be readily retrofitted on standard injection molding machines.
The Xaloy[R] LSR Package includes a specially designed screw, barrel, seal, valve, and nozzle, along with other components where needed, such as a feed-pipe adapter. Nordson recommends the package for manufacturers of seals, gaskets, cushioning pads, medical devices, infant feeding items, ruggedized electronic devices, and kitchenware such as baking pans and spatulas.
"The low-viscosity liquid ingredients for LSR pose a very different set of mixing and metering requirements from those of thermoplastics, and their temperatures must be maintained below the curing point until homogenized material reaches the mold cavity," says Mark Colella, global product manager for the Xaloy brand. "Our LSR package addresses these unique challenges, yet can be retrofitted on a standard injection molding machine in what amounts to a bolt-on conversion."
Multiple components are included in Xaloy LSR Package:
* A single-flight, wear-resistant, 12:1 to 14:1 L/D screw is designed to provide optimum homogenization of catalyst and crosslinking agents without increasing the temperature of the compound.
* With a feed port moved downstream and two welded cooling jackets, the barrel is designed for a low L/D ratio and provides the intensive cooling required to hold the LSR compound below crosslinking temperature. The Xaloy X800[R] barrel inlay is a nickel-based alloy with tungsten carbide, providing the abrasion and corrosion resistance needed with certain LSR compounds.
* The rear seal is installed on the barrel or as a seal ring on the screw shank.
* An Xaloy spring-loaded valve ensures immediate shutoff with low-viscosity LSR compounds.
* And the shutoff nozzle is provided by a partner company that is a longtime supplier to the LSR industry, reports Nordson.