Malpensa, Italy — Elkem Silicones USA Corp. in York, S.C., has revealed a new Elkem LSR Select range of liquid silicone rubber products in Shore hardnesses of 25A, 35A, 50A and 70A.
LSR Select is aimed at low temperature LSR molding, but is also capable of achieving faster cure at normal mold temperatures.
Ted Johnson, senior staff chemist at the silicone rubber materials producer, presented the materials Nov. 27 at the Smithers Rapra Silicone Elastomers World Summit in Malpensa.
Johnson noted that traditional LSR molding involves a supply of uncured "A" and "B" components in a 1:1 ratio sent to a static mixer, with color additives supplied when required, and fed as a still uncured mixture via a cold runner system for injection into a hot mold to form finished cured moldings.
Elkem's LSR Select solution involves pre-mixed "A" and "B" materials from a single drum, to which an inhibitor additive, catalyst and colors are added ahead of the static mixer via precise dosing valves.
This approach enables easier startup and shutdown, as well as saving material by eliminating the need for purging material with incorrect "A"-to-"B" ratios, Johnson said. He also claimed improved repeatability and reduced final part variance.
He added that curing can run 25-36 percent faster than conventional LSR.
Johnson showed that two drums of LSR Select can be used to combine materials of different hardness as a means of tailoring hardness and stiffness with inline blending. He said using two drums with the same grade enables production to continue when the first drum is empty.