Sprueless Molding for LSR

Two new valve-gate systems for runnerless molding of liquid silicone rubber were introduced at the recent International Plastics Fair in Tokyo.

Two new valve-gate systems for runnerless molding of liquid silicone rubber were introduced at the recent International Plastics Fair in Tokyo. The Rudiz System from Seiki Corp. of Japan is available here from Mitsui Plastics Inc., Glendale Heights, Ill. It is said to avoid drool and scorching at the nozzle by means of a pneumatic valve pin, a special moving runner bushing, and an air gap and cooling bushing that separate the cold runner from the hot mold. The valve pin and runner bushing retract from the gate before injection begins. The runner bushing moves forward to contact the gate for injection. After filling, the gate is sealed by a separate motion of the pin. During cure, the runner bushing retracts from the gate to prevent scorching or sprue solidification. Another new LSR valve-gate system comes from Fisa Corp. of Japan (U.S. office in Shelbyville, Tenn.). It has a spring-loaded valve pin that is pushed back from the gate by pressure of material injection. The spring forces it closed with an air-tight seal as soon as injection pressure ceases. The nozzle body is insulated and has an internal water-cooling channel that spirals around the flow channel down to the tip. Gate balancing can be adjusted in the press with a simple hex wrench.