Coextrude Silicone Rubber and Intumescent Foam

FinnProfiles Oy, a processor of specialty silicone gaskets in Vammala, Finland, believes it is the first in the world to coextrude silicone rubber over an intumescent ceramic to make a fire-safety gasket for trains.

FinnProfiles Oy, a processor of specialty silicone gaskets in Vammala, Finland, believes it is the first in the world to coextrude silicone rubber over an intumescent ceramic to make a fire-safety gasket for trains. Called FP FireCombi, the gasket consists of a flame-retardant silicone profile surrounding a strand of intumescent ceramic. Foaming of the ceramic is triggered at 120 C, so it expands inside the gasket and seals the fire door shut. Typically, the ceramic is inserted by hand into the silicone profile in a secondary operation. The problem with coextruding them is that silicone extrudes at 120 to 160 C, which would cause the ceramic to foam. FinnProfiles developed a process using two extruders and a special crosshead die to keep the silicone profile from contacting the intumescent strand until it has cooled. Tel: +358 (3) 512-5200 • www.finnprofiles.com