Kalrez® Perfluoroelastomer seals, a product of DuPont Dow Elastomers, are impervious to more than 1,600 chemicals and solvents, inert to most chemically induced swelling, useful in temperatures from –20°F to 600°F, and last much longer then other elastomer seals. Unfortunately, at about $2,000 per pound, Kalrez is also a very expensive design material, even in medical and chemical resistant applications for which no other seal material is nearly as durable.
We have been using Kalrez for solenoid valve plunger seals in applications where nothing else would do. These long lead-time, molded Kalrez seals often more than doubled the price of comparable valves incorporating other elastomer seals. And Kalrez is s tough material to form: It sticks in the mold, and is difficult to maintain dimensional accuracy in complex shapes…not to mention cost of Kalrez rejects and molding waste (which are not easily disposable).
But…design engineering to the rescue. Our Senior Design Engineer William Milish has helped develop a procedure for laser cutting Kalrez seals from 3” square sheet stock. “It took a little practice,” says Bill, “but we’ve now been able to cut the amount of Kalrez used per seal by about half, reducing the cost per seal, even in relatively small quantities, by about 40-60%.” Currently limited to 3/32” and smaller orifice sizes, the valve plunger assembly has been slightly modified to use a stainless steel cup to attach the Kalrez seal to the plunger. The use of the cup actually governs the plunger length better, and two tiny notches on the seal circumference allow the seal to vent gases from within the plunger. The result: A bubble-tight seal for the most difficult chemical applications, without the use of Teflon. “It’s an elegant solution to an expensive problem,” according to Bill Milish.