Adhesive ensures balance, bond strength

Yacaipa, CA--Ney Dental manufactures equipment for use in dental laboratories. Among its products is the Hurricane, a handpiece used to shape crowns and bridges for patients.

Design of the high-speed, low-torque, air-driven device presented Ney with several challenges. Foremost among them was determining the best way to bond components in the handpiece's turbine assembly, which, when hit by air, makes the shaft spin at 300,000 rpm. The turbine assembly consists of a shaft, bearings, turbine, and other components which slide onto the shaft.

"We had to retain the inner race of the ball bearings from spinning on the main spindle shaft," explains engineering consultant Howard Konishi, who designed the Hurricane product. Engineers required high bond strength and reliability. Ease of assembly was also important, since Ney manufactures several hundred Hurricane devices each month.

"We had several options, including press fit and clamping methods. But we chose an adhesive because it reduced the overall number of parts and eliminated the need for threaded parts. Plus, it gave us the opportunity to relax some of the very, very close tolerances that are inherent in this type of equipment.

We needed an adhesive that would flow easily and offer uniformity," he says. "It also had to have good gap-filling abilities because, with the shaft spinning at 300,000 rpm, balance is very critical."

Loctite(reg) RC(TM) 609 from Loctite Corp. (Rocky Hill, CT) fit the bill. It can be used on slip fits up to 0.005-inch diametrical clearance, fixtures in 10 minutes on unprimed steel at room temperature, and provides a shear strength of 3,000 psi at full cure.

Loctite RC 609 is now used in the Hurricane turbine assemblies, as well as in Ney's slip-fit assemblies with gaps from 0.002 to 0.003 inch. "Even when used 8 hours a day, the average life of the Hurricane handpiece is one to three years," says Andy Dybicz, manager of quality assurance at Ney. "Usually the bearings wear out first, with the Loctite adhesive still holding. So we replace the bearings, apply Loctite RC 609, and the handpiece is good as new."

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