Machine Design

Adhesives hold electric motors together

Edited by Lawrence Kren & Victoria Reitz

Electric motors are smaller, faster, more powerful, and more prevalent on automobiles than ever before. This is forcing motor designers to find new ways to shave cost in production and assembly. One area getting more attention these days is fasteners. Choose the right one and you can cut production and warranty costs, reduce vehicle weight, and enhance product performance.

Engineers at Loctite, Rocky Hill, Conn., have developed a range of fasteners and adhesives used in typical electric motors. Recent additions include Durabond epoxies and urethanes that bond structural metal and plastic components; Proform hot melts for bonding engineering plastics, including polyolefins and high-temperature polyamides; and Encap potting and encapsulating compounds to protect electric parts from exposure to chemicals, moisture, and thermal shock.

A new acrylic adhesive, Loctite 3920, dampens noise on magnet bonding and bearing mountings in electric fans. Traditional mechanical fasteners transmit amplified fan clatter to the passengers. The acrylic absorbs sound and is better suited to automated assembly methods, since it requires only minor adjustments to adapt to different flange types.

Loctite 3920, a two-part no-mix acrylic, cures on contact with Loctite 7380, a solventless activator. Special dispensing equipment accurately applies minute amounts to bond magnets to the frame. These bonds are so strong, magnets shattered during pull tests while the adhesive remained intact.

Loctite fastening technology is also used to hold magnets in place for in-tank fuel pumps. These delicately balanced motors stay submerged in gasoline and use neodymium-iron-boron magnets for unsurpassed strength in a compact size.

Magnaquench International of Anderson, Ind., produces these magnets, which are about an inch long and a tenth-of-an-inch thick. Two are installed in each pump. Magnaquench ships finished magnets to Baron Industries in Madison Heights, Mich., where they are impregnated with Loctite Resinol RTC to add strength and protect them from the degrading effects of gasoline. Resinol RTC penetrates pores and closes off all voids and leak paths while hardening into an impenetrable thermoset shield.

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