Washdown motor anatomy

Industrial electric motors have inherently rugged designs, but still require extra protective features to handle pressurized washdowns and cleaning agents used in food and beverage processing, pharmaceutical manufacturing, and related packaging applications.

In particular, the industry workhorse ac induction motor has been enhanced with “washdown-duty” features, and every major motor manufacturer offers a line of such motors. Washdown features combined with the induction motor’s rugged, simple construction result in a truly tough rotating machine. Motor torque comes from interaction of a rotating magnetic field created in the stator and the resulting alternating currents “induced” in the rotor. The magnetic field rotates at synchronous speed (V S ) which, depending on the supply frequency and the number of poles, has typical values of 1,800 and 3,600 rpm (for 60 Hz motors). For metric (IEC, 50 Hz) motors, comparable synch speeds would be 1,500 and 3,000 rpm. Actual speed of induction motors is always less than synchronous, by an amount called slip speed , which typically ranges 2-5% of V S at operating speed. Common enclosure varieties are TEFC (totally enclosed, fan cooled) and TENV (totally enclosed, non-ventilated). See “Anatomy of an induction motor” ( CE , Dec. 1999, p. 68) for more on the basic machine.

Looking at “inside” features of a washdown motor, a double-dip and bake varnish process encapsulates the stator windings to add extra protection against moisture and internal contaminants (see graphic). Typically, the precision-balanced rotor receives an epoxy primer to resist corrosion. Rust and corrosion receive further attention at the output shaft made of 300 Series stainless steel. Special lubricant is often standard in the double-sealed rolling-element bearings of these motors to improve lubrication life and resistance to washout, rust, and corrosion. A slinger and contact lip seal fitted to the output shaft extension provides added protection against contaminants.

Washdown motors feature special exterior paint on outside surfaces. White paint is typical for food processing applications (graphic). Baldor Electric, for one, uses auto-deposition surface preparation to achieve five times more resistance to corrosion and chipping in the finish coat than with prior methods. For still harsher usage, stainless-steel motor construction offers an alternative to exterior painting.

In TEFC motors, the high-grade plastic external fan resists cleaning agents and caustic solutions. Other washdown motor features include neoprene rubber gaskets, providing a waterproof seal on the conduit box, and provision of drain holes/fittings in each end plate, designed to ease draining of condensate in any motor mounting position.

Servos, steppers included

Key featuers of a washdown-duty induction motor seek to seal out moisture, resist corrosion, and protect against harsh cleaning agents or pressurized water streams. (Image courtesy of Baldor Electric Co.)

In sheer numbers, induction motors typify the image of washdown-duty motors, but, brushless servo and stepper motors increasingly are applied in that harsh environment. Permanent-magnet dc washdown motors also are available from some suppliers.

So-called “food-grade” ac servo motors are specifically designed for food and beverage packaging/handling. Typically, epoxy paint and bearing grease are food-grade in these servo motors rated up to IP67 ingress protection, while shaft and fasteners are stainless steel. A positive air-pressure system is an option for further protection against liquid entry.

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