Preload Springs, Spacers and Washers

Preload springs, spacers and washers are used to provide end-play take up or a constant preload for bearings, gears and other mechanical components and assemblies. They are made of convoluted ductile, high-strength metal alloys and are available in machined, welded and open-ring configurations. There are several basic types of products. Belleville washers are rounded, compact springs pressed into a dish-like shape, then hardened and tempered. Bowed, curved, or bent-spring washers are designed for axial play take up. Conical force spacers, adjustable spacers and load rings are used as replacements for shims or wave springs in assemblies that require highly accurate bearing settings, including preload. Finger washers use resilient fingers on the outer periphery to assure balanced pressure while directing pressure away from the inner diameter. Wave washers or wave springs are wavy metal washers that are designed to provide a compensating spring force, absorb shock, and sustain a load. Other types of preload springs, spacers and washers are also available.

Important specifications for preload springs, spacers and washers include inside diameter (ID), outside diameter (OD), thickness or working height, and rated or working load. ID and OD are measured in English units such as inches (in) or metric units such as centimeters (cm). Thickness or working height is the thickness of the product material, or the working height (installed height) of preload springs, spacers and washers. Rated or working load is the maximum or optimal working load. Typically, suppliers specify rated load in pounds (lbs) or kilograms (kg). Other specifications for preload springs, spacers and washers include shaft diameter clearance, number of turns, number of waves per turn, wire thickness, and spring rate.  

Preload springs, spacers and washers are made of metallic elements such as aluminum, copper, nickel, and titanium. Sintered bronze, a copper-based alloy, is porous and can be impregnated with oil, graphite, or polytetrafluorethylene (PTFE). Nickel-based alloys contain nickel and one or more other metals, usually copper. Steel, a commercial iron that contains carbon in any amount up to 1.7%, is used in many preload springs, spacers, and washers. Spring steel contains high amounts of carbon and provides high tensile properties. Suppliers recommend selecting spring steel based on both the application and the type of spring. Common spring steel types range from plain carbon grades to chromium, chromium-vanadium, nickel-chromium-molybdenum, silicon-manganese and silicon-manganese-chromium-molybdenum types. Hardened steel cannot absorb much shock or impact without breaking. Stainless steel is chemical and corrosion resistant and can have relatively high pressure ratings. Some preload springs, spacers and washers are anodized or plated with tin, zinc, or zinc chromate. Others are galvanized or coated with black oxide or phosphate.

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