Preload springs, spacers, and washers are meant to maintain tension in an assembly where some slack may be present. Their capabilities can eliminate rattle, compensate for expansion or contraction of the assembly materials, or absorb intermittent shock loads. These products are made of elastic deformable materials, most commonly convoluted ductile, high-strength metal alloys which come in machined, welded, and open-ring varieties.

Types of Preload Springs, Spacers, and Washers

All of the preload devices covered in this selection guide lend their mechanical properties to the elastic deformation defined by their materials and dimensions. In preload washers, the raised irregularities of the spring washer flatten to a predetermined degree, while providing proportional resistance. Wave springs, better nominated as wave washers, are subject to axial stress that deflects similarly as spring washers. Preload spacers are unique products that offer axial deflection of up to .07 inches before plastic deformation occurs. As such, their capabilities are reduced to applications with fine tolerances.

Configurations

Preload Springs

Preload Spacers

Preload Washers

Specifications

Individual specifications for preload washers and preload springs can be found on their individual pages. There are several collective specifications that are relevant to all three products, however.

Dimensions

• Inner diameter is the measurement directly across the cavity from inner edge to inner edge in springs, washers, and spacers. This is important when supplying preload springs, spacers, and washers that will fit over a shaft.

• Outer diameter is the measurement directly across the cavity from outer edge to outer edge in springs, washers, and spacers. This is especially important when computing a washer's limits

• Thickness or working height is the thickness of the product material, or the working height (installed height) of preload spring, spacer, or washer.

Rated/Working Load

This is the maximum or optimal degree of stress the spring, spacer, or washer can attain before breaking or permanently deforming.

Spring Rate

Spring rate is the measurement of the load needed to deflect a preload mechanism a predetermined distance.

Materials

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.

Finishes

The versatility of preload hardware means that it may be employed in environments with corrosive or oxidizing materials. By providing a protective finish, the life span of the spring, spacer, or washer will be extended considerably.

• Anodizing is a finishing process for aluminum alloys that consists of a protective oxide coating. It is resistant to corrosion and abrasion, and is typically transparent. This coating is very durable.
• Black oxide coating is a special black rust that does not change the workpiece dimensionally. This coating is more aesthetic than functional.
• Phosphating is a chemical or electrochemical treatment of the metal surface. It is corrosion resistance, and is suitable carrier for paints.
• Galvanization is the process of coating a metal in molten zinc that metallurgically bonds to the substrate. This shields the base metal as well as reacting with corroding agents before the base metal.
• Nickel plating provides corrosion and wear resistance, as well as an appealing appearance.
• Tin plating covers the workpiece in a ductile layer of tin, which is also corrosion resistant and provides sacrificial anode for non-ferrous metals.

• Zinc oxide coatings do not affect the surface integrity of the workpiece and acts as a barrier to further oxidation.

• Zinc chromating provides a durable, yellow zinc coating to the material. It has becoming increasingly rare because of its toxicity.

Applications

The need to take up slack or play in assemblies is a universal manufacturing requirement. Some specific household and domestic examples where preload springs, spacers, and washers may be found include, but are not limited to: plumbing valves and pumps, pipe flanges, protection components in circuit breakers, lawn tractors and lawn mowers, sprinkler systems, boat motors, vehicle transmissions and braking systems, sewing machines, air compressors, blenders and mixers, and many other simple machines and systems.

Resources

Temper Corporation - Temper Load Rings

Wave Washer Specification Guide

Spring Washer Specification Guide

Image credit:

JiuGuang Spring Co. | Smalley | Temper Corp. | International Industrial Springs