Load washers, HS and HDS: when a specialty disc spring beats a flat washer

A flat washer spreads load. A load washer spreads load and stores energy. Load washers are specialty disc springs used to improve the security of bolt connections, with a linear or progressive load deflection characteristic and a long, predictable service life under dynamic load. SCHNORR supplies them in HS and HDS versions, manufactured to DIN 16983 and DIN 16984.

The question comes up in almost every joint review: does this need a plain washer or something that does more work? The honest answer depends on whether anything in the joint is going to move.

What a load washer actually does

A plain washer distributes the bearing load and protects the surface. That is the whole job. It has no compliance, so when the joint settles, relaxes or heats up, the preload simply changes.

A load washer is a disc spring in a washer footprint. It carries load along its axis with a defined load deflection characteristic, so a small change in the joint length changes the load far less than a rigid stack would. That compliance is why it is described as improving the security of bolt connections rather than just seating them.

When to choose a load washer over a flat washer

• The joint sees dynamic load rather than a single static clamp.
• Thermal cycling changes the grip length.
• The clamped material can settle, relax or creep, for example gaskets, castings or coatings.
• You need a known force rather than a known torque.
• The assembly is opened and reclosed on a maintenance cycle.

If none of those apply, a plain washer is the right, cheaper part. If two or more apply, a disc spring washer for bolted joints is usually the difference between one build and an annual retorque.

HS and HDS

SCHNORR offers two HS and HDS load washers families. Both are specialty disc springs supporting dynamic processes under extreme force and load conditions, and both are manufactured to the same standards as the disc spring range, DIN 16983 for quality requirements and dimensions and DIN 16984 for calculation. The choice between them is a load and thickness conversation, so it is worth having with a drawing or a duty cycle in hand.

Materials, and the environments they answer

• C60S (1.1211) standard spring steel to DIN EN 10132-4, used exclusively for serrated safety washers and load washers.
• X22 CrMoV4 (1.8159) to DIN EN 10269 and X39 CrMo 17-1 (1.4122) to DIN EN 10088-2, quenched and tempered chromium molybdenum vanadium grades for a high temperature washer. Neither is considered a corrosion resistant grade.
• Inconel X718 (2.4668), virtually cobalt free, often used in nuclear reactor technology.
• CuSn8 bronze (2.1030) to DIN EN 1654, an anti-magnetic copper tin alloy that keeps its spring characteristics through cold forming, with considerably lower strength values and spring forces than standard material.

Available surfaces are blackened, zinc flake coatings and nickel plated finishes.

Two things to get right on the drawing

First, specify the force, not just the part. A load washer is chosen for a load deflection characteristic, so the useful information is the clamp force you need and the movement you expect.

Second, do not confuse a load washer with a locking element. A load washer manages force. A serrated safety washer prevents loosening through friction and mechanical locking, and held pretension force after 2,000 cycles in Junker testing. Some joints want one, some want the other, and plenty of joints want both, on the understanding that safety washers should never be stacked with plain washers under them.

• Load washers are specialty disc springs used to improve the security of bolt connections.
• They offer a linear or progressive load deflection characteristic and a long, predictable service life under dynamic load.
• SCHNORR load washers are available in HS and HDS versions and are manufactured to DIN 16983 and DIN 16984.
• C60S (1.1211) standard spring steel is used exclusively for serrated safety washers and load washers.
• X22 CrMoV4 and X39 CrMo 17-1 are quenched and tempered high temperature grades and are not considered corrosion resistant.
• Inconel X718 is virtually cobalt free and often used in nuclear reactor technology.
• CuSn8 bronze is anti-magnetic, with considerably lower strength values and spring forces than standard material.
• Available surfaces are blackened, zinc flake coatings and nickel plated finishes.