The problem is simple, but persistent. Vibration quickly loosens fasteners. Temperature changes causes expansion and contraction. Materials settle, and bolts simply come apart. A flat washer can’t resist.
Enter the Belleville washer. It’s shaped like a cone, which makes it behave as a mini-spring, full of tension whenever other components attempt to relax.
How Belleville Washers Work
It’s all about the shape So one side is taller than the other until you put some pressure on it, then it flattens out but existing height provides spring action. As you can see in this infographic, there are four factors that affect travel distance and force applied until bottoming out of washer. These are free height, thickness, inner bore, and outer diameter.
There are three principal series of rod designed to achieve these goals by how tall and narrow the cone is compared to the overall depth of the taper. In general, the steeper the cone the harder it push back at you. So a shallow cone has a more linear but gentler response that is suited to vibration control. As the cone tap tapers in from this angle it gets stiffer as it compresses. Then there’s the cone with maximum height which provides heavy hit first before snapping through center if pushed too far. Get the right series for the task and avoid premature wear out or limp performance.
And when you start stacking things? That’s different too. Stacking a few washers so that all their legs point the same way will multiply force but not increase travel. If they’re turned opposite one another, force remains constant but travel is increased. And by mixing those two patterns, engineers can exactly tune the right blend of movement and load that any given joint requires. The chart’s diagrams reveals those relationships instantly.
Geometry is important, but material choice is just as critical. Standard carbon steel works for most indoor or moderate-temperature applications, but it need protection against rust. If you need something to stand up to chemicals and moisture, use stainless steel. If it’s extreme heat like in a turbine or engine, use nickel alloys. Having the proper alloy maintains the spring action at the expected temperature range.
They are also loaded to 75% of their full deflection and those numbers appear on the charts as well. That’s not an accident. Operating a washer up against flat position will cause it to become permanently set and wear out prematerly. Avoiding that limit by staying just below it allows the strength to remain intact for hundreds of thousands or maybe thousands of cycles.
The first key is to choose the right size. The bolt diameter matter because the washer should not only seat well on surface being clamped but also leave enough room to clear the threads. Series and thickness are selected based off how much you need to clamp down (clamping force) and how far apart everything needs to fit. The reference tables turns this process, which used to be based on trial and error, into a straightforward lookup.
Belleville washers are there for their purpose, which is not to take the place of a coil spring or a lock washer, but to do one thing and do it well, namely stay put when the rest of assembly begins to loosen up. That’s why they get their money’s worth. And that’s what a Belleville washer does too; it just silently and faithfully does one thing.
