When two shafts rotate relative to each other inside a housing, there’s a little ring called a thrust washer sandwiched between them and the housing. Its job is to soak up force that could tear apart expensive metal pieces. Thrust washers deals with axial loads. In other words, this is pressure applied directly along axis of the shaft, not at an angle to the shaft as it rotates. On paper, it sounds like an easy task, but in real life, selecting the incorrect washer for the application can make precision machinery a slow-motion demolition project.
They visually separate out imperial vs. Metric sizing with no guessing about what system is in play whether it’s your moddern pump or some old beat up car from yesteryear. This is mistake number one for most folks who just think of any washer as just another spacer. They are not, they come in a trio: thickness, outer diameter, and most important, inner diameter. If the inner diameter is even a hair too small for the shaft then the washer won’t turn free and will heat up quickly. If it is too big, it will grab on edges and catch and tear as it turns. The chart helps you find the right combination of those three numbers. This ensures an exact fit so it does its work instead of fighting assembly.
How to Choose the Right Thrust Washer
Size fit is important but so is material choice: Depending on environment, certain materials has more tolerance for heat and friction different than others. A good bronze washer will be a go-to material for handling moderate loads of up to 25 megapascals in pressure due to its great self-lubrication. Hardened steel is what you want when facing extreme ranges of force, such as high-performance automotive engines or heavy industrial gearbox. It resists deformation at higher temperatures and can absorbs nearly triple the load. At the opposite end of things, Teflon, or PTFE washers, offer ultra-low friction which will save your bearing from wearing down. But they give up practically all structural strength, making them suitable for light-duty applications where smooth rotation is name of the game.
When it comes time to put it back together, there’s not exactly one size washer you grab off the shelf that fits into the hole, but a little detective work (and calipers) can help you choose the right one. First you want to measure the shaft size with your calipers, then you’re looking for a slightly loose fit so that there is still some room on the shaft for it to spin freely without touching inside bore. Next, determine the highest amount of axial force you’ll experience in this application and add a safety factor to make sure it won’t exceed max load of the bearing material.
In particular, this holds true for dynamic applications. These experience vibrations that add random bursts of forces, causing instant cracks in more brittle materials. The importance of considering both temperature and speed when choosing a bearing is shown in the selection flow chart above; even though the surrounding air may feel cool, high speeds creates heat. You can plan carefully but it’s often what you do at the end that undermines all of your best efforts.
There is no compromise when it comes to clean mating surfaces. A single grain of sand captured beneath a washer becomes a local stress point where force will concentrate until the metal fails. And never start things up dry. Apply some form of assembly lubricant to both thrust faces prior to any tightening. Dry starts immediately scuffs the smooth surface finish.
Torque everything into place and then use a dial indicator to test the end-play so the shaft has just a little bit of axial movement without binding or rattling. That slight play makes the difference between a quiet humming machine over the years and one that screams after an hour.
It isn’t the largest washer in the world. It is just the one that fits your space, provides enough friction to hold it in place without causing extra wear on the wall or the washer, and holds the weight of whatever falls onto it. Align these three things and you’ll have a quiet little ring, happily humming away for years after you would of forgotten about it.
