How Do You Press-Fit and Retain a Plastic Bushing Without Cracking It, and What Interference Does It Need?
The maker builds the interference into the bushing, so your job is the housing bore: hold the maker’s tolerance, chamfer and deburr the edge, press the bushing in square with a flat press, and measure its bore only after it is in. A pressed-in bushing closes in by roughly the amount of the interference, so […]
What Compliance Documents Should I Ask for When a Plastic Bushing Is Used in a Food Plant?
Ask the bushing maker for a written statement that the exact grade meets the food-contact rules for your market. In the US that means the 21 CFR section it falls under, a certificate of conformance or letter of guaranty, the resin grade and whether it is virgin, proof that the additives are listed, and migration […]
How Do I Measure Wear on a Plastic Bushing, and When Should I Replace or Take It Out of Service?
Measure the clearance, not just the look. Wear on a plastic bushing shows up as a larger bore, which means more play between the bushing and the shaft. Measure the installed bore and the shaft with the right tool, because calipers press into soft plastic. There is no single wear limit for plastic bushings. The […]
When Should I Use a Plastic Bushing Instead of a Bronze or Steel One, and What Changes If I Swap?
Use a plastic bushing where the load is light to moderate, the joint is wet, corrosive or hard to grease, noise matters, or you want to drop the grease. Keep bronze or hardened steel where the load is heavy or shocked, the heat is high, or you can really keep it greased. A swap is […]
What Shaft Material, Hardness and Surface Finish Should You Use With Plastic Plain Bearings?
Use a hard shaft. A metal bearing, or a hard plastic with a high Shore D rating, can wear away a shaft surface under about 30 HRC, so aim for at least 50 HRC in dirty, abrasive places. Keep the finish neither too smooth nor too rough. Ranges differ from maker to maker, from roughly […]
What Running Clearance Should a Plastic Bushing Have, and Why Does Heat Make a Pressed-In Bushing Tighter, Not Looser?
A plastic bushing needs more clearance than a metal one, and its own fit. Three things change the clearance in service: the press-fit (the bore only reaches its final size after the bushing is pressed in), moisture (nylon swells) and temperature. Temperature works in the opposite direction from what most people expect. A bushing pressed […]
How Do You Calculate the PV Limit and Load Capacity of a Plastic Plain Bearing?
Work out three numbers for your bushing: the pressure on it (p), the speed it slides at (v), and their product, PV, which measures the frictional heat. Each must stay within the limit the material’s maker gives, with room for shock, misalignment and dirt. Pressure is the load divided by bore times length. For a […]
Do Plastic Bushings Need Lubrication, or Can They Run Dry, and What Lubricant Is Compatible?
Often they can run dry. Many plastic bushings are self-lubricating, so they need no grease as long as pressure, speed and PV all stay within the limits of the grade. Beyond those limits you must lubricate or change the material. Where grease is allowed, the lubricant must suit the grade, and in dirty places it […]
How Do You Choose Between Acetal (Delrin), UHMW, Nylon and Polyurethane Bushings for an Industrial Machine?
Pick by the main demand. Acetal (Delrin) for a precise, stiff pivot that must hold its size. UHMW for wear, impact and wet or washdown places, where it is soft but very tough. Nylon for shock, as long as you allow for it swelling in water. Polyurethane where you want a bushing that gives and […]
Sleeve, Flanged, Split or Thrust Washer: Which Plastic Bushing Form Do I Need, How Long and Thick Should It Be, and How Do I Avoid Edge Loading?
Choose the form by the loads it must carry and by how it must be fitted. A plain sleeve takes radial load only. A flanged bushing adds a thrust face and keeps itself in place. A thrust washer takes axial load. A split bushing can be fitted without pulling the shaft, but it is weaker. […]
Why Does a Plastic Bushing Wear, Seize, Squeak, Swell, Crack or Walk Out of Its Housing?
Almost always it is one of five things: too much load or speed (heat), a shaft that is too soft or too rough, a bore that closed up or opened out, a housing fit that lost its grip, or grit, water, chemicals or temperature that the material does not suit. The debris and the damage […]
What Is the Maximum Operating Temperature of a Plastic Bushing, and What Happens as It Heats Up?
There is no single maximum for plastic bushings. Each grade has its own continuous limit, a higher short-term limit, and often a lower temperature above which the bushing needs to be secured in its housing. The temperature that counts is the ambient plus the heat the bushing makes itself. As it heats up, a plastic […]