A worn stabiliser bushing or a shaft support can bring a whole line to a stop, and a metal or rubber part in its place often lasts only a few weeks. Polyurethane bushings, rods and rings carry the load longer, dampen vibration and do not swell in oils. Below we look at where these parts sit in assemblies, how they are mounted, how to choose hardness and why, by the numbers, polyurethane beats rubber and metal.
What polyurethane bushings, rods and rings are for
These parts dampen vibration and shock, compensate for misalignment and work as sliding bearings and seals in moving assemblies. A bushing sits in a mounting seat and separates two parts that must not touch metal to metal, a rod works as a guide or pusher, a ring seals or centres. Where metal knocks and wears out and rubber gives up quickly, polyurethane delivers stable operation of the assembly.
Applications cover many industries. In transport, polyurethane bushings reduce vibration and improve suspension handling, in mechanical engineering they stabilise shafts and rotating assemblies, in the oil and gas sector sealing rings keep joints tight. In printing and pulp and paper production, rings and bushings centre rollers and guides, improving the stability of material feed.
Advantages of polyurethane over rubber and metal: the numbers
Polyurethane combines wear resistance, light weight and vibration damping, something neither rubber nor steel offers all at once. Rubber is soft but wears away quickly, steel is strong but heavy, corrodes and transmits shock to the structure. The table shows this with specific reference values.
| Parameter | Cast polyurethane (PU) | NBR rubber | Structural steel (St3, St45) |
|---|---|---|---|
| Abrasion, DIN 53516 | 38-39 mm³ | 80-150 mm³ | n/a |
| Working temperature | -60 to +100 °C | -30 to +100 °C | -40 to +500 °C |
| Density | 1,05-1,25 g/cm³ | 1,0-1,3 g/cm³ | 7,7-7,9 g/cm³ |
| Tensile strength | 39-87 MPa | 10-25 MPa | 370-700 MPa |
| Hardness | 50 Shore A to 70 Shore D | 40-90 Shore A | 120-250 HB |
The two most telling rows. By abrasion, polyurethane loses 38-39 mm³ against 80-150 mm³ for NBR rubber, meaning it wears out several times slower. By density, polyurethane at 1,05-1,25 g/cm³ against 7,7-7,9 g/cm³ for steel means a part of the same size comes out roughly six times lighter and, on top of that, dampens vibration, whereas steel transmits it. The abrasion of steel by the DIN 53516 method is not rated, because it is a test for elastomers, which is why n/a stands in that cell.
How polyurethane bushings are mounted and serviced
Mounting depends on the type of part. Cylindrical bushings are pressed into a seat or fitted with a slight interference, rings are centred in a groove, rods are fixed in a guide. It is important to hold the fitting dimension and ensure reliable fixing, so that under load the part does not turn or shift, otherwise play appears and the edges wear faster.
Servicing comes down to periodic inspection for wear and mechanical damage. Thanks to the repairability of polyurethane, a worn part can be recast or built up while keeping the metal sleeve, which is cheaper than replacing the whole assembly. Typical bushing, rod and ring items are collected in the catalogue.
Engineer’s tip: choose hardness to match the function of the part, not on the principle that harder is always better. For a silent block that has to dampen vibration take 70-90 Shore A, and for a loaded sliding bearing, where holding the dimension matters, 95 Shore A to 70 Shore D. A bushing that is too hard in place of a soft one will transmit vibration to the body and the seat, one that is too soft in place of a hard one will give play. Clean the mounting seat of burrs and dirt before mounting.
Open casting technology
Bushings, rods and rings are made by open casting, where liquid polyurethane is poured into a mould, it cures chemically, after which the part is machined to its final dimension. The method allows a part of almost any shape and thickness to be cast to a customer’s drawing or sample without an expensive mould, which is why it is cost effective for both single parts and runs.
This approach is convenient for repairs: given an old worn part, the factory reproduces its geometry and sets the required hardness for the operating conditions straight away. More on the material and technology is on the about polyurethane page, and a list of production services is in the services section.
How to order manufacture to size
An order begins with a description of the assembly: fitting dimensions, load, temperature, presence of oils or abrasive, vibration requirement. From this data the process engineer chooses hardness and formulation and estimates the tooling. The simplest option is to send a drawing or the part sample itself, then the geometry is reproduced exactly.
Practical conclusion
Polyurethane bushings, rods and rings are a reliable replacement for rubber and metal parts in loaded assemblies: they wear many times less than rubber, are several times lighter than steel and dampen vibration. Send a drawing or sample to the TIMOL factory via contacts, and the engineers will select the hardness and calculate the manufacture for your equipment.