Plastic vs Bronze Bushings

Created: Thursday, 23 February 2017 Written by Don Green

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I have done a number of tests to find a suitable replacement to bronze bushings in sheaves which eventually corrode. I think that the use of iglide® plastic bushings are probably superior to bronze particularly Oilite bushings which were invented in 1930 by Chrysler. Even very large ships are now using similar plastic bushings, see http://www.orkot.com.

Plastic vs Bronze bushings:
Plastic bushings have already replaced sintered bronze bearings in thousands of applications from a wide range of different industries, including agricultural machinery, lawn mowers, medical equipment, food processing machinery, fitness equipment, pumps and valves, and many more.

Bearing construction

Oil-impregnated sintered bronze bearings rely on a capillary action to create a lubricating oil film. Critically, however, high speed and rotational motion are both required to draw the oil out and maintain a full film of lubricant. Shaft oscillation, slow speed and intermittent use can all inhibit this process.

If movement stops, the oil on the surface of the bearing dries up. This can lead to squeaking and an increase in the coefficient of friction. High temperatures can also break down the oil.

Further disadvantages with this type of bearing include low chemical resistance and sensitivity to dirt, edge pressure, and impacts.

iglide® self-lubricating plastic bushings are proven to deliver a longer service life than oil-impregnated sintered bronze bearings.

iglide® self-lubricating plastic bushings do not suffer from any of the pitfalls of sintered bronze bearings, because they are injection molded from a blend of thermoplastic materials, embedded reinforcing fibers and solid lubricant.

The fiber reinforced materials maintain the bushing’s strength and resistance to high forces and edge loads. The solid lubricants help to lower the coefficient of friction. Since the lubricant is embedded inside millions of tiny chambers, it can not be pressed out. From these chambers, the plastic bushings release tiny amounts of solid lubricant during movement.

iglide® plastic bushings have a low wear rate, superior chemical resistance to sintered bronze bearings, and operate quietly. They are dirt, dust, UV, and corrosion resistant and have a high load capacity.

Plastic bushings are usually underestimated at high temperatures, yet short-term temperatures over 572° Fahrenheit and long-term temperatures of up to 482° Fahrenheit are possible.

Their dry-running nature means dirt particles do not stick to the surface, but instead deflect off it. For this reason, optimal performance can be maintained even in extremely dirty environments.

Bearing shafts

Another consideration, whether you are using plastic bushings or sintered bronze bearings, is which shaft to use. This is the most important factor after the bushing material has been determined. This is because it is in direct contact with the bearing and is affected by relative motion.

A shaft that is rough is too abrasive and will separate small particles from the bearing surface during movement. On the other hand, very smooth shafts can lead to higher wear because not enough lubricant can be transferred onto the shaft to have an effect.

Sintered bronze bearings function best on very hard, expensive, precision ground shafts. In contrast, plastic bushings can run on all types of shafts.

Acetal sheave with plastic bushing

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