Bronze Backed Bushings

What are bronze backed bushings?

Bronze backed bushings are thin-walled, self-lubricating plain bearings made from a layered strip that is rolled into a cylinder. Instead of the steel backing used on standard wrapped bushes, they have a solid bronze backing, which gives much better resistance to corrosion. On top of the backing is a porous sintered bronze layer filled with a PTFE-based lining, which forms the low-friction bearing surface. They run dry without oil or grease, and are ideal for wet, corrosive, and marine conditions where a steel-backed bush could rust.

A standard bronze backed bushing is made up of these layers, from the outside in:

• A bronze backing, which gives the bush its strength and corrosion resistance, and carries heat away from the bearing surface
• A thin tin or copper-tin coating, which adds extra protection against corrosion
• A porous sintered bronze layer, which holds a reserve of the lining material and helps conduct heat
• A PTFE-based lining, which fills the bronze pores and forms a smooth, low-friction bearing surface.

The bronze backing is the key difference.

• Bronze does not rust, so the bush keeps working in water, steam, and damp or chemical environments where a steel backing could corrode.
• Bronze also conducts heat well and is non-magnetic, which can be useful in some electrical and instrument applications.

Like other wrapped bushes, bronze backed bushings have a split joint along their length, which closes when the bush is pressed into its housing.

Why are bronze backed bushings essential?

Bronze backed bushings combine the benefits of a self-lubricating PTFE bearing with the corrosion resistance of bronze. They need no oil or grease, run with very low friction, prevent stick-slip, and handle rotating, oscillating, and sliding movement, all while resisting water and many chemicals.

This makes them the right choice wherever a maintenance-free bearing must cope with moisture or corrosion, such as on boats, in water treatment, in food and drink machinery that is washed down, and in outdoor equipment exposed to the weather.

Typical applications include:

• Marine and boat equipment
• Water pumps, valves, and water treatment equipment
• Food and drink machinery with washdown cleaning
• Outdoor and agricultural equipment
• Chemical and process equipment
• Medical and laboratory equipment
• Hydraulic and pneumatic equipment in damp conditions
• Electrical and instrument equipment needing non-magnetic parts

The main types of bronze backed bushings

• Plain bronze backed bushes - Straight, cylindrical bushes with a PTFE lining. They are pressed into a housing to support a shaft radially, and are designed to run dry.
• Flanged bronze backed bushes - Bushes with a flange at one end, which locates the bush in the housing and takes light axial loads.
• Bronze backed thrust washers - Flat washers made from the same layered material, for axial loads alongside a bush.
• Metric bronze backed bushes - Made in metric sizes, with bore, outside diameter, and length in millimetres, from small sizes up to large diameters.

How to choose the right bronze backed bushings?

• Environment - Choose a bronze backed bush rather than a steel backed bush where the bearing will be exposed to water, steam, damp, or corrosive chemicals.
• Size - Choose a bush with a bore to suit the shaft, an outside diameter to suit the housing, and a length to suit the space available.
• Plain or flanged - Choose a flanged bush where the bush needs locating in the housing or where there is a light axial load.
• Housing and shaft tolerances - Like all wrapped bushes, bronze backed bushes rely on the housing to close them to the correct size, so check the housing and shaft are machined to the recommended tolerances.
• Shaft material - In wet or corrosive conditions, use a corrosion-resistant shaft, such as stainless steel, so the shaft does not corrode against the bush.
• Load and speed - Bronze backed bushes suit light to medium loads at moderate sliding speeds, and can run dry or in water.

Essential references and specialised ranges

How the numbering works:

Bronze backed bushes are usually referenced by a type code and their bore, outside diameter, and length, in millimetres. For example:

WMUB242725 = plain bronze backed PTFE-lined bush, 24mm bore, 27mm outside diameter, 25mm long

WMUB22022570 = plain bronze backed PTFE-lined bush, 220mm bore, 225mm outside diameter, 70mm long

FMB1017 = flanged bronze backed bush, 10mm bore and 17mm long, with a 12mm outside diameter

The flange diameter and thickness are given in the product details for each flanged bush.

Suffixes:

B = bronze backing, used to tell bronze backed bushes apart from steel backed versions

F = flanged bush

Suffix codes vary between manufacturers, so check the supplier’s catalogue for the exact meaning.

FAQ - All you need to know about bronze backed bushings

What is the difference between bronze backed and steel backed bushes?

Both are thin-walled, self-lubricating bushes with a PTFE lining. Steel backed bushes are stronger and lower in cost, but the steel can rust. Bronze backed bushes resist corrosion, so they suit wet, marine, and chemical environments.

Do bronze backed bushings need lubrication?

No. The PTFE-based lining is self-lubricating, so the bush is designed to run dry. It can also run in water or oil, but grease is not needed.

Can bronze backed bushes be used underwater?

Yes. The bronze backing resists corrosion and the PTFE lining does not need oil or grease, so they are well suited to underwater and wet applications.

Can I ream or machine a bronze backed bush?

No. The PTFE lining is very thin and would be removed by reaming or machining. The bush is designed to reach its correct bore size when pressed into a correctly sized housing.

How do I fit a bronze backed bush?

Press the bush squarely into a clean, correctly sized housing using a press and a fitting mandrel, never by hammering directly on it. Position the split joint away from the main load if possible, and check the shaft runs freely once fitted.

How do I identify the bush I need?

Check the reference on the old bush or in the machine’s parts list. If it cannot be read, measure the bore, outside diameter, and length, and on a flanged bush, the flange diameter and thickness. Check whether the backing is bronze or steel, as bronze has a yellow or brown colour.

How can I tell if a bronze backed bush needs replacing?

Warning signs include:

• The PTFE lining worn through to the bronze underneath
• Squeaking, noise, or increased friction
• Play or wobble in the shaft
• The bush turning or moving in its housing
• Scoring on the shaft or bush
• A bush that has cracked or opened at the joint