Wrapped Bronze Bushings

What are bronze wrapped bushings?

Bronze wrapped bushings are thin-walled plain bearings made from a strip of solid bronze that is rolled, or wrapped, into a cylinder and then sized. They are usually made from CuSn8 tin bronze, and have diamond-shaped pockets or through holes in the bearing surface that hold grease. As the shaft moves, the grease is gradually released from the pockets to lubricate the bearing. This gives a strong, compact, and economical bush that copes well with heavy loads, shock, and dirty conditions.

A standard bronze wrapped bushing is made up of:

• A wall of solid CuSn8 bronze, wrapped from strip and calibrated to size
• Diamond-shaped lubrication pockets, or through holes, in the bearing surface, which act as grease reservoirs
• A split joint along its length, where the ends of the strip meet
• A plain cylindrical shape, or a cylinder with a flange at one end.

The grease pockets are what make bronze wrapped bushes so durable.

• The pockets are filled with grease when the bush is fitted, and release it steadily as the shaft moves.
• Regular relubrication pushes fresh grease through the bearing, which also flushes out dirt, making the bush ideal for contaminated environments.

Bronze wrapped bushings are sized by their bore, outside diameter, and length.

Why are bronze wrapped bushings essential?

Bronze wrapped bushings are a practical, economical bearing for general machinery and repair work. Because they are made from solid bronze, they carry high loads and resist shock and vibration at slow speeds, while their thin wall keeps housings compact. Their grease pockets give reliable lubrication between services, and regular greasing keeps dirt out.

They work across a temperature range of around -40°C to +150°C and resist corrosion well, so they are widely used on construction, agricultural, and handling machinery, where pivots and pins work in tough, dirty conditions.

Typical applications include:

• Construction and earthmoving machinery pivots
• Agricultural machinery and implements
• Hydraulic cylinder eyes and clevis pins
• Lifting equipment, tail lifts, and forklifts
• Steering and suspension linkages on vehicles
• Conveyors and material handling equipment
• Hinges, levers, and linkages
• General machinery repair

The main types of bronze wrapped bushings

• Plain bronze wrapped bushes - Straight, cylindrical bushes with grease pockets in the bore. They are pressed into a housing to support a shaft or pin radially.
• Flanged bronze wrapped bushes - Bushes with a flange at one end, which locates the bush in the housing and takes axial loads in one direction.
• Bushes with diamond-shaped pockets - The most common design, with a pattern of indents across the bearing surface that hold grease.
• Bushes with through holes - Bushes with holes through the wall, which let grease be fed into the bearing from a grease nipple in the housing.
• Bronze wrapped thrust washers - Flat bronze washers with grease pockets, used to take axial loads alongside a bush.

How to choose the right bronze wrapped bushings?

• 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 an axial load.
• Pockets or through holes - Choose bushes with grease pockets for general use, or bushes with through holes where grease will be fed from a nipple in the housing.
• Load and speed - Bronze wrapped bushes suit high loads at low speeds, and oscillating or intermittent movement. They are typically rated up to a sliding speed of around 1 m/s.
• Housing and shaft - Use an H7 housing, a suitably toleranced shaft, and a smooth, hardened shaft surface for the best life.
• Maintenance - Bronze wrapped bushes need greasing when fitted and at regular intervals. Where greasing is not practical, consider a self-lubricating bush instead.

Essential references and specialised ranges

How the numbering works:

Bronze wrapped bushes are usually referenced by a type code and their bore, outside diameter, and length, in millimetres.

In the widely used SKF range:

PRM = plain wrapped bronze bush

PRMF = flanged wrapped bronze bush

Examples:

PRM121415 = plain bush, 12mm bore, 14mm outside diameter, 15mm long

PRM161820 = plain bush, 16mm bore, 18mm outside diameter, 20mm long

PRMF455045 = flanged bush, 45mm bore, 50mm outside diameter, 45mm long

Other ranges use their own codes, such as bushes with through holes, which may carry an H suffix.

Suffixes:

F = flanged bush

H = through holes for lubrication

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

FAQ - All you need to know about bronze wrapped bushings

Do bronze wrapped bushings need lubrication?

Yes. Fill the grease pockets before fitting, and relubricate regularly in service. Regular greasing also pushes out dirt, which helps the bush last longer in contaminated environments.

What is the difference between bronze wrapped and solid bronze bushes?

Both are bronze and need grease. Bronze wrapped bushes are thin-walled and made from rolled strip, so they are compact and economical. Solid bronze bushes are thick-walled and machined from cast bronze, and can be reamed or machined to size.

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

Bronze wrapped bushes are solid bronze throughout and are lubricated with grease. Bronze backed bushes have a bronze backing with a PTFE lining, and are self-lubricating, so they run without grease.

Why does a bronze wrapped bush have a split?

The bush is made by rolling a flat strip into a cylinder, so there is a joint where the ends meet. When the bush is pressed into its housing, the joint closes and the bush is held firmly at the correct size.

How do I fit a bronze wrapped bush?

Fill the grease pockets, then press the bush squarely into a clean, correctly sized housing using a press and a fitting mandrel, never by hammering directly on it. Line up any through holes with the grease nipple, and position the split away from the main load if possible. Grease the shaft and check it runs freely.

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. Note whether the bush has grease pockets or through holes.

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

Warning signs include:

• Squeaking, knocking, or grinding from the pivot or pin
• Play or wobble in the shaft or pin
• Grease pockets worn away or no longer visible
• Scoring caused by a lack of grease
• An oval or heavily worn bore
• The bush moving or turning in its housing