A bimetal bearing is a plain bearing made from two bonded metallic materials. A typical structure combines a steel backing with a bronze, copper-alloy or aluminum-alloy bearing layer.
The steel provides structural support, while the inner bearing layer forms the sliding surface in contact with the shaft. This combination allows each material to perform a different function within a relatively compact bearing wall.
Bimetal bearings are not automatically self-lubricating. Most steel-backed bronze designs require oil or grease unless the specific bearing material is approved for dry or boundary-lubricated operation.
How Is a Bimetal Bearing Constructed and How Does It Work?
A common bimetal bushing consists of an outer steel backing and an inner copper-alloy bearing layer. The two materials must be securely bonded so that load and movement can be transferred through the complete bearing wall.
Each part of the structure has a separate role:
- The steel backing provides rigidity, mechanical support and stable installation in the housing.
- The bearing layer provides the required friction, wear and sliding characteristics.
- The bonded interface keeps the layers working as one component under load.
- Oil grooves, holes or pockets can distribute lubricant across the sliding surface.
During operation, the shaft moves against the bearing layer rather than directly against the steel. A correctly selected lubricant forms a film between the shaft and bearing surface, helping reduce friction, heat and direct metal contact.
The thickness of the bearing layer is not universal. It depends on whether the part is made from thin-wall bimetal strip, an engine-bearing shell or a heavier custom steel-copper composite blank. A single lining-thickness value should therefore not be applied to every bimetal bearing.
Why Combine Two Different Metals?
Bimetal bearings were developed to separate the structural and sliding functions of a plain bearing.
Steel is strong and economical as a backing material, but an untreated steel surface does not normally provide the sliding and anti-seizure properties required at the shaft interface. Bronze and other bearing alloys offer more suitable surface characteristics, but the complete wall does not always need to be made from these materials.
Combining the two allows the steel backing to support the bearing while a thinner bearing-alloy layer provides the working surface. Compared with a solid bronze bushing, this can reduce the amount of copper alloy used and create a thinner, more rigid bearing structure for restricted installation space.
This does not mean that a bimetal bearing always performs the same as a solid bronze bushing. Its suitability depends on the lining material, bonding quality, lubrication, load, speed, shaft condition and required wear allowance.
What Are the Main Types of Bimetal Bearings?
The term covers several structures rather than one standardized product.
| Bimetal bearing type | Basic construction | Typical characteristics |
|---|---|---|
| Thin-wall wrapped bushing | Steel-backed bimetal strip formed into a sleeve | Compact wall, standardized or custom bore features |
| Flanged bimetal bushing | Wrapped or machined body with an integral flange | Supports radial load and provides an axial locating surface |
| Custom steel-copper bearing | Steel support bonded to a copper-alloy working layer | Used for larger, thicker or special-shaped components |
| Engine bearing shell | Precision steel-backed half shell with copper- or aluminum-based bearing metal | Designed for controlled clearance and lubricated shaft positions |
| Bimetal thrust washer or strip | Flat steel backing with a metallic bearing surface | Used for axial load or guided sliding movement |
Bearing layers may use leaded or lead-free copper alloys, aluminum-based alloys or other bearing metals. Their load, speed, temperature and lubrication limits are material-specific and should be checked against the relevant grade data.
How Are Bimetal Bearings Different From Other Bushings?
Bimetal bearings are sometimes confused with solid bronze and metal-polymer bushings, but their structures and selection reasons are different.
| Bearing type | Basic structure | Lubrication | Typical reason for selection |
|---|---|---|---|
| Bimetal bearing | Steel backing with a metallic bearing layer | Usually oil or grease | Thin, rigid structure with a controlled bearing surface |
| Solid bronze bushing | Bronze or another copper alloy throughout the wall | Depends on material and design | Greater machining allowance and thicker wear material |
| Graphite-plugged bronze bushing | Solid bronze with embedded solid lubricant | Reduced external lubrication in suitable conditions | Slow, heavily loaded movement with limited lubrication access |
| Metal-polymer bushing | Metal backing with a polymer-based sliding layer | Some grades permit dry running | Low friction and limited installation space |
A metal-polymer bushing may contain steel and bronze within its multilayer construction, but it should not automatically be classified as a traditional bimetal bearing. Its functional sliding surface is polymer rather than metallic.
Selection should therefore be based on the complete material structure—not simply on whether two metals are present.
Where Are Bimetal Bearings Used?
Bimetal bearings are used where a supported metallic sliding surface is needed within a controlled installation space.
| Equipment or position | Typical movement or requirement |
|---|---|
| Engines and connecting-rod positions | Repeated rotation or oscillation under lubricated conditions |
| Pumps and compressors | Supported shaft movement with controlled clearance |
| Agricultural and construction machinery | Loaded pivots and intermittent movement |
| Hydraulic equipment | Pins, joints and guided components |
| Gearboxes and industrial machinery | Rotary shafts or oscillating connections |
| Thrust and guide positions | Axial load or linear sliding contact |
A bimetal bearing is not suitable for every bearing position in these machines. Different positions within the same equipment may require solid bronze, rolling bearings, metal-polymer composites or graphite-plugged components.
What Should Be Checked When Selecting a Bimetal Bearing?
Start with the actual operating conditions rather than choosing only by dimensions. Important information includes:
- radial and axial load, including shock or impact;
- shaft speed and calculated PV condition;
- rotary, oscillating or reciprocating movement;
- oil or grease type and lubrication frequency;
- operating and ambient temperature;
- shaft material, hardness and surface finish;
- housing dimensions, fit and installation method;
- required running clearance and wall thickness;
- exposure to dust, water, chemicals or abrasive particles;
- bearing-layer material and applicable standard;
- dimensional tolerances and expected service life.
Load capacity or maximum speed should not be assigned to “bimetal bearings” as one general category. These limits depend on the specific bearing alloy, lubrication regime, heat dissipation, shaft condition and component design.
Where the existing part has failed, wear location, lubrication condition, alignment and shaft damage should also be reviewed. Reproducing the same dimensions without identifying the cause may reproduce the same problem.
Custom Bimetal Bearings From JEDBUSHING
JEDBUSHING manufactures custom bimetal bearings from customer drawings or reference samples. Available forms include sleeve bushings, flanged bushings, thrust washers, strips and special steel-copper composite parts.
Manufacturing support can include:
- confirmation of material grades, dimensions and tolerances;
- machining of bores, flanges, slots and special profiles;
- production of oil holes, grooves and lubricant-distribution features;
- dimensional inspection using two large CMMs;
- material certificates and inspection reports when required;
- bonding-related inspection according to the drawing or agreed inspection plan.
The bearing-layer material, wall construction and lubrication features should be matched to the equipment rather than copied from an unrelated standard part.
Send your drawing to JEDBUSHING for a manufacturing and material review.
FAQ
Can a worn bimetal bearing be rebored?
Only when sufficient bearing-layer thickness remains and the drawing permits additional machining. Excessive boring can remove the functional lining and expose the steel backing. The remaining layer and final clearance should be confirmed before reworking the part.
What are common signs of a bonding problem?
Possible signs include local lifting, cracking, blistering or separation of the bearing layer from the backing. Surface appearance alone may not reveal every internal defect, so the inspection method should be selected according to the structure and project requirements.
What should be checked during installation?
Keep the bearing and housing clean, use tooling that does not damage the lining, align oil holes correctly and avoid forcing a misaligned part into the housing. After installation, verify the final bore, running clearance and lubricant path before operation.