Sliding bearings, also known as plain bearings, journal bearings, or bushings, are one of the simplest and oldest types of bearings. Unlike rolling-element bearings (which use balls or rollers), sliding bearings operate on the principle of sliding motion.
High performance EPEN Sliding Bearing
A basic sliding bearing consists of two main parts:
Bearing Shell/Housing: The outer structure that holds the bearing material.
Bearing Liner/Material: The inner surface, made of a special low-friction material, that is in direct contact with the rotating shaft (journal).
The shaft slides against the inner surface of the bearing, and the key to their operation is maintaining a film of lubricant (oil, grease, or sometimes a solid) between these two surfaces to prevent wear and overheating.
Fundamental Operating Principles
The functionality of sliding bearings hinges on a few key principles:
Boundary Lubrication:
This occurs at low speeds, during startup, or under very high load.
The lubricant film is very thin, and there is occasional metal-to-metal contact.
The bearing material must have inherent "anti-friction" properties and be able to withstand this temporary contact.
Hydrodynamic Lubrication (The Ideal State):
This is the primary principle for most high-speed sliding bearings.
As the shaft rotates at speed, it "drags" lubricant into a wedge-shaped converging gap between the shaft and bearing.
This action generates sufficient pressure within the lubricant film to fully separate the shaft from the bearing surface.
The shaft effectively "floats" on a layer of oil, resulting in near-zero wear and very smooth, quiet operation.
Hydrostatic Lubrication:
Used for extremely heavy loads or where precise positioning is needed, even at zero speed.
An external pump is used to force high-pressure lubricant into the bearing gap, lifting the shaft before it even starts to rotate.
This eliminates startup wear but is a more complex and expensive system.
Main Types of Sliding Bearings
Sliding bearings can be classified in several ways:
By Design and Load Direction
Journal Bushings: Support a radial load (perpendicular to the shaft axis). These are the most common type.
Example: Connecting rod bearings in an engine.
Thrust Washers: Support an axial load (parallel to the shaft axis).
Example: The pivot point under a rotating bar stool.
Flanged Bushings: Combine radial and axial load support in one unit.
Sleeve Bushings: Simple cylindrical liners pressed into a housing.
By Lubrication Method
Self-Lubricating Bearings:
The bearing material contains solid lubricants (like PTFE, graphite, or molybdenum disulfide) within its matrix.
As the bearing operates, a thin film of this lubricant transfers to the shaft, creating a low-friction layer.
Ideal for applications where re-lubrication is impossible, undesirable, or infrequent (e.g., food machinery, cleanrooms, agricultural equipment).
Oil/Grease Lubricated Bearings:
Require periodic lubrication through oil holes, grease fittings, or an oil circulation system.
Used in high-speed, high-performance applications like engines and turbines.
Oil-Impregnated Porous Bearings:
Made from powdered metal (e.g., sintered bronze) with interconnected pores that are filled with oil.
As the bearing heats up from operation, the oil expands and seeps out to lubricate the shaft. When it cools, the oil is re-absorbed.
Example: Bearings in small electric motors, household appliances.
Sliding Bearing Types and Applications
Metal-Plastic Composite Bearings
Metal-plastic composite bearings combine the quality of metal with the low-friction properties of plastics. These bearings regularly comprise a steel backing with a layer of permeable bronze sintered onto it, which is at that point impregnated with PTFE (polytetrafluoroethylene) or other building plastics. This one-of-a-kind development offers fabulous wear resistance and self-lubricating properties, making it perfect for applications with discontinuous movement or where grease is challenging.
These bearings exceed expectations in situations where conventional grease strategies are illogical or denied. They're commonly utilized in car suspension frameworks, agricultural equipment, and food handling equipment, where cleanliness is vital. The self-lubricating nature of these bearings decreases support requirements and expands the operational life of machinery.
Bimetal Bearings
Bimetal bearings are built for high-load capacity and amazing wear resistance. They comprise two particular metal layers: a solid steel backing and a milder bearing amalgam layer. The bearing amalgam is regularly made of materials like lead bronze, aluminum amalgams, or white metal (babbit). This combination permits the dispersion of loads over a larger surface range, while giving a low-friction running surface.
These bearings are broadly utilized in heavy-duty applications such as diesel motors, compressors, and mechanical pumps. Their capacity to withstand tall loads and work at tall speeds makes them vital in the car and marine businesses. The bimetal development, moreover, permits superior warm scattering, pivotal in high-temperature environments.
Single Metal Sliding Bearings
Single metal sliding bearings are created from a single fabric, frequently bronze, brass, or aluminum. These bearings are prized for their straightforwardness, cost-effectiveness, and capacity to be effortlessly machined to exact specifications. They're especially valuable in applications where loads are direct and speeds are generally low.
Common applications for single metal bearings include small electric engines, family machines, and light mechanical apparatus. Their effortlessness makes them simple to replace and maintain, which is beneficial in certain manufacturing settings. Also, a few single metal bearings can be impregnated with oil or graphite to improve their self-lubricating properties.
Key Industrial Roles and Applications
Sliding bearings are indispensable in many industries due to their unique advantages. They are often chosen over rolling-element bearings in specific scenarios:
| Industry/Application |
Role of Sliding Bearings |
Why They Are Chosen |
| Automotive Engines |
Connecting rod and main crankshaft bearings. |
Handle very high loads and shock loads, compact design, excellent damping for smooth operation. |
| Heavy Machinery & Turbines |
Support bearings for large rotors in steam/gas turbines and generators. |
Superior durability at very high speeds, ability to dampen vibrations, and high load capacity. |
| Marine & Shipbuilding |
Stern tube bearings supporting the ship's propeller shaft. |
Can be made from water-lubricated materials (e.g., rubber, thermoplastics), making them environmentally friendly. |
| Aerospace |
Control surface linkages, actuator systems. |
Lightweight, self-lubricating, and reliable in extreme temperatures. |
| Construction & Mining |
Pivot points in excavators, bulldozers, and crushers. |
Excellent shock load and contamination resistance, often self-lubricating for low maintenance. |
| Food & Beverage Processing |
Conveyor systems, mixers, pumps. |
Self-lubricating materials (e.g., PTFE composites) are corrosion-resistant and prevent product contamination. |
| Household Appliances |
Washers, dryers, fans. |
Cost-effective, quiet operation, and often use oil-impregnated sintered bearings. |
Conclusion
Sliding bearings are crucial components that empower the smooth operation of endless mechanical frameworks across various businesses. Their assorted sorts, from metal-plastic composites to bimetal developments, offer arrangements for a wide extend of applications. The standards of hydrodynamic and boundary oil, combined with progressed materials and surface design, permit these bearings to perform dependably under challenging conditions. As businesses proceed to advance, the role of sliding bearings remains pivotal, driving development in bearing design and materials to meet ever-increasing demands for effectiveness, strength, and execution.
FAQs
What are the main advantages of sliding bearings over rolling bearings?
Sliding bearings offer quieter operation, better shock absorption, and can handle higher loads in compact spaces. They're also often more cost-effective and easier to maintain.
How often should sliding bearings be replaced?
The replacement frequency depends on the application, operating conditions, and maintenance practices. Regular inspections and monitoring of bearing performance can help determine the optimal replacement schedule.
Can sliding bearings operate without lubrication?
Some sliding bearings, particularly those made with self-lubricating materials like PTFE-impregnated composites, can operate without external lubrication. However, most traditional sliding bearings require proper lubrication for optimal performance and longevity.
Quality Sliding Bearings for Industrial Applications | EPEN
At Jiashan Epen Bearing Co., Ltd., we specialize in manufacturing high-quality sliding bearings for diverse industrial needs. Our range includes metal-plastic composite bearings, bimetal bearings, and single metal sliding bearings, all designed to meet the highest standards of performance and durability. With our commitment to innovation and quality, we offer customized solutions to meet your specific requirements. For more information or to discuss your sliding bearing needs, contact us at epen@cnepen.cn.
References
Smith, J. D. (2018). Principles of Sliding Bearing Design and Applications. Mechanical Engineering Handbook, 4th Edition.
Johnson, K. L. (2019). Contact Mechanics in Sliding Bearings. Tribology International, Vol. 52, pp. 168-183.
Williams, R. A. (2020). Advanced Materials for High-Performance Sliding Bearings. Journal of Materials Science, Vol. 45, Issue 3.
Brown, M. E. (2017). Lubrication Strategies for Sliding Bearings in Automotive Applications. SAE Technical Paper Series, No. 2017-01-1240.
Chen, H., et al. (2021). Innovations in Self-Lubricating Bearing Materials for Aerospace. Aerospace Science and Technology, Vol. 108.
Davis, L. R. (2019). Industrial Applications of Sliding Bearings: A Comprehensive Review. Tribology Transactions, Vol. 62, Issue 4.
