Bearing Bushing, also known as a, is a simple, cylindrical component used to reduce friction between two moving parts. It consists of a cylindrical inner surface, an outer surface, and a lubrication film between them. Bearing bushings are often made from materials like bronze, brass, steel, or polymer composites.Bearing bushings are essential components used to reduce friction and support loads in various industrial applications. Their advantages, such as low friction, self-lubrication, and cost-effectiveness, make them an attractive choice for many engineers and designers.
1. The difference between bushings and bearings
2. The main types of bearings
3. The missing link between bearings and bushings: sleeve bearings
4. What are the best bushing materials?
5. Why is tribology important when designing bearings?
1. The difference between bushings and bearings
Bearings vs bushings? There is really no difference: a bushing is a type of bearing. Generally speaking, a "bearing" facilitates movement between two parts while reducing friction. A typical bearing is a simple design with two surfaces rolling against each other, allowing the two mating parts to move without friction.
Depending on whether they are used for rotary or linear motion, they can be roughly divided into radial bearings, thrust bearings, and linear bearings.
A "bushing" is a specific bearing used for a specific purpose. To summarize: a bushing is a bearing, but a bearing is not always a bushing.
Now that we have that cleared up, let's consider the different types of bearings and how bushings differ from rolling bearings.
2. The main types of bearings
The different types of bearings have the same basic structure and purpose. As we mentioned, they have two surfaces that move against each other, allowing the mating parts to move easily and without friction. The main difference is whether they perform rotational or linear motion. Here is our at-a-glance guide to the main bearing types:
-Ball Bearings
Ball bearings support a rotating shaft while reducing friction between it and a stationary component. The balls (usually steel, but sometimes ceramic for use at high temperatures) fit between an inner and outer ring. Bearing assemblies can have single or multiple rows, depending on the application.
Broadly speaking, there are two types of ball bearings: deep groove ball bearings, which have a high radial load capacity, and angular contact ball bearings, which can handle both high radial and axial loads. Ball bearings are used in a wide range of applications, from complex aerospace engineering to everyday skateboards.
-Roller Bearings
Roller bearings can handle higher loads than ball bearings. They are cylindrical or tapered and fit between an inner and outer ring. Their job is to minimize friction between a moving shaft and a stationary component.
Cylindrical roller bearings are typically made of stainless steel and are used to carry heavy radial loads. They are ideal for high-speed applications because their low-friction design does not generate heat or noise. You'll find cylindrical roller bearings in gearboxes, electric motors, and pumps in a variety of industries, including automotive, mining, and construction.
For slow-speed applications, use spherical roller bearings. These self-aligning bearings can handle severe misalignment, vibration, and sudden shocks. When mounted in a double row, they can handle extremely heavy radial and axial loads. Roller thrust bearings have similar misalignment management characteristics.
- Needle Roller Bearings
Needle roller bearings are small but very strong. They get their name from their needle-thin appearance and are used to reduce friction in small applications. These rigid bearings are ideal for applications with oscillating motion. They're also handy if you need to save weight or have limited clearance area. You'll find them in a variety of applications, including household appliances.
- Rod End Bearings
Compact, lightweight, and easy to install, rod ends are a reliable choice for heavy alternating loads. The basic design is a round head with an integral shaft that carries a spherical plain bearing. However, rod ends don't have the misalignment characteristics that some other bearing types have because they are fixed.
Rod end bearings belong to a group of mounted bearings that fit inside bolted components, including pillow-type bearings. They are often used in machines with exposed rotating shafts. Cam followers are another variation. They have thicker outer rings, and softer inner rings to absorb shock. They work with cams to convert rotary motion into linear motion.
Spherical bearings mounted on rod ends require a constant contact area to minimize stick-slip and keep friction consistent. Lubrication is essential, which can cause problems in applications where impurities cannot be tolerated.
Learn more about Bearing Bushing as a spherical bearing bushing.
3. The missing link between bearings and bushings: sleeve bearings.
Sleeve bearings, also called bushings, journal bearings, plain bearings, or slide bearings, are the simplest bearing design. Sleeve-type bearings are often used in applications that use rotating or sliding parts. Sleeve bearings are made from a variety of materials, with plastic being the lowest-cost option.
All-metal bearings have a lower coefficient of friction, but can cause rattling at high speeds. Steel sleeve bearings can be lubricated; however, a quieter, lower maintenance and more reliable friction alternative is to use self-lubricating materials such as PTFE.
Simple cylindrical bearings are suitable for radial loads, while flanged sleeve bearings can accommodate axial loads. For high loads, a combination of thrust washers and cylindrical bearings works well.
Sliding bearings
4. What are the best bushing materials?
The design may be simple; however, the performance and function of the bushing can vary greatly depending on the material it is made of.
-Metal sliding bearings
Metal sliding bearings are usually made of alloys of different metals, such as aluminum, tin, zinc, bismuth or copper. Metal sliding bearings are particularly suitable for hydrodynamic conditions and can therefore be used in applications with high sliding speeds: engine bearings, turbine bearings or gearboxes. The formation and maintenance of the lubricating film are particularly important for such sliding bearings, as direct contact between the sliding bearing material and the mating parts leads to increased friction and wear.
Metal sliding bearings made of bronze have excellent durability and a long service life. They do not corrode and are not easily deformed.
-Sintered bearings
As the name suggests, sintered bearings are different from the above-mentioned metal sliding bearings. Sintering creates small cavities in the metal structure, which can be filled with lubricants (graphite, MoS2) and/or impregnated with oil. As a result, sintered bearings generally have better emergency running properties, as the cavities can absorb oil like a sponge and then release it as a lubricant. Sintered bearings are used in automotive engineering, for example in starter motors, fuel pumps, and even household appliances.
However, metal and sintered bushings do require a lot of lubrication during operation, so they are more expensive to maintain than plastics.
-Plastic Bushings
Plastic bushings are popular and are a low-cost, low-friction and low-maintenance option. They are self-lubricating and ideal for hard-to-reach parts. They can also be used in wet environments as there is no risk of corrosion.
There are both advantages and disadvantages to using plastic as a bearing material, as described below.
- Advantages of Plastic Bushings
Plastic bushings offer many operational advantages. They are self-lubricating, so they require no maintenance and have a low coefficient of friction. Plastics are best suited for simple plain bearings, as they reduce weight and maintenance, and they do not show any indentation. (Indentation is permanent indentation damage caused by a ball bearing to a hard surface.) That being said, we are seeing an increase in the use of plastic ball bearings and bushings.
Overall, plastic has many advantages over metal. It can be used in wet environments and is easier to maintain sanitation in cleanroom environments. FDA-approved food-grade plastics may be suitable for certain industrial applications, while polyethylene has traditionally been used for orthopedic bearings.
When specifying plastic bearings, it is easier to find off-the-shelf options that can be dropped right into your shopping cart. Custom options are also relatively inexpensive to produce.
-Limitations of Plastic Bushings
For heavy loads, plastic is not recommended as a bushing material. Plastic bushings can crack under high loads. This can damage not only the bearing itself, but also the mating component and increase its friction. Another problem can be easy misalignment if manufacturing or assembly is not absolutely precise-a real problem with off-the-shelf bushings.
Plastic may be quieter than metal, but it is not inaudible. In fact, if the fit is not exact or the clearance is not right, hard plastic sleeve bearings can rattle just as loudly as metal bearings.
One unexpected problem is the damage that can occur with high-temperature EFI. This softens the plastic material, causing permanent thinning. The solution to this problem is to use a stainless steel backing. This negates the advantages of a pure plastic bushing, but does improve wear resistance and enable EFI. Learn more about the disadvantages of plastic bushings in our blog, 5 Reasons to Switch to Plastic Bushings.
However, there are many different types of plastic, and if plastic is specified, the preferred engineered plastic material is usually PTFE.
-PTFE Bushings
PTFE (polytetrafluoroethylene), better known by the brand name Teflon™, is a low-friction, self-lubricating plastic used in many everyday items. PTFE is a popular engineered plastic because it has a low coefficient of friction and maintains constant torque within a certain tolerance range. Another huge advantage for the automotive industry is its noise reduction properties, where noise is lethal.
PTFE is highly resistant to high temperatures, corrosion, and water, and can be used in a variety of applications. It is a great bushing material for high-performance bearings, but unlike other plastic bearings, it is not always a low-cost option. It may also be difficult to connect and unsuitable for environments with high radiation levels.
5. Why is tribology important when designing bearings?
Tribology, the study of friction, plays an important role in our research and development. Through tribology, we can better understand the wear process of materials and apply this to the design of bearings. For example, we work with automotive engineers to create consistent, controlled friction to reduce noise, vibration, corrosion and wear.
Talk to a bearing expert
Not sure which material to use for your bearing? From a simple flange to a heavy-duty roller bearing, the material used in your application has a significant impact on its operating performance and service life.
Talk to our experts, engineer by engineer. We will discuss your options and together we can ensure your bearings and bushings are strong, reliable and suitable for your application.https://www.welfinebearing.com/