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The Ultimate Guide to Sleeve Bearings and Bushings
In today’s industrial system, sleeve bearings, bushings and bearings have become indispensable components. There is an appropriate metaphor that “bearings have become the food of industry”. The main function of sleeve bearings, bushings and bearings is to support the rotating body to reduce friction as much as possible, effectively reduce noise, reduce power consumption, maximize machine efficiency and speed up application, and greatly extend the service life of the machine. But in the field of fasteners, sleeve bearings, bushings and bearings, it is difficult to say that there is a common name. For example, incomplete statistics indicate that there are than 400,000 types of bearings. Even different names may represent the same bearing. Sleeve bearings and bushings, the main difference between bearings or bushings lies in their different applications. Choosing the right type of sleeve bearing, bushing or bearing for your industrial application to meet certain requirements requires a wealth of knowledge. You need to know the key differences between sleeve bearings, bushings, bearings, their applications in industry and manufacturing, and . In this article, we’ll take an in-depth look at the characteristics and applications of sleeve bearings, bushings, and bearings, clarifying their functions, materials, and key differences.
Short and simple: Sleeve bearings and bushings are equal. Sleeve bearings are sleeves or tubes that allow linear or rotational movement. This is exactly what bushings are for. The terms sleeve bearing and bushing are used interchangeably. Therefore, in the description that follows, the author of this article will use these two terms randomly. In fact, sleeve bearings, sliding bearings, journal bearings and sliding bearings can all be used as bushings; these terms describe different styles of bushings. In short, a bushing is always a bearing, but not all bearings are bushings.
What is a bushing (sleeve bearing)?
Bushing – often called a sleeve bearing, is a cylindrical bearing used to support the load on an operating shaft that slides back and forth between moving surfaces. Bushings are special bearings that can be made from a variety of materials and slide on a rod or shaft, providing extremely low friction movement, excellent shock absorption, and minimizing energy consumption, noise and wear while providing an effective seal , protected from dust and moisture. . Fortunately, bushings are self-lubricating, making them ideal for low- or maintenance-free operation. Self-lubrication is achieved through a uniform pattern of dimples on the bushing surface, which act as grease reservoirs. Regardless of the type or size of sleeve bearings used, they have an advantage over traditional ball or roller bearings due to their lower coefficient of friction due to their minimal contact area. This makes bushings ideal for applications where speed, accuracy and durability are critical. With these benefits in mind, it’s easy to see why sleeve bearings are so popular in many industries today. Bushings are widely used in automobiles, white goods, drilling tools, motors, hydraulic external gear pumps, etc. In the automotive industry, for example, sleeve bearings provide rotary linear motion in hinges, seat adjustment systems and steering wheels. Some nylon bushings can operate without the use of lubricants and are particularly suitable for the food and textile industries where dry applications are preferred.
What types of bushings are there?
There are several bushings with different types on the market. Generally, bushings can be classified based on material and shape. Sleeve bearings can be made from a variety of materials. These include metals, bimetals, ceramics, stone, graphite, composites and plastics. The function of the sleeve bearing depends on the choice of material, as the material will determine the strength, elasticity, coefficient of friction, etc.
Classified by material, there are three common types of bushings: composite bushings, metal bushings, and plastic bushings. According to the shape classification, bushings can be divided into six types: ordinary sleeve bushings, flange bushings, thrust washers, split bushings, composite bushings, and flange composite bushings.
Polymer or composite bushings
Polymer bushings are mostly chemically inert; they have low water absorption and can operate at high temperatures without deforming. Polymer bushings can also be called composite bushings. They are suitable for heavy load conditions and are the most commonly used bushings. Composite bushings provide low friction and wear resistance, minimizing machine damage caused by improper lubrication. They are made of materials with high resistance to environmental factors, heat resistance, low coefficient of friction and non-adhesive properties. The only drawback is that they are very flexible, which means they can get twisted while working. By adding fillers, this problem can also be solved and enable manufacturers to offer highly versatile sleeves. Polymer or composite bushings are used to transmit rotational motion and can replace traditional bearings in hazardous environments. Polymer or composite bushings can be used in a variety of industries, including construction equipment, hydraulic systems, medical equipment, aerospace and .
POM bushings
POM bushings are developed with self-lubrication in mind, offering good wear resistance and a low coefficient of friction. Suitable for heavy loads running at low speeds to reduce machine vibration and noise. POM sleeve bearings also help reduce heat buildup caused by friction, extending bearing life up to four times longer than bearings made from other conventional materials (steel). Polyoxymethylene sleeves or POM sleeves are typically made from a steel backing and coated with a sintered copper/bronze layer. Finally, a POM layer is added over the copper/bronze layer, which contains grease pits that retain the lubricant. Applications of POM bushings are widely used in agriculture, civil engineering, machinery and construction industries.
PTFE bushings
PTFE bushings are made of two different materials, polytetrafluoroethylene and metal, and are commonly used in various industries. Its core function is to reduce friction between moving parts in machines. PTFE bushings are suitable for a variety of industrial applications due to their ability to withstand high temperature fluctuations and can be used in industries as diverse as electrical, thermal, nuclear, chemical, pharmaceutical and even power plants.
Nylon bushings
Nylon bushings are strong and durable and are increasingly replacing metal bushings in many applications. Nylon has excellent wear resistance and requires no external lubrication. It’s worth noting that nylon bushings don’t make as much noise when running as metal bushings. They have a low coefficient of friction and high resistance to weak acids, fuels and alkalis.
Metal Bushing
As we all know, metal bushings are made of metal or metal alloys. These metal bushings have very high mechanical strength and are particularly suitable for high speed and high load applications involving lubrication. Which metal bushing is used depends on the industrial environment or type of application. Metal bushings have different lubrication methods depending on their size, construction and application.
Bronze bushing
Bronze bushing is the material of choice for metal bushings. Bronze bushings are resistant to deformation and breakage than sleeve bearings made of other materials. Like plastic, bronze bearings are strong and rust-resistant. Bronze bushings are widely used in food processing, injection molding, automotive machinery, earthmoving machinery, steel manufacturing, etc. Bronze bushings offer excellent durability and long service life. They do not corrode and are not easily deformed. However, bronze bushings do require significant amounts of lubrication during operation, making them expensive to maintain than plastic bushings.
Graphite bushings
Graphite bushings are used in many applications due to their unique mechanical and physical properties. Graphite bushings have a very low coefficient of friction, helping to increase the efficiency, productivity and performance of spinning machinery. Graphite, a naturally oily mineral, is the best material for bushings because it reduces friction without the use of additional fluid. Notably, graphite has the highest temperature stability, maintaining its shape and structure at temperatures up to 5000°F. Graphite liners are used in a variety of applications including furnaces and ovens, food applications, chemical industry, automotive industry, metals, and .
Steel Bushings
Steel Bushings, As the name suggests, steel bushings are made of steel or stainless steel. These bushings are constructed from highly durable steel, making them ideal for low speed pivot applications. Steel casings are manufactured using environmentally friendly production methods that increase material yield and reduce chipping.
Brass bushing
Brass bushing is made of brass and is usually a component of the pivot shaft that helps protect the body from any damage caused by any force transmitted through the shaft. Brass bushings are mostly used in electric motors, automobile engines, etc. Additionally, brass bushings come in a variety of sizes as they can fit thin and thick walls, flanges, cylindrical, flanged, etc.
Aluminum bushings
Aluminum bushings are preferred for their hardness, ensuring a long service life. Initially, it was used on bicycles, but gradually it was used on cars and is currently used on a variety of different machines. Aluminum bushings can withstand large axial and radial loads, making them an important candidate for use in the aerospace and agricultural industries. Some of the common applications for aluminum bushings include use in hydraulic cylinders used to mount instrumentation (such as drain plugs/fluid fills, fluid sight glasses, or vent elements), vessels, and tanks.
Bimetallic sleeve Bearings
Bimetallic sleeve Bearings are made of two different metals. In most cases, the first metal is steel, while other metals may range from copper to aluminum or even brass. The bimetallic layer acts as an internal covering for the bushing, providing good protection against wear. They are particularly useful in applications that run moderate loads at medium speeds or high loads at low speeds.
Bushing Types by Shape
In terms of shape, there are six main types of bushings.
Plain Sleeve Bushings
Plain Sleeve Bushings are generally cylindrical in shape and made to industry standard dimensions. The cylindrical bushing has backings on the inside and outside that support the sliding layer in the middle. Cylindrical bushings are stronger than bearings and can withstand higher loads than metal bearings, making them ideal for one-way variable loads, pivoting motion and axial guide bearings.
Material: Typically made of bronze, brass or other self-lubricating material.
Design: Cylindrical with inner and outer diameters.
Application: General applications requiring low friction and medium load carrying capacity.
Flange Bushing
Flange bushings are similar to cylindrical bushings, but with one obvious difference: they have a flange on one end. Flanges can be used for a variety of purposes, from mounting or aligning bushings to convenient installation. Flange bushings, commonly used in through-bolt applications, allow the use of smaller diameter bolts to reduce weight without resulting in less fastener support surface for the spar wall, while also reducing stress on the mounting bolt threads.
Design: Similar to a regular sleeve bushing, but with a flange on one end to provide axial support.
Application: Used when the bushing needs to resist axial movement.
Thrust Washer
The thrust washer itself is not a bushing, but it is a very important component. They appear to be a flat washer that sits between the stationary component and the rolling surface, supporting axial loads or side-to-side motion on the shaft and restricting any movement along the shaft. They form a surface on top of which the bearing or bushing is supported.
Design: Flat or flanged washer-like bushing.
Application: Designed to carry axial loads, usually in combination with radial bushings.
Split Bushing
Design: These bushings come in two halves and can be easily installed and removed without the need for additional removal equipment.
Application: Ideal for applications where disassembly is challenging or time-consuming.
Composite Bushing
Materials: Made from a combination of materials such as a metal backing and a layer of PTFE (polytetrafluoroethylene).
Application: Low friction, high wear resistance and self-lubricating properties make it suitable for a variety of applications.
Flange Composite Bushing
Design: Similar to composite bushings but with flange for axial support.
Application: Combines the advantages of composite materials with increased axial stability.
Advantages of sleeve bearings
Sleeve bearings are ideal for many applications because of their simplicity and durability. They reduce energy consumption during operation by providing low friction between the shaft and bearings. Sleeve bearings also have a small footprint, making them suitable for applications where space is limited. Additionally, due to its simple design, it can be easily assembled or disassembled. Sleeve bearings provide superior protection against dust particles, dirt and other contaminants, as well as wear caused by high temperatures. Additionally, these bushings require no maintenance because they do not require lubrication like most other types of bearings. Therefore, sleeve bearings are a cost-effective solution that improves operational efficiency while reducing operating costs. Additionally, they can be used in both dry and wet conditions without any modifications.
The reliability of sleeve bearings makes them an attractive choice for industrial machinery that requires reliable motion control components; therefore, it is no wonder that many companies rely on this type of bearing when designing equipment. All in all, sleeve bearings are versatile components that allow for smooth operation at a lower cost than alternatives like ball or roller bearings. Having said that, it’s clear why they continue to remain popular within the industry.
Disadvantages of sleeve bearings
Sleeve bearings are not designed for high speeds, with studies showing their top speed is around 5,000 RPM. This limitation can cause a number of problems in applications that require higher speeds, such as motors and fans. Another problem with sleeve bearings is that they tend to have a limited life expectancy when used in heavy-duty applications such as large industrial machines. Their design also makes them unsuitable for radial loads as they easily deform under pressure. Over time, the amount of dirt that gets into the sleeve bearings increases, which can lead to premature failure.
Bushing load and speed limits
Bushings are typically used for heavier loads and slower speeds. Industrial metal wheels benefit from durable bushings that can withstand heavy load transfer and shock loads. For bushings, frictional heating must be considered. The two main factors affecting heat are unit pressure (P) and surface velocity (V). The product of unit pressure and surface velocity is pressure velocity (PV). To determine whether a bushing is suitable for any application, first find the limiting PV value from the manufacturer. For safe operation, the PV value calculated by the application must be below the manufacturer’s limiting PV value.
Calculate the PV value of the application: PV=P×V
Determine surface speed (V): V=0.262×rpm×D Rpm = Shaft revolutions per minute D = Shaft diameter (inches)
Pressure (P): P = Total Load (lbs) / Contact Area (in²) Contact Area = D (shaft diameter in inches) x L (casing length)
The effect of limiting the PV value can be seen in this graph, which compares velocity versus load for bronze and Nyloil bushings.
In an internal engineering study, Nyloil bushings and C93200 Bronze bushings were used together to test the effect of: PV limits of the bushing. As mentioned previously, bushings are typically used for heavier loads at slower speeds. This is evident in the diagram as neither bushing is capable of handling significant loads at high speeds. The faster the speed, the lower its load capacity. P-max (psi) and V-max (fpm) values are provided by the manufacturer for each product. P-max is the maximum load at 0 rpm and V-max is the maximum speed at light load (maximum shaft rpm). For practical applications, compare the calculated P, V, and PV values to the maximum tolerances to determine if the bushing will operate. Ensure that the bushing operates within a range below the limiting PV curve.
Bearing or bushing?
Factors to remember when deciding between bushings or bearings should include the following (in order of preference):
Speed and load: Carrying heavier loads at slower speeds or lighter loads at higher speeds? Where high speed is a factor, bearings offer a better solution, while bushings respond well to low-speed, heavy-load applications.
Smooth operation: Due to the “stick-slip” phenomenon, a common problem with bushings, bearings are a better choice for smoother operation.
Maintenance/Lubrication: Maintenance-free applications with self-lubricating capabilities, especially in the dry food and textile industries, often favor bushings.
Operating noise: When quiet operation is a key consideration, bushings are generally quieter than bearings.
Budget: Bushings tend to cost six to ten times less than bearings.
When choosing between bearings and bushings, the specific application, its operating environment, and various operating conditions and limitations must be considered. Understanding the advantages and disadvantages of each type can help determine which type provides the best solution.