Bearings are machine components that are designed to reduce friction between moving parts and support relative motion.
In recent years, you have likely encountered a fidget spinner at some point. These popular toys took the world by storm and were enjoyed by people of all ages. When individuals became tired of the existing designs, they started creating their own versions, incorporating ball bearings and adding unique features.
Fidget spinners are a popular toy that utilize ball bearings (Photo Credit : ViChizh/Shutterstock)
So, what exactly is a ball bearing? Let’s explore!
Types of Bearing Surfaces
A ball bearing is one type of machine component that is designed to reduce friction between moving parts and support relative motion.
The Different Types of Bearings
1. Sliding Bearings
Sliding bearings are the simplest form of bearings, consisting of plain or grooved surfaces on which machine elements can slide. They are cost-effective to manufacture and can support both linear and rotary motion.
Pedestals containing sliding bearings for shaft movement with lubrication port (green cover) (Photo Credit : nayladen/Shutterstock)
A basic example of a sliding bearing is a shaft in a hole. The shaft can rotate within the hole or move linearly along it. Without bearings, the movement of the shaft in the hole can cause erosion of the shaft or the hole walls.
Rotary sliding bearings are designed as sleeves in which the shaft rotates. The sleeve fits into the hole and provides support for the shaft’s movement. Depending on the specific application, the sleeve can be a single piece (bushing) or a split piece (journal bearing).
On the other hand, linear sliding bearings allow the shaft to move along the hole. Sliding bearings require external lubrication to minimize friction between the moving parts.
Engine blocks use journal bearings to facilitate smooth movement of the crankshaft (Photo Credit : aSuruwataRi/Shutterstock)
Sliding bearings are low-cost to maintain and can be made from various materials, including cast iron, Babbitt, bronze, and other zinc-based alloys. Depending on the application, bushings can also be made from rubber.
There are various examples of sliding bearings, such as:
- Journal bearings used in crankshafts of car engines
- Bushings used in door hinges
2. Rolling Bearings
Rolling bearings are the most commonly used type of bearings. They consist of rolling elements enclosed in a housing, allowing relative motion between machine components. The rolling elements can be balls or cylindrical rollers, depending on the application. Cylindrical element bearings have a larger contact area and can bear higher loads compared to ball element bearings of the same size. They can be arranged in a straight line to support linear motion or around a circumference to support rotary motion.
Rolling bearings can have spherical, cylindrical, or circular elements to reduce friction between moving parts (Photo Credit: Maxx-Studio/Shutterstock)
Rolling bearings come in various configurations, such as tapered bearings, needle bearings, and conical bearings. They are usually made of stainless and chrome steel, but can also be made of silicon nitride. Lubrication is necessary for optimal performance, although specially manufactured dry bearings can be used for high-temperature applications. Some common examples of rolling bearings include:
- Bicycle pedaling mechanisms
- Drawer sliders
- Skateboard wheels
3. Flexure Bearings
Lids of mint boxes, like the ones shown, are common examples of flexure bearings (Photo Credit: Robson90/Shutterstock)
Flexure bearings are a type of bearings that address failure due to repeated flexing. They connect two surfaces that move relative to each other by bending or stretching. These bearings are made of a material engineered to withstand repeated stress cycles without fatigue failure. However, excessive stretching can shorten their life cycle and cause premature failure. Flexure bearings can be made of metals or plastics and can have linear or spiral shapes, depending on their application.
One common example of a flexure bearing is the flip lid found on plastic boxes containing mints. They are also used with long beams to allow for beam movements, such as sagging.
Why Use a Bearing?
When machine parts move relative to each other, the surfaces in contact can erode, leading to material loss. This can result in reduced efficiency and even complete failure of the machine. Bearings act as sacrificial contact surfaces that are designed to withstand friction and heat cycles. They are stronger than the machine components they are in contact with, so any deterioration due to friction is limited to the bearing surfaces, preventing costly repairs.
Bearing Life
The theoretical life of a bearing is often represented by the L10 number. This refers to the number of hours a bearing can operate before 10% of its surfaces have failed.
The L10 number is a theoretical estimation of the lifespan of a bearing under ideal conditions, including optimal lubrication, a dust-free environment, and proper alignment. However, in real-world situations, these conditions are often not possible, making it challenging to predict the actual lifespan of a bearing.
Unconventional bearings can offer alternative solutions in various applications. One example is jewel bearings, which are commonly used in mechanical watches. These bearings have surfaces lined with synthetic sapphire or ruby, reducing friction and maintaining dimensional accuracy.
Magnetic bearings are another type of unconventional bearing that utilize levitation through a strong magnetic field. Although they are not widely adopted yet due to their size and cost, they have the potential to function without lubrication and in a vacuum. They are increasingly used in machines like compressors, turbines, motors, generators, and pumps.
Fluid bearings are contactless bearings that rely on a thin layer of pressurized fluids to prevent surface contact. They offer advantages such as minimal wear and noiseless operations, making them suitable for high-speed and high-precision applications. Hard drive motors and air hockey tables are common examples of where fluid bearings are used, providing a “floating” effect on the surfaces.