Differences between ball bearings and plain bearings – Which type of bearing is right for you?

Ball bearings and plain bearings are two basic types of bearings used in a variety of mechanical systems in mechanical engineering. The main task of bearings is to enable defined movements of components and thereby reduce friction as much as possible. Although both types of bearings have a common goal, there are fundamental differences in design, functionality and application. This blog article describes the most important differences between ball bearings and plain bearings.

Ball bearings as a type of rolling bearings

Rolling bearings are among the most common bearing types. They use rolling elements to compensate forces between the bearing surfaces. The rolling elements are positioned between an inner and an outer ring. Rolling bearings are often used to support shafts and axes because they can carry both axial and radial loads depending on their design, allowing rotation of the mounted shaft.

Ball bearings are a subset of rolling bearings and support rotating movements with the lowest possible friction. They consist of inner and outer rings, between which there are balls that act as rolling bodies. This design significantly reduces the friction between the moving parts of a machine or system. During operation, the embedded balls distribute the loads that occur, thus enabling smooth and efficient rotation.

Grooved ball bearings

Grooved ball bearings are a widely used type of ball bearings that are characterized by recessed raceways for the balls. This design allows them to absorb both radial and low axial loads. They are widely used in many industrial and mechanical applications due to their simple design and efficiency. They are characterized by a high load-bearing capacity and durability.

Self-aligning ball bearings

Self-aligning ball bearings have properties similar to grooved ball bearings, but have an inner ring with two rows of balls guided in grooves. The raceway of the outer ring has the shape of a hollow ball. This design allows the self-aligning ball bearing to adjust for small misalignments between the inner ring and outer ring. The resulting angular mobility can be used to compensate for skewed positions or alignment errors.

Angular Ball Bearings

Angular ball bearings are special-purpose ball bearings, which - in contrast to grooved ball bearings - do not have a symmetrical design when regarded from the side. The outer ring and inner ring are provided with a respectively opposing one-sided shoulder, which allows an oblique force profile.

In addition to radial loads, they can therefore accommodate higher axial loads than, for example, grooved ball-bearings. Single-row angular ball bearings can only be axially loaded from one side, while double-row angular ball bearings can absorb loads from both directions.

Axial ball bearing

Axial ball bearings are characterized by the ability to withstand particularly heavy loads in the direction of the shaft. They are particularly suitable in applications subjected only to axial forces. Depending on the design of the axial bearing, it can absorb one-sided axial forces (one-sided axial bearing), changing axial forces (two-sided axial bearing), axial and moderate radial forces (axial angular ball bearing). Axial ball bearings consist of shaft washers, Housing Washers, and ball sets.

Plain bearings

Plain bearings are bearings that do not require rolling elements, such as balls. One of their most common applications is to guide and securely position shafts running low speeds or performing incomplete circular movements. The rotational movement of the shaft is not made possible by rolling bodies, but by sliding the shaft surface on the contact surface of the plain bearing. Slide plates are used for sliding linear movements.

To minimize friction between the surfaces, plain bearings with self-lubrication or an external supply of lubricant are used. The lubricants used can facilitate movement between the two surfaces and minimize friction.

Plain bearing bushings

Plain bearing bushings, or glides bushings, are bearings that allow low-friction and vibration-damping movement between two components. They ensure linear or rotating movement between the components.

Plain bearing bushings are divided based on their design into plain bearing bushings with collar and plain bearing bushings without collar, also called cylindrical plain bearing bushing. Due to the mechanical stop, a plain bearing bushing with a collar can absorb moderate axial forces.

Plain bearing bushings are furthermore distinguished by their lubrication.

• Simple plain bearings are maintenance-efficient and are either not lubricated or are lubricated with grease.
• The hydrostatic bearing point is absorbed under constant lubrication. The bearing point is lubricated at all times as long as the circulation is ensured by a pump. Hydrostatic bearings must be carefully monitored and are expensive bearings. The advantages are low friction and low bearing wear, even with different loads.
• Hydrodynamic bearings only achieve the lubricated state at a certain speed of rotation because the lubricant is distributed by hydrodynamic effects. Since these effects do not take place in the hydrostatic state, the bearing slides at low speeds under the influence of dry friction and in the transitions in mixed friction.

Thrust washers

Thrust washers, or also plain bearing washers, are disc-shaped bearings that act as axial shaft bearings. Plain bearing washers are inserted or fixed on one side depending on the application.

Fixed/floating bearing

A fixed/floating bearing arrangement usually consists of two bearings. Fixed bearings secure a shaft in radial and axial direction, that is, they must be able to absorb radial forces and axial forces on both sides. By contrast, floating bearings can only absorb radial forces to compensate for axial movement or displacement by thermal expansion, manufacturing tolerances, etc.

Support bearing arrangement

The support bearing arrangement also consists of two bearings, both of which absorb a radial force. In contrast to the fixed/floating bearing, these bearing arrangements can only absorb axial forces in one direction. Support bearings are differentiated into two versions: adjusted bearing and floating bearing arrangements.

On adjusted bearing arrangements, the two bearings are positioned against each other - one could also say in a mirror image. The shaft is axially fixed in one direction by one of the bearings and in the opposite direction by the second bearing. This bearing arrangement is often used to guide the shaft under pretension and precise rotation. Angular contact bearings or tapered roller bearings are often used for adjusted bearings. Depending on the arrangement of the bearings, thermal expansion of the materials used leads to changes in the pretension of the bearings, which can significantly stress and destroy them.

The floating bearing has many similarities with adjusted bearing. However, the floating bearing allows a certain axial play s, i.e. the shaft can move - or float - axially over a certain distance. Floating bearings are used if there is no tight axial guide. Bearing types suitable for floating bearings are deep groove ball bearings or spherical ball bearings.

Criteria for selecting plain bearings and ball bearings

The fundamental difference between the two types of bearings lies in their structure and their functionality. When deciding for or against one of these types of bearings, it is helpful to consider the following distinguishing features:

• Friction and efficiency: Ball bearings use rolling elements, usually balls, that roll between the inner rings and the outer rings, thus allowing low-friction movement. Since the balls absorb a large part of the load, friction in ball bearings is generally low, which in turn leads to an efficient transfer of torques and enables higher speeds. Plain bearings use the principle of direct friction between two surfaces. Here, a sliding film, usually made of lubricant, is produced between the shaft and the plain bearing. Since the movement occurs on a surface with a lubricant as a sliding medium, the friction in plain bearings is generally higher than in ball bearings.
• Stress and shock sensitivity: Plain bearings are advantageous in applications with lower rotational speeds of rotation and high radial forces, but ball bearings are suitable for higher speed of rotation. Because ball bearings generally have lower friction torques than plain bearings, they develop less heat, so no additional cooling is required. With regard to the impact load, plain bearings are advantageous because the material load is higher in ball bearings due to the smaller bearing surface of the roller bodies and ball bearings are more sensitive to impact loads. Even vibrations at rest can easily damage ball bearings , and the low vibration damping of the ball bearings is accompanied by a wide variety of vibrations, noise and oscillations. Plain bearings, on the other hand, are able to dampen vibrations caused by vibrations.
• Service life and maintenance effort: Plain bearings have a comparatively long service life, while ball bearings are usually only designed for a limited service life. Compared to ball bearings, plain bearings require less maintenance since wear is rather low even at the highest loads. They are also more resistant to dirt than ball bearings and are therefore better suited for use in harsh environments. Ball bearings would have to be elaborately sealed for this use to prevent dust and dirt ingress. Ball bearings, on the other hand, can be integrated into assemblies with less effort, since they are internationally standardized components. Ball bearings are generally better suited than plain bearings, particularly at high rotational speeds, whereas plain bearings are better suited for pivoting movements.
• Installation and costs: While ball bearings require comparatively large installation space, plain bearings are one-piece and compact and thus require minimal space. They are also easier to assemble. Another difference is the cost factor. Plain bearings are the somewhat less expensive variant compared to ball bearings because ball bearings cause higher design costs, including for the bearing itself as well as for housings, mounting surfaces and fasteners.

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The application example is a glass circuit board conveyor. The bearing of the rollers is implemented with ball bearings. The appropriate components to design your bearing can be found in the MISUMI shop:

• Retaining Rings, Retaining Washers and Circlips
• O-Rings