Elements for securing axial bearings

In many industrial and mechanical applications, bearings are critical components that provide low friction, reproducible movement between moving parts, shafts, or axes. Depending on their installation location and function, these bearings must allow different degrees of freedom and be securely fixed. In addition to many other options, locking elements such as retaining rings or slotted nuts or shaft nuts are used to secure machine parts such as rolling bearings, bolts, or shafts against axial displacement.

Importance of securing bearings

Shafts and bearings can shift their position due to vibration, rotation or even under the influence of thermal expansion. This can result in undesirable play, excessive wear, or even complete machine failure. Conscientious design planning taking into account the necessary freedom of movement is a prerequisite for securing bearings efficiently and thus contributes to the longevity of the entire system. Unintentional loosening or displacement of a bearing or shaft in a machine can lead to serious accidents in addition to machine failure. Bearing locks and shaft locks prevent such undesirable movements and thus contribute to the safety of operators and operational safety of the machine. In addition, certain regulations and guidelines must be observed in some industries and applications, which consequently require bearing locks to ensure safety and reliability.

Depending on the application and the required degree of freedom, there are various bearings, e.g. fixed bearings and floating bearings. A fixed bearing prevents movement of a component or structure in a specific direction, while a floating bearing allows free movement. This can be advantageous with thermal expansion or other force effects.

You can find more information on bearings and bearing arrangements in our blog on bearing types .

Standardized components for securing bearings

There are various standardized parts and design solutions for securing bearings and shafts. The following solutions are available in the MISUMI shop:

Slotted nuts and shaft nuts

Slotted nuts - or shaft nuts - are a subset of adjustable fastening and locking elements. They are a special type of lock nut designed to hold or tighten machine elements on a shaft, axis, or bolts against a component or thrust bearing. They require a thread onto which they are threaded. Depending on the design, the use of a spring pin, an axially projecting groove, or other design adaptation to the shaft is also necessary.

Slotted nuts are commonly used to hold components such as bearings, wheels, or belt pulleys in place while also allowing them to be adjusted.

The design of slotted nuts is characterized by two or more cross grooves distributed evenly on the outer diameter. These grooves allow the nut to be tightened using a suitable tightening tool such as a hook wrench or socket wrench. Shaft lock nuts often have a fine thread on the inner diameter that has a self-locking action. In this case, the position is secured by tightening the groove nut against the machine element to be secured (e.g. a rolling bearing inner ring located on a shaft segment). When a torque is applied, the corresponding tightening force on the internal thread of the clamping nut is exerted on the external thread of the bolt onto which it is threaded, and the rolling bearing inner ring is fixed in its position.

Adjustability is a great advantage because it allows the position of a component to be adjusted along a shaft or threaded rod without having to remove the nut completely. However, due to their design, nuts have a lower load capacity compared to other types of nuts, such as hex nuts. Slotted nuts are typically made of steel or stainless steel.

Slotted nut with locking plate and spring washer, as needed

Locking plates - or Retaining Washers - are often used in combination with nuts if the nuts are not self-locking, thus calling for a separate captive locking feature. A prerequisite for using a locking plate or a Retaining Washer as a captive locking feature is that the shaft has a keyway for the slotted nut in the region of the thread.

The locking plate, which is often visually similar to a toothed washer, has a "guide tooth" on the inner circumference that is guided by the keyway on the shaft. This guide prevents the Retaining Washer or the locking plate from rotating. Once the desired position of the nut threaded onto the shaft is reached, the tooth of the locking plate matching the slotted nut is bent into the groove on the outer circumference of the nut, thus preventing the nut from rotating. The locking plate is plastically deformed and prevents the nut from detaching from the position on the thread by the shape lock.

An additional spring washer (shaft spring washer) can be used to ensure axial preloading, while also accounting for any potential elongation of the shaft. This is an advantage over other types of fasteners because oscillations, shocks and thermal dimensional changes can be compensated by the spring action with corresponding dimensioning.

The advantages of slotted nuts with locking plate are:

• No autonomous loosening
• Can be mounted without stresses due to shape lock with shaft groove
• Assembly with defined preload force possible with spring washer

Slotted nuts with Grub Screw

In a further embodiment, slotted nuts can have axially or radially arranged set screws or grub screws that are used for securing. These connections are easily detachable. The corresponding slotted nuts can be locked in any position without much effort.

Locking with lock nut

Another method is the use of a second slotted nut as a lock nut, which is tightened against the first slotted nut. This method is used when the nut is not tightened against a thrust bearing or a rolling bearing inner ring, but is threaded freely onto the bolt. Locking by means of lock nut is a commonly used method when a defined clearance to the thrust bearing or a defined dimension is to be set on the Full Thread Screw.

Shaft retaining elements

Shafts are usually secured against sliding out of the bearing seat with Retaining Washers (shaft lock). In the application, the washers are simply clicked into the groove of the shaft with a suitable hard object. In these cases, the assembly is radial. Loosening is just as simple and can be achieved with a mandrel or screwdriver that levers the washer away from the shaft at the recess. Other versions, so-called clamping rings, clamping washers and also sprocket rings, can be pushed axially onto the end of the axis. They rely on their clamping force to engage into the outer diameter of the shaft or in a groove and thus secure the washer in position. Retaining Washers provide a flat surface that evenly distributes the pressure to help the bearing stay in place. Retaining Washers, such as key-type washers or spring washers, are often used, for example, to hold screws and bolts securely in place and to prevent loosening by vibrations. Retaining Washers can be made of a variety of materials, including spring steel, stainless steel or plastics such as nylon.

You can find more information on shaft locking elements in the blog on locking pins.

Bearing retaining ring for bore holes and shafts

Locking rings - or circlips - are closely related to Retaining Washers. These are slotted rings that expand or constrict and fit into a groove of a shaft or hub, depending on the design. Consequently, a distinction is made between bore retaining rings (inner rings) and shaft retaining rings (outer rings). The prerequisite for using retaining rings is that the groove radially runs around the entire circumference of the axis or bore hole, and that according to the technical data sheets, the groove is oversized compared to the thickness of the ring. If play and rattling are to be completely avoided in the axis direction, additional spring washers or crowned or spring-loaded Retaining Rings are used, where the spring action of Retaining Ring located in the groove presses the latter against the element to be secured with a friction lock. Retaining Rings are preferably used to secure ball bearings and roller bearings, for example, in order to secure the bearings in housings and to prevent axial movements. Bearing covers can also be used in some cases instead of retaining rings.

Retaining Rings are usually made of spring steel or stainless steel. Spring steel allows the rings to constrict or expand due to their elasticity and to snap into a groove or seat. Stainless steel, on the other hand, is often chosen when corrosion resistance is required.

One advantage of retaining rings is that they are cost-effective and can be reused when properly removed. They are also generally easy to install without complex tools or procedures. One disadvantage here is that due to the required groove, there may be a notch effect in the shaft, which should be taken into account by design.

Hydraulic nut

Hydraulic nuts are tools that facilitate the assembly and disassembly of bearings. The hydraulic nut is screwed onto the shaft next to the component to be clamped. A defined pressure is then built up in the hydraulic nut via a hydraulic connection. This pushes a hydraulically moving element of the hydraulic nut against the bearing or the bushing. By means of a defined hydraulic pressure, the hydraulic nut can exert a defined preload force on machine elements, e.g. large rolling bearings, but also screws. This facilitates the assembly of the bearings as well as the insertion and installation of the corresponding locking elements, such as slotted nuts, Retaining Washers and Retaining Rings. A major advantage when using hydraulic nuts is the time saved during assembly and disassembly. In addition, the risk of machine damage is reduced because hydraulic nuts can be applied without friction and exert uniform pressure. They are often used to secure difficult-to-access components or to clamp rotating components.

Individual components for bearing locks

In practice, bearing locks are implemented as a combination of standardized parts and stops on shafts and bores holes. These shafts and bore holes can be produced directly from the CAD model using the "meviy" tool without having to generate a derivative drawing.