A RENCOL® Tolerance Ring is a custom-designed component that has waves, or other features, that are used to join cylindrical mating components. When the tolerance ring is assembled between the components, the waves compress to keep them all in position.
Each wave acts as a spring; the more you compress it, the larger the force it creates. This force holds the components together while also satisfying other performance requirements, like the load it needs to withstand. If you are interested in the theory of this, take a look at our How a Tolerance Ring works.
Tolerance rings can be manufactured from high quality spring stainless steel, carbon steel or alloys. They are normally one part of a 3-part system:
All three of these elements work together allowing the RENCOL® Tolerance Ring to: mount components, transfer torque, act as slip clutch and allow axial force control (slip) between mating components with designed forces.
There are many applications that tolerance rings are used in, but can be broadly categorized into 4 main types:
The tolerance ring is compressed between two components, resulting in an engineered fastening.
These are static fixings and are designed so that none of the components move in relation to each other. Examples of this type of use are:
Tolerance rings can be used as very elegant slip clutches. A slip clutch is an overload protection device that is designed to disengage two components when a certain torque is reached.
Slip clutches are used in many different areas and are often used to prevent damaging motors or gearing systems when an unwanted load is applied to the system.
Transferring torque drive from one mating component to another, working in a similar fashion to a spline or keyway. Examples of this are.
The tolerance ring’s slip capability can also be used for positioning components. This is the ability to set an object in a position which is then held. A tolerance ring allows the system to move smoothly when moved by the user. Its position is then maintained when no external force is applied.
A tolerance ring is a usually a curved metallic shape, that looks like an open cylinder. Around the outside or inside of the shape, waves or other features like fingers are formed or pressed. Typically, a tolerance ring will have a slit down the side of them, allowing them to be pulled open or squeezed closed. They come in all shapes and sizes from around 3mm in diameter up to 110mm and even in some cases, over 250mm in diameter. Typically, they are between 10 - 50mm wide.
The waves, or corrugations, can be designed to face inwards or outwards, and their shape will be specifically designed so that they perform how you need them to. Adjusting various parts of the wave geometry allows the spring performance of the tolerance ring to be tuned for the application and desired performance. There are two main types of tolerance rings:
When the tolerance ring is mounted into the housing first, it’s known as a housing variable (HV). These types have waves pointing inwards.
In the free, or unassembled, state, this type of tolerance ring will have a large gap between the ends of the ring. During assembly the gap is squeezed closed, the tolerance ring is inserted into the bore then allowed to spring open, creating a force against the housing and retaining the tolerance ring.
When the tolerance ring is mounted onto the shaft first, it’s known as a shaft variable (SV). These types have waves pointing outwards.
This style of tolerance ring has closed, or overlapped ends. This means that during assembly the ring is prized open, slid over the shaft, then released, allowing the tolerance ring to spring closed and retaining it on the shaft. SV rings are usually more common when using automated assembly as the closed gap can prevent tangling during handling.
Depending upon the application, and specific requirements, the tolerance ring can be made from a number of different materials. The most widely used are;
• Carbon Steel
• Stainless Steel
The choice of material used depends on what the requirements of the tolerance rings are. Generally, if a higher force for a given size is needed, carbon steel is used.
Thermoclad material is a new, bi-metallic material that has been specially designed for improved thermal transfer through the tolerance ring. The material has a strong stainless steel core, that provides the mechanical performance, with a softer outer metal that provides improved thermal transfer. Find out more about RENCOL® Thermoclad.
Other materials, such as; Inconel® or Hastelloy® can be used if there are specific needs for things like corrosion resistance or when in conditions with strong chemicals.
For systems that act like a slip clutch then it is often necessary to use a lubricant. This can either be in the form or a separate grease, or as a coating that is applied directly to the tolerance ring as it is being manufactured. The lubrication is sometimes needed if there are many slip cycles or if the value of torque you are trying to achieve has a tight tolerance.
There are several steps to making a tolerance ring. RENCOL® Tolerance Rings are custom made so each type, each design is unique. In this 60 second explainer video we show the manufacturing process at our site in Bristol, UK.
A tolerance ring can help reduce the force level required to mount parts when compared to a press fit assembly. As the force generated by the tolerance rings is directly related to the wave features, a maximum force will be generated once the wave features are fully engaged between the mating components in the assembly. After this, the force level for the remainder of the assembly process will be stable and comparatively lower than an equivalent press fit assembly.
The spring nature of the waves also provides a more consistent assembly force across a temperature and mating component tolerance stack up range.
The spring properties of the tolerance ring waves is useful when fixing two components that are not made from the same materials. When systems are subject to thermal cycling, often the two different materials will shrink or grow at different rates, which increased or reduced the interference/gap between them. An example of this is when a steel bearing is pressed into an aluminium housing. In these cases, the tolerance ring gives a much more consistent range of forces over this temperature range because of the spring properties. It helps to create a secure retention and can prevent damage by too high load, such as Brinelling on the bearings.
For certain applications, such as bearing mount, mating component tolerances and precision requirements of the bearing housing can be relaxed. The spring properties of the tolerance ring can be tailored to facilitate achieving this, providing the option to create a cost-efficient system by using less precise parts; at least with the same level of performance.
Interested in finding out more? Contact us to speak to an engineer about how you could use a RENCOL® Tolerance Ring.