Depending upon the application, and specific performance requirements, a RENCOL® Tolerance Ring can be made from a number of different materials. The most widely used are:
Alternative options include:
The choice of material used depends on what the requirements of the tolerance rings are. Our engineers work with you to pick the base material depending on criteria such as load or torque requirements, size and handling. In some cases, there are specific requirements around NVH or thermal transfer where we will select specialist materials like Aluclad or CLD to meet those requirements.
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.
Tolerance rings are used extensively in the automotive industry and with the shift to EV the demands being placed on component parts is changing. Cost and weight reduction have risen up the priority list and created a demand for lighter weight materials. The impact of this change and the use of alternative materials has resulted in new challenges:
The RENCOL® Aluclad Tolerance Ring is a bimetallic material that has been specially developed to solve the problem of thermal transfer, an issue which has become more prominent in electric motors. The challenge for standard RENCOL® materials was to increase the thermal transfer capability of tolerance rings so they could be used more effectively to fix motor stators into housings. The result was the development of Aluclad; a bi-metallic technology combining a robust steel core, providing the mechanical performance, with a softer outer metal that provides improved thermal transfer.
The combined benefit of Aluclad with our tolerance rings can help with both the thermal management and the production of electric motors (which are fast becoming a part of everyone’s future).
Our tests have shown that our new Aluclad technology increases the thermal transfer capability of tolerance rings by up to four times. This means the gap between the best-performing thermal adhesive and a tolerance ring has closed – thanks to RENCOL® Aluclad bimetallic material.
The aluminium cladding also offers benefits with its increased coefficient of friction when compared to the more traditional stainless steel solution. As a result, higher retention forces can be achieved without excessive radial loading on the components, or where the design envelope limits the radial forces that can be achieved by the tolerance ring. An example may be a bearing mount application that requires a high retention force, where the standard approach of increasing the radial force to achieve this may excessively load the bearing resulting in reduced efficiency.
Aluclad provides the advantages of using a tolerance ring: secure retention, low cost and greener production (no carbon-intensive heating and cooling stages), combined with the benefits of a high coefficient of friction and a high-performance thermal adhesive.
Noise Vibration Harshness (NVH) is becoming a topic that is getting more and more attention. The ability to reduce vibration and therefore noise from a system is an attractive proposition that improves the perceptions of product quality. This has become especially important for electric and hybrid vehicles; previously the internal combustion engine masked noises from electronic ancillary systems but this concealment has been removed, drawing attention to the noise and vibration of other motors and electric machines.
Our RENCOL® CLD (Constrained Layer Damping) Tolerance Ring has been designed to reduce vibration amplitude at resonance. Tolerance rings are radially sprung fasteners, where the stiffness can be tuned, enabling noise reduction by isolation only. A traditional tolerance ring is manufactured from steel, a material that that has low damping and therefore cannot resolve noise challenges in all cases. The solution is a new material that is comprised of three layers: a damping membrane layer that reduces the resonance peaks that is sandwiched between two outer steel layers that provide mechanical performance and the ability to tune the stiffness of the tolerance ring.
Using a CLD material gives us control of more than the stiffness; we can now reduce the amplitude peaks and minimise the force at the problem frequency.
If you have a problem with noise in your system our team of engineers can help by identifying the amplitude peaks and design a product that can either reduce the peaks by isolating the periodically excited vibrations, move the peak outside of the operating range by changing the stiffness of the interface or a combination of both; depending on the system moving the operating condition combined with damping effects can bring the noise level across the operating range to within acceptable levels.
The RENCOL® CLD Tolerance Ring can be used in any application that has resonance; a stator mount in an electric motor was the original application that triggered the development of the CLD tolerance ring.
There are a number of reasons stainless steel is the long-established material choice for tolerance rings; it is extremely corrosion resistant, is lightweight, has excellent tensile strength yet can be easily formed at cold working, ambient temperatures with good ductility. And, because stainless steel is typically created from about 70% scrap metal, and it can be 100% recycled it’s a more sustainable choice. This blend of characteristics makes stainless steel the ideal choice from both performance and environmental perspectives.
The austenitic stainless steel alloy used to make RENCOL® Tolerance Rings retains high elasticity and high fatigue resistance after forming. United these properties create tolerance rings that can withstand significant plastic deformation under tensile stress without fracturing. Using stainless steel gives us control over: torque performance, retention force and tolerance compensation. Our engineers will gather your requirements during the design phase to develop a custom-made tolerance ring to resolve your challenges.
All RENCOL® carbon steel Tolerance Rings are formed in the material’s (soft) annealed state before it is heat treated. Forming the tolerance ring first makes it possible to add more waves to thicker material and manufacture smaller diameters. The austempering, heat treatment process, hardens the carbon steel material, converting it from its annealed state to a bainite material structure, a material known for its strength and durability, to produce tolerance rings that can withstand higher forces.
Because each RENCOL® Tolerance Ring is custom-made the performance requirements and design space determine the choice between stainless steel and carbon steel for each application. The percentage of carbon content in our carbon steel tolerance rings is 0.65-0.75%, producing a high carbon steel. This delivers tolerance rings that are hard and strong with low ductility.
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.
Coating on a RENCOL® Tolerance Ring
Interested in finding out more? Contact us to speak to an engineer about how you could use a RENCOL® Tolerance Ring.