October 23rd, 2020
Effective thermal transfer is essential within an electric motor if you want it to have a long and reliable working life. However, motors are having to work harder, more efficiently and in tougher conditions – and our team at Saint-Gobain has spotted a problem with thermal transfer. Standard tolerance rings are simply not optimised for the thermal transfer levels required.
To overcome this, we have developed a brand-new, bimetallic technology, combining a robust steel core with a softer, thermally conductive material.
Our tests have shown that our new RENCOL® Aluclad technology increases the thermal transfer capability of tolerance rings – up to four times.
How can these new Aluclad rings make such a difference? Firstly, we need to rethink how thermal transfer works in practice.
Over the years, tolerance rings have been engineered from a variety of different materials, in an attempt to improve the thermal transfer properties. High-strength beryllium copper, for example, has been a popular choice.
However, choosing a material based on conductivity alone doesn’t actually help a great deal. We carried out trials at Saint-Gobain. We used stainless steel as the benchmark, going up to aluminium, which has 12x the conductivity of the steel. The results showed that even when we tested highly conductive materials like aluminium, the thermal conductance of the system was only increased by 30%.
Figure 2: Single material tolerance rings have limited impact on the heat transfer coefficient.
So, a single material approach will never get to a step change in thermal performance. The technology behind Aluclad is based on our discovery that the body conductance is only one part of the thermal transfer mechanics: the other part lies in the joint.
Because the tolerance ring joins two other components, the interaction between these other parts is also critical in allowing heat to pass through. This is “joint conductance”.
How does a bimetallic material improve thermal transfer? Joint conductance is a function of the overall area that is in contact, and if there are microscopic gaps, this leads to the illusion that there is more contact than is actually present. The result – the joint conductance is reduced.
To improve this, you have two choices: increase the pressure at the contact or reduce the hardness of the material. Unfortunately, with traditional tolerance rings, if you reduce the hardness, you also further reduce the pressure.
By designing a bimetallic tolerance ring, we have provided the perfect solution.
The steel core of Aluclad provides the pressure (plus the mechanical performance of the ring, such as load capability). The soft cladding provides the low-hardness and high-conducting interface at the joint.
This combination of materials increases the thermal transfer by up to four times (compared with standard, single-material tolerance rings). Contact conductance, rather than just thermal conductance, is the answer for improved thermal transfer.
Figure 3: RENCOL® Aluclad material significantly improves the thermal transfer capabilities of tolerance rings.
Our internal tests show that the gap between the best-performing thermal adhesive and a tolerance ring has closed – thanks to RENCOL® Aluclad bimetallic material.
You get 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-performance thermal adhesive.
By simply switching to a bimetallic tolerance ring, you can improve the performance and life of the motor. To find out more about RENCOL® Aluclad, please contact us at Saint-Gobain.
For a more in-depth look at RENCOL® Aluclad, its applications and our research, please read our Aluclad white paper.