FEATURE SPRINGS & SHOCK ABSORBERS The right solution for medical applications
In an exclusive interview with Design Solutions, Simon Ward, technical manager at TFC, discusses wave springs, their benefits and how they can be used in medical applications
What are the benefits of wave springs compared with coil springs? The main advantage is that they produce the same spring force as traditional coil springs but at a reduced operating height. This reduces the spring cavity, creating a smaller, more lightweight assembly, that is helpful in applications with tight space constraints.
What types of wave springs are suitable for medical applications? Crest-to-Crest is a good alternative to traditional coil springs for medical applications that require lower spring rates. Single- turn wave springs also provide a precise and dependable solution when the application involves short deflections and low-medium forces. Finally, linear springs are also suitable when a straight load bearing system is required.
Do wave springs provide the same functionality as coil springs? The short answer is yes because both apply force axially when compressed. Like a coil spring, the wave spring starts at a free height and, when load is applied, is compressed to the working height where the spring is required to operate. The main difference that designers need to be aware of is that, as load is applied, the waves on a wave spring begin to flatten to provide upward force. However, coil springs twist as they compress, so not all the force is necessarily aligned with the axis.
Why should designers use wave springs for medical applications and what do they need to know before including them? As mentioned earlier, one of the major benefits of wave springs is that they save space — up to 50%. While they generally provide similar forces and loads as traditional springs, wave springs achieve this at around half the height. The knock-on effect is that they can be used in the more compact designs that are often found in medical settings. A smaller spring cavity also creates a lightweight
assembly, saving production time and material costs. It is always important to consider size and material requirements of your
application before specifying the wave spring. While we have an extensive range of standard parts available, we can design a custom wave spring if you have any specific size or material requirements.
What types of medical applications are wave springs used for? In medical settings, handheld instruments and tools, for example, need to be compact, lightweight and balanced. They also have precise loading characteristics – and this makes wave springs an ideal choice. For example, we have designed Crest-to-Crest springs for insulin
pens that help control and measure the dosage that is injected into the patient. Another example is surgical and dental tools that use precision bearings to operate at high speed. To help optimise bearing life in dental tools, we have specified single turn wave springs to compensate for manufacturing tolerances. In addition, Crest-to-Crest springs can also be used in medical lighting products.
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What materials can designers choose for their wave springs? The most common materials used on wave springs for medical applications are 302 and 316 stainless steel. These can withstand temperatures of up to 200˚C, as seen during cleaning and sterilisation processes, without compromising spring properties. These springs are all ISO 13485:2016 certified, therefore complying with a Quality Systems Standard specific to medical device manufacturers.
What other industries could use wave springs? There are an infinite number of applications where designers can use wave springs. They are being applied in aerospace, automotive and oil and gas settings. For example, both Single-Turn and Overlap wave springs can be used to assemble electrical connectors in the aerospace industry. Crest-to-Crest springs can also be used to control linear displacement in flow valves. The applications are endless! For applications outside of the medical industry, there is an even wider
range of alloys to choose from. Standard materials for general purpose include carbon and stainless steel. However, we offer special alloys such as Inconel and Elgiloy for more extreme environments. Many of these can be used in cryogenic and high temperature environments as well as highly corrosive settings. Our team of engineers can help you choose the right material for your application.
Unit 1, Latimer Road Industrial Estate
Latimer Road, Wokingham Berkshire RG41 2YD Email
sales@simpsonsprings.co.uk
Tel: 0118 978 6573 Fax: 0118 989 4434
www.simpsonsprings.co.uk
8 JULY/AUGUST 2020 | DESIGN SOLUTIONS
How are wave springs helping in the fight against Covid-19? Wave springs can be used in respiratory devices that help treat patients with more advanced symptoms. For instance, the tighter radial and axial space made them ideal for electrical connectors in ventilators. We’re always happy to advise design engineers on how wave springs can be used in devices like these.
TFC
www.tfc.eu.com
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