It is IST’s experience that selection of the material from which a spring is to be designed is usually accomplished by the end user of the spring. The
made from 302 stainless steel. Both companies are happy that their springs are reliable, and have the philosophy that if it isn’t broken, don’t fix it. Their
selection is usually based upon the designer’s knowledge of springs that have worked satisfactorily in the past. Hence one end user will have experience of CrV steel working well and will tend to design all future springs in this material. Another very similar end user will have experience of 302 stainless steel working sat-isfactorily, and so will base all their designs on this material grade.
This then leads to company A, a manufacturer of pneumatic valves, say, having all their springs made from CrV, perhaps with Typical pages from the new Spring Material Selection CD-ROM. asks for a price reduction.
springmaker will take a similar view: Each grade of spring steel is readily available and works well for their respective companies, so why should a cheaper alternative be offered to either?
Then company B asks for a year-on-year price reduction with no loss of quality or reliability. The springmaker will have confidence in offering the cheaper CrV as a substitute for the stainless steel, and the spring should work OK.
However, company A also
Dacromet coating when corrosion protection is required; and their main competitor, company B, having all their springs
Will drawn carbon steel or music wire function well enough, and will company A accept this new material as a viable means to achieve its ends? The customer probably won’t pay for the testing to prove whether or not the new material is satisfactory. To provide all the data to persuade company A that the new material will do the job, the spring manufacturer might produce CAD printouts for all of Company A’s springs in the new material. Still, company A will be uncertain about the relative merits of the reliable material they are used to and the new material that they are being offered.
To provide a comparison of spring materials properties, the European Spring Federation commissioned IST to develop a Spring Material Selector CD ROM, and this has very recently been completed.
The Spring Material Selector CD ROM contains information about all the international specifications for spring wire and strip materials from Europe, the
U.S. and Japan, including many obsolete specifica-tions as well as some proprietary grades. It enables the opportunity to directly compare the chemical analysis and tensile strength of a particular wire size. It also has indicative data about the fatigue, relaxation and corrosion performance of each spring material. Finally, the CD contains information about many of the major international suppliers of each grade of spring material.
The moral of this Cautionary Tale is that compression spring material and other materials may not be selected by the most informed person in the supply chain, and this may lead to the use of non-optimum materials. Now, for the first time, there exists an authoritative and independent tool that spring manufacturers may use to help their customers to select the best material for their springs.
The Spring Material Selector CD ROM will be featured on IST’s stand 17A24 at wire 2006 in Düsseldorf, and can be viewed on IST’s Web site, www.ist.org.uk
Mark Hayes is the Senior Metallurgist at the Institute of Spring Technology (IST) in Sheffield, England. Hayes manages IST’s spring failure analysis service, and all met¬allurgical aspects of advice given by the Institute. He also gives the majority of the spring training courses that IST offers glob¬ally. Readers are encouraged to contact him with comments about this Cautionary Tale, and with suggested subjects for future installments, by phone at (011) 44 114 252 7984 (direct dial), fax at (011) 44 114 2527997 or e-mail at email@example.com.