SPRINGS & SHOCK ABSORBERS FEATURE
components being used in the automotive industry as the pleasing black finish offers good corrosion resistance. Shot peening, a mechanical process
that de-stresses the surface of the spring, typically uses a turbine wheel to throw steel or glass beads at the component with great force. This has the effect of welding together imperfections on the surface, reducing the likelihood of fractures due to the formation of cracks; and it significantly increases fatigue strength, extending the service length of the spring. Of course it is possible to eliminate the
HIGH TECHNOLOGY finishes spring into action
Emma Burgon, engineering director at William Hughes, looks into the benefits of applying high technology finishes to springs
T
he performance of springs can be significantly affected by corrosion, and
this can result in early fatigue failure. The surfaces therefore need to be protected against elements that could cause corrosion during their storage and use. It is important to be aware, however, that there are some finishes and plating processes that should be avoided. This is due to their effect on the fatigue life of the spring that could result in premature failure as a result of hydrogen embrittlement. Processes that can lead to this include cathodic protection, phosphating, pickling and electroplating. Processes that involve exposing the springs to temperatures in excess of 200˚C should also be avoided as they may adversely affect the characteristics of the spring. But what other reasons are there for wanting to apply a surface finish to springs? Where springs will be seen – such as in some automotive applications – they need to have ‘the right look’, so many manufacturers specify a black finish. Springs may also need to be colour coded to identify their characteristics, for example where the same style of spring needs to have different strengths for different applications. While stainless steel is a popular
choice for its corrosion resistance, manufacturing processes such as bending and machining may contaminate the surface. By passivating the surface, any free iron (exposed iron on the surface of the part) is removed, leaving a thin,
passive layer usually comprised of chromium and its oxides. Since chromium is corrosion resistant, this layer provides greater protection to the already resistant base metal. In addition, springs can be finished
with an inorganic micro layer zinc flake coating such as Delta- Tone, which provides a metallically bright silver coating with a high corrosion protection. Not only does the cured coating have great flexibility but the low stoving process means there is no risk of hydrogen embrittlement. Delta Seal is a similar finish that, when cured, provides an adhesive, thin, extremely resistant coating that is available in a range of colours. This has very good surface wetting properties, making it an ideal choice for work pieces with complicated geometry – torsion springs, for example. An alternative is the use of an
electrophoretic coating process which uses a special paint that is electrically charged and attracted to the components being painted. This process provides a very uniform deposit over components that would be hard to paint using conventional painting processes. It is popular for
High specification automatic in-house finishing includes an electrophoretic paint line
need for a finishing process completely by using wire stock that is already surface coated with copper, tin, zinc or plastic, etc. As well as this wire stock being more expensive, care has to be taken with storage and handling so as not to damage the coating, and there may also be restrictions on the maximum allowable bending radius. However, the use of ready coated wire does have applications in the automotive industry (for windscreen wiper springs, for instance) and in the electronics industry where, for example, a tin coating enables springs to be soldered.
“Springs may need to be
colour coded to identify their characteristics, for
FOR CRITICAL APPLICATIONS Certain applications – such as those found in the aerospace, medical and defence industries – require specialist cleaning and finishing processes for parts, assemblies and components to ensure that any lubricants and debris from the manufacturing process are removed. This is especially important for components being used in oxygen, hydraulic and other critical applications. These processes need to be
example where the same style of spring needs to have different strengths for different applications”
carried out under clean room conditions and, to comply with the requirements of the aerospace industry, the processes need to be carefully controlled and audited annually. Components are usually 100% inspected and
individually bagged and sealed to ensure they are protected until they are ready to be used. As the demand for springs for critical
applications has continued to grow, manufacturers have had to expand their operations to include a wide range of finishes and cleaning processes. In fact William Hughes has recently invested in a new cleanroom which is being constructed to Class 7 standards in accordance with ISO 14644-1. This will enable an extended range of cleaning services to be offered to the aerospace industry.
Emma Burgon
William Hughes T: 01963 363377
www.wmhughes.co.uk
DESIGN SOLUTIONS | DEC/JAN 2016 19
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52