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Colour variations in materials

TFC Ltd News and PR from TFC Ltd - Published 06 December 2018 Smalley retaining rings and wave springs can be manufactured in many different types of alloys. Each of these materials has specific properties which make them appropriate for use.
Common alloys used include:

Carbon steel
Stainless Steel (302, 316, 17-7)
A-286
Inconel (X-750, 718, 625, etc.)
Elgiloy®
MP35N®
Beryllium Copper

Operating environment must be considered when choosing materials; because temperature, atmosphere, and presence of contaminants will heavily influence material choice. In order to ensure that our parts function properly when operating in these different environments, a number of processes are often used.

Post-Production Procedures
Heat treatment is a process that enhances the material properties of the metal, such as tensile strength and/or hardness. Open air heat treatment is the standard practice at Smalley, and in this type of heat treatment, there is no special control to the atmosphere. This may cause heat scale to form, which can alter the colour of the metal. Atmosphere controlled heat treats may be used in some cases that reduce the colour variation after heat treat.

Stress relieving is a heating process that removes internal stresses created by the coiling process. Without stress relief, the diameter of the part can open up, which is not detrimental for internal rings which cling on the outside diameter, but for external rings, it is problematic since it could reduce the cling.

Passivation is performed on stainless steels using an acid based solution to dissolve or loosen iron particles and other substances that are embedded on the surface of the material. This allows for the formation of a better oxide layer to enhance the corrosion resistance of stainless steels.

Colour Change
All of these methods can cause a colour change in metals. Colour variations are strongly influenced by the environment, temperature, and length of time exposed to these temperatures. Below are some typical colour variations:

17-7 stainless: blue, brown, or grey
A-286: blue or grey
Carbon steel: blue, black, or grey
Steel is commonly thought of as silver or grey in colour, so it can come as a shock when steel rings or springs arrive in a different colour. These colour changes do not have an effect on the fit, form, or function of the parts. These changes are a side-effect from improving the properties of the material to make them more effective in the application.

What to do about colour variation in materials
The most important thing to remember is, once again, that these colour changes will not affect your part in any way relating to its performance. TFC always works with you to get you the exact part you need, so from the start of the design process, we will urge you to consider exactly what is important for your ring or spring. If a part is visible and the colour is critical to your application’s needs, we offer a number of different solutions like vacuum heat treatment, passivation, special finish, polishing or plating. It is important to consider the added time and cost of adding these supplementary manufacturing processes, though; if the part cannot be seen, it is likely to be an unnecessary expenditure.

You can learn more about our material selection by downloading our Material Selection Guide or contact us on our website. TFC’s Expert Engineers are also available to discuss your design’s most critical components with you. Contact our technical team for more information.
TFC's Smalley Spirolox Retaining Rings - Colour variation in materials

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