Color Variations in Metals

China Wave Spring 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(R)
• MP35N(R)
• 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 treating, there is no special control to the atmosphere. This may cause heat scale to form, which can alter the color of the metal. Atmosphere controlled heat treats may be used in some cases that reduce the color 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 that 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.

Color Change

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

• 17-7 stainless: blue, brown, or gray
• A-286: blue or gray
• Carbon steel: blue, black, or gray

Steel is commonly thought of as silver or gray in color, so it can come as a shock when steel rings or springs arrive in a different color. These color 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 Color Variation in Materials

The most important thing to remember is, once again, that these color changes will not affect your part in any way relating to its performance. China Wave Spring 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 color 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, our manufacturing process, or contact us at our website. Smalley’s Expert Engineers are also available to discuss your design’s most critical components with you.