What Does It Mean When Metal, Glass, And Other Materials Are Annealed?

If you’ve ever had to buy spring washers for mechanical equipment or an annealed glass shower door or cabinet panel, you may wonder what that qualifier actually means. If steel, glass, or other material is annealed, it has undergone a special treatment that changes its properties at a fundamental level. For some applications, annealed materials can be very favorable, but in others, it may be a disadvantage. For information to help you make the right choice of material or product, read on.


What Is Annealing?

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Annealing is a process that mostly pertains to metallurgy. In simple terms, it is a specific heat treatment that’s combined with a carefully controlled cooling process. When a material is annealed, it has been heated to a certain temperature that alters atomic structure. This is known as its recrystallization temperature. Once the material is heated to this point, its rigidity and strength are usually reduced.

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The next stage of annealing is the cooling process. Typically, this is a very slow, controlled process in which the temperature of the material gradually decreases at a consistent rate. This means that the air must be still to prevent any significant temperature fluctuations. Alternatively, annealing may also be completed through a process known as quenching, which rapidly reduces its temperature. Quenching is usually necessary when annealing silver and copper-based alloys.   

Once the material has thoroughly cooled, this may be sufficient for altering its properties, but often additional hot working or cold working may be performed to further modify the restructuring of its atoms. As this happens, tensile strength can be altered and further ductility can be introduced on a molecular level.

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The result of annealing is usually a material that can bend and flex on impact and return to shape. For an example of the difference between an annealed and non-annealed part, simply compare steel flat washers with Belleville, wave spring washers or annealed spring steel washers. The washer made from standard steel will provide a sturdy and inflexible surface that supports connections between fasteners. Conversely, spring washer manufacturers use annealed steel to stamp washers that bend and deflect force. These devices can be compressed and then return to shape once the force is relaxed.

What Are Annealed Materials Used For?

The most commonly annealed materials are metal and glass. Annealed metals include steel, copper, bronze, cast iron, and aluminum. The annealing process for each of these metals will vary, but the result is typically enhanced flexibility or ductility and reduced rigidity. Annealed metals are used to create flexible parts like wire, springs, shells and housing, pipes, jewelry, and a range of other components and products.

Glass is another material that can be annealed for improved ductility. Annealed glass is applied to fixtures and furnishings that may be subject to stress or impacts that would cause untreated glass to crack or shatter. Annealed glass is used to create shower doors and glass panels that are applied to doors, cabinets, tabletops, and other furniture. Annealed glass is also used on sporting equipment, display cases, and various decorative elements. This type of glass is commonly confused with tempered glass, but tempering glass creates a material that is significantly harder than untreated glass.

When Should Annealed Products Be Used?

Anytime flexibility, deflection, or workability is desired for the manufacturing process or in a finished product, annealed materials are favorable. Since annealing is an additional treatment, these materials can be somewhat more expensive than non-annealed versions, but the trade-off is better resistance in certain applications.

If more rigidity or hardness is needed in an application, then annealed materials should be avoided. Other treatments, such as tempering, can be used to enhance the strength of materials without adding ductility or affecting resistance or rigidity.

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