Solution Annealing – Process, Stages & Furnaces

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Annealing is one of the most common processes in manufacturing. It is used to change the properties of a product, using heat to make it more malleable. Solution annealing furnace suppliers build ovens that facilitate the annealing process in a controlled environment. The control provided by the oven allows for better control of the process, including quality control. As a vital manufacturing process, annealing ovens are used in a range of industries.

The annealing process

Annealing is a process where heat is used to alter the physical or chemical properties of a material. The purpose of the treatment is usually to make it more malleable. This is achieved by reducing the hardness and increasing the ductility of the material. To achieve this, we have to heat the material above its recrystallisation temperature and then hold it there for certain duration before cooling it down. This is followed by recrystallisation.

The heat treatment changes the crystal lattice of an object with atoms migrating within the structure. This changes its hardness and ductility. This is followed by the cooling period when the recrystallisation occurs. The material properties of some products, such as composition and the grain size depend on the rates of heating and cooling. Since the material properties change, we may need a secondary application of heat to achieve the desired results. The heat may be applied for varied stages of hardness, since every stage has unique properties and malleability.

Stages of annealing

The solution annealing furnace suppliersequipment has three stages in the annealing process — recovery > recrystallisation > grain growth.

Recovery

The recovery is the stage where the material is softened. This is achieved by removing linear defects. This removes the internal stress in the object. But it must be completed before the strain free grains appear. It is conducted in the lowest temperature setting in the entire annealing process. This stage has no effect on the grain size and shape.

Recrystallisation

The strain free grains have appeared by this stage. At this stage the grains grow and replace the grain displaced by the removal of internal stress. The third stage is optional, allowed if we want grain growth to take place. The substance again starts to change. Sometimes hardness can weaken with continued annealing. We have to harden the substance to retain its usage.

Annealing furnaces

Needless to say, we need very controlled environment for the entire process to take place. One of the challenges in annealing is the oxidation of the surface. To avoid this, we have to use special conditions, such as presence of endothermic gas and forming gas. An annealing oven is the ideal solution.

Solution annealing furnace suppliers use the same process of annealing in a furnace. The furnace is an ideal place to carry out the annealing process. We can take the product to a desired temperature quickly and then hold it for as long as we want. Annealing ovens are typically large in size. It must be at least big enough to hold the product in place and move it. Post the annealing process, some products are left in the oven to cool down gradually, while some are taken out for ‘quenching’. This can be accomplished by oil, salt, air or water. Salt is used in the form of brine. It is better than water for cooling purposes.

Most ovens are made of aluminium and stainless steel. Since annealing is carried out in very high temperatures, the metal used to construct the oven must be able to withstand high heat. It should also accommodate temperature fluctuations — high heat and then rapid cooling, apart from other weathering effects.

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