Welding:

Once the sheets are bent they are welded together to form cylindrical shape for this purpose carbon arc welding is used. It is the process in which a pure graphite rod of 4 to 19mm diameter and 300 to 400mm length. Non-consumable electrode is used to create an arc between it and work piece by holding it in electrode holder with an electrode extension of 15 to 125mm welding can be done with or without the addition of filler material. The arc which is called carbon arc is a soft arc and is usually of 25 to 40mm length, the temperature of the weld pool can be easily controlled by varying the arc length.

First the curved sheets are welded together to form the base of tank than one sheet with small curvature is welded over the two sheets and are welded with flat sheets to form another cylindrical tank on the outer periphery of the tank. Small pieces of plates are longitudinally welded such that they are at right angles to the surface of cylinder. On open side of the plates another curved sheet is welded such that it creates a hollow space between the inner and outer surface, thickness of this hollow space is equal to length of metal plates provided to fill insulating material of low thermal conductivity such as glass wool.

The cylinder is then tested for leakage with the help of UV light. The space between the cylindrical tank is filled with insulating material, in case of powder it is important that material is only filled in such a way that air gap between the material is maintained otherwise thermal conductivity will change. The insulating material should not contain any moisture. After this tank is painted from outside and a non-sticky coating is provided inside. The tank is mounted on the wheelbase and connected with necessary pipings.