2. The Kettle
The kettle holds the liquid molten zinc used for general galvanizing of steel articles conforming to the valid standards (BS 729 or CEN 262). The kettles are made from special steel plates, normally 50 rom thick and when in operation are heated in special furnaces. The inside surface of the kettle due to the chemical reaction between zinc and steel is attacked by the zinc causing wear to this surface.
The demand put to a kettle is on of a long life at a high production rate. A kettle failure results in high costs mainly because of the loss of production, loss of zinc, costs of repair and new investment. Today these requirements can be fulfilled by the use of suitable kettle materials with an appropriate steel th ckness, the use of suitable construction and fabrication techniques adapted to the use of the kettle as well as carefully designed heating systems. During the heating up phase it is necessary to keep to the prescribed temperature to minimise the stresses in the steel of the kettle. In the last 30 years the demand for a longer kettle life has resulted in a kettle which can be used at high production rates without trouble until it needs to be replaced to at the end of its service life. The materia1 used, the construction and the manufacture of the kettle are all of equal importance.
2.1 Kettle•material
For a long kettle life it is necessary to slow down the reaction between the steel and the liquid zinc to a minimum. Therefore only steel with a low carbon and silicon content can be used. All other alloying elements must also be low. Segrations (doublings) in the steel are not allowed.
2.2 Kettle construction (Practical hints) Kettle Wall Thickness
- Common (approved) steel thickness: 50 mm
- Other thicknesses: 30 to 40 mm (only for small and shallow kettles}
For higher production rates (for instance coil or wire galvanizing kettles) thicker kettle walls may be needed oi walls which have been made thicker by weld cladding
- Thickness of the kettle flange is normally the same as the
thickness of the kettle wall •