PRODUCTION AND QUALITY ASSURANCE SYSTEM
Rolls are tailor made products and therefore need careful production planning. Rolls are cast in chiller moulds with a controlled allowance for contraction and machining. It is therefore necessary to have a mould of the desired size. A new mould is required to be made if one is not available. After obtaining an order from a customer and a drawing for the required Roll, a method drawing for casting is made, according to which the mould for casting of the Rolls is made. Melting of metal is carried out in any of the several Induction melting units available and as per requirement of metal. The melting charges are selected as per the required chemistry of the metal. Upon melting, samples are analyzed and necessary adjustments for various alloying elements made through additions of Ferro-alloys. Fracture tests are made and temperature measured to control the same through Immersion Pyrometers. Metal is poured in the moulds through geared ladles of various capacities in a pre-determined time to ensure clean metal in the mould.
After casting, the mould is allowed to cool for a pre-determined period of time before removing the cast roll from the mould. Then the cast roll is examined for casting defects and dimensional deviations, before sending the same for machining.
During machining, samples are taken for examination of microstructure and machining is allowed to proceed only if the microstructure is found proper. Hardness of the Rolls is checked on the barrel surface as well as the face of barrel to check the depth of useful hardness. The machined surfaces are also examined for any surface defects like blowholes, inclusions, dross and cracks etc. Stage inspection of dimensions is carried out. A final dimensional check is carried out at the end of all machining operations. Once clearance is obtained from the Q.A. Department, Roll is finally painted with anti-corrosive paint and packed for shipping.
In order to maintain dimensional accuracy of the Rolls, all measuring instruments are periodically checked for deviations against a set of Standard Instruments duly calibrated and certified from authorized centers.
Samples are also taken out periodically from barrel of some Rolls to test the mechanical properties of Roll materials. All alloy steel rolls are ultrasonically tested for flaws and Centrifugal Cast Rolls are checked for proper bonding between the Shell and the Core by ultrasonic testing.