Measurement of Defects in Rolls used by Steel Industries

• Non Destructive Testing. Non destructive testing is very important when the prime importance is given to not to affect the physical or chemical properties of the product. Although production rate is reduced slightly but then the rejection of the material or product by the customer is reduced tremendously. As said "Prevention is better than Cure", the same rule applies in case of NDT. Mostly used by steel industry , but has variety of uses in other industries as well.

• Non Destructive Testing Equipments, X Ray Machines, Hardness Testers, Thickness Gauges, X Ray Accessories .

• In the hot and cold mills of the Steel and aluminium industries , several types of Rolls are applied .thes rolls are often used under extreme cicumstances, the mechanical stress on the rolls is very high. As a result of these circumstances, defects may occur on both surface and inside of the roll. These defects are very minute and often cannot be found out by human inspection . These can only be found out by means of Non Destructive Testing(NDT).

• Defects on the roll surface ,like cracks ,may cause unwanted markings on the product and may grow ,which may lead to spalling or even to complete roll failure. Not only the roll gets damaged beyond repair but it also leads to production loss and damage to the rest of the mill. Small internal problems do not necessarily create a problem but they often grow , with the same harmful results. It is important to discover these defects at an early stage , to track their possible growth and to test them against approve/reject criteria.

• The wear of roll surface is ground off at set times by means of special grinding machines . based on experience or on the instructions supplied by the manufacturer , a certain amount of material is ground off. Final inspection of the surface is often done visibly. The majority of the rolls are usually not checked for internal defects because mostly one has to resort to time consuming manual ultrasonic measuring techniques . The more special , more expensive back up rolls are often, although manually but none the less scanned.

• To simply and quickly measure the condition of most rolls automatically ,a combination of two NDT techniques are used. Cracks and local structure changes or bruises on the surface of the roll are traced with the eddy current measuring technique . By means of ultrasound technique internal defects in the roll can be traced.