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Types of Damage

MAIN FAILURE (BREAKING) TYPES IN ROLLING MILL ROLLS
One of the main factors which damages rolling mu rolls is inadequate and wrong kind of cooling. If there is regional heat differentiation in the rolling mill roll, the roll gets broken or sudden heat change results in thermal stress. For this reason, cooling process should be taken into serious consideration. To minimise damages and failure, some precautions should be taken. These precauitons are listed below:

• Each rolling mill roll should be cooled separately.
• Cooling water should be neither very hot nor very cold.
• Cooling should be implemented from the part where the material goes out.
• Rather than the amount of water, it is important where and how the water is used.
•The most efficient cooling is made on the working calibre channel of the rolling mill roll and the mast heated part of the calibre channel.
• Cooling water pressure should be two-four atu in the sprinkler system.
• Water of body must be cut down on in long waiting times. Cooling process can be continued in neck rolls. Water of body is cut completely it creates thermal stress.
•Fiber linings should be cooled with the highest care.
• If any wrapping occurs, the water is cut completely and rolling mill rolls must be separated from each other quickly. Main failure and damage types and causes of those are listed above.

In the Graph 1, it is seen that breaking accus in the joint place coupling or cotter and ball bearing. The reason for this is that this joint part has not been designed properly in the design process of the rolling mill roll.
Radisus must be formed in the parts where there are diameters changes and sharp cornered transitions must be avoided. Thrugh this, stress concentration will be prevented if there is overloading.



Graph 1 : Breaking in the joint place of clouding or cotter and ball bearing 

In the Graph 2, it is seen that neck roll is broken at the bottom of the radius that is between felt spaces and ball bearing. The reasons for this problem are that if fracture surface is white, it means that diameter of the neck is not adequate and to eliminate this problem, safety ratios between neck and diameter of the roll should be in accordance with each other. On the other hand, if the fracture surface is blue, it means that breaking results from overheating and to eliminate this problem, there must be proper cooling process and implementation. 



Graph 2 : Breaking in the joint place of clouding or cotter and ball bearing 

In the Graph 3, breaking results from worn coupling or cotter. The reason for this fiacture-breaking is that passing share of coupling and cotter is too much. If any improper construction has been done during designing process or if tolerance has not been set properly or if proper coupling or cotter passing has not been done, breaking occurs.



Graph 3 :Worn coupling or cotter.

In the Graph 4, it is seen that breaking occurs in the ioint part of felt spacer and body. The reason for this is resonance tension which occurs on the rolling mill roll. To reduce this tension, al unions and inuion nuts must be tightened. Through this, breakings may be prevented.



Graph 4: Breaking occurs  in the joint part of felt spacer and body

In the Graph 5, it is seen that breaking occurs on the middle of the body part of the rolling mill roll as if it is cut by a knife. The reason for this is that the steel rolled is colder than the heat of the rolling.



Graph 5 :Breaking on the miidle of the body part of 1he rolling mill roll as if if is cut by a knife

In the Graph 6, it is seen that breaking occurs on the middle of the body part of the rolling mill roll as if it is cut by a knife (if there is any sign of local burning on the surface where there are cuts and breakings). This brea- king or fracture results from the sudden heat changes where heat differentiation is too much between the rolling mill roll and the material/product. The reason of the extreme heating in the rolling mill roll is that no proper cooling has been done or implemented. To eliminate this problem, there must be proper cooling and the amount of the cooling must be increased.



Graph 6 :Breaking on the middle of the body part of the rolling mill roll as if it is cut by a knife

In the Graph 7, cross breaking occurs on the body part of the rolling mill roll. The reason for this is that the rolling mill roll is not on the adjustment level.



Graph 7 : Cross breaking on the body part of the rolling mill roll

In the Graph 8, the reason for the breaking on the body part of the rolling mill roll as if it is cut by a knife is deep fire crack. To eliminate this problem, it is needed to shut down the cooling water when the operation of rolling stops. This kind of breaking/fracture is shown in the graph 8.



Graph 5 :Breaking on the body part of the rolling mill roll as if if is cut by a knife.