- Time of issue:2020-07-10
(Summary description)Reasonable roll maintenance not merely ensure rolls to be recovery from fatigue caused by long time service，but also can significantly reduce roll consumption.
- Time of issue:2020-07-10
Reasonable roll maintenance not merely ensure rolls to be recovery from fatigue caused by long time service，but also can significantly reduce roll consumption.
1. Make a record of roll history
Make a record of roll history . Content includes : roll diameter before and after mill service; time of in and off the mill ; amount of product for each campaign (tonnage or kilometers); stock remove for each grinding ; the inspection results after grinding; reason of roll change; measures and results of disposal in case ofroll accidents; etc.
2. Reasonable grinding specifications
Roll grinding should be done after roll suface temperature cooling down to ambient temperature; And after grinding, rolls need to be placed for certain period to eliminate grinding stress . These factors require steel mills to set up reasonable campaign period and quantity of standby rolls. The campaign length will need to be balanced with the grinding practice to ensure optimum performance. Including grinding wheel selection, feed amount, grinding amount and coolant control, to prevent grinding burn.
3. disposal meas ures of accident rolls
When accidents or abnormalities in the rlling process occur, such as strip welding, cobbles, slip, strip broken, overload and so on, the damaged layer must be removed from the roll barrel and confirmed by eddy current and ultrasonic detection. Then test hardness of the damaged area, if the hardness is almost the same with the normal condition, the roll is acceptable for mill service; Otherwise, should grind more stock off and retest.
Remark: Above is the empirical data. The specific sizes of damaged layer shall be determined by nondestructive detection and grinding.
4.Hardness test ofbackup roll
Test the hardness across the length of the backup roll barrel after grinding. If the average hardness exceeds 3 HSc (15 HLe) points above the predicted hardness, then grind more stock off of the barrel and retest. If the average hardness is within 3 HSc (15 HLe) points of the predicted hardness, then the roll is aceptable for mill service. The purpose for grinding the roll until the sur face hardness is less than 3 HSc above the predicted hardness is to ensure that the majority of work hardening that was induced during mill service is removed. Ensure that all repairs to back-up rolls result in complete removal of all cracking and spalling. All repairs should be performned using the crteria given above in the Repair Procedure section.
5.Reasonable edge chanfering of roll
When rolls are ground and loaded into the mill the stress distribution at the point of contact between the back-up roll and work roll is uniform. However as the campaign progresses the barrel profle of back-up rolls change as a result of wear quickly at the barrel centre positions. This change in profile results in an increase in contact stress at the barel edges. Ensure adquate edge relief/chamfering is applied to back up rolls to alleviate localized contact stress, to prevent backup roll shoulder break / spalling and work roll spalling at the contact area of the barrel edge
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