Sintered cast grinding rolls are gaining greater prominence by cementmill maintenance operators, asthey do not require intermediate hard facing repair. On the other hand, some producers have been reverting to regular hard facing of mill tyres and table liners, as breakage and abnormal loss of profile is often observed on sintered cast grinding rolls. This can result in a substantial lossof throughput and an increase in power consumption compared to similar output of grinding media by Ni-Hard castings.
Analysis provided in this article looksat how both types of castings can be intelligently applied, by keeping in mind the basic objective of achieving maximum plant availability and rated mill capacity throughput.
Myth or fact?
Sintered cast rolls are non-weldable?
Myth. Where minimum sinter materialis still visible, a small amount of surface preparation will enable welding to be carried out which could potentially increase working life by 6000-8000h – resulting in substantial savings for the plant. A successful trial at a South African cement plant has already demonstrated such encouraging results. The alternative is to replace the sintered cast table liners.
Complete hardfacing of sintered castings is not possible?
Myth. With the use of gauging flux cored wires and air gauging, a clean surface can be almost be achieved, which is suitable for hardfacing. Therefore, a number of welded repairs can be carried out.
There is no loss of profile in sintered cast?
Myth. The regular interaction with plant
Many arguments have been put forward in terms of best practice for maintaining mill grinding components. The two main solutions are hardfacing and sintered cast grinding rolls and table liners. However, it is not always clear when a cement plant should weld or when to simply replace components. By dispelling some common maintenance assumptions, this article how both types of castings can be applied to ensure best mill availability.
Figure 1: worn-out sintered cast table lines
WELDING & REPAIR
Figure 2: repaired by welding for additional life
operation and maintenance engineers suggest that there is a loss of profile after a year or between 5000-6000 working hours. Plant personnel can be faced with a dilemma since they can neither repair the roller profile to restore optimum
grinding efficiency nor replace the rolls as they are not worn enough. In such cases, selection on the basis of loss of sinter from the contact surface, hardfacing can be considered by adapting partial gauging onsite and then repairing the castings.
DECEMBER 2013 ICR XX
WELDING & REPAIR
Best practice study
One collaborative study undertaken by a hardfacing services provider and a cement plant maintenance team found the following measures enabled best mill availabiity:
Use Ni-Hard casting primarily for slag and clinker grinding, due the higher abrasive nature of both these materials Hi carbon Ni-Hard casting are best.
The reduction in profile was found to
be gradual and can be repaired while maximum life and throughput can be achieved with very low wear of less than 1g/t.
Sinter casts are good for raw mill
and coal mill grinding components. Throughput should be monitored closely and selective hardfacing be carried out to recover grinding efficiency.
Before throwing any castings, sintered or Hi carbon cast iron, consideration should be given to the saving resources given the costs involved in making new purchases. Even casting that has been
About the authors...
Abhijit Dhodapkar has worked closely with various Indian cement plants during his tenure as managing director of UK–MNC dealing in onsite hardfacing. As chairman of his new venture, FerroClad solutions, he is working with his Chinese counterparts on new collaborations using the latest techniques to repair sinter cast grinding components for cement plants in India, Africa and Middle East.
Graham Hughes has served 27 years as workshop chief for repairing grinding components. He is now general manager of Chinese Flux Cored Wire Manufacturing and Services Company, Beijing, Open Arc Welding Alloys.
Sinter casts are good
for raw mill and coal mill grinding components. However, throughput should be monitored closely and selective hardfacing can be carried out to recover grinding efficiency.
worn out up to 45mm on radius can be hardfaced with a close study of the best profile during the lifecycle of the casting. ? Losses in power consumption during and after the loss of the roll profile
need to be monitored closely so that
an informed decision can be made
and backed by efficient data collection management.
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