Cement, Energy and Environment

regenerated since 1998 with VAUTID. In 2004, VAUTID won a 5-year contract with a large cement producer in South America, promising to lengthen the part replacement cycle by 30 per cent and thereby increase profit. This increase in the service life was achieved by applying the technology of hardfacing for protection against wear. The experience with the VAUTID products was so positive that the contract was extended to 2015. The service life achieved with VAUTID products was increased once again in 2008 by optimizing the hardfacing material. The company has shown that hardfacing is feasible up to 152 mm. This is how part replacement cycles can be lengthened and operator costs reduced. The experience gained by regenerating the grinding rolls and grinding discs was utilized in a further project in 2007. At this time, segments of a grinding disc were coated with the material VAUTID W73 and then welded with a hardfacing combination of VAUTID 100 and VAUTID 143. This combination enables a long service life through the use of hardfacing materials and provides an extra margin for wear in the cast part for continuing production in case the grinding elements cannot be replaced as planned. Applications in beater mills The beater mill material is accelerated at high speeds up to 70 m/sec and then thrown against an impact surface. During this process, blow bars made of chilled chrome casting and hammers made of bi-metal castings are used. Bi-metal hammers are tools with an underlying steel surface that connects the working surface made of chilled chrome casting. This combination of materials has connector elements on the steel surface that can be machined mechanically and used to connect other system components through joint welding. The chilled casting side of these components is also very resistant to wear. By using bi-metal hammers instead of hard manganese steel, the service life of the respective components in the South America cement plants could be increased from 6 to 46 weeks. This resulted in significant savings (with regard to maintenance and repair costs), a minimization of the downtimes and a consequent increase in productivity based on longer machine operating times. Beater mills used for grinding coal are protected against wear with partial hardfacing on the impact plates and selective hardfacing of bio– metal plates. The first third of the impact plate was targeted for regeneration with VAUTID 100 Mo, since this is the area of the plate that is subject to the most wear. This provided a more cost efficient solution than the replacement of the entire impact plate. Furthermore, the use of the VAUTI 0 material leads to a significant increase in the tool– service-life when compared to all of the other alternate products that were tested. Summary When abrasive materials are transported or stored, wear occurs primarily on the edges, e.g. exit and transfer points. In most cases, partial protection against wear through the hardfacing of these positions is sufficient to equally extend the service life of the rest of the equipment. The spiral crown of the screw is subject to extreme wear through abrasion and necessitates the partial or full surface protection of the screw against wear. This can be accomplished with hardfacing or by attaching cast parts made of bi-metal for screws with oversize diameters. Grinding rollers and grinding discs can be regenerated repeatedly with hardfacing. The welding can take place on the component while installed (in-situ) or after removal. An emergency reserve layer still exists on the wear resistant base material after the protective surface is worn down when chilled chrome casting is used as a backing material. By using such hammers, made of bi-metal instead of hard manganese, the service life was substantially increased for applications in beater mills. Impact plates in coal mills could be regenerated with partial hardfacing, thereby increase service life in comparison to the solutions that were originally used. Protecting components against wear in cement plants is one of the main maintenance topics and the proper applications of these protective measures plays an important role in controlling maintenance costs. In order to develop an appropriate measure of protection, each individual application must be analysed separately depending on the occurrence of the wear. Casting and welding methods offer a wide range of solutions for reducing expenses associated with maintenance issues. Courtesy: World Cement, January 2010, Pp59-62. ----- 1 RY i ~ '"CIAT:·.·· I \ \ 17