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WEAR PARTS

I Wear-proofing performance

by Castolin Eutectic SA, Switzerland

F

riction, abrasion, erosion, cavitation and impact are the main causes of wear of key process equipment in the cement industry. The presence of chemicals in the form of corrosion and oxidation often aggravates their impact, particularly in high-temperature environments.

While improving the wear resistance in the equipment is vital for the overall performance of the cement plant, a solution that goes beyond extending lifetime is more important. The ideal solution will improve the equipment’s performance and allow it to perform as it was designed, over a longer time. This will then both increase efficiency, reduce power usage and extend the lifecycle and outage intervals. In addition to this, it is also important to find a solution that can shorten the outage time at maintenance stops.

The most effective way of improving the wear resistance of these wear parts is to apply “wear-facing” welding solutions.

This will not only protect against wear but also provide a tough, shock-resistant shield against impact that is better than hard, brittle solutions.

Component repair rather than replacement produces immediate costs savings and reduces expensive downtime waiting for part delivery. In addition, it avoids the need to operate with inefficient

Wear-facing welding solutions are an effective route to providing wear resistance in key production equipment. They will not only help to extend the lifetime of such equipment but also increase efficiency, reduce power usage and maintenance time. Castolin Eutectic explains how they can improve the performance of vertical roller mills.

Controlled preparation and welding of VRM Rollers in our dedicated CastoLab Services workshops

ICR article draft process equipment while waiting for new part delivery.

Thanks to research, field tests and highly-skilled people, Castolin Eutectic is continuously developing innovative products to support maintenance departments. One of many solutions provided by Castolin Eutectic is the vertical roller mill refurbishment.

Vertical roller mill refurbishment

Vertical roller mills (VRMs) have grown to become a dominant grinding technology in cement plants due to their high energyefficiency and excellent drying capacity.

The VRM components are, however, subjected to severe wear which can increase dramatically when high silica content is found in the raw materials or where mills are grinding slag. Even if these grinding technologies are energyefficient, wear problems are still a large part of the energy consumption in cement manufacturing and will significantly reduce On site VRM welding with dedicated mobile container at the the plant efficiency. cement plant, to ensure highest quality and performance

Wear-facing technologies Field experience together with R&D and its advanced welding wire manufacturing plant allowed Castolin Eutectic’s VRM team to develop special anti-wear products and advanced welding processes.

For instance, the new TeroMatec® wire EO 8338 (open arc wire) can provide an extra smooth surface and an extremely resistant coating. In one recent application in the Middle East, this new EO8338 wire was able to reduce wear on the rollers by 300 per cent when built up to a 40mm thickness on a four-roller system. Cement plant applications in the areas of clinker crushing, transport and grinding include fan blade leading edges, screw and deflection plates.

Another development is the first of a series of NanoAlloy™ welding consumables that provides outstanding abrasion, grinding and erosion resistance. The weld deposits are slag free, reaching 71HRC hardness and withstand repeatable thermal cycles with temperatures up to 750°C. In the cement plant, the NanoAlloys™ are ideal for protection of air guide cones or air guide plates, for example. Cement plant applications in the areas of clinker MAY 2012 ICR xx

WEAR PARTS

crushing, transport and grinding include fan blade leading edges, screw and deflection plates.

For the wear protection of large surface areas such as chutes, coal mill cones, separator discs, blades or housings, the ideal solution is a CastoDur Diamond Plate® (CDP). CDP wear plates consist of an easy-to-weld steel plate over-laid with abrasion-, erosion- or impact-resistant alloys by means of arc welding, metal fusion or plasma coating. Among Castolin Eutectic’s innovations are the patented powder fused plate, the first XuperWave® weld bead concept; PTA overlay plates with 60 per cent tungsten carbide, the first impact-resistant plates and doublesided CDP wear plates – a top solution, for example, for feeding cones inside vertical roller mills.

different VRM models for more than 20 different cement companies throughout the world. From small VRM (roller: φ1.65m and table: φ2.75m) to large ones (roller: φ3.2m and table: φ5.5m), Castolin Eutectic has achieved successful results on equipment manufactured by Polysius, Loesche and FLSmidth. Castolin is also able to wearface rolls and tables in Pfeiffer mills without any need for dismantling the parts.

As an international programme, the company’s VRM specialists are supported not only by the group's International CEMTEC industry team and R&D but also benefit from the unique TeroLink® database of Castolin Eutectic which contains more than 7600 fully-documented, approved case studies. Thanks to this unique database its VRM experts enjoy the know-how Worldwide experience and experience of thousands of wear VRM refurbishment has been performed specialists coming from all over the on over 70 units, with 80 per cent being world. The case studies include pictures, on-site repairs but also many repairs in the application descriptions and cost-saving company’s CastoLab® Services workshops. analyses.

Repairs have been made on more than 30 The experience during the past decades has proved that refurbishment For the wear protection of large surface areas such as chutes, and preventive maintenance coal mill cones, separator discs, blades or housings, Castolin on VRM and roller presses Eutectic has developed the CastoDur Diamond Plate® (CDP) will increase plant efficiency, reduce power usage, extend lifecycles and shorten maintenance stops.

With trends towards downsizing of maintenance departments and consequent outsourcing, the knowledge and innovation of external services provided to the cement plant becomes a critical choice to improve the cement plant performance.

Mexican case study The application is a special VRM repair on rolls and table in Mexico on an Atox 27.5 coal mill in a cement plant.

This particular Atox mill had the following features: • table dimension: φ275cm • size rolls: φ165cm • track width of table and rolls: 55cm • grinding performance before repair: 38-40tph • coal meal fineness required: five per cent +90µm XX ICR MAY 2012

• table speed: 33.8rpm • proportion of coal and petcoke mix: 80/20.

This mill is considered as one of the smallest, making it extremely difficult for the installation of welding equipment inside the mill as well as the supervision of the repair works. The cement plant considered dismantling the rollers and the grinding tables to refurbish the worn parts and segments in the workshop. In most cases, the plant operator does not have enough time to do this overhaul with the result of further reduced efficiency.

For these reasons, two main objectives were agreed: • to rebuild the roller and table's geometric forms to their original optimised state • to coat the wear surfaces with a special alloy to extend the service life of these new rollers and table profiles.

It is important to note that the materials from which the segments are fabricated are Ni-hard alloy castings with high hardness (up to 55 HRC) and carbon levels. This demanded particular attention to temperature control and cracking geometries so that the parts are not damaged during the welding process.

Consequently, it was necessary to analyse the composition of the cast base metal to select the right alloy and welding procedure. The analysis showed high levels of carbon and chromium. The textbook solution to preheat large castings at site is completely impracticable and special alloys and welding procedures are needed to ensure success without preheating.

With the correct welding process, neither overheating nor high dilution occurred. The entire previous weld overlay had worn away from the rollers and table so that the EO 8338 product was applied directly on the base metal.

Conclusions Before the refurbishment, the equipment was milling 38-40tph. One month after the refurbishment the unit was grinding 45-50tph at a fineness of 4.3 per cent +90µm. This represents a 25 per cent efficiency increase of the VRM after refurbishment.

Moreover, the VRM was returned to production after only 72 hours out-ofservice, dramatically saving the plant downtime. ________________________ I