Abrasive wear lining specialist, Mitak, operates one of the largest dedicated high chrome white iron (HCWI) foundry in the world. MechChem Africa visits the proudly South African company’s stand at Electra Mining Africa and talks to Graham Anderson, business development director, about its mill lining aftermarket offering.
“We have been in business for 45 years now and in all that time we have been sharply focused on the development and supply of cast high chrome white iron products for use in highly abrasive applications,” begins Anderson.
“Starting with small impactors in the asbestos industry to replace the manganese that was more commonly used, we quickly branched out into the manufacture of other wear parts suitable for HCWI. Now, grinding parts, slurry and dredge pump spares and chute linings,” are also now part of Mitak’s high-value HCWI offering,” says Anderson,
“HCWI typically contains between 17 to 28% chromium, but we tend to narrow that to between 22 and 25%, with carbon levels most commonly between 2% up to 4.5%” he explains, adding that this makes the material very hard – with Brinell hardness numbers typically above 600 BHN.
“When compared to harder ceramics, HCWI offers improved impact resistance while retaining excellent hardness from the embedded carbides. This combination makes it a surprisingly versatile material in many high-stress mining applications – including mill linings. What’s more, it offers superior wear resistance to rubber in many applications. This is particularly the case with sharp, angular ore types that tend to cut the rubber on low angles of attack,” he adds.
Most high chrome white iron can only be air quenched in order to achieve the desired hardness and the wear resistant properties of the material.
“For many years in South Africa, we have been working with Welding Alloys South Africa, a market leader in weld overlay cladding technology, to improve its lining solutions. We developed and continue to supply a base casting to them, which is suitable for welding but, because it is a high chrome substrate, should the abrasive wear penetrate through the weld overlay layers, the component’s structure is not quickly destroyed.
“While this is not new technology, it still has the potential to change the weld overlay market, because the harder and tougher substrate offers far better protection than can be achieved if cladding onto traditional steel castings,” Anderson tells MechChem Africa.
The local mill liner offering
While work hardenable manganese steel is the preferred liner material for jaw and cone crushers, and large semi-autogenous (SAG) mills in South Africa tend to be cast in CrMo steel, Anderson says that fully autogenous grinding (FAG) mills as well as rod and small ball mills are ideal candidates for the installation of HCWI replacement liners.
”Even though we have made HCWI mill liners for many years, it has not been a major focus of ours and we have not really tackled the end-user mill liner market in any major way,” Anderson continues. “In doing so now, we do not see ourselves competing with the OEMs, which are our main customers after all, but with aftermarket imports being brought into South Africa in massive volumes from China, Canada, USA, Indonesia and Malaysia,” he notes. “In the mines of Africa, CrMo liners are sometimes preferred for the fully autogenous mills. More and more operators are expected to begin taking the braver HCWI decision, though, because they have realised that a similar investment on high chrome mill linings may last at least twice as long,” he points out. Read more.
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