HIGH chrome white irons (HCWI) are renowned in mining ore processing plants for their hard-wearing, abrasion-resistant qualities. They have proven ideal for highly durable mill liners and for protecting ore-chutes.
Johannesburg-based Mitak is one of the largest dedicated HCWI foundries globally. “Mitak was established in 1973 and, over the years, we have developed a great understanding of the HCWI alloy range. This has laid the foundation for our competence and capability,” said Graham Anderson, Business Development Director of Mitak.
In mining, two of the harshest applications for cast components are in mill linings and in ore-handling chute linings. Both are typically subject to extreme levels of erosive, corrosive and gouging wear. Over the decades, Mitak has developed a range of what it describes as singularly effective HCWI alloys suited to these conditions.
To enhance wear resistance, castings are all through-hardened with their final hardness being from 550BHN to in excess of 713BHN, depending on the application.
The company specialises in abrasion-resistant solutions and possesses extensive knowledge in the area of corrosion retardation. Mitak manufactures liners for use in wet or dry milling applications, for ball, rod and fully autogenous grinding (FAG) mills.
“Over the past 45 years, we have manufactured nearly 500 sets of mill liners and, in the process, built up a vast reservoir of expertise about a wide range of comminution and materials handling applications and enabled the development of specialised alloys that meet world-class mill liner standards,” Anderson said.
Employing more than 500 people, Mitak currently casts more than 850 tons a month, with the capacity to cast up to 1,000 tons a month. It is one of the few foundries in the world that can cast HCWI castings weighing up to 18 tons finished mass.
“A major advantage offered by Mitak is that we are a ‘one-stop’ supplier. The entire manufacturing process, from pattern-making, casting, machining, heat treatment and inspection, is carried out at the Alrode site. This allows for stringent quality control at every step of the process,” he said.
These manufacturing processes are supported by Mitak’s metallurgical and application knowledge.
“At Mitak, we have the ability to reverse-engineer existing liners with the use of the latest laser and optical equipment. The company can then render the liners as solid models and supply full digital assemblies of the mill,” he added.
More cutting-edge technology assists Mitak in the manufacture of the patterns and the company has invested in one of the country’s largest CNC-controlled, 5-axis pattern millers which ensures the pattern exactly matches the solid model from which it is derived. Mitak also has the capability to manufacture patterns with great accuracy using additive printing processes.
“We further employ some of the latest advancements in moulding and heat treatment to manufacture the cast components, which ensures the correct level of quality and that the casting concerned mates accurately with existing components,” Anderson said.
Finally, Mitak uses the latest digital technology to check the parts after they are cast.
The development team also conducts ongoing research into new applications for HCWI; as well as new techniques to improve the wear-resistance and mechanical strength of the liners it produces.
“Our success as a supplier of mill liners is based primarily on our ability to fully understand our customers’ needs and to work cooperatively to provide optimal solutions. Our primary focus at Mitak is to improve wear life and thereby ensure better grinding performance for longer and, ultimately, a lower cost-per-ton milled.”
Some 75% of Mitak’s castings are currently exported, principally to Europe mostly through the major OEMs of process equipment. Anderson said many of the company’s components are frequently exported back to South Africa to be put into service in mines in Africa as part of completed OEM equipment.