Company converts from electric arc furnace melting to induction furnace melting to reduce emissions to achieve environmental compliance, achieve quality improvements, reduce direct costs and enhance its safety incident awareness accordance.

For over 35 years Grinding Media South Africa has been supplying grinding media for the platinum, gold, ferrochrome, base metals, power generation and cement industries. The company’s first manufacturing plant – a high chromium ball plant – was commissioned in 1985 to meet the requirements of the cement and platinum industries, while still under the stewardship of Scaw Metals, a company within the global mining company Anglo American plc. Subsequent investments saw major technological improvements and capacity expansions at the company’s Union Junction base in Germiston, Gauteng.

Grinding Media South Africa has made a major investment in its melt shop revitalisation programme to reduce the company’s environmental impact. The company has converted from electric arc furnace melting to induction furnace melting to reduce emissions to achieve environmental compliance, achieve quality improvements, reduce direct costs and enhance its safety incident awareness accordance

High chromium media
High chromium media has been established as the accepted standard grinding media for the comminution of cement and platinum ores. Comminution is a process of reducing the size of ore particles to liberate the minerals in preparation for extraction in downstream processes, and classification is installed to ensure that liberated minerals enter the recovery section of the process plant and those not ready are recycled.

Forged steel media
Forged steel media is largely consumed by the gold, copper and base metal mining industries. The Forged Plants are situated on the Union Junction site with the feed stock being supplied from Scaw’s rolling mills.

The forged steel media plant was commissioned in December 2002 and in December 2006, Scaw expanded its forged steel media capacity by installing Africa’s first roll-former. This investment assured the mining industry of Scaw’s long-term commitment to be a world-class grinding media supplier.

Union Junction site in Germiston
The high chrome ball plant is an extensively automated foundry with three production lines producing cast, high chromium white iron balls with a chromium content range of between 10% and 32%.

The forged media ball plant has three operating lines forging round bar feedstock into forged steel balls through either an upset forging process or a roll forming process.

The equipment Grinding Media South Africa decided to purchase are three Inductotherm 8 000kW VIP Power Trak power supply and three 10-metric-ton steel frame coreless furnaces, each equipped with an air operated clam shell for slag removal, integral high-velocity close-capture fume collection covers (hoods) and lining/refractory push out systems. The Inductotherm equipment is represented in South Africa by Cerefco

Human capital development and housekeeping has been a prominent theme throughout the project. An example is shown on the new melting platform where employees are given graphic examples of where to place their tools

The company supplies grinding media predominantly into the southern, central and west African markets and across the African continent giving us deep insights into the African minerals extraction industry. Key raw materials, which include ferrous scrap, ferrochrome and round barstock, are all sourced locally with suppliers within close proximity to the plants.

The division is one of the few grinding media operations globally with the capability and intellectual property to produce both high chromium and forged grinding media, allowing the business to offer an optimal grinding media solution for the end-user.

Magotteaux becomes Strategic Equity Partner of Grinding Media South Africa
In March 2018 the Industrial Development Corporation (IDC) and Magotteaux International S.A. announced that they had reached an agreement on extending their partnership regarding Grinding Media South Africa (GMSA). The Scaw Metals Group already had a long-term relationship with Magotteaux, as the company had been manufacturing high chromium media under license from Magotteaux for over 30 years.

At the time GMSA was a newly created company that had been spun out of the Scaw Metals Group, an industrial group that the IDC had a 74% stake in. The IDC was part of an investment consortium that had acquired Scaw Metals in 2012 from Anglo American plc when Anglo American plc had decided to disinvest non-core assets.

A custom built control room has been built

Inductotherm furnace body A, one of three new furnace platforms and systems

The partnership introduced Magotteaux as a Strategic Equity Partner in GMSA and was part of the
state-owned IDC’s announcement of the restructuring of its steel subsidiary Scaw Metals into three standalone entities that are now made up of GMSA, the foundry division Cast Products South Africa, which is owned by Amsted Rail and the rolled and wire rod products division, which is owned by the Barnes Group.

Since 1985, GMSA had operated electric arc furnaces (EAF) for primary melting of metal used to manufacture heat-treated high alloy (high chrome) balls on three state-of-the-art Disa greensand moulding system lines that include laser controlled pouring devices and automatic moulding units to eliminate the usual casting defects associated with sand-cast media. Different quench and temper heat-treatment cycles are used to impart special metallurgical properties to the balls depending on the intended application, whether wear mechanisms be predominantly impact, abrasion or corrosion. Sizes from 17mm to 90mm are manufactured in various grades.

Because of increasing competition from other foundries, the need to improve its productivity and concern about excessive emissions and environmental impact, the company reviewed alternate processes for casting production. It found that one of the highest costs of producing a casting centred in the melt operations, prompting the decision to upgrade the melt shop in 2020. However, the feasibility and impact studies began long before 2020 when three 10-ton Inductotherm induction furnaces with individual 8 000kW VIP controls were installed.

Another view of the Inductotherm furnace body A

The ‘workings’ below the furnace

At the outset the mission was also to reduce operating costs by increasing the plant’s productivity and efficiency to survive in a low-margin, highly competitive market. Management believed that the solution was to take advantage of the competitiveness of induction furnace technology and other benefits that come with induction. For over 30 years the melt shop had operated electric arc furnaces for primary melting so to change to induction melting would not only bring benefits but would also present many challenges.

They knew that the new induction melting furnace equipment will aid in achieving the following goals:
• Minimise operating costs
• Maintain consistently good product quality
• Reduce environmental pollution
• Reduce noise pollution
• Produce steel under a cleaner working environment

Foundry management formed a team of employees to research, plan and propose a revitalised melt operation. The task included benchmarking the industry, identifying available technology, projecting capital requirements and identifying areas of potential return on investment. Energy demands, raw materials, refractory and environmental operating parameters all required evaluation and entered the equation for weighing different options prior to developing a final proposal for consideration.

Reducing footprint
“One of the main driving factors was to reduce our footprint on the environment by using less power and water and using them more efficiently and working smarter, such as reducing the loss of heat by adding hoods on the furnace bodies, reducing the dependence on and amount sent to the dump sites, reducing dust emissions, optimising every aspect of the operational process such as electric motors and upgrading the infrastructures and auxiliaries to better serve our purposes,” explained Martin Volkwyn, who has been Development Manager for Grinding Media South Africa since the company was established in 2018. Prior to that Volkwyn had worked at Scaw Metals for over 30 years and had a similar position whereby he would implement new projects at the company.

Each of the three furnaces has its own 8 000kW VIP Power Trak power supply

The Melt Manager system keeps track of many different aspects of the melting process

Electric arc furnace versus coreless induction furnace
“Electric arc furnace melting is an attractive option because it can melt almost anything and has low capitalisation costs, but the team didn’t feel it was the right choice for the foundry because of environmental concerns, the dust generation and the large volume of effluent it creates.”

“We were already in that situation and our brief was to improve our casting process in all departments.”

“Electric arc furnaces are the standard for steel melting and refining and are typically high capacity, forgiving furnaces that take large, dirty, and less expensive scrap and produce up to 100 tons per hour. Although electric arc furnaces are less expensive to maintain than coreless induction furnaces, in the short-term, disadvantages include greater dust volume and oxidation loss, high noise levels, ongoing electrode costs and power disturbances.”

“Induction melting uses no electrodes and are more environmentally friendly. In addition, induction furnaces, typically smaller in size, now provide greater capacity. With a growing demand for a greater environmental focus, and the increased capacity of induction furnaces, the previous gap between the two furnace types is rapidly narrowing.”

“When considering melt furnaces types, there are several factors involved, the top three of which are the rising cost of electrodes, electricity load and pollution control. You must also take into account the cost of charge materials and scrap, labour, refractories, maintenance materials, spare parts and of course waste disposal.”

“Dust collection is still necessary with induction furnaces, however, at an approximately 85% lower rate.”

“Along with a lower capital investment, reduced emissions inside and outside of the foundry and friendliness to shaky power grids, the use of induction furnaces allows for better temperature control and lower metal losses.”

A first in South Africa is this unique valve that regulates the temperature of the water passing through it and thus eliminates any shutdowns

The cooling system

“However, induction furnaces require smaller, cleaner, scrap, both of which are more expensive, and while induction furnaces are more efficient and cost-effective in the long-run, there is significant initial cost to convert from an electric arc furnace to an induction furnace.”

“There is also a significant investment in culture change and a steep learning curve for management and employees.”

Three 10 ton Inductotherm coreless induction furnaces with VIP Power Trak power supply
“The equipment we decided to purchase are three Inductotherm 8 000kW VIP Power Trak power supply and three 10-metric-ton steel frame coreless furnaces, each equipped with an air operated clam shell for slag removal, integral high-velocity close-capture fume collection covers (hoods) and lining/refractory push out systems. The entire package of equipment is cooled with a totally closed, zero make up water system.”

“Due to a need for continued production, construction occurred over phases. Included in the installation of the coreless furnaces and its support equipment (ladle cars to move transfer ladles in toward the furnace for tapping, the charge pan, alloy batching system and dust collector) is an area dedicated to the melt area.”

“Each of the three furnaces has its own transformer and custom built charge conveyor car, designed and manufactured by Kwatani, that is capable of holding the entire charge burden. Each charge conveyor sits atop an integral weight frame built into the melt deck that provides charge crane operators feedback as the conveyor is filled. A newly designed alloy addition system allows alloy batching from pre-programmed recipes for bath chemistries and temperatures.”

“The new furnaces use a computerised control system for overall melt furnace management. This system is managed from a central elevated control room with line of sight monitoring of each furnace. Remote control stations adjacent to each furnace provide full local control for furnace operators on the melt deck.”

“The power setup is a 33kV/60Hz, 24 pulse rectifier system which research has shown is the best for our situation.”

Inductotherm is represented by Cerefco in South Africa.

Saveway measuring system: Continuous measurement of remaining lining thickness
“We have also invested in the Saveway continuous measurement system and already in the short time that it has been operating we have had two ‘saves’.”

“The Saveway system allows the continuous measurement of remaining lining thickness during furnace operation. It is the only technology used in security monitoring, which measures the actual remaining lining thickness. In addition to visible signs of wear, such as erosion and worn-out areas, covered wear conditions are detected reliably, like dangerous metal penetrations and metal fins.”

Each of the three Inductotherm furnaces has its own transformer

230 metres of stainless steel pipe was used in the project

“The system also offers the option to switch between “melting mode” and “drying mode”, so that the sinter charge can be monitored on metal penetration. The detection of coil leakage, such as those occurring on coreless induction furnaces, completes the service range of the Saveway technology.”

Local participation
“Wherever possible we try and use local manufacturers for all of the equipment, fabrication and infrastructure requirements. For example we have worked very closely with Allied Minerals for our refractory requirements. They have designed and manufactured special refractories for us.”

“Evapco have designed and constructed an elevated platform to house the five cooling towers, which saves a sizeable amount of floor space. But it is the annual water savings from this plant – six million litres in a year – that is meaningful to our environmental impact goals.”

Foseco’s Kaltek insulating ladle lining systems
“Like all other melt shops we are under increasing pressure to improve productivity, temperature control and metal cleanliness. As a result we have converted to Foseco’s Kaltek insulating ladle lining system. The Kaltek insulating lining materials provide excellent performance with respect to heat loss, energy usage and metal quality in metal transfer vessels.”

“Foseco has also developed a multi-life Kaltek recipe that can survive the extreme conditions of thermal cycling and wear resistance here at GMSA. It is a cold start system that eliminates the need for preheating of the ladles, and ensures superior temperature retention compared to any other conventional system currently available in the market.”

Kwatani custom built charge cars
“One of the unique features of the melt platform is the flexibility of the design which was purpose built to suite the specific needs of this project. Some of these features are the innovative chute geometry that eliminates material hang-ups and in turn removing operator intervention. Furthermore, the brute force feeder component was specifically designed with the material properties in mind allowing for adequate throughput and adjustability. Kwatani, a leading vibratory equipment OEM with which GMSA has a longstanding track record and a large existing equipment population of over 140 vibratory feeders throughout the existing production plant, was the manufacturer of the three charge cars for the three furnaces.”

Air filtration system
“Local company Aircure have developed an air filtration system for us. It starts with the hoods on the furnace bodies. These covers are designed to effectively collect smoke, dust and airborne pollutants during all phases of furnace operation. This is followed by placing the Aircure patented Cycloducts before the bag filters so as to separate the larger particles before they reach the filter bags. This represents a huge saving in bag replacement with extended life.”

Infrastructure
“We have also constructed a 4 000m² building for scrap separation. This includes a new bunker system for better scrap handling and separation.”

“The furnace infrastructure includes a three metre encasing and is built under normal floor level. This in itself presented numerous challenges because of what we came across while excavating. You can imagine it. The site has been occupied since 1925 and there have been many additions, improvements and alterations with not many readily available infrastructure plans.”

“We have also included an emergency pit in front of every furnace for just that, which we hope never happens.”

Production culture: Total training
“As I said earlier one of the biggest challenges was to change the culture of the staff from one of electric arc furnace production to one of induction furnace production. We have taken this very seriously and brought in experts like Tom Richards to help to devise a learning schedule according to our requirements.”

“All staff are required to have three weeks of ‘classroom’ learning and then to enhance their understanding they have to participate in the online learner management system whereby they are regularly required to log on and complete refresher courses.”

Each of the three Inductotherm furnaces has its own hydraulic room with the system feeding the mechanical operations

“Evapco have designed and constructed an elevated platform to house the five cooling towers, which saves a sizeable amount of floor space. But it is the annual water savings from this plant – six million litres in a year – that is meaningful to our environmental impact goals.”

“We have also contracted engineers from the various engineering disciplines to teach our staff. And to complete what we think is a total learning and training experience we contracted a life coach who is a psychologist.”

“When melting chrome there are generally more risks involved than when melting other metals so the management of these risks is paramount to avoid any ‘nasties’ happening.”

“The bottom line is the rands per ton of product produced but it should not be at the expense of the environment. The resulting legacy we leave behind should be addressed by all of us. We have proved that there are cost efficient and environmentally friendly ways to spend your money and still increase production and efficiencies and achieve the required cost savings while enhancing quality of product and life and its surrounding environment.”

For further details contact Grinding Media South Africa on TEL: 011 842 9000 or visit www.grindingmedia.co.za