“South Africa’s mining industry is one of the largest consumers of medium-voltage electrical-motor repairs in the world,” explains M&C MD Gavin Garland.
He explains that the reason for this is simply because of the depth and size of South Africa’s underground mines.
If compared to Australia, for example, he says that the mediumvoltage ac repair market there is only 20% to 30% the size of South Africa’s.
“Australia mines more tons of material but the majority of its mines are opencast, where most of South Africa’s are underground mines.” The main applications for motors are in fans, pumps, compressors and winder motors, which are all related to the underground mining industry, making motor repairs a bigger industry in South Africa.
As South Africa has such an extensive motor-repairs need, companies in the industry, such as M&C, have had to upgrade their facilities in order to supply state-of-the-art services.
In line with this, the South African repair industry has implemented an advanced technology called vacuum pressure impregnation (VPI). “This is a system of insulating the conductor,” explains Garland.
“The VPI technology has replaced resin-rich insulation and is now seen as the winding insulation technology of choice.
“Using this technology has resulted in the quality of repair work in South Africa being far better than in most other countries.” The 1990s saw a big capital and technology infrastructure push in the repair industry; this has allowed South African companies to perform on a world-class level.
In 1996, M&C installed what was then the largest VPI tank (3,2 m in diameter) in the industry, giving it an advantage over its competitors.
M&C has now taken this a step further and automated its entire process.
“The old system relied on oper- ator input and experience; a controller was required to control the entire eight-stage process. Now, however, the control and monitoring of the pro- cess is fully automated,” explains Garland.
“This was one of the last enhance- ments that was required in order to improve the quality of the rewound stator.” The automated system has removed human error and has ensured predict- ability and repeatability of the results.
There were some partially- automated VPI processing facilities in the country prior to M&C’s upgrade. However, the company is believed to be the first to automate the pressure-vessel control and the oven, as well as the interaction between these two components.
Garland explains that there are several stages that the rotor or stator goes through.
“The component is firstly placed in the oven where it is preheated to the prescribed temperature. “During this process, the actual component temperature is monitored as opposed to the air temperature in the oven. “‘This ensures that the component is heated to the correct temperature.” He goes on to explain that, once the prescribed temperature is reached, the component is transferred from the oven to the pressure vessel. A vacuum is drawn in the pressure vessel so as to remove all the air from within the layers of insulation tape in the rotor or stator. “This is a critical stage in VPI as it eliminates voids being formed within the main wall of the insulation system,” he emphasises.
The next step is to introduce resin until the pressure vessel is filled to a level above the component. The vessel is still under vacuum so it is vented, and then pressurised to force the resin into the cavities between the layers of tape of the insulation system.
At the end of the pressure cycle, optimum resin fill has been achieved and the component is returned to the oven for curing. “The time lag between removing the component from the resin and starting the curing process is critical as resin will seep out of the insulation during this time,” explains Gar-land. “This time is automatically monitored and recorded, and an audible alarm system is triggered to alert the operator of the remaining transfer time.” Garland emphasises that this is very important, as reducing the transfer time will increase resin retention. The component is cured in the oven at a predetermined time and temper- ature. Both the pressure vessel and oven are controlled through mimic panels which were developed using Scada software and interfaced with the PLC system. All relevant details are recorded at each stage of the VPI process to facilitate accurate data management.
“With the monitoring and recording of the process parameters continuing up to the end of the pressure stage, any defects can be rectified prior to curing,” explains Garland.
“The whole methodology behind this is to be able to create a well-doc- umented set of results, summarising the different para- meter values for customer satisfaction,” he adds.
The customer can see that no short cuts have been taken and that the process was well controlled.
“Our drive for doc- umentation control and record keeping is in line with our strategy of striving towards an original-equipment manufacturer (OEM) approach,” explains Garland.
“What I mean by an OEM approach is that, in the past, the repair philosophy has been one of reverse engineering – in other words to repair it back to the specifications with which it was received, with little upfront engineering and in- adequate documentation and control.
“Our approach is to repair to OEM standards, where engineering is done upfront and where there is a high level of written procedure and doc-umentation control,” he adds.
This approach has seen the company form partnerships with certain OEMs, especially as there has been a marked increase in the rate of attrition of the high technical skills required in the electric motor repair and remanufacture industry in the past few years, with many experienced artisans having left the industry or retiring. Garland says that despite numerous training programmes, equity targets and skills-development programmes, there has still been a net loss of skills to the industry.
In line with this, the company has formed strategic partnerships with a number of international OEMs.
“This type of relationship with an OEM provides us with access to its proprietary information, such as design data, specifications, detailed drawings and work procedures. “By disseminating this information to the shopfloor level, we are able to ensure that repairs are controlled according to OEM standards.” He notes that, as these relationships have grown, the company’s culture has evolved too.
With the company’s drive towards an OEM-driven repair standard and its new state-of the-art technology, it feels that it is benefiting South Africa as a whole.
“When we start investing in this type of fine-tuning of already-advan- ced systems we can hold our heads up high in the knowledge that the repair industry serving the mining industry today is, without a doubt, world-class.
“The mines are demanding accurate record keeping and well-organised data and are regularly auditing the companies in the repair industry, which is leading to all companies upping their game.
“The mining industry has been the catalyst for the move towards world-class facilities and, across industries, some R2-billion is spent on motor repairs each year.
“There are a number of repair companies in South Africa, but there are only a few of us that serve the mining industry that have world-class operations,” Garland ends.
M&C’s main mining clients are AngloGold Ashanti, Anglo Platin-um, Lonmin, Gold Fields, Impala Platinum, Placer Dome and Har-mony.