Mining takes a heavy toll on equipment, causing wear on lift mechanisms, slewing rings, bridge pieces and hinge points on mining machinery. Transporting many of these pieces of equipment to a machine shop where repairs are commonly made incurs significant costs. Expenses include the obvious hard costs for transportation to and from the machine shop. However, overall downtime associated with having the heavy equipment off site also adds up, especially when repairing the damaged equipment can often take weeks.
Mining and field service companies have found that the latest generation of portable machine tools now possesses the power and precision required to make quick work of repairing heavy equipment, even in the most remote locations.
Recently such portable machine tools were tested for their performance, precision and ruggedness at a remote South American mine where a 133-in.-diam slewing ring on a shovel used at the mine had become worn. The flatness of the contact surface of the superstructure measured 0.274 mm—significantly out of tolerance to the 0.200 mm product specification guidelines.
The equipment owner called in a field service company to do the work of re-machining the slewing ring, and the service company first evaluated the repair options available for the worn shovel. Dismantling the equipment and transporting it to a machine shop was not an option. It was estimated it would take a minimum of 24 hours one way to transport the shovel at a cost of $10,000 to $15,000—making off-site repair too expensive to consider. Additionally, the shovel under repair was one of three being used, and taking the shovel out of service for a long period of time would cut production by one-third. The field service company also considered buffing-out the surface’s deep nicks. In the end, the company also rejected this option too because this process would not produce the precise tolerance set by the manufacturer.
The field service company ultimately concluded the optimal approach would be to do the machining on site using a heavy-duty portable milling machine. The repair crew mounted the milling machine to the ring area and used the self-aligning bearings of a portable boring machine for the center shaft. The team machined the problem shovel area to a depth of 1.25 mm, removing all the deep nicks on the contact surface. Laser inspection of more than 100 points on the ring area showed the milled area was within a 0.098-mm tolerance. Because the machining was completed on-site, the crew was able to repair and reassemble the shovel and have it back in action within four days.
This example illustrates why using portable milling machines for on-site machining is a more efficient and cost-effective method for making repairs compared with sending heavy equipment off-site to a machine shop. Other portable machine tools are also viable options for different types of equipment repairs. Portable boring machines, for instance, are used for re-boring worn hinge pieces, bridge pieces and lift mechanisms. Those from leading manufacturers have high power, high torque, and high-speed operation to boost productivity, and can be adaptable to a range of bore diameters. The BB8100 from Climax Portable Machine Tools, for example, has a rotational drive that can be mounted on either end of the bar if clearance is a problem. An optional dual action boring/facing arm increases facing range and allows for both boring and facing without switching equipment.
If a repair calls for machining large-diameter flange faces like slewing rings, portable flange facers have a high degree of accuracy, are easy to position, and have a uniform rotation rate. One of the newest machines on the market features a tool head that can be rotated a full 360°, infinitely variable feed rates, and remotely adjustable air-powered feedbox so radial and axial feeds can be controlled quickly and safely.
Many mine operators, heavy equipment owners and field service companies purchase portable machine tools so they are readily available when heavy equipment breaks down, but these tools can also be rented. In addition, training on the machines is available so that machinists can be instructed in the safest, most productive use of the tool.
Andy Becker is vice president of new business development at Climax Portable Machine Tools (www.cpmt.com).
