By Blaine Scarr
The growth in the size of mining equipment places a priority on safety and workshop efficiency. Advancements in technology continue to offer opportunities to dramatically improve safety performance and to achieve operational excellence while maintaining mining equipment. With the use of the latest technologies, several new pieces of purpose-built equipment not only improve methods for accessing and handling heavy, hard-to-handle components, they also allow the shop manager to use all of the bays all the time (See Figure 1).
As the size of mining equipment grows, traditional methods for handling components have become more hazardous. No one knows this more than the technicians working on haul trucks at large open-pit mines. The introduction of ultra-class trucks in the mid-1990s allowed the mines to move more ore or coal. The components that maintenance personnel must routinely handle, such as tires, hubs and struts, drive lines, wheel motors, suspensions, etc., all have increased in size and weight. The problem, however, is not just the size and weight. The sheer size requires additional reach and height to access them.
Size and weight have increased progressively with each new model. On a Komatsu 730 haul truck for example, the weight of the tire (a 37.00 R57) is a little more than 9,600 lb and has a diameter of 11.5-ft. For the Komatsu 830E, the tire (a 40.00 R57) grew to more than 11,300 lb and 12.5 ft in diameter. The Komatsu 930E has a tire (a 50.00 R57) that weighs more than 15,700 lb and measures 12.6 ft. On the Komatsu 960E, the tire (a 56.00 R63) weighs 16,500 lb and stands 12.7 ft in diameter. There are bigger tires and some tire diameters exceed 13 ft.
Traditionally, these components are moved by medium-sized pieces of equipment such as tire-handlers, mobile cranes and forklifts. These items have limitations due to their physical size, maneuverability and safety. A number of incidents occur every year involving the machines used in this manner. A small hub and strut weighs about 700 or 800 lb. One of the traditional methods used to remove it is a forklift. As the components get larger, however, using the same techniques just does not work. When technicians use the same forklift to remove a final drive on a Cat 793 haul truck, the forks hit the ground and the back wheels are in the air. Someone has either not calculated or miscalculated the weight and center of gravity.
The 400-ton Cat 797 haul truck is one of the largest pieces of mining equipment. A recent 797 repair job in Indonesia required eight people or more to pull the transmission. The photo (to the right) shows see six people on the truck. There is another person operating the mobile crane off to the side with another person outside giving instructions to the crane operator. They are using several chain blocks to level the transmission, while they try to manhandle it with their feet. These guys are pretty far off the ground without handrails and the tray is on the truck. That is an accident waiting to happen.
A lot of the issues that maintenance technicians face involve having the right tools to do the job. In this case, the right machines to remove the components and to handle them. Over the years, mechanics have worked with slings and chains wrapped around tires and wheel motors. They have used cribbing and assorted wood blocks to creatively level hubs and struts. These techniques place people in compromised positions.
These methods also have a negative impact on the workshops as well. A series of renderings shows an existing workshop with a Cat 797 drawn to scale (See Figure 2) . A mobile crane sits on one side and a forklift with a tire handler sits on the other side. Both of these pieces of equipment have a 46-ft turning radius. If they are going to perform any work, the bays on both sides of the truck have to be empty.
When maintenance personnel remove a transmission from a Cat 797 using traditional methods, a mobile crane must access the truck from the side. The mine could remove the tray, which takes about eight hours, and use an overhead crane. If the mine opts not to remove the tray and it uses the crane, they will still encounter the previously mentioned manhandling issues.
The movement around a workshop is constrained during big projects within a limited workspace. A shop manager obviously wants to use all of the bays and they usually cannot afford to build a new, bigger building. There are better, safer ways to do this work.
New Technology Workshop
The design of future workshops (See Figure 3) needs to focus on handling these large heavy components safely and easily in restricted spaces. Hedweld has designed machines to do the tasks more safely and efficiently. These renderings show how a modern workshop should be designed. All of the equipment is drawn to scale and the all of the machines are real and they are either available now or they will soon be available.
Figure 4 shows a transmission removal device lifted into place with an overhead crane. The tray is on the truck. Both of the bays on either side are being used. The unit has handrails and has been specifically built for this type of operation. A set of parallel arms moves a winch forward into position to pick the transmission up parallel based on its center of gravity. A set of cylinders on the sides of the winch allows the transmission to be rotated to align the spline.
Figure 5 shows two machines, a tire handler (left) and a work platform. The work platform allows the technicians to get into place. It has an overhead jib to suspend a spring balance for pneumatic tools. Once the tire is removed, the maintenance technicians have to access to the nuts on back and remove them with impact wrenches. The breaker bars used for this job are long and heavy and technicians often struggle with tools. The spring balances assists with tool handling and removes those safety issues.
The tire handling device in Figure 6 is remote controlled. It can handle tires for the Cat 797. The arms capture the tire so it cannot move or fall. The machine can articulate the tire up and down, sideways, rotate it, and move it forward and back. The technicians can get a very fine adjustment. The wheels on the machine turn 90˚ and the machine easily handles the tire in a confined space. It traverses through the workshop and out the door, but it could go anywhere as long as the floor is concrete.
All of the machines have the ability to maneuver between bays and carry heavy loads. Most are radio remote controlled and the remote hangs around the technician’s neck. The speed is variable and unit can operated precisely and slowly. The technician does not have to rely on another person to give them hand signals, decreasing the possibility of getting crushed. They are confident that they are safe and they are not going to get pinned.
Figure 7 shows multiple machines working simultaneously in a confined space. The jacks in the middle of the slide are being used to remove a wheel motor, but the same system could be used to remove a final drive. The jacks serve two purposes. They not only assist in lifting the truck and removing the part, they also lock in and serve as certified work stands. It removes the extra tasks associated with lifting the truck, setting the stands and lowering the truck again.
One machine a lot of mines have requested is one work platform that will accommodate several working heights. Many shops have several fixed-height platforms that apply to certain types of equipment. This unit (Figure 6) uses an electronically-operated actuator that will adjust the height. It incorporates a set of stairs with handrails. Some of the handrails are removable for working on items such as the fuel tank.
This is an overview of a modern workshop. All of the bays are used. All of the machines are doing different task with small footprints. They are all carrying large, awkward loads. These machines are purpose-built to carry these loads. Wheel motors now exceed 23 tons—that’s a large component even by mining standards.
It should also be noted that most of the machines shown are basically the same machines with different arrangements on top for each task. One is moving a wheel motor, one is moving a tire, and one moving a hub and strut, but they could just as easily be used to remove a dump cylinder, which requires a lot of reach. One carrier performs multiple tasks.
Tire and components sizes have increased substantially over the last 14 years. Height, reach, weight and access have increased the difficulty in maintaining these types of vehicles. There are many safety- and efficiency-related issues involving size and space and size. These machines can help mines overcome these issues. Safety and efficiency has been a key factor in the design of this technology.
In addition to safety, these machines could assist mines in world where skilled labor is tough to find. It will reduce the number of people performing those tasks. Two people can replace the seven or eight mechanics in Indonesia pulling with a lot less risk. This has to be evaluated by the mines using risk analysis and safety assessments. And, never underestimate the importance of having a couple of guys looking out for each other
Overall, new technology has given mining companies the ability to increase safety and efficiency if properly implemented. The technology itself is great, but training is equally important. To properly implement the technology, maintenance personnel must be trained accordingly. Similar to any aspect of mining, if a company buys the equipment, they should invest in the training. If the miners do not know how to use it properly, these machines will not reach the desired potential.
About the Author
Scarr is the group manager for Hedweld, a company based in Newcastle, New South Wales, Australia, which designs and builds machines for maintaining mining equipment. He can be reached at: blaine.scarr@hedweld.com.au. This article is based on presentation that he made at Coal Age’s Haulage & Loading conference, which was held during May 2011, in Phoenix, Ariz.
