The beauty of engineering is its design and construct tools and equipment to increase the volume and efficiency of human endeavours. The mighty haul truck is an iconic example, able to move more material in one load than over 8000 workers with buckets.
However, machines might make light of the toughest work but they also wear out and require regular repairs and maintenance to keep them operating shift after shift. Our current line boring technical feature covers an important area of maintenance, where the pin bores of almost every hydraulically operated machine must eventually be bored back to round, reclaimed with weld and machined back to a tight OEM tolerance – all while remaining in perfect alignment with all the other bores in that articulated joint.
Morgan Engineering, in Singleton, NSW, has featured regularly in the AMR and are at the forefront of modern machining techniques and employ the latest machining equipment to provide the very best all-round service to mining clients. So, the AMR was interested in running this story on their unique solution to a very expensive problem – re-machining the tapered bores mounted on the chassis of CAT haul trucks. These bores serve as the locating and pivot points for the steering mechanism and are subjected to enormous side loads as huge hydraulic loads change the angle of the front wheels to provide steering for trucks that can weigh over 400t. Add moisture, dust and dried grease to these already stressed bores and it is a recipe for grinding paste and accelerated wear.
Anyone who has driven anything from a ride-on mower to a prime mover will understand that play in the steering does not instill a great deal of confidence. Increase the mass a few hundred times and place that vehicle on a steep incline and the level of confidence plummets even further. All levity aside, steering wear in haul trucks is unsafe and unacceptable.
New Solution
In the past, the only way to repair the tapered steering bores was to cut them off the chassis, send them out to be machined off site and then re-weld them into place. The very nature of cast iron welding creates its own risks and it takes a skilled welder to perform the job successfully without inducing cracking around the area. The most significant problem with this method, however, is the loss of production caused by truck downtime. Typically, the remove, repair, replace method can take three or four days to complete and that translates to thousands of tonnes of lost throughput.
Following the age-old philosophy of improvise, adapt and overcome, Morgan Engineering developed their own proprietary equipment and techniques to machine these steer box tapers in-situ – eliminating the entire removal and offsite repair process and substantially reducing equipment downtime.
Supporting Morgan Engineering’s extensive service exchange program for CAT haul truck steering components, the company implemented an innovative, state-of-the-art, process to reclaim and re-machine the chassis tapered bores back to original OEM standard. Morgan can now carry out this work onsite – anywhere in Australia – and complete the repair in only 12-14 hours as opposed to three or four days.
The cost of the repair is around 60% less than a new replacement part and the cost reductions – by saving over three-days of downtime on a machine – are significantly greater again.
In-House Development – Third-Party Certified
This unique, portable, solution was developed in-house along with custom designed and engineered tooling. The complete tooling assembly fits neatly into a single box that can be transported anywhere in the country and quickly deployed onsite.
The complete process has been third-party certified to ensure both component and machine integrity are maintained. This extra level of quality assurance provides clients with the confidence their assets are repaired to specification, with an exceptionally high standard of tooling and operator expertise.
Strict Repair Procedure
Once the tooling arrives on site and the work centre is set up in a suitable location next to the haul truck to be repaired, the technician follows a strict procedure to repair worn tapers.
- The steer taper contact surfaces are thoroughly cleaned before being crack tested using the magnetic particle method.
- After the taper has been found to be crack free, an initial inspection is carried out to determine current steer taper dimensions and wear. Again, all tapered bores are cleaned to ensure they are free from grease, oil, smeared ball stud material and other debris. Next, they are cleaned with a bore hone to remove any corrosion and pitting. Then, bearing blue is applied to test ball stud to taper contact. At this point, the ball stud depth in the steer taper is also measured.
- The results of these measurements are then compared to CAT’s specifications to determine whether internal welding of the bore is required.
- If welding of the tapered bore is required, the surface is pre-machined with a finishing reamer to ensure it is free from foreign material, corrosion and pitting. The bore is then pre-heated before it is set up for continuous welding to reclaim lost material. The newly welded part is then wrapped in thermal blankets and allowed to slowly cool to a pre-determined temperature. This minimises the risk of cracks developing from being allowed to cool too quickly.
- After cooling, the reclaimed taper is rough machine bored with a roughing reamer to more quickly remove unnecessary weld material.
- To ensure a perfect fit, with perfect tolerances, the bore is then machined with a finishing reamer to OEM specification depth. It is important for the client’s sake to ensure that the finishing depth is close to top tolerence of the OEM specification. This maximises the life of the repaired taper.
- Once all sharp machined edges are removed, and all surfaces are cleaned, the technician tests the ball stud to taper contact again, using bearing blue, to ensure the taper is finished to OEM specification.
- After checking the spot face counter bore to ensure it is square to the taper, a complete final inspection is carried out before the area is repainted Morgan Engineering’s ID tag is fitted with all the relevant details included.
Real World Application
AMR had the opportunity to talk with the maintenance manager of a prominent gold mine in NSW in relation to refurbishment of one of their CAT 789 haul trucks. As part of the site’s scheduled maintenance program, they identified significant wear in this particular truck’s steer box and were then faced with a potentially very expensive dilemma. A new steer box had to be imported from the USA, which is not only expensive but meant a 10-week wait for the parts to arrive.
The wear was discovered part way into the truck’s two-week maintenance program (carried out every 10,000 hours) and that meant that best case, it would be down for an additional eight weeks while the parts arrive – then even more time after that as the time-consuming and tricky job of removing the old steer tapers and welding in the new ones was carried out.
Bear in mind that this truck carries 200t of ore per run, it does approximately 12 runs per shift, two shifts a day, seven days a week. Over an eight-week period, that translates to over 268,000t of lost production.
However, the mine contacted Morgan Engineering instead. They sent their specialised machining equipment and personnel to site and also brought one of their service exchange bell cranks with them.
The team from Morgan Engineering where able to machine and repair the four steer box tapers and bring them back to OEM spec. Once complete, the mine’s maintenance crew where able to swing back into action and carry on with completing the truck’s maintenance program in order to get it back on the haul road.
The company’s maintenance manager was delighted that the truck was returned to service only three days over the service interval, not 10 weeks. The truck was back in operation – good for another 10,000 hours of non-stop work – and the company did not lose over a quarter of a million tonnes of production.
This real-world example demonstrates exactly how cost-effective Morgan Engineering’s onsite tapered steer box machining system actually is. The mining company saved eight-weeks of unscheduled downtime on and the structural integrity of their truck’s cast chassis remains intact, without the need for cutting and welding and the risk of inducing cracking at the site of those repairs.
The beauty of a well-engineered solution.
Morgan Engineering
02 6572 2032
www.morganengineering.com.au