December 1, 2013
By Mark W. Sprouls
Caterpillar studies show that rigid-frame haulers most often deliver the lowest cost per ton in high-volume aggregates operations that manage the trucks as part of a system. Truck maintenance planning and execution is a key component of the system, but loading and operating techniques, as well as haul road design and upkeep, have big impacts on truck productivity and mechanical availability.
Keeping quarry trucks rolling is largely a routine job. Following the inspection guidelines and maintenance intervals detailed in your truck’s operation and maintenance (O&M) manual is the way to keep operating costs down. And, when coupled with a good fluids condition-monitoring program, it’s a big part of avoiding mechanical failures that result in costly unplanned downtime and lost production.
Routine maintenance is a shared responsibility of maintenance technicians and truck operators. The pre-shift truck inspection conducted by the operator is both a safety inspection and a maintenance inspection. Ideally, the operator would use a checklist for the walk-around inspection (for a full checklist, go to http://bit.ly/174Nvbj).
The problems that the operator detects and reports during the walk-around inspection and during the operating shift often can avert costly mechanical failures. With the growing sophistication of onboard machine information systems, the operator can play an even greater role in catching developing problems before they create major downtime.
Similarly, remote monitoring of trucks can improve overall fleet management effectiveness. For example, Cat Product Link sends event reports and diagnostic codes, as well as hours, fuel, idle time, and other detailed information to a secure web-based application, VisionLink. VisionLink includes powerful tools to convey information to managers.
Regardless of who is conducting inspections and monitoring machine health, truck systems and components require regular routine maintenance to work optimally and to achieve their design lives. Here’s an overview of maintenance recommendations for key systems.
Oils and scheduled sampling
Regular sampling and analysis of oils in major truck systems, such as the engine crankcase, torque converter and transmission, differential and final drives, steering system, and front wheels, is recommended. Monitoring the condition of these oils helps establish appropriate change intervals and helps identify problems before they lead to mechanical failures. Fluids analysis is an integral part of machine health monitoring and machine management. Such a program can significantly lower operating costs and increase mechanical availability of your trucks.
Consult your O&M manual to determine the appropriate oil sampling intervals for the systems noted. For example, we recommend every 500 service hours. Of course, those oil levels should be checked every operating day as part of the pre-shift inspection, and trucks have a number of bearings that must be lubricated every 50 operating hours or weekly, at the least. Recommended oil change intervals for different systems are available in the O&M manual and can be adjusted based on results of oil analyses.
Using clean oil, and keeping it clean through proper maintenance procedures, is another key to getting long, reliable life from truck components. Similarly, clean fuel improves the life and efficiency of engine fuel systems, and clean hydraulic oil adds life and helps maintain efficiency of hydraulic components. Data from mines around the world have shown that thorough contamination control procedures result in lower costs. It’s worth taking a look at the way your maintenance department handles oils, fuel, and maintenance procedures. Cleaning up the shop and the lube and fuel trucks, and adding appropriate filters and tank breathers may provide a big return on a low investment.
Most of the newest quarry trucks sold in North America have engines designed to meet U.S. EPA Tier 4 emissions requirements. To accommodate the aftertreatment devices, these engines require the use of ultra-low sulfur diesel fuel and low ash engine oil. Some Tier 4 trucks have additional maintenance requirements. Check for changes in the O&M manuals of your new trucks.
A coolant level check should be performed daily or as part of the walk-around inspection before operation. A sight gauge enables the operator to check coolant levels on most trucks. If the coolant level is low, follow the directions for adding coolant in the O&M manual. Always add the same coolant type that is in the truck. Mixing different types can reduce effectiveness of the coolant and can shorten the coolant life.
Coolant sampling and analysis is recommended every 500 operating hours to help maintain appropriate levels of coolant additives. In addition to freeze protection, the antifreeze additives protect against corrosion and effectively raise the boiling point of the coolant, which reduces cylinder liner pitting. Extended operation of diesel engines without antifreeze has shown cylinder liner pitting to perforation.
The suspension cylinders, or struts, are charged with oil and nitrogen. Check strut pressure at least every 500 hours or three months. Improperly charged struts will result in reduced tire life, uncomfortable ride and poor handling, and even reduced frame life and accelerated component wear. See the O&M manual for proper checking procedures.
Frame and body
A thorough frame and body inspection should be performed at least every 1,000 hours or six months. Thoroughly washing the truck is the first step to enable an inspector to see cracks. If repairs are needed, consult your dealer for repair procedures. Proper weld repairs may be needed to stop further cracking and to avoid high cost failures.
Regularly washing quarry trucks pays other benefits, too. In addition to spotting cracks, inspectors can more easily identify leaks, loose fasteners, and other problems. And a clean truck won’t carry the dead weight of dirt and mud that burns more fuel as it is transported around the quarry. Also, accumulations of mud can contribute to overloading, which prematurely wears all components.
Daily tire inspections are recommended, while tire inflation should be checked every 50 operating hours or at least weekly. Always obtain the proper tire inflation pressure from your tire supplier. Low tire pressure can be hazardous, because it affects truck steering and braking. Additionally, low inflation pressure reduces load-carrying capability, allows the tire to heat up quickly, and increases rolling resistance. The result is accelerated tire wear and higher haulage costs.
Caterpillar offers the Ton Mile per Hour (TMPH) Tire Monitoring system on quarry trucks. This program takes the payload value from the Cat Truck Production Monitoring System onboard, combines it with ambient air temperature, machine speed, and the manufacturer’s TMPH rating for your tires and calculates tire condition continuously. As a tire approaches its temperature limits, the truck operator gets a warning inside the cab. Such systems can be an important tool in your efforts to extend tire life.
Of course, the tires in a dual tire configuration should be the same brand, the same type, and the same construction. The tires also should be the same designated size and have the same amount of wear to minimize overloading of a single tire and undue stresses on the drive train.
Routine truck maintenance, condition monitoring through fluids analysis, and the right approach to operations is the route to getting the most out of quarry trucks. Do the right thing, and higher productivity and lower costs will result.
Mark W. Sprouls has worked with and within the mining industry since 1974 and now writes about mining equipment topics for Caterpillar Inc. He is based in Tucson.