By Russ Carter, Western Field Editor
It’s safe to say that in both surface and underground mining operations, cost per ton reigns as the main measure of mining efficiency. And, when the cost per ton yardstick is applied to mine loading and haulage operations specifically, it becomes immediately clear this critical measure of effectiveness is actually a gauge indicating how well mine management can maximize its average tons per hour rate while minimizing cost per hour. Although a myriad of factors with the ability to impact either ton/hour or cost/hour can be in play at any given time, OEM studies have shown that extending machinery component life is one of the most effective strategies for boosting uptime while reducing operating costs.
Component life, according to Simon Bishop, a product support specialist with Caterpillar Global Mining, is a function of basic design, proper application, and quality of maintenance and repair. A major factor within “quality of maintenance” is selection of the proper fluid(s) required by a component, such as fuel, oil, grease, coolant or hydraulic fluid—and implementing the correct procedures to ensure these fluids aren’t contaminated before, during or after installation.
It’s estimated that equipment maintenance and repair expenses account for about one-third of overall haulage costs. Taking it one step further, Caterpillar reports that maintenance/repair costs involving transmissions, hydraulics, final drives/differentials and fuel injectors typically total up to 70% of overall machine operating costs. And to top it off, some studies show an estimated 75% of component failures are the result of surface degradation caused by fluid contamination. So, it’s simply good business to pay attention to the fluids that keep major components functioning as originally designed.
How, exactly, is fluid contamination defined? According to Bishop, it’s anything found in a fluid that doesn’t belong there. Contaminants generally fall within two basic areas: particulates (dirt, metals and fibers), and other unwanted ingredients such as water, air—even heat. Although many of the latest oils, greases and coolants are, for the most part, high-tech products designed for use in high-tech equipment, the process of contamination often begins at a very low-tech level that can involve everything from whether and how well a vehicle is washed before it enters the shop, to what type of material the maintenance crew uses to soak up accidental oil spills. Contamination problems aren’t always apparent to the naked eye; even particulate contaminants that are considered large are still less than one-fifth the thickness of a human hair, while small particles are about one-third the size of the big ones.
Fluid contamination control in all phases of off-road equipment operation is a concept that has rapidly gained traction in recent years, due in no small part to new technologies, tighter regulations, basic business economics and other factors that are forcing equipment owners and operators to consider the expensive consequences that can result from lax fluid storage and handling practices. As Caterpillar’s Bishop explained in a presentation at the 2010 Cat Global Mining Forum, inattention to contamination control can be disastrous to an operation’s bottom line—and conversely, a well-planned and executed CC program can yield millions of dollars in reduced repair and replacement costs over a haulage fleet’s life cycle.
Citing a case history involving an African open-pit mine, he noted that after the operator implemented “world-class” fluid cleanliness practices for the mine’s fleet of Cat 785C haulers, component life-cycle increases ranging from more than 28% for truck engines to almost 62% for wheel group assemblies were achieved, wheel bearing life was extended to 20,000 hours, and by eliminating one rear powertrain replacement over the course of a 785C’s life cycle, the mine was able to save $90,000 per truck, equating to a $3-million savings across the fleet. In addition, the mine had to replace only 16 fuel injectors in a fleet comprising 24 machines with 20,000 hours—representing one injector replacement every 35,562 operating hours.
Among the many factors that comprise a well-planned defense strategy against premature parts wear, injector longevity has grown to be an area of major concern in recent years as new engine technology puts these precision components under increased duress. According to Pall Corp., a global supplier of fluid filtration and separation products, there are three types of engine fuel injection system failures attributed to the presence of particulate contamination:
• Mechanical failures from component wear and blocking component movement;
• Electrical failures (typically as injetor solenoid burnout) from silting around the poppet valve stem, restricting movement; and
• Performance failures from blocking of injector nozzles and altering injector spray patterns.
The Port Washington, New York-based company notes that as diesel fuel injection technology has progressed, so has its sensitivity to contamination. With new technology such as Electronically Controlled Unit Injectors (EUIs), injector nozzle openings are 6-7 μm in diameter. These openings can become blocked or suffer erosion from particulate contamination as diesel fuel is passed through them at high pressures. Nozzle shape can be changed or spray patterns altered, adversely impacting engine performance in the form of reduced power output and poor fuel economy.
The High Pressure Common Rail (HPCR) fuel injection technology used in the latest off-road diesels offers improved power and fuel efficiency and lower exhaust emissions. To achieve these results, however, HPCR systems operate at pressures in excess of 2000 bar and have injector nozzle openings in the 2-3 μm diameter range. This requires diesel fuel 30 times cleaner than that which is acceptable for standard EUIs and more than 100 times cleaner than what is typically dispensed at the pump. According to Pall, this level of cleanliness cannot be achieved with onboard filtration alone; supplementary bulk and point-of-fill filtration is required.
The risk of fuel system problems also increases with the use of ultra-low sulfur diesel fuels, which newer engines are required to use. While it has been reported the removal of sulfur has shown no detrimental effects in engine performance, the removal of other compounds in the refining process can lower the lubricity of fuel, resulting in potential injector system component wear, especially with modern fuel technology such as MEUI, HEUI and HPCR systems, which are far more sensitive to inadequate lubrication from low lubricity fuels.
As previously mentioned, studies have shown major component life-cycle costs (calculated by determining cost to rebuild a component divided by component life in hours) represent the lion’s share of total machine operating costs—and engine costs alone represent about 40% of that share, followed closely by final drive/differential, transmission/torque converter and miscellaneous costs. Given the potential damage contaminated fuel can cause in modern diesels, plus the sheer volume of fuel that large mines require for operation, one of the largest payoffs from a contamination control effort would likely originate from a mine’s fuel handling and storage facilities. Proper bulk storage of fluids—sometimes a forgotten link in the chain of fluid cleanliness—can play a huge role in combating contaminants.
Size Systems Carefully
As Pall Corp. points out in its technical literature, funding for capital projects such as fuel system upgrades can sometimes be difficult to justify. Even when an upgrade has proven to be a necessity or at least a viable proposition, cost is one of the main defining attributes a mine site looks at when making a purchasing decision. The size of a filtration system is one of the main contributors to this cost.
Diesel filtration systems are typically sized using a formula that takes into account the pump flow rate (or rate of delivery required), fuel viscosity, fuel density, and system pressures. Once these factors are known, a system can be sized. However, according to Pall, in many cases fuel filtration solutions being presented to mine sites are drastically undersized for their intended purposes. Why? Because these systems are often missing one key aspect in the sizing formula—the annual fuel quantity being used at the mine site and the levels of contamination that this fuel carries.
It’s not unusual for a mine to consume more than 200 million liters of diesel fuel per year, and some larger mines may use more than 400 million liters annually. When dealing with these huge volumes, it’s important to understand the amount of contamination that the filtration system is expected to remove. Pall’s experience indicates that for a mine site with annual diesel fuel consumption of 200 million liters a year, with a delivered fuel cleanliness level of ISO 21/19/16, the amount of contamination removed by a filtration system each year can total as much as 1.6 tons. Additionally, with a water contamination level of 500 ppm, a coalescer system would be expected to remove some 100,000 liters of water each year.
Using this fuel volume as an example, it’s important to understand the actual capacity of the filter elements typically installed in mining bulk diesel systems. Pall says it is common at mine sites to see filter installations sized to handle 1,200 liters/min of diesel fuel; such a system may have dirt-holding capacities as low at 900 grams for the three elements in the housing at the given flow rates. Taking into account the 1.6 t of annual contamination, this equates to an annual consumption of 1,388 elements.
That rate of filter consumption, and its attendant costs, might overshadow any benefits from the installation at all. Pall, which in addition to its filtration/separation product line offers fluid analysis services and component cleanliness auditing, thus emphasizes that many factors including pump flow rates, viscosity, density, temperature and pressure must be considered in any formula used to size a bulk filtration system—a task best performed by an experienced vendor.
Going Under Analysis
The care and cleanliness of engine lubricating oil is another critical area that can yield significant benefits from contamination control measures coupled with an oil analysis program. Oil analysis services are available from many sources, and recent developments in this technology now allow thorough analysis at almost real-time rates (See sidebar, p. 48).
WearCheck, a company that specializes in oil analysis, emphasizes that the effectiveness of any oil analysis program is strongly affected by how well the maintenance staff understands the program and by the quality of their input to the testing service. An important fact to bear in mind, according to the company, is that oil analysis should not be viewed as a replacement for normal maintenance techniques. It is a first-stage monitoring tool that identifies a problem; diagnostic tools are then required to physically confirm the problem and isolate the defective component. Oil analysis complements diagnostic tools, it does not replace them. When the information from all testing sources is combined, the result is a powerful management tool for monitoring and controlling machine health.
Oil analysis works on the principle of detecting progressive wear by establishing a baseline of normal wear metal and contaminant levels and trending the results from subsequent samples. WearCheck recommends implementing a set of basic policies that can maximize the effectiveness of any oil analysis program.
• Ensure total commitment from top management all the way down to the workshop floor.
• Make members of the maintenance team aware that their efforts do make a difference to the longevity of the machines.
• Clearly define and communicate sampling policy and frequency.
• Appoint and train responsible people to take the samples and complete the sample submission forms accurately.
• Appoint a competent senior mechanic to carry out troubleshooting and ensure all physical diagnostic tools are available.
• Train a clerk to keep accurate records of oil analysis and physical tests carried out on components at se vice intervals and during troubleshooting.
• Ensure feedback is returned so that oil analysis records can be updated and the information is available to the diagnosticians.Counting the Costs
It’s been estimated the actual costs of basic contamination control and overall systems cleanliness in an operation often amount to less than 3% of potential total costs incurred due to fluid contamination—not bad for an investment that has the potential capability to reduce an operation’s maintenance budget, increase fleet mechanical availability by significant single- or even double-digit percentage points, and even improve employee morale and accountability.