The Problem
Mobile mining equipment hydraulic systems are typically exposed to very high solid particle ingression rates. A mine was experiencing premature component failure on its excavator due to high particle contamination. In the first 27 months of operation, costs included four variable speed piston pump replacements ($20,000 per exchange, $34,000 new), three swing motor replacements, two drive motor replacements, numerous servovalve repairs or replacements, 42 hydraulic hose-related problems, and 16 instances of contamination sensors requiring cleaning. The oil was highly contaminated, yielding excess oxidation after 2,255 service hours and needed to be replaced. Other associated costs included excessive unplanned equipment downtime, more than 39 hours, and unplanned maintenance costs.
The machine was not operating reliably and was approaching the end of the warranty period. The goal was to eliminate premature pump and servovalve failures, minimize costly component repairs or replacements, and increase the overall productivity of the operation. The shovel is the critical piece of equipment in the mining process. When the shovel is down, several haul trucks are also down and no coal is being produced.
The Solution
Fluid cleanliness levels per ISO4406:1999 were consistently monitored from 22/20/17 to 21/19/15. Based on the criticality of the hydraulic system components and the cost of unplanned downtime, the mine set a target fluid cleanliness code of 15/13/10 . The recommendation was a total system cleanliness approach. It is important to keep in mind that each drop in ISO code means that the number of particles is roughly cut in half, so reducing the four-micron channel from 22 to 15 would effectively mean reducing the number of particles four-microns and larger from roughly 30,000 to only about 240 per milliliter.
Step 1
Various maintenance practices were implemented to minimize the introduction of contaminant into the system from new hoses. All new hoses were cleaned by forcing projectiles through the hoses in both directions until clean to avoid introducing contaminant. The hoses were then capped to prevent contamination during storage and handling before installation. Training and procedures were established to minimize ingression during hose replacement and installation.
Step 2
The original hydraulic fluid was rated for 4,000 hours, but showed signs of oxidation after only 1,000 hours and was severely oxidized after 2,250 service hours. Acids typically begin to form as the oxidation level rises. The fluid was upgraded with a higher performance hydraulic oil to enhance component wear protection, prevent possible varnishing and deposit formation across hydraulic pumps, valves and motors.
Step 3
The original OEM return-line filter element was a 10-micron nominally rated cellulose media. Based on the high ingression rate from the large cylinders and the environment during service, excessive vibration and dynamic system conditions, the action plan included upgrading the existing filter media (with a Beta rating of 1.4 at 10 microns) to a 12-micron (Beta of 1,000 at 12 microns) dynamic filter efficiency-rated glass media elements from Hy-Pro to flush and stabilize the system. Then a six-micron glass media (Beta rating of 1,000 at seven microns) was installed to achieve and maintain the target fluid cleanliness.
It was determined that the location of the housing inlet port was causing damage to the pleated media compromising element efficiency. A perforated flow deflector was added to the Hy-Pro element to protect the element from damage in service. Inspection of spent elements indicated abrasion and that the original elements were not sealing properly with the housing so gasket seals were added, where the OEM element had no seals, to prevent element bypass.
Step 4
Oil sampling procedures were standardized and personnel were trained per new procedures to ensure a more consistent sampling technique. The mine continues to use bottle sampling as its primary means of oil analysis. The ideal scenario would be the installation of sampling ports in several locations to allow on-line particle counting to minimize sampling error from bottle background contamination, dirty sample valves/ports, and potential exposure to airborne contamination during sample collection. Additionally, sample ports provide a place for contamination to accumulate and on-line particle counting allows you to determine when the sampling port is free and clear of particle deposits that can artificially inflate counts.
With an on-line particle counter connected to a sampling port, the counts will trend downward as the port is flushed. Once the counts stabilize, the port is clean and ready for sampling. The flushing interval can range from several seconds to several minutes. With proper sampling ports, correct port location selection and on-line particle counting, the most accurate picture of fluid cleanliness may be achieved.
The Result
The impact of the fluid change was seen almost immediately. Copper levels, indicative of pump shoe wear, dropped by an average of 70 percent and overall component wear metals were also reduced. The fluid service life was extended to 17,000 hours, far exceeding the OEM-rated fluid service of 4,000 hours. The 12-micron flushing element was replaced after 50 hours of service. Once the six-micron element was installed, a target cleanliness better than ISP 15/12/9 was achieved. After a cleanliness equilibrium was reached and the runaway contamination problem was under control, the filter element replacement interval was extended from 500 to 1,000 hours of operation. When upgrading from cellulose to high-efficiency glass media elements, the interval between element changes typically may be extended, thus minimizing planned service down time. There were no differential pressure gauges or pressure gauges on the original equipment near the filter assemblies. A device was installed but damaged in service. The element service interval has been extended to 1,000 hours based on oil analysis data. More attempts are being made to install differential pressure gauges to help maximize filter element life. Overall hydraulic fluid cleanliness levels have greatly improved by controlling contamination levels and reducing component wear over the past four years. This resulted in the elimination of four pump replacements, 39 hours of shovel downtime, and a 400 percent increase in hydraulic fluid life.
Cost Savings
To approximate the cost savings in implementing these changes, revenue enhancement, process improvements and expenditure reductions were all considered.
Succeed with a Total Systems Cleanliness Approach
The visible cost of proper contamination control and total systems cleanliness is less than three percent of the total cost of contamination when not kept under control. Keep your head above the surface and avoid the resource- draining costs associated with fluid contamination issues including:
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Downtime and lost production
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Component repair and replacement
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Reduced useful fluid life
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Wasted materials and supplies ($)
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Root cause analysis meetings
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Maintenance labor costs
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Unreliable machine performance
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Wasted time and energy ($)
Developing a total system cleanliness approach to control contamination and care for fluids from arrival to disposal will ultimately result in more reliable plant operation and save money. Several steps to achieve total systems cleanliness include the following:
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Evaluate and survey all hydraulic and lubrication systems
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Establish an oil analysis program and schedule
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Insist on specific fluid cleanliness levels for all new fluids
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Establish a baseline and target fluid cleanliness for each system
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Filter all new fluids upon arrival and during transfer
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Seal all reservoirs and bulk tanks
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Install high-quality particulate and desiccant breathers
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Enhance air and liquid filtration on existing systems wherever suitable
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Use portable or permanent off-line filtration to enhance existing filtration
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Improve bulk oil storage and handling during transfer
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Remove water contamination
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Make a commitment to fluid cleanliness
