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Hot-Oil Filtration Improves Die-Casting Efficiency and Pump Life.

Twin City Die Casting, Minneapolis, MN, improved the efficiency of its heat-transfer systems, reduced downtime and costs, and tripled the life of its heat pumps by implementing a hot-oil filtration system from Liquid Process Systems, Inc., of Charlotte, NC.

The company uses the hot-oil heat-transfer systems for heating dies in the manufacturing process. The plant uses 13 heating systems for starting up and keeping dies hot. Each process has its own individual electric heating unit which is portable and includes its own heater, reservoir, pump and controls to continuously provide hot oil to the process.

Heat-transfer fluid is circulated between the heater and the dies to provide consistent, uniform heating for the manufacturing of parts. Over time the oils and systems fall victim to natural processes of oxidation and general wear, creating such contaminants as coke and sludge and fouling heater-element surfaces and oil passageways in the dies. The hydrocarbon oil used in these systems eventually breaks down, producing carbon that turns the oil black. Concentrations of carbon turn to coke and sludge. If not filtered, these fine particles quickly build up and coat the heat-transfer surfaces and foul the dies, heater elements, pump internals and seal faces.

These particles become cemented onto the heater elements and any low-flow areas of the circulation loop. At the Twin City operation, coke and sludge also made the operation of the relief valve sluggish and sometimes the poppet spool would stick. "All of these impediments made the work of producing components more costly and inefficient, so we began looking into hot-oil filtration systems," says Don Jenkins, corporate equipment manager for Twin City.

Benefits of the hot-oil filtration system

"The end result of installing the Liquid Process Systems' filters was less frequent repairing of pumps," says Jenkins, "which meant an overall cost savings in labor and downtime. Since installation in late 1996, our pumps last on average three times longer." Before installation, cost of pump repair and labor was about $700 per pump per breakdown. Currently, the company has 20 units equipped with individual filters from Liquid Process Systems.

Operating at temperatures up to 500[degrees]F, the filters clean and maintain efficiency of heat-transfer fluid and oil, continuously clean the fluid without disrupting system operation, reduce wear of such rotating assemblies as pump rotors, impellers, seals, valves and stems, increase the life of the heating system and reduce downtime. Costs due to fluid degradation have been reduced, wear of dynamic seals is optimized and burnout or cracking of the heater surfaces has also been minimized.

When implementing the Liquid Process Systems' filters at Twin City Die Casting, the differences between the used oil that was filtered and the oil that was unfiltered were noticeable to the naked eye. The unfiltered oil had more coke. The filter had improved the oil's viscosity. The improved viscosity and reduced particle count indicates that oxidation has been reduced and the oil will last longer.

The pumps themselves now need to be replaced less often due to filtering, according to Jenkins. Cost of a typical pump is approximately $1,200. The cost of each filter paid for itself within the first few weeks of installation and implementation, according to Twin City. Liquid Process Systems notes that these filters and systems normally pay for themselves within the first six months of installation by eliminating previously required maintenance costs.

Jenkins also found that the amount of sludge that accumulated in the systems heating chambers was reduced and that the relief valves did not gum up or stick. Improved operation of these relief valves is an increased safety benefit due to the potentially dangerous high temperatures and pressures involved with these systems.

Advanced filtration

Traditional hot-oil filtration incorporates a strainer before the system pump. Strainers are designed to protect a piece of equipment such as a pump, valve or flow meter. The strainer must be cleaned regularly to prevent cavitation, which causes mechanical seal failure or magnetic de-coupling.

Liquid Process Systems' filters provide an alternative filtration method because they consist of a filter housing with a fiberglass element installed on a standpipe designed to trap fine particles.

For side stream installation, recommended by Liquid Process Systems, the inlet of the filter is installed close to the discharge of the pump. The fluid is diverted through the filter, cleaned and discharged to the suction side of the same pump or to a low-pressure return line.

The life of the filter ranges from 3 to 6 months, depending on the cleanliness of the oil and on the operation. Filter element change-out is quick, resulting in minimum downtime.
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Publication:Industrial Maintenance & Plant Operation
Date:Aug 1, 1999
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