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New oil-filtration system boosts grinding productivity.

Grinding with oil provides the lubricity for obtaining high-quality finishes and tight tolerances, but it leaves you with the problem of filtering grinding swarf from oil. This has traditionally been a difficult and expensive process, usually relying on filter paper, cartridges, or vacuum equipment.

However, newer precoat filtration methods an provide exceptionally clean grinding oil, while saving money and increasing productivity. When New Hampshire Ball Bearings Inc, Peterborough, NH, replaced their filter paper and cartridges with an automatic central precoat filter system, they realized a 78 percent return on investment in their first year of operation. The system was designed and manufactured by Polyclon Inc, Woburn, MA.

New Hampshire Ball Bearing supplies commercial- and precision-grade miniature ball, spherical, and journal bearings for computer peripherals, aircraft, and precision instrumention. Previously, each of their 62 small grinders was equipped with a paper-type prefilter in the entry basket of a 20-gal sump tank and a cartridge-element filter between the sump tank and the clean-oil return line. All machines used a 75 SUS viscosity mineral oil as coolant and aluminum oxide grinding wheels for the grinding of 52100 and 440C stainless-steel bearing races.

According to NHBB's project engineer, Ken Affleck, they experienced many problems. "We had variations in coolant-oil flow, pressure, and cleanliness between grinders on a day-to-day basis, depending on the condition of the individual filters and the degree of grinding-swarf loading. Monitoring and maintaining oil quality were difficult and expensive tasks."

Sixty-micron prefilter paper, positioned in the sump-tank entry basket to remove the bulk of the large particles of grinding swarf, was supposed to be changed at least once each shift. It is was not changed, the prefilter basket overflowed and swarf settled to the bottom of the grinders' sump. This accumulation displaced up to 5 gal of coolant and caused heat buildup in the sump, and it accelerated oil degradation and depletion of extreme-pressure (EP) additives.

Rated at 25 microns, filter-cartridge elements became clogged with swarf in one to ten days and had to be changed; an expense for the element, labor, and machine downtime. At times, cartridge elements became so impacted with swarf that they required considerable time to remove. Contaminated paper/cartridge elements, with approximately 0.5 gal of oil, were disposed according to EPA requirements at significant cost--16 per 55-gal drum.

Cartridge-element rupture, improper element seating in its housing, manufacturing fault, or bypass-valve opening from excessive contaminant loading all contributed to grinding swarf remaining suspended in the coolant. Oil loaded with hard metal and abrasive-wheel fines became an effective lapping slurry. Introduced to the work surfaces at 30 to 40 psi for periods of 16 to 24 hr/day, the coolant caused wear and alteration of precision-ground carbide work fixtures such as faceplates, shoes, and drivers. The net result was increased expense, decreased tolerance-holding ability, increased reject rates, extended cycle times, and increased tooling adjustments and replacements. New centralized system

After an extensive laboratory evaluation and economic analysis, Ken Affleck recommended an automatic central precoat filtration system for NHBB's Jaffrey plant. A Model SAF 9/10.4 automatic central precoat filter system was developed by Polyclon as part of a complete turnkey coolant-filtration project. Chuck White, director of manufacturing services at NHBB explained, 'We were looking for both state-of-the-art equipment and the ability to engineer and install a filter system that met our exact needs."

The Polyclon system provides clean coolant, filtered down to the 1-micron range, at a constant flow of 140 gpm and pressure of 40 psi to the 62 machines, 24 hr/day, 5 days/wk. Contamined oil flows by gravity from the four lines of grinders into polyethylene discharge manifolds, Figure 1. Each manifold empties into its own in-ground sump containing a main and standby dirty-oil pump that pump oil to the central precoat filter's dirty-fluid holding tank. A main or standby filter pump takes the oil from the holding tank through the filter dome, Figure 2. The dome contains diatomaceous earth, supported by filter precoat tubes, that acts as a porous barrier, trapping and removing solids from the fluid, Figure 3. Trapped solids form a filter cake that contributes to the filtration process. Clean oil flows from the filter dome into a clean-fluid holding tank where main and standby pumps transfer it back to the grinders through black-iron piping.

Periodically the filter requires regeneration to remove solid contaminants. This can be initiated manually or automatically when the pressure drop across the filter reaches a predetermined point. During regeneration, clean-oil requirements are met by drawing down the clean-fluid holding tank.

At NHBB, regeneration is performed automatically once a week (Saturday at noon). It takes 15 min and involves pressurizing clean oil from the upper portion back through the filter precoat tubes, dislodging the filter cake, and it and the contaminated fluid in the dome flow into a sludge holding tank. There, a mixer keeps the solids in suspension, and the liquid is pumped into a secondary hinged-belt filter that uses paper media to separate solids in an extremely dry form for proper disposal, Figure 4. The final step is the automatic regeneration of the filter by pumping 25 lb of inexpensive diatomaceous earth mixed with clean oil through the filter precoat tubes to form a new filter cake. Results

One year after installation, the results are clean oil, increased productivity, and reduced costs. As Ken Affleck explained, "We agreed in writing on filtration levels and testing procedures. We periodically send a sample to our laboratory for testing. The results are startling. In fact, after the first set of tests, a white-room lab technician with 20 years of experience demanded to know where we had obtained anything so clean."

Melvin Power, NHBB plant engineer, has seen significant reduction in maintenance requirements in the race-grinding department. "The filter system is nearly self-operating. Adjustments are easy to make, and alarm systems detect problems. This has freed up maintenance personnel, allowing them to handle other needs. Dry sludge amounts to one 55-gal drum every three weeks, which is easy to handle."

As Chuck White summarized, "Every cost savings we expected--reduction in maintenance-related supplies, labor, downtime, scrap rates, and disposal costs, plus increased productivity--have been realized with the filter technology and service we got from Polyclon."

For more information from Polyclon on their filtration systems, circle E2.
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Publication:Tooling & Production
Date:May 1, 1984
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