A new way to look at hydraulic oil cleanliness.

A new approach to maintaining hydraulic oil throws conventional thinking out the window. But it's working in one major molding operation.

If your plant has regular procedures for maintaining hydraulic oil--and too many molders do not--now would be a good time to rethink them. The Whirlpool Corp. has developed a radically new oil-upkeep program, one rooted in a controversial view of hydraulic fluid deterioration and its role in injection molding equipment failure. At the company's facility in Findlay, Ohio, traditional filtration devices are already on their way out, and particle counting no longer plays an important role in the oil-maintenance efforts there.

Using its own diagnostic technique and a relatively uncommon device for controlling hydraulic fluid contamination, the Findlay plant has seen downtime on its five large injection presses fall significantly. What's more, the company has eliminated the expensive, twice-yearly oil changes that formerly passed for its maintenance strategy. Oil-replacement costs have plummeted by $30,000/yr, according to Robert Humphrey, the maintenance supervisor who developed the oil program. "We've started to look at our oil as an asset to be preserved, not as a commodity," Humphrey says.

PARTICLE SIZE DOESN'T MATTER

Most oil-maintenance regimens include a means of tracking the number of particles within a given size class because hard, micron-sized particulate has long been considered the chief culprit in hydraulic equipment failure. Servo valves fail, as one common scenario goes, when these particles interfere with the spool's movement.

Whirlpool, however, found that a simple count of contaminants by size would often provide a misleading picture of oil health. "Particle count never told me a whole lot about the oil condition," Humphrey says. Agreement with this view, and the research to back it up, is provided by Kleentek, a partnership between Japan's Kleentek Industrial Co. and United Air Specialists of Cincinnati.

Kleentek, which sells an oil-cleaning system, claims to address oil maintenance at the "molecular level." Noting that oil will oxidize under an injection press's normal operating conditions, Kleentek managing director Dr. Akira Sasaki blames molecular oxidation products for the bulk of contamination woes. He explains that these oxidation products start to polymerize, forming polar molecules that stick to the metal surfaces of servo valves and other hydraulic components. These tar- or varnish-like substances increase the coefficient of friction between metal surfaces--for example, between a servo valve's spool and sleeve. "The most important single variable is this change in coefficient of friction," says Sasaki. "Polymerized oil-oxidation products act like a glue." And even a little contamination can tilt the spool and stop it in the sleeve, especially with servo-valve tolerances hovering around 5 microns.

Because these oxidation products are on the order of angstroms--ten thousand times smaller than micron-sized particles--Kleentek steers clear of conventional mechanical filtration. Instead, the company's Electrostatic Liquid Cleaner (ELC) uses an electrostatic field to drive contaminants of all sizes onto a collection medium. "The ELC is unique because it address both the particles and oxidation products," Sasaki says.

While Kleentek does not discount the importance of removing larger particulate from the oil, the company claims that traditional filters fall short in removing the small oxidation products. For this reason, Kleentek does not acknowledge particle size as the most telling yardstick of contamination. "We don't even talk about contaminant size," says Sasaki. In Kleentek's conception, only three types of contaminants exist: positively charged, negatively charged and neutral.

Through a physical process called electrophoresis, the ELC's electrodes draw positive and negative contaminants of all sizes out of the oil, trapping them on the surface of the collector. As for any neutral particles or molecules, the ELC also depends on a phenomenon called dielectrophoresis. It relies on the creation of a gradient force between the two electrodes to draw neutral substances to the collector based on their dielectric constant--as opposed to their charge.

Molecular weight also enters the picture as the factor determining which contaminants stay soluble in oil and resistant to the pull of the ELC's electric field. Sasaki explains that all the "resinous matter" from oxidation products initially appears at low molecular weights. But as these byproducts polymerize, they gain molecular weight and become insoluble in oil. At a molecular weight of 500, these contaminants start to pose a threat to the working order of hydraulic components, according to Sasaki.

A NEW OIL TEST

Omitting particle counting from its oil servicing initially did leave a void in Whirlpool's maintenance program. At Kleentek's suggestion, Whirlpool first adopted a "patch test" for quick oil diagnoses. Here, a technician dilutes oil samples with a solvent and then draws them through a 0.8-micron patch filter to get a visual estimate of oil cleanliness from the contaminants trapped by the patch. While acceptable for eyeballing oil contamination under field conditions, the method lacked a means for quantification.

So, Whirlpool was still forced to rely on particle counting or sophisticated laboratory analyses--such as sediment rating or the Total Acid Number determination favored by oil suppliers--for a more scientific picture of oil condition. In his own research in Japan, Sasaki has used many test methods, including infrared spectroscopy and gravimetric analyses of contaminants collected on a patch filter. But these methods also required elaborate laboratory techniques.

Whirlpool, however, recently completed development of its own method, one based on colorimetric measurement of contaminants on the patch filter. Using a spectrophotometer, the same instrument the company uses to quantify colors for matching, Whirlpool chemists took readings of the contaminant-laden patches. A predominantly yellow coloration was found to indicate the presence of varnish-like byproducts while grays indicated ordinary dirt, according to Humphrey. Whirlpool then developed a 10-point scale from the precise color measurements of thousands of actual oil samples taken over a three-year period. New oil gives a contamination-scale reading of "one" or "two," says Humphrey.

This year, Whirlpool reached the point where it had enough data to predict machine downtime caused by oil contamination. "We found that the patch test correlated better to downtime than particle counting or sediment rating," Humphrey says. On several occasions, the other tests indicated everything was "hunky-dory" when a machine was in reality on the verge of failure. According to Whirlpool's simple scale, a "five" is a marginal reading from a maintenance perspective. Anything above "seven" means an imminent machine failure. Whirlpool moves its portable Kleentek ELC device to any press whose oil reads a "six" or more.

Based on Whirlpool's success with the spectral readings, Kleentek recently bought its own spectrophotometer and started to offer colorimetric oil-testing services to its other customers.

OIL PROBLEMS LICKED

Such intensive attention to oil maintenance may seem more than a little unusual since many molding shops do not have adequate oil maintenance procedures. "Those molders who don't worry about oil far exceed those with good programs," estimates Vern Moss, an engineer at Cincinnati Milacron's U.S. Plastics Machinery Div. in Batavia, Ohio.

Whirlpool, however, was forced into a more preventive stance by its "just-in-time" manufacturing policy. Its 1700- and 4200-ton Battenfeld injection presses mold all dishwasher tubs and doors used in the plant. "If they're down, we're scrambling for parts," says Humphrey, who estimates that each minute of downtime costs Whirlpool a few hundred dollars.

In the past, those presses had experienced some oil-related failures due to gummed-up servo valves. On one machine, a sticking valve spool caused a 50% productivity loss for three days as workers had to continually remove and clean the valve. "Any amount of contamination at all shuts down the presses because their servo valves are so sensitive," says Humphrey. "It's critical that we check these machines once a week."

Today, with an ELC in place and after fine-tuning its colorimetric diagnostic method, press utilization at Whirlpool has gone from under 80% to well over 90%, Humphrey notes happily. And those results were achieved with oil that has not been changed in over two years.

For now, Whirlpool monitors its smaller presses less frequently than the larger ones because the smaller machines, all of them from Cincinnati Milacron, have not suffered from any oil-related problems. But Humphrey would like to add a second Kleentek unit to use on these in the future. And Milacron also recognizes benefits from the ELC technology. "Oxidation-product removal is the next evolutionary step in oil maintenance," says Robert Kadykowski, operations manager of Milacron's specialty equipment business. Much of the available research has ignored "the real world of oxidation," Kadykowski adds, because the researchers work only with new oil spiked with artificial dust.

What's more, Milacron's Moss points out that the ELC, with its track record in cutting the need for oil changes, takes on an added utility for processors with a do-nothing maintenance style. "This device fits in nicely with that approach," says Moss.

Under its own CleanStat label, Milacron has included Kleentek's ELCs on several large-press orders by the automotive industry. And Kadykowski says Milacron has tentative plans to introduce integrated ELCs as a standard option on some of its larger machines at NPE '94 in Chicago next June. These would join the 20,000 Kleentek ELC devices sold in Japan since 1972.

'TOTAL PRODUCTIVE MAINTENANCE'

Given its JIT manufacturing methods, Whirlpool's program understandably has revolved around its ability to foretell and then prevent machine failure, but there is more to the story than keeping machines from breaking down. Whirlpool has also started to follow the precepts of Total Productive Maintenance (TPM)--an emerging maintenance strategy based on finding and eliminating the root causes of any production loss.

Asked about TPM, Sasaki cites numerous examples of processing problems rooted in the unsuspected source of bad oil. He tells of an appliance maker suffering from occasional scratches on parts for major-appliance door assemblies. The problem affected roughly 2% of the parts, enough to drive up regrind rates significantly. "Those scratches were one of this customer's biggest problems," Sasaki recalls. The problem was traced to an oil-induced "stick/slip phenomenon," where inconsistencies in valve-spool movement triggered erratic cycle times. Apparently, some parts simply left the mold too hot and soft to prevent them from scratching as they landed on parts produced earlier.

Sasaki links bad oil to other production losses--among them, machine speed losses, slow control adjustments, and slow startups from clogged suction strainers and line filters. Here, too, Sasaki blames the polymerized oil-oxidation products.

At Milacron, Kadykowski confirms that poorly maintained oil can cause cycle times to worsen by 20-30% on older hydraulic-clamp machines, with most of that performance loss coming from increased valve friction. "ELC can help a machine gain back its original speed," says Kadykowski.

Kleentek's national sales manager Douglas Robertson notes that processors often first recognize the need for a more comprehensive approach to oil maintenance when they install new presses that are built to tighter tolerances than old ones. "Those presses often won't run at all on oil that was satisfactory for older machines."

HOTLY DISPUTED

Despite Whirlpool's evident success, the company's focus on molecular oxidation products over larger particulate does not garner much approval from suppliers of oil filtration systems. Only Oilpure Systems of Rockford, Ill., expressed any agreement at all with the approach. Paying too much attention to micron-sized particles "is old thinking," says the company's general development manager Vichai Srimongkolkul. In place of the electrostatic cleaning approach, Oilpure sells customized chemical filtration systems to remove both the larger particles and the same sorts of oxidation products that the ELC goes after. Srimongkolkul argues, however, that Kleentek's technology is less efficient than chemical filtration because the oil needs "many passes through the ELC system."

Meanwhile, other suppliers acknowledge the existence of problematic oxidation products but say their role in oil contamination has been overemphasized by Kleentek. Howell Bowen, president of Filtroil North America Inc. of Charlottesville, Va., says his company's "kidney-loop" design, which filters hydraulic fluid outside the press, does remove some submicron-size particles. But he argues that the true issue is inhibiting oxidation in the first place by removing its catalysts--water, excessive heat, and larger metallic particles. Moog Inc., a servo-valve supplier in Aurora, N.Y., takes the same position. "Oxidation only becomes a problem when molders overheat their oil," explains product manager Greg Gleason, who adds that he hasn't seen any valve problems at customers using Filtroil systems.

However, Gleason sees a far bigger problem in molders who persist in ignoring their oil until hard particulate clogs hydraulic valves. "For them," Gleason says, "any contribution to cleaner oil is welcome."