Primary Cause of Hydraulic System Failure: Dirty Oil

By: 
April 30, 1998

Ears perked up recently at a TechTrax seminar in Ontario, CA when Van Dorn Demag president Sid Rains mentioned that all of his company's presses are now available with an "ultraclean" oil option. This decision, he said, was prompted by the results of a Van Dorn Demag study that showed that between 70 and 85 percent of hydraulic system failures and component wear problems can be attributed to solid-particulate contamination within the hydraulic system. For a machine under warranty, the costs can go back to the OEM - in this case, Van Dorn.

The ultraclean oil Van Dorn Demag is using is ISO grade 46 and guaranteed to meet NAS Class 7 and ISO Class 16/13 levels of cleanliness (Table 1). Van Dorn says oil typically provided to customers falls in the NAS Class 12, ISO 21/8 range. The hope is that by starting clean, Van Dorn and its customers can cut down on hydraulic failures.


Table 1. Oil cleanliness level recommendations
NAS Class 7 Maximum micron level per 100 ml
Micron sizes 5-15 15-25 25-50 50-100 >100
Particle count 32,000 5700 1012 180 32
ISO 16/13 Maximum micron level per 1 ml
Micron sizes >5 >15
Particle count 640 80

However, whether or not your press is a Van Dorn (or Demag), paying closer attention to oicleanliness is a necessity. Oil contamination contributes to several maintenance problems, the most common of which includes premature wear of pumps, valves, cylinder rods, and sliding surfaces; the sticking of valves (silt lock); cavitation erosion; erosion of metering orifices; and oxidation. Van Dorn Demag has assembled a handbook on hydraulic oil quality and offers some practical advice for all injection molders.

One of the first things you should recognize is that new oil does not necessarily come with a guarantee of cleanliness. Although most oil is refined, it's often stored in drums or bulk tanks. Filling lines can add metal and rubber particles, and the drums may add flakes of metal, rust, or scale. When such contaminants hit the machine, the results can be disastrous. "If you put any wear metals through your system, the pumps will get shredded. They get ripped apart," says Gunther Fischbach, technical director for Demag Hamilton, U.K.

Van Dorn reports that even oil stored under reasonable conditions can deliver metal, silica, and fibers to the machine. The company says that oil samples from reputable suppliers have, on average, counts of 30,000 to 50,000 particles above 5 um per 100 ml, with a relatively low silt level.

Putting clean oil in the machine is the first step. Next, Van Dorn recommends a filtering system. Van Dorn suggests a portable nonbypass filter with a 3-um filter element and a throughput of 10 gal/minute, plus or minus 2 gal/minute. If you use a 5- to 10-um filter element, circulate the oil in the container so that it passes through the filter a minimum of six times. At 10 gal/minute, about 33 minutes is required to circulate the oil in a 55-gal drum; about 2 hours is needed to circulate oil in a 200-gal container.

Fischbach recommends to his customers that beyond regularly changing the oil filter, they perform a periodic maintenance oil check at least twice a year. Such an assessment should check water content, oil acidity, viscosity, particle contents, and the presence of wear metals.

"The presence of wear metals tells you which part of your system is about to fall apart," he says. Van Dorn Demag has established an oil test program, or you can contact your OEM or a third-party oil lab for more assistance (see below). Refer to the documents that came with your machine for the oil specifications that apply to your press.

Third party oil labs

Cleveland Technical Center
(216) 383-8200
http://www.ctclink.com

Vickers Fluid Analysis Service
(248) 853-1100
http://www.vickers-systems.com

Wear Check
(905) 569-8600
http://www.wearcheck.com

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