Page 34 - MetalForming Magazine August 2022

spend considerable time troubleshoot- ing the problem.”
The best way to avoid varnish on servo valves and on other machine components requiring lubrication? “A higher-quality hydraulic oil will not produce varnish,” Dinwiddie says, “and it’s important to use a prefilter in the hydraulic circuit.”
“We encourage manufacturers to look at lubricant as being a component of the equipment,” Vicars explains, “and to invest in frequent and deep- dive oil-analysis exercises. A deep-dive oil analysis can help identify whether a facility needs to upgrade its filter sys- tem or implement an improved process for avoiding varnish, including switch- ing to an oil fortified with anti-varnish technology.”
Oil Viscosity and Stress on the Press
Equally, or perhaps more impor-
tant, than a sound filter system and well-developed maintenance plan: ensuring that you’re using the right lubricant viscosity for the application. “There are several different pump manufacturers,” Dinwiddie says, “and while for the most part they all rec- ommend lubricants with a similar operating viscosity, they typically pro- vide a range or minimum and maxi- mum values.
“They don’t want the oil to be too thick at cold operating temperatures” he continues, “or too thin at higher temperatures. So, a press manufacturer, for example, will recommend that a metal former use an ISO 46 hydraulic oil, without regard for the type of parts produced in the press. However, we preach that the choice of hydraulic fluid depends in part on the work that the press will perform, whether it be stamping a relatively simple part, maybe from thin sheet that doesn’t
stress the machinery, or a more com- plex part or one stamped from thicker material. When stamping parts that don’t really stress the press, an ISO 46 oil likely is sufficient. But if the stamper then opts to use the same press to form stronger materials or thicker sheet, it will stress the equipment. The hydraulic oil heats up and may thin out too much, falling below the rec- ommended viscosity. Yet, while it may seem reasonable to replace the oil with an ISO 68 lubricant to protect the machinery at high temperatures, this reduces efficiency.”
The solution, say Dinwiddie and Vicars, often lies in switching to a syn- thetic oil with a higher viscosity index.
“Because these oils don’t thin out like a mineral oil does,” Dinwiddie says, “they will keep their original viscosities. This protects the pump and reduces wear without sacrificing efficiency at cooler operating temperatures.” MF
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