Case Study 2
After Northwestern Steel & Wire Co. switched to an invertemulsion hydraulic fluid on the 12-in., 15-stand hot roughing mill at its Sterling, IL, plant, maintenance people could see the difference. Literally.
Northwestern had been using a synthetic polyol ester fire resistant hydraulic fluid, according to Bob Apple, general supervisor of maintenance. The polyol ester fluid was dark in color.
Says Apple, “In this mill, the combination of moisture, oil, and metal fines eventually turns the entire mill a dark gray to black. Dark oil blends right in. And since this mill operates around the clock, maintenance people can’t shut down equipment to do a thorough inspection for leaks. Consequently, we found our hydraulic fluid consumption was high.”
The hydraulic fluid that Northwestern switched to, Mobil Oil Corp.’s Pyrogard D, is a water-in-oil hydraulic fluid, and is milky white. Any leak is easily spotted. “We can sometimes see them from the control room platform above,” claims Dick Bennett, manager of the 12-in, mill.
In addition, the Pyrogard D fluid has a higher viscosity than the previously used polyol ester product, so it leaks less, resulting in less lubricant usage.
Its initial cost is one-third that of the polyol ester, and drum handling costs are lower because less lubricant is used. As a result of the switch, Northwestern officials calculate the company saved $45,000 the first year.
Pyrogard is a water-in-oil emulsion, in which oil is the continuous phase surrounding finely divided water droplets. Pyrogard D is called an invert emulsion because it is inverted compared to a conventional emulsion, which has water as the continuous phase. If the invert emulsion is exposed to fire or extreme temperatures, the water breaks out of the emulsion to cool and blanket the oil.
Since Pyrogard D is about 60% oil by volume, and since the oil phase contacts moving parts it has the anti-wear, anti-rust, and antioxidation characteristics of mineral oil hydraulic fluids. Mobil engineers claim it exhibits minimal water and oil separation during storage and normal use.
Experience at Northwestern proves that Pyrogard D retains its antiwear characteristics up to 150º F and tends to run cooler than conventional hydraulic fluids. In use at Northwestern, it withstood the record heat wave of 1988 without problems. Typically on hot days, it runs no more than 25º F over ambient.
Also, the product proved that it can be used at temperatures down to 15º F without separation during cold winter extremes of 1989.