pressures also require hydraulic fluids with similar safety .... ASTM D 2882, Vickers 35V25 test and a standard test ... valve through a heat exchanger, a lOp filter.
SAE TECHNICAL PAPER SERIES
921738
Thickened Water-Glycol Hydraulic Fluids for Use at High Pressures George E. Totten Union Carbide Chemicals and Plastics Co., Inc.
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921738
Thickened Water-Glycol Hydraulic Fluids for Use at High Pressures
George E. Totten Union Carbide Chemicals and Plastics Co., Inc.
ABSTRACT Thickened water-glycol hydraulic fluids, which are generally suitable for use at system pressures of < 34.5 MPa have been used by the fluid power industry for over forty years. The principle reason for the use of this class of fluids is their outstanding fire safety properties. However, when higher system pressures are encountered and fire safety is required, a polyol ester or phosphate ester based fluid is usually selected. Recently, a proprietary, thickened water-glycol based fluid has been developed for use at system pressures of up to 34.5 MPa. The fire safety and performance testing results of this fluid will be described in this paper.
INTRODUCTION Water-glycol hydraulic fluids, which are generally suitable for use at system pressures of 6.9 MPa are used in the fluid power industry because of their low cost and fire safety for over fifty years. Water-glycol fluids are formulated from a glycol, such as ethylene glycol or propylene glycol, water and an additive package. The additive package contains anti wear additives, defoamants, and corrosion inhibitors. However, many hydraulic systems operating at substantially higher pressures also require hydraulic fluids with similar safety properties. This led to the development of thickened water-glycol hydraulic fluids. These fluids contain many of the same types of additives used in water glycol fluids except that a polymeric thickener is also added. Although the use of numerous polymers have been reported, the most common class of polymeric thickeners are based on poly(alkylene glycoll-PAG copolymers (I) which are generally derived from the random copolymerization of ethylene oxide and propylene oxide: HO(C2H40In(C3HeO)mH poly(alkylene glycol}
(I)
Thickened water-glycol hydraulic fluids have been used for over forty years. This class of hydraulic fluids is often suitable for use at system pressures of 1.4-1.7 MPa. As with their non-thickened counterparts, conventional water-glycol fluids, they are principally used where optimal fire safety is required. When higher system pressures are encountered and fire safety is also required, a hydraulic fluid formulated using polyol ester or phosphate ester as the base is often selected. Although hydraulic fluids formulated from these base stocks are also grouped into the same "fire safe" classification according to the current Factory Mutual testing protocol, there are very substantial differences in their flammability characteristics. One of the objectives of this paper is to demonstrate these differences. Recently a thickened water-glycol hydraulic fluid which is suitable for use at pressures in excess of 34.5 MPa has been developed.' This fluid exhibits flammability characteristics, using the Factory Mutual testing protocol, that are analogous to the traditional thickened water glycol fluids which are used at lower pressures but is suitable for higher pressure applications where polyol ester and phosphate esters are now required. Another objective of this paper is to describe the rheological and performance testing results of this proprietary PAG thickened water-glycol hydraulic fluid. DISCUSSION PHYSICAL PROPERTIES The physical properties of two ISO viscosity grades, 46 and 68 are summarized in Table 1. These fluids are designated as HP-5046 and HP-5068 respectively. 1 It is particularly noteworthy that both fluids have relatively low pour points «-50 o CI and high viscosity indices (>200). This means that these fluids can be used over a wide range of temperatures with only a minimal impact on the bulk fluid viscosity.
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Table 1 Summaey of Physical Properties
HP-5046 HP-5068 ProQerty Viscosity cs. at OOC 440 340 64 cs. at 40°C 46 22 29 cs. at 65°C Viscosity Index pH Specific Gravity (20/20 0 F) Pour Point (OC) Appearance
>210
>210
9.1
9.4
1.092
1.089
