1. Field of the Invention
This invention relates to the use of lubricants, metalworking fluids and hydraulic fluids in which water is the base fluid.
2. Description of the Prior Art
In the technology of hydraulic power transmission, mechanical power is imparted to a fluid called "a hydraulic fluid" in the form of pressure by means of a hydraulic pump. Power is utilized where desired by tapping a source of said hydraulic fluid and thus transforming the power as pressure back to mechanical motion by a mechanism called a hydraulic motor. The hydraulic fluid is utilized as a pressure and volume transmitting medium. Any non-compressible fluid can perform this function. Water is the oldest fluid used for this purpose and is still sometimes used alone for this purpose. In the prior art, there has been a heavy emphasis on the development of petroleum oils for use as hydraulic fluids and consequently much of the equipment utilized with hydraulic fluids has been designed and manufactured specifically for use with petroleum oils. A petroleum oil in comparison with water as a hydraulic fluid contributes wear prevention properties and acts to inhibit the development of rust of the ferrous components of the mechanical equipment utilized in conjunction with hydraulic fluids (i.e., hydraulic pumps, motors, etc.). Petroleum oils have a second advantage over the use of water as a hydraulic fluid in that the petroleum oils normally exhibit a substantially higher viscosity than water and thus contribute to reduction of the leakage of the fluid in the mechanical equipment utilized. In addition, the technology relating to additives for petroleum oils has developed to such an extent that the viscosity, foam stability and corrosion prevention properties of such petroleum oil based hydraulic fluids can be further enhanced by the use of said additives.
Over the past 25 years, various substitutes for petroleum oil based hydraulic fluids have been developed in order to overcome one of the major deficiencies of petroleum oils, namely, flammability. Recent interest in the use of hydraulic fluids having up to 99% or more of water has resulted from the higher cost of petroleum oils and recent emphasis on problems of ecologically suitable disposal of contaminated or spent petroleum oil based hydraulic fluids.
Metalworking fluids of the so-called "soluble oil" type have been considered for use as hydraulic fluids. Such fluids contain mineral oil and emulsifiers as well as various additives to increase corrosion resistance, improve antiwear and defoaming properties. Such fluids when used as hydraulic fluids are not generally suitable for use in ordinary industrial equipment designed specifically for use with the petroleum oil based hydraulic fluids since such fluids do not adequately prevent wear damage in pumps and valves of such equipment. However, such fluids have found application in specially designed high cost, large size equipment which because of said large size and thus inflexibility is not suitable for use in most industrial plants. The soluble oil hydraulic fluid usage has thus been quite limited; usage has been largely confined to large installations where flexibility and size are not critical such as in steel mills.
It is known from ASLE transactions 7,398-405 (1964) that the phosphate esters utilized herein are useful as components of metalworking fluids in that they improve the load-carrying ability of the oil. They are also suggested for use in water-based metal-working fluids.
It is known from U.S. Pat. No. 3,933,658 to use as additives a mixture of a phosphate ester, a sulfur compound and a suitable oil-based vehicle in a water containing metalworking composition to obtain extreme pressure, antiwear and corrosion inhibiting properties. The phosphate ester and sulfur compound are used in combination with a suitable vehicle such as mineral oil, vegetable oil, fatty acid esters, etc. These compositions are used as emulsion type metalworking compositions. The phosphate ester is an ethylene oxide derivative of an alkyl or arylalkyl phosphate which can be used in the form of the free acid or in the neutralized form wherein the phosphate ester is neutralized with a metal hydroxide, ammonia or an amine. The sulfur-containing compound can be a derivative of 2-mercaptobenzothiazole. The metalworking compositions of this patent require the use of mineral oil, a glycol, a mineral oil-water mixture or a glycol-water mixture as vehicles in the preparation of the additive compositions. There is no indication that these metalworking additives would be effective without the use of said vehicles or that these metalworking additives would be effective as hydraulic fluids.
It is already known to use in equipment designed for use of mineral oil based hydraulic fluids flame-resistant glycol-water based hydraulic fluids such as are disclosed in U.S. Pat. No. 2,947,699. Up until now, water-based hydraulic fluids containing about 70 to 95 percent water have had very poor lubricating characteristics. While hydraulic fluids are used primarily to transmit forces, it is necessary that they provide lubrication for the impeller and other mechanical parts of hydraulic pumps in such systems in order to prevent excessive wear on such parts.
In the prior art, numerous hydraulic fluids have been proposed. Many of these fluids such as the petroleum oil type are highly flammable and unsuitable for certain uses where such fluids have frequently been the source of fire. Where these fluids are used to control such industrial operations as heavy casting machines, which are operated largely by hydraulic means, danger of fire exists. Therefore, there is a growing demand for nonflammable, hydraulic fluids. While the glycol-water based type fluids provide greatly improved fire resistance over the hydraulic fluids of the petroleum oil type, these fluids are not absolutely nonflammable and are otherwise objectionable. Therefore, it has become necessary to provide to the art a water-based nonflammable hydraulic fluid having satisfactory lubricating characteristics and excellent antiwear-extreme pressure performance.