Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1032074
LESSONS IN LUBRICATION 40 | September - October 2018 | www . machinerylubrication.com most applications. Water-in-oil emulsions have a milky appearance and are commonly manu- factured with viscosities between 100-120 centistokes and a specific gravity of 0.92. Like other water-based, fire-resistant hydraulic fluids, the fire resistance is primarily accom- plished by the water in the formulation. When exposed to high temperatures, the water turns into steam, which reduces the oil's combus- tibility. ese emulsions also maintain water droplets at a small enough size so that filtration is still an option. Water-glycol Solutions Often called water-polymer solutions, these are formulated with 60 percent glycol and 35 percent water. e glycol-based lubricants in these solutions offer some benefits, such as a lower freeze point, while the fire resistance and heat-transfer capabilities are provided by the water. ey also require additives to supply sufficient lubricity and protection from corrosion and wear. Glycol can impart a higher natural detergency and viscosity index than most other base oils. However, there is a risk of incompatibilities to other fluids, paints and coatings, as well as a tendency of shear thin- ning when viscosity-index improvers are used. Phosphate Esters Synthetic phosphate-ester base oils are some of the most fire-resistant lubricant formulations. ey gain inherent fire resis- tance from the properties of their molecular structure. Phosphate esters are noncorrosive, have excellent oxidative stability and anti-wear characteristics, and provide operability up to 150 degrees C. ey also have good lubricity, particularly in boundary conditions, and are often produced with viscosities of 22 to 100 ISO VG. eir specific gravity is higher than water. However, phosphate esters have a very low viscosity index (less than 60) and are susceptible to hydrolysis. ey are frequently used for aluminum die-casting machines, melting furnaces and steel mill applications. Other Synthetic-based Fire-Resistant Hydraulic Fluids Other synthetics, such as polyolester and polyether glycols, have varying capabilities as fire-resistant hydraulic f luids. For the purposes of fire resistance, these may not be as common as other mainstream fluids, although they may offer unique advantages, such as a higher viscosity index and excellent lubricity. Some alternative options are formulated with natural esters for enhanced biodegradability, low toxicity properties and a higher flash point than other non-aqueous fire-resistant fluids. Specialty fluids like these are often delivered with a high cleanliness level, which is important when trying to meet standard cleanliness targets for ser vo-controlled hydraulic systems. Flammability Factory Mutual (FM) provides approvals and certifications for various fire-protection equipment. Industrial fluids are tested using the FM 6930 standard to classify their flam- mability characteristics. ese evaluations can clarify the limitations of certain hydraulic fluids employed in applications where fire-resistant properties are required. e FM 6930 standard approves lubricants that meet one of the three levels of rating requirements, identified as group 0, 1 or 2 (shown on page 39). Keep in mind this standard is limited to flammability and does not include any other considerations of the fluid or lubricant. ese flammability characteristics are tested using the following performance criteria: determination of the chemical heat-release rate of a highly atomized spray of the fluid, measure- ment of the critical heat flux for ignition of the fluid, and calculation of the fluid's spray flammability parameter (SFP). Emulsion-based fluids must also meet the requirements of the separation resistance evaluation. Maintenance of Water-based Fire-Resistant Hydraulic Fluids Any formulation with higher amounts of water will be more prone to bacteria and other microbial growth. Biocide treatments should be carefully balanced in these systems, especially for oil-in-water emulsions with 95 percent water. In emulsions, the ratio between water and the base oil should be monitored to preserve effective fire resistance. Maintaining a suitable water level will require periodic testing. When restoring the desired amounts of water, always consult the lubricant manu- facturer's specifications and any corporate standards that govern fire-protection proto- cols. Water-based fire-resistant hydraulic fluids should also be periodically checked for their pH levels, corrosiveness, wear protection, controlled storage conditions and shelf life. Contamination Control As with most lubricants in industrial appli- cations, fire-resistant hydraulic fluids should be kept clean, cool and dry. e oxidative and thermal stability will vary greatly among the different types of fluids. Care should be taken to keep oil within the acceptable temperature ranges. Oil analysis is often necessary to check for abnormal levels of contamination, undesirable water concentrations, acid number fluctuations, wear debris, or other changes in the physical or chemical properties of the base oil and additives. Environmental factors should also be considered when managing the reservoir and other ingression points. Contaminants can easily enter the system when fluid is drawn from the reservoir during operation. ese contaminants not only can impair the equipment's functionality but can even alter some fire-resistant properties. Breathers with desiccants and particle filters should be sized appropriately to protect the oil from these airborne contaminants. Don't forget to seal off the headspace entry points. Otherwise, air will simply flow along the path of least resistance, which may not be through the breather element. Filtration is crucial for maintaining the longevity of most hydraulic systems, partic- ularly valves, actuator seals and pumps. Fire-resistant hydraulic fluids can be managed in much the same way, even those that are water-based. First, meet the minimum 51% of lubrication professionals use fire-resistant hydraulic fluids in the systems at their plant, based on a recent poll at MachineryLubrication.com