Metalworking lubrication is reasonably different from other kinds of machinery lubrication as described in our previous article Major Lubricating mechanisms involved in Metalworking. In this article, we will differentiate between various categories of lubricants that are used in metalworking. The choice of lubricant is made so as to maximize productivity and meet the environmental restrictions that are imposed on the plant by the government bodies.
There are five categories of metal working lubricants, which are presently used on various surfaces and materials:
Let’s look at the reactive chemical and physical properties for each group of lubricant.
Also known as vanishing oils, Evaporative lubricants are widely used lubricants in metalworking. These lubricants have very flexible physical properties and wetting capabilities which can be modified or adjusted according to the severity of the working process. The lubricant’s drying rate can also be controlled as it depends on the evaporative carrier. If the particular metal working process requires additional protection against evaporation, then extreme pressure additives can be added to the Metalworking tool and the Work-piece. Evaporating compounds are usually not cleaned from the surface of the work-piece and they usually do not require degreasing. They can easily be applied by the use of roller-coater method or airless spray method. These lubricants are ideal for coated, painted, vinyl, galvanized surfaces, ferrous and nonferrous materials. These metalworking lubricants are also useful for providing rust protection.
There has recently been a great upsurge in the use of Chemical solutions (synthetics) as metal working lubricants because they are easy to handle, environmentally safe, economical and ideal for use on galvanized, coated, cold roll steel, and even on stainless steel in some cases. Chemical solutions allow easy welding without initially cleaning and can be easily used for secondary operations like drilling, cutoff, punching and tapping. These lubricants are homogeneous mixtures formed by mixing solid, liquid and gas into liquid solvents. They are usually called chemical fluids or synthetic fluids as they don’t contain oil; they contain wetting agents, biocides (fungicides), lubricants (complex esters) and defoamers. Chemical solutions come in several different types according to their application. Heavy-duty metalworking requires soap type solutions, working with aluminium or coated steel components requires nonionic chemicals types and high strength alloys require Extreme pressure type solutions. These solutions can be sprayed or applied by roller-coater. They can also be used in certain recirculating systems that are suitably designed.
Micro-emulsions are ideally used for lubricating hot rolled and cold rolled stainless steel. Metalworking operations sometimes require lubricants which provide outstanding cooling, flushing and lubricating qualities. These lubricants provide film strength using a combination of water-soluble corrosion inhibitors, emulsifiers, organic and inorganic salts, wetting agents and also extreme pressure agents in some cases. The particles dispersed in Micro-emulsions are between 0.01 μm and 0.06 μm in size which are usually transparent or translucent in appearance. Due to its small particle size, Micro-emulsions provide excellent cooling and penetration for a large variety of metalworking applications. Apart from being roller-coated or sprayed, they can also be used in a flood-type coolant system.
Also called as soluble oils, Macro-emulsions contain suspended droplets of mineral or compound oil dispersed in them using high-quality emulsifiers. The size of these droplets is so big that it makes the lubricant appear milky (sometimes translucent). Heavy duty operations may include specially formulated emulsions to include barrier films of polymers or fats or to include extreme pressure agents of higher levels. They are commonly used in heavy-duty metalworking processes required for making automotives, furniture components or shelving.
Petroleum-based lubricants have a wide range of properties, and hence they provide the broadest range of choices for various application utilizing the variety of both chemical and physical properties of the chemicals. This family of lubricants primarily travels using the blending oil of various viscosities. Additives such as polymers, fats and wetting agents; and extreme pressure agents like sulphur, phosphorous and chlorine can be added for obtaining additional physical properties. Additives can also be added for rust protection and cleaning inducers for easier cleaning. Small parts and pieces of stainless steel and some big formed sections require petroleum-based lubricants.