Greases for metalworking

Metalworking is a complex process that requires the use of various lubricants to ensure efficiency, precision and durability of the equipment. Among these lubricants, greases play a crucial role. They are essential for reducing friction, dissipating heat and preventing corrosion during machining operations.

Types of greases

Greases used in metalworking can be classified into various categories based on their chemical composition and functional properties. The main categories include:

Lithium soap greases: These greases are composed of greasety acid metal soaps, predominantly stearic acid, combined with lithium hydroxide. They are very thermally stable and water resistant, making them ideal for applications requiring long-lasting, reliable lubrication.

Calcium Soap Greases: Composed of greasety acid (such as oleic acid) and calcium hydroxide, these greases offer good anti-corrosive properties and water resistance. They are often used in humid environments and where process water is present.

Sodium soap greases: These greases, made up of greasety acids and sodium hydroxide, offer good thermal stability. However, they tend to be less resistant to water, limiting their use to specific applications where thermal stability is crucial.

Synthetic greases: Formulated with synthetic oils such as polyalphaolefins (PAOs), esters and silicones, these greases also contain advanced thickeners such as polytetrafluoroethylene (PTFE) or bentonite. They offer superior performance under extreme temperature and load conditions and are used in high-tech applications and harsh environments.

Greases with graphite: Formulated with graphite particles, these greases offer excellent dry lubricating properties and resistance to extremely high temperatures. They are ideal for high-temperature applications such as forging and metal casting, where graphite significantly reduces friction and wear.

Greases with PTFE (Polytetrafluoroethylene): With excellent anti-friction properties and chemical resistance, these greases are suitable for applications requiring long-term lubrication. PTFE offers a very low coefficient of friction and stability at high temperatures.

Greases with molybdenum disulfide (MoS₂): Molybdenum disulfide is a solid lubricant that reduces friction and wear under heavy load and high temperature conditions. It is ideal for heavy bearings, gears and high pressure applications.

Greases with silicone: Offer a wide range of benefits thanks to the unique properties of silicone, including high thermal stability and resistance to oxidation. They are used in food processing equipment, electronic equipment and vacuum applications.

Ester-based greases: Esters are organic compounds that offer excellent lubricating properties and superior biodegradability compared to mineral oils. They are used in environmentally friendly applications and where superior lubrication is required.

Greases with anti-wear and extreme pressure (EP) additives: Formulated with additives such as sulfur, phosphorus and chlorine compounds, these greases improve the grease's ability to support high loads and prevent wear of metal surfaces. They are ideal for industrial transmissions, heavy gears and bearings subjected to high loads.

Greases Composition

Greases are made up of three main components:

Base Oil: Base oils can be of mineral, synthetic or vegetable origin. Mineral oils, derived from petroleum, offer good stability and resistance to oxidation. Synthetic oils, such as polyalphaolefins (PAOs) and esters, offer superior performance in terms of thermal stability and oxidation resistance. Vegetable oils, such as canola oil, are biodegradable and used in environmentally friendly applications.

Thickener: Thickeners give grease its semi-solid consistency. Common thickeners include metallic soaps (lithium, calcium, sodium), non-soaps such as urea, and inorganic materials such as clay and silica. Each type of thickener gives the grease specific properties, such as water resistance, mechanical stability and thermal stability.

Additives: Additives are added to improve the specific properties of the grease. Antioxidants, such as di-tert-butyl-p-cresol (BHT), prevent oxidation of the base oil. Corrosion inhibitors, such as calcium sulfonate, protect metal surfaces from corrosion. Anti-wear additives, such as molybdenum sulfide (MoS₂), reduce wear on contacting surfaces. Extreme pressure (EP) additives, such as sulfur-phosphorus compounds, improve the load-carrying capacity of the grease.

Specific applications

Metalworking greases are used in a wide range of operations, each requiring specific characteristics of the grease. Some of the main applications include:

Cold Working: During processes such as blanking, drawing and bending, they help reduce friction between the metal and the tools, preventing wear and improving the surface finish of machined parts. Lithium soap greases with EP additives are particularly effective in these applications.

Hot Working: In hot forging and extrusion processes, greases must withstand high temperatures without decomposing. Synthetic oils such as PAOs and esters, combined with thickeners such as PTFE, are ideal for these applications, facilitating metal flow and preventing material from sticking to tools.

Grinding and lapping: In these finishing operations, greases serve to cool and lubricate the surfaces in contact, improving the precision and quality of the surface finish. Mineral oils with antioxidant and anti-wear additives are commonly used.

Maintenance and protection: Greases are also used for the maintenance of machine tools and equipment, offering protection against corrosion and wear. Calcium soap greases with corrosion inhibitors are particularly effective in these applications.

Benefits in metalworking

The use of appropriate greases in metalworking offers numerous advantages:

Friction reduction: Significantly reduce friction between metal surfaces, minimizing wear on tools and machines. Anti-wear and EP additives contribute significantly to this benefit.

Heat dissipation: They help dissipate the heat generated during the manufacturing process, preventing overheating and thermal damage. Synthetic oils, in particular, are very effective at heat transfer.

Corrosion prevention: Provide a protective barrier against moisture and corrosives, extending the life of equipment and machined parts. Corrosion inhibitors in additives are essential for this function.

Improved surface finish: The use of appropriate greases can improve the surface finish quality of machined parts, reducing the need for subsequent machining. Finishing additives improve the smoothness of surfaces.