Industrial lubricants play a vital yet invisible role in enabling machinery to operate reliably at peak efficiency. While greases and oils may seem like commodities, highly-specialized fluids are crucial for tackling the intense pressures, temperatures, speeds, and contaminants found in manufacturing environments. Custom-formulating lubricants for specific applications is a complex balance of science and art.
At the heart of high-performance industrial lubricants is the base oil, which makes up 70-95% of the fluid. Synthetic base oils offer superior viscosity capabilities, purity, oxidative stability, and performance at extreme temperatures compared to conventional mineral oils. By combining different base oil chemistries, lubricant formulators can tailor the optimal blend for the application.
Feedstock sources for synthetic base oils
- Polyalphaolefins (PAOs) – Made from purified petroleum gas converted to liquid oligomers, PAOs provide excellent oxidation resistance and cold flow properties. Different viscosity grades are blended for tailored performance.
- Esters – Typically derived from vegetable oils or synthetic acids/alcohols, esters impart stability at high temperatures and compatibility with seal materials. Used for jet engine oils and high-temperature gear lubrication.
- Alkylated aromatics – Produced by alkylating benzene with long-chain olefins. Provide thermal stability with low volatility and low operating temperatures. Used in industrial gear oils.
- Glycols – Synthesized from ethylene and propylene oxide, glycols resist oxidation while retaining fluidity at low temperatures. Used in gas turbine and refrigeration compressor oils.
- Silicones – Polysiloxane fluids with methyl groups attached to silicon offer exceptional thermal stability at high temperatures. Used for aircraft engines and automotive applications.
- Polyalkylene glycols (PAG) – Made by polymerizing ethylene oxide or propylene oxide, PAGs provide excellent low-temperature fluidity compatible with multiple seal materials. Used in compressors.
Blending different base fluids achieves synergistic benefits. For example, PAOs blended with esters balance thermal stability and seal compatibility. Additives are then carefully selected to achieve crucial performance properties.
Additives make up 5-30% of lubricants and serve key functions.
- Reducing friction and wear through boundary film formation on surfaces
- Controlling oxidation by neutralizing free radicals
- Preventing corrosion by coating metal surfaces
- Retarding foam formation that reduces film thickness
- Inhibiting deposits that reduce heat transfer
- Enhancing film strength to handle heavy loads
- Dispersing soot and byproducts from combustion
- Emulsifying water contaminants to enable separation
What are the common additives available?
- Viscosity index improvers – Polymers added to maintain viscosity across wide temperature changes. As temperature rises, polymers unwind and occupy more volume, increasing viscosity. When temperature drops, polymers recoil, lowering viscosity. This alleviates the natural tendency of viscosity to decrease at higher temps and increase at lower temps. Common polymer viscosity improvers include polymethacrylates, olefin copolymers, and polyisobutylenes.
- Pour point depressants – Stop lubricant from solidifying at low temps. Work by binding to wax crystals that form as temperature drops, preventing them from coalescing into a solid structure. This lowers the pour point where fluid will continue flowing. Alkylaromatic polymers are commonly used pour point depressants.
- Anti-wear agents – Prevent direct contact between metal surfaces under high load. Work by reacting chemically with metal to form protective surface films. Under high pressure contact, films shear and replenish. Widely used anti-wear additives include zinc dialkyl dithiophosphates which form protective films on ferrous surfaces.
- Rust inhibitors – Stop oxidation that degrades metal over time when exposed to water. Polar compounds adhere to metal surfaces, creating a hydrophobic barrier that repels water. Commonly used rust inhibitors include petroleum sulfonates and alkaline earth sulfonates.
- Metal deactivators – Form a protective barrier preventing certain metals like copper from degrading the oil. Useful in gear oils where copper alloys are present. Act by forming inert complexes with metallic ions, shielding them from interacting destructively with oil additives. Common options include triazoles, thiazoles, and benzotriazoles.
- Antioxidants – Disrupt free radical chain reactions that propagate destructive oxidation. Neutralize free radicals by donating protons, stopping runaway oxidation reactions. Used antioxidants include hindered phenols, aromatic amines, and diarylamines which counter oxidative breakdown.
- Foam inhibitors – Prevent formation of foam that reduces lubricant film thickness. Foam is knocked down by destabilizing bubble structure through mechanisms like spreading agents that cause film drainage and rupture. Silicone polymers are commonly used as foam suppressants in industrial lubricants.
By leveraging different chemistries, lubricant formulators can fine-tune characteristics like viscosity-temperature profiles, shear stability, oxidative resistance, and detergency. Components are rigorously tested for compatibility to ensure additive synergies.
How are additives made?
The formulation process combines science and experience. Formulators start by considering equipment operating conditions, OEM specifications, and historical performance of incumbent lubricants. Thermo-kinetic modelling predicts lubricant behavior across temperature ranges. The intended operating environment guides the optimal balance of base oils and additives.
Extensive lab testing refines formulations to meet performance objectives determined by tribological analysis of the equipment’s friction points. Lubricants must excel in standard tests like Four Ball Wear, Falex Pin and V-Block, Timken OK Load, and others targeted to the application. For example, rust prevention and water separation ability are paramount for circulating oils while foam inhibition takes priority in paper machine lubricants.
Ensuring quality control in lubricants
The art lies in blending components for holistic performance, not just excelling in one test metric. Formulating requires judgment on priorities and compromises guided by practical equipment experience. The finished fluid must balance capability trade-offs across operating contexts the equipment will encounter.
Once created, lubricants undergo rigorous qualification testing replicating harsh conditions: elevated temperatures, sustained high speeds, shocking cold starts, excessive pressures, and contamination ingress. Performance benchmarks include viscosity retention, demulsibility, air release, copper corrosion, and foaming tendency.
Partnering with original equipment manufacturers is invaluable during formulation. OEM fluid engineers provide operating insights and requirements. OEM partnerships also facilitate on-site testing to validate lubricant performance in real-world conditions over extended durations. This can reveal limitations not evident in simulated lab tests.
The formulation process continues even after initial commercialization. Used oil analysis provides ongoing lubricant performance data. Equipment upgrades and application evolution also mandate adjustments. Formulators continually hone chemistries in pursuit of incremental improvements. Customer feedback inspires reformulations enhancing value.
Final words
The ideal lubricant achieves comprehensive performance with prolonged equipment protection. Custom formulations are essential given the stresses of modern manufacturing. Leveraging expert partners accelerates developing fluids precisely matched to equipment needs. With growing equipment sophistication, the formulation science enabling high-performance lubricants will only increase in complexity and specialization.
