Oil Analysis & Lubrication Glossary
Q: What is Abrasive Wear?
A: Material loss caused when hard particles or rough protrusions slide along a surface. This form of wear can reduce efficiency, create vibration, and ultimately cause equipment failure if not controlled. Oil analysis helps detect wear debris early to prevent breakdowns.
Q: What is Absolute Filtration Rating?
A: The size of the largest hard spherical particle that can pass through a filter under specified test conditions. Filtration is essential in precision systems to keep oil clean and extend service intervals. Absolute ratings are especially important in hydraulics and aerospace where contamination tolerance is low.
Q: What is Absolute Viscosity?
A: A fluid’s internal resistance to flow; shear stress divided by shear rate, commonly expressed in poise or centipoise. Viscosity is central to lubricant performance: too low allows metal contact, while too high causes poor circulation and overheating. It directly impacts energy efficiency, oil film thickness, and wear protection.
Q: What is Acid Number?
A: Milligrams of KOH needed to neutralize one gram of oil; indicates acidity and oxidation (ASTM D664/D974). Tracking acid number reveals oil degradation. Rising values indicate oxidation, additive depletion, or contamination, signaling the need for oil replacement or corrective action.
Q: What is an Additive?
A: A compound blended into base oil to enhance properties such as oxidation resistance, wear protection, or foam control. Additives extend lubricant performance by counteracting wear, oxidation, foaming, and corrosion. They are essential in modern lubricants, without which most machines could not operate reliably.
Q: What is Adhesive Wear?
A: Wear from localized bonding between contacting surfaces, causing material transfer or loss. This leads to scuffing or galling under high load. Adhesive wear can rapidly damage components such as gears or bearings if lubricants fail. Oil analysis helps identify early adhesive wear by detecting transferred particles.
Q: What is AGMA?
A: American Gear Manufacturers Association; sets standards for gears and gear lubricants. These standards ensure consistent performance, compatibility, and safety across the gear industry worldwide.
Q: What is Analytical Ferrography?
A: A technique that deposits wear particles from oil for microscopic identification of wear modes. Analysts interpret the shape, size, and composition of particles to identify issues like cutting wear, fatigue, or corrosion. This diagnostic method is powerful for predictive maintenance.
Q: What is Aniline Point?
A: The lowest temperature at which equal volumes of aniline and a petroleum product are miscible; a measure of solvency. Oils with low aniline points dissolve more rubber and plastics, which can affect seals and hoses.
Q: What is an Anti-Foam Agent?
A: An additive (e.g., silicone oils or polymers) that reduces foam formation in oils. Foam reduces lubrication efficiency, causes cavitation, and damages pumps. Anti-foam agents ensure stable operation in hydraulic and circulating systems.
Q: What is an Anti-Friction Bearing?
A: A rolling-contact bearing using balls or rollers; not literally friction-free. These bearings reduce energy losses compared to plain bearings and are widely used in rotating machinery.
Q: What are Anti-Oxidants?
A: Additives that increase a lubricant’s resistance to oxidation, extending service life. They slow the formation of acids, sludge, and varnish caused by oxygen exposure.
Q: What is an Antistatic Additive?
A: An additive that raises fuel or oil conductivity to dissipate electrostatic charge during handling. This reduces the risk of sparks and explosions in storage and transfer systems.
Q: What are Anti-Wear Additives?
A: Additives that reduce friction and wear between contacting surfaces. Common examples include ZDDP. They protect heavily loaded machine parts such as gears and hydraulic pumps.
Q: What is API?
A: American Petroleum Institute, the trade association for the oil and natural gas industry. API establishes lubricant standards such as API engine oil classifications.
Q: What is API Gravity?
A: A measure of petroleum liquid density relative to water; values greater than 10 float on water, values less than 10 sink. API gravity is used to classify crude oils and refined products.
Q: What is Ash?
A: The inorganic residue remaining after burning an oil sample; reported as percent by weight. Ash levels are monitored because excessive ash causes deposits, spark plug fouling, and catalyst poisoning.
Q: What are Asperities?
A: Microscopic surface peaks on metals. When opposing asperities contact, friction and wear occur. Lubricants create a film to keep asperities separated and reduce damage.
Q: What is ASTM International?
A: A standards body that develops materials and test method standards (formerly American Society for Testing and Materials). ASTM test methods provide consistency in oil and fuel testing worldwide.
Q: What is Atomic Absorption Spectroscopy?
A: Elemental analysis measuring light absorbed by free atoms to quantify elements in a sample. Used in oil analysis labs to detect wear metals, contaminants, and additives.
Q: What is Babbitt?
A: A family of soft-bearing alloys (tin/lead/copper/antimony, etc.) used as plain bearing surfaces. They embed small dirt particles and conform to shaft surfaces, protecting machinery.
Q: What is a Bactericide?
A: A chemical additive that prevents bacterial growth in fluids. Used in water-containing fluids such as metalworking coolants.
Q: What is Base Number?
A: Milligrams of acid needed to neutralize one gram of oil; indicates reserve alkalinity (ASTM D974/D2896). A declining base number signals loss of protection against acidic corrosion.
Q: What is Base Stock?
A: Refined petroleum or synthetic base fluid into which additives are blended to make finished lubricants. Base stock quality defines the starting point for oil performance.
Q: What is a Beta Ratio (β)?
A: Upstream count of particles of a given size divided by downstream count across a filter under test conditions. Indicates filter efficiency.
Q: What is Biodegradability?
A: Extent to which a substance breaks down to CO₂ and water via microorganisms (readily, inherent, or persistent). Important for environmentally sensitive lubricants.
Q: What are Black Oils?
A: Dark, low-grade lubricants used for slow-moving or rough machinery when premium oils are impractical. They offer minimal performance and are used only in non-critical applications.
Q: What is a Blotter Test?
A: Paper chromatography method to assess soot, dispersancy, and contaminants (e.g., glycol, diesel) in engine oil. Provides a quick field check of oil condition.
Q: What is Boundary Lubrication?
A: Lubrication without a full fluid film; additives strengthen the film to prevent scoring under severe service. Common under high load or low speed.
Q: What is Brookfield Viscosity?
A: Apparent viscosity at low temperature/low shear measured by ASTM D2983. Indicates pumpability at cold conditions.
Q: What is BS&W?
A: Bottoms, sediment, and water—the material that settles at the bottom of storage tanks. Indicates contamination in bulk oils.
Q: What is Carbon Residue?
A: An indicator of an oil’s coke-forming tendency at high temperatures. Fuels and lubricants with high carbon residue can cause deposits.
Q: What is a Catalyst?
A: A substance that accelerates a chemical reaction without being consumed. Used in refining and sometimes harmful in oil oxidation.
Q: What is Cavitation?
A: Formation and collapse of vapor bubbles due to low pressure in a liquid. Causes metal erosion, noise, and vibration in pumps and engines.
Q: What is Centipoise (cP)?
A: A unit of dynamic (absolute) viscosity equal to 0.01 poise. Widely used in oil viscosity reporting.
Q: What is Centistoke (cSt)?
A: A unit of kinematic viscosity equal to 1 mm²/s. Standard for reporting viscosity at 40°C or 100°C.
Q: What is Channeling (grease)?
A: The tendency of grease to form a flow channel in a bearing, leaving shoulder reservoirs that act as seals. While this can help retain grease, it may reduce fresh grease supply to the contact area.
Q: What is Channeling (liquids)?
A: The undesired trough formation in viscous lubricants during cold conditions, leading to marginal lubrication until warmed. This can cause temporary metal-to-metal contact and accelerated wear during cold starts.
Q: What is Channeling Point (gears)?
A: A low-temperature test indicating the tendency of gear lubricants to resist flow and form plastic structures. Oils that channel easily may not lubricate effectively under cold conditions.
Q: What is Chromatography?
A: A family of separation techniques (liquid, gas, gel permeation, paper) used to analyze and fingerprint lubricants. Oil analysis laboratories use chromatography to identify contaminants, additives, and degradation byproducts.
Q: What is Cloud Point?
A: The temperature at which wax crystals cause a fluid to appear cloudy upon cooling. It indicates cold flow performance, particularly in fuels and lubricants used in low-temperature environments.
Q: What is Compounded Oil?
A: Petroleum oil blended with animal or vegetable oils for improved metal affinity and load-carrying. These oils have better lubricity but less oxidation stability, limiting their use in high-temperature applications.
Q: What is Condition Monitoring?
A: Assessing machine condition by interpreting periodic or continuous measurements while running. This includes oil analysis, vibration monitoring, and thermal imaging. Condition monitoring helps predict failures before they occur.
Q: What is Consistency (grease)?
A: Grease softness or hardness measured by cone penetration (ASTM D217). Classified by the National Lubricating Grease Institute (NLGI). Correct consistency ensures grease stays in place without excessive drag.
Q: What is a Contaminant?
A: Any foreign or unwanted substance that degrades system performance or reliability. Examples include dirt, water, fuel, soot, and wear particles.
Q: What is Contamination Control?
A: Planning and actions to achieve and maintain a specified contamination level in systems. Involves proper filtration, seals, and maintenance practices.
Q: What is a Coolant?
A: A fluid used to remove heat. In machining, coolants also lubricate and flush away chips. In engines, they maintain operating temperature.
Q: What is Corrosion?
A: Chemical or electrochemical attack on materials, often metals, causing property deterioration. Water, acids, and oxygen accelerate corrosion in lubricated systems.
Q: What is a Corrosion Inhibitor?
A: An additive that protects metal surfaces from chemical attack, often by forming protective films or emulsions. Essential in oils exposed to moisture or acids.
Q: What is a Cutting Fluid?
A: Fluid applied to cutting tools to cool, lubricate, and improve machining. Reduces tool wear and improves surface finish.
Q: What is Cylinder Oil?
A: High-viscosity oil for lubricating steam/air compressor cylinders and related components. Formulated to withstand high temperatures and pressures.
Q: What are Dark Metallo-Oxide Particles?
A: Partially oxidized ferrous wear particles indicating high heat, often from lubricant starvation or boundary lubrication conditions. Their presence is a red flag in oil analysis.
Q: What is Demulsibility?
A: An oil’s ability to separate from water after mixing. High demulsibility ensures water can be drained off easily, preventing corrosion and additive depletion.
Q: What is a Demulsifier?
A: An additive that promotes oil–water separation in fluids exposed to water or steam. Used in turbines, hydraulics, and circulating systems.
Q: What are Deposits?
A: Oil-insoluble materials from oxidation and contamination (e.g., sludge, varnish, lacquer, carbon). Deposits reduce efficiency and may block oil passages.
Q: What is a Detergent?
A: Additive, often metallic, that helps control deposits and neutralize acids, usually used with dispersants. Essential in engine oils.
Q: What is Dielectric Strength?
A: Voltage an insulating fluid can withstand without failure (e.g., ASTM D877). Key property of transformer and insulating oils.
Q: What is a Dispersant?
A: An additive that keeps insoluble oxidation and combustion byproducts suspended to prevent deposits. Works with detergents in engine oils.
Q: What is the Distillation Method for Water?
A: A method that distills water from a sample with an immiscible solvent and measures the collected volume. Used in lubricants to detect contamination.
Q: What is the DN Factor?
A: Bearing speed factor (bore in mm × rpm) guiding lubricant selection for rolling-element bearings. Helps determine grease type and relubrication interval.
Q: What is Dropping Point (grease)?
A: Temperature at which grease transitions from semi-solid to liquid (ASTM D566). Indicates maximum service temperature.
Q: What is Elastohydrodynamic Lubrication (EHL/EHD)?
A: A regime where elastic deformation and high load temporarily increase viscosity, forming a protective film. Critical in rolling-element bearings and gears.
Q: What is Emission Spectroscopy?
A: Elemental analysis using emitted light intensity from excited atoms (flame, plasma, arc, spark). Used in oil analysis for wear metals and additives.
Q: What is Emulsibility?
A: A non-water-soluble fluid’s tendency to form an emulsion with water. Indicates how oils interact with water contamination.
Q: What is an Emulsifier?
A: Additive that promotes stable oil–water emulsions (e.g., metallic soaps, polar compounds). Used in cutting fluids and fire-resistant fluids.
Q: What is an Emulsion?
A: A two-phase liquid with droplets of one liquid dispersed in an immiscible continuous phase (oil-in-water or water-in-oil). Common in coolants.
Q: What is an Extreme Pressure (EP) Additive?
A: Additive that forms protective films under high load/temperature to prevent seizure of sliding surfaces. Sulfur, phosphorus, or chlorine compounds are typical EP agents.
Q: What is False Brinelling?
A: Fretting-type wear with mild adhesion from small-amplitude oscillations under load. Appears as elliptical wear marks in bearings stored under vibration.
Q: What is Fatigue Wear?
A: Wear caused by crack initiation and growth from repeated stress cycles, leading to pitting or spalling. Common in rolling-element bearings.
Q: What is Ferrography?
A: Magnetic separation and analysis of wear particles in oil to assess wear severity and modes. Powerful predictive maintenance tool.
Q: What is Fire Point?
A: Temperature at which a heated liquid produces vapors that burn continuously when ignited. Indicates flammability of lubricants.
Q: What is a Fire-Resistant Fluid?
A: Hydraulic fluids that resist ignition, e.g., water-oil emulsions, water-glycol, or low-volatility synthetics. Used in steel mills, mines, and power plants.
Q: What is Flash Point?
A: Temperature at which liquid vapors ignite momentarily under test conditions (e.g., ASTM D92). Used to assess handling safety.
Q: What is Fretting?
A: Small-amplitude oscillatory motion between contacting surfaces that can cause surface damage. Produces reddish wear debris (oxidized iron).
Q: What is Friction?
A: Resistance to motion between contacting surfaces; includes static and kinetic components. Friction generates heat and energy loss in machinery.
Q: What is FTIR Spectroscopy?
A: Infrared analysis of lubricants for additive depletion, contamination, and base-stock degradation. Common in used-oil analysis programs.
Q: What is Full-Fluid-Film Lubrication?
A: A continuous lubricating film completely separates surfaces, typically via hydrodynamic action. Provides the lowest wear.
Q: What is a Fungicide?
A: Additive that kills or inhibits fungi in fluids, often those containing water. Important in metalworking coolants.
Q: What is Gas Chromatography?
A: Chromatography using an inert gas as the carrier to separate and analyze components. Applied to fuels, lubricants, and contaminants.
Q: What is Grease?
A: A semi-solid lubricant comprising a thickener dispersed in a liquid base oil, plus additives as needed. Grease provides sealing and stays in place under gravity or pressure.
Q: What are Heat Transfer Oils?
A: Oils formulated as heat-transfer media with low volatility and resistance to cracking/sludging. Used in chemical processing and heating systems.
Q: What is Hydraulic Fluid?
A: A power-transmission medium in hydraulic systems; requires proper viscosity and performance additives. Properties include anti-wear, oxidation stability, and foam resistance.
Q: What is Hydrodynamic Lubrication?
A: A full-film regime where relative motion and geometry generate pressure to separate surfaces. Essential in journal bearings.
Q: What is Hydrolysis?
A: Chemical breakdown of fluids due to heat, water, and metal catalysts. Leads to acid formation and performance loss.
Q: What is Hydrolytic Stability?
A: A lubricant’s resistance to decomposition by water (hydrolysis). Critical for hydraulic fluids.
Q: What is Hydrostatic Lubrication?
A: Lubrication where externally supplied pressure separates static opposing surfaces by a fluid film. Used in machine tools and precision bearings.
Q: What does Immiscible mean?
A: Liquids that do not mix without phase separation (e.g., water and petroleum oil). Immiscibility impacts oil–water contamination issues, especially in lubrication systems.
Q: What is Infrared Spectroscopy?
A: Analytical method using IR absorption to assess used-oil properties and contaminants (see FTIR). It is valuable for identifying oxidation, additive depletion, and contamination.
Q: What is an Inhibitor?
A: An additive that suppresses undesirable chemical reactions, improving product performance. Examples include antioxidants, rust inhibitors, and corrosion inhibitors.
Q: What are Insolubles (used oil)?
A: Contaminants precipitated by solvents (e.g., pentane); further fractionated into toluene-soluble/insoluble resins (ASTM D893). High insolubles signal oxidation or contamination.
Q: What is Interfacial Tension (IFT)?
A: Energy per unit area at the boundary between two immiscible liquids (ASTM D971). Used to monitor oil oxidation and contamination.
Q: What is an Invert Emulsion?
A: A water-in-oil emulsion used as a fire-resistant fluid where oil is the continuous phase. Common in mining and steel industries.
Q: What is the ISO Cleanliness Code (ISO 4406)?
A: A code classifying particle counts at ≥4 µm, ≥6 µm, and ≥14 µm size ranges. Used to monitor hydraulic fluid cleanliness.
Q: What is an ISO Viscosity Grade?
A: A grade defined by the midpoint viscosity at 40°C (e.g., ISO VG 32 is 28.8–35.2 cSt). Standardized system for lubricant selection.
Q: What is Karl Fischer Titration?
A: Coulometric or volumetric titration to measure trace water in samples (commonly ASTM D6304). Highly sensitive for detecting ppm levels of water in lubricants.
Q: What is Kinematic Viscosity?
A: Absolute viscosity divided by fluid density; commonly expressed in centistokes (cSt). Primary measure for oil specification.
Q: What is Lacquer?
A: A hard, high-temperature deposit from oxidation/polymerization; harder than varnish. Lacquer impairs oil flow and valve function.
Q: What are Laminar (reworked) Particles?
A: Large, thin wear particles formed when thicker particles are squeezed through rolling contacts. Their presence indicates advanced fatigue wear.
Q: What is Load-Carrying Capacity?
A: A lubricant’s ability to maintain a separating film under load without failure. Measured in laboratory tests like four-ball EP.
Q: What is Load-Wear Index (LWI)?
A: A four-ball EP-derived measure of a lubricant’s wear protection under load. Higher values indicate better wear resistance.
Q: What is a Lubricant?
A: Any substance between moving surfaces that reduces friction and wear. Lubricants may be oils, greases, or solids.
Q: What is Lubricity?
A: An oil or grease’s ability to lubricate—often called film strength. Lubricity affects wear, energy efficiency, and component life.
Q: What is a Micrometer (µm)?
A: A unit of length equal to one millionth of a meter; often called a micron. Commonly used for particle sizing in contamination control.
Q: What is a Micron?
A: One millionth of a meter; common unit for particle size in contamination control. Synonymous with micrometer (µm).
Q: What is Microscopy (particle counting)?
A: Optical counting/sizing of particles using a microscope. Provides detail on particle shape and wear mode.
Q: What is Mineral Oil?
A: Oil derived from petroleum, as opposed to vegetable or animal sources. Mineral oils are the most common lubricant base stock.
Q: What does Miscible mean?
A: Capable of mixing in any proportion without phase separation. Oils miscible with additives ensure uniform performance.
Q: What is Molybdenum Disulfide?
A: MoS₂; a solid lubricant and additive providing residual lubrication and high-temperature performance. Often used in greases.
Q: What is a Multigrade Oil?
A: Oil meeting multiple SAE viscosity grades, usable over a wider temperature range than single-grade oils. Essential for automotive engines.
Q: What does Naphthenic mean?
A: Pertaining to petroleum fluids rich in cyclic (naphthenic) hydrocarbons from naphthenic crude. Such oils have low pour points and good solvency.
Q: What is Neutralization Number?
A: Obsolete measure of acidic/basic constituents; replaced by Acid Number and Base Number.
Q: What is a Newtonian Fluid?
A: A fluid whose viscosity at a given temperature is independent of shear rate. Most mineral oils behave as Newtonian fluids.
Q: What is Nitration (engines)?
A: Formation of acidic, deposit-forming products during combustion, especially with excess oxygen; accelerates oxidation. Nitration causes varnish and piston deposits.
Q: What is NLGI?
A: National Lubricating Grease Institute; establishes grease consistency grades and promotes grease technology.
Q: What are NLGI Consistency Grades?
A: A penetration-based system rating grease consistency. Ranges from 000 (fluid) to 6 (block).
Q: What is Nominal Filtration Rating?
A: A manufacturer’s non-standard micrometer rating; deprecated due to poor reproducibility. Replaced by beta ratio testing.
Q: What is a Non-Newtonian Fluid?
A: A fluid (e.g., grease, polymer-modified oil) where shear stress is not proportional to shear rate. Exhibits properties like shear thinning or thickening.
Q: What is Oxidation (of lubricants)?
A: Reaction with oxygen that degrades petroleum products; accelerated by heat, metals, water, acids, and contaminants. Leads to sludge, varnish, and acidity.
Q: What is an Oxidation Inhibitor?
A: An antioxidant additive that mitigates oxidation by decomposing peroxides or deactivating catalysts. Extends oil life.
Q: What is Paper Chromatography?
A: A drop-on-paper test observing ring development to assess dispersion and contamination. Simple field test.
Q: What does Paraffinic mean?
A: Relating to petroleum fluids rich in straight-chain saturated hydrocarbons; often with cold-flow limitations but good oxidation stability.
Q: What is Particle Count?
A: A test quantifying particles above selected sizes per unit volume, often expressed per mL. Standard for fluid cleanliness.
Q: What is a Patch Test?
A: Filtering a fixed volume through a membrane and visually comparing discoloration to contamination standards. Used to assess varnish or wear debris.
Q: What is pH?
A: A measure of acidity/alkalinity in water-based fluids; pH > 8 typically inhibits corrosion of ferrous metals.
Q: What is a Polar Compound?
A: A molecule with separated charges; in oils, provides metal-wetting, emulsifying, or detergent action. Polar compounds improve additive performance.
Q: What are Polyglycols?
A: Synthetic base fluids (ethylene/propylene oxide polymers) with high VI, low volatility, and good hydrolytic stability. Used in fire-resistant fluids.
Q: What is Polymerization?
A: Chemical combination of similar molecules to form larger molecules (polymers). Leads to varnish and deposits in oils.
Q: What is a Polyolefin?
A: A polymer made by polymerizing simple olefins (e.g., polyethylene, polyisoprene). Polyolefins are used in packaging and lubricants.
Q: What is a Polyol Ester?
A: A synthetic base stock formed by reacting fatty acids with polyols; high-temp stability and low volatility. Common in aviation lubricants.
Q: What is Pour Point?
A: The lowest temperature at which an oil will flow under specified conditions. Critical for cold weather operation.
Q: What is a Pour Point Depressant?
A: Additive that hinders wax crystal effects to lower the pour point. Ensures oil flow at low temperatures.
Q: What does PPM mean?
A: Parts per million; concentration by weight or volume, e.g., mg/kg. Used for wear metals, contaminants, and additives.
Q: What is Pumpability?
A: Low-temperature, low-shear flow characteristics ensuring adequate oil supply to pumps and components. Assessed by MRV (Mini-Rotary Viscometer).
Q: What is Quenching Oil?
A: Oxidation-resistant oil used to cool metal parts during manufacturing; balances heat removal and distortion risk. Critical in heat-treating processes.
Q: What is R&O Oil?
A: Rust-and-oxidation inhibited oil; highly refined oils for long-service circulating and machinery lubrication. Common in turbines.
Q: What is Re-Refining?
A: Processing used oils to restore properties similar to virgin stocks via filtration, adsorption, or other methods. Supports sustainability.
Q: What is Rheology?
A: Study of deformation and flow of matter; for greases, measured by penetration and apparent viscosity. Important in lubricant formulation.
Q: What is Rolling Contact Fatigue?
A: Crack initiation/propagation under repeated rolling loads, leading to pits or spalls. A common failure mode in bearings.
Q: What is Rolling Oil?
A: Lubricant for metal rolling operations, aiding feed, heat removal, and roll life; may include EP agents or emulsifiers.
Q: What is a Rust Inhibitor?
A: A corrosion inhibitor specifically protecting against rust on ferrous surfaces.
Q: What is a Rust Prevention Test?
A: A test measuring an oil’s ability to prevent rusting in the presence of water.
Q: What is Saturation Level (water)?
A: The amount of water a fluid can dissolve at a given condition. Beyond saturation, free water separates and accelerates corrosion and oxidation.
Q: What is Saybolt Universal Viscosity (SUS/SUV)?
A: Seconds for 60 mL of fluid to flow through a standard orifice at set temperature (ASTM D88). An older viscosity measure, largely replaced by centistokes (cSt).
Q: What is a Semisolid?
A: A material with properties between solid and liquid; deformation depends on magnitude and rate of force. Grease is an example.
Q: What is Shear Rate?
A: Relative velocity between adjacent fluid layers; typically expressed in s⁻¹. Critical in defining how lubricants behave under flow.
Q: What is Shear Stress?
A: Frictional force per area between fluid layers during flow; relates to viscosity and shear rate.
Q: What is Soluble Oil?
A: A milky metal-working fluid composed of water, oil, emulsifiers, and additives where cooling dominates. Used in machining operations.
Q: What is Solvency?
A: A fluid’s ability to dissolve materials and polymers, related to aromatic content. Oils with high solvency keep engines clean but may attack seals.
Q: What is Specific Gravity?
A: Ratio of a liquid’s weight to that of an equal volume of water. Indicates density relative to water.
Q: What is Spectrographic Analysis?
A: Elemental analysis of oil using emitted or absorbed energy to quantify wear, contaminants, or additives. A cornerstone of oil analysis labs.
Q: What is Spindle Oil?
A: Light-bodied oil for textile spindles and other high-speed, lightly loaded machinery. Provides minimal drag.
Q: What is Static Friction?
A: Force required to initiate motion between two bodies under load; also called break-away friction. Higher than kinetic friction.
Q: What is Sulfated Ash?
A: Ash content of fresh, compounded oil measured by ASTM D874; indicates metallic additive level. High sulfated ash can damage after-treatment devices.
Q: What is a Surfactant?
A: Surface-active agent that lowers interfacial tension and can affect foam, wetting, and emulsification.
Q: What is a Synthetic Lubricant?
A: A chemically engineered base fluid with tailored properties; often higher VI, stability, and service life. Includes PAOs, esters, polyglycols.
Q: What is a Tackifier?
A: High-molecular-weight polymer added to improve grease adhesiveness (tack). Helps grease stay in place on open gears or chains.
Q: What is Thermal Stability?
A: Ability of a lubricant to resist oxidation and decomposition at high temperatures. Critical in turbines and compressors.
Q: What is Thermography?
A: Non-contact temperature measurement using infrared radiation from surfaces. Used in predictive maintenance.
Q: What is Thixotropy?
A: Tendency of some materials (e.g., greases) to soften under shear and recover when shear stops. Important in grease pumpability.
Q: What is Tribology?
A: The science of interacting surfaces in relative motion—covering lubrication, friction, and wear. Tribology integrates physics, chemistry, and materials science to extend machine life.
Q: What is Vapor Pressure?
A: The equilibrium pressure of a vapor above its liquid at a given temperature; indicates volatility. Higher vapor pressure means faster evaporation.
Q: What is Reid Vapor Pressure (RVP)?
A: A standardized vapor pressure at 100°F used to assess vapor-lock tendency and emissions. Important in fuels.
Q: What is Varnish (in lubricants)?
A: A hard, baked-on coating from oxidation byproducts on hot surfaces that can accelerate wear. Causes sticking of valves and tight clearances.
Q: What is a Viscometer?
A: An instrument used to measure a fluid’s viscosity. Common types include capillary and rotational.
Q: What is Viscosity?
A: A measure of a fluid’s resistance to flow; depends strongly on temperature and test method. Central property of lubricants.
Q: What is Viscosity, Absolute?
A: Shear stress divided by shear rate; commonly expressed in centipoise. Also called dynamic viscosity.
Q: What is Viscosity, Kinematic?
A: Absolute viscosity divided by density; commonly expressed in centistokes (cSt). Used in most lubricant specifications.
Q: What is Viscosity, SUS?
A: Saybolt Universal Seconds—the flow time for a standard volume at a specified temperature (ASTM D88).
Q: What is a Viscosity Grade?
A: A classification system defining viscosity ranges for specific lubricant applications. Includes ISO VG and SAE grades.
Q: What is Viscosity Index (VI)?
A: A unitless measure of how viscosity changes with temperature; higher VI means less change. Critical for multi-grade oils.
Q: What is a Viscosity Index Improver?
A: A polymeric additive (viscosity modifier) that increases an oil’s VI. Enables multigrade performance.
Q: What is Volatility?
A: A measure of a fluid’s tendency to evaporate; higher volatility means lower boiling point and greater loss. Impacts oil consumption.
Q: What is a Way Lubricant?
A: A lubricant formulated for machine-tool sliding ways to minimize stick-slip and provide film strength. Includes tackifiers to adhere to surfaces.
Q: What is White Oil?
A: Highly refined, light-colored mineral oil used in pharmaceuticals, cosmetics, and sensitive applications. Non-toxic and odorless.
Q: What is ZDDP?
A: Zinc dialkyldithiophosphate; a widely used anti-wear and antioxidant additive. Provides wear protection in engines and hydraulic systems but can poison catalysts in exhaust systems.