An oil lubricant typically contains 95% base oil (most often mineral oil distillate of petroleum) and 5% additives, while greases blend that same base oil with a soap thickener to form a semi-solid [S3].
Grease becomes fluid at a dropping-point temperature of 200 to 500°F, depending on the thickener system and additive package, which is the first number a fabricator should write down when comparing products [S1].
Four Lubricant Forms Used on a Fabrication Floor
Oils, greases, pastes and waxes, and bonded coatings are the four categories most often specified for industrial power-transmission and machine-tool duty, and the boundary between them is set by thickener or carrier rather than by additive chemistry [S3].
Selection rule: if the equipment can be re-lubricated on a regular interval, a general-purpose mineral or semi-synthetic oil is usually enough; if it is "lubricated for life" or runs in a sealed housing, the design justifies a synthetic specialty oil such as a polyalphaolefin (PAO) or synthetic ester with higher viscosity index and oxidation stability [S3].
Paste lubricants add solid particles (commonly graphite, MoS2, or PTFE) to the base oil and are most often used for assembly, threaded fasteners, and slow-sliding surfaces where a fluid film cannot be sustained [S3].
Base-Oil Chemistry: Mineral, Synthetic, Semi-Synthetic, Bio-Based
Mineral oil lubricants are distillates of refined petroleum and remain the most common type in general industrial service because they are cost-effective, seal-compatible, and adequate for moderate temperature and load [S5].
Synthetic lubricants, typically PAOs or synthetic esters, are produced from defined chemical feedstocks rather than refined from crude, and they deliver higher viscosity index, better oxidation resistance, and wider operating-temperature windows; semi-synthetic blends sit between the two on cost and performance [S3][S5].
Bio-based lubricants (vegetable-oil-derived) are specified where biodegradability and low toxicity matter, for example in utilities, agriculture, or near waterways, but they trade away some of the thermal ceiling that mineral and synthetic oils offer [S5].
How to Read a Lubricant Specification Sheet
A plant-grade lubricant specification normally carries four blocks: scope of application, physical and chemical properties, performance properties, and product approvals; the example pattern in the reference is "API Group II mineral gear oil with EP additives for gearboxes up to 160°F on bath or circulation" [S2].
Physical and chemical properties are anchored to ASTM methods: ISO viscosity grade to ASTM D2422, viscosity index to ASTM D2270, aniline point to ASTM D611, flash point to ASTM D92, and thickener type declared explicitly; performance properties ride on tests such as copper corrosion (ASTM D130), demulsibility (ASTM D1401), and grease dropping point (ASTM D2265) [S2].
Product-compatibility notes catch the most expensive mistakes: a polyalkylene glycol (PAG) gear oil is not miscible with mineral oil or with PAO, so a switch must be flushed, not topped up [S2].
Selection Criteria Mapped to Operating Conditions
The five inputs that drive every lubricant decision are speed, temperature, load, environment (moisture, dust, chemicals), and maintenance interval; each of these either narrows the base-oil family, the additive package, or the thickener choice [S8].
For high-load gearboxes and rolling-element bearings, an extreme-pressure (EP) additive package with anti-wear (AW) chemistry is the default, while high-speed spindles typically need lower-viscosity ISO VG 32 or VG 46 oils with defoam and demulsifier additives [S1][S2].
For low-temperature service, synthetic base oils are typically preferred over mineral oils because they have a lower pour point, which keeps the fluid flowing at start-up and prevents starved lubrication [S7].
Comparison: Oil, Grease, Paste, Bonded Coating
Oils deliver the lowest friction in high-speed, well-sealed housings and are easy to filter; greases simplify sealing and extend re-lube intervals but add churning losses; pastes handle boundary lubrication on slow slides and threaded joints; bonded coatings (dry-film lubricants) are the right call where the surface runs hot, dusty, or wet enough to wash out an oil film [S3][S8].
Decision snapshot: bath or splash gearbox, oil; electric-motor rolling bearings, polyurea- or lithium-thickened grease; lead-screw or open gear, MoS2 or graphite paste; oven conveyor chain or paint-line conveyor, bonded PTFE or graphite coating [S1][S3].
Common Failure Modes and What They Tell the Spec Writer
A lubricant that darkens fast, builds varnish on filters, or shows a rising acid number (TAN) is oxidising, which usually means the operating temperature is above the oil's design ceiling or the oil is being held in service too long [S2][S5].
Grease that bleeds oil in storage is a thickener-capacity problem, while grease that hardens in service points to either contamination, water ingress, or a base oil that has evaporated under sustained heat [S1].
For food, pharma, and cosmetic fabrication lines, the spec must additionally call out an NSF H1 or equivalent food-grade registration, and synthetic base oils are often preferred there for the same low-temperature and long-life reasons that apply in any other industry [S7].
Approvals, Standards, and Where to Stop Reading the Datasheet
Plant-grade specifications should pin down the OEM approvals explicitly: AGMA for gear oils, NLGI consistency grade for greases, and any machine-builder endorsement that the warranty requires; a lubricant that only "complies with" a standard is not the same as one that is certified to it [S2].
For a useful baseline on lubricant families, the encyclopedic entry on industrial lubricant types and uses is a good cross-reference when trialling a new vendor, and the broader decision flow for industrial adhesive selection is a useful parallel when both materials are being specified on the same assembly line.
For the relevant spec sheets and selection criteria, see industrial borescope.