Straight cutting oils

Identity and boundaries

MOTOREX reports ASTM D130 copper corrosion 1B for ORTHO S 22 and 4A for ORTHO TX 15, without duration or temperature. Those grades do not establish performance on every copper alloy. The two products are neat oils intended for use without water dilution. OSHA metalworking-fluid classes

Master Fluid Solutions uses “straight mineral oil” for additive-free petroleum oil. A straight cutting oil can have other base fluids and additives. Master Fluid Solutions glossary, straight oil and straight mineral oil NIOSH metalworking-fluid functions

Base fluids and additive roles

A base-fluid description and a performance-additive description answer different questions. MOTOREX identifies SWISSCUT ORTHO S 22 as a low-aromatic mineral-oil product containing anti-aging, corrosion-protection, and extreme-pressure additives. It describes that product as free of chlorine and heavy metals. The sheet gives no additive concentrations or active-sulfur assay. ORTHO S 22 technical sheet, March 9, 2023, code 20

Esters can supply boundary lubrication. Extreme-pressure, or EP, additives have a different stated mechanism. Chlorine, sulfur, or phosphorus compounds can react at contacting metallic surfaces to form lubricating films and reduce chip welding. These are ingredient roles, not a formulation recipe. An ester can be a lubricant base or part of an additive system. The term does not establish vegetable origin, renewable fraction, or finished-fluid biodegradability. Master Fluid Solutions glossary, ester, polyol ester, EP additives, and EP lubricity

Master Fluid Solutions describes TRIM OV 2200 on its US English page as a vegetable-based, bio-based straight oil made with a proprietary renewable blend. Its application description concerns difficult alloys and stainless steels and mentions sensitive aluminum and copper alloys. The page supplies no exact renewable percentage or complete formula. Its claims about medical-industry restrictions do not name a particular specification or approval. Those claims therefore do not establish qualification for an unidentified medical component. TRIM OV 2200 product description, undated web snapshot

MOTOREX's DECO BX 10 sheet separately reports more than 25% renewable raw materials and a declaration against EN 16807. It names OECD 301 B biodegradability and OECD 201, 202, and 203 ecotoxicity tests. The sheet provides neither underlying test reports nor numerical degradation or toxicity results. Its two bio symbols do not establish that every neat oil is biodegradable or harmless. DECO BX 10 technical sheet and symbols, August 25, 2023, code 20

ROCOL's ULTRACUT 550 technical sheet identifies severely refined mineral oil, lubricity additives, and chlorinated EP additives. The sheet describes a ready-for-use neat fluid for applications including automatic lathes, high-tensile steels, broaching, and hobbing. This is not a chlorine-free product description. ULTRACUT 550 technical sheet, February 2009

Supplied-product data and source versions

The following values describe the named supplied products in the cited sheets. They are not current-lot certificates. MOTOREX's footnotes retain testing and production tolerances and the right to change data. The ROCOL sheet bases its information on experience and customer reports and disclaims responsibility for factors outside its knowledge. A download folder dated 2026 does not change the older date printed inside a document.

Sources for the complete product-data rows are the ORTHO S 22 sheet, ORTHO TX 15 sheet, DECO BX 10 sheet, and ULTRACUT 550 sheet.

ExxonMobil's English GB-region Mobilmet 427 page also displays a four-grade Mobilmet 420 family table. For the 427 column, it reports the following distinct basis. The page has no displayed technical revision date. Mobilmet 427 and family table

The same page describes the family as chlorine-free and suitable for light to moderate cutting. Its multi-service hydraulic and machine-lubrication description requires appropriate viscosity selection. It is not evidence that another straight cutting oil is a suitable hydraulic fluid. Mobilmet 427 applications

Quantities and conditional comparisons

Kinematic viscosity has units of mm²/s, equivalent to cSt. Dynamic viscosity has units of mPa·s, equivalent to cP. Dynamic viscosity equals kinematic viscosity multiplied by density on a consistent temperature and unit basis. For example, mm²/s multiplied by g/cm³ gives mPa·s. These units are not interchangeable without density. The public ASTM D445-24 scope describes the relationship and its Newtonian-flow limitation. This is a historical edition, not a claim that it is the latest edition. ASTM D445-24 public scope

Synthesis. The table's 40 °C viscosities and 20 °C densities do not give an exact 40 °C dynamic viscosity. Combining those temperatures silently would add an unsupported density assumption. Density in g/cm³ and kg/L is numerically equivalent at the same temperature. Relative density or specific gravity is dimensionless and needs a reference basis. A missing method, test temperature, or result stays unknown rather than becoming zero.

Synthesis. ORTHO S 22's reported viscosity exceeds TX 15's at the common 40 °C test condition. That observation establishes neither lower cutting temperature nor longer tool life. A flash point, pour point, and viscosity reference temperature also describe different tests. None is a recommended machine operating temperature. The greater-than sign on a flash point remains a bound rather than an exact value. Open-cup and unspecified-method results do not support an unqualified numerical ranking.

Sulfur activity and material compatibility

Active sulfur is a test-dependent quantity. ASTM D1662-24's public scope covers sulfur reactive with copper powder at 150 °C, including natural and added sulfur. Its public significance statement says reaction rates depend on the metal, temperature, and time. It explicitly leaves the relationship between measured active sulfur and cutting-fluid field performance unestablished. That 150 °C condition is analytical, not a cutting-temperature target. ASTM D1662-24 public scope and note

Master Fluid Solutions states that TRIM OM 303 contains no active sulfur and associates that statement with nonstaining behavior. Its page names aluminum and steel alloys, cast iron, copper, brass, and bronze. The statement does not report total sulfur, an inactive-sulfur percentage, or a complete copper-test protocol. Absence of active sulfur therefore cannot be rewritten as absence of all sulfur. TRIM OM 303 US English product description

Synthesis. TX 15's listed nonferrous applications coexist with its reported 4A copper-corrosion grade. Neither fact erases the other. S 22 and DECO BX 10 report 1B, but omit test temperature and duration. Mobilmet 427 explicitly reports three hours at 100 °C. These are not complete matched tests across all four products. Copper-strip data do not by themselves establish compatibility with every aluminum alloy, coating, seal, adhesive, or subsequent finishing process. None of the sampled MOTOREX technical sheets identifies an active or inactive sulfur concentration.

Performance claims and exposure limits

MOTOREX describes low evaporation, low mist, surface quality, and tool-life benefits for its sampled products. Its sheets provide no matched emissions measurements, tool-life endpoint, cutting protocol, or numerical volatility result. TX 15's broad material list is an application statement, not a guarantee for every alloy and finish requirement. ORTHO TX 15 description and footnote

OM 303's maker claims low misting, easier washing, and favorable tool life against certain other oils. The page does not provide a complete comparative protocol, cleaner chemistry, residue endpoint, or numerical improvement. Clean-running and easy-washing descriptions do not establish residue-free parts, paint adhesion, welding suitability, or medical cleanliness. TRIM OM 303 performance descriptions

NIOSH's October 6, 2008 bulletin reports recommended exposure limits of 0.4 mg/m³ thoracic particulate mass or 0.5 mg/m³ total particulate mass. The basis is a time-weighted average for up to ten hours per day during a forty-hour workweek. These are airborne exposure recommendations, not fluid concentrations or guarantees of no effect. NIOSH also reports health effects below exposure limits. Mist, splashes, and contaminated surfaces can expose workers even when a product has a low-mist claim. NIOSH bulletin and exposure basis

Safety-document limits and unresolved evidence

ROCOL's linked ULTRACUT 550 GB-English SDS is version 7.0, revised February 8, 2023. Every page is marked draft. Section 3 lists hydrotreated naphthenic distillate, CAS 64742-53-6, at 15–30% in a column headed percent. This is a partial disclosure, not a full formula or lot assay. Section 2 describes the mixture as not classified, while sections 11 and 12 contain additional statements about skin dryness, harm to breast-fed children, and aquatic toxicity. The unresolved wording and draft status prevent a current compliance or hazard-absence conclusion. ULTRACUT 550 draft SDS, sections 2, 3, 11, 12, and 16

The draft describes a brown liquid, whereas the technical sheet lists pale yellow. It reports approximately 25 mm²/s at 40 °C and a 200 °C flash point without a listed method. Its relative density of 0.9 lacks a reference temperature. Those fields cannot silently replace the technical sheet's density. Its VOC entry is 0 g/L without a stated analytical method. A VOC entry does not measure airborne oil mist. ULTRACUT 550 draft SDS, sections 9 and 15

This review covers the complete one-page technical sheets cited above, their tables and footnotes, the eight-page ULTRACUT 550 draft SDS, the Mobilmet web table, relevant maker glossary entries, and the cited public occupational-health and standards summaries. It does not include full normative standards or underlying product qualification tests. Current final SDS coverage for the sampled MOTOREX and TRIM products remains incomplete. Proprietary additive identities, exact ester content, current-lot composition, solids content, numerical evaporation loss, and customer-specific compatibility remain unknown. The evidence establishes neither a manufacturing formula nor a customer-qualified machining, maintenance, cleaning, or disposal process.

Related reference

Surface-finishing processes gives context for downstream requirements. Cutting-fluid application claims alone do not establish compatibility with a subsequent finish.