Iso Viscosity Grade
What does 'VG 46' mean?
It means the oil's nominal kinematic viscosity at 40°C is 46 cSt, with an acceptable range of 41.4 to 50.6 cSt.
Does a higher ISO VG always provide better protection?
No; higher viscosity improves film thickness but increases internal drag, energy consumption, and cold-start resistance. The correct grade balances lubrication demand and pumpability.
Why is 40°C used?
ISO VG uses 40°C as a standardized benchmark for comparing industrial lubricants under a temperature representative of many machinery conditions.
ISO Viscosity Grade (ISO VG) is the ISO 3448 classification that assigns industrial lubricants a nominal kinematic viscosity at 40°C, expressed in mm²/s (cSt). Each grade has a ±10% tolerance. It standardizes oil thickness for hydraulic, spindle, way, and gear oils, enabling comparison across brands.
On a CNC shop floor, ISO VG dictates the fluid's flow and film strength. Technicians select grades based on machine OEM specs for hydraulic reservoirs, spindle bearings, and slideways. A mismatch—using ISO VG 68 when 32 is specified—causes sluggish axis motion, pump cavitation, or overheating. Conversely, too thin oil leads to leakage and boundary wear. Common grades: ISO VG 32 for hydraulic systems, 46 for general purpose, 68 for heavier loads. The grade ensures the oil pumps correctly at 40°C reference, but real-world temperature shifts must be considered. This selection affects machine responsiveness, tool life, and component reliability.
Brand Mislabeling: Two hydraulic oils from different brands may have different ISO VGs, causing sluggish actuators or pump starvation if the wrong grade is installed.
Performance Assumption: ISO VG does not guarantee anti-wear or oxidation resistance; a correct viscosity oil can still fail if the additive package is inappropriate.
Temperature Blindness: ISO VG is rated at 40°C, but actual machine temperature varies; cold starts may cause poor flow, while high heat can collapse film strength.