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Oil analysis is the most cost-effective diagnostic tool for servo press gear systems. A 30 USD oil sample can prevent a 50,000 USD gearbox failure. Here is how to interpret the results.
## What to Test For
Send samples to a lab that reports:
- Viscosity at 40C and 100C
- Water content (Karl Fischer method)
- Particle count (ISO 4406 cleanliness code)
- Wear metals: iron (Fe), copper (Cu), aluminum (Al), chromium (Cr)
- Additive metals: zinc (Zn), phosphorus (P), calcium (Ca)
## Interpreting Viscosity Results
Compare to the new oil specification. Acceptable range: within 10% of nominal.
- Viscosity too low: oil is thinning due to contamination or thermal degradation. Change oil.
- Viscosity too high: oil is thickening due to oxidation. Change oil.
## Interpreting Water Content
Target: under 0.05% water.
- 0.05-0.1%: investigate source, increase monitoring frequency
- Over 0.1%: change oil immediately, find and fix the water source
Water in gear oil causes hydrogen embrittlement of bearing surfaces and accelerates fatigue failure.
## Interpreting Wear Metals
Iron (Fe): comes from gears and bearing races. Baseline for a healthy system: under 50 ppm. Rising trend indicates gear or bearing wear.
Copper (Cu): comes from bronze bushings and thrust washers. Baseline: under 20 ppm. Rising trend indicates bushing wear.
Chromium (Cr): comes from bearing races. Any significant chromium (over 5 ppm) is a warning sign.
## Action Levels
Normal: all metals within baseline, viscosity within spec, water under 0.05%
Monitor: any single parameter 2x baseline, increase sampling to monthly
Investigate: any parameter 3x baseline or rapid increase between samples
Act immediately: water over 0.1%, viscosity out of spec, any metal over 5x baseline
## Sampling Procedure
Sample from the same location every time (drain plug or dedicated sampling valve). Sample when the oil is at operating temperature. Use clean sampling equipment. Label with machine ID, date, and oil hours since last change.