Grease Life Factor⚠ unverified
Mechanical / Lubrication · Compute the temperature-corrected grease life
Parameters
| Input | Symbol | Unit | Default | Description |
|---|---|---|---|---|
| T | T | degC | 1.0 | Operating temperature |
| base_life | baselife | h | 1.0 | Reference grease life at 40 degC |
| Output | Symbol | Unit | Description |
|---|---|---|---|
| result | life | h | Temperature-corrected grease life, in hours (h) |
The science & history
Understanding the Parameters
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Operating temperature $T$ — the dominant factor in grease life. Every ~15 °C above the reference roughly halves the life, because oxidation (an Arrhenius-rate chemical process) speeds up exponentially with temperature and the base oil bleeds and evaporates faster. A bearing running 30 °C hotter needs re-greasing ~4× as often. (This is why the sign must be a decay, not growth.)
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Base life — the reference re-lubrication life at 40 °C, from the grease manufacturer's data or a bearing-life chart (itself a function of bearing type, size, and speed factor $n\,d_m$).
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The decay constant (0.05/°C) — sets the halving temperature. With the (correct) magnitude 0.05/°C, life halves about every 14 °C — consistent with the standard grease-life rule. The registry's positive sign inverts this behaviour.
Derivation (Approaching a Proof)
Grease life is limited chiefly by oxidative and thermal degradation of the base oil, a chemical reaction whose rate follows the Arrhenius law:
$$\text{rate} \propto e^{-E_a/(k_B T)},$$
so the reaction rate rises exponentially with temperature and the life (inversely proportional to the degradation rate) falls exponentially:
$$\text{life}(T) = \text{base\_life}\cdot e^{-\beta(T - T_{\text{ref}})}.$$
Linearising the Arrhenius temperature dependence about the 40 °C reference gives the constant $\beta$; the empirical grease-industry value corresponds to a halving per ~15 °C, i.e. $\beta = \ln 2/15 \approx 0.046$/°C $\approx 0.05$/°C. The negative sign is essential — it is the same Arrhenius origin as Viscosity Temperature (viscosity falls) and the reason all lubricants have a maximum operating temperature. The registry's positive exponent contradicts this well-established behaviour and is almost certainly a sign error; the magnitude (0.05) is right, only the sign is wrong.
Dimensional check. The exponent $0.05(T-40)$ is dimensionless (per-°C × °C), so $[\text{life}] = [\text{base\_life}] = \text{h}$. ✓
History and Development
Temperature-halving rules for grease and oil life are long-standing lubrication-engineering practice (SKF, NLGI grease guides), rooted in the Arrhenius kinetics of oil oxidation. Grease re-lubrication intervals as a function of bearing speed factor ($n\,d_m$) and temperature are tabulated by bearing manufacturers and underpin maintenance scheduling. The temperature sensitivity is why high-temperature applications use synthetic (PAO, PFPE) greases with far lower degradation rates.
Related Concepts: Viscosity Temperature, Bearing Life Modifier, Bearing Rating Life L10, Viscosity Required, Stribeck Curve
Notes: Likely sign bug — grease life should decrease with temperature ($e^{-0.05(T-40)}$, halving ~every 15 °C); the registry's positive exponent is inverted (see note). Reference 40 °C. High-temp applications need synthetic greases.