Evaluation / how a changeover is decided
What we gather, what we measure on site, what comes back, and the trial that decides it.
Written for the people who run the mill: the mill manager, the process engineer and the reliability superintendent. It sets out how CMD evaluates a change of open-gear lubricant on a girth gear. Nothing changes until the baseline is on paper.
01What we gather
Seven things, and the site holds most of them already.
Most of it is in the mill's own records. Send what you have; the gaps are filled on site. They are seven of the eight lines the quote email asks for.
| Item | Why it matters |
|---|---|
| Mill OEM, and how many mills | A Whitmore approval or specification may already exist for that OEM. |
| Mill size | Diameter, length and drive power. The consumption estimate starts from gear diameter and face width. |
| The product in use, and since when | Type, grade and how it is applied. |
| Consumption | Kilograms a day or drums a month, as the store records it. |
| The gear set's history | Age, condition, previous grinding, pinion replacement. |
| The problem as the site sees it | Consumption, wear, leakage, pumpability, spillage, root build-up. |
| The spray system, and where the nozzles point | Girth gear or pinion; pattern, pressure and interval. |
02What we measure
Three are taken with the mill running, two with it stopped, and one is a calculation.
| Check | How | What it shows |
|---|---|---|
| Thermal images | Pinion and girth gear, across the face. | The temperature profile. A gradient across the face points to misalignment or a coverage gap. |
| Pinion bearings | Vibration and temperature, drive end and non-drive end. | The condition the trial is compared against. |
| Strobe inspection, running | Where the film is transparent, the running flanks are lit at gear speed and photographed. | Contact pattern and film in service. |
| Stationary inspection | Flanks examined with the mill stopped. A grease-type film is cleaned off first. | Pitting, scuffing, wear steps, root build-up. |
| Spray system | Pattern, pressure and nozzle placement, onto the girth gear or the pinion. Checked locked out. | Whether the film lands where the load is. |
| Consumption | Estimated from gear diameter and face width, then compared with what the store issues. | Whether the application rate suits the gear. |
The running checks need no stoppage. The two stationary checks wait for a planned stop. The pattern, strobe and thermal checks are described in the spray-nozzle article.
03What you get back
Where the set-up can improve, what a changeover would change, and which OEM listings apply to your mill.
| Part | What it covers |
|---|---|
| The set-up | Spray pattern, pressure and nozzle placement; temperatures and vibration; the condition of the flanks. Often the spray system improves before any product changes. |
| The changeover | What a different class of lubricant would change: viscosity, pumpability, load capacity, wear protection, and whether the flank surface recovers. Compared with the product in use, property by property. |
| OEM listings | The approvals and specifications that apply to your mill's OEM, each with its basis. |
It is written down so the trial has something to be measured against.
04The trial
Ore, weather and gear age all drift. A switchback trial cancels them and puts a number on the lubricant.
Switch the product in and out in random order, and compare each ON period with its paired OFF period. Slow changes in ore, moisture and ageing cancel inside each pair. A short conditioning window after each switch is left out of the analysis. paper §8
| Endpoint | Role | Why |
|---|---|---|
| Open-gear lubricant consumption | Fast, confirmatory | The effect is large, about 70% in the field record, so it shows in a few pairs. paper §8 |
| Mill specific energy | Primary | The signal is about 4% against large ore and throughput swings, so the trial needs enough pairs. paper §8 |
| Reducer wear metals | Supporting | Iron and copper in the oil move slowly; temperature, power and oil condition carry the weight meanwhile. paper §8 |
The trial length is calculated, not guessed. The noise term was measured in the 2015 South African gold-mine trial. paper §8 It is σd = 0.73 kWh/t at SCADA logging resolution. paper §8 To detect a 4% saving at 95% confidence and 90% power, one-sided, takes 9 ON/OFF pairs. paper §8 The paper recommends 12 pairs, for margin: roughly three to four months of logging. paper §8 Logging stays at SCADA resolution; coarse snapshots multiply the pairs needed many times over. paper §8
Surface improvement can take months to show on the flanks. The trial is read over the long view, not the first week.
Integrity precedes efficiency. paper §9 The lubricant's first duty is to preserve the gear; energy is a by-product, measured rather than promised. The switch is reversible, and the trial halts on any adverse gear indication: temperature, vibration, visual or oil analysis. paper §8
05Four kinds of open-gear lubricant
Which class a product belongs to says which lubrication regime it aims at. Asphaltics are not greases.
| Class | Made from | Regime it aims at |
|---|---|---|
| Fluids and residual compounds, asphaltic and non-asphaltic | Resins, polymers and petroleum distillates; asphalt in the older products. | Hydrodynamic and elastohydrodynamic: a full film. |
| Oil-type open-gear lubricants | Synthetic or semi-synthetic base oils with additives. | Hydrodynamic and elastohydrodynamic: a full film. |
| Greases and semi-fluid greases | Thickener systems. | Boundary. |
| Gel and polymer-thickened | Polymer thickeners. | Like a semi-fluid grease, but it builds a film viscosity. |
For mill girth gears, CMD's first choice is a full-film class: a fluid or an oil-type lubricant.
Reference: “Practical Lubrication of Open Gearing”, machinerylubrication.com.
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