Industrial Lubrication and Oil Analysis: Plan and Diagnosis

What industrial lubrication and oil analysis are

Industrial lubrication means applying the right lubricant, in the right amount, at the right point and at the right time to cut friction, heat and wear. Oil analysis is the periodic laboratory test of a lubricant sample: it shows the condition of the oil, its contamination and the internal wear of the machine without opening it.

The two form one loop. The lubrication plan defines what to apply and when; oil analysis checks that the plan works and warns of failure before breakdown. It is the practical core of preventive and predictive maintenance on gearboxes, hydraulic systems, compressors and bearings.

Visual map of the lubrication schedule and oil analysis

The map sums up the schedule, the grease calculation, contamination and how to read viscosity and the ISO 4406 code.

The lubrication schedule: what it must contain

A lubrication schedule is a list of lube points, and each point answers six questions: which lubricant, how much, how often, by what method, who does it and what to do if something looks abnormal. The schedule feeds the maintenance plan as dated tasks with an owner, and the operator's route under TPM autonomous maintenance.

The table is an example. Real amounts and intervals come from the OEM manual, temperature, speed and equipment criticality.

How much grease: calculation for rolling bearings

Over-greasing overheats bearings as often as under-greasing does. A widely used rule of thumb for the relubrication quantity is:

G (g) = 0.005 × D × B

where D = bearing outside diameter (mm) and B = total width (mm). The manufacturer's manual always overrides the rule.

Example: a 6310 bearing, D = 110 mm and B = 27 mm.

• G = 0.005 × 110 × 27 = 14.85 g per bearing.
• A route with 20 identical bearings: 20 × 14.85 = 297 g per round.
• With 6 rounds a year (every 2 months): 297 × 6 = 1,782 g, about 1.8 kg per year.

The same number sizes grease consumption and stock in the storeroom.

Contamination: the lubricant's number one enemy

Most lubricant-related failures come from contamination, not from the quality of new oil. The four most common contaminants:

• Solid particles: dust, sand and metal chips. They score surfaces and speed up abrasive wear.
• Water: enters through breathers, poor seals and condensation. It thins the oil film, promotes rust and oxidizes the oil.
• Heat: speeds up oxidation. The oil darkens, thickens and forms sludge.
• Product mix-up: incompatible oil or grease, or the wrong viscosity.

Control starts before the lab test: desiccant breathers with filters, sound seals, labelled and closed containers, dedicated pumps and hoses per product, and filtering new oil before filling.

How to read an oil analysis report

The lab returns a report with several tests. The main ones:

Viscosity example: ISO VG 68 has a nominal viscosity of 68 cSt at 40 °C, with a range of 61.2 to 74.8 cSt (±10%). A sample reading 82 cSt is (82 − 68) ÷ 68 = +20.6%: out of range, pointing to oxidation, loss of light fractions or the wrong product. A reading of 55 cSt would be −19.1%, typical of dilution or shear-related degradation.

ISO 4406 cleanliness: the code has three numbers (particles above 4, 6 and 14 µm per mL). Each code step means roughly double the particles. If the target is 17/15/12 and the sample comes back 19/17/14, that is two steps in every size range, or about 2 × 2 = 4 times more particles than acceptable. The action is to filter, find where the contamination gets in and resample.

How to take a sample without spoiling the result

1. Sample with the machine running or just after shutdown, while the oil is warm and mixed.
2. Always use the same point, preferably a sampling valve, in the flow and away from the reservoir bottom.
3. Use a clean bottle from the lab and single-use tubing or pump.
4. Label it with equipment, point, date, running hours, oil type and last change date.
5. Send it promptly and keep the history: one sample says little, the trend says a lot.

Set the frequency by criticality: critical equipment (press hydraulics, a single-line gearbox) deserves monthly or hour-based sampling; secondary equipment, quarterly. Cross-check with vibration analysis: rising iron in the oil plus rising vibration on the same bearing confirms the diagnosis. The results can feed a CMMS with limit alerts.

Common mistakes

• Greasing "until it comes out": too much grease causes heat and leaks.
• Changing oil by calendar without checking condition, or never changing it.
• Mixing products of different suppliers or bases without checking compatibility.
• Sampling from the reservoir bottom or with a dirty pump.
• Reading only the latest report, not the trend.
• Treating the symptom (an oil change) without removing the source of water or dust. For repeat failures, use the 5 Whys.

Frequently asked questions

What is oil analysis used for?

To assess oil condition, contamination and internal machine wear, and to act before failure.

How often should oil be analyzed?

It depends on criticality: monthly or per running hours for critical equipment, quarterly for secondary. Adjust by trend.

How much grease goes into a bearing?

A rule of thumb is G = 0.005 × D × B, in grams. For a 6310 (110 × 27 mm), 14.85 g. Always check the OEM manual.

What does ISO VG 68 mean?

An oil with a nominal viscosity of 68 cSt at 40 °C, with a range of 61.2 to 74.8 cSt.

What does an ISO 4406 code of 19/17/14 mean?

Particle levels above 4, 6 and 14 µm per mL. Each higher number means roughly double the particles.

Can I mix different greases?

Only with compatibility confirmed by the manufacturer. Incompatible thickeners can soften or harden the grease.

About the author

Vagner Soares

Lean Manufacturing & Behavioral Management Specialist

Over 20 years in the automotive and metalworking industries (GM and Dana), Lean Manufacturing practitioner since 2006. SENAI instructor and mentor in Brazil’s Brasil Mais Produtivo program, delivering consulting, training and audits for 50+ companies, combining quality, productivity and people development.

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