1. Scope and Purpose
This guide defines the technical procedures for grease condition analysis, chemical compatibility determination and relubrication planning for rolling element bearings used in high-precision machine tools. Proper maintenance is critical to prevent premature failure due to fatigue, contamination or thermal degradation. The procedure applies to spindles, asynchronous motors, motorized axes and screw-nut assemblies. The objective is to guarantee the maximum useful life of the components while maintaining nominal kinematic performance.
2. Safety Precautions
WARNING: DANGER OF SUBCUTANEOUS INJECTION. Manual and pneumatic grease guns can generate pressures in excess of 300 bar. Never check for grease leaks or blockages with your hands or body parts. Wear oil-resistant gloves and eye protection.
DANGER: DANGEROUS ENERGY. Before any intervention, carry out the Lockout/Tagout (LOTO) procedure on the machine's main switch. Check the absence of residual voltage and discharge any accumulations of kinetic or potential energy (e.g. mechanically blocked vertical axes).
The use of appropriate PPE (nitrile gloves, S3 safety footwear, protective glasses) is mandatory during all phases.
3. Tools and Materials Required
| Tool/Material | Specify | Quantity |
|---|
| Infrared thermometer | Accuracy +/- 0.5 °C | 1 |
| Grease gun | Calibrated with pressure gauge | 1 |
| Vibration analyzer | Accelerometer technology | 1 |
| Compatibility analysis kit | Solvent/Mixing Test | 1 |
| Lubricating grease | Compliant ISO 15243 (NLGI grade 2) | Q.B. |
| Industrial rags | Lint-free cotton | Q.B. |
4. Pre-Maintenance Checklist
| Article | Control | Acceptance Criteria | Notes |
|---|
| Operating temperature | Thermal detection | T < 70 °C (stable) | Measure close to the housing |
| Vibrations | Spectral analysis | ISO 10816-3 (Class 1/2) | Absence of anomalous peaks |
| Integrity of seals | Visual inspection | No cracks or wear | Check for watertightness |
| State of the fat | Color/odor analysis | Homogeneous colour/neutral odour | Absence of burning smell |
5. Step-By-Step Procedure
- Preparation and Safety: Run LOTO. Clean the external area of the bearing support to prevent the entry of contaminants (metal dust, coolant) during lubrication.
- Grease Analysis: Take a small sample of grease from the purge area or inlet. Check for the presence of metal particles or color changes. Do not force the seals open; avoid damaging them.
- Compatibility Check: If you intend to change the type of grease, perform an ASTM D6185 compatibility test. Never mix greases based on different soaps (e.g. Lithium with Calcium Sulfonate) without a prior check.
- Calculation of the Speed Factor (n*dm): Calculate the n*dm factor (n = rpm, dm = average bearing diameter in mm = (d+D)/2). For n*dm > 500,000, use low viscosity synthetic greases.
- Relubrication: Inject the calculated quantity (G = 0.005 * D * B, where D is the external diameter in mm and B the width in mm). Proceed at low flow rates. Avoid overdose; excess fat causes overheating due to agitation.
- Post-lubrication check: Operate the machine at reduced speed for 15 minutes. Monitor temperature; if it rapidly rises above 80°C, stop immediately.
6. Post-Maintenance Verification Checklist
| Test | Expected Result | Result Obtained | Pass/Fail |
|---|
| Temperature | Stabilization < 65 °C | - | - |
| Noise | Smooth operation | - | - |
| No leaks | Dry seals | - | - |
7. Troubleshooting Guide
| Symptom | Probable Cause | Corrective Action |
|---|
| Overheating | Excess fat | Purge off excess; check levels |
| Metallic noise | Contamination or wear | Inspect tracks and balls; replace bearing |
| Fat loss | Damaged gasket | Replace sealing gasket |
8. Recommended Maintenance Schedule
| Activities | Frequency | Estimated Duration | Skill Level |
|---|
| Thermal inspection | Weekly | 5 min | Basic technician |
| Vibration analysis | Monthly | 15 min | Expert technician |
| Relubrication | Second calculation n*dm | 30 min | Specialized technician |
9. References for Spare Parts
| Description | Typical Specification | UNITEC-D category |
|---|
| High Speed synthetic grease | NLGI 2, synthetic base | Special lubricants |
| High precision bearing | Class P4 / P2 | Rolling bearings |
To select certified components and lubricants for your machine tool, consult our online technical catalogue: https://www.unitecd.com/e-catalog/
10. Regulatory References
The procedures described follow the UNI EN ISO 9001 regulations for quality, ISO 15243 for the analysis of bearing failures and the DIN 51825 guidelines for the classification of lubricating greases.
