1. Introduction
The destruction of the key joint on the shaft of the ABB 3HAC8578-1 motor is usually manifested by an unexpected increase in the level of vibration, the appearance of a characteristic metal knock when changing the direction of rotation, or a complete loss of torque transmission. These symptoms indicate a critical degradation of the mechanical interface that requires immediate intervention to prevent damage to the bearing assemblies and the shaft itself.
2. Overview of the component
The ABB 3HAC8578-1 is a key element of the drive system of an industrial robot or servo drive. The key joint is designed to transmit torque between the shaft and the attached mechanism (pulley, gear or clutch). According to the requirements of the ISO 773 standard, the key must provide reliable fixation under conditions of cyclic loading, operating temperatures up to 80°C and significant dynamic moments of inertia.
3. Evidence of refusal
During the disassembly of the node, the following signs were recorded:
- Wrinkling of the working faces of the key and shaft groove (plastic deformation).
- Detection of signs of fretting corrosion (wear products in the form of fine oxide powder).
- Vibration measurements exceed the threshold of 4.5 mm/s (RMS) in the range of 10-1000 Hz.
- The gap in the shaft-key connection exceeds the nominal tolerance according to ISO 286 by 0.08 mm.
4. Study of root causes
Analysis using the Ishikawa diagram method revealed three main vectors of destruction:
- Dynamic loading: Constant start-stop cycles result in significant alternating loads that exceed the endurance limit of the key material.
- Installation errors: Using the wrong fit tolerance resulted in micro-movements (fretting) between the shaft and the key.
- Stress concentration: Rounding radii in the corners of the keyway of the shaft did not meet the specifications, which created foci of fatigue crack initiation.
5. Identified reasons (ranking)
- Cyclic fatigue of the material (65% probability): Mismatch between the actual operating moment and the calculated strength of the key.
- Incorrect fit (25% chance): Increased clearance caused shock loads when reversing.
- The quality of metal processing of the groove (Probability 10%): Insufficient surface cleanliness led to stress concentration.
6. Corrective actions
Immediate:
- Replacement of the key with a new one made of steel of strength class not lower than 10.9.
- Measuring the shaft groove for wear; if necessary — restoration by surfacing or replacement of the shaft.
Preventive:
- Use of anaerobic fasteners of threaded and keyed connections to eliminate microdisplacements.
- Establishing strict landing tolerances according to ISO 286.
7. Diagnostic checklist for personnel
Use this list during a scheduled tablet inspection:
- [ ] Check the vibration level on the shaft (max. 3.5 mm/s).
- [ ] Visually check the presence of backlash in the connection.
- [ ] Check for signs of corrosion around the key.
- [ ] Measure the width of the groove of the shaft and the key (caliper with an accuracy of 0.01 mm).
- [ ] Assess the condition of the fastening bolt (tightening by torque).
- [ ] Check the temperature mode of the unit.
- [ ] Check the condition of the lubricant if the connection is open.
- [ ] Exclude extraneous sounds when changing the direction of rotation.
8. Prevention strategy
It is recommended to implement a maintenance schedule with an interval of 2000 hours of operation to check the state of the connection. Vibration monitoring should become part of a predictive maintenance system. When modernizing nodes, you should consider switching to a tension fit or using conical joints, if the design allows.
9. Summary
Fatigue failure of a key joint is the result of accumulated microdamage due to incorrect tolerances or excessive loads. Systematic control of vibration parameters and compliance with installation regulations allow you to avoid emergency shutdown of the equipment. For the selection of original components or their certified counterparts, contact the UNITEC-D E-Catalog.
10. Links
- ISO 773: Keys are prismatic.
- ISO 286: System of admissions and landings.
- DSTU EN 60034-1: Electric rotating machines.
- ABB technical documentation (Maintenance Handbook 3HAC8578-1).
