In order to determine whether a faulty component or the entire system needs to be replaced or repaired, and to establish the most suitable preventive maintenance schedule or procedures, it is essential to rely on the diagnostic results obtained during machine operation. Before any repair work begins, it's crucial not to rush into disassembling the equipment. Instead, a thorough pre-demolition inspection—both static and dynamic—should be conducted to gather as much information as possible for fault analysis. Based on this analysis, a preliminary repair plan can be developed. Blindly dismantling without proper diagnosis may lead to unnecessary damage, reduce equipment accuracy, or even cause new issues.
Diagnostic operations typically involve both no-load and load testing to identify key problems in mechanical systems. These diagnoses should be combined with operator reports, daily logs, parts replacement records, accident analyses, and maintenance files to focus on the root causes of failures. No-load diagnostics often rely on human senses such as hearing, sight, smell, and touch to detect equipment malfunctions. Key aspects include:
1. Identifying abnormal noises from gearboxes. If unusual sounds occur at certain speeds, related components like gears, shafts, bearings, or discs might be damaged or worn. Further inspection of the gearbox cover can reveal visible damage such as fractures, deformations, pitting, or wear. A micrometer can measure shaft distortion, and bearing clearance can be checked for excessive looseness.
2. Diagnosing overheating in rotating or sliding parts. For example, sliding bearings may overheat due to severe wear, increased friction, or improper clearance. Rolling bearings may overheat due to tight clearance or poor lubrication. Excessive heat can lead to discoloration. Diagnosis should start with checking lubrication and clearance, followed by further tests and disassembly if needed.
3. Investigating equipment vibrations. Faulty vibrations are often caused by unbalanced rotating parts, worn supports, loose mechanisms, misalignment, or poor contact between moving parts. To locate the source, start by analyzing vibration frequency and measuring the main frequency to pinpoint the issue based on transmission relationships.
4. Identifying oil leaks in lubrication and hydraulic systems. Leaks can be caused by design flaws, incorrect seal selection, or cracks in components. Through trial and error during idle operation, the root cause can be identified and resolved.
5. Determining the cause of movement disorders in mechanical components. If there’s an interruption in motion or incomplete function, observing the machine during no-load operation can help locate the faulty part. Load operation diagnostics involve checking wear in critical components like guides or bearings, and assessing how improper assembly affects accuracy.
During load operations, the performance of the equipment under stress is evaluated, particularly in terms of vibration, temperature, noise, and functional loss. Experimental methods are often used to accurately identify the fault location and its main cause. Common techniques include:
1. **Isolation Method**: By estimating potential causes based on the equipment’s working principle, specific components can be isolated for testing. This helps eliminate non-fault causes and identify the primary issue. For example, if a lathe’s spindle box is making strange noises, individual gears can be tested one by one to find the problematic one.
2. **Heuristics**: When the fault isn’t clear, adjustments are made based on the most likely cause. Changing the gap size or other parameters and observing the effect can help identify the root problem. For instance, excessive play between slides in a lathe may be the cause of machining errors.
For complex faults involving multiple factors, a combination of diagnostic methods is often necessary. Using isolation to narrow down the problem, comparison and heuristics to identify specific components, and measurement or replacement to confirm the solution ensures accurate and efficient troubleshooting. This approach not only improves diagnostic accuracy but also enhances overall efficiency. In practice, most faults are resolved through a comprehensive evaluation rather than relying on a single method.
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