Introduction
Combine harvesters are vital machinery in agriculture, and like any complex machinery, they require proper maintenance for optimal performance. One often overlooked but crucial aspect of this maintenance is rotor balancing. Balancing rotors on combine harvesters may appear to be a generic task similar to other rotary machines like fans, crushers, and centrifuges. However, every machine has its distinct nuances, and in this article, we delve into the specifics of balancing rotors in combine harvesters.
Importance of Rotor Balancing in Combine Harvesters
Balancing the rotors in combine harvesters is imperative for several reasons:
- Reduced wear and tear on bearings
- Improved energy efficiency
- Minimized vibration, thereby reducing structural fatigue
- Enhancing the longevity of the machinery
Types of Rotors in Combine Harvesters
In rotary combine harvesters, the primary rotor that often requires balancing is the main threshing drum. In keyboard harvesters, the focus generally lies on the threshing drum and the beater. Among these, straw chopper rotors are notoriously challenging to balance due to potential structural weaknesses.
Common Challenges in Rotor Balancing
Time Consumption
While a well-maintained chopper may take around an hour to balance, machines requiring repair can take an entire day or even longer.
Structural Weakness
Structural problems such as imperceptible cracks can arise due to heavy vibration during operation. This weakens the chopper body, making it prone to resonance phenomena and hindering stable vibration amplitude and phase readings.
Loose Components
Loose or dangling parts like the straw spreader can cause inconsistencies during the balancing process. They must either be removed or securely welded to the rotor body.
Bearing Issues
Worn-out or improperly tightened bearings can cause excessive vibrations. Always replace old bearings and avoid over-tightening the new ones.
Pre-balancing Checklist
Inspect Old Weights
Examine the condition of existing balancing weights. If the securing nuts are worn, remove the weights to prevent them from dislodging during operation.
Blade Integrity
Check for jammed or misaligned blades that may not self-correct due to centrifugal force, leading to intermittent imbalances.
Idler Pulleys and Belts
Inspect idler pulleys and remove belts to check bearing backlash. Replace if necessary.
External Interference
When using a vibrometer, be aware that rollers operating at similar RPMs to the shredder can interfere with vibration measurements. Monitor readings in vibration meter mode for anomalies.
Shaft Curvature
Use a dial gauge to check for shaft misalignment or curvature. Self-aligning bearings may offer some level of compensation.
Balancing Procedures
Step-by-Step Balancing
Start by installing vibration sensors perpendicular to the rotor’s axis and mount the tachometer on a magnetic stand. Attach reflective tape to the pulley for RPM sensor targeting. Connect all sensors to the Balanset-1A, which should be linked to a laptop running specialized balancing software.
Initialize the software and opt for two-plane balancing. Weigh a test weight, note down its mass and the radius where it will be installed. Run the rotor and measure its initial vibration levels.
Place the test weight on the first plane, which is the side corresponding to the first sensor. Initiate rotor rotation and record vibration data again, ensuring a minimum 20% change in either vibration amplitude or phase. Remove the test weight from the first plane and place it on the second plane, associated with the second sensor. Rotate and measure for the third time.
Based on these measurements, the software will indicate the optimal mass and angular position for corrective weights on both planes. Remove the test weight, and then measure and weld the corrective weights at the suggested angles. Verify the rotor’s balance by running it again and observing the vibration levels. If additional mass is recommended by the software, weld it in place and reconfirm the balance.
In case of very high vibration levels, perform balancing two or three times :
- Low-Speed Balancing: Start by balancing the rotor at a low speed.
- Medium-Speed Balancing: Repeat the process at a medium speed.
- High-Speed Balancing: Finally, perform the balancing at the operational speed.
Corrective Weights
When installing corrective weights, use only half of the weight recommended by the software to account for system non-linearity.
Placement of Weights
Use washers of varying sizes as corrective weights, preferably placed on special perforated discs at the rotor’s edges. If unavailable, weights can be attached to the bolts securing the blades.
Conclusion
Balancing rotors in combine harvesters is a nuanced task requiring a meticulous approach. Negligence can lead to structural problems, decreased efficiency, and reduced lifespan of the machinery. Adhering to a systematic pre-balancing checklist and step-by-step balancing procedures can significantly improve the reliability and performance of your combine harvester.
