De 10 vanligaste problemen och lösningarna för grävmaskiner

De 10 vanligaste problemen och lösningarna för grävmaskiner

Excavators are indispensable machines across various industries, playing a crucial role in construction, mining, and many other heavy-duty operations. However, like all complex machinery, excavators are prone to experiencing mechanical issues over time. These problems can significantly disrupt productivity and lead to costly downtime if not addressed promptly and correctly. In this blog, we will delve into ten of the most common problems encountered with excavators and provide detailed solutions to help operators and technicians maintain optimal performance and extend the lifespan of these essential machines.

1. Gear End Face Grinding: The Importance of Precision and Cleanliness

Problem: Over time, the gear end face of an excavator’s gear pump is subjected to wear and tear, necessitating grinding to restore its original surface. However, improper grinding techniques can lead to inaccuracies that compromise the performance of the entire system.

Lösning: When it becomes necessary to grind the gear end face, it is imperative to use a high-precision grinder, and equally important is ensuring that a highly skilled and experienced technician performs the operation. The workbench where the grinding takes place must be kept absolutely clean, free from any dust or debris. Even the smallest particle of dust can cause a misalignment between the ground plane and the vertical line of the bearing hole. This misalignment can result in the gear pump not operating as smoothly as it should, leading to further wear and potential damage. By paying meticulous attention to the cleanliness and precision during the grinding process, the gear pump’s efficiency and longevity can be preserved, reducing the likelihood of future problems.

2. Assembling the Gear Pump: Ensuring Proper Orientation and Lubrication

Problem: During the operation of an excavator, the pump housing, particularly in the oil inlet chamber, is susceptible to wear. This wear can adversely affect the overall performance of the gear pump, leading to inefficiencies and potential failures.

Lösning: If the pump housing shows signs of wear, and it is designed symmetrically, one effective solution is to rotate it 180 degrees. This rotation allows the less worn side to take on the load, potentially extending the housing’s usable life. However, care must be taken during reassembly, especially with the passive gear. It is crucial not to swap the ends of the passive gear, as it typically wears more on one side due to its specific orientation during operation. Marking the gear before disassembly is essential to ensure it is reinstalled in the correct orientation. The active gear, which is integrated with the rotating shaft, cannot be turned over and must remain in its original position. After reassembly, it’s important to add a small amount of lubricating oil and rotate the pump by hand. The rotation should feel smooth and free of resistance, indicating that the assembly has been done correctly and that the gears are properly aligned and lubricated. This attention to detail during assembly can prevent premature wear and ensure the pump operates efficiently.

3. Bearing Replacement: The Importance of Simultaneous Replacement

Problem: In many cases, the wear of the bearings on the gear pump’s end face is uneven, which can lead to operational issues if not addressed correctly during maintenance.

Lösning: When the time comes to replace the bearings on the end face of the gear pump, it is crucial to replace both bearings simultaneously, rather than just one. This is because the wear on the pump’s end face is often caused by an increased clearance in the bearings, leading to the gear swinging during rotation. If only one bearing is replaced, the imbalance between the new and old bearings can cause further issues, potentially leading to more significant wear and even failure of the pump. By replacing both bearings at the same time, the pressure distribution across the end face is evened out, reducing the likelihood of future wear and ensuring that the gear pump operates smoothly and efficiently. This practice not only extends the life of the bearings but also helps to maintain the overall integrity of the gear pump.

4. Safety Valve Pressure Adjustment: Addressing Cone Valve and Valve Seat Issues

Problem: A common issue encountered during maintenance is the inability to adjust the safety valve pressure, even after ensuring that the damping hole is not blocked. This can be frustrating and can lead to further complications if not properly diagnosed and corrected.

Lösning: In most cases, the root of this problem lies in the connection between the cone valve and the valve seat. If the cone valve is not tightly closed against the valve seat, the oil pressure in chamber C cannot be established, making it impossible to adjust the safety valve pressure correctly. To resolve this issue, it is essential to inspect the cone valve and valve seat closely. Ensure that they are both in good condition and that they fit together snugly without any gaps or looseness. If any wear or damage is detected, the affected parts should be replaced. Once the cone valve and valve seat are properly fitted, the oil pressure in chamber C will build up as expected, allowing for the correct adjustment of the safety valve pressure. This ensures that the hydraulic system operates safely and efficiently, preventing potential damage to other components and reducing the risk of downtime.

5. Detecting and Correcting Gear Plane Verticality Issues

Problem: Changes in the verticality of the ground gear plane relative to the bearing hole can lead to significant operational challenges, often only discovered during the reassembly of the gear pump.

Lösning: When assembling the gear pump, any issues with the verticality of the ground gear plane and the bearing hole alignment become apparent. The clearance between the end face and the gear is usually very small, typically around 0.05mm. If the verticality is off, the gear shaft may become stuck after assembly, preventing smooth rotation. In such cases, loosening the locking screw slightly may still not resolve the issue, and the gear pump may need to be disassembled for further inspection. Upon disassembly, scratches on the end face often indicate that the plane and the bearing hole are not perpendicular. This misalignment can cause friction and resistance during operation, leading to further wear and potential damage. To correct this, it is necessary to re-grind the end face with precision, ensuring that the plane is perfectly perpendicular to the bearing hole. This correction will allow the gear shaft to rotate smoothly, reducing wear and extending the life of the gear pump.

6. Crawler Movement Issues: Resolving Unidirectional Motion

Problem: One of the more perplexing issues that can arise with an excavator is when one side of the crawler moves forward but fails to move backward. This problem can significantly hinder the machine’s maneuverability and efficiency.

Lösning: The root cause of this issue is often found in the travel motor’s overload relief valve. Excavators are equipped with two overload relief valves designed to protect the travel motor from excessive pressure. If one of these valve cores becomes stuck in the overflow position, the system pressure will drop on that side, preventing the crawler from moving in both directions. To resolve this, the travel motor should be inspected, and the stuck valve core should be carefully removed and cleaned or replaced if necessary. Ensuring that both overload relief valves are functioning correctly will restore full bidirectional movement to the crawler, allowing the excavator to operate smoothly and efficiently. Regular maintenance and inspection of these valves can help prevent this issue from occurring in the first place.

7. Slow Crawler Movement: Diagnosing Flow Insufficiencies

Problem: In some cases, an excavator’s crawler may move very slowly on one side, but if another action, such as rotation, is performed simultaneously, the crawler’s speed improves. This behavior can be puzzling and indicates an underlying issue with the hydraulic system.

Lösning: This problem is often caused by insufficient flow from the piston pump to the travel motor. When the excavator performs another action at the same time, such as rotating, it effectively increases the overall hydraulic flow, temporarily alleviating the issue. However, the root cause may not necessarily be a damaged piston pump but rather an improperly adjusted flow control valve. The flow control valve regulates the amount of hydraulic fluid supplied to the travel motor, and if it is not set correctly, the motor may not receive enough fluid to operate at full speed. To fix this issue, the flow control valve should be inspected and adjusted to ensure that it provides the correct amount of fluid to the travel motor. This adjustment will restore the crawler’s speed and improve the excavator’s overall performance.

8. Heavy Travel Control Handle: Addressing Mechanical Wear and Hydraulic Pressure

Problem: Operating an excavator should be a relatively smooth process, but sometimes the travel control handle can become incredibly heavy and difficult to turn, making it almost impossible to operate the machine effectively.

Lösning: The travel distribution valve in most excavators differs from other distribution valves because it is often operated mechanically through a pull rod rather than hydraulically. Over time, wear and tear on the distribution slide valve can cause issues, such as increased clearance between the valve and its housing. This wear allows high-pressure oil to leak from the oil channel into the spring cover, where it builds up pressure. The increased pressure forces the distribution valve to move toward the spring, making the control handle feel heavy and difficult to operate. To resolve this issue, the distribution slide valve should be inspected for wear. If the valve is worn, it may need to be replaced or re-machined to restore the correct clearance. Additionally, any seals or gaskets in the spring cover should be checked and replaced if necessary to prevent oil leaks. By addressing these issues, the travel control handle will return to its normal, smooth operation, allowing the excavator to be controlled with ease.

9. Engine Stall During Startup: Troubleshooting Variable Mechanism Problems

Problem: A common and frustrating issue encountered by excavator operators is the engine stalling or the speed dropping significantly when the travel levers are operated simultaneously during startup. This can delay operations and lead to potential engine damage if not addressed.

Lösning: This problem is often linked to the variable

mechanism of the plunger pump, which controls the hydraulic flow rate based on the engine speed and load. If the plunger pump’s variable mechanism is malfunctioning, it may allow too much hydraulic flow even when the engine is idling, overwhelming the engine and causing it to stall. To diagnose this issue, the variable mechanism should be inspected for wear or damage. If the mechanism is found to be faulty, it may need to be repaired or replaced to ensure that the plunger pump operates correctly at all engine speeds. Additionally, the hydraulic system should be checked for any blockages or leaks that could be affecting the flow rate. By addressing the underlying issue with the variable mechanism, the engine will be able to handle the load more effectively, preventing stalling and ensuring smooth operation during startup.

10. Track Movement Issues at High Throttle: Understanding Distribution Plate Wear

Problem: After recent repairs, an excavator may exhibit a peculiar issue where the track moves faster at a small throttle but fails to move at all when the throttle is increased. This problem can be particularly frustrating after investing time and resources into repairs.

Lösning: This issue is often a result of over-grinding the distribution plate during maintenance, which reduces the pressure between the distribution plate and the cylinder surface. At low throttle, the hydraulic pressure is lower, making it easier for the distribution plate to maintain contact with the cylinder surface. However, when the throttle is increased, the hydraulic pressure rises, causing oil to leak between the distribution plate and the cylinder surface due to insufficient contact pressure. This leakage prevents the track from moving at higher throttle settings. To remedy this, a gasket can be added to the spring that applies pressure to the distribution plate, increasing the overall pressure and improving the seal between the plate and the cylinder surface. If the spring is a butterfly type, adding an additional butterfly spring can further enhance the pressure. By making these adjustments, the distribution plate will maintain better contact with the cylinder surface, allowing the track to move properly at all throttle settings and ensuring the excavator operates at peak efficiency.

Slutsats

Maintaining and troubleshooting excavators require a deep understanding of the machine’s mechanics and a keen eye for detail. By familiarizing yourself with the common problems outlined in this blog and applying the corresponding solutions, you can significantly reduce downtime, prevent costly repairs, and ensure that your excavator remains in top working condition. Regular maintenance, precise repairs, and careful attention to the condition of critical components are key to extending the lifespan of your excavator and maximizing its productivity on the job site.

FRÅGOR OCH SVAR

1. What should be done if the excavator’s gear end face requires grinding?

• Svara: The gear end face should be ground using a high-precision grinder by an experienced technician. It’s crucial to ensure that the workbench is completely clean to avoid misalignment between the ground plane and the bearing hole, which can affect the gear pump’s performance.

2. Why is it important to replace both bearings on the gear pump’s end face simultaneously?

• Svara: Replacing both bearings at the same time ensures even wear and pressure distribution. This prevents the gear from wobbling during rotation, which could lead to further damage and inefficiencies in the gear pump.

3. What could cause one side of an excavator’s crawler to move forward but not backward?

• Svara: This issue is typically caused by a stuck overload relief valve core in the travel motor. The valve’s malfunction leads to a loss of system pressure, preventing the crawler from moving in both directions.

4. How can slow movement of one side of the crawler be addressed?

• Svara: Slow crawler movement is often due to insufficient hydraulic flow from the piston pump. Adjusting the flow control valve to ensure adequate hydraulic fluid reaches the travel motor can resolve this issue.

5. What might cause the engine to stall when operating the travel levers during startup?

• Svara: Engine stalling during startup can be caused by a malfunctioning variable mechanism in the plunger pump, which may allow too much hydraulic flow at idle, overwhelming the engine. Inspecting and repairing the variable mechanism can prevent this issue.