Damage of seals affects maintenance of hydraulic equipment
In the machining industry, hydraulic transmission systems are widely used, particularly in various types of semi-automatic hydraulic lathes. However, during operation, these machines often experience issues such as vibration, crawling, and sudden impacts. When troubleshooting and repairing such problems, the root cause is typically traced back to hydraulic control components like pumps or valves, making maintenance challenging. In many cases, the actual failure is found in the actuator—specifically, due to severe wear of the cylinder piston seals. This issue is especially common with "O" ring seals.
Figure 1 shows the hydraulic system of a CB3463-1 program-controlled hexagonal turret lathe. The main components include the cylinder, stop valve, and speed control valve. Figure 2 illustrates the hydraulic system of a CE7120 copying lathe tool holder.
Example 1: A CB3463-1 programmable six-point turret lathe experienced an issue where the feed speed of the turret could not be adjusted. Even after closing the stop valve (Fig. 1), the turret still exhibited crawling and jerking movements and failed to stop at the end of the cylinder stroke, rendering the machine inoperable. During inspection, all hydraulic control components were checked, including the speed control valves, but no issues were found. Replacing parts of the speed control valve did not resolve the problem. Upon disassembling the cylinder, it was discovered that the piston’s "O" ring seal had worn significantly, allowing hydraulic oil from both chambers to mix. This caused internal pressure imbalance, leading to erratic movement. The worn seal increased the clearance between the rod and rodless chambers, effectively creating a bypass. When the speed control valve or stop valve was closed, the system couldn’t maintain stable pressure, causing the piston to move unpredictably. After replacing the "O" ring, the machine returned to normal operation.
Example 2: A CE7120 hydraulic profiling lathe experienced frequent issues where the cutting tool would drop unexpectedly during vertical feeding, resulting in damage and reduced productivity. Initial checks revealed no faults in the hydraulic control elements, leading to confusion in the repair process. Further inspection of the longitudinal cylinder showed that the "O" ring on the piston had flattened, and the piston diameter was smaller than standard by 0.8 mm, creating excessive clearance between the piston and cylinder wall. This allowed communication between the two chambers, causing pressure imbalances. During operation, when the copy tool carrier descended, a horizontal force acted on the piston, causing it to move rapidly. Due to the large gap, the pressure in one chamber exceeded the other, leading to uncontrolled movement. Replacing the piston and the "O" ring resolved the issue, restoring smooth operation.
These examples highlight the importance of checking the integrity of hydraulic seals, especially "O" rings, during maintenance. Many real-world repairs have confirmed that even minor wear or misalignment can lead to significant operational problems. By focusing on the condition of seals and ensuring proper fit, technicians can prevent costly downtime and improve the reliability of hydraulic systems.
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