Damage of seals affects maintenance of hydraulic equipment
In the machining industry, hydraulic transmission systems are widely used, particularly in semi-automatic hydraulic lathes of various types. However, during operation, these machines often experience issues such as vibration, crawling, and impact. When diagnosing and repairing such problems, it is common to find the root cause in hydraulic control components like pumps and valves, which can make maintenance challenging. In many cases, the actual failure is traced back to the actuator, specifically due to severe wear of the cylinder piston seals. This issue is especially prevalent with "O"-ring seals.
Figure 1 shows the hydraulic principle of a CB3463-1 program-controlled six-point turret lathe, where the cylinder, stop valve, and speed control valve are key components. Similarly, Figure 2 illustrates the hydraulic system of a CE7120 copying lathe tool holder.
Example 1: A CB3463-1 programmed hexagonal turret semi-automatic lathe experienced an issue where the feed speed of the turret tool holder could not be adjusted. Even after closing the stop valve, the machine still exhibited crawling and jerking, and the turret would not stop at the correct position, making the machine inoperable. During inspection, all hydraulic control components were checked, including the speed control elements, but no faults were found. Replacing parts of the speed control valve did not resolve the issue. Upon dismantling the cylinder, it was discovered that the piston’s "O"-shaped seal had worn significantly, causing hydraulic oil from the two chambers to mix. This led to unbalanced pressure and improper movement of the piston.
The analysis revealed that the worn "O"-ring allowed communication between the rod and rodless chambers of the cylinder. When the speed control valve or stop valve was closed, the oil return path was cut off. Normally, this should create a balanced force on both sides of the piston. However, due to the gap created by the worn seal, pressure oil flowed from the high-pressure side to the low-pressure side, disrupting the balance and causing the piston to move until an external force stopped it. Replacing the "O"-ring restored normal operation.
Example 2: A CE7120 copying lathe experienced frequent issues where the profiling knife holder would drop suddenly during vertical cutting, resulting in tool damage and production loss. After checking all hydraulic components and finding no fault, the problem was traced to the longitudinal cylinder of the tool holder. The "O"-ring on the piston was flattened, and the piston itself had an incorrect diameter—0.8 mm smaller than standard. This caused excessive clearance between the piston and cylinder wall, allowing the two oil chambers to communicate.
During repair, replacing the piston and the "O"-ring resolved the issue. The reason for the problem was that when the tool holder descended, a horizontal thrust force acted on the piston, increasing the pressure in the rod chamber. Due to the worn seal, the pressure difference caused oil to flow between the chambers, leading to sudden movement of the piston and the punching phenomenon. Once the faulty components were replaced, the machine operated smoothly again.
These two examples demonstrate how seal wear in hydraulic cylinders can lead to significant operational issues. Through careful diagnosis and replacement of damaged seals, maintenance teams can restore proper function and avoid costly downtime. Such cases have been repeatedly verified in practice, proving the importance of regular inspection and timely replacement of critical sealing components.
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