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How seals are used in hydraulic equipment

by:ORK      2022-11-17
In the machining industry, hydraulic transmission is widely used, such as various semi-automatic hydraulic transmission lathes. During the use of these machine tools, failures such as impact and crawling often occur. When diagnosing and repairing, the cause of the failure is often found on the hydraulic control components (such as various pumps and valves), resulting in the maintenance work. In the end, the cause of this kind of failure is often found on the actuator, that is, the serious wear of the cylinder piston seal. Such phenomena are especially“O”See more shape sealing rings. Example 1: A CE7120 hydraulic profiling lathe, during the work, the profiling tool holder leads the knife down and turns the longitudinal feed to cut the knife, resulting in frequent knife punching and scrapping, and the machine tool cannot work normally. Inspection and maintenance: Check that all hydraulic control components are free of faults, and the maintenance work will enter the blind spot for a while. Disassemble and inspect the longitudinal oil cylinder of the tool holder, and find the piston oil seal“O”The outer circle of the seal ring has been ground flat, and it is found that the outer circle of the piston does not meet the requirements (because of the machine tool manufacturing), the diameter direction is smaller than the standard size of 0.8MM, and the gap between the piston and the cylinder block is large, resulting in the intercommunication of oil between the two chambers of the longitudinal cylinder. At the time of maintenance, a qualified piston was replaced and“O”Troubleshooting of the punching tool of the machine tool after forming the sealing ring. The reason is that at the moment when the profiling tool holder pulls the knife down into place, the tool holder as a whole is subjected to an impulse F'. After the force is decomposed, a horizontal thrust F'1 acts on the piston rod of the longitudinal oil cylinder. At the same time, the solenoid valve 34E1-25B works, the rod cavity of the longitudinal cylinder is connected to the pressure oil, the rodless cavity is connected to the return oil circuit of the speed control valve, the force F of the rod cavity of the piston is completed by two parts, one is F'1, the other is F1= A1P1, where A1 is the force area of ​​the rodless cavity, then F=F'1+F1. Under normal circumstances, the piston starts to move to the rodless cavity under the action of the force F. Due to the incompressibility of the hydraulic oil, the rodless The hydraulic oil pressure in the cavity rises sharply to form a back pressure on the piston, and the force balance of the piston moves smoothly according to the speed set by the speed control valve. At this moment, due to the effect of %F'1, the pressure P2 in the longitudinal cylinder cavity will be greater than P1. In practice, the two cylinder chambers are channeled due to the gap. At the moment of P2> P1, the hydraulic oil flows from the rodless cavity in the high pressure area to the The low-pressure area has a tendency to flow in the rod cavity. Once the flow occurs, P2 decreases, P1 increases, and F1 increases. The force on the piston is out of balance, and the piston drives the tool holder to move quickly toward the rodless cavity. After an instant, the horizontal thrust F'1 acting on the piston of the longitudinal oil cylinder disappears by itself because the downward movement of the profiling tool holder ends, the rapid movement of the piston ends, the tool movement of the tool holder tends to be stable, and the punching phenomenon ends. Example 2: A CB3463-1 program-controlled hexagonal turret semi-automatic lathe, during use, has a fault phenomenon that the feed speed of the turret tool post cannot be adjusted. The bottom of the oil cylinder can only stop, and the machine tool cannot be used normally. Inspection and maintenance: Check all hydraulic control components, especially the speed control components, and found no problems. Replaced part of the speed control valve, the fault has not been eliminated. After dismantling and inspecting the cylinder, it was found that the piston“O”The seal ring is seriously worn, causing the hydraulic oil in the two chambers of the cylinder to channel each other. analyze the reasons for this“O”After the sealing ring is worn, the gap between the rod cavity and the rodless cavity of the cylinder increases and communicates. When the speed control valve 3 or the stop valve 2 is closed, it is equivalent to cutting off the oil return path of the rod cavity of the cylinder. Theoretically speaking, when the pressure oil enters the rodless cavity of the cylinder, a thrust F is formed on the piston, which makes the piston tend to move to the rod cavity. The back pressure makes the two ends of the piston balanced and stationary. At this time, F with = F without, and the oil pressure without cavity is different due to the different force area of ​​the piston, that is, P with> P without. In practice, due to the interconnection between the two chambers of the cylinder, the pressure oil in the cylinder chamber tends to flow from the high-pressure area to the low-pressure area. As soon as the flow occurs, the pressure P in the chamber decreases, but P does not increase, and the thrust acting on both ends of the piston F no> F yes, the piston loses balance and moves to the rod cavity to find a new balance point. In this way, the piston moves until there is an external force to stop it. The occurrence of the above phenomenon has a great impact on the maintenance work of the machine tool, and the replacement of the cylinder piston“O”After the sealing ring is removed, the failure of the machine tool is eliminated and the operation returns to normal. The troubleshooting methods for the above two faults have been verified in many practices, and the maintenance work has achieved good results. Company website: https://www.orksealing.com/
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