Damage to seals affects hydraulic equipment

In the machining industry, hydraulic transmission applications are very extensive, such as various semi-automatic hydraulic transmission lathes. During the use of these machines, faults such as impact and creep often occur. During diagnostic maintenance, the cause of the failure is often found on the hydraulic control components (such as various types of pumps and valves), which causes the maintenance work to be in trouble. In the end, such failures are often found on the actuators, that is, the cylinder piston sealing components are severely worn. This type of phenomenon is particularly seen with "O" shaped seals.

Example 1: A CB3463-1 program-controlled hexagonal turret semi-automatic lathe. During the use, there is a fault phenomenon that the feed speed of the turret cannot be adjusted. After the shut-off valve 2 is closed, there is still crawling and rushing, and until The bottom of the cylinder can be stopped and the machine cannot be used normally.

Inspection and repair: Check all hydraulic control components, especially the governor components, for no problems. Some speed control valves have been replaced and the fault has not been eliminated. After the dismantling of the cylinder, the piston "O"-shaped sealing ring was seriously worn, which caused the hydraulic oil in the two chambers of the cylinder to smash. Analyze the reason, because the "O"-shaped seal ring wears, the cylinder has a gap between the rod cavity and the rod-free cavity. When the speed control valve 3 or the shut-off valve 2 is closed, it is equivalent to cutting off the oil return of the rod chamber. road.

Theoretically speaking, when the pressure oil enters the rodless cavity of the cylinder, a thrust F is formed on the piston, which causes the piston to move toward the rod cavity. Because the cylinder has the rod cavity returning to the oil, the oil in the cavity is rapidly formed. Back pressure, so that the two ends of the piston are balanced and still, at this time F = F no, and no cavity oil pressure is different due to different piston bearing area, that is, P has > P no. In practice, due to the gap between the two chambers of the cylinder, the pressure oil in the cylinder chamber has a tendency to flow from the high pressure zone to the low pressure zone. When the flow occurs, the pressure P in the cavity decreases, P does not rise, and the thrust acts on both ends of the piston. F no>F, the piston loses balance and seeks a new balance point to move with the rod cavity. In this way, the piston moves until it has an external force to stop. The occurrence of the above phenomenon has a great impact on the maintenance work of the machine tool. After replacing the "O" shaped seal ring of the cylinder piston, the machine fault is eliminated and the operation returns to normal.

Example 2: A CE7120 hydraulic profiling lathe, in the work of the profiling tool holder, the cutter is turned down and the longitudinal feed is cut, so that the knife and waste phenomenon occur frequently, and the machine tool cannot work normally.

Inspection and maintenance: Check that all hydraulic control components are fault-free, and the maintenance work enters the blind zone at one time. The longitudinal oil cylinder of the tool holder was dismantled and found that the outer circumference of the "O" ring of the piston oil seal had been smoothed. At the same time, the outer diameter of the piston was found to be unsuitable (because of the machine tool manufacturing), the diameter direction was smaller than the standard size of 0.8 mm, and the piston and cylinder body clearance were It is very large, causing the two cylinders of the longitudinal cylinder to communicate with each other. During maintenance, the machine tool is trouble-shooted after replacing the qualified piston and the “O” ring seal.

The reason for the analysis is that at the moment when the contouring knife guide is lowered into position, the tool holder as a whole is subjected to a momentum F', and after the force is decomposed, a horizontal thrust F'1 acts on the longitudinal cylinder piston rod, and at the same time, the solenoid valve 34E1-25B works, the longitudinal cylinder has a rod cavity to connect the pressure oil, and the rodless chamber is connected to the speed control valve to return to the oil circuit. The piston has a rod cavity force F which is completed by two parts, one is F'1 and the other is F1= A1P1, where A1 is the force-bearing area of ​​the rodless cavity, then F=F'1+F1. Under normal conditions, the piston starts to move to the rodless cavity under the action of force F. Due to the incompressibility of the hydraulic oil, the hydraulic oil pressure in the rodless chamber rises sharply to form a back pressure to the piston, and the piston is balanced by the speed regulating valve. Set the speed to go smoothly. At this moment, due to the effect of %F'1, the pressure P2 in the longitudinal cylinder chamber is greater than P1. In practice, the two chambers of the cylinder are vented due to the gap. At the moment P2>P1, the hydraulic oil has a tendency to flow from the rodless chamber in the high pressure region to the rod chamber in the low pressure region. Once the flow occurs, P2 decreases, P1 increases, and F1 increases. Large, the piston is unbalanced by force, and the piston drives the tool holder to move quickly toward the rodless cavity. After the moment, the horizontal thrust F'1 acting on the longitudinal cylinder piston disappears spontaneously due to the end of the contouring tool holder. The rapid movement of the piston ends, the tool holder moves toward stability, and the punching phenomenon ends.