In the machining industry, hydraulic transmission applications are very extensive, such as various types of semi-automatic hydraulic transmission lathes. During the use of these machine tools, there are often such problems as impact, crawling, etc. When diagnosis and repair are performed, the cause of the failure is often found in the hydraulic control elements (such as various types of pumps, valves), and the maintenance work is in trouble. In the end, such failures are often found on the actuator, which is the result of severe wear of the cylinder piston sealing elements. This type of phenomenon is especially seen with "O" seals.
1. Cylinder 2. Stop valve 3. Speed ​​control valve Figure 1 CB3463-1 program-controlled six-point turret semi-automatic lathe turret hydraulic principle
Fig. 2 Hydraulic principle of CE7120 copying lathe tool holder
Example 1: A CB3463-1 programmed hexagonal turret semi-automatic lathe has a failure phenomenon that the feed speed of the turret tool holder cannot be adjusted during use. There is still crawling and kicking after the closing valve 2 (Fig. 1) is closed. , And can not stop until the bottom of the cylinder, the machine can not 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 failure has not been eliminated. After the dismantling of the cylinder, it was found that the piston “Oâ€-shaped seal ring was seriously worn, causing the hydraulic oil in the two-cylinder oil chamber to be squeezed by each other. Analysis of the reasons, due to the "O"-shaped seal wear, the cylinder rod cavity and rodless cavity clearance to increase intercommunication, when closing the speed control valve 3 or the stop valve 2, it is equivalent to cut off the cylinder rod cavity back to the oil road. Theoretically speaking, when the pressure oil enters the rodless cavity of the cylinder, a thrust force F is not formed on the piston, so that the piston moves toward the rod cavity, because the oil cylinder has a rod cavity oil return and the cavity oil quickly forms. Back pressure, so that the two ends of the piston are balanced and remain stationary. At this time, F =F is absent, and no cavity oil pressure is different because of different force areas of the piston, that is, P has >P none. In practice, because the two chambers of the oil cylinder form a gap, the pressure oil in the cylinder chamber flows from the high pressure area to the low pressure area. When the flow is generated, the pressure P in the chamber is reduced, and the pressure P is not increased. The thrust acting on both ends of the piston is F No> F Yes, the piston loses its balance and moves to the rod cavity to find a new balance point. In this way, the piston moves until it stops with an external force. The above-mentioned phenomenon has brought a great influence on the maintenance work of the machine tool. After replacing the “Oâ€-shaped sealing ring of the oil cylinder piston, the machine tool failure is eliminated and the operation returns to normal. Example 2: A certain CE7120 hydraulic profiling lathe, the work of the profiling knife holder knife knife down the vertical feed cutting when the punching knife, resulting in the knife, waste and frequent occurrence of the phenomenon, the machine can not work. Inspection and maintenance: Check that all the hydraulic control components are not faulty, and maintenance work will temporarily enter the blind spot. The longitudinal cylinder of the tool holder was dismantled, and the outer circle of the “Oâ€-shaped sealing ring of the piston oil seal was found to have been flattened. At the same time, the size of the outer circle of the piston was found to be unsatisfactory (because of the machine tool manufacturing reasons), and the diameter direction was less than the standard size of 0.8 mm. The gap between the piston and the cylinder body was removed. Very large, leading to vertical oil tank two chambers to communicate with each other. During the repair, the replacement of the qualified piston and the "O" seal ring will eliminate the problem of machine tool punching. The reason for the analysis is that at the instant when the copy tool carrier is lowered into position, the tool holder is subject to an impact F' (Fig. 2). After this force is decomposed, a horizontal thrust force F'1 acts on the longitudinal cylinder piston rod. At the same time, the solenoid valve 34E1-25B work, the longitudinal cylinder rod chamber pressure oil, no rod chamber connected to the speed control valve back to the oil, piston rod chamber force F is completed by two parts, one is F'1, another One is F1=A1P1, where A1 is the force area of ​​rodless cavity, then F=F'1+F1. Under normal circumstances, the piston starts to move to the rodless chamber under the action of the force F. Due to the incompressibility of the hydraulic oil, the pressure of the hydraulic oil in the rodless chamber suddenly rises to form a back pressure on the piston, and the piston is balanced according to the speed control valve. Set a smooth speed. Due to the effect of %F'1 at this moment, the pressure in the longitudinal cylinder P2 will be greater than P1. Actually, the two chambers of the fuel tank are open due to the clearance. At the moment of P2>P1, the hydraulic oil has a tendency to flow from the rodless chamber in the high pressure area to the rod chamber in the low pressure area. Once the flow is generated, P2 decreases, P1 increases, and F1 increases. Large, the piston is out of balance due to force, and the piston drives the tool holder to move toward the rodless cavity quickly. After the instant, the horizontal thrust F'1 acting on the piston of the longitudinal cylinder disappears on its own due to the end of the descending of the profiling knife holder, and the rapid movement of the piston ends, and the cutter knife moves steadily, and the punch knife phenomenon ends. The troubleshooting of the above two cases has been verified in many practices and the maintenance work has achieved good results.
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