Metal deforming – With means to drive tool – Including pneumatic- or fluid-actuated tool support
Reexamination Certificate
1999-08-10
2001-08-21
Jones, David (Department: 3725)
Metal deforming
With means to drive tool
Including pneumatic- or fluid-actuated tool support
C072S416000, C029S751000
Reexamination Certificate
active
06276186
ABSTRACT:
The invention relates in the first place to a method for operating a hydraulic pressing device having a stationary part and a moving part, the moving part being displaced in relation to the stationary part until a predetermined pressure is reached.
Hand-operated or motor-driven hydraulic tools are often employed for certain joining procedures, such as for example the pressing-on of cable eyes onto electrical conductors, or for riveted connections. These tools are provided with an excess pressure valve which limits the oil pressure, and thus the compressive force of the moving part against the workpiece to be pressed, to a maximum value. In order to ensure a well-made joint, e.g. of a cable eye to an electrical conductor, it is known for the excess pressure valve to act only when a prescribed minimum compressive force is reached. This makes sure that the full required compressive force was effective. After release of the excess pressure valve, the pressing device, or rather the moving part thereof, is returned manually to the initial position, i.e. the open position.
Having regard to the above-described state of the art, the invention is addressed to the technical problem of providing a method for operating a hydraulic pressing device of the type under discussion, such as for example a cable eye (connector) pressing device, or a riveting tool pressing device, in which method the handling aspect is especially improved.
This problem is solved in the first place and to a substantial extent by the subject matter of claim
1
, it being provided that the moving part returns automatically and completely back into its initial position, released by the predetermined pressure being reached. Accordingly, on achievement of a maximum pressure, there occurs an automatic opening of the pressing device and complete return of the moving part into the initial position. The user is spared having to intervene manually in order to open and return the moving part. The user is simultaneously given an optical signal also, by the return movement of the moving part, that the joint has been properly made with the prescribed maximum pressure.
The invention relates moreover to a method for operating a hydraulic pressing device, such as for example a pipe clamping tool, that has a stationary part and a moving part and an automatically actuating return valve, the moving part being biased into its initial position by means of a return spring. In this type of hydraulic pressing device, especially a pipe clamping tool, it is known for the return stroke of the hydraulic piston to take place automatically once the switch-off pressure has been reached. Only for emergencies is an additional, manually operated, return valve provided. In normal operation, the pressing or the joint formation can only be ended after the maximum pressure has been exceeded and the tool opens by the automatically returning hydraulic piston which carries the moving part with it. Known constructional solutions of the desired manner of operation consist of using an excess pressure valve which, after release, is arrested by a mechanical stop mechanism and thus permits complete return travel of the spring-loaded piston. On renewed actuation of the pressing device, for example when the motor is switched on, the arresting is mechanically disconnected and the excess pressure valve falls back into the closed position. In order to provide a hydraulic pressing device of the general type here under discussion, such as for example a pipe clamping device, which is characterised in particular by an advantageous arrangement from the handling aspect, it is provided that the return valve is held open by the force of the return spring, and returns automatically to its initial closed position after removal of the restoring force. As a result of this method according to the invention, no mechanical components are required for arrest of the piston or the moving part in the initial position, which furthermore obviates structural solutions for disconnecting the arresting when the pressing device is in use. In the method according to the invention, the restoring force, which is present anyway, of the return spring, is advantageously used for returning the moving part, so as to keep the return valve open over the entire return stroke of the moving part. No further arrest means are needed. After completion of the return movement, there is no further hydraulic pressure, owing to a limiting abutment of the spring-biased hydraulic piston, which results automatically in a return displacement of the return valve into the initial, closed position. The limiting abutment of the hydraulic piston also gives rise, shortly before an end position, to the smallest hydraulic pressure effective to keep the return valve open.
The invention relates further to a hydraulic pressing device with a stationary part and a moving part, the moving part being displaced relative to the stationary part by a hydraulic piston and being movable back to an initial position by means of a return spring, the return displacement being releasable in dependence on a predetermined pressure by actuation of a return valve. In order to provide a hydraulic pressing device of the kind under discussion with improved functional reliability and handling properties, it is proposed that the automatically acting return valve be retained in the open position, throughout the entire return stroke of the hydraulic piston, by the pressure of the returning oil. Mechanical arrest of the return valve during the return stroke of the hydraulic piston or of the moving part can be dispensed with by means of this arrangement, which offers special advantages in operation. Known structural solutions consist, for example, in the use of an excess pressure valve which, after actuation, is arrested by a mechanical stop mechanism and thus makes possible a full reverse stroke of the spring-loaded piston. On a fresh actuation of the pressing tool, for example by switching the motor on, the arresting is mechanically disconnected and the excess pressure valve goes back into the closed condition. But in accordance with the invention, the pressure of the returning oil, which is present anyway, after actuation of the return valve, is used for maintaining the return valve in the open position. The return valve acts automatically when a predetermined oil pressure is exceeded. The pressure of the returning oil, which decreases during the return of the hydraulic piston, is sufficiently high over the entire return stroke to keep the return valve in the open condition. It is found especially advantageous in this connection for the return valve to be formed as a valve piston, a partial piston surface area, effective in the closed condition, being calculated having regard to the maximum pressure. To this end, the return valve consists for preference of a valve piston having for example a needle point which closes off a bore connecting with the pressure space. The smaller partial piston surface effective by reason of the bore diameter is engaged by the oil in the course of pressing by the hydraulic pressing device. If the oil pressure exceeds a value predefined by the bore diameter, the valve piston of the return valve is raised from its sealing seat by way of the partial piston surface, whereupon a substantially greater piston area comes into effect. The return valve in this position operates with a substantially lower limiting pressure than in the closed condition. The limiting pressure in this position is no longer defined by the smaller partial piston surface area, but rather by the total surface area of the valve piston, formed, as it is, as a longitudinally sliding piston. As an example, a ratio of 400:1 can exist between the total piston area and a smaller, partial piston surface area which co-operates with the sealing seat. In consequence, the limiting pressure in the open position of the valve piston is 400 times smaller than the actuation pressure in the seated position, i.e. in the initial closed condition. As a result of this arrangement,
Gustav Klauke GmbH
Jones David
Trexler, Bushnell Giangiorgi, Blackstone & Marr, Ltd.
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