Motors: expansible chamber type – With motive fluid valve – Contracting chamber exhaust valve controlled by expanding...
Patent
1996-12-13
1998-11-10
Nguyen, Hoang
Motors: expansible chamber type
With motive fluid valve
Contracting chamber exhaust valve controlled by expanding...
60468, 60494, F15B 1108
Patent
active
058328076
DESCRIPTION:
BRIEF SUMMARY
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a hydraulic control for a dividing machine tool.
Such hydraulic controls are used, in particular, in shearing presses or cutting presses by which workpieces are brought to predetermined lengths. Thus, for instance, scrap shears are known by which railway rails can be divided into pieces of short length before melting or recycling.
In such machine tools one distinguishes essentially between three individual strokes, during the first of which strokes (the closing stroke) the cutting tool is closed. This is then followed by the working stroke, in which the work piece is cut in two, while a last stroke performs the return movement, i.e. the opening of the tool in order to be able to remove or shift the workpiece.
In order to prevent an uncontrolled lowering of the cutting tool, a back pressure acts on the working piston of the machine tool during the closing stroke, it approximately compensating for the weight of the parts to be lowered.
In this way, assurance is had that the workpiece of the machine tool does not descend solely due to its own weight, so that the hydraulic pump must always operate against the back pressure and thus the hydraulic cylinder is always filled with hydraulic fluid.
During the working stroke, i.e. during the cutting of the workpiece, the back pressure is decreased so that the maximum cylinder force can be used for the actual cutting process.
Upon cutting the workpiece, the entire hydraulic pressure continues to act on the working piston, so that the latter is accelerated immediately after the cutting until the hydraulic pressure decreases due to the control of the machine tool and the return movement of the tool is commenced. This sudden acceleration of the working piston can lead to a tearing apart of the oil column on the pressure side in the work cylinder so that there is a sudden, uncontrolled movement of the working piston. This sudden change in speed of the work piston is also known as the "cutting shock" and it can lead to damage to the drive and hydraulic components of the machine tool.
SUMMARY OF THE INVENTION
In contradistinction to this, the object of the invention is to create a hydraulic control for a dividing machine tool with which, with a little apparatus expense, uncontrolled movement of the working piston can be prevented.
According to the invention the measure of providing a damping device, a damping pressure which opposes the downward movement of the working piston can be applied at the moment that the workpiece is cut through, so that the oil column on the pressure side in the work cylinder does not tear apart and thus sudden load peaks are counteracted.
The damping device is advantageously provided with means for limiting the maximum pressure so that hydraulic fluid can be expanded into a hydraulic tank when a maximum system pressure is exceeded.
A particularly simple control of this pressure-limiting valve device is obtained if, on the control side thereof, a predetermined control pressure is applied during the closing stroke which produces a back pressure which becomes inactive when an adjustable work level is reached and which can have a damping pressure superimposed on it or be replaced by a damping pressure which is greater than the control pressure. Thus, during the closing stroke, a back pressure acts which becomes inactive upon the work stroke when the work level is reached and then, upon the parting, increases to a higher damping-pressure level so that the cutting shock is reduced.
In accordance with an advantageous further development of the invention, the expansion control pressure can be taken from the feed line to the work cylinder, while the control pressure during the closing stroke is advantageously obtained from the return line.
The pressure in the feed line can then advantageously be fed by a bypass line into the control circuit of the pressure-limiting valve device. In this connection, a non-return valve and a flow valve, for instance a nozzle, can be arranged in series
REFERENCES:
patent: 3906991 (1975-09-01), Haussler
patent: 4172582 (1979-10-01), Bobnar
patent: 4244275 (1981-01-01), Smilges
patent: 4624445 (1986-11-01), Putnam
patent: 4727792 (1988-03-01), Haussler
patent: 5211196 (1993-05-01), Schwelm
patent: 5611259 (1997-03-01), Nagata
Biermann Klaus
Rausch Georg
Wilkens Heinrich
Zoller Georg
Farber Martin A.
Mannesmann Rexroth AG
Nguyen Hoang
Thyssen Industrie AG
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