EP0482488A2 - Forming machine, in particular screw press - Google Patents

Abstract

In a forming machine with indirectly acting overload-securing means for a machine frame prestressed by means of tie rods (6), in particular a screw press with a screw (9) arranged in the press frame (1), a flywheel (16) driven by a motor, and a pressure-medium-actuated clutch, the press frame (1) being assigned a measuring device (30) which determines the ram force as a function of the column expansion and whose output signal releases the friction clutch before an overloading of the press frame, at least one of the tie rods (6) is hollow-bored and receives a measuring tie (29) which is provided with the force-measuring device (30). <IMAGE>

Description

The invention relates to a forming machine with indirectly acting overload protection of a machine frame pretensioned by means of tie rods, in particular a screw press with a spindle arranged in the press frame, a flywheel driven by a motor and a clutch operated by pressure medium, the measuring frame being assigned a measuring device which detects the tappet force as a function of the column expansion , whose output signal releases the friction clutch before the press frame is overloaded.

With e.g. Known for eccentric forging presses, the press force monitoring device protecting the machine from overload, the press force is electrically linked to the control via the expansion of the machine. When the set maximum force is reached, the pressing force limit is displayed by warning and the control is switched off if it is exceeded.

For example, in a clutch screw press, the coupling of the spindle to the flywheel must occur at a time when the desired pressing or impact force has been reached, and the exact observance of this time is crucial for the precision of the work performed in the screw press. The Switch-off time can be determined depending on the path of the ram or depending on the force on the ram, which is measured directly on the press frame or from the slippage in the friction clutch or from the inertia of a control mass connected to moving parts of the screw press from its deceleration.

Switching off depending on the path of the plunger has the disadvantage that e.g. when forging insufficiently heated or oversized blanks, overloading of the screw press during short-stroke stamping can occur, which results in a correspondingly continuing slippage in the coupling with corresponding wear (US Pat. No. 2,278,243).

When switching off as a function of the force on the tappet (DE-B-1 502 276), the switching command is preferably derived from the slip occurring in the friction clutch, for example by a switching element actuated directly by the slip in the friction clutch (DE-C-28 37 253 ), or the switching command is derived from the inertia force occurring with the deceleration of a control mass connected to moving parts of the screw press (DE-C-33 22 064), the particular advantage of the arrangement according to DE-C-28 37 253 being therein that the slippage-actuated actuator directly relieves the pressure chamber of the clutch, with short connections between the actuator and the pressure chamber of the clutch, which ensures a quick shutdown of the clutch on a correspondingly short slip path with little wear. On the other hand, the switch-off in direct dependence on the force acting on the tappet by the pressure sensor assigned to the press body, the output signal of which disengages the clutch when the required force is reached on the tappet, has no practical significance.

Numerous solutions have been proposed and continuously developed in order to record the column expansion for overload protection of the presses and then to be able to trigger a switch-off pulse for the coupling when the permissible expansion is exceeded, and it is from the magazine "Der Maschinenschaden", volume 516, volume 1959, pages 79 and 87 have long been known to determine the expansion of the stand of a toggle press by means of a force measuring device arranged on the stand, which consists of a dial gauge connected to a rod. Such a rod transmission rod is also known for a screw press of the type mentioned or similar forming machine from DE-C-3 505 933. There, a safety valve designed as a seat valve is attached to the top of the press frame. On the valve body of the safety valve, a rod designed as a long rod engages via an adjusting device, the lower end of which is attached to a projection of the press frame at the level of the press table. As soon as the stand of the frame stretches excessively due to an overload, the safety valve opens against the force of a spring, and a coupling line connected to the relief valve can drain into a tank. However, this can only achieve overload protection and, moreover, this known control or clutch release device is extremely susceptible to vibration and is subject to considerable bending stresses, so that falsifying measurement and switching results cannot be avoided.

Finally, in relation to the prior art, JP-A-90-108 495 is to be mentioned, by which a hydraulic pressure cushion arranged between the spindle nut and the plunger of a screw press is known. In this clutch screw press, which switches off depending on the travel, the pressure cushion serves as overload protection and is connected to a pressure relief valve which relieves the pressure cushion when the set maximum load is reached. The clutch is switched off via a pressure relief valve that switches to the pressure chamber of the clutch with the pressure drop on the pressure cushion. The switching off of the clutch accompanying the relief of the pressure pad is not suitable for the regular, force-dependent switching off of the screw press because of the coupling of the switching processes; Furthermore, there is also a great problem in deriving the high pressure present in the pressure cushion because of the necessary flexible connection to the switching elements.

Finally, it must be taken into account that in clutch screw presses on the sliding surfaces between the spindle and its mounting and the spindle nut, the coefficient of friction and thus the friction torque, which counteracts the torque introduced via the clutch, increases with the forming path. In the case of slip-dependent and also inertial force-dependent switching of the friction clutch, these deviations in the friction behavior lead to incorrect switching due to fluctuating friction losses.

The invention has for its object to provide a measuring device for a metal forming machine, the safe measurement of the pressing force, in particular for triggering a switching pulse for decoupling the flywheel, or a shutdown, possibly additionally for decoupling, the control of a press when the permissible maximum force and a rapid, as direct as possible actuation of a pressure relief valve to the pressure chamber of the friction clutch of a clutch screw press that switches off depending on pressure, are permitted.

This object is achieved in that at least one of the tie rods is hollow drilled and receives a measuring anchor provided with the force measuring device. In addition to the protected installation position of the measuring anchor and measuring device in the tie rod, the central position enables a direct, largely inertia-free detection of the pressing forces, which is unaffected by bending stresses.

The measuring devices can be operated electrically or hydraulically. They can advantageously be switched on and off variably, so that it is possible in the case of measuring anchors arranged in all four tie rods to determine by switching which measuring device is used for the measurement. In an electrically operating measuring device, however, a sufficiently fast switching pulse cannot be achieved, which, for. B. a clutch screw press may be only a few milliseconds to separate the flywheel from the spindle with the plunger, as soon as a pre-set pressure force is available. Since it is used to control the pressing force and to protect against overload, e.g. B. in an eccentric press or a forging press, such a fast switching sequence as for the pressing operation of a clutch screw press is not important, an electrically working measuring device is thus particularly suitable for overload protection, d. H. for switching a clutch pulse when a maximum value of the pressing force is reached. This is so that an overload e.g. not to endanger the machine or press frame and the tie rods.

For a rapid triggering of a switching pulse, a hydraulically operating measuring device is therefore recommended, for which it is proposed that the measuring armature includes the tie rod at the bottom with an anchor plate and at the top with a piston-cylinder unit which produces the cut-off pressure, the pistons of which in a cylinder supported by the press frame Includes pressure space.

The press frames pretensioned by means of tie rods can be designed with a defined elongation, and the piston-cylinder units that generate the cut-off pressure switch accordingly.

If the pressure chamber is advantageously connected via a line to a pressure relief valve to the pressure chamber of the friction clutch in such a way that when the expansion of the press frame corresponding to a set tappet force and the associated pressure increase in the pressure chamber opens, the pressure relief valve opens, a quick release for decoupling the flywheel is made possible.

In a further embodiment of the invention, the pressure chamber of the cylinder can be directly connected to the control piston of the pressure relief valve in the simplest manner, a passage valve opening when an adjustable pressure is reached being provided in the line between the pressure chamber and the control piston. It is necessary that a sufficient amount of oil can flow out of the pressure chamber when opening the two-way valve to open the pressure relief valve. For larger presses and to shorten the switch-off time, an embodiment of the invention can therefore also be provided in which the pressure chamber of the cylinder is connected to the control piston of a valve which opens depending on an adjustable pressure and of a line fed with high-pressure oil and leading to the control piston of the pressure relief valve.

It is recommended that measuring devices connected in pairs be used for the measurement. Here the two front or the two rear measuring devices are preferably connected together, the switching pulse being able to be triggered on the basis of an average value. However, a switching pulse is triggered in any case as soon as there is a maximum value with only one measuring device; Otherwise, any value of the pressing force is suitable as a switching pulse and can be preset on the press. Furthermore, diagonally opposite measuring devices could also be interconnected, so that a very variable circuit arrangement can be set, for example in order to take eccentric loads on the screw press into account in the measurement.

Figur 1

eine Gesamtdarstellung einer Kupplungs- Spindelpresse mit einer erfindungsgemäßen Meßeinrichtung in einem Schnitt nach der in Figur 2 eingetragenen Schnittlinie I-I;

Figur 2

einen horizontalen Schnitt nach der in Figur 1 eingetragenen Schnittlinie II-II;

Figur 3

in größerem Maßstab einen Ausschnitt der Spindelpresse gemäß Figur 1; und

Figur 4

eine Darstellung gemäß Figur 3 mit abgewandelter ölhydraulischer Schaltung.

The invention is explained in more detail below for a clutch screw press on the basis of exemplary embodiments shown in the drawings. Show it:

Figure 1

an overall view of a clutch screw press with a measuring device according to the invention in a section along the section line II shown in Figure 2;

Figure 2

a horizontal section along the section line II-II entered in Figure 1;

Figure 3

on a larger scale a section of the screw press according to Figure 1; and

Figure 4

a representation of Figure 3 with a modified oil hydraulic circuit.

From Figures 1 and 2 it can be seen that the screw press has a frame 1, which consists of a lower yoke 2, an upper yoke 3, between these arranged stilts 4 and both ends provided with threads 5 tie rods 6 with threaded nuts 7 on the threads 5. The frame 1 is prestressed by means of the threaded nuts 7. In a crest bearing 8 in Oberjoch 3 a spindle 9 is rotatably mounted. A plunger 10, which is guided vertically in the frame 1 and is provided with a threaded nut 11 fastened in it, is moved downward from the spindle 9 engaging with a threaded part 12 in the threaded nut 11. Pistons guided in retraction cylinders 13, which are connected to the plunger 10 by pull rods 14, move the plunger 10 back into the starting position after the working stroke has ended
For the downward stroke of the tappet 10, the spindle 9, which is connected in a rotationally fixed manner above the comb bearing 8, but is axially movably connected to a clutch disc 15, is coupled to a flywheel 16, which is held in circulation by a motor (not shown) by means of belts 17. For coupling, an annular piston 19 and an annular space are arranged in a cover 18 of the flywheel 16, in which the annular piston 19 closes off a clutch pressure space 20. The annular piston 19 rests on a thrust washer 21, which causes the clutch return springs 22 to release the clutch via anchor bolts 23, while for the downward stroke of the tappet 10, the annular piston 19 acts out of the clutch pressure chamber 20 and for coupling a frictional engagement of the clutch disc 15 with the flywheel 16 is brought about by interposed friction linings 24. The torque that can be transmitted by the clutch can be adjusted by a pressure regulating valve 25, and thus also the pressing force that the screw press can apply in each case.

To carry out a stroke, a valve 26 is temporarily brought from its closed rest position into the open working position until the oil pressure specified by the pressure control valve 25 has been established in the pressure line 27 and thus in the clutch pressure chamber 20. With an adjustable time delay, the valve 26 returns to the closed rest position.

With the work or the impact of the plunger 10 with the upper tool on the lower tool, a force corresponding to the pressing or impact force builds up in the frame 1 of the press and leads to the elastic expansion of the frame 1. The tie rods 6 experience an expansion, and the pressure stilts 4 expand with a corresponding decrease in the pretension. The pressing or impact force is opposed by the difference between the force stretching the tie rods 6 and the residual prestress in the pressure stilts 4 as the reaction force.

As can be seen in detail from FIGS. 3 and 4, the tie rods 6 are provided with a bore 28 along their length. At least one of the tie rods 6 or also each tie rod 6 receives a measuring anchor 29 in the bore 28, which is provided at its lower end with an anchor plate 31 held by a nut, with which the measuring anchor 29 is held relative to the lower end of the tie rod 6 . At the upper end of the tie rod or the anchor 29, a measuring device 30 is arranged, which has a piston 33 held there by a nut 32. This includes in a cylinder 34, which is supported on the upper end face of the tie rod 6, a pressure chamber 35, which is connected via a pipe 36 to a pressure oil source, in the exemplary embodiment a pump 37, which fills the pressure chamber 35 with oil and with biased relatively low pressure. A check valve 38 prevents the pressure medium from flowing back via the pressure medium source (pump 37). As the tie rods 6 expand, the pressure in the pressure chamber 35 increases with a corresponding and corresponding increase in the tensile stress in the measuring anchor 29. The pressing or impact force required for carrying out the work in the screw press corresponds to a certain elongation of the tie rods 6 and this corresponds to a pressure in the pressure chamber 35. A pressure limiting valve 39 is set to this pressure for the respective work procedure.

In the exemplary embodiment shown in FIG. 3, the pressure limiting valve 39 is actuated when the set pressure is reached, and the pressure chamber 35 is thereby connected via the pipeline 36 to a pipeline 40, which leads via a rotatable line coupling 41 to the control piston 42 of a 2/2-way valve 43 . The 2/2 way valve 43 thus switches into its working position in which a control line 44 to the closing piston 45 of a pressure relief valve 46 is connected to a return line 48 leading to an oil tank 47 and the closing piston 45 is relieved of pressure. Thus, the pressure relief valve 46 opens, the clutch pressure chamber 20 is depressurized and the friction clutch is released under the action of the springs 22. With a time delay, the 2/2-way valve 43 returns to its rest position - as shown.

A prerequisite for the embodiment according to FIG. 3 is that from the pressure chamber 35 of the piston-cylinder unit 33/34 of the measuring device 30 a sufficient amount of pressure oil after opening the pressure relief valve 39 via line 40 is sufficiently quick and with sufficient pressure on the control piston 42 of the 2/2-way valve 43 is available. The embodiment according to FIG. 4 is independent of this requirement, in which a line 51, which is fed from a pressure oil source, in the embodiment of a pump 50, with oil under high pressure, can be connected to a line 52 through the pressure limiting valve 39, which line leads to the control piston 53 of 2-way valve 54 leads. The connection of the lines 51 and 52 through the pressure relief valve 39 and thus the action on the control piston 53, which switches the 2/2-way valve 54 into the working position, takes place when the pressure set on the pressure relief valve 39 in the pressure chamber 35 of the piston-cylinder unit 33 is reached / 34 of the measuring device 30, as already explained for the exemplary embodiment according to FIG. 3.

For the working position of the 2/2-way valve 54, a closing piston 55 of a pressure relief valve 56 is connected to a return line 57 leading to the oil tank 47, so that the pressure relief valve 56 opens. A pressure relief valve 58 is arranged downstream of the pilot pressure relief valve 56. With the opening of the pressure relief valve 56, the closing piston 59 of the pressure relief valve 58 is depressurized and the pressure relief valve 58 opens, so that the clutch pressure chamber 20 connected via line 27 is depressurized and the friction clutch is released under the action of the springs 22. The release of the friction clutch under the action of the springs 22 is facilitated by the fact that the pressure relief valve 58 is directly associated with a drain cylinder 61 on its discharge line 60, from which the outflowing oil displaced from the pressure chamber 20 is initially taken up in the return line 57 regardless of the flow resistance . A piston 63, which is only slightly loaded by a spring 62, gradually leads the initially deflected piston 63 back to the starting position when the oil pressure is displaced by the return line 57.

It is advantageous to prefill the line 40 in the exemplary embodiment according to FIG. 3 or the line 52 in the exemplary embodiment according to FIG. 4 with moderate pressure, which is done by connecting the lines 40 and 52 to the low-pressure oil source (pump 37) and the oil in lines 40 and 52 is held by a check valve 64.

Basically, it is possible to provide only one measuring armature 29 with a piston-cylinder unit 33/34. However, in order to be able to detect the maximum elongation on a tie rod of the press frame 1 or the mean value of the elongation on all four tie rods of the press frame 1, for example in the case of eccentric loads on the screw press, a tie rod 29 with a piston-cylinder unit 33/34 can be assigned to each tie rod , with appropriate switching (individually, in groups, combined) of the pressure rooms 35.

By dimensioning the measuring armature 29 in relation to their spring characteristic and the piston-cylinder units 33/34 in relation to the effective piston surface of the pressure chamber 35, an adaptation to the expansion behavior of the press frame 1 can be achieved.

Claims (7)

Forming machine with indirectly acting overload protection of a machine frame pretensioned by means of tie rods (6), in particular a screw press with a spindle (9) arranged in the press frame (1), a flywheel (16) driven by a motor and a clutch operated by pressure medium, the press frame (1) being one the ram force is assigned as a function of the measuring device (30) which detects the column expansion, the output signal of which releases the friction clutch before the press frame is overloaded,
characterized,
that at least one of the tie rods (6) is hollow drilled and receives a measuring anchor (29) provided with the force measuring device (30). Screw press according to claim 1,
characterized,
that the measuring armature (29) includes an anchor plate (39) at the bottom and a piston-cylinder unit (33, 34) producing the cut-off pressure at the top, the tie rod (6), the piston (33) of which is supported by the press frame (1) Cylinder (34) includes a pressure chamber (35). Screw press according to claim 2,
characterized,
that the pressure chamber (35) is connected via a line (36, 40, 52) with a pressure relief valve (46, 56, 58) to the pressure chamber (20) of the friction clutch in such a way that when the expansion of the press frame (1 ) and the associated pressure increase in the pressure chamber (25) opens the pressure relief valve (46, 56, 58). Screw press according to one or more of claims 1 to 3,
marked by
Measuring devices (30) connected in pairs. Screw press according to one or more of claims 1 to 4,
characterized,
that the measuring devices (30) can be variably switched on or off. Screw press according to one or more of claims 2 to 5,
characterized,
that the pressure chamber (35) of the cylinder (34) is in direct line connection (36, 40) with the control piston (42) of the pressure relief valve (46) and in the line between the pressure chamber (35) and the control piston (42) one of an adjustable pressure depending opening pressure relief valve (39) is arranged. Screw press according to claim 6,
characterized,
that the pressure chamber (35) of the cylinder (34) with a control piston (53) of the valve (39) which opens as a function of an adjustable pressure and a line (52) fed to high pressure oil and leading to the control piston (53) of the pressure relief valve (56, 58) connected is.

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