AT519581A1 - Piston-cylinder unit - Google Patents

Abstract

A piston-cylinder unit for a forming machine comprising - a first chamber (2), - a hydraulic pump (3) connected to the first chamber (2) for pressurization with a pressurized hydraulic fluid, and - a reset device (4) ) for returning a piston (5) of the piston-cylinder unit (1) in a direction which direction of a direction of action of the first chamber (2) is substantially opposite, wherein the restoring device (4) has a second chamber (6) of the piston Cylinder unit (1) and a pressure accumulator (7), which pressure accumulator (7) with the second chamber (6) is connected and / or is formed integrally with the second chamber (6).

Description

Summary

Piston-cylinder unit for a molding machine with

- a first chamber (2),

- A hydraulic pump (3) which is connected to the pressurized hydraulic fluid with the first chamber (2), and

- A resetting device (4) for resetting a piston (5) of the piston-cylinder unit (1) in one direction, which direction is essentially opposite to an effective direction of the first chamber (2), the resetting device (4) having a second chamber (6 ) of the piston-cylinder unit (1) and a pressure accumulator (7), which pressure accumulator (7) is connected to the second chamber (6) and / or is formed integrally with the second chamber (6).

(Fig. 1a) / 23

81116 32 / nm

The present invention relates to a piston-cylinder unit for a

Molding machine according to the features of the preamble of claim 1.

Molding machines can be understood to mean injection molding machines, injection presses, presses and the like.

Generic piston-cylinder units include a first chamber, a hydraulic pump, which is connected to the pressurized hydraulic fluid with the first chamber, and a resetting device for resetting a piston of the piston-cylinder unit in one direction, which direction a direction of action of the first chamber is substantially opposite. Resetting devices for piston-cylinder units can be used in molding machines if only the action of the piston-cylinder unit in the direction of action of the first chamber is important for the molding cycle itself. Then the piston-cylinder unit must be returned to the starting position, for which the reset device is available. It is known in the prior art to carry out the resetting through a second chamber of the piston-cylinder unit, which is connected to the pump of the hydraulic system (or another pump). By pressurizing the second chamber, the piston-cylinder unit can be returned to the starting position.

However, this has the disadvantage that time for resetting the piston-cylinder unit is lost during the shaping cycle. In addition, a relatively high volume of hydraulic fluid is required in the system of the second chamber and the pump must be activated to reset.

Specifically, in the case of pressure cushions, i.e. piston-cylinder units for building a clamping force in a clamping unit of a molding machine, the pressure in the first chamber must first be reduced for this purpose (clamping force reduction). Only then can the piston be reset by pressurizing the second chamber.

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To improve this situation, electrical (DE 10 2005 051 787 A1) or mechanically resilient (US 2016/0067898 A1) means for automatic resetting have been proposed in the prior art. However, this resulted in much more complex and complex constructions (see the figures of the prior art documents addressed). In particular, when using mechanical springs, there is also the problem that it is difficult to adapt to the height of the mold, which is to be mounted in a clamping unit, since the length and spring strength of the mechanical spring cannot be adjusted. This problem does not occur with an electrical reset, but an electrical drive must be provided in a basically hydraulic shaping machine that requires additional precision parts (for example a threaded spindle) and is more complex. In addition, the hydraulics for the second chamber and the electric drive must be controlled in a coordinated manner.

The object of the present invention is therefore to provide a reset device which is simpler in comparison with the prior art and which does not cause a design-related delay in the shaping cycle or only causes it to a small extent.

This object is achieved by a piston-cylinder unit with the features of claim 1.

This happens because the reset device has a second chamber of the piston-cylinder unit and a pressure accumulator. The pressure accumulator is connected to the second chamber or is formed integrally with the second chamber. By supplying the first chamber with a hydraulic fluid and fulfilling the actual task of the piston-cylinder unit, hydraulic fluid is displaced from the second chamber into the pressure accumulator and the pressure accumulator is thereby charged. In an embodiment in which the pressure accumulator is formed integrally with the second chamber, the pressure accumulator is loaded directly.

If a pressure present in the first chamber is now released, the pressure accumulator is automatically discharged and the piston is reset at the same time as the pressure is released.

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The present invention thus makes it possible to use a simple piston

Construction and at the same time reset without loss of cycle time. Apart from a hydraulic drive, no other drives are necessary.

In addition, by changing the amount of hydraulic fluid in the second chamber together with the pressure accumulator, it is easy to set a basic position (up to which it is reset).

Hydraulic oil can be used as the hydraulic fluid.

Further advantageous embodiments of the invention are defined in the dependent claims.

In a particularly simple embodiment of the invention, the resetting of the piston is permitted until the pressure accumulator is completely discharged, which results in a reproducible resetting, since the discharged pressure accumulator and corresponding pressure loss stop the resetting quickly.

Piston-cylinder units according to the invention can be used, for example, to apply clamping force to the clamping units of molding machines. Ejectors of a clamping unit can also be driven with a piston-cylinder unit according to the invention. Ejectors are used to remove a product molded in a molding machine or mold from the corresponding mold or tool.

The pressure accumulator can be designed particularly simply as a bladder accumulator and / or membrane accumulator.

Bladder accumulators have a pressure container in which hydraulic fluid and a compressible medium are separated from each other by a flexible bladder. The hydraulic fluid can also be completely displaced from the pressure vessel by the pressure medium when the pressure accumulator is unloaded. In particular, gases can be used as pressure medium / 23. An example of a print medium would be

Nitrogen. The resetting (“spring constant”) can be easily adjusted by adjusting the gas filling pressure.

With a diaphragm accumulator, a diaphragm is used instead of a bladder to separate the compressible medium from the hydraulic fluid.

The first chamber can be a rod-side chamber of the piston-cylinder unit. Particularly in the case of clamping units of injection molding machines in a two-plate construction with mostly four bars, a particularly small-sized clamping unit can be created in this way, which also has a quick and automatic bar reset.

The second chamber can have a smaller pressure-effective cross section than the first chamber. This is particularly advantageous if a particularly high force is to be generated by the piston-cylinder unit, for which a high pressure-effective cross section of the first chamber is beneficial. Due to the smaller pressure-effective cross section of the second chamber, the counterforce, which acts against the force of the first chamber by loading the pressure accumulator, is also lower.

A small pressure-effective cross-section of the second chamber can, for example, be produced relatively simply by the second chamber being delimited by an extension of the piston, the extension having a smaller cross-section than the piston. In particular in the case of piston-cylinder units whose first chamber is a rod-side chamber, such designs can be used advantageously.

It can be provided that the second chamber is connected to the pump and / or a further pump, a check valve being provided in a connecting line between the pump and / or the further pump on the one hand and the second chamber on the other hand. A mold height adjustment or an adjustment of the position up to which the resetting device brings about a resetting of the piston (basic position) can thereby be implemented particularly easily. By opening the check valve, hydraulic fluid can flow into the second chamber (or the / 23

Pressure accumulator) are transported. When the pressure accumulator is unloaded, it is automatically reset to the position that corresponds to the volume of the

Hydraulic medium in the system from the second chamber and pressure accumulator corresponds.

The first chamber can have a discharge line for hydraulic medium, a shut-off valve preferably being provided in the discharge line. This enables a particularly simple and quick resetting of the piston, since in a state in which the first chamber is pressurized and therefore the pressure accumulator is loaded, only the shut-off valve in the discharge line has to be opened in order to simultaneously reduce the pressure in the first chamber and the To cause the piston to reset.

Protection is also sought for an arrangement of at least two - preferably four - piston-cylinder units which are designed according to the invention, the second chambers of the at least two piston-cylinder units being connected to a single pressure accumulator.

Protection is also sought for a molding machine with such an arrangement or at least one piston-cylinder unit according to the invention.

Displacement sensors can be provided with which the position of the piston in the cylinder can be detected. This can be advantageous in particular in the case of an embodiment with an arrangement in which a plurality of second chambers use a single pressure accumulator. When resetting, only the signals from the displacement sensor need to be observed for each individual piston-cylinder unit and the resetting movement must be stopped as soon as the desired position is reached. The resetting movement can preferably be stopped by means of an already mentioned shut-off valve arranged in the discharge line.

Further advantages and details of the invention emerge from the figures and the associated description of the figures. Show

1a, 1b two embodiments of the invention in a first position, Fig. 2a, 2b two embodiments of the invention in a second position, Fig. 3a, 3b two embodiments of the invention in a third position, / 23

4a, 4b two embodiments of the invention in a fourth position,

5 shows an arrangement according to the invention with several according to the invention

Piston-cylinder units

Fig. 6 shows a piston-cylinder unit according to the invention for driving a

Ejector as well

7 shows a molding machine according to the invention.

FIG. 1a shows a piston-cylinder unit 1 according to the invention with a first chamber 2, a piston 5 and a second chamber 6. The first, rod-side chamber 2 is used, for example, for the clamping force in a clamping unit 15, an injection molding machine. For this purpose, the first chamber 2 is connected to a pump 3. The second chamber 6 is connected to the pressure accumulator 7.

In the embodiment according to FIG. 1a, the discharge line 12 is at the same time the feed line 14 to the first chamber 2. In the discharge line 12 there is also a check valve 11. In addition to the connection to the pressure accumulator 7, the second chamber 6 is also connected to the pump 3, namely via the connecting line 9. A connection from the second chamber 6 to a tank for hydraulic fluid (without reference number) is also established via the connecting line 9. Also in the connecting line 9 there are two check valves 11 - one for the connection of the second chamber 6 to the pump 3 and one to the tank.

Hydraulic oil is used as the hydraulic fluid.

The check valves 11 are preferably designed as seat valves. These offer a high degree of tightness, which is advantageous since the amount of hydraulic medium in the system comprising the second chamber 6 and the pressure accumulator 7 and corresponding lines is then as constant as possible.

The constancy of the amount of hydraulic fluid in the system comprising the second chamber 6 and the pressure accumulator 7 results in a reproducible and constant position up to which the resetting device 4 according to the invention resets the piston 5.

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The pressure accumulator 7 is designed as a bladder accumulator, with nitrogen, for example, having a minimum supply pressure p ₀ of approximately 10 bar as the pressure medium

Use can come.

Figure 1b shows a variant of the embodiment of Figure 1a. It differs in that the second chamber 6 does not have the same cross section as the first chamber 2. This is achieved by an extension 8 of the piston 5, which extension 8 has a smaller cross section than the piston 5. The cylinder is shaped accordingly.

Another advantage of the embodiment with a low-section extension 8 is that the counterforce exerted by the loading of the pressure accumulator 7 against the effect of the pressurization of the first chamber 2 is smaller than is the case with the embodiment according to FIG. 1a , because the pressure-effective cross-section of the first chamber is larger than that of the second chamber in this case.

Another difference between the designs according to FIGS. 1a and 1b is the hydraulic connection. In the embodiment according to FIG. 1 b, the first chamber 2 has a separate discharge line 12 which opens into a tank. The feed line 14 to the second chamber, like the discharge line 12 and the connecting line 9, has corresponding shut-off valves. It should be noted that the hydraulic interconnections according to FIG. 1a and FIG. 1b can also be used in other embodiments.

FIGS. 1a and 1b show the respective embodiments in an idle state in which there is no pressure on the chambers 2, 6.

A basic positioning of the piston 5 is shown in FIGS. 2a and 2b. By opening the shut-off valve 11 in the connecting line 9 (towards the tank) and opening the shut-off valve 11 in the feed line 14 (or, in the case of FIG. 2a, line 12), the amount of hydraulic fluid in the second chamber 6 can be reduced (piston 5 moves to the right). The quantity can be increased by operating the pump 3 and correspondingly changing the switching position of the check valves 11.

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FIGS. 3a and 3b show the respective variants when the first chamber 2 is pressurized. As a result, the pressure accumulator 7 is loaded, which in the

Figure can be seen from the deformed membrane of the bladder accumulator.

The pump 3 pumps hydraulic medium into the first chamber 2. The check valve 11 required for this is open. The other check valves 11 are closed.

FIGS. 4a and 4b show the provision according to the invention by the pressure accumulator for the respective variants. By opening the check valves 11 in the outlet 12, hydraulic medium escapes from the first chamber 2 and flows back into a tank (in the case of FIG. 4a via the pump 3). The pressure accumulator 7 now takes effect and at the same time as the pressure in the first chamber 2 decreases, the piston 5 returns to the basic position which was described in connection with FIGS. 2a and 2b, the pressure accumulator 7 in the basic position in accordance with these statements is completely discharged.

As long as there is hydraulic fluid in the pressure accumulator, a certain minimum supply pressure is made available (gas filling pressure). If the total amount of oil is withdrawn, the supply pressure is no longer automatically available and the connected consumer will stop at this point.

FIG. 5 shows an embodiment of an arrangement with four piston-cylinder units 1 according to the invention, the second chambers 4 of which are each connected to a single pressure accumulator 7. Each of the displacement sensors 13 detects the positioning of the piston 5.

The hydraulic connection is a parallel connection to that shown in FIG. 1a.

In this arrangement, the check valve 11 in the derivation 12 is opened for the resetting. As a result of the action of the pressure accumulator 7, the pistons 5 are reset.

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The displacement transducers 13 can be used to control certain positions. As soon as the corresponding position has been reached (or shortly before), the corresponding shut-off valve 11 in the outlet 12 can be closed. The hydraulic fluid locked in the first chamber 2 of the corresponding piston-cylinder unit 1 then prevents further resetting beyond the desired positioning. The desired positioning of the piston-cylinder units 1 approached in this way can correspond or be different.

6 shows an embodiment of a piston-cylinder unit 1 according to the invention, which can be used, for example, with an ejector of a clamping unit 15 of an injection molding machine. The second chamber 6 is a rod-side chamber of the piston-cylinder unit 1.

To eject a molded part, the first chamber 2 is pressurized. As a result, the piston 5 and thus the ejector (not shown) attached to it moves to the right in the illustration. As a result, the pressure accumulator 7 is also loaded. To withdraw the ejector, only the hydraulic fluid has to be drained from the first chamber 2. The hydraulic circuit shown between pump 3 and first chamber 2 is self-explanatory.

7 shows a molding machine 10 according to the invention - in this case an injection molding machine. This consists of a clamping unit 15 and an injection unit 16 with a plasticizing screw.

The clamping unit 15 has mold clamping plates which are moved relative to one another by rapid lifting cylinders for mounting a mold. A large clamping force must be applied to the platen when injecting. The piston-cylinder units 1 (pressure pads) are provided for this. As described in connection with FIG. 5, the piston-cylinder units 1 could also be connected to a single pressure accumulator 7.

The hydraulic connection - especially the hydraulic worm drive and the rapid lifting cylinder - is also self-explanatory.

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The present invention is not limited to the exemplary embodiments shown here. For example, the piston-cylinder unit 1 can also be designed as a rotary piston. The pump 3 can consist of a system of several pumps 3. The cylinders and pistons 5 of the piston-cylinder unit 1 can each be cylinders in the geometric sense with a circular, polygonal or even more complex base area.

Innsbruck, on January 27, 2017/23

81116 32 / eh

Claims (15)

claims 1. Piston-cylinder unit for a molding machine with - a first chamber (2), - A hydraulic pump (3) which is connected to the pressurized hydraulic fluid with the first chamber (2), and - A resetting device (4) for resetting a piston (5) of the piston-cylinder unit (1) in one direction, which direction is essentially opposite to an effective direction of the first chamber (2), characterized in that the resetting device (4) has a second one Chamber (6) of the piston-cylinder unit (1) and a pressure accumulator (7), which pressure accumulator (7) is connected to the second chamber (6) and / or is formed integrally with the second chamber (6). 2. Piston-cylinder unit according to claim 1, characterized in that the piston-cylinder unit (1) is used for clamping force in a clamping unit of a molding machine. 3. Piston-cylinder unit according to claim 1 or 2, characterized in that the piston-cylinder unit (1) serves as a drive for an ejector of a clamping unit of a molding machine. 4. Piston-cylinder unit according to one of the preceding claims, characterized in that the pressure accumulator (7) is designed as a bladder accumulator and / or membrane accumulator. 5. Piston-cylinder unit according to one of the preceding claims, characterized in that the first chamber (2) is a rod-side chamber of the piston-cylinder unit (1). 6. Piston-cylinder unit according to one of the preceding claims, characterized in that the second chamber (6) has a smaller pressure-effective cross section than the first chamber (2). 12/23 7. Piston-cylinder unit according to one of the preceding claims, characterized in that the second chamber (6) is delimited by an extension (8) of the piston (5), the extension (8) having a smaller cross section than the piston ( 5). 8. Piston-cylinder unit according to one of the preceding claims, characterized in that the second chamber (6) is connected to the pump (3) and / or a further pump, wherein in a connecting line (9) between the pump (3 ) and / or the further pump on the one hand and the second chamber (6) on the other hand a check valve (11) is provided. 9. Piston-cylinder unit according to one of the preceding claims, characterized in that the first chamber (2) is connected to a discharge line (12) for hydraulic medium, wherein in the discharge line (12) a check valve (11) is preferably provided. 10. Piston-cylinder unit according to one of the preceding claims, characterized in that a displacement transducer (13) is provided, which is set up to detect a position of the piston (5). 11. An arrangement of at least two - preferably four - piston-cylinder units according to one of claims 1 to 10, wherein the second chambers (6) of the at least two piston-cylinder units (1) are connected to a single pressure accumulator (7) , 12. Molding machine which includes at least one piston-cylinder unit according to one of claims 1 to 10 and / or an arrangement according to claim 11. Innsbruck, January 27, 2017 13/23 1.7 14/23 81116, ENGEL AUSTRIA GmbH 2.7 15/23 81116, ENGEL AUSTRIA GmbH