DE4239240A1 - Method for controlling and / or monitoring a hydraulic accumulator - Google Patents

Abstract

The proposal is for a method of monitoring and/or controlling a hydraulic pressure reservoir on a diecasting or injection diecasting machine, in which the operating point of a pressure reservoir is subjected to very accurate detection or monitoring and control. In this arrangement, the operating point of the pressure reservoir can be varied by means of a number of different influencing variables, control being performed by an actual/desired value comparison involving predetermined tolerance values. <IMAGE>

Description

The invention relates to a method for regulating and / or Monitoring a hydraulic accumulator on a diecasting or Injection molding machine or the like according to the preamble of Claim 1.

State of the art

In die casting machines, the drive of the casting unit takes place usually by one or more hydraulic accumulators. In Considering the very short casting times, as in the case of Filling a mold cavity are required, it comes very much on the fact that the casting piston at high speed is driven. The casting piston moving the casting piston must therefore at the transition from the slow forward phase to fast form filling phase are accelerated. Order for This time a correspondingly high pressure energy in the Drive hydraulics available, is the required amount of liquid in a hydraulic tank stored and kept under pressure. This container will Accumulator or hydraulic accumulator called. From the  Reference Ernst Brunnhuber "Praxis der Druckgußfertigung ", 3rd edition, 1980, page 70 et seq. Are various types of accumulators have become known. On Such accumulator consists of a standard version Steel bottle in which an inert gas, in particular Nitrogen is included as blowing agent. The High pressure pump of the machine hydraulics promotes the Hydraulic fluid in the accumulator against the pressure of enclosed gas. This "return promotion" happens until the maximum pressure that can be set on the pump is also reached reached in the memory. Liquid and nitrogen are standing under the same pressure, the so-called accumulator pressure. By Control of the maximum pressure at the hydraulic pump can at existing systems also change the memory pressure.

The pressure energy stored in the pressure accumulator is enclosed Opening of the firing valve for driving the drive piston and thus the casting piston available. It will do that out through the accumulator fluid volume flowing through Replaces nitrogen, d. H. the nitrogen expands and causes a pressure drop. To this pressure drop in relative To keep narrow limits, one measures the under pressure memory to be kept amount of nitrogen correspondingly large, resulting in a or several additional nitrogen bottles happening on the Casting drive attached and connected to the accumulator are.

Usually, the pressure accumulator for die casting machines built as a so-called piston accumulator. Here separates in the Accumulator movable piston the compressed gas (nitrogen) from the hydraulic fluid. Through this flying piston it is avoided that the nitrogen in the Can swirl hydraulic fluid. Furthermore, one is Foaming or carryover of nitrogen in the Hydraulic system of such a piston accumulator trained accumulator not possible.  

Unless the static end pressure for a given casting should not be sufficient for densification so-called multipliers used. This is about a Piston translation achieved an increase in pressure of the casting pressure. In this case, the multiplier device can be a separate one Accumulator be assigned, as in the cited Reference Brunnhuber (supra) is shown on page 75. Such a multi-stage pressurizing agent is also from DE-PS 20 21 182 removed.

From the factual context described above, it becomes clear that the state of the storage charge of the pressure accumulator a important size in the die casting process. As mentioned, the Preload of the respective pressure accumulator by regulating the Maximum pressure to be changed on a hydraulic pump. The Position of the piston in the pressure accumulator or piston accumulator determines the amount of hydraulic pumped into the piston accumulator and the pressurized gas compressed thereby as a blowing agent. This "charging" of the accumulator can be based on a Charging curve to be tracked by a first Initial position of the piston (precharge point) to a second Position of the piston (operating point) runs. This is the compressed gas by the hydraulic medium to a certain Volume displaced in accumulator, the pressure in Accumulator is increased to a certain operating pressure. The volume displacement of the compressed gas thus causes the Increasing the pressure in the accumulator, the so-called Operating point the "charged state" of the pressure accumulator characterized.

The invention aims to improve the described Operating conditions. Since the state of the pressure accumulator a decisive influence on the quality of the die-cast parts can have, the invention is based on the object To improve these settings.  

Advantages of the invention

The inventive method aims a control and / or monitoring the pressure accumulator in particular a die casting machine, this principle also at a Injection molding machine or on a similar acting Hydraulic machine or plant is usable. there is a core idea of the invention is that the Operating point of the accumulator of a most accurate detection or monitoring and regulation. It can the Operating point of a pressure accumulator through a series of various influencing variables are changed, the in particular by the state of the precharge pressure and the Gas volume are affected. By changing the The most diverse parameters in the system can also be the Change the operating point of the accumulator, as this is not solely determined by the storage pressure of the propellant. For example, the memory pressure alone does not determine Reliable the operating point, as this crucial too by the storage volume or the hydraulic volume or the Location of the piston in the working memory is determined.

Through this most accurate determination and determination of the Operating point can be a monitoring or regulation of this Operating point are possible, the scheme by an actual value setpoint comparison including predetermined tolerance values. This will always be created reproducible working conditions that lead to a Consistent quality, for example, Diecasting to lead. In particular, the monitoring can also errors recorded in the storage system during operation and, if necessary, be eliminated. This reduces the Scrap quantity. Furthermore, downtimes of Die casting machine due to required Memory monitoring omitted.

The invention results in further detail from the Illustrated drawings in connection with the following description. Here is the Invention described with reference to a die casting machine, without that the invention is limited to such a machine.

Show it

Fig. 1 shows a schematic representation of the Gießantriebs for a die casting machine with an additional multiplier system,

Fig. 2 is an illustration of the operation of a piston-pressure accumulator,

Fig. 3 shows an embodiment for detecting the position of the piston in the pressure accumulator,

Fig. 4 is an overview of the operation of a computer in a control circuit,

Fig. 5 is a flowchart for the monitoring of the restart a machine,

FIG. 6 is a flowchart for monitoring prior to initiation of the casting cycle . FIG.

Fig. 7 is a schematic representation of an automatic compensation of the propellant pressure and

Fig. 8 is a schematic representation of the system for the removal of leakage oil in the compressed gas storage.

Description of the invention

The invention is based on automatic monitoring and Control of the hydraulic accumulator of a die casting machine described.

The Gießantrieb 1 shown in Fig. 1 is used for actuating a shot assembly 2, consisting of a casting chamber 3 having contained therein the molten metal 4 and a casting plunger 5 for insertion of the molten metal 4 in a non-illustrated mold cavity. The casting piston 5 is connected via a casting piston rod 6 with the casting drive 1 . The casting drive 1 consists of a front press cylinder 7 and a pressure piston 8 guided therein, which serves as a drive piston 8 for the associated piston rod 6 . The pressing cylinder 7 has a front cylinder chamber 9 and a rear cylinder chamber 10 , which are separated by the plunger 8 . The front cylinder space 9 is connected to a pressure medium connection 11 .

The pressing cylinder 7 is followed by a multiplier device 12 , in which an axially displaceable multiplier piston 13 is arranged. The multiplier piston 13 divides the associated cylinder chamber 14 into a front cylinder chamber 15 and a rear cylinder chamber 16 . The multiplier piston 13 has a first piston rod 17 extending toward the casting assembly 2 , which extends through the cylinder wall of the multiplier cylinder housing into the rear cylinder chamber 10 of the compression cylinder 7 . In addition, the multiplier piston 13 has a rear piston rod 18 , which likewise extends over the multiplier cylinder housing into a rear cylinder chamber 19 of an additional connection housing 20 . The multiplier piston 13 with front piston rod 17 and rear piston rod 18 is penetrated by a central longitudinal bore 21 , in which a check valve 22 is located.

As described in DE-PS 20 21 182, the present device also operates according to the so-called 3-phase system of a cold chamber die casting machine. In this case, in the first and second working phase, only the pressing piston 8, which acts directly on the casting piston 5, is subjected to pressure medium, and during the third working phase, the multiplier device is connected for an increased holding pressure.

For pressure medium of the plunger 8 and the multiplier piston 13 , the pressure accumulator 23 , 24 shown in FIG. 1 are provided, which are formed as a so-called piston accumulator, each with a piston 25 , 26 movable therein. Below the piston 25 , 26 is the hydraulic fluid 27 , 28 , above the respective piston 25 , 26, the generally formed as nitrogen pressure medium 29 , 30th In order to increase the gas volume of the pressure medium, each pressure accumulator 23 , 24 are each assigned two additional nitrogen bottles 31 , 31 'and 32 , 32 '. The pressure accumulator 23 is connected via a connecting line 33 and a control valve 34 to the rear cylinder chamber 19 of the terminal housing 20 , the pressure accumulator 24 via the connecting line 35 and a control valve 36 to the rear cylinder 16 of the multiplier cylinder 14 .

At the 3 phase casting operation, a flow valve is at the release of the shot first opened 37, and conveyed by a pump 38 hydraulic fluid flows into the rear cylinder space 19 of the terminal housing 20 and from there through the longitudinal bore 21, the check valve 22 to the rear cylinder chamber 10 for acting upon the Plunger 8 . As a result, the plunger 8 and thus the casting piston 5 in slow forward movement (first phase) moves forward. At the same time, the hydraulic medium located in the front cylinder chamber 9 is emptied via the line 11 via the flow valve 37 into a tank 40 .

After completion of the slow flow, the casting piston is accelerated to high speed for the Formfüllhub. This is done by a switching point by means of a control cam 41 on the casting piston rod. 6 The control cam signal is supplied via a line 42 to a computer 43 which provides via line 44 an output signal or pulse to the firing valve 34 . This pulse opens the firing valve 34 , so that the hydraulic fluid 27 can suddenly get from the pressure accumulator 23 in the pressure chamber 19 and thus in the pressure chamber 10 to accelerate the plunger 8 .

As soon as the mold cavity is completely filled with liquid metal, the casting piston 5 is abruptly decelerated. Now, instead of the previous flow pressure, the full accumulator pressure builds up in the pressure chamber 10 of the compression cylinder 7 and also in the space 19 of the connection housing 20 , the check valve 22 being closed. Now, the further shot valve 36 is opened at a suitable time via the computer 43 via the line 45 , so that the hydraulic medium 28 of the second pressure accumulator 24 via line 35 in the rear pressure chamber 16 of the multiplier cylinder 14 can empty. During this third phase, a re-compaction of the liquid metal takes place to compensate for shrinkage of the casting metal. During this phase, the piston rod 17 pushes into the cylinder chamber 10 to cause an increase in pressure.

The above explanations make it clear that the operating point of the storage charge of the two pressure accumulators 23 , 24 represent an important variable in the die casting process. The location of the operating point of the pressure accumulator has a decisive influence on the quality of Diecasting.

For the pressure accumulator 23 , 24 , the position of the operating point for further explanation in Fig. 2 is shown in an example. As can be seen from this diagram, the operating point of a pressure accumulator can be changed by various factors. In the upper diagram in FIG. 2, the abscissa represents the volume V and the ordinate shows the pressure p of the gaseous pressure medium (nitrogen), as is present in the cylinder space 29 , 30 and the additional tanks 31 , 32 in FIG . In the lower half of FIG. 2, the pressure accumulator 23 , 24 shown, with a first piston position 25 ', 26 ' in the precharge point 46 and a second piston position 25 , 26 at the operating point 47th The two points 46 , 47 are connected by the charging curve 48 .

In the precharge point 46 , the piston 25 , 26 is in its lowest position, ie, the entire hydraulic fluid 27 , 28 has been pressed out of the respective pressure cylinder 23 , 24 at the end of the casting process.

To produce a new pouring thrust, the hydraulic fluid 27 , 28 must be pumped back into the pressure accumulator 23 , 24 , so that the pistons 25 , 26 move in these pressure accumulators. By this displacement of the pistons 25 , 26 , the gas 29 , 30 in the embodiment of FIG. 2, for example, from a volume of 60 Ltr. Compressed to a volume of 44 Ltr., That is, 16 Ltr. Hydraulic medium in the pressure accumulator 23 , 24th pressed. By this compression of the pressure medium 29 , 30 , the pressure of this gas increases from the pressure p ₀ of z. B. 110 bar to the pressure p _B of 150 bar along the charging curve 48th The precharging point 46 is thus characterized by the size V ₀ , p ₀ , the operating point 47 is characterized by the compressed volume V _B and the compressed pressure p _B. This charging process of the respective pressure accumulator 23 , 24 takes place along the charging curve 48 in FIG. 2.

Malfunctions can be caused by the following factors arise:

• 1. The precharge pressure p ₀ is too large. The cause of this may be an incorrect precharge or heating of the gas volume during operation.
• 2. The precharge pressure p ₀ may also be too small, which may be caused by a false precharge, by leakage at the separating piston of the pressure accumulator or by leaks on the gas side of the pressure accumulator.
• 3. The total gas volume V ₀ may have become smaller, which may be caused by a leakage of the separating piston 25 , 26 in the pressure accumulator, whereby the gas volume with hydraulic medium may be "contaminated".
• 4. The operating pressure p _B can not be achieved. This can be due to an incorrect precharge of p ₀ . Furthermore, the hydraulic pressure for charging or the time for charging the pressure accumulator may not be sufficient.
• 5. The operating pressure p _B may be exceeded, which can be done by an incorrect pressure setting of the hydraulic, in particular, the hydraulic pressure for loading the pressure accumulator may be too large.

These various sources of error in the adjustment of the operating point 47 with the most accurate values for the operating pressure p _B and the volume V _B may be sources of error in die casting. If the operating point is outside of predetermined tolerance values, this results in faulty casting results. The automatic adjustment of the correct position of the operating point within predetermined tolerance limits and the determination of the errors in the storage system during operation of the die casting machine is therefore the broader object of the invention, thus turning off the machine for checking the hydraulic pressure accumulator and a manual reloading of the Memory is unnecessary. This can account for downtime of the die casting machine with regular memory verification.

FIG. 3 shows an exemplary embodiment for monitoring or regulating the pressure accumulator 23 , 24 . In this case, the position of the separating piston 25 , 26 can be measured in the pressure accumulator by means of an ultrasonic transducer 49 . At the output of an evaluation electronics 50 , an analog path signal s _K is available, which is supplied to the computer 43 .

On the gas side, the gas pressure of the pressure medium 29 , 30 or the pressure in the gas cylinders 31 , 32 is measured by means of a pressure sensor 51 and this value is also supplied to the computer 43 . With the aid of these values, the superordinate computer can make an evaluation of the exact position of the pressure piston 25 , 26 at the operating point 47 or in the precharge point 46 (lower position of the piston 25 ', 26 ').

In Fig. 3, the hydraulic valve 52 for the application of the pressure accumulator 23 , 24 with pressure medium by means of a pressure medium pump 53 is shown. A check valve 54 in a supply line 55 prevents backflow of the pressure medium.

An overview of the operation of the computer 43 is shown in Fig. 4.

The following values are specified on the computer:

• Tolerance field for the precharge pressure p ₀ and for the operating pressure p _B (arrow 56 );
• - Tolerance field for the accumulator piston _stroke s _K (arrow 57 ).

The actual values for the Speicherolbenhub s _K (arrow 58 ) and the gas pressure p (arrow 59 ) are also fed as inputs to the computer.

In a new charging of the machine (when the memory is in a desired state), the respective hydraulic chamber of the pressure accumulator 23 , 24 is acted upon by means of the pressure medium pump 53 via the hydraulic valve 52 with hydraulic medium. During this charging process, the data for the piston travel s _K and the accumulator pressure p are stored as actual values in the computer 43 by applying the signal "drive reference curve" (arrow 60 ). In this case, for example, with each pressure change of p = 5 bar, the associated travel values of the separating piston s _{K can} be stored as actual values. Thus, an assignment of pressure and piston travel is stored in the computer 43 , which has been driven as a reference curve. By means of the input of a "tolerance field" for the piston travel, an assignment of the reference piston travel to the target value of the piston travel is formed in the computer. From the values determined via the reference _curve for the piston travel s _KRef , setpoint values are thus formed in the computer taking into account the tolerance field.

This can be represented by the following table, for example become:

s _{KRef ssoll} s _{K (0)} s _{K (0) min} - s _{K (0) max} s _{K (1)} s _{K (1) min} - s _{K (1) max} , , , , , , s _{K (n)} s _{K (n) min} - s _{K (n) max}

In the casting operation, an assignment of the pressure p to the actual value of the piston stroke s _{KIst is} stored in the computer 43 during each charging process of the hydraulic _accumulator . In this case, it is useful if the values of the piston travel s _K are stored at the same pressures as during the recording of the reference data, ie the actual values of the piston travel s _KIst are stored as a function of the pressure, for example in the following table:

bar (p) mm (s _KIst ) 110 s _{K (0)} 115 s _{K (1)} 120 , , , 125 , , , etc. @ 150 s _{K (n)}

With this stored data, the computer 43 forms by a comparison output signals for the piston travel, the piston stroke s _{K is} a function of the pressure s _K = f (p). This comparison in the computer is shown in FIG. 4 below the arrow 61 , ie the computer compares the actual values of the piston travel with corresponding setpoint values of the piston travel over the distance of the charge curve. It should be noted that this comparison is made on the points 1 to n of the measured values of the charging curve.

With these signals, a precise indication of the errors in the hydraulic storage system is possible without interrupting the casting operation. It is advantageous that the display of the errors in plain text or with a corresponding symbol representation on a screen 61 . Another advantage according to the invention is to utilize the outputs on the computer by means of a downstream control so that an automatic compensation of the pending errors is carried out without the casting operation being interrupted.

In Fig. 4, therefore, the essential contents of the task of the computer 43 is shown, where the values of the inputs are added to 60 56. In the computer, the reference data are stored in a first step 62, the tolerance fields are formed in a further step 63 and setpoint data are generated, the actual data 64 are stored in a subsequent step and a comparison is made in a further step 65. As outputs on the computer results in a piston travel curve s _{K of} the separating piston as a function of pressure (arrow 61, ) and an actual reference value comparison of the precharge pressure p ₀ in the precharge point 46 (arrow 66 ).

In Fig. 5, the normal sequence in the casting operation is shown in principle as a flow chart, with a monitoring at a restart of the machine is usually performed once a day.

The restart takes place when the machine is switched on (item 67 ). First, an actual setpoint comparison of the precharge pressure p ₀ in position 68 is performed. If the actual value is not equal to the nominal value of the precharge pressure (position 69 ), a comparison of these values takes place in the computer 43 . If p _{0 is} greater p _{0 setpoint} (position 70 ), an indication is made on the screen 61 that p _{0 is} too large. Likewise, an indication is made on the screen 61 in a comparison p _0Ist less p _0Soll (position 71 ). Both times, the nitrogen precharge is manually changed accordingly (position 72 in FIG. 5) or there is an automatic compensation in a separate subroutine. This process takes place in a circulation loop 73 until the actual value of the precharge pressure p ₀ corresponds to the input desired value, so that the program takes the computer path 74 from the starting point 68 . In position 75 , it is thus determined that the precharge pressures p _{0 are} in order and that an automatic storage charge release takes place.

If a time interval of 5 to 10 seconds has elapsed for charging the accumulator, position 76 of the flow chart is used to monitor the piston travel s _{K of} the separating piston 25 , 26 as a function of the gas pressure p _V (s _K = f (p)). If the computer _detects deviations here, ie _{if it} is not equal to _sColl , a display on the screen 61 is made under position 77 that the storage _bottles 31 , 32 are filled, for example, with hydraulic medium due to a leaking separating piston. This causes the machine to be switched off under position 78 in order to remedy the error. For example, the storage bottles 31 , 32 can be emptied of the hydraulic medium manually or by means of an automatic emptying in a subroutine.

If the computer comparison under position 76 determines that the actual value of the piston travel s _{K is} equal to the predetermined desired value s _KSoll , a release for the engine start takes place under position 79 .

The flow chart according to FIG. 5 therefore shows the preparation of the machine with regard to the charging of the pressure accumulators in order to obtain an optimum operating point 47 . In this case, both the exact starting point of Vorladepunkts 46 and the achievement of the optimum operating point 47 is ensured.

In the diagram according to FIG. 6, an additional monitoring before the casting cycle is triggered after the release for the machine start according to FIG. 5 is shown for the normal course of the casting operation. FIG. 6 accordingly follows position 79 in FIG. 5.

In the flow chart of Fig. 6, the monitoring is performed before the casting cycle is triggered after the engine start release (position 79 ). First, under position 80, it is determined if the mold is closed. Thereafter, the pressure accumulator monitoring starts under position 81 . Under position 82 , it is first checked whether the pressure p _{B of} the operating point 47 is in order. If it is determined under position 83 that the operating point is too small or too large, then under position 84 at too low an operating point p _B an indication will be displayed on the screen 61 in that the operating point p _B is to be increased by a manual setting change on the die casting machine. or that this pressure p _B has to increase automatically via a subroutine. Under position 85, a display on the screen 61 is alternatively carried out as a fault indication to the effect that the operating pressure p _B is to be reduced by manual adjustment change to the die casting machine, which can also be carried out automatically in turn optionally substituted at a p to large operating pressure _B. This is done via the computer loop 86 until the operating point is in order, which is indicated under position 87 .

If the operating point p _B is correct, a comparison of the piston travel s _K as a function of the accumulator pressure p (s _K = f (p)) takes place again at position 88 . If it turns out that the measured actual values of the path of the separating pistons 25 , 26 are not equal to the predetermined nominal values, a separation takes place under position 89 in the flow diagram according to FIG. 6 into the respective possibilities. Under position 90 , at a s _KIst greater than _{KSoll, it} is indicated that the precharging point 46 generates too great a precharging pressure p ₀ due to an impermissible gas heating. If the measured actual value of the piston travel is smaller than the predetermined target value of the piston travel, it is indicated under position 91 on the screen 61 that the precharge pressure p _{0 is} too small, which may have a cause in the gas loss in the pressure accumulator 29 to 32 . The cause gas heating is indicated by reference numeral 92 , the cause gas loss by reference numeral 93 . In both cases, that is to say when the precharge pressure p ₀ is too great and too small, an opening of the mold takes place under position 94 , whereby the machine start is aborted and under position 95 the precharge pressure p ₀ is to be changed automatically or automatically by means of a subroutine.

If it is detected under position 88 that the actual value of the piston travel s _KIst always corresponds to the nominal value of the piston value s _KSoll , a release for the metal metering takes place under position 96 and thus a firing trigger via the firing valves 34 , 36 .

As described above, z. B. following errors in the operation of the pressure accumulator 23 , 24 occur:

• - precharge pressure p ₀ too high due to wrong precharge;
• - precharge pressure p ₀ too low due to wrong precharge;
• - The gas volume of the pressure medium 29 , 30 in the pressure accumulator 23 , 24 and in the gas cylinders 31 , 32 is due to a partial filling with hydraulic medium wrong, which can be done by a leaking separating piston 25 , 26 ;
• - The gas space of the gas medium is leaking;
• - The gas volume has heated inadmissible;
• - The operating pressure p _{B of} the gas volume at the die casting machine is set incorrectly;
• - There is a pressure drop in the hydraulic system of the hydraulic medium 27 , 28th

FIGS. 7 and 8 show, in each case one exemplary embodiment, how the abovementioned errors can be automatically compensated. The prerequisite for such an automatic compensation is the use of the monitoring system previously described in FIGS. 5 and 6.

In Fig. 7 is shown how the precharge pressure p ₀ can be automatically set to the correct value. Like parts are designated by the same reference numerals as in the preceding figures. For this purpose, reference is made in particular to FIGS. 1 and 3.

By means of a control unit not shown in detail in FIG. 7 or a control unit connected in parallel to the computer 43 , two valves 97 , 98 are actuated. When the valve 97 is actuated, additional pressurized gas is supplied to the pressure accumulators 23 , 24 including the gas cylinders 31 , 32 via the line 100 from a transportable compressed gas cylinder 99 , wherein the precharging pressure p ₀ can increase. By the pressure measuring device 51 , the valve 97 is de-energized when reaching the necessary precharge pressure p ₀ , so that the access to the pressure bottle 99 is closed. The measurement of the actual value of the precharge pressure p ₀ is thus carried out by means of the pressure sensor 51 under evaluation in the computer 43 . This measurement signal is fed to the control device, not shown, to actuate the valve 97 .

When the valve 98 is activated, compressed gas can be discharged into the atmosphere via the line 101 from the gas space 29 to 32 assigned to the pressure accumulator 23 , 24 .

This reduces the precharge pressure p ₀ . The shutdown of the valve 98 in turn via the control device, not shown, when the measured actual value of the precharge pressure p ₀ corresponds to the setpoint p _0soll . This again takes place by means of the pressure sensor 51 .

By means of the arrangement according to FIG. 8, an automatic emptying of the pressure accumulators 23 , 24 associated gas cylinders 31 , 31 'and 32 , 32 ' of hydraulic medium 27 , 28 is effected. Due to a possibly leaking separating piston 25 , 26 in the pressure accumulators 23 , 24 can hydraulic medium 27 , 28 via the leads 101 to the compressed gas cylinders 31 , 32 reach. The compressed gas cylinders 31 , 32 can therefore, as shown symbolically in FIG. 8, partially fill with hydraulic fluid 27 , 28 . This results in a distortion of the total volume of the gaseous pressure medium.

For automatic emptying of the gas cylinders 31, 32, 32, valves 102, 103 is provided, via which the hydraulic fluid can be drained off via line 104 and 105 are for the respective gas cylinder 31. The valves 102 , 103 may only be switched to passage as long as hydraulic fluid is present in the discharge lines 104 , 105 . To detect this condition, the drainage of the drain lines 104 , 105 by biased check valves 106 , 107 is prevented. In this case, the distinction as to whether there is hydraulic fluid or compressed gas flowing off in the discharge lines 104 , 105 can be effected, for example, by means of a temperature probe 108 , 109 . When gas flows at this measuring point, a sudden temperature difference arises, which is used as an evaluation signal and fed to a corresponding control device. This control process is indicated schematically by the lines 110 , 111 . Instead of temperature probes 108 , 109 , it is also possible to use electronic medium sensors 112 , 113 , whose output signals are in turn fed to the valves 102 , 103 via a control device 112 ', 113 ' via the lines 110 , 111 . In this case, the electrical resistance is measured between two sensor pins 114 , 115 . When the feeler pins 114 , 115 are acted upon by hydraulic fluid 27 , 28 to be discharged from the gas cylinders 31 , 32 , the measured electrical resistance is lower than during the passage of this line or of the measuring sensor with pressurized gas.

The arrangement according to FIG. 8 therefore represents a further advantageous supplement to carrying out the method according to the invention.

The invention is not limited to that described and illustrated Embodiment limited. She became just an example to the application in a die-casting machine described. Of course, this can be done analogously in a Apply injection molding machine or similar hydraulic machinery.

Claims (12)

1. A method for monitoring and / or control of a hydraulic accumulator on a Druckgieß- or injection molding machine o. The like., Wherein the drive of a casting unit ( 2 ) o. The like. Via a hydraulic piston / cylinder unit ( 7 , 12 ) takes place is acted upon by a charged hydraulic, preferably designed as a piston accumulator pressure accumulator (23, 24), wherein the piston accumulator (23, 24) includes a gas reservoir (29-32) is associated with gaseous pressure medium, which, as drive means, in particular for the separating piston (25 26 ) of the piston accumulator ( 23 , 24 ), wherein the separating piston ( 25 , 26 ) in the charged state of the piston accumulator ( 23 , 24 ) a certain "operating state" ( 47 ) and in the discharged state of the piston accumulator ( 23 , 24 ) a certain "Vorladezustand" ( 46 ) occupies, characterized in that the "operating state" of the charged piston accumulator ( 23 , 24 ) as an "operating point" ( 47 ) with information of actual values via the pressure p _B , the gas volume V _B and optionally further parameters in a computer ( 43 ) can be detected and that these actual values are compared in the computer ( 43 ) with predetermined set values while maintaining tolerance limits and that in case of impermissible deviation of the actual values of the set values a manual or automatic correction and / or an error indication (monitor 61 ) of the respective operating state takes place. 2. The method according to claim 1, characterized in that an error correction of the actual value of the "operating point" ( 47 ) and / or the "Vorladepunktes" ( 46 ) takes place during a work cycle or in the next working cycle. 3. The method according to claim 1, characterized in that the gas volume in the piston accumulator ( 23 , 24 ) by a position detection (s _K ) or position detection (s _K ) of the separating piston ( 25 , 26 ), preferably an ultrasonic transducer ( 49 ) is used. 4. The method according to claim 1, characterized in that the pressure in the piston accumulator ( 23 , 24 ) or the gas pressure of the pressure medium ( 29 , 30 ) in the, the piston accumulator ( 23 , 24 ) downstream gas storage ( 29-32 ) by means of a Pressure sensor ( 51 ) detectable and a computer ( 43 ) can be fed. 5. The method according to claim 1, characterized in that the operating state of the discharged piston accumulator ( 23 , 24 ) in the computer ( 43 ) can be detected, said "precharge" by a "precharge" ( 46 ) with values for the precharge volume (V ₀ ), the precharge pressure (p ₀ ) and optionally the position S _{K0 of} the separating piston ( 25 , 26 ) is characterized. 6. The method according to one or more of the preceding claims, characterized in that in the computer ( 43 ) has a reference curve or charging curve ( 48 ) for the boost pressure p between the precharging point ( 46 ) (p ₀ , V ₀ ) and the operating point ( 47 ) (P _B , V _B ) is entered in the production of good parts, that at each reload an actual value / setpoint comparison with tolerance fields with this reference curve ( 48 ) and in case of impermissible deviation an error signal and / or a correction control during the work cycle or in the following Working cycle takes place. 7. A method, in particular according to one or more of the preceding claims, characterized in that an automatic adjustment of the precharge pressure p _{0 is provided} to a correct value, wherein by means of a control unit at least a first valve ( 97 ) between the gas reservoir ( 29-32 ) the piston accumulator ( 25, 26 ) and an additional compressed gas reservoir ( 99 ) are controlled in such a way that the pressure is increased to the precharge pressure p ₀ , the valve ( 97 ) closing after reaching the precharge pressure p ₀ and a second controllable valve ( 98 ) is provided to the gas reservoir ( 29-32 ) to optionally reduce above the precharge pressure (p ₀ ) increased pressure. 8. The method, in particular according to one or more of the preceding claims, characterized in that the gas reservoir ( 29-32 ) is associated with a further valve arrangement ( 102 , 103 ) in a separate discharge line ( 104 , 105 ) that a drain of hydraulic fluid ( 27 , 28 ) from the gas reservoir ( 29-32 ) detectable and a control device ( 108 ', 109 ', 112 ', 113 ') can be fed and that the valve assembly ( 102 , 103 ) after the emptying of the hydraulic fluid ( 27 , 28 ) from the gas storage ( 29-32 ) closes. 9. The method according to claim 8, characterized in that the gas flow through the discharge line ( 104 , 105 ) by means of a temperature sensor ( 108 , 109 ) or by means of an electronic medium sensor ( 112 , 113 ) is monitored. 10. The method according to one or more of the preceding claims, characterized in that on a die casting machine for casting drive of the plunger ( 8 ) and / or the multiplier piston ( 13 ) each have a piston / cylinder unit ( 7 , 12 ) is provided, each of a piston accumulator ( 23 , 24 ) with hydraulic pressure medium ( 27 , 28 ) can be acted upon and that each piston accumulator ( 23 , 24 ) one or more, in particular two gas accumulators ( 31 , 32 or 31 ', 32 ') are assigned. 11. The method according to one or more of the preceding Claims, characterized in that the detection of all possible error in the memory system in the operating state of Die casting machine takes place and thus downtime for the manual inspection of the hydraulic storage system accounts. 12. The method according to one or more of the preceding Claims, characterized in that the compensation of the detected by the computer errors in the storage system takes place in the operating state of the die casting machine.