DE102019202883A1 - Hydraulic control arrangement and drive unit - Google Patents

Abstract

Disclosed are a hydraulic control arrangement and a drive unit embodied with such a hydraulic control arrangement, in particular for a casting machine, the control arrangement having a hydraulic cylinder to which a control block is assigned. The position of a piston of the hydraulic cylinder is detected by means of a position sensor, which according to the invention is received at a distance from the inflow region of the hydraulic cylinder or of the control block.

Description

The invention relates to a hydraulic control arrangement according to the preamble of claim 1 and a drive unit designed with such a control arrangement.

The drive unit can be used, for example, to drive the casting piston of a casting unit of a casting machine, for example a die casting machine, a thixomolding machine or an injection molding machine.

• - Vorfüllen/Vorschieben
• - Einspritzen/Schuss und
• - Nachverdichten/Druckaufbau

über eine hydraulische Schaltung mit proportional verstellbaren Wegeventilen und Schaltventilen mit einem Hochdruckspeicher oder einem Niederdruckspeicher oder einem Tank verbunden werden. Diese drei Gießphasen sind detailliert im eingangs genannten Stand der Technik beschrieben, so dass weitere Erläuterungen entbehrlich sind.The basic structure of such a drive unit of a die casting machine is, for example, in the documents DE 10 2017 220 836 A1 and DE 10 2017 220 832 A1 described, both of which go back to the applicant. Accordingly, the drive unit for a casting unit of a die casting machine has a casting cylinder which is designed as a differential cylinder. A piston rod of the differential cylinder drives a casting piston, via which the respective molding material can be injected into a cavity of a tool. The pressure chambers of the differential cylinder can be used to initiate the three casting phases

• - Filling / feeding
• - injection / shot and
• - Post-compression / pressure build-up

can be connected to a high-pressure accumulator or a low-pressure accumulator or a tank via a hydraulic circuit with proportionally adjustable directional valves and switching valves. These three casting phases are described in detail in the prior art mentioned at the outset, so that further explanations are unnecessary.

In a compact solution, the hydraulic circuit with the directional / switching valves and possibly with the pressure accumulators is integrated in a control block, which can be attached to the differential cylinder. In principle, however, the control block can also be arranged separately from the casting cylinder.

In the compact solution, the casting cylinder and the control block together form a cylinder and inflow chamber which is delimited by the piston. The stroke of the piston is detected by a position sensor which is attached to the bottom of the inflow chamber in conventional solutions and which projects with a sensor rod into a sensor recess which extends into a piston rod of the piston. This sensor rod interacts with a position magnet which is arranged on the piston. A pressure connection opens into this piston-side inflow chamber and is pressurized with high pressure, for example in a die-casting machine, for compression, which can be, for example, in the range of over 400 bar. A pressure chamber of the hydraulic cylinder on the piston rod side is connected to a tank, so that the force is built up very quickly. The associated high pressure medium inflow forces can cause the sensor to be bent or deformed, so that the function of the hydraulic control arrangement, in particular the measurement accuracy, is impaired when determining the piston position.

In contrast, the invention has for its object to provide a hydraulic control arrangement and a drive unit executed therewith, in which a proper function is guaranteed even at high pressures.

This object is achieved with regard to the hydraulic control arrangement with the features of patent claim 1 and with regard to the drive unit with the features of patent claim 14.

Advantageous developments of the invention are the subject of the dependent claims.

The hydraulic control arrangement according to the invention has a hydraulic cylinder, in particular a casting cylinder, to which a hydraulic control block is preferably attached, via which the pressure medium connection of the hydraulic cylinder to high-pressure or low-pressure accumulators or a tank is controlled.

The hydraulic cylinder has a piston which is guided in a cylinder housing and, in sections, delimits a piston-side cylinder chamber to which an inflow chamber adjoins or which is designed with an inflow chamber section. A pressure medium connection opens into this inflow chamber.

To detect a piston position, the control arrangement is designed with a position sensor which is supported in the area of the cylinder chamber and projects into a sensor recess of the piston with a sensor rod. According to the invention, the sensor rod is not attached to a bottom of the inflow chamber, as in conventional solutions, but to a holder which supports the sensor offset toward the piston or towards the transition area between the cylinder chamber and inflow chamber / inflow chamber section. The bracket preferably extends approximately as an extension of the sensor rod or position sensor. The holder is positioned in such a way that the sensor is no longer located directly in the inflow area of the pressure medium, for example the control block-side inflow chamber, and accordingly the holder and not the sensor is acted upon by the pressure medium inflow forces. However, this can be in simply be designed so that it withstands the inflow forces even at high pressures. The sensor is then preferably supported in the transition area from the control block-side part of the cylinder chamber or the inflow chamber to the actual cylinder housing, for example a cylinder tube - in this transition area and in the adjoining flow area of the sensor, the pressure medium forces are significantly lower than in the inflow area, so that the Problems described at the beginning with a deformation of the sensor do not occur.

The terms “cylinder chamber” and “inflow chamber” are to be interpreted relatively broadly, the inflow chamber or the inflow chamber section also being able to be formed by a corresponding configuration of the cylinder chamber, which then extends, for example, into the control block. The area of the piston-side pressure chamber that extends into the control block is referred to as the inflow chamber / inflow chamber section in the following embodiments.

Due to the axial displacement of the sensor towards the piston / cylinder space, a shorter sensor can be used than in conventional solutions in which the sensor is supported on the bottom of the cylinder or inflow chamber, preferably on the control block, in which case a sensor rod has the inflow chamber without overlapping with the Piston penetrates and is therefore exposed to the pressure forces. The holder can easily be dimensioned so that it does not deform. Even a possible deformation of the bracket would not affect the measurement quality of the sensor.

In a particularly preferred solution, the holder is designed with a holding tube which is supported on the control block side and on the piston-side end section of which the sensor is held. This end section preferably engages around the sensor in sections. This holding tube then acts both as a holder and as a protective tube, over which the sensor is partially covered, so that the sensor is not directly pressurized in this area.

The support of the sensor can be further improved if the holding tube and / or the sensor is supported radially in the area of the cylinder chamber or the cylinder housing via a support ring arrangement.

In such an embodiment, the pressure medium connection to the sensor recess of the piston can take place through recesses / openings in the support ring arrangement, via which the pressure medium flow is calmed.

According to an advantageous development of the invention, a sensor base of the sensor carrying the sensor rod, preferably in the area of the support ring arrangement, is prestressed against a support shoulder via a clamping device in the holding tube.

A risk of damage to the sensor can be further reduced if the sensor rod is surrounded by a jacket tube which is attached to the holding tube, so that the entire sensor is encased and thus protected.

According to one embodiment, the sensor rod (in the case of a position sensor which is not provided with a jacket tube) or the jacket tube is supported / guided in the radial direction via a suitable support / guide inside the piston - or in the case of a differential cylinder - within the piston rod.

It is particularly preferred if an end section of the casing tube which is removed from the holding tube is closed with an end piece which supports the sensor rod in the radial direction, so that the relative positioning of the sensor takes place in a defined manner within the casing tube.

In principle, however, the casing tube can also remain open in the area of the end section, so that the pressure medium can flow into the casing pipe and / or the holding pipe from the end section - this area, however, is not subjected to the inflow forces explained at the beginning.

The pressure medium flow to the sensor recess is optimized if its mouth on the cylinder chamber side is expanded in a funnel shape towards the cylinder chamber.

In order to ensure the inflow and outflow of pressure medium even under unfavorable operating conditions, in one embodiment of the invention an annular gap is formed between the sensor rod and the peripheral wall of the sensor recess or between the sheathing of the sensor rod and the peripheral wall of the sensor recess, which is designed such that in Operation even with high pressure medium loads, there is no contact between the peripheral wall and the sensor rod / jacket tube.

The signal transmission and power supply of the sensor is particularly simple if the holding tube is also designed as a cable bushing for the sensor cable. As a result of this development, the sensor cable, which in principle extends through the cylinder chamber and the inflow chamber to the control block, is hermetically sealed from the pressure medium.

In a particularly preferred exemplary embodiment, the hydraulic cylinder is designed as a differential cylinder, the sensor recess extending into a piston rod of the piston.

According to the above, the concept according to the invention is explained with a position sensor held at a distance from an inflow region using the example of a hydraulic control arrangement. In principle, it is also conceivable to apply this concept generally when a sensor is subjected to external forces, for example as a result of mechanical vibrations or from turbulences in the flows of fluids / gases, and then to avoid interactions with the sensor, the holder from this fault area is brought out. The applicant reserves the right to make its own claims to this general concept.

In the above-described exemplary embodiments, the position sensor is held / encased by means of tubular structures. Of course, other structures for holding / covering can also be used.

In a simply constructed embodiment, instead of a two-part protection with a holding tube and a casing tube, a single holding / protective tube can also be used, which then on the one hand in the area of the control block and / or the cylinder chamber and on the other hand in the area of the piston or the piston rod in the radial direction is led. Of course, it is also possible to design the holding tube and / or the casing tube in several parts.

The support tube or a corresponding component in the control block can also be supported in a variety of ways and is not limited to the specific embodiment described below.

• 1 zeigt eine Prinzipdarstellung einer Gießeinheit einer Druckgussmaschine;
• 2 zeigt ein Schaltschema zur Ansteuerung einer Antriebseinheit der Gießeinheit gemäß 1;
• 3 zeigt eine Schnittdarstellung einer erfindungsgemäßen hydraulischen Steueranordnung mit einem einen Gießzylinder bildenden Hydrozylinder, der an einen hydraulischen Steuerblock angebaut ist;
• 4 zeigt eine Detaildarstellung eines steuerblockseitigen Bereichs der Steueranordnung gemäß 3;
• 5 zeigt eine Detaildarstellung eines Übergangsbereichs zwischen dem Steuerblock und dem Hydrozylinder;
• 6 zeigt eine Detaildarstellung eines kolbenstangenseitigen Endabschnitts der Steueranordnung gemäß 3 und
• 7 zeigt ein Detail B aus 6.

Preferred exemplary embodiments of the invention are explained in more detail below with the aid of schematic drawings.

• 1 shows a schematic diagram of a casting unit of a die casting machine;
• 2nd shows a circuit diagram for controlling a drive unit according to the casting unit 1 ;
• 3rd shows a sectional view of a hydraulic control arrangement according to the invention with a hydraulic cylinder forming a casting cylinder, which is attached to a hydraulic control block;
• 4th shows a detailed representation of a control block-side area of the control arrangement according to 3rd ;
• 5 shows a detailed view of a transition area between the control block and the hydraulic cylinder;
• 6 shows a detailed representation of an end section on the piston rod side of the control arrangement according to FIG 3rd and
• 7 shows a detail B. 6 .

The basic structure of a die casting machine is in 1 shown. In the present patent application, only a few components of the die casting machine that are essential for understanding the invention are explained. With regard to further details, reference is made to the publications mentioned at the beginning.

According to 1 the die casting machine has a drive unit with a control arrangement 1 that a casting cylinder, hereinafter hydraulic cylinder 2nd called, which means by means of a control block 4th arranged hydraulic circuit is controllable. In the illustrated embodiment, the control block 4th via a connection plate 6 in a compact design on the hydraulic cylinder 2nd scheduled. This is a differential cylinder with a cylinder housing 8th executed in which a piston 10th with a piston rod 12 is led. The piston 10th delimits a cylinder chamber on the piston bottom 14 . The ring surface of the piston 10th and the piston rod 12 delimit an annulus 16 of the cylinder housing 8th . The piston rod 12 is on the face of the cylinder housing 8th led out and drives a casting piston 18th at the one in a gun barrel 20th is guided and with this a shot chamber 22 limited. A filling opening or an inlet opens into this 24th for the melted or doughy molding material to be processed. The gun barrel 20th is a tool 26 with two separable tool halves 28 , 30th scheduled. These form a cavity 32 out by moving the casting piston 18th the molding material via a pouring channel 34 can be inserted / injected. The cavity 32 is designed according to the shape of the workpiece to be manufactured. The two tool halves 28 , 30th can be designed with appropriate cores to form an inner contour.

We mentioned above are the hydraulic controls for controlling the hydraulic cylinder 2nd and thus to drive the casting piston 18th essentially in the control block 4th added. At the in 1 The illustrated embodiment is the control block 4th to the hydraulic cylinder 2nd scheduled. In principle, however, it is also possible to use the control block 4th at a distance from the hydraulic cylinder 2nd to arrange and the pressure medium connection over To manufacture pipes or ducts. According to the invention, however, the compact solution shown is also attached to the hydraulic cylinder 2nd attached control block 4th .

2nd shows the hydraulic circuit diagram of the control arrangement in a highly simplified form 1 . The hydraulic cylinder described above is shown 2nd and in the control housing 4th recorded hydraulic components required for control.

Accordingly, the control arrangement 1 a high pressure accumulator HD and a low pressure accumulator ND, both via a variable displacement pump 36 can be loaded. A 2/2-way valve 36 is arranged in a line leading to the low-pressure accumulator ND, via which the pressure medium connection to the low-pressure accumulator, ND can be opened or closed. The high-pressure accumulator HD is a proportionally adjustable directional valve 38 assigned, via which the opening cross-section to / from the high-pressure accumulator HD can be set proportionally. The outlet of both valves 36 , 38 is with a pressure line 40 connected in fluid communication with the cylinder chamber 14 stands, so that depending on the control of the directional valve 36 or the proportional adjustable directional valve 38 the cylinder chamber 14 can be connected to the high-pressure accumulator HD or the low-pressure accumulator ND.

From the pressure line 40 further branches off a connecting line in which a proportionally adjustable connecting valve 42 is arranged. This connecting line 44 is with the annulus 14 and with a tank line 46 connected. In the latter there is also a proportionally adjustable tank valve 48 arranged, which controls a pressure medium connection to a tank T. The proportionally adjustable connection valve 42 and the proportionally adjustable tank valve 48 are both designed as two-way valves. All of the aforementioned valve components are controlled via a common control unit (not shown) of the die casting machine. Further details of the hydraulic control of the die casting machine according to the invention can be found in the publications mentioned at the beginning.

In 3rd is a section of a concrete embodiment of the hydraulic control arrangement according to the invention 1 shown. This is used, for example, as a drive unit for the casting piston 18th the die casting machine used, being attached to the hydraulic cylinder 2nd the hydraulic control block 4th is grown. The aforementioned valves and control devices are provided for controlling the pressure medium supply and pressure medium discharge. In the illustrated embodiment, the control block 4th Made of panel construction, with the front connection plate 6 with a cylinder tube 50 executed cylinder housing 8th of the hydraulic cylinder 2nd by means of a cylinder flange 52 is scheduled.

In the control block 4th is an inflow chamber 54 trained, in which a pressure medium connection 56 flows through the pressure medium, for example with high pressure ( 420 bar) inflow or outflow of pressurized medium. The inflow chamber 54 goes into the cylinder chamber 14 about that according to the presentation 1 to the left through the piston 10th is limited. In the shown retracted position of the piston 10th is the volume of the cylinder chamber 14 minimal. The piston rod 12 limited with the cylinder barrel 50 the annulus 16 which has a further pressure medium connection 60 and an indicated control block part 62 with the tank or the cylinder chamber 14 is connectable. The one from the control block 4th distal end portion of the cylinder barrel 50 is by means of a multi-part end flange 64 closed by the end portion of the piston rod 12 is enforced. In the area of this end flange 64 are guiding and sealing elements of the hydraulic cylinder 2nd arranged, the details of which, however, are irrelevant for the present application. In the illustrated embodiment, the end flange 64 with a support flange 66 clamped over longitudinal struts, not shown, which in turn on the cylinder tube 50 is set. Between the support flange 66 and the end flange 64 is an extension of the cylinder barrel 50 extending connection socket 68 arranged, in which the pressure medium connection described above 60 is formed and to which the control block part 62 is scheduled. The latter is via indicated pipelines 70 with the control block 4th connected. In the area of the connection socket 68 are the guide and sealing elements mentioned above 72 added.

For actuating the casting piston 18th are, for example, in a first phase for advancing the piston 10th with the piston rod 12 both pressure medium connections 56 , 60 via the directional valve 36 and the connection valve 42 connected to the low pressure accumulator ND so that the piston 10th extends due to the area difference.

In a subsequent shooting phase, the annulus becomes 14 via the pressure medium connection 60 and the tank valve 48 connected to the tank T and the connection valve 42 controlled so that the piston 10th extends at a comparatively high speed.

During the subsequent compression, the pressure medium connection 56 connected to the high pressure accumulator HD (up to 400 bar), the tank valve 48 remains open so that pressure builds up within a short time to compress the molding material. The travel speeds of the piston 10th and with it the casting piston 18th can be adjusted by adjusting the opening cross-sections of the proportionally adjustable valves 38 , 42 , 48 Set so that the phases described starting, injection and pressure build-up can be controlled independently of each other and the tool is filled in an optimal way so that even highly complex workpieces can be produced.

The control in the control block takes place during these phases 4th (62) recorded directional valves also depending on the position of the piston 10th and the piston rod 12 . This position is via a position sensor 74 recorded, which, as will be explained in more detail below, in the control block 4th by means of a holding tube 76 is supported and with a sensor rod 78 in a sensor recess 80 in the piston 10th and the piston rod 12 immersed.

Further details are given in the 2nd to 5 explained.

4th shows that part of 3rd in which the holding tube 76 is shown. This is at the control block 4th supported, in this a recording 82 is formed, in which an end portion of the holding tube 76 is inserted. The one from the recording 82 protruding part of the holding tube 76 penetrates the inflow chamber 54 and extends into the area of the cylinder chamber 14 that with the inflow chamber 54 forms a pressure chamber together. In this transition area between the inflow chamber 54 and the cylinder chamber 14 is in the end portion of the holding tube 76 the position sensor 74 with a sensor base 84 used. This contains the elements of the position sensor required for signal transmission and energy supply 74 arranged. The signal and energy connection to the control block 4th takes place via a sensor cable 86 that goes through the holding tube 76 through to the control block 4th extends and is therefore reliably sealed against the pressure medium. The sensor stick 78 is on the sensor base 84 attached and is - as explained in more detail below - by means of a jacket tube 88 covered against the pressure medium. This casing tube 88 is also sealing in the in 4th illustrated end portion of the holding tube 76 used.

At the in 4th illustrated embodiment has the holding tube 76 a radial shoulder lying in the area of the sensor-side end section 90 , on the one hand the casing tube 88 and on the other hand the sensor base 84 are supported. The latter is via a clamp tube 92 on the radial shoulder 90 held that in the holding tube 76 is inserted. The clamping takes place via a clamping ring 94 that in the holding tube 76 is screwed in and over the clamp tube 92 the sensor base 84 against the radial shoulder 90 presses. The position of the holding tube 76 in the recording 82 done through a mother 96 that the holding tube 76 with one shoulder 98 against a support ring 100 presses so that the holding tube 76 is fixed in the axial direction.

According to 5 (Detail A from 3rd ) is this support ring 100 Part of a support ring arrangement 102 , which also has an intermediate ring 104 belongs in which one to the support ring 100 widening channel section 106 is trained. The support ring 100 is according to 5 as a kind of perforated disc with a large number of openings / openings 108 formed a pressure medium connection between the inflow chamber 54 and the cylinder chamber 58 form. The support ring arrangement 102 is on the one hand on a support shoulder 110 in the control block 4th and on the other hand on a radial surface 112 of the cylinder barrel 50 supported.

As shown in 5 is the sensor recess 80 in the mouth area to the cylinder chamber 14 with a funnel-shaped extension 114 running a pressure fluid flow from the cylinder chamber 14 or from the inflow chamber 54 into the sensor recess 80 in cooperation with the also funnel-shaped channel section 106 and the breakthroughs 108 evened out.

A ring-shaped position magnet 116 of the position sensor 74 is in the area of the funnel-shaped extension 114 on the piston 10th held and is held by the sensor rod 78 enforced.

6 shows that from the control block 4th distal end portion of the hydraulic cylinder 2nd . As stated above, in this area is that in the annulus 16 opening pressure medium connection 60 educated. A section of the control block part is also visible in this illustration 62 . As stated above, the cylinder tube is 50 by means of one of the piston rod 12 sealingly penetrated end flange 64 or an end flange arrangement is closed. The sealing and guide elements mentioned at the beginning are also in this area 72 the piston rod 12 arranged. The sensor recess 80 ends in this area, being accordingly in the retracted position of the piston rod 12 the sensor rod 78 extends into this area. This end section is in the 6 and 7 marked as detail B.

How in particular 7 removable, is the end portion of the casing tube 88 by means of an end piece 118 locked. This can, for example, on the end section of the casing tube 88 be screwed on and is with a conical cap 120 executed, which further optimizes the flow around.

In that of the cap 120 distal end portion of the tail 118 is a blind hole 122 formed into which the end portion of the sensor rod 78 with little play or with a press fit. The tail 118 is a perfect fit in the jacket pipe in this area 88 used so that the sensor rod 78 in the radial direction within the casing tube 88 is supported.

The outer diameter of the casing tube 88 and the inner diameter of the sensor recess 80 are coordinated so that there is an annular gap 124 with a gap width S that is large enough that even under unfavorable pressure and flow conditions there is contact between the jacket tube 88 and the piston rod, or the peripheral wall of the sensor recess 80 is avoided and thus the sensor rod 78 always runs at a distance from this peripheral wall. This gap width S also facilitates the inflow and outflow of the pressure medium during the extension and retraction of the piston rod 12 .

Under certain circumstances can on the jacket pipe 88 be dispensed with - in this case too, it is advantageous to use the above-described gap width S between the peripheral wall of the sensor recess 80 and the sensor rod 78 to provide.

Disclosed are a hydraulic control arrangement and a drive unit embodied with such a hydraulic control arrangement, in particular for a casting machine, the control arrangement having a hydraulic cylinder to which a control block is assigned. The position of a piston of the hydraulic cylinder is detected by means of a position sensor, which according to the invention is received at a distance from the inflow region of the hydraulic cylinder or of the control block.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102017220836 A1 [0003]
• DE 102017220832 A1 [0003]

Claims (14)

Hydraulic control arrangement with a hydraulic cylinder (2), to which a hydraulic control block (4) is attached, the hydraulic cylinder (2) having a piston (10) which partially delimits a cylinder chamber (14), which is preferably connected to an inflow chamber (54) of the control block (4), wherein a pressure medium connection (56) opens into this or the cylinder chamber (14) and with a position sensor (74) for detecting a piston position and with a sensor rod (78) which is in a sensor recess (80) of the piston (10) protrudes, characterized by a holder which displaces the position sensor (74) towards the cylinder chamber (14) and / or towards the piston (10), preferably in the transition area between the inflow chamber (54) and the cylinder chamber (14). Tax order after Claim 1 , wherein the holder has a holding tube (76) which is supported on the control block side and through the piston-side end section of which the position sensor (74) is held and preferably encompassed in sections. Tax order after Claim 2 , with a support ring arrangement (102), via which the holding tube (76) and / or the position sensor (74) is supported in the cylinder chamber (14) or in the cylinder housing (8). Tax order after Claim 3 , wherein the support ring arrangement (102) has at least one opening (108), preferably a plurality of openings (108) for the passage of the pressure medium. Control arrangement according to one of the Claims 2 to 4th , wherein a sensor base (84) carrying the sensor rod (78), preferably in the region of the support ring arrangement (102), is prestressed against a radial shoulder (90) via a clamp in the holding tube (76). Control arrangement according to one of the Claims 2 to 5 , wherein the sensor rod (78) is surrounded by a jacket tube (88) which is attached to the holding tube (76). Control arrangement according to one of the Claims 1 to 5 or 6 , wherein the sensor rod (78) or the casing tube (88) in the piston (10) or a piston rod (12) is supported or guided radially. Tax order after Claim 6 or 7 , wherein an end section of the casing tube (88) remote from the holding tube (76) is closed with an end piece (118) which supports the sensor rod (78) in the radial direction. Control arrangement according to one of the Claims 2 to 8th , A mouth of the sensor recess (80) on the cylinder chamber side being widened towards the cylinder chamber (14) via a funnel-shaped extension (114). Tax order after Claim 9 A position magnet (116) is held in the area of the funnel-shaped extension (114) and is penetrated by the sensor rod (78). Control arrangement according to one of the preceding claims, wherein an annular gap (124) is formed between the sensor rod (78) and the peripheral wall of the sensor recess (80), which is designed such that no contact between the sensor rod (78) or the Jacket tube (88) and the peripheral wall of the sensor recess (80). Control arrangement according to one of the Claims 2 to 11 , wherein a sensor cable (86) of the position sensor (74) is led through the holding tube (76) to the control block (4). Control arrangement according to one of the preceding claims, wherein the hydraulic cylinder (2) is a differential cylinder and the sensor recess (80) extends into a piston rod (12) of the piston (10). Drive unit for a casting unit, with a control arrangement according to one of the preceding claims.

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