Abstract:
The invention relates to a venting unit for a die casting device which has a mold cavity that is adapted to be filled with liquid casting material and a gas suction device that is connected to the mold cavity for extracting gas from the mold cavity by suction, the venting unit comprising a flow labyrinth, the inlet of which is adapted to be connected to the mold cavity and the outlet of which is adapted to be connected to the gas suction device. In order to develop the venting unit in such a way that it makes improved evacuation of the mold cavity possible without the risk that liquid casting material can escape from the venting unit, it is proposed according to the invention that the flow cross-section of the flow labyrinth is variable. Furthermore, a die casting device with a venting unit of this kind is proposed.

Description:
[0001]    This application is a continuation of international application number PCT/EP2008/006180 filed on Jul. 26, 2008 and claims the benefit of German patent application no. 10 2007 054 520.9 filed on Nov. 6, 2007. 
         [0002]    The present disclosure relates to the subject matter disclosed in international application number PCT/EP2008/006180 of Jul. 26, 2008 and German application number 10 2007 054 520.9 of Nov. 6, 2007, which are incorporated herein by reference in their entirety and for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    The invention relates to a venting unit for a die casting device which has a mold cavity that is adapted to be filled with liquid casting material and a gas suction device that is connected to the mold cavity for extracting gas from the mold cavity by suction, the venting unit comprising a flow labyrinth, the inlet of which is adapted to be connected to the mold cavity and the outlet of which is adapted to be connected to the gas suction device. 
         [0004]    The invention also relates to a die casting device with a venting unit of this kind. 
         [0005]    Die casting devices are known, for example, from DE 20 2005 019288 U1. They have a mold cavity, into which liquid casting material, for example molten aluminum or magnesium, can be injected. To avoid air bubbles being trapped in the casting material, which is at first liquid and then hardens in a very short time, with the trapped air bubbles possibly impairing the quality of the casting produced, the air can be extracted from the mold cavity by means of a gas suction device. The extraction of air from the mold cavity may take place before and during the filling of the mold cavity. To avoid liquid casting material being able to escape from the mold cavity and reach the gas suction device or a venting valve disposed upstream of it, disposed between the mold cavity and the gas suction device is a venting unit which forms a flow labyrinth, the inlet of which is adapted to be connected to the mold cavity and the outlet of which is adapted to be connected to the gas suction device. The inlet may, for example, be connected to the mold cavity by way of a venting channel, and the outlet of the flow labyrinth may be connected to the gas suction device by way of a suction line. The flow labyrinth can be used for extracting gas from the mold cavity. If liquid casting material enters the flow labyrinth, it solidifies within the flow labyrinth, so that the flow connection between the mold cavity and the gas suction device is interrupted. Venting units of this kind, which can be used for extracting gas from the mold cavity and in the flow labyrinth of which entering casting material solidifies, are also referred to as chill block systems or washboards. 
         [0006]    The main task of the gas suction device of a die casting device is to evacuate a certain amount of air from the mold cavity within a short time, i.e. within a few seconds. The air is in this case sucked out of the mold cavity through relatively narrow gaps. The narrow gaps impair the extraction capability. In many cases it has been found that, even though powerful gas suction devices are provided, the mold cavities are only evacuated unsatisfactorily. 
         [0007]    It is an object of the present invention to develop a venting unit of the type mentioned at the beginning in such a way that it makes improved evacuation of the mold cavity possible without the risk that liquid casting material can escape from the venting unit. 
       SUMMARY OF THE INVENTION 
       [0008]    This object is achieved according to the invention in the case of a venting unit of the type mentioned at the beginning by the flow cross-section of the flow labyrinth being variable. This provides the possibility of reducing flow losses within the flow labyrinth when gas is extracted from the mold cavity, since a relatively large flow cross-section can be chosen for the flow labyrinth for the extraction of gas from the mold cavity. The evacuation of the mold cavity can be significantly improved as a result. However, to be able to avoid liquid casting material being able to flow through the flow labyrinth and escape from the venting unit, the flow cross-section of the flow labyrinth can be reduced, so that it is ensured that inflowing casting material reliably solidifies within the flow labyrinth. 
         [0009]    It is of advantage if the flow cross-section of the flow labyrinth is adapted to be varied by liquid casting material flowing into the flow labyrinth. This provides the possibility of choosing the flow cross-section to be comparatively large at the beginning of the casting operation, in order to be able to extract gas effectively from the mold cavity. The extracting operation may continue until casting material filled into the mold cavity enters the flow labyrinth. The inflowing casting material can then bring about the reduction in the flow cross-section of the flow labyrinth, for example by the inflowing casting material impinging with great force on a portion of the wall of the flow labyrinth. The impingement of the portion of the wall with the surge of inflowing casting material can then be used for reducing the flow cross-section. 
         [0010]    It may be provided, for example, that the flow labyrinth has first and second projections, which are opposite to one another and disposed offset in relation to one another in the direction of flow and the spacing between which is variable. The inflowing casting material undergoes a deflection in each case at the first and second projections, a considerable momentum being transferred to the first and/or second projections, so that the projections change their relative position and, as a result, reduce the flow cross-section of the flow labyrinth. 
         [0011]    The first projections preferably are adapted to be offset in relation to the second projections in the direction of flow. The first projections are consequently movably held, whereas the second projections are fixedly formed. If the inflowing casting material impinges on the first projections, as a result the latter change their position in relation to the second projections and thereby reduce the flow cross-section of the flow labyrinth. 
         [0012]    In the case of a configuration of the venting unit according to the invention that is structurally particularly simple, the first projections are held on a movable mounting. The mounting may, for example, take the form of a displaceable slide, which is movable back and forth between a first end position, in which the flow labyrinth has a relatively large flow cross-section, and a second end position, in which the flow labyrinth has a comparatively small flow cross-section. The slide is preferably held on a linear guide, which may be formed, for example, as a dovetail guide. 
         [0013]    As already explained, it is advantageous if the first projections are adapted to be offset by liquid casting material flowing into the flow labyrinth. It may be provided, for example, that the first projections can be displaced by the liquid casting material, the flow cross-section of the flow labyrinth being reduced as a result. 
         [0014]    It is of advantage if the first projections are adapted to be offset counter to an elastic restoring force. As a result, the first projections can be transferred from a rest position, which they assume as long as they are not impinged by liquid casting material, into a working position, in which the flow labyrinth has a flow cross-section that is reduced in comparison with the rest position. The transfer from the rest position into the working position takes place counter to the action of the elastic restoring force. If the first projections are no longer impinged by the casting material, they automatically resume their rest position on account of the restoring force acting on them. 
         [0015]    It is particularly advantageous if the first projections are adapted to be arrested in their working position. It has been found that this makes it easier to remove the solidified casting material from the flow labyrinth, since the arresting of the first projections means that the solidified casting material is not subjected to any force by the elastically prestressed first projections. 
         [0016]    Liquid casting material is usually injected into the mold cavity by means of an injection piston, then fills the mold cavity as completely as possible and then flows at very high speed to the inlet of the flow labyrinth. To avoid the movable first projections being damaged by the casting material flowing into the flow labyrinth at high speed, it is of advantage if the liquid casting material first impinges on a fixed projection and only then on a movable projection, undergoing a deflection at each of the projections. Inflowing casting material consequently first impinges on a fixed projection, at which it is deflected and thereby transfers a considerable momentum to the fixed projection. As it flows further into the flow labyrinth, the liquid casting material then impinges at already reduced speed on a movable projection, at which it undergoes renewed deflection, this movable projection at the same time being offset in relation to the fixed projection while thereby reducing the flow cross-section of the flow labyrinth. The then clearly slowed liquid casting material may subsequently impinge on a further fixed projection, at which it is once again deflected to impinge again subsequently on a movable projection. This process may be repeated a number of times, the respective deflection of the casting material at a movable projection leading to an additional movement of the movable projections on account of the transfer of momentum occurring, and consequently leading to a further reduction in the flow cross-section of the flow labyrinth. 
         [0017]    Within the flow labyrinth, the entering casting material cools down greatly and finally solidifies. It is therefore of advantage if the flow labyrinth is formed by a material that conducts heat as much as possible, since particularly effective heat removal can be ensured as a result. 
         [0018]    In the case of a particularly preferred configuration of the venting unit according to the invention, it comprises a venting block with a first and a second block part, the first block part being fixable on a first die half of the die casting device and the second block part being fixable on a second die half of the die casting device, and the two block parts forming between them a flow channel, into which first projections, disposed on the first block part, and second projections, disposed on the second block part, protrude to form a flow labyrinth, the first projections and/or the second projections being movably held respectively on the first and second block part. The mold cavity of the die casting device is usually formed by two die halves, the first die half being movably held and the second die half being fixedly held, so that, after completion of the casting operation, the casting produced can be easily removed from the mold cavity by the first die half being moved away from the second die half. The venting unit forms a venting block with two block parts. In this case, the first block part may be disposed on the movable die half and the second block part may be disposed on the fixed die half, so that, by opening the mold cavity, the flow labyrinth disposed between the two block parts can also be opened. The flow labyrinth is formed by the projections disposed on the respective block part, and to change the flow cross-section of the flow labyrinth the first and/or second projections are movably held on the respective block part. 
         [0019]    In the case of an advantageous embodiment of the invention, the first and/or second projections are fixed on a holding plate movably mounted respectively on or in the first or second block part. The holding plate may take the form of a slide which is, for example, displaceably mounted on or in the respective block part by means of a linear guide. 
         [0020]    It is advantageous if the holding plate is displaceable counter to the action of an elastic restoring force. A first end position is automatically assumed by the holding plate on account of the elastic restoring force acting on it as long as liquid casting material still does not enter the flow labyrinth. When liquid casting material enters, the holding plate can be displaced out of the first end position while thereby reducing the flow cross-section of the flow labyrinth. 
         [0021]    At least one end position of the holding plate is preferably adjustable. An adjusting element, for example an adjusting screw, may be used for this purpose, forming a stop for the holding plate against which the holding plate is pressed on account of the elastic restoring force acting on it as long as casting material still does not enter the flow labyrinth. 
         [0022]    It is advantageous if the position of the first and/or second projections can be sensed by means of a measuring sensor. This makes improved monitoring and documentation of the casting operation possible by allowing a measuring record to be prepared in each case for the castings produced and from which the position of the first and/or second projections during the production of the casting can be taken. 
         [0023]    An electrical signal transmitter may be used, for example, as the measuring sensor, in particular it may be provided that the position of the first and/or second projections can be sensed by means of a position encoder. The signal transmitter may be connected to a control unit of the die casting device by way of a signal line. 
         [0024]    The holding plate on which the first or second projections are held is advantageously arrestable. This makes it easier to open the flow labyrinth to remove casting material solidified in it. 
         [0025]    As explained at the beginning, the invention relates not only to a venting unit of the type stated above but also to a die casting device with a venting unit of this kind. The die casting device comprises a mold cavity that is adapted to be filled with liquid casting material and a gas suction device that is connected to the mold cavity, the venting unit being connected between the mold cavity and the gas suction device. The mold cavity may be connected to the inlet of the flow labyrinth of the venting unit by way of a venting channel of the die casting device, and the outlet of the flow labyrinth may be connected to the gas suction device by way of a suction line. It is advantageous in this case if a suction valve is connected in the suction line. 
         [0026]    The following description of a preferred embodiment of the invention serves for more detailed explanation in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  shows a schematic representation of a die casting device according to the invention with a venting unit according to the invention; 
           [0028]      FIG. 2  shows an enlarged representation of the venting unit from  FIG. 1  with movable projections in a first end position and 
           [0029]      FIG. 3  shows an enlarged representation of the venting unit from  FIG. 1  with movable projections in a second end position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    Schematically represented in  FIG. 1  is a die casting device  10  according to the invention, which has a first, movable die half  11  and a second, fixed die half  12 , which interact in the customary way with a die closing unit that is known per se, and therefore not represented in the drawing. Said closing unit comprises a movable platen and a fixed platen, which are not represented in the drawing to achieve a better overview and on each of which one of the two die halves  11 ,  12  is held in a known way. By means of the die closing unit, a predeterminable closing force can be exerted on the two die halves  11 ,  12 . The two die halves  11 ,  12  form between them a mold cavity  14 , which has the form of a casting to be cast and into which a casting material, for example a molten metal, preferably liquid aluminum or magnesium material, can be injected. For this purpose, the mold cavity  14  has an inlet opening, which is usually referred to as the “gate” and in  FIG. 1  is provided with the designation  15 . By way of an inlet channel  17 , the gate  15  is in connection with a casting chamber  18 , which has a filling opening  19  and in which an injection piston  21  is displaceably mounted. 
         [0031]    The injection piston  21  is held on a piston rod  22 , which is fixed by its end that is remote from the injection piston  21  on a working piston  24 . The working piston  24  is displaceably mounted in a working cylinder  26  of a drive unit provided overall with the designation  27 . The drive unit  27  has a pressure cylinder  29 , which is hydraulically coupled to the working cylinder  26  and in which a pressure piston  30  is displaceably mounted. On its end face that is toward the working cylinder  26 , the pressure piston  30  has a thrust pin  31 , which enters the working cylinder  26  on the side of the working cylinder  26  that is remote from the piston rod  22 . 
         [0032]    The pressure cylinder  29  is in flow connection by way of a pressure line  33  with a pressure accumulator which is known per se, and therefore not represented in the drawing, and which receives pressurized hydraulic fluid. An electrically controllable control valve  34  in the form of a solenoid is connected into the pressure line  33  and can be used for opening and closing the flow connection between the pressure accumulator (not represented in the drawing) and the pressure cylinder  29  in a defined manner. 
         [0033]    The working cylinder  26  is in flow connection by way of an outlet line  36  with a storage tank  37  for hydraulic fluid, so that hydraulic fluid can be delivered from the working cylinder  26  to the storage tank  37  by way of the outlet line  36 . 
         [0034]    Approximately midway along it in the longitudinal direction, the piston rod  22  carries a bush  39 , fixed on which is a carrying arm  40 , which at the end carries a measuring rule  41 , which interacts with a position encoder  42 . 
         [0035]    The position encoder  42  is in connection by way of a signal line  44  with an electrical control unit  46 , to which the control valve  34  is also connected by way of a control line  48 . 
         [0036]    The die casting device  10  has a gas suction device  50 , which is known per se, and therefore only schematically represented in the drawing, and which is in flow connection with the mold cavity  14  by way of a venting channel  52  extending from the mold cavity  14 , a venting unit  55  adjoining the venting channel  52  and a suction line  57  adjoining said venting unit. An outlet valve  59 , which is configured as a solenoid and is connected to the control unit  46  by way of a control line  60 , is connected into the suction line  57 . 
         [0037]    The venting unit  55  is shown enlarged in  FIGS. 2 and 3 . It forms a venting block  62  with a first block part  63 , which is fixed on the movable die half  11 , and with a second block part  64 , which is fixed on the fixed die half  12 . The two block parts  63  and  64  form between them a flow channel  66 , which adjoins the venting channel  52  and is connected to the suction line  57  by way of an outlet channel  67  passing through the second block part  64 . Protruding into the flow channel  66  are rib-shaped first projections  69  and likewise rib-shaped second projections  70 , which are opposite to one another and disposed offset in relation to one another in the direction of flow, engaging in one another in a comb-like manner and forming between them a flow labyrinth  72 . 
         [0038]    The first projections  69  are fixed by means of a screw connection that is known per se, and therefore not represented in the drawing to achieve a better overview, on a holding plate  74 , which is formed in the manner of a slide and is mounted displaceably in a recess  77  of the first block part  63  with the aid of a linear guide  75 , for example a dovetail guide. By way of a thrust rod  79 , the holding plate  74  is acted upon by a compression spring  80  with an elastic restoring force. The compression spring  80  is disposed in a spring housing  82 , which is fixed on the outside of the first block part  63 , on the side remote from the movable die half  11 , and is passed through by the thrust rod  79 , which at its free end carries an extension arm  83 , which interacts with an electrical position encoder  85  and in the first end position of the holding plate  74 , represented in  FIG. 2 , lies against a switching contact  86 . The position encoder  85  and the switching contact  86  are connected to the control unit  46  by way of respective signal lines  87  and  88 , which are only shown in part in the drawing to achieve a better overview. 
         [0039]    Disposed between the spring housing  82  and the extension arm  83  is an arresting mechanism  90 , which is passed through by the thrust rod  79 . The arresting mechanism  90  has in a way known per se, and therefore not represented in the drawing, arresting means, for example tensioning means, with which the thrust rod  79 , and thereby also the holding plate  74  and the first projections  79 , can be arrested in any position desired. 
         [0040]    The holding plate  74  is acted upon by the compression spring  80  with a spring force in the direction of the movable die half  11 . In the position represented in  FIG. 2 , the holding plate  74  lies with an end face  92  remote from the thrust rod  79  against an adjustable stop in the form of an adjusting screw  93 , which predetermines the position of the holding plate  74 , and consequently also the position of the first projections  69 . 
         [0041]    A temperature measuring sensor  95 , which is connected to the control unit  46  by way of a signal line  96 , enters the first block part  63 . 
         [0042]    The second projections  70  are immovably fixed on the second block part  64 , it likewise being possible for a screw connection that is known per se, and therefore not represented in the drawing, to be used to fix them. 
         [0043]    The holding plate  74 , and consequently also the first projections  69 , are displaceable back and forth between the first end position, represented in  FIG. 2 , in which the holding plate  74  lies with its end face  92  against the adjusting screw  93 , and the second end position, represented in  FIG. 3 , in which the end face  92  assumes a distance from the adjusting screw  93 . In the first end position, the first projections  69  assume a relatively great distance from the second projections  70 , so that the flow labyrinth  72  has a relatively large flow cross-section. With increasing displacement of the holding plate  74  into its second end position, the flow cross-section of the flow labyrinth  72  is reduced. This is particularly clear from  FIG. 3 . 
         [0044]    To produce a casting, a molten metal is injected into the mold cavity  14  by means of the injection piston  21 . At the beginning of the casting operation, the injection piston  21  assumes a withdrawn position, in which it exposes the filling opening  19 , so that the molten metal can be filled into the casting chamber  18 . Subsequently, the injection piston  21  is pushed into the casting chamber  18  by means of the drive unit  27 . The path covered by the injection piston  21  can be sensed by means of the position encoder  42 . At first, the liquid casting material is transported up to the gate  15  by means of the injection piston  21  and at the same time air and casting gases are extracted from the mold cavity  14  by means of the gas suction device  50  by way of the venting channel  52 , the flow labyrinth  72 , the outlet channel  67  and the suction line  57 , with the outlet valve  59  being open. 
         [0045]    Once, according to the signal of the position encoder  42 , the injection piston  21  has reached a position in which the molten metal has reached the gate  15 , the drive unit  27  is activated by the control unit  46  by way of the control valve  34  in such a way that the injection piston  21  is pushed at high speed further into the casting chamber  18  within a very short time and the previously evacuated mold cavity  14  is completely filled with liquid casting material. The liquid casting material  100  finally reaches the inlet  98  of the flow labyrinth  72  and is first deflected by a second projection  70 , to subsequently impinge on a first projection  69 . This is represented in  FIG. 2 . The liquid casting material  100  thereby impinges at very high speed on a first projection  69 , to which a considerable momentum is transferred as a result. This has the consequence that the first projection  69  is displaced together with the holding plate  74  counter to the action of the compression spring  80  in the direction away from the adjusting screw  93 , so that the initially considerable flow cross-section of the flow labyrinth  72  by way of which gas is extracted from the mold cavity  14  is reduced. The successive deflections that the liquid casting material  100  undergoes within the flow labyrinth  72  have the effect of slowing the casting material  100 . At the same time, heat is dissipated from the liquid casting material  100  to the block parts  63  and  64  as well as to the projections  69  and  70  and to the holding plate  74 , so that the temperature of the casting material  100  is greatly reduced and it finally solidifies within the flow labyrinth  72 , still before the casting material  100  reaches the outlet  99  of the flow labyrinth  72 . 
         [0046]    The casting material  100  hardening in the mold cavity  14  can be subjected to a very high pressure by the injection piston  21  for the secondary compression of the casting material  100 . 
         [0047]    Once the casting operation has taken place, the mold cavity  14  can be opened by displacing the movable die half  11 , the flow labyrinth  72  also being opened at the same time, since the first block part  63 , fixed on the movable die half  11 , is brought along with the movable die half  11  to a distance from the second block part  64 . The casting material  100  that has hardened within the flow labyrinth  72  can consequently be easily removed from the flow labyrinth  72 . To make the removal easier, the holding plate  74  can be arrested together with the first projections  69  in their second end position, represented in  FIG. 2 , by means of the arresting mechanism  90 , so that the casting material  100  that has hardened in the flow labyrinth  72  is not subjected to any force by the first projections  79 . 
         [0048]    After removal of the solidified casting material  100  from the flow labyrinth  72  and removal of the casting from the mold cavity  14 , the first block part  63  together with the movable die half  11  can be moved again in the direction of the second block part  64 , or in the direction of the fixed die half  12 , so that a renewed casting operation can subsequently be carried out. 
         [0049]    The movable mounting of the first projections  69  allows the flow labyrinth  72  to have a considerable flow cross-section at the beginning of a casting operation, so that the mold cavity  14  can be reliably evacuated by the gas suction device  50 . However, to avoid liquid casting material  100  being able to flow through the flow labyrinth  72  during the casting operation, the flow cross-section thereof can be reduced on account of the movable mounting of the first projections  69 , the first projections  69  being displaced by the casting material  100  that enters the flow labyrinth  72 . This dispenses with the need for electrical, hydraulic or pneumatic control of the movement of the first projections  69 .