Abstract:
An injection unit for a hot-chamber die-casting machine has an injection portion with a gooseneck and a nozzle adaptor. The injector portion has a base portion at an end of the gooseneck adapted to receive a molten medium supply. A nozzle at an end of the nozzle adaptor is adapted to inject the molten medium supply in a die cavity. A channel between the base portion and nozzle is adapted to convey the molten medium supply therethrough. A piston chamber in the base portion is actuatable to draw the molten medium supply therein and to direct the molten medium supply in the channel for injection into the die cavity. An actuation portion is connected to the gooseneck to actuate the piston chamber. Heating cartridges are received in the injection portion adjacent to the channel to control temperature of the molten medium supply in the channel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. patent application Ser. No. 10/368,626, filed on Feb. 20, 2003, now U.S. Pat. No. 6,978,823 and claims priority on International Patent Application No. PCT/CA03/00213, filed on Feb. 13, 2003. 

   FIELD OF THE INVENTION 
   The present invention generally relates to die casting and, more particularly, to a parting-line injection, multiple-slide die-casting machine that can be used with various casting media, e.g., magnesium, zinc, aluminum. 
   BACKGROUND OF THE INVENTION 
   Magnesium alloys have become increasingly popular for their distinct characteristics. Magnesium is the lightest of all structural materials, and has excellent strength-to-weight ratio and stiffness. Also, magnesium has EMI shielding properties, and is thus widely used in electronic devices. For example, magnesium is now used in cellular phones, cameras, CD players and other handheld devices. Accordingly, die-casting machines have been adapted over the years to produce components in magnesium. 
   In the die-casting industry, there are generally two types of casting machines. The conventional die-casting machine has a moving platen and a fixed platen, the platens having complementary die portions. The moving portion is displaceable so as to form a cavity with its die portion and the die portion of the fixed platen. An injection unit is positioned in the fixed part and is supplied with molten medium from an injector unit so as to fill the cavity with the molten medium. The molten medium solidifies in the cavity in the shape thereof. The cast piece is then ejected from the cavity by the separation of the moving part from the fixed part. The injection unit is either directly positioned in a molten metal bath, in the case of a hot chamber die casting machine, or receives a molten metal supply from a surrounding furnace, in the case of a cold chamber die-casting machine. 
   In parting-line casting, a multiple-slide die-casting machine is used, and has two or more moving slides each having a die portion. The slides meet to form a die cavity from all of the die portions. The injection unit is generally positioned on the parting line between a pair of slides, hence giving it the name “parting-line injection/casting.” More complex parts can be cast in parting-line casting than in conventional casting. However, more complex motions are also involved. Typically, the slides are each displaceable. The die, resulting from the cooperation of the slides, and the injection unit must meet for the injection. Therefore, there must be some relative displacement between the injection unit and the slides. 
   One of the ways to perform the cooperation between the slides and the injection unit is to provide mobility to the injection unit. The injection unit has a portion thereof in a bath of molten casting medium from which it supplies the die. In the case of conventional magnesium die-casting, the bath of molten magnesium has a film of shielding fluid on a top surface thereof to reduce oxidation between the molten magnesium and the ambient oxygen. Displacements of the injection unit in the bath create an exposure of the molten medium, but the shielding film on the surface of the bath ensures that the molten magnesium is not overexposed to oxygen, or to air moisture. However, in previous attempts to cast pieces in magnesium in parting-line casting, because of the reactive nature of molten magnesium due to its relatively high melting point, the displacement of the injection unit in the molten bath of magnesium causes waves in the liquid metal. The waves disturb the shielding gas, and this results in oxidation, thereby necessitating frequent cleaning to remove the oxide build-ups. 
   Magnesium has a relatively high melting point, but a relatively low specific heat. There is a risk of solidification of the magnesium prior to the molten magnesium reaching the die. Therefore, temperature control is an important aspect of magnesium die-casting. 
   Also, molten magnesium is highly reactive and safety measures must be taken when magnesium is cast. For instance, extensive use of hydraulic fluid should be limited. It is desirable to adapt parting-line die-casting technology to magnesium, to enable the casting of more complex cast products. 
   SUMMARY OF THE INVENTION 
   It is a feature of the present invention to provide a novel parting-line multiple-slide die-casting machine to be used, although not exclusively, with magnesium. 
   It is a further feature of the present invention to provide a die-casting machine in which oxidation of casting medium is reduced. 
   It is a still further feature of the present invention to provide a die-casting machine incorporating the above two features of the present invention. 
   It is a still further feature of the present invention to provide a novel injection unit for hot chamber die casting. 
   It is a still further feature of the present invention to adapt the injection unit to the magnesium die-casting machine of the present invention. 
   According to the above features of the present invention, from a broad aspect, there is provided a multiple-slide die-casting machine for casting of magnesium pieces, comprising: a frame; a table operatively mounted to the frame; a slide guiding mechanism secured to the table and having at least two slides, each said slide having a die section at an operating end thereof, the at least two slides being actuatable in a close/open action such that the die sections mate at a parting line therebetween to form a die cavity; an injection unit mounted to the frame and adapted to be connected to a molten magnesium supply means, the injection unit having a nozzle and being adapted to inject molten magnesium from the supply means into the die cavity through the nozzle for casting a piece; and a relative displacement configuration between the table and the injection unit such that the die sections on the table are engageable with the nozzle of the injection unit at the parting line of the die sections for casting of a product in said die cavity, and such that the die sections on the table are disengageable from the nozzle for ejection of the casted product from the die cavity. 
   According to a further broad aspect of the present invention, there is provided a method for die casting magnesium pieces with a multiple-slide die-casting machine of the type having an injection unit and at least two slides mounted to a table, the table and the injection unit being relatively displaceable with respect to one another, the slides having die sections and being actuatable in a close/open action to form a die cavity at a parting line therebetween, comprising the steps of: closing the die sections to form the die cavity; engaging a nozzle of the injection unit with the parting line of the die sections by relative displacement of the table with respect to the injection unit, such that the nozzle is in fluid communication with the die cavity; injecting molten magnesium in the die cavity wherein the molten magnesium will solidify in the die cavity to form a magnesium cast product; disengaging the die cavity from the nozzle of the injection unit by relative displacement between the table and the injection unit; and opening the die sections to release the magnesium cast product. 
   According to a still further broad aspect of the present invention, there is provided a die-casting machine comprising: a frame; a table having pivoting means so as to be pivotally mounted to the frame; a slide guiding mechanism secured to the table and having at least two slides, each said slide having a die section at an operating end thereof, the at least two slides being actuatable in a close/open action such that the die sections mate at a parting line therebetween to form a die cavity; an injection unit fixed to the frame and adapted to be connected to a molten medium supply means, the injection unit having a nozzle and being adapted to inject molten medium from the supply means into the die cavity through the nozzle for casting a piece; and actuation means to displace the table with respect to the injection unit for engagement of the die sections with the nozzle at the parting line for injection of molten medium in the die cavity to cast a product, and for disengagement of the die sections from the nozzle to eject the casted product from the die cavity. 
   According to a still further broad aspect of the present invention, there is provided an injection unit for a hot-chamber die-casting machine, comprising: a gooseneck injector having a base portion at a first end of the gooseneck injector and adapted to receive a molten medium supply, a nozzle at a second end of the gooseneck injector adapted to inject the molten medium supply in a die cavity, a channel between the base portion and the nozzle adapted for conveying the molten medium supply therethrough, and a piston chamber in the base portion actuatable to draw the molten medium supply therein and to direct the molten medium supply in the channel for injection into said die cavity; an actuation portion connected to the gooseneck injector to actuate the piston chamber; and heating cartridges received in the gooseneck injector adjacent to the channel to control a temperature of the molten medium supply in the channel. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which: 
       FIG. 1  is a front right-side perspective view of a die-casting machine constructed in accordance with the present invention; 
       FIG. 2  is a front left-side perspective view of the die-casting machine; 
       FIG. 3  is a rear right-side perspective view of the die-casting machine; 
       FIG. 4  is a front left-side perspective view of a frame and a table of the die-casting machine, without a slide guiding mechanism; 
       FIG. 5A  is a side elevational view of the table of  FIG. 4 , on the frame of the die-casting machine; 
       FIG. 5B  is a side elevational view of the table of  FIG. 4  being pivotally adjusted with respect to the frame of the die-casting machine; 
       FIG. 6A  is a front right-side perspective view of the table of the die-casting machine, with the slide guiding mechanism; 
       FIG. 6B  is a front elevational view of the table of the die-casting machine, with the slide guiding mechanism; 
       FIG. 7  is a perspective view of a pivot mechanism of the frame of the die-casting machine; 
       FIG. 8  is a cross-sectional view, fragmented, of a table connector of the pivot mechanism; 
       FIG. 9A  is a perspective view of an adjustment mechanism of the die-casting machine, for positioning the table in a maintenance position with respect to the frame; 
       FIG. 9B  is a side elevational view of the adjustment mechanism being used between the table and the frame of the die-casting machine; 
       FIG. 10  is a front right-side perspective view of an injection unit secured to the frame; 
       FIG. 11  is a rear right-side perspective view of the injection unit and frame of  FIG. 10 ; 
       FIG. 12  is a rear elevational view of the injection unit and frame of  FIG. 10 ; 
       FIG. 13A  is a side elevational view of a gooseneck in a casting position with a die; 
       FIG. 13B  is across-sectional view of the gooseneck and the die taken along cross-sectional line XIIIB—XIIIB; 
       FIG. 14A  is a rear left-side perspective view of the gooseneck; 
       FIG. 14B  is a front right-side perspective view of the gooseneck; 
       FIG. 15A  is a rear left-side exploded view of the gooseneck and heating cartridges thereof; 
       FIG. 15B  is a front left-side exploded view of the gooseneck with the heating cartridges thereof; 
       FIG. 16A  is a front left-side perspective view of a hot chamber of the die-casting machine of the present invention; 
       FIG. 16B  is a rear right-side perspective view of the hot chamber; 
       FIG. 17A  is a rear left-side perspective view of a nozzle adapter of the gooseneck; 
       FIG. 17B  is a front right-side perspective view of the nozzle adapter; 
       FIG. 18A  is a rear left-side perspective view of a base portion of the gooseneck connected to an actuation portion of the injection unit; 
       FIG. 18B  is a front right-side perspective view of the base portion of the gooseneck and the actuation portion of the injection unit; 
       FIG. 19A  is a rear right-side perspective view of the actuation portion of the injection unit; 
       FIG. 19B  is a front right-side perspective view of the actuation portion of the injection unit; 
       FIG. 20A  is a top perspective view of a panel of the hot chamber of the die-casting machine; 
       FIG. 20B  is an exploded view of the panel of  FIG. 20A ; and 
       FIG. 21  is an exploded view of a crucible with respect to the hot chamber of the die-casting machine. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to the drawings and, more particularly, to  FIGS. 1 ,  2  and  3 , a die-casting machine in accordance with the present invention is generally shown at A. The die-casting machine A is configured for parting-line multiple-slide die-casting. The die-casting machine A consists of four major parts, namely the frame F, the injection unit J, the table T and the hot chamber C (i.e., the furnace). As will be described hereinafter, although the die-casting machine A is shown having a hot chamber C in  FIGS. 1 ,  2  and  3 , the die-casting machine A can be adapted for cold-chamber die-casting. 
   The frame F is the structure for the die-casting machine A. The injection unit J and the table T are supported by the frame F, so as to be cooperative. When supported by the frame F, the injection unit J is also operatively connected to the hot chamber C. For simplicity purposes, components of the frame F referred to in the present description and drawings will be prefixed with the letter “F.” 
   The injection unit J supplies casting medium from the hot chamber C to the table T. For simplicity purposes, components of the injection unit J referred to in the present description and drawings will be prefixed with the letter “J.” 
   The table T comprises the slide guiding mechanism, including the slides, which are actuatable to form the die cavity with die portions. The injection unit J is positioned at a parting line of the die portions with respect to the table T. The multiple slides are actuated in a close/open action in a die-casting cycle for casting followed by ejection of the cast product. For simplicity purposes, components of the table T referred to in the present description and drawings will be prefixed with the letter “T.” 
   The hot chamber C has a furnace in which casting medium is liquefied prior to casting. The hot chamber C ensures that the casting medium, in its highly reactive liquid state, is isolated from property-altering reactions, e.g., oxidation, and from air moisture. For simplicity purposes, components of the hot chamber C referred to in the present description and drawings will be prefixed with the letter “C.” 
   Vectors will be referred to throughout the present description and drawings to illustrate the operative relations between the components of the die-casting machine A. The vectors will be prefixed with the letter “V.” 
   Die-Casting Cycle 
   Referring to  FIGS. 6A and 6B , the table T is illustrated having a table portion T 10  with two slides T 11 . Obviously, the table T may be equipped with more than two slides, e.g., four slides T 11  (positioned in a cross) with two horizontally displaceable slides and two vertically displaceable slides, part of the slide guiding mechanism. The slides T 11  are operatively mounted to the table portion T 10 , and are thus displaceable in a close/open action as illustrated by vectors V 1  and V 2 . 
   In a closing action, the slides T 11  are actuated so as to bring die portions T 12  together at a parting line to form a die cavity in which casting medium will be cast. In an opening action, the slides T 11  are displaced away from one another to separate the die portions T 12  for ejection of the cast product from the die cavity. In a typical parting-line die-casting cycle: 
   (1) The slides T 11  are closed in the closing action, thereby bringing the die portions T 12  together at a parting line; 
   (2) The table T and the injection unit J are brought together at the parting line between the die portions T 12 ; 
   (3) A casting medium is injected in the die cavity by the injection unit J; 
   (4) After a solidification period, the table T and the injection unit J are separated to break off the cast product in the die cavity from the injection unit J; and 
   (5) The slides T 11  are opened in the opening action, so as to separate the die portions T 12  from one another for the ejection of the cast product from the die cavity. 
   Referring to  FIGS. 13A and 13B , the die portions T 12  are shown in a casting position, i.e., abutted against a gooseneck unit J 10  (hereinafter gooseneck J 10 ) of the injection unit J. The gooseneck J 10  has a tip J 19  thereof aligned with a channel T 13  formed by the die portions T 12  at the parting line T 14 . The channel T 13  forms a conveying passage to the die cavity T 15  (i.e., the cavity in which the casting medium is molded), through which casting medium is fed from the injection unit J to the die cavity T 15 . As illustrated in  FIG. 4 , the table portion T 10  has an opening T 16 , through which the nozzle adapter J 11  passes to abut against the die portions. 
   Relative Motion Between the Table T and the Injection Unit J 
   In the above-described steps (2) and (4) of the typical parting-line die-casting cycle, relative motion must be performed between the table T and the injection unit J. In the preferred embodiment of the present invention, the table T is displaceable with respect to the frame F, so as to meet the injection unit J, which is stationary on the frame F, thereby not disturbing the surface of the molten metal bath in the hot chamber C. 
   Referring to  FIGS. 4 ,  5 A and  5 B, the table T is pivotally mounted to the frame F. Accordingly, the table T can perform motions illustrated by vectors V 3  and V 4  with respect to the frame F. It is pointed out that the table T is illustrated without slides thereon for clarity purposes. 
   More precisely, the frame F has a pivot mechanism F 10  by which the table portion T 10  is pivotally supported by the frame F. The pivot mechanism F 10  is best illustrated in  FIGS. 7 and 8 , and has an elongated body at ends of which table connectors F 11  are pivotally mounted. A bottom edge of the table portion T 10  sits on the table connectors F 11 , which have fasteners to secure the table portion T 10  thereto. As shown in  FIG. 8 , the table connectors F 11  have spherical bearings F 12  (only one of which is shown). Although the table T is pivoted in one degree of freedom (one DOF) with respect to the frame F, three DOFs are provided so as to compensate for misalignments of the table T on the pivot mechanism F 10 . Accordingly, 3-DOF bearings will have a greater life in supporting the table T than would 1-DOF bearings. 
   Referring generally to  FIG. 3  and more specifically to  FIGS. 5A and 5B , the frame F has an arch structure F 20  (hereinafter arch F 20 ). The arch F 20  is an upstanding structure of the frame F that will support the injection unit J and the pivoting actuation group for the pivoting displacement of the table T with respect to frame F and the injection unit J. 
   The pivoting actuation group has pivoting actuators F 21  that interconnect the arch F 20  to the table portion T 10 . The pivoting actuators F 21  are typically hydraulically, pneumatically, or electrically actuated cylinders that will pivot the table T between the casting position, illustrated in  FIG. 5A , and a break-off position (not shown). The table T is illustrated in  FIG. 5B  in a maintenance position with respect to the frame F, as will be described hereinafter. In the preferred embodiment of the present invention, two pivoting actuators are provided. The pivoting actuators F 21  are pivotally secured to both the arch F 20  and the table T, to be in accordance with the pivoting motion therebetween, illustrated by vectors V 3  and V 4 . 
   The pivoting actuation group is also preferably provided with shock absorbers F 22 , to dampen the movement of the table T, especially toward the casting position. In the casting position, the table T abuts against the injection unit J. It is therefore desired to have the shock absorbers F 22  slowing down the motion of the table T toward the casting position to lessen the impact on the injection unit J. Preferably, the shock absorbers F 22  are hydraulic cylinders with controllable flow between chambers thereof to adjust the shock-absorbing action. 
   Finally, the pivoting actuation group is provided with a limit switch F 23  that is secured to the shock absorber F 22 . The limit switch F 23  must be triggered at the casting position of the table T for injection to take place. This safety feature ensures that the table T is in the casting position for injection to occur. An adjustment mechanism F 23 ′ is provided to adjust the limit switch F 23  with respect to the casting position. 
   Referring to  FIG. 5B , the table T is shown in a maintenance position with respect to the arch F 20 , and is held in that position by an adjustment mechanism. The adjustment mechanism F 24  is a turnbuckle, as illustrated in  FIGS. 9A and 9B . The turnbuckle is pivotally connected to the arch F 20  and the table portion T 10 . The turnbuckle can change length, i.e., in the direction of vectors V 5  and V 6  ( FIG. 9A ). This is performed by adjusting the position of the buckle portion F 25  with respect to the threaded portion F 26 . The pivotal connection between the turnbuckle, the arch F 20  and the table portion T 10  transforms the translation resulting from the change in length of the turnbuckle to the pivoting displacement of the table T with respect to the pivot mechanism F 10 , i.e., in the direction of vectors V 3  and V 4  ( FIG. 4 ). As shown in  FIG. 5B , the pivoting actuators F 21  and shock absorber F 22  are disconnected so as not to impede the pivoting of the table portion T 10  toward the maintenance position. 
   Other configurations are contemplated for the displacement between the table T and the injection unit J. For instance, the pivot mechanism F 10  could be positioned on the arch F 20  such that the table portion T 10  would be pivoting about a top edge thereof. In such a configuration, the pivoting actuation group would interconnect the frame F to a bottom portion of the table T. However, it is advantageous to have the pivoting mechanism F 10  below the table T, as the center of gravity of the table T is horizontally closer to the pivoting axis when the pivoting mechanism F 10  is at the bottom. This has a direct effect on the sizing of the components of the pivoting actuation group. Also, if the center of mass of the table T is below the pivoting mechanism, the components of the pivoting actuation group must support the weight of the table T in displacing it between positions, which is not so with the opposite, whereby the components must be specified for greater loads. 
   In another configuration, a translation system could be provided for the relative displacement of the table T with respect to the injection unit J. 
   The Injection Unit J 
   Referring to  FIGS. 14A ,  14 B,  18 A and  18 B, the injection unit J generally consists of two major components, namely, the injection portion, including the gooseneck J 10  and the nozzle adapter J 11 , and an actuation portion J 30 . The nozzle adapter J 11  is secured to a top end of a base portion J 20  of the gooseneck J 10 . More precisely, the nozzle adapter J 11  receives a feed of casting medium from the base portion J 20  and supplies the die cavity T 15  therewith. As shown in  FIGS. 13A ,  13 B,  17 A and  17 B, the nozzle adapter J 11  has a tip J 19  thereof that abuts against the die portions T 12 . The nozzle adapter J 11  has a generally cylindrical body with a longitudinal channel J 15  generally concentric with the cylindrical body. An opposed end of the nozzle adapter J 11  has a connector J 12  by which the nozzle adapter J 11  is releasably connectable to the base portion J 20 . 
   As the casting medium is in a molten state, the temperature differential between the inner walls that define the channel J 15  of the nozzle adapter J 11  and the casting medium must be controlled to avoid solidification of the casting medium in the channel J 15 . Accordingly, a plurality of heating cartridges J 13  extend longitudinally in the cylindrical body, generally parallel to the channel J 15 , but radially spaced therefrom. Thermocouples J 14  are also provided in the cylindrical body to measure the temperature, such that the temperature can be controlled. 
   Referring to  FIGS. 13A ,  13 B,  14 A and  14 B, the base portion J 20  of the gooseneck J 10  has an upstanding cylindrical portion that is adapted to be received in a bath of molten casting medium, to extract the medium therefrom through inlet J 21 . The base portion J 20  preferably has a single-piston configuration. An expansion of a piston chamber will cause an injection of the medium in the piston chamber from the molten metal bath. Thereafter, a compression of the piston chamber will cause the medium to be conveyed to the die cavity T 15  through the nozzle adapter J 11 . 
   The base portion J 20  has a connector J 22  on a box-shaped head portion J 24  at an outlet thereof, by which it is matingly coupled to the connector J 12  of the nozzle adapter J 11 . When the nozzle adapter J 11  is coupled to the base portion J 20  to form the gooseneck J 10 , a channel J 23  ( FIG. 13B ), extending from the piston chamber to the connector J 22 , is operatively aligned with the channel J 15  of the nozzle adapter J 11  to form a continuous channel through which the casting medium is conveyed to the die cavity T 15 . 
   The base portion J 20  of the gooseneck J 10  is equipped with a sleeve J 20 ′ ( FIGS. 14A and 15A ) defining the piston chamber, in which the injection piston slides. The sleeve J 20 ′ is removable from the base portion J 20  such that it can be replaced by a new sleeve when the sleeve J 20 ′ becomes worn. It is pointed out that in prior art goosenecks, a bore or a non-removable sleeve in the base portion defines the piston chamber. The bore or sleeve must be resurfaced according to various techniques (e.g., re-boring, honing) as it wears out after a given number of casting cycles, and the injection piston and rings thereof must be modified as a result of diametrical changes to the bore, after the gooseneck has been removed from the die-casting machine. The removable feature of the sleeve J 20 ′ thus substantially decreases the time required to repair the gooseneck J 10 . Access is provided at a bottom end of the base portion J 20  to press the sleeve J 20 ′ out of the base portion J 20 . The sleeve J 20 ′ can exit through the opening J 27  in the head portion J 24  ( FIGS. 14A and 15A ). Moreover, as the internal diameter of the new sleeve is the same that the previous sleeve J 20 ′, the process parameters of the die-casting operation remain essentially constant, whereas with the injection units of the prior art, the internal diameter of the bore or sleeve is increased at each re-boring, which progressively reduces the metal pressure at injection, for any given pressure in the hydraulic system. 
   Referring to  FIGS. 12 ,  15 A and  15 B, the head portion J 24 , by which the gooseneck J 10  is connected to the actuation portion J 30 , is shown having heating cartridges J 25  that will heat the base portion J 20  to prevent medium solidification in the channel J 23 . The vertical cartridges J 25  are positioned in flanged-head sleeves J 26  that will facilitate their removal from the gooseneck J 10 . Thermocouples J 14  are provided to control the temperature. An opening J 27  is defined in the head portion J 24 , and is provided for receiving an actuation rod of the actuation portion J 30  for the actuation of the piston in the base portion J 20 . 
   Other suitable heating means can be used to prevent solidification of the medium in the channel J 23  of the gooseneck J 10 . For instance, the gooseneck J 10  may be provided with heating conduits in which a heating liquid is conveyed to maintain the surface of the channel J 23  at an appropriate temperature, or with any other suitable arrangement, to prevent solidification of magnesium. 
   Referring to  FIGS. 18A ,  18 B,  19 A and  19 B, the actuation portion J 30  is shown having an actuator J 31 , in the form of a cylinder. An actuation rod J 32  has a threaded end by which it is releasably connectable to the piston J 32 ′ of the base portion J 20 . Therefore, the actuator J 31  will displace the piston J 32 ′ of the base portion J 20 , and thus control the injection of casting medium in the die cavity T 15  ( FIG. 13A ). 
   The actuation portion J 30  has a casing that supports both the actuator J 31  and gooseneck J 10 , via the base portion J 20 . More precisely, a bottom end J 33  of the casing defines a shape adapted to cooperatively connect with the head portion J 24  of the base portion J 20  such that the head portion J 24  can slide into engagement with the bottom end J 33  and be accurately positioned. A safety cylinder J 34  is secured to a top end of the casing and is actuated to lock the actuator J 31  when the piston chamber of the piston portion J 20  is filled with casting medium. The safety cylinder J 34  cooperates with the actuation rod J 32  to prevent an unwanted displacement of the actuator J 31 , especially when the die portions T 12  ( FIG. 6A ) are separated from one another. For instance, the actuation rod J 32  can have a sleeve J 32 ″ thereon with a throat portion and the safety cylinder, a corresponding fork portion cooperating with the throat portion. A removable transparent door (not shown) is removably secured to the open face of the casing, so as to hermetically close the casing, while allowing to see the movement of the actuation rod J 32 . 
   It is pointed out that, although the injection unit J described above has a single-piston configuration, double-piston technology may be used in the die-casting machine A. A double-piston injection unit typically has a first piston provided for conveying molten casting medium from a source to the die, and a second piston provided to block/open the passage between the first piston and the die. 
   The Injection Unit J on the Frame F 
   Referring to  FIGS. 10 ,  11  and  12 , the injection unit J is secured to the arch F 20 . In the preferred embodiment of the present invention, the injection unit J is stationary with respect to the frame F, and the table T is pivoted into engagement with the injection unit J during casting cycles. The injection unit J, although being stationary during casting cycles, is secured to the arch F 20  so as to be adjustable in the vertical plane of the arch F 20 . More precisely, two DOFs are provided between the injection unit J and the arch F 20 , such that the nozzle adapter J 11  of the gooseneck J 10  can be aligned with respect to the parting line of the die portions T 12  of the channel T 13  ( FIG. 13B ). Therefore, in total, three DOFs are provided, if the one DOF of the adjustment mechanism F 24  is considered ( FIGS. 5A and 5B ). 
   As shown in  FIG. 12 , vectors V 7  and V 8  illustrate the direction of the first adjustment DOF, whereas vectors V 9  and V 10  show the direction of the second adjustment DOF. The casing of the actuation portion J 30  has a pair of flanges J 35  having oblong holes J 36  ( FIGS. 19A  and  19 B). The injection unit J is secured to the arch F 20  by the pair of flanges J 35  being slidingly received in corresponding channels of the arch F 20 . The sliding engagement therebetween allows the translation of the actuation portion J 30  in the direction of vectors V 7  and V 8 . Adjustment mechanism F 30 ′ is provided for adjusting the vertical position of the actuator portion J 30  with respect to the arch F 20 . The adjustment mechanism F 30 ′ typically consists of a threaded bolt/nut combination for precise positioning of the actuator portion J 30 . The oblong openings J 36  cooperate with fasteners F 30  to set the actuation portion J 30  in the direction of vectors V 7  and V 8 . The fasteners F 30  are manually tightened to exert pressure on the channels receiving the flanges J 35 . 
   As best seen in  FIG. 12 , the arch F 20  has a plate F 31  that is slidingly moveable in the direction of vectors V 9  and V 10 , with respect to the rest of the arch F 20 . Fasteners F 32  squeeze the plate F 31  in position with respect to the rest of the arch F 20 , and adjustment mechanisms F 33  allow the finer adjustment of the horizontal position of the plate F 31 . 
   The configuration of the injection unit J allows for the gooseneck J 10  to be removed from the arch F 20 , while the actuation portion J 30  remains on the arch F 20 . 
   The Hot Chamber C 
   Referring to  FIG. 3 , the hot chamber C is shown in position with respect to the frame F. Referring to  FIGS. 16A ,  16 B and  21 , the hot chamber C has a generally box-shaped furnace C 10  that is on rollers C 11 , so as to be displaceable with respect to the frame F. The furnace C 10  has a top surface with an opening through which is inserted a crucible C 20 . When the crucible C 20  is in the furnace C 10 , an access door portion C 12  and an injection access portion C 13  cover the opening. The molten casting medium in the crucible C 20  is in a reactive state. To avoid oxidizing of the molten casting medium, the bath of molten casting medium in the crucible C 20  must be exposed as little as possible to ambient air. For instance, a shielding gas is typically used to form a shielding fluid layer on the molten medium bath. It is known to use SF 6  mixed with other gases, or any other suitable equivalent as shielding gas. 
   In a preferred embodiment of the present invention, the injection access portion C 13  consists of three panels, which are shown at C 14 A, C 14 B and C 14 C in  FIGS. 20A and 20B . The panels C 14 A and C 14 B define an opening C 15 , which sealingly receives the base portion J 20  of the injection unit J, such that a bottom portion of the base portion J 20  is in the bath of molten casting medium of the crucible C 20 . The panel C 14 C is adjacent to the panel C 14 B. The panels C 14  are interconnected by keyed connection at junctions thereof, with mating keyed connector portions shown in  FIG. 20B , whereby the panels C 14  can be opened individually to access the inside of the crucible C 20 , while being hermetically connected to one another. More particularly, the panel C 14 C can be removed in the presence of the injection J, for accessing the inside of the crucible C 20 , e.g., for maintenance and cleaning. Various gaskets/seals C 17  ensure the air tightness of the injection access portion C 13 . For instance, one of the seals C 17  is provided at a periphery of the opening C 15 , whereby the base portion J 20  is received in a generally airtight fashion. 
   Ports C 18  are provided on the panels C 14  such that the shielding fluid (e.g., SF 6 ) can be injected to form the shielding layer on the surface of the molten casting medium. The layer of SF 6  will reduce the oxidation of the casting medium, as it will form a barrier between the casting medium and ambient air. As shown in  FIG. 18A , one such port C 18  is provided on the casing of the actuation portion J 30  of the injection unit J, as the molten casting medium of the crucible C 20  is exposed thereat to ambient air. 
   The access door portion C 12  has a panel that is pivotally mounted to a frame portion, so as to be pivoted between opened and closed positions. The opened position of the access door portion C 12  is illustrated in  FIG. 16A , whereas the closed position of the access door portion C 12  is illustrated in  FIG. 16B . Ingots of solid medium are fed through the access door portion C 12  by way of an automated system (not shown), or manually. Suitable sealing (e.g., gaskets) is provided to hermetically seal the periphery of the access door portion C 12  in the closed position, to substantially prevent air infiltration in the furnace C 10 . 
   The crucible C 20  has a concave bottom, such that material precipitated from the casting medium can accumulate at a bottom of the crucible C 20 , and be readily scooped out of the crucible C 20 . The outside C 21  of the crucible C 20  is preferably a stainless steel layer roll bonded on mild steel, to prevent oxidation of the outside of the crucible C 20  in case of an overflow of casting medium from the crucible C 20 . Moreover, a strip of stainless steel or equivalent (e.g., ceramic) is overlaid on a top portion of the inside C 22  of the crucible C 20 , to inhibit corrosion of the inside C 22  of the crucible C 20  in the event that the layer of shielding fluid is incorrectly adjusted (e.g., too high concentration of SF 6 ) or that the moisture content of air is excessively high. The crucible C 20  may also all be constructed of stainless steel, or may have a stainless steel internal cladding preferably of low nickel content to avoid contamination of the molten magnesium, and a stainless steel external cladding suited for sustaining high temperatures with minimal corrosion. 
   A door C 30  is provided at a bottom of the furnace C 10  so as to provide an outlet for leaking casting medium. The frame may be provided with an absorbent in an overflow reservoir (not shown). The absorbent is typically dry sand in polyethylene bags, with the overflow reservoir being positioned opposite the door C 30 , to collect the casting medium. 
   Interconnection Between the Injection Unit J and the Hot Chamber C 
   Referring to  FIG. 16B , the furnace C 10  is provided with a removable support bracket C 40 , to be used for removing the gooseneck J 10  from the furnace C 10 . The base portion J 20  is received in the opening C 15 , with one of the seals C 17  ( FIG. 20A ) ensuring the air tightness therebetween. The removable support bracket C 40  can be fastened to the top of the head portion J 24  of the gooseneck J 10 , such that the support bracket C 40  can serve as a connector for, e.g., a crane to lift the gooseneck J 10  to remove it from the furnace C 10 . 
   As mentioned previously, the actuation portion J 30  of the injection unit J often remains on the arch F 20 , while the gooseneck portion J 10  (i.e., nozzle adapter J 11  and the base portion J 20 ) are removed. In such a case, the support bracket C 40  supports the base portion J 20 , such that the latter is supported when disconnected from the actuation portion J 30 . Similarly, the gooseneck J 10  can be installed individually on the furnace C 10 , as supported by the support bracket C 40 , to then be connected to the actuation portion J 30  by displacing the hot chamber C toward the arch F 20 , until the base portion J 20  engages with the actuation portion J 30 . 
   The support bracket C 40  can be disconnected from the furnace C 10 , to serve as a connector for removing the gooseneck J 10  from the furnace C 10 . As the gooseneck J 10  is subjected to high temperature while it is in contact with the molten casting medium, it is preferred to use supporting structures (e.g., a crane), to remove the gooseneck J 10 . For such purposes, the detached support bracket C 40  can be used as a connector between the gooseneck J 10  and, for instance, a crane. 
   Casting Media 
   The parting-line multiple-slide die-casting machine A of the present invention can be used to mold various metals and metal alloys. This die-casting machine of the present invention is adapted for casting magnesium, with appreciable results. Problems of known die-casting machines have been addressed by the die-casting machine of the present invention. 
   For efficient die casting of magnesium, the oxidation of the molten magnesium has to be reduced. One major cause of oxidation in known die-casting machines is the constant displacement of the injection unit in the molten magnesium bath. In a preferred embodiment of the present invention, the table T, incorporating the slides, is pivotally mounted to the frame F, so as to be displaceable toward the stationary injection unit J and hot chamber C. Therefore, when the injection unit J is adjusted in position, it remains stationary, and thus does not disrupt the barrier of shielding fluid on the top surface of the molten medium bath. 
   Another source of oxidation is the improper feed of the shielding gas to the furnace C 10  of the hot chamber C. In the present invention, additional ports C 18  are provided to ensure the adequate feed of shielding gas to the furnace C 10 . Also, the air tightness of the interactions (e.g., injection unit J secured to the furnace C 10 ) also helps in reducing the level of oxidation. 
   Moreover, the crucible C 20  has been coated with layers of stainless steel to be protected from the higher temperature of molten magnesium when compared to other casting media (e.g., zinc). Also, the addition of several heating cartridges in the piston portion J 20  and the nozzle adapter J 11  will prevent the magnesium from solidifying in the injection unit J. 
   It is preferred to use electrical power for safety purposes and accurate control when die casting magnesium. A mixture of molten magnesium and hydraulic oil (e.g., in the event that a hydraulic heating line leaks) can be highly reactive, whereby electrical power is preferred when possible for the die-casting machine A. For instance, the hot chamber C is preferably electrically powered, as are the heating cartridges of the piston portion J 20 . 
   It is within the ambit of the present invention to cover any obvious modifications of the preferred embodiment described herein, provided such modifications fall within the scope of the appended claims.