In a die-casting machine for producing castings from metals or metal alloys, which castings have a low content of gas, pores and oxides, melt is drawn by means of a vacuum out of a holding device (10) via a suction tube (11) into a casting chamber (3). A casting plunger (7) closes the inlet opening (16) to the casting chamber (3). In order to achieve as low as possible mechanical surface pressure due to flow of the melt, and fluviatile erosion of the die-side end of the inlet opening (16), and thus avoid high wear of this inlet edge or of the casting chamber with casting plunger, a planar or linear inlet cross-section (24, 27) as well as a curved deflection surface (20) on the casting plunger (7) are provided.

BACKGROUND OF THE INVENTION 
The invention relates to a die-casting machine for producing castings from 
metals or metal alloys, which castings have a low content of gas, pores 
and oxides. 
The journal "GieBerei" 69 (1982) No. 19, page 521 ff. as well as "GieBerei" 
70 (1983) No. 19, page 517 ff. have disclosed die-casting machines which 
work with the so-called vacuum die-casting process. Referenced is made to 
the advantages mentioned in this literature for the use of die-casting 
machines of this type. 
EP No. 0,051,310 B1 (corresponding to U.S. Pat. No. 4,476,911) has 
disclosed a corresponding die-casting machine which likewise uses this 
vacuum die-casting process. 
The present invention relates to a die-casting machine of this known type 
and combines the advantages associated with these processes. 
In the application of these known die-casting machines in the vacuum 
die-casting process, the melt is drawn by the vacuum present in the die 
and in the filling chamber or casting chamber out of the holding furnace 
via a suction tube into the casting chamber. Here, the suction tube, at a 
short distance in front of the retracted casting plunger, leads 
perpendicularly from below into the casting chamber; i.e. the vertical 
surface normal to the inlet cross-section in perpendicular or virtually 
perpendicular to the horizontal longitudinal axis of the casting chamber. 
The inlet cross-section of the suction-tube feed leading into the casting 
chamber is reduced with the forward movement of the casting plunger, i.e. 
when the front edge of the casting plunger crosses the inlet opening. At a 
uniform vacuum in the casting chamber, the flow velocity of the melt and 
thus also the type of flow of the melt are thereby increased as the 
cross-section of the inlet opening becomes smaller. In the case of a 
circular-cylindrical inlet cross-section and a front closing edge of the 
plunger, the inlet-opening cross-section, in the shape of a circular 
segment in plan view, becomes constantly smaller and ends finally in a 
pointlike discharge opening. This melt flowing at high velocity leads to 
erosion of the cross-section, which is becoming smaller and smaller, i.e. 
to removal of material from the cross-sectional region of the inlet 
opening of the suction tube to the casting chamber, which cross-sectional 
region is still open in the end phase. This fluviatile erosion acts 
especially in the region of the virtually point-like discharge 
cross-section in the end phase. 
The melt likewise flows at high velocity in the end phase into the casting 
chamber and sprays with a sharp jet against the opposite side of the 
casting chamber and likewise leads here to removal of material. Metal 
particles (flake formation) arise through inclusion and solidification of 
the melt in this scouring, which metal particles have adverse effects on 
the production and the quality of the parts. Furthermore, turbulence, 
which is undesirable in the end phase, develops in the casting chamber. 
On account of its high mechanical surface pressure due to the flow, the 
sharp melt jet arising in the end phase therefore leads to removal of 
material (fluviatile erosion) in particular from the die-side end of the 
inlet opening of the suction -tube feed to the casting chamber and thus to 
the gradual scouring of this transition. In this way, however, the closing 
times of the suction-tube inlet bore to the casting chamber change 
depending on the degree of edge wear. This leads to different metering and 
flake formation in the casting chamber. 
The pronounced nozzle effect of the melt jet during the final phase of the 
casting plunger crossing the inlet opening is therefore disadvantageous in 
connection with wear, associated herewith, of the casting chamber and 
metering of the melt. 
SUMMARY OF THE INVENTION 
Against this background, the die-casting machine according to the invention 
has the advantage that the geometric shape of the inlet opening in 
connection with the closing edge of the casting plunger as well as the 
casting plunger itself are designed in such a way that lower surface 
loading occurs at the locations at risk or erosion. This is achieved in 
particular in that the melt flow in the end phase no longer occurs in a 
point-like manner with a pronounced nozzle effect but in a planar or 
linear manner at a lower flow velocity. For this purpose, the 
inlet-opening cross-section in the die-side end region is not only 
designed as a pure circular segment but is widened in its planar form, in 
particular rectilinearly. The pronounced nozzle effect of the melt jet in 
the end phase of the closing operation is thereby greatly reduced, since 
it is no longer a point-like jet but a planar jet which discharges from 
the inlet opening. But this leads to lower loading of the edges at risk of 
erosion. 
In order to relieve both the casting plunger and the casting chamber with 
regard to erosion and, furthermore, in order t obtain as far as possible a 
laminar flow of the melt, the inlet opening of the suction tube leading 
into the casting chamber is arranged beneath the front plunger region of 
the retracted casting plunger, and the casting plunger, at its lower side 
facing the inlet opening of the suction -tube feed, is given a shape which 
produces a directed, largely turbulence-free flow. For this purpose, the 
casting plunger, at its side facing the inlet opening of the suction-tube 
feed, is especially designed in such a way that a uniform or even 
deflection of the melt jet is effected. This can be, for example, a 
tube-bend-shaped or a cylinder-barrel-shaped deflection. The deflection 
surface can also be formed by the casting plunger being designed as a 
paraboloid of revolution in its front region. 
The transitional planar region of the inlet opening of the suction-tube 
feed to the casting chamber is preferably designed in its half facing the 
die as a cross-sectional region rectangular in plan view, the discharge 
opening being formed by the tangents at a circular cross-section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With regard to the general construction as well as the essential mode of 
operation of the die-casting machine according to the invention, reference 
is made to the literature mentioned at the beginning and in particular to 
EP No. 0,051,310 B1 (corresponding to U.S. Pat. No. 4,476,911). 
The fixed platen 1 of a die-casting machine (not shown in more detail) is 
shown in FIG. 1, which platen 1 has the fixed die half 2, which interacts 
with the movable die half (not shown in more detail). The filling chamber 
or casting chamber 3 is fixed in the fixed platen 1 as well as in the 
fixed die half 2. A vacuum is applied on the die side 6 to the cylindrical 
inner space 4 having a horizontal axis 5 of symmetry of the casting 
chamber 3. A casting plunger 7 having a plunger rod 8 travels horizontally 
in the casting chamber 3 in the direction of the die 6. The melt 9 is 
drawn out of a holding device 10 via a suction tube 11 into the inner 
space 4 of the casting chamber 3. For this purpose, a vertical bore 13 
having a vertical longitudinal axis 14 is located in the lower wall 
section 12 of the casting chamber 3, which bore 13 is connected to the 
connecting flange 15 of the suction tube 11. This detail "II" is shown in 
greater detail in FIG. 2 with corresponding reference numerals. The plan 
view of the inlet opening 16 of the vertical bore 13 to the inner space 4 
of the casting chamber 3 is shown in FIG. 5 (as seen the direction of 
arrow A in FIG. 2). 
To feed the melt 9 through the suction tube 11 and the feed bore 13 into 
the casting chamber 3, the opening cross-section of the inlet opening 16 
must be open. For this purpose, the casting plunger 7 must be retracted to 
the right in FIG. 1 and FIG. 2 or must be appropriately recessed at its 
front lower region to such an extent that the inlet opening 16 remote from 
the die. In FIG. 2, the two edges 17, 18 lie one above the other, i.e. the 
closing edge 17 of the casting plunger 7 starts to push across the inlet 
opening 16. During the movement of the casting plunger 7 in arrow 
direction 19, the inlet opening 16 is gradually closed by the closing edge 
17. The casting plunger 7 is not flat in its front region but is designed 
with a particular deflection surface 20 so that the open inlet opening 16 
lies below the front region of the casting plunger. This deflection 
surface 20 is designed as a tube-bend-shaped deflection surface 21 in FIG. 
2 and as a cylinder-barrel-shaped deflection surface 22 in FIG. 3. 
According to the representation in FIG. 4, the front region of the casting 
plunger 7 is designed as a paraboloid 23 of revolution for forming a 
corresponding deflection surface. In the embodiments of FIGS. 2-4, the 
closing edge 17 is arranged on the vertical tangent 34 of the respective 
deflection surface. The deflection surfaces 20-23 serves to smoothly 
deflect the melt, drawn in out of the suction tube 11, into the inner 
space 4 of the casting chamber 3, to produce a largely laminar flow. The 
more the closing edge 17 of the respective casting plunger 7 pushes across 
the inlet opening 16 and thus reduces the inlet cross-section, the higher 
becomes the flow velocity of the inflowing melt. If the closing edge 17 of 
the casting plunger 7 is located just in front of the die-side end (edge 
24) of the inlet opening 16, the melt discharges at a very high velocity 
on account of the nozzle effect and has to be deflected via the deflection 
surface 20-23 in the horizontal direction, i.e. in the direction of the 
longitudinal axis 5. The casting plungers 7 in FIGS. 1 to 4 are therefore 
designed in their front region in such a way that the flow of melt is 
smoothly deflected at the deflection surface 20-23 especially when the 
closing edge 17 moves across the opening cross-section or the inlet 
opening 16 on account of the movement of the casting plunger in arrow 
direction 19. 
The radius "r" of curvature of the tube-bend-shaped 21 (FIG. 2) or the 
cylinder-barrel-shaped 22 (FIG. 3) deflection surface 20, 21, 22 in the 
front lower region of the casting plunger is approximately the same size 
as or is slightly larger than the radius r.sub.1 of the cylindrical inner 
space 4 of the casting chamber 3. If the closing edge 17 of the casting 
plunger is virtually on the end edge or closing edge 24 of the 
casting-chamber wall, the melt jet acting in a nozzle shape is deflected 
very smoothly by the deflection surface. The radius r of curvature of the 
paraboloid 23 of revolution can be about 3/4 the size or r.sub.1. 
Various positions of the closing edge 17 are schematically shown in FIG. 5. 
When the inlet opening 16 is completely open, the closing edge 17 is 
located in the region of the edge 18 of the inlet opening 16. In the end 
phase of the closing movement of the casting plunger 7, the closing edge 
17 moves into the position 17' so that, in the case of a circular inlet 
cross-section 16, only the circular-segment region hatched with reference 
numeral 25 remains as an inlet area for the melt leading into the casting 
chamber 3. If the closing edge 17'' is located directly in front of the 
die-side end of the inlet opening 16, i.e. virtually on the edge 24, a 
point-like inlet jet remains at the point 26 in the case of a circular 
inlet cross-section 16. This leads to exceptionally high loading of the 
remaining discharge cross-section so that the removal 35 of material shown 
schematically in FIG. 2, i.e. a type of U-shaped scouring at the remaining 
inlet edge in the area of the point 26 of the lower wall section 12, is 
unavoidable. 
The deflection of such a jet, acting in a nozzle shape, via the deflection 
surface 20-23, prevents the melt from impacting on the opposite side of 
the inner space 4 of the casting chamber. The determining factor for the 
considerable removal of material on this opposite side of the casting 
chamber is likewise the pronounced nozzle effect on account of the finally 
point-like discharge cross-section at point 26. 
In order to obtain a lower flow velocity and thus less removal of material 
in the region of the inlet edge or closing edge 24 of the casting-chamber 
wall 12, the inlet opening 16 in the region of the die-side end, as a 
cross-section, is not of circular design but--as shown in FIG. 5--is of 
rectangular design. Accordingly, three tangents 27, 28, 29 at right angles 
to one another and having corresponding recesses are placed against the 
circular cross-section 16, which tangents 27, 28, 29 from a planar and no 
longer only a point-like end discharge cross-section; i.e. in the very 
last phase the melt not only flows at point 26 but over the full width b 
of the closing edge 24, 27 formed by the tangent 27, i.e. over the full 
width b of the inlet opening 16', which is now rectangular in this region. 
If the closing edge 17' is located in the position indicated in FIG. 5, 
the inlet cross-section or the inlet opening 16' is formed by the corner 
points 30-33. The circular segment 25 of a circular inlet cross-section is 
therefore considerably enlarged so that the flow velocity and thus the 
removal of material are reduced. In connection with the optimally 
deflected melt jet at the deflection surface 20-23, optimum guidance of 
the melt jet with the least possible damage to the material is thus 
achieved. 
The invention is not restricted to the exemplary embodiment shown. On the 
contrary, it also comprises all further developments and refinements by 
persons skilled in the art within the scope of the basic idea according to 
the invention. In particular, the shape of the die-side inlet opening can 
also be designed differently than indicated in FIG. 5. Instead of placing 
tangents 27-29, certain curve shapes for influencing the guidance of the 
metal jet and for reducing the flow velocity are also possible. The 
closing edge 24, 27 ;of the inlet cross-section leading into the casting 
chamber can also be arranged in such a way as to be displaced in the 
direction of the die beyond the position shown in FIG. 5, so that an 
enlarged rectangular or trapezoidal inlet cross-section results. The 
determining factor is to obtain as large a cross-section of throughflow as 
possible until the casting chamber is finally filled with melt. 
Furthermore, the embodiments of the deflection surfaces 20-23 formed with 
respect to the plunger 7 can also be designed differently than shown in 
the figures provided they achieve the same effect.