EP0790090A2 - Vacuum die-casting machine - Google Patents

Abstract

A vacuum die-casting machine has a die formed of fixed and movable halves (3,4) which are sealed against one another, during evacuation and casting processes, by ,an elastic sealing element (16). The die is connected to a casting chamber (6) with a piston (7) and a suction pipe (9) for supply of melt from a holding furnace (10). Evacuation of the die cavity (5) and the casting chamber takes place by means of an evacuation unit (11). Gas entry into the furnace, during die closure is avoided by a blocking process which continues until the excess pressure in the die cavity and the interior (22) of the chamber is substantially eliminated.

Description

The invention relates to a vacuum die casting machine according to the preamble of claim 1.

State of the art:

From EP 0 051 310 B1 a die casting machine has become known which works according to the so-called vacuum die casting method. In this method, the molten metal is drawn from a holding furnace through a suction pipe into the casting chamber by means of negative pressure, the negative pressure being applied to the mold engraving of the mold via a vacuum system. This patent also addresses the problem of sufficient degassing of the melt during the casting process. In particular, the aim of the vacuum pressure casting method is to obtain an improvement in the casting quality by evacuating the die and extracting the reaction gases from the mold and the casting chamber. The negative pressure also serves to transport the melt from the holding furnace into the casting chamber.

The cited reference also mentions the problem of existing residual gas and swirling of the melt, which can lead to considerable losses in quality. To remedy this To create, it was proposed in this patent to provide several vacuum connections to improve evacuation. For example, another vacuum connection must be provided on the casting piston itself.

The casting mold consists of a movable and stationary mold half, the latter being generally connected to the casting chamber with casting pistons and the holding furnace leading via a suction pipe to the part of the casting chamber facing away from the casting mold.

The movable mold half is moved against the fixed mold half for a casting process, an elastic and temperature-resistant seal surrounding the mold cavity and sealing the mold halves against one another. Such a sealing arrangement is shown for example in EP-A1-0 230 660, Fig. 1 with reference numeral 64.

When the mold halves are moved together, the seal protrudes with a small distance of the order of 2 mm, for example, from the contact surfaces of the mold halves in order to act as a seal when the mold halves are pressed together. The circumferential seal encompasses a surface area which, in conjunction with the protruding height of the seal, leads to a remarkable cavity for the inclusion of air. For example, if you take a medium-sized mold with a rectangular arrangement of seals of 700 x 900 mm and a protrusion of the seal over the flat surface of, for example, 2 mm, this leads to an air trap with a volume of 1.26 liters. If you press the surfaces quickly against each other, this volume of air within the mold cavity and the casting chamber must be displaced, which leads to an undesirable increase in pressure. The disadvantage of this is that this enclosed gas can reach the holding furnace for the melt via the casting chamber and the suction pipe and acts on the melt in the holding furnace with an air blast.

This leads to undesired additional gas inclusions within the melt, which in turn can have a negative effect on the casting quality.

Object of the invention:

The invention has for its object to avoid the disadvantages described above and in particular to prevent an additional air supply to the holding oven by this effect.

Solution of the task and advantages of the invention:

This object is achieved according to the invention by the characterizing features of claim 1.

Advantageous and expedient developments of the measures specified in the main claim are listed in the subclaims.

The invention has the advantage over the known prior art that the air enclosed when the mold halves are moved together by the sealing arrangement cannot pass through the suction pipe into the holding furnace. The gas recoil through this air cushion is kept away from the holding furnace at least until a pressure reduction in the casting mold or the casting chamber leads to a pressure equalization which prevents the gas or the enclosed air from flowing into the holding furnace. This pressure reduction takes place e.g. through the evacuation valve connected to the atmosphere. In this way it is avoided that an additional gas application to the melt in the holding furnace and the associated disadvantages occur.

The conclusion or the closing of the holding furnace is achieved in a particularly simple manner in that the suction pipe for Holding furnace is separated from the mold cavity, which can preferably be done by means of the casting piston itself. For this purpose, the casting piston is arranged in the casting chamber during the moving together of the mold halves in such a way that it is positioned in front of the mouth of the suction pipe, ie between the mold cavity and the mouth of the suction pipe. As a result, the gas recoil cannot lead to air being applied to the melt in the holding furnace.

Casting sets have become known from various literature references which, after a casting process has been carried out, carry out an idle stroke of the casting piston within the casting chamber, for example in order to expel tinsel from the inside of the casting chamber and / or to apply spray oil lubrication to the inside wall of the casting chamber (see, for example, DE 43 16 927 A1). This additional stroke during the return stroke can, according to the invention, serve to position the casting piston between the mouth of the suction pipe into the casting chamber and the mold cavity during the mold closing. In this case, the gas recoil cannot affect the holding furnace. The pouring plunger is only finally retracted when the closing process has ended and, if appropriate, the pressure has been released via the evacuation device still connected to the atmosphere.

The suction pipe can also be used with other means, e.g. Cut off the gate valve or the like opposite the casting chamber so that this gas recoil does not affect the melt in the holding furnace when the mold halves are moved together. However, this increases the technical effort.

By arranging the casting piston in the front position when the mold halves are brought together, the interior of the casting chamber is closed off from the mold cavity. After the mold halves have been brought together, the casting piston is pulled backwards in the direction of the intake pipe, which is a kind of additional evacuation or

Production of a negative pressure or compensation of the pressure rise caused by the closing process of the mold halves.

Drawings:

Further details of the invention also emerge from the drawings and the exemplary embodiment explained below.

Fig. 1

die Darstellung einer Vakuum-Druckgießmaschine mit sich schließenden Formhälften im Ausgangszustand und

Fig. 2

die gleiche Anordnung nach Fig. 1 jedoch mit geschlossenen Formhälften.

Show it:

Fig. 1

the representation of a vacuum die casting machine with closing mold halves in the initial state and

Fig. 2

the same arrangement according to FIG. 1 but with closed mold halves.

Description of the embodiment:

With regard to the general structure and the essential functional features of a vacuum die casting machine, reference is made to the above-mentioned literature reference EP 0 051 310.

betragen.In Fig. 1 of a die casting machine 1 is only indicated, the fixed platen 2 with attached fixed mold half 3, which cooperates with the movable mold half 4. The mold engraving or the mold cavity 5, which is to be filled with molten metal, is located between the fixed 3 and the movable mold half 4. For this purpose, a casting chamber 6 with a casting piston 7 is provided, into which the molten metal 8 is drawn in from a holding furnace 10 via an intake pipe 9. In the vacuum die-casting process, the molten metal is sucked out of the holding furnace 10 or a holding device by applying a vacuum. For this is located at the Mold halves 3, 4 a vacuum valve 12 with a vacuum connection line 13, which leads to an evacuation device 11, not shown. The mold cavity 5 is connected to the evacuation device 11 via a suction channel 14, the negative pressure being applied in the mold engraving 15 of the casting mold consisting of the mold halves 3, 4. As is known, the two mold halves 3, 4 are sealed by a circumferential elastic and temperature-resistant seal 16 which can be designed, for example, as a silicone cord. The sealing arrangement 16 spans, for example, the mold cavity 5 in a rectangular or square shape, the surface sealed thereby being formed by the height h ₁ and the width b ₁ , not shown, leading into the plane of the drawing in FIG. 1. For example, a surface ${\text{H}}_{\text{1}}{\text{xb}}_{\text{1}}\text{= 700 x 900 mm}$

be.

gebildet, was zu einem Lufteinschluß in diesem Hohlraum führt. Nimmt man beispielsweise Werte von ${\text{h}}_{\text{1}}{\text{x b}}_{\text{1}}{\text{x l}}_{\text{1}}\text{= 700 x 900 x 2 mm}$

, so führt dieser Lufteinschluß zu einem Volumen von V₁ = 1,26 Liter.In the exemplary embodiment, the seal 16 is inserted in a groove 17 of the fixed mold half 3 and it has a diameter d ₁ in the unloaded state. In order to achieve a sealing effect when the two mold halves 3, 4 move together, the seal 16 projects in the unloaded state by an amount l ₁ relative to the end face 18 of the mold half 3. In the illustration according to FIG. 1, the seal 16 just touches the end face 19 of the mold half 4 when the two mold halves 3, 4 move together. The protrusion l ₁ results in a volume of ${\text{H}}_{\text{1}}{\text{xb}}_{\text{1}}{\text{xl}}_{\text{1}}$

formed, which leads to an inclusion of air in this cavity. For example, if you take values of ${\text{H}}_{\text{1}}{\text{xb}}_{\text{1}}{\text{xl}}_{\text{1}}\text{= 700 x 900 x 2 mm}$

, this inclusion of air leads to a volume of V ₁ = 1.26 liters.

When the two mold halves 3, 4 move further together until the two end faces 18, 19 come to rest as shown in FIG. 2, this additional volume V must be compressed. Usually this creates a Pressure increase in the remaining volume, formed from the mold cavity 5 and the volume of the casting chamber 6, including the connecting lines, resulting in a pressure surge via the suction pipe 9 into the melt 8 of the holding furnace 10. In order to avoid such air or gas exposure to the melt 8, the die casting machine and in particular the casting set is controlled or regulated in such a way that the casting piston 7 is brought into a position during the moving together of the two mold halves 3, 4, which is between the Mold cavity 5 or the volume V ₁ and the mouth 20 of the suction pipe 9 is located. Such a shut-off position of the casting piston 7 is shown in FIGS. 1 and 2. As a result, the air volume V ₁ cannot get into the holding furnace 10 when the mold halves are pressed further together. The position of the casting piston 7 can be stationary or movable as long as the casting piston is in front of the mouth 20.

The increased volume V ₁ from the gap with the width l ₁ can be compensated for by increasing the volume of the casting chamber 6 and / or by suction using the evacuation device 11 or by releasing the vacuum valve to the atmosphere. By withdrawing the piston 7 in FIG. 2 to the right (see arrow 21), the chamber volume 22 of the casting chamber increases. Depending on the previous position of the casting piston 7, the pressure can be reduced and an underpressure can be generated in the casting chamber and / or in the mold cavity 5. The starting position of the casting piston 7 in its forward position is therefore optimized as a function of the other parameters and in particular also the volume of the mold cavity 5. If the volume V _{2 of} the mold cavity 5 is very small due to the cast part to be produced, the casting piston must rather be arranged in a rear position (to the right in FIG. 2), since only a small volume can be evacuated when the casting piston 7 is retracted. Vice versa In the starting position, the casting piston can be arranged very far in the front position, near the mold half 3, if the volume V _{2 of} the mold cavity 5 is very large. In this case, this can easily compensate for the additional volume V ₁ . There is accordingly an adjustment between the optimal position of the casting piston 7, the mold cavity 5 and the evacuation device 11.

The invention is not restricted to the exemplary embodiment shown and described. Rather, it also encompasses all professional modifications within the framework of property rights claims.

Claims (6)

Vacuum die-casting machine with a casting mold consisting of a stationary (3) and a movable (4) mold half, which are sealed against each other via an elastic seal (16) during the evacuation process or casting process and with a casting chamber () which is assigned to the stationary mold half (3) 6) with a pouring piston (7) into which an intake pipe (9) for supplying the melt (8) from a holding furnace (10) opens, the negative pressure acting on the mold cavity (5) and the casting chamber (6) by means of a on the mold cavity (5) connected evacuation device (11), characterized in that a gas supply into the melt-holding furnace (10) during the closing process of the mold halves (3, 4) is avoided by a shut-off, the shut-off being carried out until the overpressure in the mold cavity (5 ) or in the interior of the casting chamber (22) is largely removed. Die casting machine according to claim 1, characterized in that the holding furnace (10) is shut off by arranging the casting piston (7) between the casting mold (3, 4) and the suction mouth (20) of the suction pipe (9). Die casting machine according to claim 1 or 2, characterized in that the casting piston (7) returns during or after the closing process of the mold half (3, 4) of the casting mold from a front position close to the casting mold (3, 4) for pressure reduction. Die casting machine according to claim 1, characterized in that the mouth (20) of the suction pipe (9) is closed by a slide. Die casting machine according to Claim 1 or 2, characterized in that a valve arrangement (12) is provided which, after the mold half has closed, remains in a switch position until the overpressure has been released, which represents a connection between the mold cavity (5) and the atmosphere. Die casting machine according to one of the preceding claims 1 to 4, characterized in that a valve arrangement (12) is provided which switches briefly to evacuation during the closing process of the mold halves.

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