EP0790090B1 - Vacuum die-casting machine - Google Patents

Description

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

State of the art:

A die casting machine according to the preamble of claim 1 is known from EP 0 051 310 B1 become after the so-called vacuum die casting process is working. In this process, the molten metal is made a holding furnace through an intake pipe into the casting chamber sucked in by means of negative pressure, the negative pressure via a Vacuum system is applied in the mold engraving of the casting mold. This patent also addresses the problem of sufficient Degassing of the melt addressed during the casting process. In particular, the aim of the vacuum die casting process is one Improvement of the casting quality by evacuation of the Die casting mold and extraction of the reaction gases from the mold and the gun chamber. In addition, the Negative pressure to the melt from the holding furnace in the Transporting the casting chamber.

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

The mold consists of a movable as well fixed mold half, the latter generally with the casting chamber is connected to the casting piston and the Holding furnace via an intake pipe to the casting mold part of the casting chamber facing away.

The movable mold half is used for a casting process drove the fixed mold half, with an elastic and temperature resistant gasket surrounds the mold cavity and the Form halves sealed against each other. Such Sealing arrangement is for example in EP-A1-0 230 660, 1 with reference numeral 64.

When the mold halves are moved together, the seal stands with a small distance on the order of e.g. 2 mm against the contact surfaces of the mold halves in order to Compress the mold halves to act as a seal. Here the circumferential seal spans a surface area that definitely in connection with the overhang height of the seal leads to a remarkable cavity for air entrapment. Take, for example, 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 e.g. 2 mm, this leads to an air inclusion with a volume of 1.26 liters. If you quickly press the surfaces against each other, so this volume of air within the mold cavity and the casting chamber are displaced, resulting in an undesirable Pressure increase leads. The disadvantage of this is that this trapped gas via the casting chamber and the suction pipe can get to the holding furnace for the melt and the A blow of air is applied to the melt in the holding furnace.

This leads to undesirable additional gas inclusions within the melt, which in turn adversely affects the Casting quality can affect.

From document EP-A-0 559 920 is a vertical die casting machine in which the Mold cavity with a sprue after closing the Mold halves is evacuated. During this process, the the casting chamber connected to it by means of a double one Piston arrangement closed. The vacuum serves at one such system not to transport the melt from one Holding furnace. Rather, this is via a metering device entered in the casting chamber.

DE-A-43 10 755 is a horizontal die casting machine became known, in which by means of a Pressurizing the mold cavity and a sprue and part of the casting chamber is evacuated. One serves Subdivision of the casting chamber into two casting chamber halves by means of a fitting that no melt prematurely in the Mold cavity can get.

Object of the invention:

The invention has for its object the above Avoid disadvantages and especially an additional one To prevent air supply to the holding oven by this effect.

Solution of the task and advantages of the invention:

This object is achieved by the characterizing Features of claim 1 solved.

In the subclaims are advantageous and expedient Developments of the measures specified in the main claim listed.

The invention has compared to the known prior art Advantage that when moving the mold halves together Sealing arrangement air not trapped by the Intake pipe can get into the holding oven. The gas recoil through this air cushion is at least as long from Heated holding oven held until a pressure release in the mold or the casting chamber leads to a pressure equalization that it prevents the gas or trapped air from entering the Holding furnace flows. This pressure reduction takes place e.g. by the evacuation valve connected to the atmosphere instead. This avoids that an additional Gas exposure to the melt in the holding furnace and the so associated disadvantages occur.

The conclusion or closing of the Holding oven achieved in that the intake pipe to Holding furnace is separated from the mold cavity, what can preferably be done by means of the casting piston itself. For this purpose, the pouring plunger is pushed together during the Mold halves arranged in the casting chamber so that it is in front the mouth of the intake pipe, i.e. between mold cavity and Mouth of the intake pipe is positioned. This allows the Gas recoil does not cause air to melt in the Run a holding oven.

Casting sets are from various references become known, the one after a casting process Carry out an empty stroke of the casting piston inside the casting chamber, for example tinsel from the inside of the gun chamber eject and / or spray oil lubrication on the Apply the inner wall of the casting chamber (see e.g. DE 43 16 927 A1). This additional stroke during the Return stroke can be used according to the invention when Form closing the plunger between the mouth of the Intake pipe into the casting chamber and the mold cavity position. In this case the gas recoil cannot Affect holding oven. Only then will the casting piston permanently withdrawn when the closing process ends and if necessary via the still associated with the atmosphere Evacuation device for pressure reduction has taken place.

The intake pipe can also be used with other means, such as e.g. Gate valve or the like opposite the casting chamber separate so that this gas recoil when the Mold halves do not affect the melt in the holding furnace. However, this increases the technical effort.

By arranging the casting piston in the front position at Bringing together the mold halves is the interior of the casting chamber closed off from the mold cavity. After merging of the mold halves, the casting piston is directed towards the rear Intake pipe pulled, which is a kind of additional evacuation or

Production of a vacuum or compensation of the Pressure increase due to the closing of the mold halves causes.

Drawings:

Further details of the invention also result from the Drawings and the one explained below Embodiment.

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:

Regarding the general structure and the essential Features of a vacuum die casting machine is based on reference EP 0 051 310 mentioned at the beginning is referred to.

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 purpose, there is a vacuum valve 12 on the mold halves 3, 4, 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 drawing plane of FIG. 1. For example, an area h ₁ x w ₁ = 700 x 900 mm.

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 forms} a volume of h ₁ xb ₁ xl ₁ , which leads to an air inclusion in this Cavity leads. If you take values of h ₁ xb ₁ xl ₁ = 700 x 900 x 2 mm, for example, this air inclusion 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. This normally results in an increase in pressure which is distributed in the remaining volume, formed from the mold cavity 5 and the volume of the casting chamber 6, including the connecting lines, with a pressure surge occurring through 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 assembly 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. Conversely, 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 based on that shown and described Embodiment limited. Rather, it includes everyone professional modifications in the context of Property rights claims.

Claims (6)

1. Vacuum die-casting machine with a mould formed by a stationary mould half (3) and a moving mould half (4) which are sealed from one another by an elastic seal (16) during the evacuation process or casting process and with an injection chamber (6) associated with the stationary mould half (3) with injection piston (7) into which there opens an intake pipe (9) for feeding the melt (8) from a holding furnace (10), wherein the vacuum supply to the mould cavity (5) and to the injection chamber (6) and the aspiration of the melt into the injection chamber are effected by means of an evacuation system (11) connected to the mould cavity (5), characterised in that, to prevent the feed of gas into the melt-holding furnace (10) during the closing of the mould halves (3, 4), a shutoff means is provided for shutting off the holding furnace (10) from the mould cavity (5), shutting off being effected until the excess pressure in the mould cavity (5) or in the interior of the injection chamber (22) has dropped very substantially.
2. Die-casting machine according to claim 1, characterised in that the holding furnace (10) is shut off by arranging the injection piston (7) between mould (3, 4) and intake orifice (20) of the intake pipe (9).
3. Die-casting machine according to claim 1 or 2, characterised in that the injection piston (7) travels back from a leading position located close to the mould (3, 4) during or after the closing of the mould half (3, 4) of the mould.
4. Die-casting machine according to claim 1, characterised in that the orifice (20) of the intake pipe (9) is closed by a slide.
5. Die-casting machine according to claim 1 or 2, characterised in that a valve arrangement (12) is provided which, after the closing of the mould half until the drop in excess pressure, remains in a switched position in which the mould cavity (5) communicates with the atmosphere.
6. Die-casting machine according to one of the preceding claims 1 to 4, characterised in that a valve arrangement (12) is provided which switches momentarily to evacuation during the closing of the mould halves.

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