WO1996008210A1

WO1996008210A1 - Arc melting and casting device

Info

Publication number: WO1996008210A1
Application number: PCT/EP1995/003222
Authority: WO
Inventors: Joachim Weissflog; Norbert Solger; Bernd Niesler
Original assignee: Dentaurum J.P. Winkelstroeter Kg
Priority date: 1994-09-17
Filing date: 1995-08-16
Publication date: 1996-03-21
Also published as: DE4433159C1; EP0955943A1

Abstract

The invention concerns an arc melting and casting device (10) having a housing which comprises a melting chamber (14) and a casting chamber (16). The melting chamber (14) is disposed above the casting chamber (16) and is connected thereto via a passage (20). The melting chamber (14) and the casting chamber (16) can be closed in a gastight manner. In the melting chamber (14) a first electrode is connected to a crucible (34) and a second electrode (42) terminates above the crucible in the gas volume of the melting chamber (14). According to the invention, in order to attain a compact construction and uniform melting of the material, the second electrode (42) is supported such that it can be driven so that the end (44) of said electrode, which end is opposite the crucible (34), can perform circular movements.

Description

Arc melting and casting device

The invention relates to an arc melting and casting device for melting and casting dental metals and alloys with a housing comprising a melting chamber and a casting chamber, the melting chamber being arranged above the casting chamber and connected to it via an opening, and wherein the melting chamber and the Casting chamber can be closed gas-tight. A first electrode is connected to a crucible in the melting chamber. Above the crucible, a second electrode ends in the gas space of the melting chamber between the crucible and the crucible or the material to be melted arranged in the crucible during the operation of the arc melting device.

This type of arc melting and casting devices are known, for example, from US Pat. No. 5,168,917 and are primarily used for melting and casting small amounts of metals, as are usually used in dental technology for casting crowns, bridges, etc. . This arc, melting and casting device is particularly also for melting oxidation-sensitive metals, such as Titanium, usable, since one can work under a protective gas atmosphere and the melted material can be poured directly into the casting muffle, which is arranged in the casting chamber below the crucible, without having to take it out of the protective gas atmosphere.

With larger dimensions of the material to be melted (also called ingot) it is problematic that a strong one at points Overheating can occur. Such overheating leads to partial evaporation of the liquid material, especially when the thermal conductivity of the material to be melted is not particularly high. If alloys are used, this can mean that certain alloy components evaporate from the melt and the alloy composition thus changes during melting. An attempt was made to remedy this problem by deflecting the arc via electromagnetic fields (cf., for example, US Pat. No. 4,762,165).

A reaction of the molten metal or the molten metal alloy with the surrounding crucible material can occur as a further overheating effect.

In order to be able to influence the position of the arc with electromagnetic fields, a complex control for the arc is required and, moreover, a larger size of the device is required.

Since the arc melting and casting devices mentioned above are used above all as laboratory devices, an increase in the dimensions of the device is a particular disadvantage. The devices can then no longer be designed as table-top devices, as is required for dental laboratories.

The object of the present invention is to develop an arc melting and casting device of the type described in the introduction such that a uniform melting of the material to be melted can be achieved with a compact structure. This object is achieved according to the invention in the arc melting and casting device described at the outset by holding the second electrode drivable so that the end of the electrode opposite the crucible can carry out circular movements.

Thus, a movement of the end of the electrode opposite the crucible can be carried out by a simple rotary drive and so the thermal energy acting on the metal to be melted or the metal alloy to be melted can be applied uniformly to the material surface, so that selective overheating of the material to be melted or the melt can be avoided. In this way, ingots with a relatively large diameter can also be melted, in which the thermal conductivity of the melt or of the material to be melted is not particularly pronounced. In addition, granular or lumpy material can be melted in this way.

The user of the arc melting device can thus easily adjust the arc movement himself, which is not possible or can only be achieved with the greatest control effort in the case of electromagnetically guided arcs.

In a preferred embodiment of the invention, the electrode is held on a swash plate, the stroke of the nutation movement and thus the diameter of the circular movement being preferably adjustable.

By mounting the second electrode on a swash plate that carries out a nutation movement, the problem of sealing the electrode passage through the wall of the melting chamber can be solved particularly elegantly, since the swash plate is arranged in a rotationally fixed manner relative to the housing during the nutation movement. The swashplate can be attached to the NEN can be stored via a ball joint or spherical plain bearing or also via a cardanic suspension, which is preferred, since this storage can be implemented with a low expenditure on components.

In order to ensure the gas tightness of the melting chamber, it is only necessary that the electrode be held gas-tight on the swash plate when it extends to the outside of the melting chamber. For sealing, the swash plate is preferably connected gas-tight to one end of a cylindrical bellows, the other end of which is connected gas-tight to the melting chamber. The bellows has folds running in the circumferential direction, which are stretched or stretched when the swashplate is used.

In order to ensure that the bellows is stressed as little as possible, the pivot point for the nutation movement of the swash plate is preferably moved out of the interior of the melting chamber, so that relatively small nutation movements of the swash plate result in a relatively large diameter of the circular movements of the end of the plate opposite the cup lead second electrode.

In some cases, it may be desirable to coat particularly large areas with the arc. For such cases, it is advisable to mount the swash plate eccentrically on a turntable and to superimpose the rotary movement of the turntable on the nutation of the swashplate.

In a preferred embodiment of the invention, the second electrode has a coaxial bore which extends from the end of the second electrode lying outside the melting chamber into the interior of the melting chamber or into the interior of the Bellows extends, the bore outside of the melting chamber being connectable to a gas supply line.

In this way, a supply for the protective gas, in particular argon, can be produced in an elegant manner, which is introduced into the chamber after the melting chamber has been evacuated to ignite the arc.

It is preferably provided that the length of the second electrode immersed in the melting chamber is adjustable. This is particularly easy if the seal between the melting chamber and the swash plate is produced by means of a cylindrical bellows, since the cylindrical bellows can then compensate for the change in length or change in distance of the swash plate from the wall of the melting chamber without the sealing system for producing a gastight closure of the chamber changes are to be made. The same applies if, instead of the swash plate, a simple turntable is used, on which the electrode is rotatably and eccentrically held.

Preferably, the melting chamber and the casting chamber are formed in one piece, i.e. produced from a block or cast as a block and more preferably the melting chamber and the casting chamber adjoin one another with a common wall which forms the bottom of the melting chamber on the one hand and the cover of the casting chamber on the other. This wall then also contains the breakthrough mentioned above, which connects the melting chamber to the casting chamber.

Preferred materials for the manufacture of the melting chamber and the casting chamber are aluminum and aluminum alloys. Here the low thermal conductivity of the aluminum miniums or its alloys and their low specific weight used.

The melting and casting chambers arranged one above the other are accessible to the front through two openings also arranged one above the other in each side wall of the chambers and can thus be charged with the material to be melted or the casting muffle. The openings are preferably closed in a gas-tight manner by means of a common door, with separate seals again preferably being provided for the individual openings.

In a further preferred device, the side walls of the melting chamber are equipped with heat radiation reflecting sheets, preferably made of polished, austenitic stainless steel sheets, which prevent the radiant heat emanating from the arc and the melted material from directly reaching the walls of the melting chamber to meet. The door area of the melting chamber is preferably also provided with a heat radiation protective plate.

The arc melting and casting device according to the invention will preferably be provided on the outer wall of the melting chamber and optionally also on the casting chamber with cooling fins which support the cooling of the outside of the melting chamber by means of air. Due to the interaction of the heat radiation protective plates in the interior of the melting chamber and the cooling fins on the outside of the melting chamber, forced cooling, for example by means of cooling water, can be dispensed with.

A tiltable crucible is preferably used as the crucible in the interior of the melting chamber, which is held in a horizontal position for melting the metal or the alloy and which can be tilted downwards for pouring off the melt, where then the melt runs through the opening in the common wall of the melting chamber and the casting chamber into the casting muffle arranged in the casting chamber.

The center of gravity of the crucible is preferably selected with the greatest possible distance from the axis of rotation of the crucible.

It is preferably provided that the crucible can be locked in its horizontal position and that the locking for releasing the melt can be released, so that the crucible then automatically performs the tilting movement under the influence of gravity.

For this purpose, for example, a tongue protruding from the rear of the crucible in the rearward direction is suitable, which can be snapped into a releasable holding element of the crucible holder.

The crucible shape itself is preferably derived from a parallelepiped-shaped body which, with two projections projecting laterally from the rear, is supported on two supporting bolts of the crucible holder which guide the crucible between them. The projections also form the pivot bearing on the support bolts.

The cuboid base of the crucible preferably has a flat depression on the top, which receives the melted material in the form of a drop held together by the surface tension. Due to the flat shape of the gel, which essentially avoids side walls, there is no heat loss laterally due to heat conduction; in this way a minimal contact area of the melt with the crucible material is ensured, so that minimal heat absorption from the melt results through the crucible material. The crucible material can therefore cool down for a sufficiently long time The melt acts so that a solid layer of the material to be melted is retained on the surface of the crucible, which prevents the molten material from reacting with the crucible material. The cooling effect of the crucible body can be calculated in such a way that the heat capacity of the crucible is sufficient during the entire melting process to ensure the solid layer of material to be melted on the crucible surface, so that the tie is cooled separately by water ¬ gel material can be dispensed with.

In order to ensure safe positioning of the melt in the crucible despite the flat design of the crucible, a shallow depression is preferably provided on the surface of the base body, which has a conical recess in the center with an opening angle of approx. 130 ° to approx . Has 160 °. This flat conical recess is sufficient on the one hand to stabilize the melt drop sufficiently centrally and on the other hand prevents larger melt residues from remaining in the crucible during pouring. In addition, the contact surface of an ingot to be melted on the top of the crucible is limited to an annular surface, which in turn minimizes the heat transfer from the material to be melted to the crucible.

Preferably, the conical recess in the radial direction is adjoined by annular, stepped surfaces which serve to receive and center cylindrical ingots. It should be emphasized at this point that the device according to the invention, in particular also the crucible designed according to the invention, is suitable for melting cylindrical ingots, but also that granular material can also be melted.

The shallow depression of the surface of the base body of the angel preferably extends via an eccentric to the conical recess, which adjoins the stepped ring surfaces radially arranged, slightly beveled ring area into the upper side, the eccentrically arranged ring area at the front of the crucible base body opening into a flat channel which is also slightly inclined towards the center of the conical recess and leads to the front edge of the base body. The eccentrically arranged ring area and / or the channel leading to the front edge of the base body are slightly inclined at approx. 8 to 12 ° against the surface of the crucible base body.

The front of the crucible base body preferably has a groove in the area of the channel mouth, so that the heat capacity of the crucible base body is reduced in the area of the tear-off edge for the melt flow during pouring. On the other hand, the crucible base body should have sufficient mass to offer a sufficient cooling effect during the melting of the metallic material, while on the other hand it should be possible to tilt the crucible body as steeply as possible, so that all melt components can be poured out of the crucible.

The cuboid crucible base body is therefore preferably chamfered on its underside in the rear region at an angle of approximately 20 to 45 ° to the lower surface and running parallel to the rear side. This allows the crucible base body to pivot in a large angular range, i.e. up to 70 ° without the crucible having to perform a translatory movement away from the crucible holder.

In a preferred embodiment of the invention, the projections projecting laterally in the rear region of the crucible base body are selected such that they roll on the support bolts without causing a translatory movement of the base body away from the crucible holder. There- the pivoting movement of the crucible is further facilitated by. Due to the weight of the crucible, an uncontrolled rolling of the lateral projections onto the support bolt is sufficient for a reliable guidance of the movement, so that nothing is lost in the precision of the pouring process of the melt.

The underside of the crucible base body in the front part, i.e. on the front side of the crucible base body is preferably also chamfered running parallel to the front side, in the angular range of approximately 40 to 70 ° with respect to the underside of the crucible base body.

However, the crucible base body will preferably form an angle of at least 90 ° to the channel surface, at least in the region of the mouth of the channel, at a height of between one and two millimeters. This design of the front edge of the crucible has proven to be particularly suitable for an effective pouring of the melt with well-tearing drops of melt.

In order to give the crucible a position as defined as possible in the horizontally locked position, it can be provided that the support bolts of the crucible holding device have transverse grooves in which complementary strips of the projections projecting laterally from the crucible base body engage. When the crucible is tilted, the strips disengage from the transverse grooves and allow the rolling movement of the laterally protruding projections of the crucible base body onto the support bolt.

Secondly, the transverse grooves and the strips of the laterally projecting projections engaging in the transverse grooves bring about a larger-area electrical contact of the crucible base body with the crucible holder. The crucible is preferably made of copper, as is the crucible holder.

From the preceding description it is clear that the crucible according to the invention can be used regardless of the type of arc melting device and also represents an independent invention.

The breakthrough connecting the melting chamber to the casting chamber is preferred from a downward, i.e. funnel tapering towards the casting chamber. This funnel can simply be inserted into the opening or can be screwed into it. The lower end surface of the funnel wall is preferably chosen to be convex, a preferred radius of curvature of this end surface being in the range from approximately 30 to 50 mm.

A pneumatically liftable plate is preferably arranged in the casting chamber itself, on which the casting muffle can be placed. When the casting muffle is lifted pneumatically, its upper side is then placed sealingly against the lower end face of the funnel wall and a good seal is achieved by the preferred radius of curvature of the lower end face of the funnel wall.

These and other advantages of the invention are explained in more detail below with reference to the drawing. In particular, they show:

1 shows a sectional view through an arc melting and casting device according to the invention;

Fig. 2 is a sectional view taken along line 2-2 in Fig. 1; 3 shows a plan view of a crucible holder according to the invention;

Fig. 4 is a sectional view taken along line 4-4 in Fig. 3;

Fig. 5 is a sectional view through a crucible according to the invention.

1 shows an arc melting and casting device according to the invention, generally designated by reference number 10, having a housing 12 in which a melting chamber 14 and a casting chamber 16 are formed. The volume of the melting chamber 14 is usually kept smaller than the volume of the casting chamber 16. The melting chamber 14 adjoins the casting chamber 16 via a common partition 18, which contains a breakthrough 20, via which the melting chamber 14 is connected to the casting chamber 16.

The melting chamber 14 and the casting chamber 16 are open to the front (in FIG. 1, this corresponds to the left side) and are closed by means of a common door 22. The door is preferably provided in the area of the melting chamber with a sight glass for optical control of the melting process. For gas-tight sealing of the melting chamber 14 and the casting chamber 16, separate seals 24, 25 are provided in the door 22, which surround and seal the opening for the melting chamber 14 and the casting chamber 16, respectively.

A crucible holder 28 is fastened to the rear wall 26 in the melting chamber 14 via spacers 30. The crucible holder 28 essentially consists of a square plate, from which two guide bolts 32 project in the direction of the front of the melting chamber 14, which form a guide between them for a pivotable crucible 34. The crucible 34 is electrically connected via the crucible holder 28 and the electrical feed line 36 to a voltage supply 38, which is not shown in detail and not described, and forms a first electrode. A second electrode 42 is held in the upper end wall 40 of the melting chamber 14, which ends with its lower end 44 above the crucible 34 and essentially centered on it. The second electrode 42 passes through the upper end wall 40 and is drivably held in the electrode holder 46, designated overall by reference numeral 46, so that the lower end of the second electrode or its electrode tip 44 has circular movements, for example a simple circular movement, around the Crucible center can perform.

The second electrode 42 is electrically connected to the voltage supply 38 at its end 48 located outside the housing 12 via a feed line 50.

The second electrode 42 is preferably tubular over a certain length, starting from the outer end 48, so that a tubular inlet is connected via a gas inlet connection 52 and the tubular part of the second electrode 42 to the interior of the melting chamber 14 Some part of the electrode 42 allows ventilation or the feeding of protective gas into the melting chamber 14.

In order to be able to produce a protective gas atmosphere in the melting chamber 14, this is provided in the lower region of the rear wall 26 with a suction opening 54, via which the melting chamber 14 can first be evacuated before the protective gas atmosphere is built up via the gas inlet 52 and the second electrode 42 . In the opening 20 of the bottom 18 separating the melting chamber 14 from the casting chamber 16, a funnel part 56 is preferably inserted, preferably screwed in, which directs the melt flow into a casting muffle 58 arranged in the casting chamber 16 when pouring a melt formed on the crucible 34.

The casting muffle 58 is usually inserted into a holder 60 or placed on a plate, which can be raised pneumatically via a lifting device 62, so that the upper edge of the casting muffle 58 comes to bear sealingly against a lower funnel wall end 64. The casting chamber 16 contains, in the rear wall 26, in analogy to the melting chamber 14, a suction opening 66 through which the casting chamber 16 can be evacuated.

Before individual components of the arc melting and casting device according to the invention are described in more detail with reference to FIGS. 2 to 5, the operation of the device during melting and casting, in particular of oxygen-sensitive materials, will be briefly discussed here.

In the casting chamber 14, the metal to be melted or the metal alloy to be melted is first introduced into the crucible 34 held in a horizontal position in the form of granular or lumpy material or in the form of the ingot 68 shown in FIG. 1. In the melting chamber 16 below, the casting muffle 58 is inserted into the holder 60 and raised by means of the pneumatic lifting device to such an extent that the upper end of the casting muffle 58 lies against the lower edge 64 of the funnel 56.

The common door for closing the front openings of the melting chamber 14 and the casting chamber 16 is then closed and the two chambers 14 and 16 are evacuated via the suction openings 54 and 66. While the casting chamber 16 is further evacuated, a protective gas atmosphere is built up in the melting chamber 14 via the gas inlet 52, which can be lower than atmospheric pressure, but can also assume a higher pressure, for example an overpressure of approximately 0.8 at. Argon is preferably used as the protective gas used. After an arc is ignited between the electrode tip 44 and the material of the ingot 68 to be melted, the material of the ingot 68 is melted until a drop of melt forms on the crucible surface 34. A lock is then released in the crucible holder 28 so that the tie 34 can tip down due to gravity and the melt drop can flow via the funnel 56 into the casting muffle 58 and can fill the cavities formed there.

The shaping of the cavities in the casting muffle 58 can be supported by an increase in pressure in the melting chamber after the melt drop has been poured off from the crucible 34 by an increase in pressure in the melting chamber 14. Gas fractions, which are present in the cavities of the casting muffle 58, are broken down by the porous casting muffle material due to the maintained differential pressure between the casting muffle and the casting chamber 16, which is still evacuated, so that void-free castings can be obtained.

In order to achieve an optimal result when the ingot 68 melts, the electrode 42 can execute a circular movement with its tip 44, the radius of which can be adjusted. This results in heating of the metallic material over a substantially larger area of the ingot 68, as a result of which overheating of individual portions of the metallic material is avoided. In order to obtain an optimal arc geometry, the immersion depth of the electrode 42 in the melting chamber 14 can also be adjusted by adjusting the length of the electrode 42. The circular movement of the electrode tip 44 is also advantageous in the case of granular or lumpy material, since this results in a rapid sintering of these materials.

In order to avoid heating the housing of the melting and pouring device 10, a protective plate arrangement reflecting the heat radiation can be provided in the interior of the melting chamber 14, which extends into the space between the crucible holder 28 and the rear wall 26.

While the housing 12 is preferably made of aluminum, the heat radiation protective plates are preferably made of polished, austenitic stainless steel. The door 22 can also be equipped with a heat radiation protective plate at the openings of the melting chamber 14. The upper end wall 40 and, to a large extent, the parts of the electrode holder 46 facing the melting chamber 14 can also be protected by means of a heat radiation and splash guard, again preferably made of polished austenitic stainless steel. The rear wall 26 can be provided in the region of the melting chamber and optionally also in the region of the casting chamber with cooling ribs (not shown), which often produce a sufficient cooling effect, so that water cooling of the housing can be dispensed with.

The crucible 34 is preferably made of copper, as is the crucible holder 28. Based on the heat capacity of the crucible, it is calculated based on the permissible quantities of metal or metal alloys to be melted and, in particular, the reduced contact area between the flat crucible shape the melting drop and the crucible material, there is no need to cool the crucible 34, since if the crucible material has a sufficient heat capacity, it becomes a solidified layer of the metal to be melted forms the crucible surface, which at the same time prevents reactions or alloy formation between the material to be melted and the crucible material.

2 now shows in detail the structure of the electrode holder 46.

The electrode holder 46 is inserted in the upper end wall 40 of the melting chamber 14 into an annular and stepped opening 70 and is electrically insulated from the upper end wall 40 via a first glass ceramic ring part 72, which has a stepped design on the outside thereof. complementary to the stepped shape of the opening 70.

The glass ceramic ring part 72 is pressed against the upper end wall 40 from the outside via a glass ceramic clamping part 74 to be placed thereon, which also has a ring shape. In the opening 70, an annular seal 74 is arranged, via which a gas-tight connection between the ceramic part 72 and the upper end wall 40 is established.

The center of the glass ceramic ring part 72 has a step-like recess, which initially accommodates an essentially cylindrical tantalum sheet metal jacket, which is supported on the glass ceramic part 72 with an end flange 79. The cylindrical tantalum sheet metal jacket 78, in turn, is held via its flange 79 by an overturned cylindrical bellows 80 via its annular base 81 on the ceramic part 72, the base part 81 being provided on its underside with an annular groove into which a sealing ring 82 is inserted becomes. At its end facing away from the foot 81, the bellows 80 carries a disk 84 into which a sleeve-shaped holder 86 for the electrode tip 44 can be screwed. The bellows 80 is finally surrounded by a cylindrical housing part 88, which is likewise supported on the glass ceramic ring part 72 and has a threaded section 89 on its cylindrical outer surface. The cylindrical housing part 88 is encompassed at its lower end by the glass ceramic clamping part 74 which is supported on a flange-like extension at the lower end of the cylindrical housing part 88 and thus holds the cylindrical housing part 88 between itself and the glass ceramic ring part 72.

On the other hand, since the cylindrical housing part 88 is supported on the foot 81 of the bellows 80 via an inwardly projecting flange, the bellows 80 is thus also held on the glass ceramic ring part 72 and the tan sheet metal jacket 78 is in turn held over the foot 81.

A ring 90 loosely rests on the tantalum sheet metal jacket 78, which closes the tantalum sheet metal jacket 78 upward towards the sleeve part 86 and thus prevents spritzers of the melted material from the melting chamber 14 from reaching the bellows 80, which occurs at the high temperatures , e.g. of titanium melts, could easily lead to damage to the bellows material and thus to leakage of the bellows.

The sleeve 86 is sealed with respect to the disk 84 via an aluminum sealing ring 91, so that overall a gas-tight mounting of the second electrode 42 results in the opening 70 of the upper end wall 40.

The threaded portion of the sleeve 86 screwed into the disk 84 continues beyond the disk 84. The disc 84 itself comprises on its side facing away from the bellows 80 a cylindrical part 92 onto which a ring part 94 with a spherical surface is pushed. The ring part 94 with the spherical outer surface is fixed on the disc 84 by a ring 96 screwed onto the outer threaded section of the sleeve 86. A rotationally symmetrical, essentially hollow cylindrical bearing part 98 is screwed onto the threaded section 89 of the cylindrical housing part 88, which is closed at its outer end with a base 100 which has a central bore 102 in the center, which has a slide bearing 104 for the ring part 94 with a sparse outer surface. Via this slide bearing 104 and the ring 94 with a spherical outer surface, the electrode 42 is pivoted on all sides about the pivot point P.

Following the screwed-on ring part 96, the sleeve 86 carries a radial bearing 106 which carries a swash plate 108 with its outer bearing ring.

The bearing part 98 carries a setting wheel 112 via a radially projecting flange 110, with the aid of which the bearing part 98 can be screwed further onto the thread 89 of the cylindrical housing part 88 or unscrewed therefrom. The immersion depth of the electrode 42 in the melting chamber 14 is thus set.

Above the F-flange 110, the bearing part 98 continues with a cylindrical section 114, on the external thread of which a hollow cylindrical bearing part 116 is screwed. This bearing part 116 carries the outer ring of a radial bearing 118, the inner ring of which in turn carries a drive wheel 120. The drive wheel 120 can be driven, for example, by a belt drive to make a rotary movement and has a central opening 122 in which the housing wall 40 is removed. The end of the sleeve 86 receives the radial bearing 106 arranged on the sleeve and the swash plate 108 fastened thereon.

In addition, the swash plate 108 is connected in a rotationally fixed manner to the drive wheel 120 via a spherical head bolt 124, the bolt being screwed into the swash plate 108 in the radial direction and engaging with its spherical head or spherical head part in a radial bore 126 of the drive wheel 120 . The swash plate 108 is non-rotatably connected to the drive wheel 120 via the bolt 124.

The hollow cylindrical bearing part 116 carries, via a radially projecting flange 128, an adjusting wheel 130 with which the hollow cylindrical bearing part 116 can be screwed further onto the external thread of the cylindrical section 114 or unscrewed therefrom. If the hollow cylindrical bearing part 116 is further screwed onto the external thread of the cylindrical section 114, the drive wheel 120 moves in the direction of the upper end wall 40 and thereby swivels the swash plate 108, which is coupled to the drive wheel 120 in a rotationally fixed manner, in Clockwise. At the same time, the second electrode 42 also pivots clockwise around the point P.

On the other hand, if the hollow cylindrical bearing 116 is unscrewed further from the thread of the cylindrical section 114 via the adjusting wheel 130, the drive wheel 120 moves away from the upper end wall 40 and the swash plate 108 is pivoted in the counterclockwise direction, just like the electrode 42.

If the drive wheel 120 is now driven to rotate, and the hollow cylindrical bearing part 116 is out of it Neutral position, in which the electrode 42 is arranged substantially perpendicular to the upper end wall 40, rotated out, so the swash plate 108 also performs a rotary movement, but a nutation is superimposed. Due to the rotational decoupling of the second electrode 42 via the radial bearing 106, the latter is decoupled from the rotary movement of the drive wheel 120 and only executes a pivoting movement along a cone shell. This allows a connection 132 of a gas supply line 134 and the electrical connection line 136 to be simply fastened. This connection is additionally facilitated in that the pivot point P is selected such that it is arranged in the upper third of the electrode 42, so that for the outer end to which the gas line 134 and the electrical line 136 are connected there is only a slight circular movement or a circular movement with a small diameter compared to the diameter of the circular movement of the electrode tip 44.

The electrode tip 44 is fastened in the lower end of the sleeve 86 via a clamping area with radially slotted clamping elements (not shown) and a coupling sleeve (not shown in detail) which compresses the clamping elements via a cone when the sleeve is screwed in, and thus the electrode tip 44 firmly clamped. Adjacent to the lower end of the sleeve 86 or adjacent to the electrode tip 44, that part of the gas-ceramic ring part 72 which projects into the melting chamber 14 is preferably protected from splashes of the melted material by a cylindrical protective plate 138 which bears a radially outwardly projecting edge, which are otherwise under certain circumstances can lead to damage to the glass ceramic part 72.

3 and 4 show the crucible holder 28 in detail, which consists of an essentially square base plate 140 with a central opening 142, in which a locking mechanism 144 for holding the crucible 34 is inserted in a horizontal position. The locking mechanism 144 comprises a pivot bolt 146, which spring-loaded overlaps a tongue 148 protruding from the rear side of the crucible 34.

The crucible 34 also lies on the guide bolts 32 protruding from the front of the plate 140 on both sides via projections 150 protruding laterally on the rear side of the crucible 34, the base body of the crucible 34 being guided between the guide bolts 32 (cf. FIG. 3).

If the swivel bolt 146 is pivoted out of its rest position, for example by a plunger, in its lower region (in the counterclockwise direction in FIG. 4), it releases the tongue 148 protruding from the back of the crucible 34 and the crucible 34 tilts due to its eccentric mounting by the projections 150 the guide pin 32 down.

For the exact positioning of the crucible 34 on the crucible holder 28, the projections 150 have strips 152 projecting downwards, which in the horizontal position of the crucible, i.e. that is, in the position in which material is melted, into complementary transverse grooves 154 of the guide bolts 32. With the lateral guidance of the guide bolts 32 and the engagement of the strips 152 in the transverse grooves 154, an exact and reproducible positioning of the crucible 34 on the holder and in particular with respect to the electrode tip 44 is possible.

5 finally shows the crucible 34 in cross section, the following details in particular being pointed out. The essentially cuboid base body of the crucible 34 has a flat recess 156 on its upper side, which comprises a conical depression 158 aligned with the normal position of the electrode tip 44. Subsequent to the conical recess 158, the opening angle of which is approximately 150 ° here, there are graded ring regions 160, 161 and 162, which each serve as supports for ingots 68 to be melted. Depending on the diameter of the ingot, it will rest on the ring surface 160, 161 or 162. The ring surfaces on the one hand provide sufficient electrical contact between the crucible 34 and the ingot, but at the same time avoid the ingot resting on the crucible 34 over a large area, so that the heat absorption of the crucible material by the ingot material is limited to a minimum.

In a further step, the outermost stepped ring surface 162 is adjoined by an eccentrically arranged ring surface 164, which opens into a channel 168 in the region of the front edge 166 of the crucible 34. Both the ring surface 164 and the channel 168 are slightly inclined towards the center of the crucible or its recess 156. The preferred angle of inclination here is approximately 8 to 12 °.

The underside of the crucible 34 is chamfered over a large area on the rear side, the surface 170 formed thereby forming an angle of approximately 30 ° to the plane of the underside 172. A chamfer 174 is also attached to the underside parallel to the front edge and forms an angle of approximately 45 ° with the plane of the underside 172. It is important for the melt's tear-off behavior when pouring out the drop of melt that an area approximately vertical to the channel bottom with a height of 1 to 2 mm is subsequently formed on the front edge 166 in the region of the mouth of the channel 168. The described shape of the crucible 34 ensures on the one hand that the center of gravity of the crucible is as far as possible from the axis of rotation of the crucible during the tilting movement and that on the other hand a sufficient tilting movement of the crucible is possible so that the melt residue remaining in the crucible is minimized.

Claims

EXPECTATIONS

1. Arc melting and casting device for melting and casting dental metals and alloys with a housing comprising a melting chamber and a casting chamber, which are arranged one above the other and connected to one another with an opening, the melting and casting chambers being gas-tightly closable, and with a crucible arranged in the melting chamber, connected to a first electrode and a second electrode ending above the crucible in the gas space of the melting chamber, characterized in that the second electrode is held on a disk which can be driven to move, so that the end of the electrode opposite the crucible performs circular movements.

2. Apparatus according to claim 1, characterized in that the disc is a swash plate which can be driven to a Nuta¬ tion movement, the stroke of which is preferably adjustable.

3. Apparatus according to claim 1 or 2, characterized gekenn¬ characterized in that the swash plate is mounted on a spherical plain bearing on the housing.

4. Device according to one of claims 1 to 3, characterized ge indicates that the second electrode is held gas-tight on the swash plate and extends to the outside of the melting chamber.

5. The device according to claim 4, characterized in that the swash plate is arranged with its fulcrum outside the melting chamber and gas-tightly connected to one end of a cylindrical bellows, the other end of which is gas-tightly connected to the melting chamber.

6. The device according to claim 4 or 5, characterized gekennzeich¬ net that the second electrode has a coaxial bore which extends from the end of the second electrode lying outside the melting chamber to the inside of the melting chamber and which outside the melting chamber Chamber can be connected to a gas supply line.

7. Device according to one of the preceding claims, da¬ characterized in that the immersed in the melting chamber length of the second electrode is adjustable.

8. Device according to one of claims 1 to 7, characterized ge indicates that the melting chamber and the casting chamber are integrally formed and with a common wall that forms the bottom of the melting chamber on the one hand and the cover of the casting chamber on the other, adjoin each other.

9. The device according to claim 8, characterized in that the melting chamber and the casting chamber are made of aluminum or aluminum alloy.

10. Device according to one of claims 1 to 9, characterized ge indicates that the melting chamber and the casting chamber are accessible through two mutually arranged openings in each side wall of the chambers and that the openings are gas-tightly closed by means of a common door .

11. Device according to one of the preceding claims, da¬ characterized in that the side walls of the Schmelzkam¬ mer with heat radiation reflecting sheets, preferably from polished, austenitic stainless steel sheet, are equipped.

12. Device according to one of claims 1 to 11, characterized in that the rear outside of the melting and optionally also the casting chamber is provided with cooling fins.

13. Device according to one of claims 1 to 12, characterized in that the melting chamber comprises a crucible holder arranged adjacent to the rear wall.

14. The apparatus according to claim 13, characterized in that the crucible is pivotally held on the crucible holder about an axis of rotation spaced from the center of gravity of the crucible.

15. The apparatus according to claim 14, characterized in that the crucible has a cuboid base and with two extending laterally from the rear front of the projections on two of the crucible between them guide the supporting bolt of the crucible holder.

16. The apparatus according to claim 15, characterized in that a tongue extends in the rearward direction from the rear front of the crucible, which tongue can be latched into a releasable holding element of the crucible holder.

17. Device according to one of claims 15 or 16, characterized in that the cuboid base body of the crucible on the surface of a shallow depression has, which has a conical recess in the middle with an opening angle of approximately 130 to 160 °.

18. The apparatus according to claim 17, characterized in that the flat recess radially to the conical recess then has at least one stepped annular surface for receiving and centering an ingot.

19. The apparatus of claim 17 or 18, characterized gekenn¬ characterized in that the flat recess comprises an eccentrically arranged to the conical recess, slightly inclined to the center of the conical recess annular surface area, which is adjacent to the front of the crucible base body in a flat, also to the center of the conical Exception inclined and leading to the front edge of the basic body opens channel.

20. The apparatus according to claim 19, characterized in that the annular surface area and / or the channel against the surface of the crucible base body has an inclination of approximately 8 to 12 °.

21. Device according to one of claims 19 or 20, characterized in that the front of the Tiegelgrundkör¬ pers has a groove in the region of the channel.

22. The device according to one of claims 15 to 21, characterized in that the underside of the crucible base body in the rear part is chamfered against the lower surface parallel to the back at an angle of 20 to 45 °.

23. The device according to one of claims 15 to 22, characterized in that the underside of the crucible base body is chamfered in the front part with an angle of 40 to 70 ° running parallel to the front.

24. The device according to one of claims 17 to 23, characterized in that the underside of the crucible base body in the region of the conical recess is substantially flat and parallel to the top of the crucible body.

25. Device according to one of claims 15 to 24, characterized in that the support bolts of the crucible holding device have transverse grooves in which complementary bars of the projections projecting laterally from the crucible base body engage.

26. Device according to one of claims 23 to 25, characterized in that the part of the front of the crucible base body adjoining the channel forms an angle of approximately 90 ° with the channel and has a height of approximately 1 to approximately 2 mm .

27. Device according to one of the preceding claims, characterized in that the breakthrough connecting the melting chamber to the casting chamber is formed by a funnel tapering downwards.

28. The apparatus according to claim 27, characterized in that the lower end surface of the funnel wall is convex.

29. The device according to claim 28, characterized in that the lower end face of the funnel wall has a radius of curvature of approximately 30 to approximately 50 mm.