WO1985000964A1 - Casting apparatus particularly for dental works - Google Patents

Abstract

Casting apparatus comprising an oscillating casting cylinder (18) enabling, by means of a simple mounting and after a prolonged operating time, to obtain the required melting temperatures. To this effect, the resistance heating elements (32, 34) surrounding a crucible (30) are based on MoSi2? and are formed so as to enable a free radiation. Furthermore, the heating elements (32, 34) are bent with an L configuration in their upper part and are hard-soldered, a copper tube (42) being used as electric connection. The casting apparatus has a cover (64) which may be opened or closed in two steps.

Description

Gießgerat f or _^ J nsbesondere zahntech ijiche work

The invention relates to a casting device for, in particular, dental technology-related work, comprising a casting cylinder which is rotatable about a horizontally arranged shaft, a melting pot which is surrounded by preferably U-shaped heating elements and which can be closed with a lid, and at least one from the casting cylinder leading electrical connection.

Corresponding casting devices intended for dental technology are used, for example, to pour molten gold or alloys thereof into a model embedded in a casting mold. For this purpose, the metal to be melted is first placed in a crucible. A resistance heater surrounding the crucible is then switched on in order to achieve the required melting temperature. The resistance materials consist of precious metal alloys, which are firmly embedded in insulators and are at a distance from the crucible. Due to this arrangement, corresponding resistance heaters in the crucible generate a maximum end temperature of approx. 1450 ° C.

The resistance heaters are connected via quick connections to an electrical connection leading out of the housing. Due to the arrangement of the heating conductors, which are usually embedded in a ceramic mass, temperature losses occur, by means of which the required final temperature is not reached ^" . During the melting process itself, the crucible should only be filled with protective gas, whereas in the casting process, pressurized air is required to press the molten metal into the casting mold. According to the prior art, this requires complex connections which are to be connected to the compressed air or protective gas source. For example, the connection to the protective gas source, such as an argon bottle, must be interrupted when the casting device is pivoted about the horizontally running shaft or shaft sections.

The object of the present invention is to design a casting device of the type described above so that, with a simple structure, the required temperatures can be reached without problems even after a long operating time, the device itself being designed to be low-maintenance. Furthermore, there should be the possibility of establishing a connection to a protective gas or compressed air source with simple means without, for example, having to remove the connection to one of the sources when the device is pivoted.

The object is essentially achieved in that each heating element is a freely radiating resistance conductor, the free upper leg of which is preferably angled in an L-shape and held by clamps made of ceramic material, and is hard-soldered to a connecting tube, one of which in turn is brazed flexible current conductor, one of which is connected to the electrical connection leading outside the casting cylinder. The high-temperature resistant resistance material is preferably a cermet material that consists of molybdenum disilicide (MoSi ") and ceramic additives.

Characterized in that the resistance material in the area of the holder made of ceramic material is brazed to a tube, preferably made of copper, in which a flexible tube It is ensured that conductors such as copper, which is crimped and soldered, are prevented from oxidizing even at high temperatures, which would lead to high transition resistance which would reduce the efficiency of the heating elements. This ultimately ensures that the casting device is extremely maintenance-friendly with regard to the heating elements and that the heating has a long service life.

In a further embodiment of the invention to be emphasized, the electrical connection runs coaxially to the shaft of the housing and consists of a metal core with a ceramic sheathing and a copper sheathing applied thereon, which is brazed to a rotatably mounted section of the shaft surrounding the connection. This has the advantage that the connection between the casting cylinder and the exterior can be pressure and vacuum resistant, so that leaks are excluded.

According to an independent embodiment of the invention, the (opposite) shaft section of the housing, which does not surround the electrical connection, is designed as a hollow shaft with separate coaxially arranged channels through which protective gas such as argon or. Compressed air can flow. The inner channel is formed continuously up to the crucible, so that the protective gas can be fed in without any problems. The fact that the shaft section is provided with coaxially arranged channels ensures that the connection to the compressed air source or protective gas source can be maintained continuously, which according to the prior art is not or only with constructively complex and thus frequently leading to malfunctions Funds is possible.

According to a further development of the invention, the region of the crucible and the adjacent support surface which receives the casting mold has a labyrinth seal which is essentially formed by a circumferential trapezoidal projection to which a corresponding recess of the casting mold is assigned and by which it is centered. The advantage is there two sections together, which are formed by an upper shoulder of the melting crucible and a section of the support area surrounding the casting mold. In a sectional view, the rubber base for the casting mold is composed of a middle, large, trapezoidal section that connects the melting crucible and the casting walls and the small, trapezoidal projections surrounding them. The labyrinth seal ensures that splashing and loss of the melt when the casting cylinder is tilted are almost impossible.

Finally, it is to be pointed out to a particularly noteworthy inventive design that relates to the sealing cover of the casting device. The closure cover can be pivoted about a horizontally running axis and has a central rotatable cover section from which the cover handle or lever extends. Furthermore, bearing blocks are arranged around the closure lid arranged above the crucible on the housing surface, which can optionally interact with elements actuated by the rotatable section of the lid and displaceably arranged in the non-rotatable region of the lid. A distinction is to be made between various sliding elements that perform functions. At least one element is used to hold the cover in a quasi-closed position, even if the other elements are already unlocked. This has the advantage that when a possible excess pressure builds up in the casting device when the other elements are unlocked, the cover cannot open, rather the cover is held in a closed position by the first element, which, however, enables pressure compensation between the surroundings and the inside of the casting device.

So that the sliding elements can be displaced when the middle cover section is rotated, a pin or bolt protrudes from each sliding element, which engages in a preferably curved recess in the rotatable section of the cover. The curvilinear course continues Recess of the further elements to be unlocked first, each composed of a central section extending obliquely to the pivot point of the rotatable section of the cover and of outer sections (second and third) running on circular sections.

The bolt engages in these outer sections when the cover is closed or opened. Due to the special design of the recess made up of three sections, the sliding elements are self-locking in the closed position or the open position of the cover, so that it is ensured that an uncontrolled opening or closing of the cover is not possible .

Also protruding from the first rotating element is a pin or bolt which engages in a so-called guide recess, the course of which is formed by two sections. A first section runs on a circular section with the axis of rotation as the center and a second section obliquely to the radius. The length of the sections is chosen so that when the cover is opened, that is to say when the middle section is rotated, the pin runs in the first section. In this case, the element will not be moved radially, so that it continues to interact with the bearing block. At the same time, however, the pins of the further displacement elements are moved in the central sections which extend obliquely to the radius, so that the elements are displaced in the direction of the center of rotation. Reaching out with the pedestals is achieved. This allows the cover to be raised slightly, which means that pressure equalization can take place without the cover suddenly opening; because even after unlocking the other elements, the first element continues to interact with the associated bearing block. Only when the pin of the first element is moved into the second section, which extends at an angle to the radius, is this element also unlocked, so that the cover can be raised.

Mit anderen Worten stellt der erste Schieber einen sogenannten Sicher¬ heitsschieber und die weiteren Schieber Verriegelungsschieber dar.

In other words, the first slide is a so-called safety slide and the other slide is a locking slide.

Further details, advantages and features of the invention result on the one hand from the claims — individually or in combination — and on the other hand from the preferred exemplary embodiment shown below in the drawing.

Show it:

1 shows in longitudinal section and in detail a schematic representation of a casting device according to the invention with the interior of the housing,

2 is an enlarged view of the support area for a casting mold,

Fig. 3 a cover closing the casting machine according to Fig. 1 in plan view and

Fig. 4 shows the lid of FIG. 3 in side view and in section.

In Fig. 1, a casting device is shown in the detail, which consists of two housing sections 12 and 14, between which a pivotable casting cylinder 18 is arranged about an axis 16. The housing parts 12 and 14 can consist of pluggable wall elements 20, 22 which are connected by aluminum profiles 24. The wall elements 20 and 28 consist of a wood-synthetic resin mixture _. which is temperature resistant up to approx. 36C ° C.

From the casting cylinder 18 go Wellenaϊ. sections 26 and 28, respectively, which are arranged coaxially to the axis 16. The casting cylinder 18- can be pivoted around the shaft consisting of the sections 26 and 28, into one arranged in the upper region of the casting cylinder and on this and adjacent portions of a platen 100 die 66, in which a wax model is embedded, to be able to cast molten metal. The casting mold 66 has a recess 68 to which a projection 98 is assigned. The projection 98 has a trapezoidal shape and is composed of sections 106 and 108, which are formed on the one hand by a region 106 of the circumferential outer upper edge of the crucible 30 and an associated and adjacent projection 108 of the mounting plate 100. Accordingly, an annular space is created between the circumferential projection 98 and the conical end section 110 of the crucible 30 projecting into the casting mold 66, which serves to center the casting mold 66 to be fitted. The mutually assigned projections 98 or recesses 68 form a labyrinth seal which ensures that the melt cannot splash when the casting cylinder 18 is tilted. A corresponding labyrinth seal 104 is shown clearly recognizable in FIG. 2, to which reference is expressly made. It is also evident that the rubber base for the casting mold 66 must have a shape which is composed of the elements provided with the reference numerals 100, 110, 98. For the sake of order, it should also be mentioned that the reference number 102 denotes the connection between the crucible 30 and casting channels of the mold 66.

Solid metal is first introduced into the crucible 66 in order to then melt it. For this purpose, the crucible 30 is surrounded by resistance heaters 32 and 34, which are preferably arranged concentrically around the crucible 30 in the interior 36 of the casting cylinder 18. The interior 36 is surrounded by insulating material 38, which preferably consists of aluminum oxide or a similar material.

The heating elements 32 and 34 are U-shaped and are angled L-shaped in their upper end sections so as to serve as connecting sections for the electrical leads. The heating elements 32 and 34 themselves run to the inner wall of the interior 36 and to the outer surface of the crucible 30

OMPI spaced out what needs special attention. According to a feature of the invention that is to be emphasized, the heating elements 32 and 34 are also made of cermet material consisting of molybdenum disilicide (MoSi ,,) and ceramic additives. The upper angled leg ends of the heating elements 32 and 34 are each fixed by a ceramic holder 40 and brazed on the side opposite the interior 36 with a tube 42 made, for example, of copper. A strand, for example made of copper, is squeezed into the copper tube as an electrical conductor 44 and brazed to ensure a good electrical transition. The choice of materials and the type of connection ensures that oxidation does not occur even at the high temperatures occurring during the melting process, so that an increase in the contact resistance in the region of the elements to be connected to one another is excluded, so that consequently the performance of the heating elements is not adversely affected.

The heating elements 32 and 34, which - as mentioned - are arranged concentrically around the crucible 30, are connected in series, one pole being connected to the wall 46 of the casting cylinder 18 connected to ground, whereas the other pole is connected via an electrical one Terminal 46 is led to the outside to be connected to a voltage source. The electrical connection 46 is constructed according to the invention in such a way that it consists of a metallic core as the side with the ceramic coating surrounding it and the copper coating 48 located thereon. This sheathing 48 can now be brazed to a bearing 52 accommodated in the housing part 12, so that it is ensured that the connection between the casting cylinder 18 and the housing part 12 is insulated in the region of the electrical connection 46 and is pressure and vacuum resistant is trained. The sleeve 52 is of course also welded to the housing wall 46 of the casting cylinder 18. The sleeve 52 essentially connects the shaft section 26 about which the casting cylinder 18 can be rotated. The shaft 28 opposite section 26, which projects into the housing part 14, is connected to a drive, not shown, such as an electric motor, in order to allow the casting cylinder 18 to pivot. The shaft section 28 itself is designed as a hollow shaft and has two channels 54 and 56 arranged coaxially to one another. The inner channel 54 extends into the crucible 30 in order to be able to supply this protective gas. The connection between the channel 54 and a protective gas source takes place via a fixed connection 58 which is connected to the channel 54 via an annular channel 60, so that the connection between the protective gas source and the crucible 30 is continually independent of the position of the casting cylinder 18 is made.

The outer channel 56 is connected via an annular groove 62 to a fixed compressed air source in order to pour the molten metal from the crucible 30 into the mold 66, not shown, and to press it into the cavities, not shown, inside the mold 66 when the casting cylinder 18 is tilted. The design of the channel 56 and the annular groove 62 also ensures that a connection to a compressed air source, which can of course be shut off, can be established continuously via a fixed connection.

No further explanation is required with regard to the mounting of the shaft section 28 and the drive, since on the one hand the ones shown in FIG. 1 technical symbols taken into account give information and other known elements are used.

The casting cylinder 18 can be closed by a cover 64, which is shown in more detail in FIGS. 3 and 4. The cover 64 is arranged on the upper side 70 of the casting cylinder 18 so as to be pivotable about a vertically extending axis 72. The cover 64, which preferably has a circular shape, has a handle 74 by means of which the cover 64 can be raised or lowered. At the same time, the lever 74 is connected to a rotatable cover section 76 and around a horizontal axis 78 by a certain angle

^; RE rotatable. In the exemplary embodiment, a total of four rod-shaped elements 80, 124, 126, 128 originate from the rotatable section 76, the elements 82, 112, 114, 116 in the form of, for example, fixed elements arranged on the top of the casting cylinder 18 Bearing blocks can optionally interact.

This means that the outer sections of the slides 80, 124, 126, 128 then come to rest below a horizontally extending sections 94, 118, 120, 122 which protrude in the direction of the cover 64 when the cover is closed. If the cover 64 is then to be opened, the section 76 must be rotated by the handle 74 to such an extent that the elements 80, 124, 126, 128 are in engagement with the bearing blocks 82, 112, 114, 116 or their front sections 94, 118, 120, 122. The sliding elements have different functions. They are divided into a safety slide or first slide 80 and the actual locking slide or further slide 124, 126, 128. If, for example, the cover section 76 is rotated counterclockwise via the handle 74 in the exemplary embodiment, the further sliders 124, 126, 128 are first moved radially inward in order to reach out with the bearing blocks 112, 114, 116 without the Slider _. 80 is moved. This means that the slide 80 with its outer end is still below the section 94 of the bearing block 82, so that a sudden and uncontrolled opening of the cover 64 is avoided.

This is an advantage if an overpressure should have built up inside the device. Only when the handle 74 and thus the section 76 is rotated further counterclockwise is the slide 80 also moved radially inward in order to reach the bearing block 82. Only then can the lid be opened completely. The slides 80, 124, 126, 128, which can be referred to as rod-shaped elements, are arranged in a recess in the cover 64, such as groove 84, 130, 132, 134, so as to be radially displaceable with respect to the pivot point of the cover section 76, and point to them in relation to FIG Bearing blocks 82, 112, 114, 116 facing away from a projecting pin or bolt 86, 136, 138, 140, which with guide recesses 88, 142, 144, 146 in the rotatable section 76 of the cover 64 preferably have a curved shape work together. The guide recesses 88, 142, 144 assigned to the locking slides 124, 126, 128 consist of three sections, of which a central section 92 — illustrated on the guide recess 88 — extends at an angle to the radius starting from the pivot point 78 of the section 76. Furthermore, outer (second and third) sections 90, 92 run on different circumferences with respect to the axis of rotation 78 as the center.

With regard to the safety slide 80, the guide recess 146 is formed in such a way that two sections 148 and 150 are provided, the first of which is long and runs on a circular circumference, whereas the shorter second section 150 describes an angle to the radius. The dimensioning of the individual sections to one another is selected such that the pin 86 extending from the slide 80 is moved in the first section 148 of the guide recess 146 until the other slides 124, 126, 128 are fully engaged when the cover 64 is opened the assigned bearing blocks 112, 114, 116. The pin 86 only reaches the second section 150 of the guide recess 146 when the slide 80 is to be displaced radially inward so that it is no longer hindered by the section 94 of the bearing block 82. Only then can the lid be opened.

OMPI -WIPO In addition, it should also be noted that to fix casting molds 66 of different dimensions, these interact with a cover spring (not shown) with a heat shield. This ensures that the mold is always fixed precisely over the crucible.

The teaching according to the invention provides a casting device which is optimally designed in terms of its mode of operation without the need for structurally complex measures. The choice of the heating elements and their connection to the electrical connections ensures that no high contact resistances build up even after a large number of operating hours, so that the efficiency remains unchanged. Because the resistance elements are arranged essentially freely in the interior of the casting cylinder receiving the crucible, the heat can be radiated freely, which increases the efficiency.

By constructing a shaft section as a hollow shaft, the problem of gas or compressed air supply is solved in a structurally simple manner. Finally, the lid design offers a secure closure of the casting cylinder, and because of the structurally simple components, there are not only ease of maintenance, but also manufacturing advantages. A particular advantage of the lid construction is that the lid is opened in two stages in order to compensate for pressure when opening, without the lid being able to open in an uncontrolled manner.

Furthermore, the labyrinth seal provided in the support area of the casting mold ensures that splashing and thus loss of the melt is prevented when the casting cylinder is tilted.

Finally, there is the possibility - without leaving the scope of the invention - the casting device according to the invention z. B. also in the jewelry industry or general casting technology and in the nuclear field.

Claims

 - Claims: 1. Casting device for in particular dental work, comprising a rotatable around a horizontally arranged shaft, one surrounded by preferably U-shaped heating elements Casting crucible comprising melting crucible and at least one electrical connection leading from the casting cylinder, characterized in that each heating element (32, 34) is a freely radiating resistance conductor, the free upper leg of which is angled and held by clamps (40) made of ceramic material and with each a connecting tube (42) is brazed, from which in turn a flexible current conductor (44) extends, one of which is connected to the electrical connection (46) leading to the outside of the casting cylinder (18). 2. Casting device according to claim 1, characterized in that the electrical connection (46) connected to the flexible current conductor (44) extends coaxially to the shaft (26) of the casting cylinder (18) and preferably consists of a metallic core as a conductor with a ceramic and copper sheath ( 48) exists. -ti - 3. Casting device according to claim 1 and claim 2, characterized in that the electrical connection (46) not surrounding (opposite) shaft section (28) as a hollow shaft with separate coaxially arranged channels, for example protective gas or compressed air (54, 56) is trained. 4. Casting device according to claim 2, d a d u r c h g e k e n n z e i c h n e t that the ceramic and copper casing (48) with a Connection surrounding portion (52) of the shaft is brazed. 5 «Casting device according to claim 3, so that the inner protective gas channel (54) is connected to the crucible (30). 6. Casting device according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the heating elements (32, 34) essentially from Molybdenum disilicide exist. 7. Casting device according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the connecting tube (42) is a copper tube and the current conductor (44) is a copper conductor. 8. Casting device according to claim 1, characterized in that around the melting crucible (30) arranged Ver¬ cover (64) on the housing surface (70) bearing blocks (82, 112, 114, 116) are arranged, with a rotatable section (76) of the cover (64) actuated elements (80, 124, 126, 128) slidably arranged in the non-rotatable area of the cover interact. - / s-- 9. Casting device according to claim 8, characterized in that the displaceable elements (80, 124, 126, 128) in a recess in the lid (64) such as groove (84, 130, 132, 134) are guided and each have a projecting pin or Bolt (86, 136, 138, 140) which interact with a guide recess (88, 142, 144, 146) which preferably runs in a curved manner in the rotatable section (76) of the cover (64). 10. Casting device according to claim 8, so that the lid (64) is held in at least one (first) element (80) in a position that can be raised to a limited extent with the remaining (further) elements (124, 126, 128) already unlocked. 11. Casting device according to claim 9 and 10, characterized in that the curved guide recesses (88, 142, 144) for the further elements (124, 126, 128) each have an oblique to the radius starting from the pivot point (78) ver¬ running radius and are composed of outer (second and third) sections (92, 90, 96) running with the center of rotation of the section (76) having circular sections as the center. 12. Casting device according to claim 9 and 10, characterized in that the guide recess (146) for the first element (80) on a circular circumference with the axis of rotation (78) as the center point long first section (148) and an oblique to this Has a radius-extending second section (150), wherein when the pin (86) extending from the first element (80) is displaced in the first section, only the further elements (124, 126, 128) can be unlocked and when displaced in the second section (150) the first element can be unlocked. OMPI -ii »Pouring device according to claim 1, so that a labyrinth seal (68, 98) is provided between the casting mold (66) and the support area (100) assigned to it.