| Title of Invention | "AN APPARATUS AND PROCESS FOR MANUFACTURING DENTAL ALLOY BUTTONS AND OTHER CASTINGS" |
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| Abstract | This invention relates to an apparatus for manufacturing dental alloy buttons and other castings comprising wax pattern assembly in a cluster design for crucible mould configuration, a mould in a mould pre-heating furnace, said mould having a melting cup, induction melting coil for heating a remelt bar-stock, alloy-plug to control the timing of automatic pouring of molten dental-alloy into the clustered casting-moulds for insitu melting and casting of dental alloy buttons, implants and other castings in integrally invested crucible mould shell configuration. |
| Full Text | This invention relates to an apparatus and process for manufacturing dental alloy buttons and other castings. Casting is one of the most widely used methods for the fabrication of metallic restorations of teeth. For making an exact matching restoration for the lost tooth, a pattern of the lost tooth structure is first constructed in wax. The wax pattern is then surrounded with a ceramic investment. After the investment has hardened, the wax is removed and the molten metal is poured into the cavity left by the wax. If properly made, the resulting structure is a remarkably accurate duplication of the pattern of the lost tooth. Dental clinics prefer to have the appropriate alloys in the form of small buttons weighing around 8 grams for the convenience of melting small quantity in tiny crucibles using a gas torch. These alloy buttons are generally produced from remelt bar-stock employing investment mould and vaccum-induction or air-induction melting furnaces which involves relatively high costs. Conventional induction melting and casting facilitites are not only costly to establish but also consume enormous energy and raw materials to produce clinically acceptably alloy buttons. At the same time, such a process does not give attractive metal-yield. There is, therefore, a need for a technique/process and an apparatus by which melting of ingot material and casting of alloy buttons could be done in a time & cost saving manner. The primary object of this invention is to propose an apparatus and process fop manufacturing clinically acceptable dental alloy buttons and other castings where the raw materials, consumables and energy consumptions are much-less compared to existing practice. Another object of the present invention is to provide a wax assembly design to achieve high metal yield. Yet another objectof the present invention is to propose an integral time- & cost-saving method for melting of alloy ingot and casting of dental alloy buttons. Still another object of this invention is to propose a design and use of a suitable 'alloy-plug' arrangement to control and ensure automatic pouring of molten alloy into casting mould assembly, without altering the alloy characteristics. yet another object of this invention to propose3" apparatus,and discloses its working process, to melt" and cast alloy bar stock in a ceramic investment mould without requiring separate melting crucible or pouring tundish. Following are the broad steps of the process envisaged in use of the apparatus disclosed in the present invention : a) fabrication of alloy plugs by 'known methods' employing induction melting and casting into preheated investment shells having nearly cylindrical mould cavities, b) fabrication of wax pattern assembly for dental alloy button and implants, by 'already known methods', c) investment shell moulding for insitu cruicible- mould configuration, and d) mould pre-heating, alloy melting in 'the apparatus kept in the furnace, automatic pouring of molten alloy into mould(s) when the 'alloy-plug' after melting has cleared the path for molten alloy to flow and subsequent insitu casting of alloy buttons and other castings. This process has the advantage that clean castings of dental buttons and other castings can be produced without employing costly crucibles, ceramic filters, tundish etc; at more than 90% metal yield avoiding dross and ceramic inclusions. BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWING Fig 1 is the plan and elevational view of a wax pattern assembly for casting dental alloy buttons. Fig 2 is a vertical sectional view of the apparatus for casting dental alloy buttons in the integral crucible mould assembly made with the help of above mentioned wax pattern assembly of fig.l. Detailed Description of a Preferred Embodiment First of all, a wax pattern assembly is fabricated , by any of the methods well known in the prior art. Fig-1 shows the schematic of a wax cluster comprising the patterns of a melting crucible (l), a central sprue (2) and about a thousand dental alloy button patterns which are stacked in several columns (3) and clustered in a hexagonal array for maximum packing and equal spacing from one another. Any other design of the clustered array can also be used with this invention. There is a steel tube (4) along the axis for imparting rigidity and for ease of manipulation during shell making. A cylindrical step (5) is provided between the top of the central sprue and the bottom of the crucible (1) for sealing the open bottom with the help of an * alloy-plug' during induction melting. ( The alloy-plug is the part number (11) shown in Fig-2.) There are six de-waxing holes (6) placed peripherally at the bottom of the wax assembly. Crucible-mould integrity in the investment shell is achieved by four supporting legs (7) which of course do not connect the crucible and mould cavity internally. The 'alloy-plug' is made from cobalt and chromium alloy, containing 10% of chromium by weight in the alloy. It is made into a short cylinderical shape which firmly fits into and seals the inner space in the central sprue (2). Fig-2 shows the overall apparatus where the mould (8) has been inserted into the mould pre-heating furnace (9) . The remelt bar- stock (10) is kept inside the melting cup of the mould. (1) . A cobalt - Chromium alloy plug (11), described above, is kept underneath the ingot to plug the sprue (2) during melting. The induction melting coil (12) is positioned around the ingot. An insulation sleeve (13) is placed coaxially between the induction coil and the cruicible as a protection for the coil. A ceramic tube (14) is inserted upto the insulation sleeve for passing argon around the ingot during melting down. A thermocouple (15) is placed in the mould heater to measure the shell temperature. Another thermocouple (16) is placed inside the mould, at its bottom, to indicate the melt temperature; while the pouring time is simultaneously recorded sepeperately. The mould is kept on a pedestal (17) for loading and unloading. The preheating furnace temperature is maintained at the desired level, matching with the foundry characteristics of the dental alloy used for casting of alloy-buttons, with this apparatus. The mould is inserted into the furnace alongwith the alloy plug (11) and ingot (10) in position. The induction power to the induction coils (12) is turned on, as soon as the mould temperature as registered by the thermocouple (16) reaches the desired level. At the same time, Argon gas is passed around the ingot, through the ceramic tube (14). As per the design of the apparatus, disclosed in this invention, the solid substance of the alloy plug (11) comes in contact with the molten pool, i.e. molten dental alloy, only when the entire remelt bar including its bottoms becomes fully molten. Melting of 'alloy-plug' therefore occurs when the bath temperature reaches the pouring temperature i.e. the melting point of the 'alloy-plug'. In view of this requirement the material and size of the alloy-plug is carefully designed. Typically for 20 mm diameter of the central sprue (2) , 3 mm thickness of alloy-plug of 30 mm diameter made from cobalt-chromium, containing 10% chromium by weight, is found to be very adequate to provide optimum pouring temperature of typical dental alloys and to provide for their automatic pouring using the apparatus disclosed in this invention. Such a arrangement facilitates automatic pouring of the molten dental quality alloy into the mould cavity underneath.Passing of Argan gas through the ceramic tube (14) is stopped when pouring starts. Allowing reasonable time after the pouring, say about 2 to 10 minutes, the mould is withdrawn from the furnace for further cooling and loading of next mould alongwith its alloy plug and remelt bar-stock. Although the invention has been described with reference to a specific embodiment thereof, it will become apparent to those skilled in the art that numerous modifications and variations can be made within the scope and spirit of the invention for obtaining various types of castings of selected shape and sizes using the apparatus disclosed in this invention. I CLAIM: 1. An apparatus for manufacturing dental alloy buttons and other castings comprising wax pattern assembly in a cluster design for crucible mould configuration, a mould in a mould pre-heating furnace, said mould having a melting cup, induction melting coil for heating a remelt bar-stock, alloy-plug to control the timing of automatic pouring of molten dental-alloy into the clustered casting-moulds for insitu melting and casting of dental alloy buttons, implants and other castings in integrally invested crucible mould shell configuration. 2. An apparatus as claimed in claim 1 comprising a movable pedestal to load & unload the integral shell mould-crucible configuration, a thermocouple placed inside the mould heater to measure the shell temperature and another thermocouple placed inside the mould at its bottom to indicate the temperature of melt-pouring. 3. An apparatus as claimed in claim 1 comprising a movable ceramic sleeve to protect the coil from the heat of mould heater and molten alloy. 4. An apparatus as claimed in claim 1 wherein said ware cluster comprising a melting crucible, a central, sprue, a plurality of dental alloy button pattern stacked in several columns clustered in a array for maximum packing, a central step provided between the central sprue and the bottom of the crucible for sealing the bottom with the help of an alloy-plug and with dewaxing holes at the bottom of the wax assembly. 5. An apparatus for manufacturing dental alloy buttons and other castings substantially as herein described and illustrated. |
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2874-del-1996-correspondence-others.pdf
2874-del-1996-correspondence-po.pdf
2874-del-1996-description (complete).pdf
| Patent Number | 219885 | |||||||||
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| Indian Patent Application Number | 2874/DEL/1996 | |||||||||
| PG Journal Number | 28/2008 | |||||||||
| Publication Date | 11-Jul-2008 | |||||||||
| Grant Date | 14-May-2008 | |||||||||
| Date of Filing | 19-Dec-1996 | |||||||||
| Name of Patentee | CHIEF CONTROLER RESEARCH & DEVELOPMENT | |||||||||
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| PCT International Classification Number | A61C 13/20 | |||||||||
| PCT International Application Number | N/A | |||||||||
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