US2206502A - Shaped material for casting dentures - Google Patents

Description

Patented July 2, 1940 TATES Harold A. Bell! by mesne WED MATERIAL FOR CASTING ENTURES Norristown, Pa", assixnor, cuts, to Nobilium Products,

Inc., Philadelphia, Pa., a corporation of hennylva No Drawing. Application September 29, 1938,

Serial No. 232,346

1 Claim.

This invention relates generally to dental appliances and has particular reference to cast metallic dentures such as plates, bridges and inlays. More particularly this invention relates to a compressed mixture of metallic powders which can be melted for making cast dentures.

Gold, platinum, and other precious metals and alloys of precious metals have long been used for the manufacture of cast dentures. More recently alloys of non-precious metals have been used for this purpose and several patents have been issued covering the chemical analyses of non-precious metal alloys adapted to the manufacture of dental appliances. The more frequently used alloys of this type contain as their main constituents one or more metals from the group comprising cobalt, chromium, nickel and iron, and lower percentages of metals from the group comprising manganese, silicon, vanadium, tungsten, molybdenum, beryllium, titanium, antimony, arsenic, aluminum, boron and carbon.

The adaptability of certain non-precious metal alloys to the processing of cast dentures has been proven, and they have replaced the precious met als and precious metal alloys in this held to an appreciable extent. The non-precious metal alloys produce sound castings, and the dentures are lighter in weight than similar dentures made of precious metals. They can be polished to a smooth mirror like finish, and they take and retain a high metallic luster. Castings of the nonprecious metal alloys have the physical qualities essential in a satisfactory denture-strength, resiliency, toughness and absence of brittleness, and they are highly resistant to corrosion, to tarnish and to attack by mouth liquids and foods.

The manufacture of cast dentures is a more or less specialized field, because the dentures must fit in minute detail the individual cases for which they are designed. Briefly the manufacturing process consists in making a wax pattern of the denture; investing the pattern in a suitable refractory mold after it has been so waxed as to provide the mold with sprues and a pouring cup; eliminating the wax fromthe mold by heating at a relatively low temperature; firing the mold; and then casting the molten metal into the heated mold.

The casting of non-precious metal alloys is frequently done in a centrifugal casting machine equipped with a rotating arm on the end of which the heated mold is placed in close proximity with a crucible in which the alloy is melted and from which the alloy is thrown into the mold. The alloy, in the form of small cubes, rods, or other pieces of convenient size and shape,

' lengths.

(or. 29-l60.5)

usually weighing from flve to ten pennyweight (approximately 7.5 to grams) each, is placed in the crucible and melted by an oxy-acetylene flame or other suitable means. The small pieces of alloy used for making dental castings are often called ingots by those engaged in the industry, and therefore the word ingot as used herein is to be construed as having only that meaningnamely, an ingot is a piece of metal or alloy, of suitable size and shape, used for the manufacture of cast dentures. One or more ingots are used per casting, depending upon the size and shape of the denture and the manner in which the mold is prepared.

The ingots of non-precious metal alloys for the casting of dentures are normally prepared by melting and alloying in an electric furnace or other suitable heating equipment the proportionate amounts of pure metals required to yield the desired analysis. If iron is desired in the ingot, one or more of the ingredients may be added as the ferro-alloy of that metal. After an alloy of the desired anlysis has been prepared in the furnace, it is cast into a sand mold so as to yield bars of suitable cross-sectional shape and area, and the bars are broken or cut into suitable Dimensions are chosen so as to supply ingots of convenient size and weight, for example, an ingot may be a cylinder in diameter by long, or it may be a cube.

The preparation of ingots of non-precious metal alloys for dental castings accomplished by the above procedure has the following disadvantages:- 1) the installation cost and the maintenance ofv heating equipment, (2) the fuel or power cost of melting and alloying, (3) the chemical and metallurgical control needed to maintain close analytical and physical specifications, (4) casting difliculties due to the high melting points of the alloys used, (5) there is a loss of metal in the gates and risers when casting it into bars, although this metal is later reclaimed by remelting, and so requires further expenditures, and (6) the rods must be broken or cut into small ingots. If cutting with an abrasive wheel is used, a further loss of metal is involved.

The preparation of ingots of a non-precious metal alloy suitable for dental castings in for instance an arc type electric furnace, is not therefore a simple matter. As a rule such alloys have low carbon contents and high melting points. They are not prepared simply by melting and alloying the proportionate weights of the desired metals. The proper protective and refining slags must be prepared either before-hand or in the smelting to avoid the loss of metal by oxidation or migration to the slag, and to control the ill the bath in order to obtain a product which can later be cast or worked into a suitable product.

- Additions to promote fluidity and facilitate casting may be needed, necessitating a compromise on analysis and on physical properties. The molten alloy is then cast into bars of suitable cross-sectional area and shape and the bars are broken or cut into the ingots used for casting dentures. The process must be carefully regulated to produce an alloy of uniform chemical analysis and physical characteristics, and to yield bars which are free of segregations and metallic inclusions. The bar casting and the breaking operations involve the expenditure of time and labor, and are accompanied to a greater oi! lesser extent by a loss of alloy.

It is among the purposes of this invention to eliminate the above enumerated disadvantages in the preparation of ingots for the casting of dentures of non-precious metal alloys.

It is a further purpose of this invention to provide shapes of suitable size and configuration for making small castings of non-precious metal alloys in the form of compressed tablets, pellets or lozenges containing in intimate and uniform admixture the proper proportions of metallic ingredients to yield a casting of the desired analysis. This purpose is accomplished by dry mixing the desired proportions of the metallic ingredients in powder form until uniformly admixed and commingled, and pressing the mixture into merchantible self-retaining shapes, such as tablets, pellets, or lozenges, of convenient size and weight.

The metallic ingredients of my mixture are powdered metals or powdered alloys which, when mixed in the proper proportions and melted, are adapted to yield castings of a desired analysis.

Examples of metals which I may use in powdered form are cobalt, chromium, nickel, iron, manganese, silicon, vanadium, tungsten, molybdenum, beryllium, titanium, antimony, arsenic, aluminum, and boron. Examples of alloys which I may use in powdered form are ferro-chromium, ferromanganese, ferro-silicon, ferro-vanadium, and others. The scope of the invention permits the use as a metallic ingredient of the mixture of any powdered metal or powdered alloy having a chemical composition which adapts it, either alone or in combination with other powdered metals or powdered alloys to produce a casting of a desired analysis.

I prefer to use metals of a high degree of purity and in a finely divided state. The metals should be in such a state of subdivision that they can be passed through a U. S. Bureau of Standards No. 60 screen, and preferably so that they will pass a U. S. Bureau of Standards No. 200 screen. The invention is however not limited to the use of metals of the preferred fineness and I have found it practical to incorporate into the pellets up to 40% by weight of the mix of larger size particles, for example, particles which will pass a U. S. Bureau of Standards No. 10 screen and be retained on a U. S. Bureau of Standards No. 12 screen. Powders of metals and of metal alloys of suitable composition are commercially available, the analytical specifications of the metallic ingredients of the mixture being determined by the specifications of the desired alloy.

For the production of satisfactory dentures the castings must be uniformly alloyed, solid, and free from oxide inclusions and blow-holes. For this reason I have found it advantageous to include in the mixture from which the pellets are made suitable fluxing agents, deoxidizing reagents and degasifying reagents. As fluxes I may use borax, fluorspar, lime, or mixtures of fluorspar and lime: the deoxidizing agents usually used in metallurgical practice, such as manganese and silicon are applicable to the process of this invention; and the presence of very small percentages of aluminum tends to eliminate both oxides and gases.

To illustrate the manner in which the invention is practiced four examples are given below, to which examples the invention of course is by no means limited. In these examples the intimately mixed and finely divided starting materials were compressed into tablets approximately one-half inch in diameter and one-eighth of an inch thick by the application of pressure to a regulated quantity of the material in a suitable die, the tablets being subjected to a forming pressure of 1000 pounds. In every case tablets of sufllcient physical strength for handling, shipping, etc. were obtained. When the tablets were used in the processing of cast dentures, full sound castings resulted.

The analyses of the metal powders were as follows:

In the tabulations below are listed the analyses of the alloys desired, the mixtures used, and the I analyses of the resulting castings.

Analyses desired Example I Exafiiple Exaimiple Exfiple Percent Percent Percent Percent Chromium 30. 18. 00 30. 00 30. 00 c 26. 00 22. 00 Cobalt- 24. 00 55. 00 60. 00 60 00 Iron 7. 50 7. 50 Tungsten. 17. 00 3. 00 0. 50 0. 50 Si1icon 1. 50 l. 00 0. 20 0. 20 Vanadium 0. 50 bon 0 25 (max.) 0.40 0.50 0 60 Mixtures used Example I Exafiiple ExarInple Exlalmplo Parts Parts Parts Parts Glaromium pow- 31. 0 18. 31

er. Nickel powder 26. 0 22. 0 Cobalt powder.... 24. 5 56. 2 61.2 61. 2 lion powder 7. 0 Ferro chromium 24. 5

powder. Tungsten powder- 17.0 3.0 0 5 0. 5 Silicon powder.. 1. 75 1. 25 0 Vanadium pow- 0.

er. Aluminum pow- 0.

- der. Lime 0. Fiuorapar 0. Borax Analyses of castings Example I EXBIIIDPIB Exgple Exariaple Percent Percent Percent Percent Chromium 29. 64 18. 30 31. 70 83 Nickel 25. 97 22. 12 24. 06 55. 76 59. 94 60. 21

alloyed at temperatures in the neighborhood of 2700 F. to 2900 R; and as the result of their use the casting procedure was simplified because of the absolutely uniform composition of the tablets, and because the tablets contained their own fluxes and thus eliminated the necessity for haphazardly adding "a pinch of flux at the willof the processor, as is usually done when casting ingots of alloys. Because of the uniformity of the starting material, and the greater simplicity of the procedure, a more uniform product is possible than with the use of ingots of nonprecious metal alloys.

In the making of the tablets or pellets of this invention dry pressing the mixture without the addition of binders is the preferable procedure. It is within the scope of this invention, however, to include in the mixture such binding agents as dextrin, gum, starches, sulfite, pitch, sodium silicate, etc. for the purpose of adding strength to the pellets. Such binders, when used in small quantities have no appreciably deleterious effects on the products and permit the formation of the tablets or pellets at somewhat lower forming pressures, but as tablets of satisfactory physical strength can be made by the use of pressure alone, I prefer to work without additional binders.

Having thus described and exemplified my invention, to which examples the scope of the invention is by no means limited, I claim:

As a new article of manufacture for prosthetic dentistry, a compressed mixture for casting dentures consisting of chromium powder about 31 parts, cobalt powder about 61.2 parts, iron-bearing powder about 7 parts, tungsten powder about 0.5 part, silicon powder about 0.45 part, aluminum powderabout 0.20 part, and borax about 0.50

part.

A. HEILIGMAN.