US2570355A - Metal alloy - Google Patents

Description

Patented Oct. 9, 1 951 i; 1.11

A UNITED STATES. PATENT 1 OFFICE T idney Mass. 5 I I No Drawing. Application April 9, 1949, Serial N0. 86,589

My invention relates to improvements in metal alloys and is directed more particularly to a metal alloy which is especially adapted for casting dental bridges and like appliances.

This application is acontinuation in part of an application bearing Serial Number 44,595 and filed by me on August 16, 1948, nowabandoned. The principal object of my invention is the provision of a new casting alloy which is; adapted for dental appliances and the like, which is highly resistant to corrosion encountered in investments of plaster of Paris and the like, which possesses good ductibility enhancing the working characteristics thereof; which has a pleasing color and appearance as well as good machinability, and Whichhas a low melting point of about 2300 F.

The novel features of my invention are accomplished by the combining of certain elements which are selected for their individual characteristics and function and combine for producing an alloy possessing superior properties for the casting of dental bridges and the like.

- The alloy of my invention includes elements within the percentage ranges as follows: I

"Carb0n 0.50% Max. 'Manganese 2.0% Max. -Silicon 2.0% Max. Nickel 50.0--70.0% Chromium 10.0-20.0% Copper 3.020.0%

Molybdenum 3.0-4.0%

,Aluminum 0.02-2.0%

Titanium r -s--- 1.0% -Max. Zirconium 1.0% Max. Silver l 2.0% Max.

Carbon is primarily an impurity necessarily tolerated in my alloy. Whenever possible, the carbon content isheld to approximately 0.05% as I' have found that an increase in the carbon content tends to increase the hardness and strength of the alloy and that it also tends to decrease the ductility and corrosion'resistance. I have found that the carbon content should not exceed 050% under any conditions.

Manganese servesas an aid to the melting of the alloy. Furthermore, as is Well known, man- .ganese is used to .clean up a melt prior to tapping. It increases the fluidity of the alloy per- =mitting lighter sections to be successfully cast. I have found that the manganese content should not exceed 2.0% under any conditions.

Silicon, as manganese, serves as an aid to the melting of thealloy as well a tone alloying. additionS. It too is used to cleanup a me t prior to Y 1 Claim. (01. 75-471) tapping. Furthermore, it serves to increase the corrosion resistance of the'resistant alloy in oxidizing media. As with manganese, silicon erves to increase the fluidity of the alloy permitting lightersections to be successfully cast. I have found that the silicon content should not exceed 2.0% asa maximum.

Nickelserves as a very excellent base to which the alloying additions may be made. Nickel possesses fair corrosion resistance qualities aridja reasonably low melting point. The other alloying additions may be readily added to the nickel base, as will presently be observed, since all are readily soluble in both molten and solid nickel.

Ifdesired, cobalt in like quantity may be substituted for nickel, or these elements may be used incombination with each other within the scope of my invention. Cobalt behaves very similarly to nickel although cobalt bearing alloys are more difiicult to machine. 1

Chromium is added in quantities from 10 20% in order to increase the corrosion resistance of thematerial. When the chrominm content is less than'10%, the material is not corrosion resistant enough, particularly in the weak solutions of lactic acid present in the human mouth.

Chromium contents greater than20% areavoided in order to maintain a reasonably low melting point and to avoid the difliculties or the chromium combining with the sulphur in plaster of In my alloy, I provide a maximum of 20.0%

1 copper whereas other alloys known in the art employ a maximum of 10.0%. In such priorart alloys, the copper content is held below 10.0% to prevent free copper from being thrown from. the solution when the alloy solidifies.

these prior art alloys will not prevent the sulphur in gypsum bound investments from combining 'with the surface of the casting. Furthermore copper in amounts below 20% will in- I crease the corrosion resistanceof the alloy in the human mouth.

- combination of aluminum and copper in my alloy permits higher copper additions to be made without the subsequent precipitation of free copper. The copper and aluminum must be added in the form of a master alloy shortly to be described as I have found that additions of metallic copper and aluminum will not result in the desired alloy. g

I have- -found that copper in the amounts present in jectiona-ble features.

loys of other known types. I have found that the Zirconium content should not exceed li'%.

The silver is added to furthertenhance: its core rosion resistance. I have found that the silver content should not exceed 2.0%.

A minimum of iron is desired so that none is intentionally included. Iron would react unfavorably with any 3 sulphurpresent in theinvestm'ent in which the alloy is cast-and would tend to raise the melting point both of which areob- Particularly desirable results have 'been obtained where the proportions are as follows:

Carbon 0.05% Max. Manganese s d 0.60%, Max. Silicon n a 0.60% Max. Nickel 55.0'-62.0% Chromium 14.0-17.07; Jopper 13.0-20.0%

Molybdenum 3.040% Aluminum 0.02410 Titanium. 0.40-0.60"%

Silver 0.600.80%'v More specifically; the proportions as follows provide an alloy which is easily andreadily'usable for producing dental bridges and thelike:

has very marked resistance to the action of sulphur which is present in the usual investments inwhich casstings are made. Plaster of Paris is an ordinary -material' used for investments; Also, the alloy is very low in iron which is nec-- essary to overcome corrosion and hold the melt- "ing point below a range where expensive and complicated equipment must be used.

Castings made from the alloy when taken from the mold have a pleasingly bright and clean appearance, are ductile, and possess good machinef ability.

The combination of elements" provide-a casting having an outer layer or skin which is rich in 1 copper and aluminum, which is desired for its 1 resistance tosulphur attack in the-mold. This is-only a fewmillionths ofan inch thick and 7 is subsequently polished off.

The elements in the specific proportions prothe strength i and hardness as compared with the carbon-alrabout 2300 F. to facilitate ready and easy casting in ordinary investments, presents a brilliant appearance, has marked resistance to corrosion, and possesses a very desirable ductibility and machineability.

The base composition used for producing my alloy comprises:

--Carbon:. 0.05% Max. Manganese 0.60% Max. Silicon 0.60% Max. Chromium 14.0-17.0% Copper 13.020.0% Aluminum 0.020.10% Nickel The balance This base composition has uses in itself. It

j maybe used in wire for resistance furnaces con- The alloy is high in copper and: aluminum and taining a sulphur bearing atmosphere as it has a high resistance to sulphur attack.

V The as cast tensile properties of this base composition are:

The copper and aluminum mus-tbe added in the form'of' amaster alloy addition ofthe following' composition:

Aluminum .9.0-1l.0%

Iron- 0'.9.0--1'.0 Copperbalance If the copper addition is not made in this manner, there is a marked change in the properties of the resultant alloy. Additions of metallic copper and aluminum will not result in the desired alloy. An alloy, having the same nominal composition, but with the copper and aluminum additions of each separate metal will be hard and brittle. Furthermore, free copper will be thrown out of' solution in the form of small nodules of copper.

When the. additions of the master alloy of copper, aluminum, and iron are made; suitable allowances. must be made for oxidation losses. A master alloy addition of 17.0% copper plus. 1.7% aluminum will result in a residual copper .and aluminum of approximately 16% and 0.05% respectively.

While the base metal composition possesses unique: and valuable properties, it is generally too soft and-ductile for dental usage. Other alloying elements. such as molybdenum, titanium, zirconium and silver are usually added to both further enhance its corrosion resistance, strength and hardness.

The-hardness and strength may also be further increased by the addition of more aluminum either by itself or in the form of a master alloy such as nickel-aluminum.

Thecontrol ofhardness and strength may also beefiected by the use of a so-called hardener melt having nominally the same composition as the base melt except that the aluminum and copper are added separately. Suitable combinations of hardener and base melts may then be made to procure any desired hardness. Oxidation that occurs during the melting together of these two types of melts will insure that no free copper will be thrown out of solution upon subsequent solidification of the combined melts.

The invention may be embodied in other vide an alloy which has a low melting point of specific forms without departin from the essential characteristics thereof. Hence, the present embodiments are therefore to be considered in all respects merely as being illustrative and not as being restrictive, the scope of the invention being indicatedby'the appended claims rather than by the foregoing description, and all modifications and variations as fall within the meaning and purview and range of equivalency of the appended claim are therefore intended to be embraced therein.

- What it is desired to claim and secure by Letters Ratent of the United States is:

l A corrosion resistant casting alloy for dentures consisting of elements having proportions as follows: carbon no more than 0.05%; manganese no inore'than 0.60%; silicon no more than 0.60%; nickelbetween 55.0% and 62.0%; chromium between 14.0% and 17.0%; copper between 13.0% and 20.0%; molybdenum between 3.0% and 4.0%; aluminum between 0.02% and 0.10%; titanium between 0.40% and 0.60%; zirconium between 6 0.40% and 0.60%; silver between 0.60% and SIDNEY LOW.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,115,239 Parr Oct. 27, 1914 1,838,130 Beckinsale Dec. 29, 1931 2,309,136 Neiman .1 Jan. 26, 1943 FOREIGN PATENTS Number Country Date 255,919 Germany Jan. 23, 1913 256,361 Germany Feb. 6, 1913 265,076 Germany Sept. 30, 1913 18,212 Great Britain July 9, 1914 of 1913