US1364353A - Method and means for holding diamonds during the polishing operation - Google Patents

Description

UNITED STATES PATENT OFFICE.

CLYDE J'. COLEMAN, OF NEW EROCHELLE, NEW YORK, ASSIGNOR TO STERN-COLEMAN DIAMOND MACHINE COMPANY, INC., OF NEW YORK, N. Y.

METHOD AND MEANS FOR HOLDING DIAMONDS DURING THE POLISHING OPERATION.

N 0 Drawing.

ing Diamonds During the Polishing Operation, of which the following is a specification.

The invention relates to a new process and means for holding diamonds during the "polishing thereof and the object of the in vention is to provide a process and means which Wlll hold diamonds during pollshmg by adhesion to the polished faces thereof, as

well as to the natural or unpolished surface.

This application is a continuation in part of my prior application, Serial No. 74,076, filed January 25, 1916, and Serial No. 34,161, filed June 15, 1915, and a continuation in part of my prior applications, Serial No. 808,280, filed December 22, 1913; Serial No.

808,279, filed December 22, 1913; Serial No.

710,622, filed Jul 20, 1912, and Serial No. 710,621, filed Ju y 20, 1912, the invention being claimed broadly herein, and more specifically in said prior applicatiops.

In the polishing of diamonds, it has been the practice to hold small diamonds and until recently large stones also in the polishin tool by partially embedding it in a body 0 metal in a semi-molten state, contained in.

a small brass basin or dop, the diamond being held in position by the metal after the metal has cooled. This method suffers from the disadvantage that it is necessary from time to time to soften the metal and readjust the diamond to expose a different part thereof for polishing, as it is not possible to expose at one time all parts of the diamond on one side of the girdle line. It is also common practice to lock the larger stones in a clamping device, but this device is very difficult to adjust so as to hold the diamond at the correct angle, as well as being subject to the disadvantages noted above. The difliculty in holding diamonds during the polishing operation, as distinguished from other precious stones, is due to the extreme hardness of the diamond, which necessitates applying great pressure, with resultant great friction and generation of great heat. Diamond polishing is particularly a difficult operation and unlike any other lapi- Specification of Letters Patent.

Application filed November 20, 1916.

Patented Jan. 4, 1921.

Serial No. 132,277.

dary work, because with all other gems there is something harder than they are, which will easily abrade them and not require any special speed or pressure to polish them, but the diamond being the hardest known substance, it must be polished with its own dust. This requires great lap speed, great pressure and also a precise grain presentation to the direction of movement of the lap, with the result that a high temperature is generated and often an almost in stantaneous rise from low red heat to white red heat is developed when a hard spot is encountered and then dropping back suddenly to the normal red heat.

The polishing of the diamond is, therefore, a radically different proposition from the polishing of other stones or semiprecious gems, with the latter so little heat is generated and so little pressure required, that ordinary silicious or wax adhesives may be used. Certain cements have been used to hold diamonds during the roughing out or bruting operation, but in such cases, the cement holds the diamond by anchorage or mechanical interlocking with the irregularities in the surface of the diamond, and not by adhesion to the surface, and hence such cements are useless for holding diamonds during the final or polishing stages, because they have not sufiicient adherence to the polished faces.

I have discovered, however, that if an adhesive be compounded which contains suflicient of an oleaginous" constituent and matter giving it a certain relative malleability and being sufficiently refractory, such an adhesive will adhere satisfactorily to the polished surfaces of the diamond so as to hold the diamond rigidly against the strains of the polishing operation with the cement applied only to the polished faces of the diamond on one side of the girdle.

nized as oily) of wetting the polisheddim mond surface. Water is sald -to he non Wetting with respect to such a surface, diamonds show great adherence to greasy surfaces, and by using an oleaginous or unctuous constituent in the adhesive, the adhesive will adhere strongly to the polished diamond surface, and I believe this is due to the fact that oleaginous or unctuous material will readily flow or spread out on such a surface, adhering to substantially all parts thereof, while with other cements the material actually touches the polished surface at few if any points, there being a thin space or layer of air between the cement and diamond surface, due to the non-wetting character of the cement upon such surface, which prevents any substantial adhesion taking place. The diamond being carbon, differs radically from other gems in this respect. Non-wetting ornon-oleaginous cements, suitable for other gems, and so-called diamond cutters cement, can therefore only hold diamonds by mechanical action or anchorage, rather than by real adhesion.

The cement or adhesive in use must, however, also possess either substantially the same coeflicient of expansion as the diamond, or else a certain malleability, such, that under the great and sudden changes in temperature, causing relative expansion and contraction between it and the diamond, the cement will not be disrupted, disintegrated, dislodged, or otherwise loosened from the diamond surface. Other gems have a considerable coefficient of expansion, like that of ordinary cements. But the coefficient of expansion of the diamond is found to be extraordinarily small. Hence, if the adhesive and diamond durin the olishing operation do not have su stantially the same coeflicient of expansion, the adhesive expands and breaks away from-the diamond. I have found that an adhesive may be made which is capable of sufficient yielding to mechanical deformation under pressure or slight shock without too much mechanical weakening, to prevent its holding the dia mond rigidly by attachment to the polished faces thereof. This does not necessarily mean elasticity, which implies a return to the original form, nor does plastic precisely express the meaning, because it signifies absence of elasticity, which is not necessarily absent. The best term to express this property of which I am aware is malleability, in the sense that in s ite of a certain elasticity, there is not su cient rigidity to prevent its yielding to excessive straimwithout breakage, and I use the term malleable with this meaning herein. This malleability maybe inherent in a single ingredient or may be produced by discontinuity of physical make up, which I may call structural malleability, the first being illustrated by certain colloids, and the second by certain plasters, as'well ,aa by'oneof the examples but.of my cement made up of flakes of material like graphite, bound together at some points, but capable of relative movement or adjustment without disintegration or breaking up of the mass. Such an adhesive will have the requisite malleability to yield in either direction to such an extent that stresses of unequal expansion or contraction by heat are compensated for by yielding without breakage of the joint.

Accordingly, in carrying out my invention I choose a substance or ingredients which will not only during the polishing operation be sufliciently refractory and rigid, but also will have the requisite malleability and contain sufiicient oleagino g matter to give good adherence to the diamond surfaces. The material is preferably oleaginous about 300, F but I find that the adhesive may be composed largelyof matter not oleaginous, as all the matter in the cement need not be oleaginous to give good results. The adhesive is preferably mixed up in the form of a paste and then baked on to the diamond. It is preferably comosed chiefly of matter refractory at 700 so that it will be infusible at 600 F.

One method of compounding such an adhesive is as follows: Take 50 parts by bulk of Dixons stove polish (composed of 60% clay and 40% graphite), selecting that which is dense, hard and of good body and not friable, crumbly, sooty or of a dirty nature, and 50 parts by bulk of pure White soapstone clay, such as the talcum or steatite varieties, and 20 parts by bulk of borax or boric acid, and 10 parts by bulk of nitrate of lead, and with these in finely divided condition, mix them thoroughly. Nitrate of antimony is then prepared in the form of a concentrated solution, by allowing strong nitric acid to act on an excess of antimony for about ten to sixteen hours. The powdered mixture is then made into a thick, creamy paste with a sufficient amount of the nitrate of antimony solution. This paste is allowed to stand for 24 hours or longer and then it is made again into a similar paste with water.

Better results have been obtained by omitting the nitrate of lead and using the antimony alone with the clay, graphite and borax. Thus 32 ,parts by weight of the Dixons stove polish, 16 parts by weight of clay, and 12 parts by weight of borax may be mixed with the antimony solution as above described, except that it is preferable to dilute the antimony solution with an equal amount of water before using it to make the paste.

In either case a convenient way of mixing the dry raw materials is to rind them together. What I have calle antimony nitrate I prefer to make by breaking the metallic antimony of good quality up into lumps about the size of a pea (i. 6.; about 35 mm.) and to place 1 oz. of these lumps in an open vessel about 1 in diameter and add 4 fluid ounces of concentrated G. l. nitric acid. This I allow to stand open, or only loosely covered over night, preferably about 16 hours in a warm place (about 75 F. to 80 F.) whereupon the liquor takes on a greenish color and the bottom is covered between the antimony lumps with whitish powder. In the morning I add four fluid ounces of water, shake thoroughly, allow to settle and decant the clear liquid through a filter into a stock bottle from which portions can be taken fromtime to time for use. This product I have called antimony nitrate but chemists tell me it is really a solution of antimonic acid further acidified with some unconsumed nitric acid. When in either case this antimony solution is used to make a paste with the dry ground Dixons stove polish, clay, etc, I prefer to make the paste of the consistency obtained by taking 134 grains of dry powder and grinding into it 34 drops of the antimony liquid on a ground glass plate with a glass pestle, just as colors are ground together or with oils for china painting, until the paste is of a smooth even consistency. This paste I then spread thin on a glass plate and allow to thoroughly dry for 24 hours in a warm room. And then break up the mass and regrind 72 grains. of it in the same way with 6 drops of saturated boracic acid solution and use it while still moist.

Obviously other materials than those mentioned may be used to mix with the clay to bring out its adhesive qualities, hence the invention is not limited to the precise materials and quantities named.

The paste is placed between the diamond and the arbor, preferably being applied in considerable body, so that it will be anchored in the arbor and will form a stem within the arbor for adhesively holding the diamond, and it is baked with the parts held together, at a high temperature, preferably in a non-oxidizing environment, as by inclosure in a retort containing carbon monoxid or nitrogen gas. The heat is first applied at a low temperature to dry the material and is gradually increased to 800 F. or higher. The temperature required will vary, however, depending upon the particular ingredients used and their proportions.

. The baking usually requires from 25 to 30 minutes. The cement is preferably gradually cooled.

Another formula which has given fair results contains a base consisting of a material known as Dixons stove polish, this material being apparently composed of clay and graphite. and I have at times replaced this stove polish by a mixture of clay and graphite, about 60% of clay and 40% of graphite, this base being compounded with the following materials in the following proportions by volume: base, 100 parts; nitrate of lead, 10 parts; nitrate of antimony 15 parts; boracic acid, 20 parts.

Other formulae which have been used with more or less success are:

(1) Carbid of iron 13 parts; borax 2 parts; tungstic oxid 3 parts; and sufficient water to make the composition into a thick paste.

(2) Powdered silica (commercially known as quartz) combined with boracic acid and phosphatic or zinc oxid cements, or a combination of calcium oxid and borax, or other constituents containing suflicient oleaginous matter.

parts finely powdered anthracite coal; 25 parts finely powdered gum shellac; 50 parts boracic acid; 25 parts chlorid of magnesium or chlorid of calcium, and a sufficient solution of caramelized cane sugar to make the whole into a stiff paste. Instead Sulfids of metals, or metals andsulfur may also be sometimes used. But in each case, however, one or more of the ingredients should either be oleaginous or contain, either inherently or as impurity, suflicient oleaginous, or diamond wetting, matter to bring about the desired adhesion to the diamond surface.

While I have described in detail certain formulae for an adhesive which may be used for securing the diamonds for polishing, it will be understood that other formulae, having different ingredients, but having the characteristics mentioned may well be used. as well as other adhesives containing the same materials, but in different quantities. Accordingly, my invention in its broader aspects is not limited to the details described.

What I claim as new and desire to secure by Letters Patent is:

1. The method of polishing diamonds peratures of the polishing operation and having oleaginous properties so as to wet all parts of the surface of the diamond brought into contact with the cement and cause adhesion of the cement to the diamond over all parts of such contacting surface, causing the cement to set, supporting the cement, and polishing the diamond on the opposite side of the girdle.

2. The method of supporting diamonds for the polishing operation which consist in embedding a diamond on one side only of its girdle in a supporting cement adapted to Withstand the high temperatures of the polishing operation and having oleaginous properties so as to Wet all parts of the surface of the diamond brought into contact with the cement and cause adhesion of the cement to the diamond over all parts of such contacting surface, causing the cement to set, and supporting the cement.

3. A setting for holding diamonds during the polishing operation comprising a support, a cement, securely held by the support, adapted to Withstand the high temperatures of the polishing operation and having oleaginous properties so as to Wet every part of a diamond surface embedded in it, and a diamond embedded in said cement on one side only of its girdle and adhering thereto throughout all parts of its entire embedded surface so as to Withstand the strains, heat and pressure of the polishing operation.

4. A setting for diamonds during the polishing operation comprising a support, a cement, securely held by the support, adapted to withstand the high temperatures of the polishing operation and having oleaginous properties so as to Wet every part of a diamond surface embedded in it and having malleable properties adapted to preserve the continuity of adhesion between the diamond and the cement during the expansions and contractions produced in the polishing operation, and a diamond embedded in cement on one side only of its girdle, and adhering thereto throughout all parts of its entire embedded surface so as to Withstand the strains, heat and pressure of the polishing operation.

In testimony whereof, I have signed my name to this specification.

CLYDE J. COLEMAN.-