US 2877105 A
Description (OCR text may contain errors)
I. B. SMITH March 10, 1959 VITRIFIED BONDED GRINDING WHEEL WITH FINE HARD SIDES Filed June 27, 1957 4g. 1 R 22 INVENTOR IAN B. SM/TH 7 r 1 '3' A NEY VITRIFIED BONDED GRINDING WHEEL WITH FINE HARD SIDES Ian B. Smith, Boylston, Mass., assignor to Norton Company, Worcester, Mass., a corporation of Massachusetts Application June 27, 1957, Serial No. 668,442
9 Claims. (Cl. 51-308) The invention relates to vitrified bonded lgrinding wheels with fine hard sides.
One object of the invention is to provide a fine hard side of better quality than heretofore to a grinding wheel. Another object is to eliminate warping in the manufacture of vitrified bonded grinding wheels with a hard side. Another object is to provide superior grinding wheels for such grinding operations as the following: grinding burrs for cutting small holes, grinding the lips of drills, grinding aircraft rivets where a sharp shoulder must be maintained, and for other similar grinding operations. Another object is to provide grinding wheels having, and which will maintain, sharp corners. so as to produce sharp angles, both external and reentrant, in pieces being ground. Another object is to provide a fine hard side in a vitrified grinding wheel of less thickness than has been heretofore practicable. Thin hard sides have been wanted since the function of a hard side is to maintain the corners of a grinding wheel. But as different abrasives have different grinding actions, it is desirable to limit the area ground by the hard side.
Another object is to make a hard sided grinding wheel with a hard side of uniform thickness. When hard sides are molded on wheels and then the wheels warp somewhat (as all wheels do) pursuant to firing, and then the wheels are sided to make them straight, hard sides of uneven thickness result.
Other objects will be in part obvious or in part pointed out hereinafter.
In the accompanying drawings, illustrating a few of many possible styles of wheel embodying the invention,
Figure 1 is a diametral sectional view of a straight grinding wheel having two fine hard sides in accordance with the invention,
Figure 2 is a view similar to Figure 1 showing a straight grinding wheel with one fine hard side according to the invention,
Figure 3 is an elevation of the wheels of Figures 1 and 2, with a portion cut away to show the structure,
Figure 4 is a diametral sectional view of a flaring cup type of wheel according to the invention,
Figure 5 is a similar sectional view of a dish type of Wheel according to the invention.
I provide abrasive grains of any suitable type and many have been used, such as fused alumina, silicon carbide, zirconia and diamonds. I provide ceramic material for forming vitrified bond and this art is now well known and the invention can be embodied in vitrified grinding wheels having any known or reasonable formula of the vitrified bond.
Referring now to the drawings, Figures 1 and 2 disclose straight wheels, which means discs which grind on the periphery. The wheel 11 of Figure 1 is a moderately thick wheel made of vitrified bonded abrasive material. The wheel 12 of Figure 2 is somewhat thinner. The wheel 14 of Figure 4 is a flaring cup type wheel used especially for grinding metal cutting tools. The wheel 15 of Figure 5 is a dish type of wheelused for similar Unite States Patent l Patented Mar. 10, 1959 "ice purposes. All of these are vitrified bonded abrasive wheels the manufacture of which is well known.
EXAMPLE I The following is the best mode for making the grinding wheel according to my invention. I provide the following materials in parts by weight.
Table I White aluminum oxide abrasive, grit size 88.6 Dry powdered bond 9.2 Water 1.7 Dextrine 0.5
The abrasive is placed in a mixing pan and is wet with the water in which the dextrine is first dissolved. The water and dextrine are simply poured into the pan while it, is rotated on a vertical axis and stationary plows churnv the abrasive which soon picks up all the water with the dextrine.
Then the dry powdered bond is slowly sifted into the still rotating pan, and the mixing is continued until all of the bond has been picked up by the wet abrasive. The dextrine makes the film of liquid on each abrasive granular somewhat sticky which is why it is used.
' The bond used was made up of the following ingredients by weight parts which were thoroughly mixed.
Table II Kentucky #5 Ball clay 31 Maine Feldspar 52 Flint (SiO 8 Whiting (calcium carbonate) 6 Magnesia (MgO) 3 This bond has the composition shown in the following table by weight parts:
This abrasive bond mixture, made up as above described, is then placed in a steel mold, of the type shown in U. S. Patent No. 2,076,833 and is pressed under a pressure of 2000 pounds per square inch. This produces a green wheel which is ready for firing. As the best mode for carrying out the invention I select the wheel 12 of Figure 2 because a single hard side is usually sufficient. In this illustrative case of the best mode of the invention the wheel 12 is seven inches in diameter by three-eighths of an inch thick with a seven-eighths inch central hole. But as is customary it is made oversize to 7%" x /2 x and trued and sided after vitrifying to the final dimensions above given. The abrasive bond charge is in this case 1.67 pounds.
The oversize green wheel is then taken to a kiln and fired to vitrify it under cone 12 firing conditions which definitely defines the heat treatment as is well known in the art. Cone 12 is reached at 1306 C. whenthe ,tem-, perature is raised 60 C. per hour. The wheel is then 3 trued and sided to reduce it to the desired dimensions of 7 x x Ms".
EXAMPLE II The following is ,another example-of the manufacture of the grinding wheel according to my invention. :1 provide the following materials in parts by weight.
Table IV Black silicon carbide, 60 grit size 84.0 Dry powdered bond 13.1 Water 2.4 Dextrine 0.5
The mixing process is exactly the same as in Example I. The bond used was made up of the following ingredients by weight parts which were thoroughly mixed.
Table V Kentucky Ball clay 60.0 Flint 13.1 Maine Feldspar 2.4 Whiting (calcium carbonate) 0.5
This bond has the composition shown in the following table by weight parts.
The manufacturing process for making the wheel is exactly the same as in the case of Example I. It also is fired at cone 12. The charge of abrasive and bond to produce the oversize wheel 7%" x /2 x 78" is 1.31 pounds. After vitrifying it also is trued on the periphery and sided on each side to reduce it to 7 x x The vitrifying process warps all wheels somewhat. In some cases this can be tolerated, but for tool wheels such as those of the invention perfect truth is wanted so it is better to make them oversize and then to true and to side them.
I apply a fine hard side or fine hard sides to the wheels in accordance with this invention. In Figure 1 there are two fine hard sides 21. In Figure 2 there is one fine hard side 22. In Figure 4 there are two fine hard sides 24a.and 24b and in Figure 5 there is one fine hard side in two portions 25a and 25b.
To form the fine hard side or line hard sides, I apply a coating of fused abrasive material the major portion by weight of which is fused crystalline metal oxide having a sharp melting point, said metal oxide being metal oxide selected from the group consisting of aluminum oxide, zirconium oxide, titanium oxide and mixtures thereof, which abrasive material is flame sprayed in situ on the side of the grinding wheel. This coatingmay be applied in accordance with U. S. Patent No. 2,707,691 granted May 3, 1955 on application of my colleague W. M. Wheildon, Jr. which describes a flame spraying gun for the purpose. Complete information for producing a coating as above defined is set forth in the Wheildon patent. The material is supplied to the gun in the form of rods. These flamespraying guns are on themarket and can be procured, for example, from Metallizing Company of America, Chicago 24, Illinois. This is the best mode of applying'the fine hard sides.
I prefer to use aluminum oxide, A1 0 as the material for thecoating 21, and this is the best mode of my invention. Fused zirconia has recently been found to be an effective abrasive material, see U. S. Patent No. 2,769,699 granted on application of my colleague F. J. Polch on November 6, 1956. This also might be used. Fused zirconia-titania has also been found to be an effective abrasive material, see U. S. Patent No. 2,653,107 granted on application of W. B. Blumenthal on September 22, 1953. Therefore it is certain that fused'titanium oxide also can be used. These three oxides are compatible in fact regular grade fused aluminum oxide contains quite a good proportion of titanium oxide. Therefore mixtures of the three or of any two in any proportion can be used.
The rods can be entirely of crystalline metal oxide and thus can be sintered rods of only the oxide or mixtures in .question, without any substantial amount of lower melting point material as bond, such as fired clay or glass. This is the best mode of my invention. What is a sintered rod is explained in the Wheildon patent by reference to others. It means that a crystalline metal oxide is self bonded by heat, no clay or silicate being included in the material. On the other hand a considerable proportion of clay or glassy bond might be included in the rod resulting in a fine hard side which has some of the characteristics of vitrified bonded fused alumina wheels. Alumina is synonomous with aluminum oxide, zirconia with zirconium oxide and titania with titanium oxide.
While the coating of oxide is being flame sprayed upon the side of a wheel it is slowly rotated, at for example 15 R. ,P. M. The operator of the gun can put a very even coating upon the side of the wheel by slowly moving the locus of flame spraying towards and from the center of the wheel. A skilled operator can put a fine hard side of the invention on a wheel which does not vary inthickness more than five percent.
Instead of using a rod spraying gun asin the best mode Imay use a powder spraying gun, such as a Metco Thermo Spray Gun manufactured and soldby Metallizing Engineering Company, Inc., Westbury, Long Island, New York. I am not aware of any patent so can not cite one. This gun sprays ceramic powders of many different kinds, including alumina base, titania base, and zirconia base powders. For many grinding operations alarge portion of silicate material is desirable in the fine hard side coating to make it free cutting by erosion of the silicate material, and any abrasive composition which has been found to be usefulin the vitrified abrasive artcan be applied as a coating with one or the other of the fiame spraying guns herein identified. This'silicate material can be made out of kaolin, ball clay, mixtures ofthese, glassy frits of any kind and mixtures too, and with the kaolin or ball clay or both and with or without the addition of feldspar, which is a flux or flint Whichjs a hardener. Silicates donthave have any sharp meltingpoint, but in the guns they are fused to a free flowingcondition. The crystalline metal oxide component does have a sharp melting pointand is fused, atomized and sprayed by the gun.
At least a major portion'by weight of the crystalline metal oxide component must function as an abrasive, and the test of this is does it, in the coating, have a sharpmelting point. Having a major portion by weight of such metal oxide the coating is abrasive and can cut metals including hard steels if the harder metal oxides are used such as those mentioned. In most cases aluminum oxide will be preferred except for the grinding of titanium and zirconium and similar metals where zicronium oxide may he preferred, or titanium oxide or mixtures.
By putting on these fine hard sides 21., 22, 24a, 24b, 25a, and 25b break down of theedges of the wheel 11, 1 2, 14 and 15 is prevented. This gives all the advantages as mentioned in the objects for grinding articles such as listed in the objects and many others where sharp corners are wanted, especially wherereentrant angles areinvolved.
The fine hard sides applied in accordance with the invention have great resistance to break-down of the corners of the wheels, in the beginning and when the wheels are diminished in diameter. In Figures 1 and 2 it is the periphery of the wheels doing the grinding and in Figure 4 it is the flat plane annular face which is doing the grinding and in Figure 5 it is the periphery which is doing the grinding. The corners referred to are just outside the junctions of the grinding surfaces with the fine hard sides and in accordance with the invention the corners are made of the coatings described.
For grinding purposes it was often preferred that the fine hard sides if they will hold the corners should be as thin as possible. In accordance with the method of producing these fine hard sides as hereinbefore explained they can be made as thin as desired. Heretofore it has been difiicult to make fine hard sides by moulding technique less than about one-thirty second of an inch in thickness. In accordance with my invention they can be made as thin as four or five thousandths of an inch if desired.
A sintered aluminum oxide rod used in the guns for flame spraying is made of alpha alumina as when alumina is used and sintered it becomes alpha alumina and most alumina is alpha alumina to start with. However, the flame spraying converts the alpha alumina to gamma alumina so my fine hard sides in the case of alumina are made of gamma alumina. So far as I am aware there never was previously a grinding wheel with a hard side of gamma alumina. The grinding Wheels 11, 12, 14 and 15 are made of bonded alpha alumina in the best mode above described and whenever alumina is used as the abrasive which will be in most cases. Thus in accordance with the best mode of my invention the grinding wheel 11, 12 14 and 15 is made of vitrified bonded alpha alumina having a fine hard side of gamma alumina, or the major portion of which is gamma alumina. Any grinding wheel made up out of abrasive grains mixed with bonding material which analyses as a group of oxides including silica SiO is known as a vitrified bonded grinding wheel or a vitrified grinding Wheel for short. The combination of oxides with silica produces a silicate.
The sintered zirconia rods used for flame spraying are usually made of zirconia which is partly monoclinic and partly cubic. However the coatings thus produced are of completely cubic zirconia. I am not aware that any hard sides of zirconia of any kind were heretofore produced but certainly not any of all cubic zirconia. The crystal form of titania rods used for flame spraying is rutile and the coatings produced thereby are of another kind, but what has yet to be determined. But no hard sides of titania on a grinding wheel were ever before produced.
It will thus be seen that there has been provided by this invention vitrified grinding wheels with fine hard sides in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As many possible embodiments may be made of the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefo-re set forth is to be interpreted as illustrative and not in a limiting sense.
1. A vitrified grinding wheel with fine hard sides essentially consisting of abrasive grains bonded with vitrified ceramic bond, and a fine hard side on said grinding Wheel consisting of a coating of fused abrasive material the major portion by weight of which is fused crystalline metal oxide having a sharp melting point, the remainder of said coating being selected from said fused crystalline metal oxide and vitrified silicate bond and said metal oxide being selected from the group consisting of gamma aluminum oxide, cubic zirconium oxide, titanium oxide and mixtures thereof which coating was flame sprayed in situ on said grinding wheel.
2. A vitrified grinding wheel according to claim 1 in which the major portion by weight of the coating of oxide is gamma aluminum oxide.
3. A vitrified grinding wheel according to claim 2 in which the abrasive grains are made of aluminum oxide.
4. A vitrified grinding wheel according to claim 1 in which the coating is a coating of gamma aluminum oxide.
5. A vitrified grinding Wheel according to claim 4 in which the abrasive grains are made of aluminum oxide.
6. A vitrified grinding wheel according to claim 1 in which the major portion by weight of the coating of oxide is cubic Zirconium oxide.
7. A vitrified grinding wheel according to claim 6 in which the abrasive grains are made of aluminum oxide.
8. A vitrified grinding wheel according to claim 1 in which the coating is cubic Zirconium oxide.
9. A vitrified grinding wheel according to claim 8 in which the abrasive grains are made of aluminum oxide.
Whitcomb et al. Dec. 14, 1937 Milligan et a1. Aug. 16, 1949