US 2238351 A
Description (OCR text may contain errors)
GRINDING WHEEL Filed Dec. 24, 1940 Patented Apr. 15, 1941 2,238,351 GRINDING WHEEL Edward Van der Pyl, Holden, Masa, assignor to Norton Company, Worcester, Mass., a corporation of Massachusetts Application December 24, 1940, Serial No. 371,543
The invention relates to metal bonded'abra sives, particularly to diamond grinding wheels, and with regard to its more specific features, to a cutting-oil wheel with a metal bonded abrasive rim and a metal center.
One object of the invention is to provide a combination metal bond for abrasives, particularly diamonds, adapted to be soldered to a metal center, particularly a steel center, giving a strong union. Another object of the invention is to provide a metal bond composition which'is strongafzd also friable. Another object of the invention is to provide a metal bond composition which is heat resistant. Another object of the invention is to. provide a metal bond composition which will hold diamondabrasive very tenaciously. Another object of the invention is to provide a metal bond which is cold moldable and has one or more of other desired characteristics, such as an afiini-ty for diamonds, resistance to heat, and friableness. Other objects will be in part obvious or in part pointed out hereinafter.
The invention accordingly consists in the features of construction, combinations of elements, arrangements of parts, and in the several steps and relation and order of each of said steps to one or more of the others thereof, all as will be illustratively described herein, and the scope of portion i3 which has a blunt'ta'per. As shown in Figure 2, notches M may be provided in the edge of the peripheral portion i3. Onto the periphery i3 I mold an abrasive mixture consisting of diamond abrasive i5 bonded with metal bond i6 forming an abrasive portion H. I take crushed, cleaned'and graded'dlamonds, for example of the order of 46 grit size and finer, preferably as fine as 100 grit size, and to the extent of preferably between 6.25% and 60% by volume, and mix them with metal powders'which are preferably very fine. While coarse particles may be used, I preier electrolytic metal which is virtually an impalpable powder. Powders in the form of metal particles the same size as the abrasive are, however, quite practical.
I make a thorough mixture of the various metal powders and thediamonds and then by the use of a mold andw-ith high pressure, mold the, mixture around the outside of the steel center E0. The mold and the procedure used may be that disclosed in my prior copending application Serial No. 295,939 filed September 21, 1939. After molding with pressure, the entire article can be readily handled and it is then placed in a sintering furnace.
Considering now the particular metals'to be used, I prefer one part of iron, one part nickel, one part tin, and one part copper. All parts are given by weight.
particles than 20% by weight of a cold moldable metal sethe mixture satisfactorily to a-steel center, such lected from the group'consisting of copper and nickel. Copper is the best cold moldable metal known to me since pure copper is quite ductile. Some other metals which are equally ductile are excluded for other reasons. For example, lead has too low amelting point. Copper melts at 1083 C. Nickel is fairly ductile and melts at 1452 C. Copper ispreferred to nickel and in my metal bond I find there should be not less than 4% by weight of copper based on the total bond.
Another feature of the invention is that not less than 2%. of the total metal bond should have a high melting point and be selected from the group consisting of iron and nickel. Iron has a melting point of 1530 C. By selecting a combination of metals including some with a high melting point, I am enabled to braze or solder as the steel center i0, without changing the character of the bond. I find it is important to have some iron in the combination and my bond, therefore, has not less than 1% of iron based on the total metal by weight. I believe the iron gives the bond an affinity for the diamonds which increases the strength of the final article. with regard to the nickel, it will be seen that there are two reasons for using nickel-because it has a high melting point and also because it is cold moldable. Nevertheless since the copper provides the cold moldability and the iron imparts high melting point characteristics, the metal nickel may be omitted altogether in some embodiments of my invention. Therefore, the bond consists of copper, iron and tin, and optionally nickel. It may be remarked, however, that the bond now known to me best suiting the conditions I desire to obtain is the one previously mentioned consisting of equal parts of the four metals named.
My bond should have not less With regard to the tin, which melts at 232 0., this is included for several reasons. Although it is desired to have the combination have a. high melting point, it should not have too high a melting point. The incorporation of the tin reduces the melting point of the entire combination. Furthermore, at the temperatures used in sintering the article, viz. preferably between 600 C. and 850 C., the tin melts and wets the other metals and goes into solution in some of them, chiefly with the copper, and assists in uniting the entire article into an integral structure. But equally important, or even perhaps more important, the tin imparts fria-bility to the entire bond. I use enough tin so that there shall be at least 2% tin in excess of that which goes into solid solution in the other three metals or inthe copper and iron if only copper, iron and tin are used.
In molding the article I prefer to use a pressure of about 50 tons to the-square inch. I prefer to sinter it between 600 C. and 850 C., for
example at 750 C., but other temperatures can be used provided the bond is capable of being sintered in the temperature range mentioned. Although the sintering, that is to say, the heating takes place after the pressing operation, nevertheless I believe the amount of pressure used has a very material bearing upon how much of the tin goes into solid solution. Under the conditions named, only asmall percentage of the tin will go into solution into the iron and nickel and remain as a solid solution after cooling. More will go into the copper and remain as a solid solution therein. I use a total amount of tin such that there is in the final article 2% of tin in excess of .the tin that is in solid solution. I believe that under the conditions named, somewhere between 15% and 16% of tin will stay in solid solupure metal powders under a pressure of about tons to the square inch, then sintering them at a temperature of 750 C. according to the following table, in which the parts are percentages and are given by weight.
Table Order of preference Cu Sn Fe Ni B Rockwell 84 14 2 0 70 84 14 1 1 10 l. 66 44. 17 44. l7 10 10 1. 66 l 87. 34 30 10 i. 66 0 88. 34 23 84 14 0 2 1 10 1. 66 87. 34 l 4 10 l. 66 88. 34 0 4 0 0 50 50 36 0 50 50 0 Soft 0 50 0 50 Soft It is believed that so far as tin forms. a solid solution with the other metals, the resulting product will be ductile and not friable. For'example, bronzes with a low percentage of tin are ductile. I believe it is the free tin which gives friability, and this is a very desirable product for an abrasive article since it reduces or eliminates loading.
tion in a mixture of copper and tin aloner Iron and nickel are believed to hold in solid solution only a minor amount of tin, a fraction of a per cent in each case, under the processes and at the temperatures herein specified.
In order to determine whether or not a particular bond has this characteristic, it can be sliced and etched in various cross sections and the areas measured to determine the amount of free tin. The rest is presumed to be in solid solution and by comparison with the amount of tin by weight introduced into the combination, it can then readily be determined whether the amount of tin satisfies the foregoing requirements. The excess of tin over that in solid solution can also be ascertained by well known freezing point" methods employing pyrometric observations. Of course, in any case, the proportions of the various metals forming the bond are known.
Another feature of the metal bond is that the fusing point of the entire bond after sintering should notbe lower than 750 C. If it is lower than this, the metal bonded abrasive portion and the steel backing or center cannot so readily be soldered or brazed together.
To avoid oxidation of the diamonds, it is pre- .ence in the table.
If insufficient copperis used, the mixture of metals is difficult to mold and the final article may be found to be spalled. Such was the case with the items marked 7 and 8 in order of prefer- Resuming the description of a specific embodiment of the invention, after the molding of the article with pressure it is stripped from the mold and placed in a slntering furnace which may comprise a closed chamber with suitable heating coils and pipe connections for the introduction of hydrogen temperature control apparatus to keep the furnace at the selected temperature.
One or more molded articles are placed in this furnace, the hydrogen is turned on, and the furnace is gradually raised to the selected temperature and kept at this temperature for a period of 1 to 6 hours after which the articles are removed. The union between the steel center In and the peripheral abrasive portion Il may not be satisfactory merely as the result of sintering. I prefer to braze or solder the parts together and this may be done as follows:
The sintered article is slowly rotated on a vertical axis and as it is rotated the rim is heated with a blow torch. The rim is heated to a temperature sumcient to melt a wire solder which melts at 718 C. The solder is melted in the reentrant angle between the steel center -10 and the abrasive. portion l1. As t'neportion I1 is heated it expands and opens a gap between it and the steel center I thus allowing the solder to flow between the parts to make a strong union. A characteristic of the metal bond in question is that it is readily wetted by silver solder which melts. at 725 C. and which may consist of silver, 20% copper, and 10% zinc. This solder also readily wets the steel center l0 andforms a strong union with it.
The final article is-mechanically strong as a whole, and the bond is strong. but yet it is friable;
that is to say, it will gradually crumble away leaving the diamond grains well exposed for cutting. But so long as it lasts it holds the diamonds very tenaciously. It is characterized as a .various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As various possible embodiments might be made of the mechanical features ofthe above invention and as the art herein described might be varied in various parts, all without departing from the scopeof the invention, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.
1. An abrasive article comprising diamonds bonded with a hard, friable, sintered metal bond capable of being sintered at between 600 C. and 850 C. and said metal bond comprising copper, iron and tin, with not less than 20% of the total metal being cold moldable metal selected from the group consisting of copper and nickel, with not less than 4% of the total metal being copper, with not less than 2% of the total metal having a high melting point'and being selected from the group consisting of iron and nickel, with not less than 1% of the total metal being iron, the total amount of tin being at least 2% in excess of the tin in; solid solution at around bond after sintering being not lower than 750 C.
2. An abrasive article comprising diamonds bonded with a hard, friable, sintered metal bond comprising copper, iron and tin, the proportions of each of said metals by weight to the entire metal bond being not less than 25%.
20 C'., and the fusing point of the entire metal 45 3. An abrasive article comprising diamonds bonded with a hard, friable, sintered metal bond comprising approximately 25% iron, 25% copper, 25% tin-and 25% nickel by weight.
4. An abrasive article consisting of a steel "backing and an abrasive portion metallurgically united thereto and comprislng' diamonds bonded with a copper, tin, iron bond.
5. An abrasive article consisting of a steel backing and an abrasive portion metallurgically united thereto and comprising diamonds bonded with a copper, tin, iron, nickel bond.
6. An abrasive article comprising abrasive grains bonded with a hard, friable, sintered metal bond capable of being sintered at between 600 C. and 850 C. and said metal bond comprising copper, iron and tin, with not less than 20% of the total metal being cold moldable metal seiected. from the group consisting of copper and nickel, with not less than 4% of the total metal being copper, with not less than 2% of the total metal having a high melting point and being selected from the group consisting of iron and nickel, with not less than 1% of the total metal being iron, the total amount of tin being at least 2% in excess of the tin in solid' solution at around 20 C., and the fusing point of the entire metal bond after sintering being notlower than 7.50 C.
'7. An abrasive article comprising abrasive grains bonded with a hard, friable, sintered metal bond comprising copper, iron and tin, the proportions of each of said metals by weight to the entire metal bond being not less than 25%.
8. An abrasive article comprising abrasive grains bonded with a hard, friable, sintered metal bond comprising approximately 25% iron, 25% copper, 25% tin and. 25% nickel by weight.
= EDWARD VAN nan PYL.