US 2384684 A
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Fatenteei gent. i949 2,384,684 GRINDING WHEELS Samuel S. Kistler, West Boylston, Mass, assignor to Norton Company, Worcester, Mass, a corpo-' ration of Massachusetts i No Drawing.
Original application May 31, 1940,
Serial No. 338,039. Divided and this application October 13, 1942, Serial No.
The invention relates to grinding wheels hav- .ing organic bond. This application is a division of my application, Serial No. 338,039, filed May 31, 1940.
One object of the invention is to provide a resilient grinding wheel. Another object of the invention is to provide a rigid grinding wheel of superior qualities for certain snagging operations. Another object of the invention is to provide a grinding wheel for snagging operations of longer life without loss of quality as determined by wheel wear and material removed. Another object of the invention is to provide a bond for grinding wheel having some of the characteristics of natural rubber without its variations in quality. Another object of the invention is to provide a bond for grinding wheels having high heat resistance.
Another object of this invention is to facilitate, for achieving such objects as those above noted, the use of certain synthetic rubbers and also to provide a simple and dependable method and means for rendering them more readily workable'for the achievement of such objects as the aforesaid. Another object is to provide a method for better controlling, in the making up of grinding wheels or the like, such synthetic rubbers as above mentioned, and for facilitating the variation, according to the intended use or purpose of the grinding wheel, of the charac-- teristics of the ultimate grinding wheel structure. Another object is to provide a grinding wheel utilizing rubber, that is, so-called natural rubber, but in smaller quantities than heretofore and yet achieve certain desired grinding wheel characteristics.
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 the application of which will be indicated in the following claims.
I have found that polymeric butadiene with sulphur makes an excellent bond for abrasive grains to form grinding wheels having some of the characteristics of rubber but many superior features. I have also found that copolymers of butadiene and acrylic nitrile with sulphur are useful for this purpose. Methyl acrylic nitrile may be substituted for acrylic nitrile. I have further found that the copolymer of butadiene and styrene is useful for the manufacture of grinding wheels.
Butadiene is a hydrocarbon of the formula, CH2=CH-CH=CH2 Butadlene is considered to polymerize in a linear chain. Acrylic nitrile may be also termed vinyl cyanide and is written,
CH2=CHCN Methyl acrylic nitrile may be written,
CH2=C(CH1) --CN and has properties similar to acrylic nitrile. It may be termed methyl vinyl cyanide. Styrene is written,
CH=CH2 'diene alone or combined with acrylic nitrile,
methyl acrylic nitrile or styrene, are thermoplastic until vulcanized with sulphur. When so vulcanized, they have more or less rigidity, depending upon the amount of sulphur incorporated into the mix. All of these substances are compatible with natural rubber and may be vulcanized with it to form a resilient or soft rubbery substance or a hard ebonite-like substance, depending upon the amount of sulphur used. The polymerization or copolymerization with sulphur is achieved by the use of heat and may be termed vulcanizing.
The polymers of butadiene and butadiene with acrylic nitrile are collectively known by the trademark Buna rubber, and a specific copolymer of butadiene and acrylic nitrile is known by the trade-mark Perbunan. This may be mixed with sulphur and abrasive grains on the mill, formed into sheets from which blanks can he died out, pressed and vulcanized to form grinding wheels. The preferred procedure is as follows:
Perbunan, which comes in the form of rubbery chunks like smoked sheets pressed together, is passed between heavy rolls to plasticize it and as this is done the required amount of sulphur, filler, accelerator and abrasive is added, the mixture being passed back and forth between heavy rolls to break down the Perbunan and mix it thoroughly with the other substances. When the mix becomes plastic and workable according to the standards known for the manufacture of rubber bonded grinding wheels, a quantity of the mixture is passed between a pair of rolls set closely together to form a sheet, blanks are died out, a number of the blanks placed in a mold, the mold is placed in a hot press, and the mixture is vulcanized therein. As a specific example of the foregoing, I may make a mixture in th manner described, of the following ingredients:
Example I Ingredient Abrasive (e. g., A130: or 810) 200 Perbunan" Sulphur 3 "Spheron black (finely divided carbon)- 70 (disulphide of mercapto benzo thiosol).
In the foregoing the abrasive may be in any grit siz desired, depending upon the proposed use for the grinding wheel. The carbon in comminuted form (Spheron" black) is a standard filler for rubber products and makes the final product relatively stiff and tough. The Altax" is a high temperature accelerator, the dibutyl amine is a booster accelerator, the zinc oxide is an activating filler, the stearic acid is a stabilizer, and the coal tar and rosin help in mmdling the product on the mill.
Grinding wheels made with the ingredients of Example I according to the method heretofore outlined are resilient due to the small amount of sulphur, that is to say, readily deformable. Nevertheless this resiliency does not approach extreme flexibility; the product is also fairly tough. One important feature of the wheel of Example I is that it is very strong. Soft rubber bonded wheels have been too weak and frequently burst. Wheels according to the present invention can stand an angular velocity as high as 12,000 surface feet per minute. Roughly speaking, the bursting centrifugal force is constant per unit of diametrical cross section for a given velocity measured in surface feet per minute at the periphery regardless of the actual diameter of the wheel within certain limits. Eight thousand surface feet per minute is adequate for practical grinding operations. A resilient or flexible rubber grinding wheel of the same elastic, limit as the wheel of Example I would not withstand an angu1ar velocity equal to 12,000 surface feet per minute. The grinding wheel made according to Example I is suflliciently deformable so that reentrant angles in a piece of steel can readily be ground and all sorts of dies, fixtures, automobide parts, etc., can be ground that could not be ground with a rigid grinding wheel without danger of taking oii. more metal in certain spots than might be desired. There is a real need for an effective grinding wheel which will conform to the work being ground and give a fairly uniform grinding action over an irregular surface and wheels made according to Example I fulfill this need.
stress of a wheel due to The invention has also been embodied in rigid wheels, as follows:
Example 11 Parts by weight Ingredient as easaaa' Example III Parts by Ingredient weight Fused alumina, No. 16 grit size 400 Perbunan i3. 75 Rubber... 41. 25 Suiphur 18 Zinc oxide. 25 C olite 15 C eium oxide 5 This. wheel was compounded and cured the same as the wheel of Example II. For comparison purposes, a wheel was made like the wheel of Examples II and III but containing 55 parts of rubber with no Perbunan. This wheel will be designated wheel A.
Still another wheel was made as follows:
Example IV Ingredient 532 3 Fused alumina No. 16 it size Perbunan" .ff Rnbber. 22. 6 Sulphur- 15 cryolite. 46 Zinc oxide 5 Calcium oxide 5 This wheel was similarly compounded and similarly cured.
Another wheel was made as follows:
Example V Ingredient 32%? aseaeee as each of the wheels of Examples II, in and IV and wheel A.
In working up, on the rolls of the mill, the mix according to marziples II, III, IV and V, the rubher gives to the mix and hence to the Perbunan a tacklness and workability in which the mix without the rubber is defective or deficient, and hence breaking down is materially speeded up.
Still another wheel was made like the wheel of Example V excepting that 45 parts of rubber was used instead of 11.25 parts of Perbunan and 33.75 parts of rubber. This wheel, hereinafter designated as wheel B, was made for comparison purposes.
As indicating the results of using Perbunan, which as aforesaid, is a copolymer of butadiene and acrylic nitrile vulcanized with sulphur, in a grinding wheel, a comparison was made of wheels of Examples II to V inclusive and wheels A and B in a regular grinding test using a swing frame grinder. The wheels A and B are standard snagglng wheels and both of them together withthe wheels of Examples II to V inclusive were 16 inches in diameter by 2 inches in thickness with a 6 inch central hole. The machine was a 16 inch swing frame grinding machine, the wheel speed for each wheel was adjusted to 9500 surface feet per minute, the pressure used was 130 lbs., the material was 18.8 Allegheny steel having a surface of 6" x 24", each run was fifteen minutes, there were flve runs per wheel, and the grinding was done on the side with the wheel tilted. The results were as given in the following table: r
Table I Wheel wear Material re- Wheel identification in cu. in. moved in per hour lbs. per hour Wheel A 49 22 Wheel of Example 11... 36. 8 18. 6 Wheel of Example 111.. 41.2 19. Wheel B 50. 0 22. 4 Wheel of Example IV 31.0 17. 4 Wheel of Example V 36. 3 20.0
The quality of a grinding wheel depends upon many factors, and especially on what results are desired. It can be easily understood that if a given factory is getting the best results from a given grinding wheel and wages are doubled, a difierent grinding wheel may be desired. Using prevailing scales of wages and if overhead is 100% of labor, you can obtain a quality number for grinding wheels for snagging purposes by squaring the material removed and dividing by the wheel wear. However, probably because of labor differential and possibly for some other reasons, certain factories desire grinding wheels with a low rate of wheel wear. The above figures show that all of these wheels have quality numbers which may be tabulated as between 16 and 20 which is not too much difference. Specifically, the B quality numbers calculated by the above formula using a cert constant was as follows:
Table 11' Wheel A 18 Wheel of Example II 17 Wheel of Example 111 16 Wheel B 18 Wheel of Example JV 17 Wheel of Example V 20 The replacement of rubber, therefore, with Perin quality, it being human" made little change seen that both the best and the worst wheel from the standpoint of quality number contained some Perbunan." However, increasing amounts of Ferbunanfl as shown in wheel wear. Grinding wheels witha low rate of wheel wear are definitely desired in many factories provided the amount of material removed does not drop too low. Accordingly for such purposes grinding wheels having butadiene products substituted for rubber in whole or in part are deflnitely found to be desirable and superior.
Another feature of butadiene products is that they have greater heat resistance than rubber products since vulcanized Perbunan softens at a higher temperature. Despite their many excellent qualities rubber bonded grinding wheels have been limited in their application by reason of the low thermal resistance of the rubber. Accordingly it is distinctly advantageous to produce a grinding wheel which has many of the characteristics of rubber bonded grinding wheels, the bond of which does not soften until temperatures higher than those which soften rubber bonds are I reached.
I have discovered that one of the reasons for the excellent results often achieved with rubber bonded wheels is the presence of sulphur. Sulphur appears to have some action at the grinding line of a chemical nature which prevents loading. In particular, I believe that the presence -f sulphur at the grinding line makes the ferrous metal chips brittle so that they do not load the wheel as readily as they otherwise would. Sulphur, therefore, appears to be an excellent filler for a grinding wheel for grinding ferrous metals. The presence of sulphur in rubber bonds was fortuitous and due to the fact that it was necessary to use sulphur to convert the rubber into a usable product. According to the present invention a compound is used which is also vulcanizable with sulphur but which, in having a higher thermal resistance than vulcanized rubber, is superior to rubber for many practical abrading purposes.
There may be enough occluded water in the butadiene products herein mentioned to cause some swelling during the cure. Calcium oxide CaO readily takes up water at temperatures above C. and becomes converted to calcium hydroxide Ca(OH)a. However, other dehydrating agents may be used, such asgActivated Alumina, silica gel, and soluble anhydrite, (38504.
It will thus be seen that there has been provided by this invention an article 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 hereinbefore set forth is to be interpreted as illustrative and not in a limiting sense.
1. An abrasive product comprising abrasive grains distributed throughout and adhered and held together by a bond that comprises the vulcanized reaction product with sulphur as a vulcanizing agent of a mixture of a butadiene compound selected from the group consisting of (1) butadiene polymer and (2.) butadiene copolymer comprising butadiene copolymerized with a vinyl compound, and unvulcanized natural rubber initially present in an amount to overcome, during working, the characteristic of the butadiene compound in resisting envelop- Table I, reduced the -whereby the abrasive and retained in the mix, shaping the resultant 25 mix, and heat-treating to effect vulcanization of (1) butadiene polymer and (2) butadiene copolymer comprising. butadiene copolymerized with a vinyl compound, together with a quantity of unvulcanized natural rubber to lessen the resistance or the butadiene compound to the inclusion therein and the adhesion thereby of i5 abrasive grain and thereby condition the mix for the reception and retention therein 01' abrasive grain, admixing therewith abrasive grain to become substantially uniformly distributed throughout the mix and to prepare the mix for shaping without mechanical disintegration and loss of abrasive grains therefrom, together with a vulcanizing agent which includes sulphur grains are enveloped by 01' the admixed natural rubber and butadiene compound to thereby set the bonding of the abrasive grains and secure them in place to function as abradants.
-3. In a method of making an abrasive article, the steps which comprise mixing a quantity of unvulcanized natural rubber into a quantity of polymerized butadiene compound for the purvulcanized 4. An abrasive product comprising abrasive grains distributed throughout and adhered and held together by a bond that comprises the reaction product with sulphur as a vulcanizing agent of a mixture of butadiene copolymerized with acrylic nitrile and unvulcanized natural rubber initially present in an amount to give the butadiene copolymer improved workability and tackiness and thereby mitigate, during working, the characteristic of r the butadiene copolymer in resisting envelopment of and adhesion to the-abrasive grains and thereby to contribute grain-retentive plasticity thereto, whereby the bond efiected by the aforesaid vulcanized reaction product substantially uniformly envelops and securely holds said abrasive grains.
5; An abrasive product comprising abrasive grains distributed throughout and adhered and held together by a bond that comprises the vulcanized reaction product with sulphur as a vulcanizing agent of a mixture of butadiene copolymerized with methyl acrylic nitrile and unvulcanized natural rubber initially present in an amount to give the butadiene copolymer improved workability and tackiness and thereby pose of giving the latter improved workability and tackiness for the reception thereinto and retention therein ct abrasive grains and admixing therewith abrasive grains to become substantially uniformly distributed throughout the mix and held therein by and to prepare it for shaping without mechanical disintegration, together with a vulcanizing agent that comprises sulphur, the latter in quantity sufiicient to eflect subsequent vulcanization under heat treatment compound andthe rubber, shaping the resultant mix, and then heat treating the shaped mix to efiect substantially concurrent vulcanization of the intermixed butadiene compound and rubber the tackiness of the mix 9 er the intermixed buadlene and thereby form a bonded body for holding and bonding the abrasive rains.
mitigate, during working, the characteristic of the butadiene copolymer in resisting 'envelopment of and adhesion to the abrasive grains and thereby to contribute grain-retentive plasticity thereto, whereby the bond effected by the aforesaid vulcanized reaction product substantially uniformly envelops and securely holds said abrasive grains.
6. An "abrasive product comprising abrasive grains distributed throughout and adhered and held together by a bond that comprises the vulcanized reaction product with sulphur as a vulcanizing agent of a mixture of butadiene copolymerized with styrene and unvulcanized natural rubber initially present in an amount to give the butadiene copolymer improved workability and tackiness and thereby mitigate, during working, the characteristic of the butadiene copolymer in resisting envelopment of and adhesion to the. abrasive grains and thereby to contribute graizr-retentive plasticity thereto, whereby the bondeffected by the aforesaid vulcanized reaction product substantially uinformly envelops and securely holds said abrasive grains.
- SAMUEL S. KIS'I'LER.