US 1616531 A
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Clarence R. @611 L E E W 2 2 IA K s B A m d u w G 1 NF T W C Feb. 8, 1927.
WW Mum Patented Feb. 8,1927.
UNITED STATES PATENT, OFFICE.
CLARENCE R. KING, OF WORCESTER, MASSACHUSETTS, ASSIGNOR TO NORTON COM- PANY, OI WORCESTER, MASSACHUSETTS. A CORPORATION OF MASSACHUSETTS.
"CUTTING-OFF ABRASIVE WHEEL.
Application filed August 8, 1922. Serial No. 580,418.
My invention relates to the abrasive art and more particularly to an abrasive wheel adapted for special operations, such as cutting ofi' lengths of objects.
Abrasive wheels used like a circular saw for cuttin ofi' pieces from articles made of metal, car, on, etc., are ordinarily made of abrasive grains bonded with an organic mawith abrasive tools.
terial such as rubber or shellac, these wheels being approximately in thickness.
The abrasive manufacturer is called upon to make a large number of wheels of different compositions and structures for cutting 'or grinding the almost endless variety of materials which are now formed or finished These wheels which consist of abrasive grains held together by various kinds of bonds such as vitrified clays, rubber, resins, etc., are graded in a series running from what is known as a soft grade to a hard grade. To illustrate these limits of grade, a wheel of the softest grade contains a minimum of bond and is of such a character that it is just barely possible to crumble away or break off the sharp edge of the wheel with the thumb nail, whereas a person cannot by muscular effort make an'indentation into the hardest grade of wheel by means of a hardened steel I of grinding. The expressions softer acting and harderacting are often used in this art as substitutes for soft grade and hard grade, owin to the fact that thesactual hardness-of t e bonditselfis not of prime 5 importance, it being merely its strength,
which give the rotating wheel an apparent hardness by virtue of which it resists being broken down by the material ground upon.
a The bond in a wheel of hard grade renders the wheel so resistant to disruption because it holds the grains so firmly in place that there is a tendency for the grains to become dulled under long usage and for the wheel to acquire a glazed appearance. Hence, in
wheel or one having softer acting characteristics, so that the grains will break away from their setting before they become sodull as to lose their ability to cut efficiently, although a soft wheel tends to wear away rapidly and have a relatively short life. The problem in making a wheel for a particular operation is therefore one which involves obtaining the maximum of service and efiiciency for the longest wheel life. I have found that in cutting such materials as hard carbon, the harder bonded Wheel tends to chip the carbon and so produce a rough and unsatisfactory cut, and if the wheel is sufiiciently soft to prevent chipping it is not economical and efiicient.
It is therefore aprime object of this invention to provide an abrasive wheel which will be efficient and economical in use, which will give high production per life of wheel and which will not injure the work or produce a badly appearing cut. Further objects will be apparent in the following disclosure.
As' a result of my experimentation I have discovered that a satisfactory grinding. wheel for such purposes may be made as a laminated structure consisting of an inner disk forming on the grinding periphery of the wheel a central zone-of vhard bonded abrasive grains which is ableto withstand the stresses of hard usa e and give high production for a long life, and outer layers integrally united therewith forming peripheral zones adjacent the wheel corners which act softer than the central zone during use and are capable of grinding and clearing the sides of the out without injuring the same.
One embodiment of my invention is shown in the accompanying drawing which represents a section of a cutting-off wheel. As there illustrated one type of a hard centered, soft sided wheel may comprise a central portion 10 of abrasive grains, such as SlllCOIl hard medium, such as vulcanized rubber, to which are integrally united side layers ll and 12 of abrasive grains bonded with "a softer composition than the rubber bond of" the central portion. The bond for the outer carbide, bonded with a suitable, durable and layers may consist of a suitable. water-proof and heat set abrasive bond, so called, such as a resin, either natural or synthetic, or a resin substitute, heat treatedto unite the grains together and cause them to adhere to the inner layer. In other types of wheel, I may employ rubber vulcanized to a lesser degree of hardness for the outer bond, and in certain cases, I have found it feasible to make the whole wheel by means of a shellac bond, the innerlayer being made harder by the addition of a hardening medium such as plaster of Paris or otherwise suitably treated to this end. Obviously, the laminae of the wheel may be made in accordance with various other methods and of many suitable compositions within the scope of my invention. One may also add soft sides to abrasive wheels of the usual types by slight modifications of the method herein described, as will be obvious toone skilled in this art, but such additions must be more than thin surface layers of abrasive grains cemented to the face of a wheel. They must be made up of disks of substantial thickness of abrasive grains bonded by hard and preferably heat set materials whlch are tough and capable of holding the grains in place under the severe strains of grinding, as well as resistant to heat and water.
As an illustration of one particular method in which the bonds are rubber and shellac, I may first form the central portion of a mixture of rubber and silicon carbide abrasive grains of a suitable size in accordance with well known practice. For example, sulphur, with or without a vulcanization accelerating agent, may be mechanically worked into the desired quantity of rubber bond, and the mass then mixed by means of rollers with a given amount of abrasive grains. This material, after having been passed through heated rollers a sufiicient number of times, is then rolled out into strips of desired thicknessand cut into a disk form corresponding with the diameter of the wheel. I The softer sides of the wheel may be added 'byplacing the proper thickness of a mixture of silicon carbide abrasive grains and powdered shellac in a mold, the ingredients having been proportioned according. to the degree of hardness desired. The'rubber disk is then placed over the la er in the mold and a further layer of the s ellac and abrasive mixture is then added above the rubber, after which the mass is subjected to pressure and heat in order to compact the sides and cause them to cohere and adhere to the central layer. The laminated wheel is subjected to vulcanization in a suitably heated apparatus in accordance with the usual practice. This heat treatment serves not only to vulcanize the rubber but to heat set the shellac and unite the grains into an integral mass in which the lines of demarka-' tion between adjacent layers are vnot pro within the scope of my invention to utilize different sizes of. grains in the different layers, either coarse in the center and line in the sides or vice versa. It however is essential that the bond of the central portion be materially harder than that of the side layers .or that, irrespective of the actual measured hardness and toughness of the bond, the side layers be bonded with such material that the grains will act softer in their cutting action and so not affect the work detrimentally. In accordance with this method, I have thus formed an abrasive wheel made up of three separate laminae, each of which is a body of bonded abrasive grains of suflicient coherence and strength to serve by itself as a grinding wheel, provided the layer is thick.
enough for this purpose. It is my belief that, owing to the outer layer being softer than the inner hard layers, in actual use the central zone formed by the rubber bonded mixture" does the major portion of the cutting, while the outer softer layers which form the peripheral corner zones become beveled or tapered so as to furnish means for gradually clearing the cut and smooth ing its sides. I have found that the outer zones should have a substantial width and ordinarily have more than a single grain depth of material' cemented to the wheel surface. If too thin and weakl bonded, this layer might be scraped off. uch outer layers function as they do, not because of essential differences in the abrasive grain but because of the characteristics of the bond employed, which make the peripheral corner zones act differently from the inner zone. I moreover employ for the outerzones bond materials which are not materially affected or changed by the heat generated during grinding orby any chemicals employed to lubricate or cool the surface 'of the cut.,
Having thus described my invention, what I claim as new and desire to cover by Letters Patent, is:
A grinding wheel adapted for cutting off lengths of objects comprising a lurality of abrasive discs integrally united and each composed of abrasive grain of substantially equal hardness united by asuitable organic acting and freer cutting than the-central bond, said discs being arranged to form a portion and form 'a substantial portion. of central zone having each side face covered thewheel periphery and serve to clear the 10 by a disc in which the grains are united by. cut during grinding.
5 a weaker bond than those of the central zone Signed at Worcester, Massachusetts; this thereby forming a peripheral cutting sur- 3rd day of Aug. 1922. face, the outer portions of which are softer CLARENCE RVKING.