US 2656654 A
Description (OCR text may contain errors)
Oct. 27, 1953 J. R. ERICKSON 2,656,654
GRINDING WHEEL Filed Jan. 6, 1950 2 Sheets-Sheet l 24J u l //A f2 2a 27 [Wewof HELE BLJDHN E ER/:KSUN /f A?,
Oct. 27, 1953 J. R. ERICKSON GRINDING WHEEL 2 sheets-sheet? Filed Jan. 6, 1950 Patented ct. 27, 1953 GRINDIN G WHEEL John R. Erickson, Worcester, Mass., assigner to Norton Company, Worcester, Mass., a corporation of Massachusetts Application January 6, 1950, Serial No. 137,245
The invention relates to grinding wheels.
One object of the invention is to provide a rugged grinding wheel of unbrittle characteristics which can be dropped on the floor (even a concrete floor) and stepped upon without even cracking, the wheel being more or less relatively thin. Another object of the invention is to provide such a grinding wheel which will not ily apart even if it is cracked by some extraordinary abuse. Another object of the invention is to provide a rugged grinding wheel which is free cutting.
Another object of the invention is to provide a grinding wheel particularly suitable for use in smoothening the welds on automobile bodies which are formed when sections of steel plate are Welded together and to provide a wheel particularly suitable for use in smoothening the welds on other fabricated metal or in smoothening protuberances, irregularities or rough spots of other kinds. Another object is to provide a grinding wheel which will take the place of coated abrasive discs (discs made out of heavy sand paper or heavy abrasive cloth) thus eliminating the frequent replacement of the abrading element, since grinding wheels made in accordance with this invention will outlast many such coated abrasive discs. Another object is to provide a grinding wheel having all the advantages of coated abrasive discs but Without the disadvantages thereof especially the disadvantage of quick exhaustion of useful life. Another object is to provide a tool which will quickly take on a bevel or mitre on the periphery, since grinding wheels so shaped are exceedingly efiicient for the purposes above indicated. Another object is to,
provide a wheel which can be used for the above purposes and also as a cutting-off wheel, for example to cut off gates and risers of castings. Another object is to provide a wheel suitable for removing rust and scale from steel plate.
Other objects will be in part obvious or in part pointed out hereinafter.
In the accompanying drawings illustrating a preferred procedure for manufacturing a wheel according to the invention and the Wheel so produced together with a representation of the power tool upon which it may be used,
Figure l is an exploded View illustrating in section theseveral components of the wheel in the raw state,
Figure 2 is a cross sectional view of a mold partly lled, that is containing some of the components of Figure l,
Figure 3 is a cross sectional view of the mold of Figure 2 completely filled and closed, that is the components having been pressed to unite to form the wheel,
i Figure 4 is a plan view of the completed wheel,
Figure 5 is a cross sectional view of the wheel after it has acquired a bevel or mitre together with the mounting disc therefor,
Figure 6 is a perspective view of a power hand tool such as used for smoothening welds, etc. having the wheel of the invention secured thereon. i
Referring first to `Figure l, I provide a quantity of dry granular mix I0 having organic bond` This comprises abrasive grains each granule of which is coated with the organic bond. As a practical matter the abrasive grains will usually be either aluminum oxide grains or silicon carbide grains. However other abrasives such as garnet or even diamonds can be used. Aluminum oxide abrasive is available in several different grades including the so-called regular grade which is a brown abrasive about A1203, the white porous variety which is about 98% pure or better and contains a small percentage of soda, and recently developed aluminum oXide abrasive produced in discrete crystals and being usually better than 99% A1203. Silicon carbide abrasive is also available in several different grades such as the black grades and the green, the latter being the purest grade. All this is known to the art and any variety of these or other abrasives can be used.
While so far as the broad aspects of the invention are concerned many diiierent organic bonds might be used I prefer to use available commercial grades of phenol formaldehyde resin otherwise known as resinoid. Unconverted phenol formaldehyde resin is available to the manufacturer in two forms, the solid phase material and the liquid phase material. For the production of a dry granular mix in which each abrasive granule is coated with an organic bond, the abrasive is placed in a mixing pan and then wet with a liquid and then, while continuing the mixing, bond in powdered form is added and eventually the abrasive coated with liquid picks up the powdered bond until each granule has an envelope of bond and the `entire mix appears to be fairly dry even though it does contain liquid phase material. Thus the abrasive grains can be wet with liquid phenol formaldehyde resin and then solid phase powdered phenol formaldehyde resin can be added to complete the formation of the dry granular mix.` On the other hand the abrasive grains can be wet with furfural `and then powdered resin added. The powdered phenol formaldehyde resin available and which is hereinafter identified contains a minor percentage of creosol formaldehyde.
In describing an illustrative embodiment of the manufacture of a wheel according to the invention, I shall describe the manufacture of a Wheel seven inches in diameter, one-eighth inch 3 thick and with a seven-eighths inch hole, the wheel having an off -set hub.
For the manufacture of this wheel a dry granular mix can be made from the following ingredients:
EXAMPLE I Dry granular mix ingredients No. 24 grit size aluminum oxide abrasive, l
regular grade pounds Powdered reactive phenol formaldehyde resin brand BR241'7 pounds-- 1.67 Carbon black do .027 Natural cryolite powder do .68 Furfural c'ubic centimeters-- 20 Anthracene fractions from coal tar do- 20 cryolite improves the grinding action of the wheel, 'makes it stronger and also improves the consistency of the mix. With this small amount of furfural in the mix about 80% of the bond .is loose in the mix. The carbon black gives a uniform color, to Wit, black.
Referring now to Figures 2 and 3, I provide a steel mold consisting of a cylindrical mold band II, a bottom plate I2, a top plate I 3, and an arbor I4. For the manufacture of a wheel with an offset centen the bottom plate I2 and the top plate I3 can be shaped as shown. Further description of the mold would seem to be superflu- `ous since the drawings are clear and molds of this general character are well known to everybody concerned the manufacture of grinding wheels.
Figure 2 shows the mold with the mold band I I, the bottom plate I2 and the arbor I4, the tcp plate I3 being absent. The mold in this condition is filled with the various ingredients to be pressed as follows:
First a layer I5 of powdered resinoid is charged into the mold and levelled as shown. For a Wheel seven inches in diameter, one-eighth inch thick and having a seven-eighths inch central hole the amount of material for the layer I5 should be about grams. For this material vI now pref-er a phenol formaldehyde powder containing a minor percentage of polyvinyl butyral. This material is procurable on the market under the brand designation No. '795. With this material I mix about 1% by weight of carbon black. This phenol formaldehyde polyvinyl butyral combination cures quickly, makes a tough resinoid which has lower heat resistant properties than ordinary phenol formaldehyde resin. The purpose of this layer I5 is to form a protective coating for the nylon and also to prevent the cured wheel from :sticking to the bottom mold plate 12. It is advantageous to have this layer heat sensitive because we want it to wear away readily during grinding.
-I next place in the mold a 2-ply layer I6 of nylon lleno cloth 'cut in the shape of a disc with a central hole. Nylon is, of course, the condensation product of hexamethylene diamine and adipic acid, while woven and knitted materials of nylon are known to everybody. The leno weave is the weave that has been known for generations for the manufacture of bolting cloth EEG 4 as well as the so-called marquisette fabric. In leno weaving the warp threads are drawn double and the harness frames instead of raising one section of the warp and lowering another section thereof move one of each. pair of warp 'ends over and across the other thereof at each pick. All of this is well known in the weaving art'. I have found that nylon leno cloth having twenty-one picks to the inch and twenty-one double sley is satisfactory. The weight of this material in a single ply is 3.6 ounces to the square yard. Furthermore this Z-ply nylon leno cloth was coated with a rubber compound of the following composition:
EXAMPLE Il Composition of rubber coating on nylon leno cloth Parts by weight Butadiene acrylic nitrile copo-1ymer 100 Zinc oxide 200 Sulphur 2 Paracumarone I 50 Carbon black 3 The above ingredients are first thoroughly mixed (only the paracumarone is a liquid) their calendered into sheets and then dissolved in enough methyl ethyl ketone to make the material of the consistency of dough or slightly thinner. The nylon leno cloth is then run double between a pair of steel rolls and this dough-like material applied at the leading edge. The rolls are set together close enough to leave only a thin coating of the rubber compound. In the illus. trative example of the invention the composition of Example II in the nylon leno cloth weighs 50% to 60% of the total of composition and cloth. After heating the cloth so treated to drive olf the methyl ethyl ketone, it is cut into 2-ply discs I5 having a one inch central hole and being about six and seven-eighths inches in diam-` eter. Making the 2-ply disc I6 slightly less in diameter than that of the nal wheel eliminates a frayed edge in the finished product. The 2-ply disc I6 does not follow the depression I'I in the mold plate I2 because it is too stiff.
I next add a layer of grams of the dry granular mix I0 which is levelled off in the mold. The mold is preferably on a revolving turn-table during filling which facilitates levelling.
I then place in the mold a single ply disc I8 of glass fabric. The glass fabric I have used had a plain weave with eighteen picks to the inch and eighteen sley and weighed 9.56 ounces per square yard. I prefer to use a single ply vglass cloth disc only six and seven-eighths inches in diameter for the above stated reason of avoiding a frayed edge on the wheel and this disc may have a one inch central hole. This glass cloth as provided by the manufacturer has a coating of oily and starchy material thereon. I have found it advisable to heat the glass `cloth vat 300 C. for three hours which drives off the oils and chars the starch. This seems to stop the discs from fraying. It makes them stiffer and facilitates handling.
I next charge the mold with ano-ther layer of 80 grams of dry granular mix IIJ and level it off. I then insert another single ply disc of glass cloth I8. I then add another layer of l0 grams of powdered resinoid I5 and level it olf. I then insert the top plate I3 and the mold is now charged and ready for hot pressing. Prior yto iilling the mold it is advisable to coat all the lthe mold is stripped and the wheel is removed.
`The pressure is not exactlycritical 'although a fairly substantial pressure should be used, for example 500 pounds or more. If the mix is very ilowable. a. low degree of pressure should be used, otherwise resin will ooze out between the top plate and the mold band. In general I have found that the pressure should be not higher `than 1500 pounds per square inch and not less than 300 pounds per square inch. In practice the movementof the top mold plate I3 is measured and when an average iigure for the best wheels isfound mold stops are set to close the -mold to the stops regardless of slight variations in pressure involved in so doing. Molding to stops is now per se well known in the art.
The completed wheel 2l) is shown in Figures 4, 5 and 6. It is a disc with an offset hub 2I and a `central hole 22, a front face 23 and a rear face 24. After grinding the welds on automobile bodies, its periphery usually acquires a taper 25 but prior to grinding it has a square edge periphery 2li. Thel front face 23 is desirably knurled and this way may be achieved as follows: the mold plate I3, being made of a soft steel such as cold rolled steel, is mounted in a lathe and then a knurling tool is fed against the inside face of the top plate I3 to make a ring of knurling and then the knurling tool is moved inwardly or outwardly and the operation is repeated until the fiat portion 21 outward of the offset forming portion 28 has been knurled all over its surface. It is practically impossible to show this feature in Figure 2 but Figure 4 shows the knurling 30 thus illustrating the pattern on the top plate I3.
This knurling of the front face 23 gives the Wheel a better appearance but additionally it improves its action when used as a cut-olf wheel. For this reason the rear face 24 may also be knurled if desired. However up to now the rear face 24 has always been flat and the wheels have been found view.
The glass cloth discs I8 give strength to the wheel so that it is found it does not break until to be superior from all points of a -speed of 30,000 surface feet per minute is reached. It is well known that grinding wheels of a given composition break at a given speed measured in surface feet per minute regardless of varying diameter provided the central hole is proportionately the same size in the dlfferent wheels, so therefore a breaking speed of so many surface feet per minute has a real meaning even though the diameter is not specified and the variation due to different ratios'of the d1ameter of the central hole is usually a small variation. The nylon leno disc on the other hand keeps the wheel from flying to pieces after it has been cracked as by a severe blow. In other words, there is a cooperation between the two reinforcements in that one (the glass cloth) acts as a primary strengthener and the other acts as a secondary strengther. Breakage of the glass cloth occurs before the nylon leno cloth breaks due to the greater stretchability of the nylon leno. Yet nylon is exceedingly strong and therefore al- 'though a cracked Wheel may not be as' useful for grinding as an uncracked wheel, nevertheless the fact that it will not ily to pieces is vitally important because a hand tool that flies to pieces usual- 1y injures the operator. Wheels according to my invention are recommended for operation up to 11,000 surface feet per minute thus leaving a large factor of safety for protection of operators. At speeds of 11,000 surface feet per minute and below these wheels are highly eicient grinding 'wheels for the purposes indicated.
The purpose of the layer of resinoid I5 at the front face 23 is, besides preventing the cured wheel from sticking to the top plate I3, to prevent the knurling plate from injuring the woven glass disc I8. Thus this layer has a double function. The purpose of the layer Iii on theirear face 24 is not only to prevent sticking to the bottom mold plate I2 but also to improve the appearance of the :wheel and furthermore I have found that both of these layers function to make the wheels stronger. made up some wheels without layers I5 on the front face 23 and they were not so strong as those having the layers I5; Hence the provision of non-abrasive outside resinoid layers has several functions and generally stated results in a stronger and more durable wheel while at the same time .it is found that it does not interfere with the grinding action. Still another reason for the provision of the layer I5 outside of the nylon disc I6 is that when the wheel is used as a cutting-off wheel the resinoid keeps the metal from cutting the nylon disc.
It has already been pointed out that the Z-ply disc I6 does not follow the depression I6 but rather lies flat in the mold. By reason of the heating of the glass cloth the discs I8 also lie flat in the mold. Thus after the disc I6 is laid down the mold being lled is a flat mold and this permits filling to achieve uniform density throughout the wheel. An air space 3l is left in the mold but as soon as the top plate I3 is pressed downwardly, the air disappears, probably along the arbor I4. At all events by proceeding as described practically perfect wheels can be produced.
The formula given in Example I represents more bond by volume than in the average resinoid bonded grinding wheel. This factor together with the large amount of free bond in the mixture (free bond is bond not attached to an abrasive granule) gives a good ow of resinoid through the glass cloth and the rubber coated nylon cloth during curing. This makes the wheels very strong. A wheel made according to Example I has about 32% abrasive by volume, the balance being practically all bond including the cryolite ller and the glass and nylon cloth. However good wheels can be made according to this invention using between 25% to 40% abrasive by volume with a porosity from 0% to 10%. The above volume percentages of abrasive are calculated on those portions of the wheel which result from the curing of the layers Ill of dry granular mix.
Many variations can be made in manufacturing this grinding wheel. For example, the coating on the nylon leno cloth could be natural rubber' instead of butadiene acrylic nitrile copolymer or other rubber substitutes such as butadiene styrene copolymer could be used and other natural products such as gatta-perche.. Instead of dissolving the rubber or synthetic rubber, all of which can be described as elastomers, in methylethyl ketone, other solvents can be used