US 2326381 A
Description (OCR text may contain errors)
Patented Aug. 10, 1943 APPARATUS Fon THE MANUFACTURE oF GRINDTNG WHEELS Lowell H. Milligan and Robert H. Lombard,
Worcester, Mass., assignors to Norton Company. Worcester, Massachusetts Mass.,
a corporation of Original application November l19, 1936, Serial No.
111,720. Divided and this 2, 1940, Serial No1. 349,824
The invention relates to apparatus for the manufacture of grinding wheels, and with regard to its more specific features to the manufacture of diamond abrasive wheels bonded with vitried ceramic bond. This application is a division from application August our copending application Serial No. 111,'720 filed November 19, 1936 which has become Patent One object of the invention is to provide a vVitriiied diamond grinding wheel of relatively large diameter at a reasonable cost. Another object of 'the invention is to provide an apparatus specifically adapted for the manufacture of a ceramic bonded wheel comprising an outer annulus of diamond abrasive material ceramically bonded and an inner disk or core of ceramically bonded granular material.
Another object of the invention is to permit the manufacture of a medium to large sized grinding wheel containing diamond abrasive Vat a reasonable cost, more especially using vitriable or ceramic bond. Another object of the invention is to make a grinding wheel of two-part construction which nevertheless acts as an integral unit so far as many physical characteristics are concerned. 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 inthe following claims.
In the accompanying drawing in which is shown oneof many possible embodiments of the mechanical features of this invention,
Figure 1 illustrates in radial section the top and bottom plates of a mold, the central plug thereof, and an interposed compressed disk of granular material and vitried ceramic bond, al1 just after stripping from the mold ring;
Figure 2 is a viewof the parts and material shown in Figure 1, with the central plug pushed. downwardly and out of the top mold plate;
Figure 3 is a view similar to Figure 2, the top mold plate having been removed;
Figure 4 shows the foregoing parts turned' over and. a diierent bottom plate in lposition thereunder; Y
Figure 5 shows the next step vcomprising the pressing of the plug into the new bottom plate;
Figure 6 shows the parts after the erstwhile bottom plate has been removed;
Figure '7 is a fragmentary view illustrating a l portion of the apparatus for the second molding operation and showing the assemblage;
Figure 8 is a radial cross sectionthrough the entire mold for the second molding operation and its supporting structure, showing also upper and lower hydraulic press plungers, being the same apparatus a fragment of which is shown in Figure '7, however Figure 8 showing a subsequent step in the method; t
Figure 9 is a further fragmentary view of the apparatus of Figures '7 and `8, but showing the upper hydraulic press plunger Velevated and the mold for the second molding operation about to be stripped from its mold ring by the lower plunger of the hydraulic press; and
Figure 10 shows the final product of the invention.
It will facilitate an understanding of the invention to refer first to Figure 10 which shows the ultimate product. This product isa grinding wheel 20 comprising an annular band 2l of diamond abrasive bonded with a suitable bond, preferably and according to many features of the invention vitriiable ceramic bond, integrally united toa central disk' 22 having a central hole 23, which disk, so far as certain features of the invention .are concerned, may be of any substance having adequate strength but, so far as the preferred form of the invention is concerned, comprises granular material bonded with ceramic ,vitriedbond, the entire Wheel 20 being vitrified or burned in a kiln in a single firing operation. To produce this integral wheel 20, the multi-stage molding and pressing operations herein disclosed and indicated in the drawing are preferably used. AIt is desired that the shrinkage characteristics of thediamond part`2| and the nondiamond part 22 be the same or' as nearly alike as possible. It is further desired that the coefficient of expansion Aof the granular part in the part 22 be as nearly as may be the same as that of the diamonds in the part -2|, all in order that the finished yproduct shall have physical characteristics asnearly as possible those of a monolith so as to avoid breakage in use .or otherwise.
Diamonds to be used as abrasive grains in the r manufacture of bonded abrasive products are so zone can be completely used up with a minimum wastag'e, in the normal grinding operations for whichthe article is used. We have found that for many practical grinding operations diamonds can be most effectively bonded with a ceramic bond. Because diamonds are oxidizable, we prefer to use low firing temperatures. While the present `invention is not limited to any specific bond, nevertheless in order to disclose the best way now known to us of carrying our inven- I tion into actual practice, we note that the bond asaassi article. It is desired toioosen beth top and bottom plates from the pressed articleV 22a and 'at the same time we desire not' to removethe .plus 21 at any time entirely from the central Example I Frit: Parts Borax 32.2 lbs. Boric acid 25.4 lbs. Silica 37.6 lbs. '15 Hydrate of alumina 1.0 lbs. Whiting 3.8 lbs. Ball clay 30 or the followingz Example II Parts Kentucky ball clay 15 Ground illint 15.5 Borax 19.5
Bonds according to both of these examples are i soft at in the neighborhood of 1000 C.
Still considering preferred examples of the bestmanner of carrying the invention into practice, we -may take four parts by weight of diamond bort of 100 mesh grit size and one part by weight of any of the above ceramic mixtures. We add thereto 4% of the whole of a 4% solution of "Glutolineas a temporary binder, to plasticize the mass and toA give it sufficient green strength.
Placing this mixture aside, we made an exactly similar mixture of bond and granular material which in the preferred form of the invention is vitreous silica (SiOz) preferably of the same grit size as that of 'the diamonds, in the illustrative example 100 grit size. The proportion by volume of bond to silica should be the samev as the proportion by volume of bond to diamonds. The vamount of this second non-diamond containing mixture is calculated to have a volume, when hole of the pressed product 22a,'as otherwise there might be a breakdown of the graixgand bond at .the central hole. Therefore, we press the plug 21 downwardly to the position as shown in Figure 2 and no further.
Figure 3 shows the parts after the top plate 26 has been removed as described. The bottom plate cannot so readily be removed from the pressed disk 22a with the plug 21 in this position, as the disk and the mold plate stick together. Referring now to Figure 4, we invert the parts shown in Figure 3 and provide a new bottom plate 3| of somewhat larger size but with a central hole the same as that of the plates 25 and 26. We now locate this new bottom plate 3| in position, as shown in Figure 4, and by means of a pressing operation we pressthe plug 21 downwardly until the parts occupy the position shown in Figure 5. All these plug pressing operations may be readily performed in any hydraulic or mechanical press in a manner well known in the art, using an undersized plug as a pusher. Plate 25 is now removed by knocking it sideways as the plug 21 is clear of it.Y The parts are then in the condition' shown in Figure 6, in which an over's'ized bottom plate 3| supports a pressed 1 green wheel mixture or disk 22a, comprising 'disk 22a although it has been pushed back and l compressed, equal to -that of the disk 22, and
likewise the volume of the diamond containingmaterial is calculated to have the volume, when pressed, of the annulus 2|. The volume of these parts may be readily calculated geometrically and the total weight for a given volume will be readily calculated by those skilled in this art.
kReferring now to Figure 1 we provide a'mold Acomprising a mold ring, not shown, a bottom plate 25, a top plate 26, and acentral plug 21.
We place" in this mold a measured quantity of?,
'non-diamond containing mixture, as described above, and press in accordance with well-known practice. We thenstrip the mold ring from the mold and there exists between mold plates 25 and 26 a "g1-een pressed. disk 22a of nondiamond containing material. Referring now to Figure 2, we next press the core 21 downwardly 0until it absolutely clears the top plate 26. This permits theA top plate 26 to be removed without injuring the pressed product 22a in any manner whatsoever as it can be slid off. After a pressing operation involving many thousand pounds to the square inch, both the top and the bottom plates stick to thc pressed material thereof and have to be removed by relative movement in the nature ofv a shear in order not to destroy the pressed silica grain and ceramic bond, there being a.
. central plug 21 of a. length equal. to the combined "thickness of plate 3| and disk 22a which has.
never been removed from the central hole in the forth therein.
By reason of the procedure indicated, the' disk 22a is handled with minimum danger of breaking oil'- any portion thereof. Referring now to Figure 8, we provide second molding and pressing apparatus including an upper press plunger or platen 35, a lower press plnunger or platen 36 and a mold'ring 31 of special`characteristics, to be hereinafter described. Referring now to Figure '7,
we now place the bottom plate 3| inside the mold ring 31. Bottom plate 3| ts in the mold ring 31 with a sliding fit, preferablya reasonably tight fit. As shown in Figure 1, the diskI 22a is still in position on the bottom plate 3l. The
' best manner of'introducing the disk3| into the ring 31 is to lower the. plunger 36 until the plate 3| can be `moved into position, clearing all obstructons, carefully centering it and then moving upwardly the plunger 36. The press which maybe used in practicing this .invention is not found illustrated in detail as dydraulic presses are well known, and we utilize a hydraulic press having low 5and high pressure in order that the low pressure may be used when it is desired to bring parts into position and the high pressure may be used when actually pressing the mixtures.
Low pressure is used 'in elevating the plunger 36 to introduce the bottom plate 3|. Y
We now take the measured quantity of diamond abrasive and bond prepared as above described and tamp it into the space between the 5 mold ring 31 andr the disk 22a, this diamond abrasive ceramic bonded material being indicated at 2|a in Figure '1. We then placel in position a top mold plate 4| which is shown in Figure 8. This plate may have a bayonet slot 42 for ready handling thereof. We now bring the plunger 35 downwardly with low pressure and the apparatus is ready for the second molding operation,
Still referring to Figure 8, the mold ring 31 is chamber 43 opening into an inner peripheral slot 44 extending all the way around the mold ring. The mold ring is an integral piece of great strength. Excepting for the slot 44, chamber 43 V 3 has been burned out, thereafter at a temperature in the neighborhood of 1000 C. in a non-oxidizing` atmosphere.
has only two entrances, viz. an opening 45 in the form of a tapped hole connected to a steel `pipe 46 of great strength with a small bore. The other opening is another tapped hole 41 closed by screw plug 48. Themold ring 31 has an integral radial flange 50 in which is located a depression 5| to receive the pipe 46. A series of massive rods 52 are located around the periphery and extend.
through the flange 50 and are secured thereto and to a reinforcing ring 53 by means of nuts 54 fittingon threaded portions 55 of the rods 52. These rods 52 extend downwardly from a portion of the hydraulic press mechanism, not shown,
and are suitably anchored thereto. 'I'he construction shown constitutes a mold ring 31 of great strength able to resist all ordinary forces in either vertical direction and having an annular chamber 43 able to hold enormous pressures.
In the chamber 43 and'extending through the annular slot 44 is an annular rubber ring 6|! of uniform cross section-around the circle and of T shape in cross section, as shown. The corners of the junction between the chamber 43 and the slot 44 are rounded, as shown, and so also is the rubber at that point. Rubber is a deformable but not compressible substance and when subjectedY to comparatively large pressures ows practically like a liquid. Simultaneously we intraduce high pressure through the pipe 46 and against the press plungers and 36. This may be done by operating three high pressure valves from a single lever. 'I'he upper and lower press plungers 35 and 36 are provided in order that the enormous pressures which are preferably used to compact the material may not split the mold ring 31 open. We prefer to use pressures of the order of 6000 lbs. to the square inch. Difference in thrust of the plungers 35 and 36 owing to the weight thereof is readily taken care of by the supporting structure for the mold ring, When this pressure is applied in the manner indicated, the mixture 2|a is compacted to the condition shown at 2|?) (Figure 8) and all parts of this mixture as well as of the disk 22a are subjected to the pressure chosen. It will be seen that even the plug 48 which seals the opening 41 is backed up by the upper plunger 35.
After the full pressure has been turned on for a few minutes, it is released in all three places and thereupon the rubber ring expands to the position shown in Figure 9. The mixture 2|a, however, is now compacted to a pressed peripheral annulus 2lb. Both plungers 35 and 36 are then moved away from the ring 31 and a stripping member of slightly less diameter than the bottom plate 3| is now placed in position and the lower plunger 36 is moved upwardly Iwith the low pressure, which strips the plates 3|, 4|, plug 21 and pressed article comprising disk 22a and pressed annulus 2| b from the ring 31. The 'upper plate 4| may n ow be readily removed by tapping it sideways. Then plug 21 may be removed by a downward pressing operation and the pressed rIn the shrinkage following the application of the maximum heat, the vitreous silica, having a coefficient of expansion fairly close to that of diamonds, contracts at a rate close to that of thea diamond abrasive. rlhe ratio by volume of silica to bond' is the same as that of diamonds to bond, and the bond in the inner portion-is the same as that in the outer portion and, therefore, no shrinkagecracks appear and the article is an integral one-piece structure so far as its physical characteristics are concerned and has no strains therein, one physical characteristic alone excepted, and that is thel abrasive properties of the annular band 2|. I
It will be seen that according to the construction shown, the pipe 46 does not move during use of the apparatus. A rigid pipe connection to the mold ring 31 is made possible by the use of two press'plungers, viz. the upper press plunger 35 and the lower press plunger 36. By using a stationary mold ring, leakage of high pressure fluid is avoided. The chamber 43 may be and preferably is filled with liquid at all times, and by reason of the provision lof the hole 41. Vand plug 48 it is possible to remove all air from the chamber 43. Notwithstanding these advantageous features, :it is a relatively simple operation to remove the m'old'ring 31 and substitute another one of a i different size. l
closed in our copending application, in an. electric furnace, rst in an oxidizing atmosphere at a low temperature until the temporary binder The uid pressure that enters the chamber 43 is preferably equalV toor even slightly greater than the pressure which was used to compact the Idisk 22a. This will insure a given grade4v hardness of the entire product and the volume percentage of abrasive, bond and pores, or granular materiakbond and pores will be very nearly consta-nt throughout the mass. Under these conditions of a final pressing operation involving a given pressure which is transmitted to the entire machine, a homogeneous product without strains results.
So far as certain features of the'invention are concerned, the apparatus may be used for molding diamond abrasive in the form of an annulus or ring upon any central disk which -will withstand the vitrifying temperature in a ceramic kiln. Certain advantages of the invention may be achieved replacing the disk 22a with a prefired abrasive disk. Furthermore, the apparatus may be used to press mixtures including bonds other than ceramic bond.
It will thus be seen that there has been provided by this invention an apparatus in which the 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 of the above invention, it is to be understood that all matter hereinbefore setv forth or shown in the accompanying drawing is to .be interpretadas illustrative and not in a limiting sense.
1. Mold apparatus for making a grinding with the space between said two pressure plates,
means for exerting pressure to force one of said pressure plates in a direction toward the other and thereby compress in an axial direction grinding wheel material received in said above-mentioned space, a deformable member inv said slot and forming a peripheral boundary for said space and operating under the action of said uid pressure to compress said grinding wheel material 'inwardly in the direction of the radii to the axis of said cylindrical face.
2. Mold apparatus as claimed in claim 1, com-v 'prising means operable, during application of fluid pressure in said chamber to said deformable member, to back up the upper and lower one of said plates and for that end of said mold` ring adjacent said onerplate and movable pressure-applying means operating upon the other of said plates and engageable, to limit the extent of axial compression of said material and to A back up the other end of said mold ring against the action of -fluid pressure` in said annular chamber upon the parts of said mold ring to either side of said slot, with the mold ring at that end thereof adjacent said other plate.
4. Mold apparatus for making a grinding lar chamber and connecting with the latter intermediate of its upper and lower axial extremes, and a deformable member in said slot forming a variable peripheral boundary for said space and having internally of said annular chamber upper and lower extensions to rest against the upper and lower portions of the internal wall of said chamberthat is intersected by said slot,
whereby, upon the application of uid -pressure in said chamber said deformable member is pressed radially inwardly against said grinding wheel material and-its upperl and lower extensions are compressed against said upper and lower wall portions of said chamber.
5. Molding apparatus for grinding wheel construction comprising means forming a space for receiving grinding wheel material, thev peripheral boundary of said spacev comprising a ring-like member of deformable material, said ring-like member being of substantial radial dimension, means for exerting pressure thereon to cause it to compress said 'grinding wheel material substantially uniformlyY throughout its periphery and inwardly in the general direction of the radii\ of said ring-like member, and two axially spaced elements, each to one side of said ring-like member,to guide said deformable member radially inwardly and against displacement axially.
6. Mold apparatus for grinding wheel construction comprising an annular mold element having a top and bottom to form a space fior receiving grinding wheel material, said annular wheel comprisingan annular mold ring having ari-'annular chamber therein connected with a source of uid pressure, said ring havingV mijn# ternal cylindrical face and telescopically receive A ing thereiriupper `andlower pressure plates having a slot extending about said cylindrical face and communicating with said chamber and with the space between said two pressure plates,
' means for exerting pressure to force one. of said pressure platesin a direction toward the other and thereby compress in an axial direction grindf ing wheel material received in said above-men tioned space, said slot being of lesser axial dlmension than the axial dimension of I"said annumold element having therein an annular chamber communicating with said space by a continuous peripheral slot that is of lesser axial dimension than that of said chamber, a deformable means seated in said slot to close it oil and having a peripheral portion exposed to said chamber that is of greater axial dimension than that portion thereof that is seated in said slot,
` and means for applying fluid pressure to said chamber to force said deformable member radi- 'ally .inwardly against. and to compress, said grinding wheel material.
.LOWELL H. rmLIGAN. ROBERT H. IMBARD.