US 3840357 A
Description (OCR text may contain errors)
United States Patent [191 Shim'izu [4 1 Oct. 8,1974
[ ROTARY GRINDING WHEEL AND ITS 3.030.743 4/l9h2 Raymond 5l/298 M TH OF MANUFACTURING 3.116986 H1964 Goepfert et al 51/298 Yozo Shimizu, l0-22-Funabori 5, Chome, Tokyo, Japan Filed: July 27, 1972 Appl. N0.: 275,702
Foreign Application Priority Data Aug. 27, 1971 Japan 46-65706 U.S. Cl. 51/297, 51/298 Int. Cl B24d 11/00, C08g 5l/l2 Field of Search 51/295, 297, 298
References Cited UNITED STATES PATENTS 4/1961 Baumgartner 5l/298 Primary Examiner-Donald J. Arnold Attorney, Agent, or Firm-William Anthony Drucker [5 7] ABSTRACT A rotary grinding wheel is provided which comprises a plurality of interconnected grinding layers and a pair of reinforcing fabrics applied to the outer surfaces of the grinding layers. The renewing action of the edge of the grinding layers occurs preferentially at the interface between the layers than in the remainder,
whereby atplurality of leading tops are formed: during use, which ensure a proper direction of cutting.
Y 9 Claims, 6 Drawing Figures The invention relates to the art of a rotary grinding wheel, and more particularly to a rotary grinding wheel for cutting purposes and a method of manufacturing same.
It is known that a grinding wheel incorporating phenol resin or other thermosetting resin as a binder has a suitable resilience for its use with cutting purposes. However, a rotary grinding wheel of such construction has a drawback that the cut surface of a workpiece is not formed straightforward because of the tendency for its edge to deviate from a predetermined path during the cutting operation. Such drawback results from a high resilience of the rotary grinding wheel which is in turn caused to a large proportion by its construction. Thus, while a fresh grinding wheel has an edge which is at an angle of 90 with respect to its lateral sides, the edge becomes abraded to a rounded form (see FIG. 1) during use, which causes the above-mentioned tendency.
In a grinding wheel of any kind, as grinding grains become abraded during the grinding operation, they tend to fall off because of reduced bonding strength, as a result of-reducedbonding area, which cannot overcome the grinding resistance, and then new grains appear to act as cutting edges, which is known as a self-dressing action of a grinding wheel. A disc-shaped rotary grinding wheel customarily comprises a reinforcing fabric embedded therein as a middle layer which prevents the self-dressing action at the edge from occurring uniformly along the thickness, with consequence that grains tend to fall off more rapidly adjacent to the sides than at the median region. This results in the formation of a leading top at the edge which is abraded to a rounded form. This increases the deviation problem referred to above, mainly because the leading top would not be constrained sufficiently to prevent it from running in a free direction.
Therefore, it is an object of the invention to provide an improved rotary grinding wheel having an edge which is capable of cutting a workpiece along a straight path without deviation from a predetermined path during a cutting operation.
Another object of the invention is to provide a method to manufacture the improved rotary grinding wheel in an improved manner.
In accordance with the invention, a rotary grinding wheel is constructed so that a plurality of leading tops will be formed in use which constrain each other to prevent one leading top to follow an arbitrary path so that the leading tops as a whole will be driven into a workpiece along a straight path. In one embodiment of the invention, the rotary grinding wheel comprises a plurality of interconnected grinding layers with their outer lateral sides covered with reinforcing fabrics such as cloths of glass fibre, for example, the respective grinding layers having boundary regions where they adjoin each other and at which the self-dressing action is to occur preferentially than the remainder.
Above and other objects and features of the invention will become apparent from the detailed description with reference to the drawings, in which:
FIG. 1 is a section of a conventional rotary grinding wheel for illustrating the abrasion of the .periphery with use together with improper paths in a workpiece followed by the grinding wheel;
FIG. 2 is a section of part of the rotary grinding wheel according to the invention;
FIG. 3 is a section of the rotary grinding wheel of the invention, illustrating the abrasion which occurs in the periphery thereof with use and illustrating, in phantom lines, the proper path which the grinding wheel follows;
FIG. 4 is a section of an apparatus suitable for use in manufacturing the rotary grinding wheel of the invention;
FIG. 5 is a section of part of a slightly modified rotary grinding wheel from that of FIG. 2; and
FIG. 6 is a section of an apparatus suitable for use in manufacturing the rotary grinding wheel shown in FIG. 6.
Referring to FIG. 1, there is shown a conventional rotary grinding wheel 1 which includes a reinforcing fabric 2 such as a cloth of glass fibre as a middle layer. The presence of such a reinforcing fabric results in abrading the edge to a rounded form illustrated, thereby forming a leading 'top 3. As indicated previously, the edge of such a shape may lose its way asindicated by arrows rather than advancing through a'workpiece 4 on a line which is aligned wheel 1.
The rotary grindingwheel constructed according to the invention is shown in FIG. 3', where it will be noted that the grinding wheel is covered with a pair of reinforcing fabrics 5a and 5b on its both lateral surfaces and includes therebetween a a pair of grinding layers 6a and 6b which are bonded together along an interface 7. Each of the grinding layers 6a and 612 comprises grinding grains 8 and binder 9 (FIG.. 2) and is constructed in a similar manner, that is, with the same parosity, grain density and degree of bonding, even though pores are not shown in FIG. 2. However, it is to be noted that the two grinding layers 6a and 6b are not prepared integrally from the outset, but are bonded together after having been formed by separate compressure moulding operations. Thus, the t vv o grinding layers6a and 6b comprise two compression moulding 'sintered together. As a result, while it may be difficult to discern the inter face 7, its presence is nevertheless evidenced by the fact that, although in each individual grinding layer 6a and 6b, the grains 8 are bonded together by the binder 9 and hence engage or intermesh each other, there is no such engagement between the, grains in one of the grinding layers and the grains in the other at the interface 7, since the confronting surfaces of the both grinding layers which abut one another to define the interface are finished flat upon compression moulding.
From close study of the self-dressing action, it is found that the length of time until grains fall off is not solely determined by the area of support for the grains afforded by the adhering binder, but is also influenced by the manner of engagement between the grains. Ob-
viously, inter-engaging grains are delayed to fall off. Referring to FIG. 2, it will be noted that those grains 8a, 8b located adjacent to the interface 7 on the opposite sides thereof exhibit reduced engagement therebetween, with the consequence that, inthe rotary grinding wheel of the invention, the self-dressing action occurs preferentially in the region of the edge adjacentto the interface than in the remainder. This is illustrated in FIG. 3 in which two spaced leading tops 10 and 11 with a plane surface of the grinding are shown formed on the edge as a result of abrasion. An edge having a plurality of leading tops thus formed is effective to provide constraint upon the movement of the individual leading tops, which therefore are prevented from running in an arbitrary direction, the overall effect of the constraint being to drive the edge straightforward into the workpiece 4, as indicated in phantom lines in FIG. 3.
FIG. 4 shows an apparatus which is used in manufacturing the rotary grinding wheel of the invention. The apparatus may be conventional, and'includes a mould l2 and a press member 13. The manufacturing step illustrated in FIG. 4, hereafter referred to as a first step,
forms a compression moulding comprising a mixture of grains 8 and binder 9 and a reinforcing fabric 5 on one side of the mixture. In this step, the mixture is uniformly laid within the mould l2 and then the reinforcing fabric 5 placed thereon, whereupon the assembly is compacted by means of the press member 13. The procedure is similar to the usual practice except that no additional mixture is laid on top of the fabric 5. However, the fabric 5 may be placed first on the bottom of the mould and then the mixture charged thereon. It will be understood that the compression moulding com prises the reinforcing fabric 5 tightly secured to one side of the mixture compact.
The method of manufacturing the rotary grinding wheel according to the invention includes a second step in which two of compression mouldings obtained by the first step are applied together with their reinforcing fabrics 5 located outside and are sintered together. The parameters of the sintering may be chosen as usual such as, for example, at a heating temperature of about 200C for about 24 hours. It is to be noted that the sintering used in the prior art has been for a single compression moulding having a reinforcing fabric as a middle layer, while the sintering used in the method of the invention is characterized by bonding a pair of com pression mouldings together. In this mannena'grinding wheel having a plurality of grinding layers 6a and 6b is formed in accordance with the invention. Although the foregoing description dealt with using the pair of compression mouldings each having a reinforcing fabric to one side thereof, an additional compression moulding which comprises the mixture alone and'does not incorporate a reinforcing fabric may be interposed between the compression mouldings of the pair, Such additional moulding may be bonded with the other mouldings in the similar manner as abovementioned.
In the construction of the rotary grinding wheel shown in FIG. 2, the grains are tightly thrusted into the tissue of the fabric, and are effective to minimize premature abrasion of the fabric which may be caused by its friction with the cut edge of a workpiece as the grinding wheel is driven-into a workpiece of substantial thickness. However, such premature abrasion of the reinforcing fabric can be minimized or eliminated in a slightly different form of the rotary grinding wheel shown'in FIG. 5. In this embodiment, the grains 8c and 80' project through the fabrics on both sides to form grinding surfaces 14 and 15, respectively.
FIG. 6 shows a modified apparatus suitable for manufacturing the grinding wheel shown in FIG. 5. This apparatus is similar to that shown in FIG. 4 except that depressions 16 are formed in the bottom of the mould 12. In the method of manufacturing a'grinding wheel allowing the grains 8 to project through the mesh of the- I fabric 5. It will be seen that the sintering as abovementioned of two of such compression mouldings produces the improved rotary grinding wheel shown in FIG. 5. Alternatively, the same result can be obtained by using a mouldv similar to that shown in FIG. 6 together with a modified press member 13 in which the depressions are formed. In this instance, the fabric is placed on top of the mixture of the grains 8 and binder 9 charged into the mould 12.
Having described the invention, what is claimed is:
I. A rotary grinding wheel comprising a plurality of superposed mutually sintered together layers of grinding material, and a layer of reinforcing fabric secured by a thermosetting resin along each outerface of said wheel whereby self-dressing action occurs ina region adjacent to the interface between the layers and forms a plurality of outer leading edges during use.
2. A rotary grinding wheel according to claim 1 in which each of said layers comprises a separate compressed moulding of grinding grains and a thermosetting resin binder, and said layers are sintered together.
3. A rotary grinding wheel according to claim 1 in which each layer includes grinding grains and thermosetting resin binder, and said reinforcing fabrics are each secured to an adjacent layer by said thermosetting resin binder. I
4. A rotary grinding wheel according to claim 3 in which each ofsaid reinforcing fabrics has grains from I an adjacent one. of said layers projecting through the mesh thereof. I
5. A rotary grinding wheel according to claim I in which the reinforcing fabric comprises a cloth of glass fibre. I I I 6. A' method of manufacturinga rotary grinding wheel comprising a first step of compression moulding a mixture of grinding grains and thermosetting resin binder to a thin disc shape on a reinforcing fabric, and a second step of applying together the fabric free faces of two of said compression mouldings obtained by the first step with their reinforcing fabric located only on the outside faces and sintering the assembly together without application of pressure. I
7. A method of manufacturing a rotary grinding wheel according to claim '6, in which the first 'step is carried out by compression-mouldingsaid fabric together with said mixture on a flat surface.
8. A method of manufacturing a rotary grinding wheel according to claim 6, in which the first step is carried out by compressiommoulding said fabric together with said mixture on a surface having depressions therein, and said fabric'being in direct contact with saidsurface. I
-9. 'A'method of manufacturing a rotary grinding wheel according to claim 6, in which the sintering step is conducted at a temperature of about 200C.