Grinding wheel having high impact resistance, for grinding rolls as installed in place

Abstract: A grinding wheel having a circular outer periphery, and a working front end face for grinding a roll as installed in place on a rolling mill or other equipment, such that the front end face is held in pressed frictionally sliding contact with an outer circumferential surface of the roll. The wheel has an annular first abrasive member (12, 44, 82), and one or two annular second abrasive member(s) (14, 46, 84) which is/are formed integrally with the first abrasive member, and disposed on corresponding at least one of the radially outward and inward sides of the first abrasive member. Each second abrasive member comprises a bonding agent different from that of the first abrasive member, and has a lower modulus of elasticity than the first abrasive member. Also displsed is a grinding wheel having a single abrasive body whose inner and/or outer circumferential surface(s) is/are tapered such that the radial wall thickness decreases in an axial direction twoard the working end face. The abrasive body may preferably contain short glass, carbon or alumina fibers.

Description: The present invention relates generally to a grinding wheel according to the preamble of claim 1. Such a grinding wheel is fused for grinding the outer circumferential surface of a roll as installed on given equipment, has high impact or shock resistance and is less likely to chip or be otherwise damaged. Rolling surfaces of working rolls on a rolling mill, for example, may be roughened due to rolling contact with workpieces such steel ingots, billets and slabs, or locally excessively worn at the opposite end portions which contact the lateral end portions of the workpieces. Similar wearing conditions are encountered on other types of rolls such as back-up rolls which are provided for backing up the working rolls. Therefore, the outer circumferential surfaces of such rolls need to be ground to desired smoothness. To this end, there has been proposed a so-called "on-line" grinding method, in which a roll is ground by a cylindrical grinding wheel, for example, while the roll is installed on a rolling mill stand. In this instance, the grinding is effected such that the grinding wheel is negatively rotated by a rotating movement of the roll, or positively rotated by suitable drive means such as a motor, while the working end face of the wheel is held in pressed frictionally sliding contact with the outer circumferential surface of the roll. Typical examples of such a method and grinding devices for practicing the method are disclosed in the documents JP-A-61-140312, JP-A-61-154706 and JP-A-62-127109. According to the "on-line" grinding method disclosed therein, the rolls may be ground with higher efficiency, with a result of higher operating efficiency or productivity of the rolling mill, than in the case where the rolls are ground after they are removed from the rolling mill. A generic grinding wheel disclosed in the document JP-A-61-154706 has an abrasive member and is adapted such that the grinding wheel is negatively rotated by the rotation of the roll to be ground, while the grinding device disclosed in the above document JP-A-62-127109 is of the type in which the grinding wheel is positively rotated by a drive motor. In a common "on-line" grinding as described above, a plurality of grinding wheels are arranged in a line parallel to the axis of rotation of the roll, such that the grinding wheels are spaced apart from each other, and the grinding is conducted while the wheels are reciprocated in the axial direction of the roll. When the "on-line" grinding is effected while the roll is engaged in a rolling process, the grinding wheel may suffer from chipping, cracking or other damages at the radially outer peripheral edge portion of the grinding end face, due to vibrations of the roll in the process of rolling a workpiece, or due to collision of the grinding wheel with irregular stepped or raised portions or protrusions formed on the rolling surface of the roll, which arise from local wearing of the rolling surface. It is accordingly an object of the present invention to provide a grinding wheel for grinding a roll as installed on a rolling mill or other equipment, which grinding wheel is suitably protected against chipping, cracking or other damage, during grinding of the rolling surface having stepped or raised portions. This object is achieved by means of the features defined in the characterizing part of claim 1. According to these features the grinding wheel further comprises at least one second abrasive member having an annular shape, formed integrally with the first abrasive member and disposed on at least one of corresponding radially outward and inward sides of the first abrasive member wherein the working front end face of the wheel is formed by the front end faces of the first and second abrasive members. Each of the at least one second abrasive member comprises a mass of abrasive grains, and a bonding agent for bonding together the abrasive grains. The bonding agent of each second abrasive member is different from a bonding agent for bonding together abrasive grains of the first abrasive member. Each second abrasive member has a lower modulus of elasticity than the first abrasive member. In the grinding wheel of the present invention which has the first abrasive member and at least one second abrasive member having a lower modulus of elasticity, as described above, the first abrasive member having a comparatively high modulus of elasticity assures a sufficiently high grinding function. On the other hand, the second abrasive member or members with the comparatively lower modulus of elasticity, which is/are radially inwardly or outwardly, or radially inwardly and outwardly of the first abrasive member, is/are highly resistant to shock or impact applied thereto at the radially outer or inner edge or radially outer and inner edges. Each second abrasive member is therefore less likely to suffer from chipping, cracking or other damages, due to vibrations of the roll being ground, or due to collision of the grinding wheel with irregular raised or stepped portions on the outer circumferential surface of the roll. Hence, the instant grinding wheel permits efficient grinding of the roll as installed in place for operation, without conventionally experienced chipping or cracking at its edge portion. The second abrasive member is provided on at least one of the radially inward or outward sides of the first abrasive member, depending upon the specific manner of grinding by the grinding wheel. More particularly, the portion of the grinding wheel which tends to be damaged varies with the operating parameters of the grinding wheel, which include the amount of offset of the axis of the wheel relative to the rotation axis of the roll, the angle of inclination of the wheel axis with respect to a plane perpendicular to the roll axis. Thus, one of the following three configurations in terms of the number and position of the at least one second abrasive member is suitably selected: one second abrasive member disposed radially outwardly of the first abrasive member; one second abrasive member disposed radially inwardly of the first abrasive member; and two second abrasive members disposed radially outwardly and inwardly of the first abrasive member, respectively. For enabling the first abrasive member to provide practically sufficient grinding capability, it is desirable that the modulus of elasticity of the first abrasive member be held within a range of 2000-7000kgf/mm². To this end, the first abrasive member is preferably constituted by: a vitrified-bond wheel in which abrasive grains such as Al₂O₃ (alumina), SiC, CBN and diamond are bonded together by an inorganic bonding agent such as feldspar, pottery stone and refractory clay; a metal-bond wheel which uses a metallic bonding agent; or some species of a resinoid-bond wheel. The second abrasive member has a higher degree of shock or impact resistance than a conventional grinding wheel, provided the modulus of elasticity of the second abrasive member is lower than that of the first abrasive member. Preferably, the modulus of elasticity of the each second abrasive member is selected within a range of 100-1000kgf/mm². To this end, the second abrasive member may consist of a resinoid-bond wheel in which abrasive grains of Al₂O₃, SiC, CBN and diamond are bonded together by phenol resin, epoxy resin, polyvinyl alcohol resin, or other resin bond, or alternatively a rubber-bond wheel which uses natural or synthetic rubber. The use of such a resinoid-bond wheel or rubber-bond wheel enables the second abrasive member to be highly resistant to chipping, cracking or other damages. Where the at least one second abrasive member consists of a single second abrasive member which is bonded to an outer circumferential surface of the first abrasive member, a volume of the single second abrasive is preferably held within a range of 5-50% of a total volume of the first abrasive member and the single second abrasive member. In this case, the grinding wheel provides practically satisfactory levels of grinding capability and impact resistance. If the volume of the second abrasive member is less than 5% of the total volume of the wheel, the impact resistance tends to be insufficient. If the volume exceeds 50%, the grinding wheel may suffer from insufficient grinding capacity. Since the grinding capacity and the impact resistance are considerably influenced by the total wall thickness of the grinding wheel, the above volumetric ratio is determined based upon the size of the grinding wheel. The second abrasive member may contain evenly distributed short fibers, such as glass fibers, carbon fibers and Al₂O₃ fibers, as a material for improving the mechanical properties including the impact resistance, whereby the second abrasive member is effectively protected against chipping or cracking. Further, the short fibers improve the toughness and rigidity of the second abravive member, thereby permiting reduction in the required working surface which contacts the roll. Since the short fibers may be more easily evenly distributed, than long fibers, the mechanical properties may be improved uniformly throughout the mass of the second abrasive member, i.e., without specific directionality in the mechanical properties. Where the coefficient of thermal expansion of the short fibers is lower than that of the bonding agent, the elastic deformation of the second abrasive member due to the thermal expansion may be restricted. The short fibers preferably have a length within a range of 1-10mm. With the length exceeding 10mm, the short fibers tend to be entangled and difficult to be evenly distributed when the fibers are mixed in the material of the abrasive member, whereby some directionality of the mechanical properties of the abrasive member may appear. If the length of the short fibers is shorter than 1mm, the fibers do not sufficiently contribute to the improvement in the impact resistance of the second abrasive member, though the evenness of distribution is enhanced. It is desirable that the short fibers consist of a plurality of bundles, each bundle consisting of 50-500 fibers, for example. This permits easy mixing procedure and even distribution of the short fibers, and facilitates counting of the number of the short fibers necessary to assure the desired mechanical strength of the abrasive member. It is desirable that the diameter or thickness of the glass fibers be about 5-10 microns, that of the carbon fibers be about 3-15 microns, and that of the alumina fibers be about 1-15 microns. However, the length, diameter and number of the fibers of each bundle are not limited to those indicated above, but may be suitably changed, depending upon the abrasive grains and bonding agent of the second abrasive member. The first and second abrasive members may be separated at their interface, and the second abrasive member may be displaced relative to the first abrasive member in the axial direction toward the working front end face, due to a difference in the amount of elastic deformation between the first and second abrasive members upon pressed contact with the roll, due to a difference in the thermal expansion coefficient between the first and second abrasive members, due to vibrations of the roll, or due to collision of the grinding wheel with raised or stepped portions on the outer surface of the roll. To prevent the above displacement, it is desirable that the bonded circumferential surfaces of the first abrasive member and the second abrasive member have recessed and raised portions which engage each other, or alternatively, the bonded circumferential surfaces be tapered such that diameters of the tapered bonded circumferential surfaces increases in an axial direction of the wheel toward the front end face. More desirably, the bonded circumferential surfaces have the recessed and raised portions, and are tapered as indicated above. The above arrangements restrict the relative displacement or separation of the first and second abrasive members, or prevent the complete removal of the second abrasive member from the first abrasive, member even if the first and second abrasive members are more or less displaced relative to each other. Thus, high safety of operation of the grinding wheel is assured. For perfect prevention of the removal of the second abrasive member, an angle of taper of the tapered bonded circumferential surfaces of the first and second abrasive members is desirably 1° or more, depending upon the bonding strength of the first and second abrasive members. The area of the front end surface and the grinding capacity of the grinding wheel suddenly decrease as the front end surface is worn, if the taper angle is excessively large. Therefore, the taper angle should be determined so as to provide an optimum compromise between the prevention of removal of the second abrasive member and the grinding capacity of the grinding wheel. The taper angle is selected generally within a range of 1-40°, and preferably within a range of about 2-6°. For improving the impact resistance of the edge portion of the second abrasive member, at least one of inner and outer circumferential surfaces of the second abrasive member which is not bonded to the first abrasive member may be tapered such that the total radial wall thickness of the first and second abrasive members decreases in an axial direction of the wheel toward the front end face. In this case, the angle of the edge portion defined by the front end face and the tapered circumferential surface is made larger, and the impact resistance to chipping or cracking is increased. While the impact resistance increases with the taper angle, the area of the front end face decreases with the taper angle. To assure sufficient grinding capability and avoid a sudden decrease in the grinding surface area while assuring improved impact resistance of the second abrasive member, the taper angle of the above-indicated at least one circumferential surface of the second abrasive member should not exceed 60°, and is usually in the neighborhood of 20°, though the optimum taper angle varies depending upon the material and modulus of elasticity of the second abrasive member. The circumferential surface of the second abrasive member which is bonded to the first abrasive member need not be tapered, i.e., may be a cylindrical surface whose axis is parallel to the axis of the grinding wheel. However, this circumferential surface may also be tapered at substantially the same taper angle as the other circumferential surface not bonded to the first abrasive member, so that the second abrasive member has a substantially constant radial wall thickness. Where both of the inner and outer circumferential surfaces of the second abrasive member are tapered, the second abrasive member may be removed from the first abrasive member in the axially frontward direction if the bonded surfaces are separated from each other. To avoid this, it is desirable that the bonded circumferential surfaces of the first and second abrasive members have recessed and raised portions which engage each other. Preferable embodiments of the invention are defined in the claims 2 to 14. The foregoing and other objects, features and advantages of the present invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings, in which: Fig. 1 is an elevational view in axial cross section of one embodiment of a grinding wheel for grinding rolls as installed on a rolling mill; Fig. 2 is a perspective view of an inner abrasive member of the grinding wheel of Fig. 1; Fig. 3 is an elevational view in axial cross section of the inner abrasive member and a backing plate secured thereto; Fig. 4 is an elevational view in axial cross section, showing an outer abrasive member of the grinding wheel, which is formed by filling an annular space between the inner abrasive member and a mold, with a mixture material which includes abrasive grains; Figs. 5, 6 and 7 are a front and a right-hand side end elevational view, and a plan view, respectively, illustrating a condition in which the grinding wheel of Fig. 1 is used for grinding a roll of a rolling mill; Figs. 8-13 are views illustrating other embodiments of the present invention; Referring first to Fig. 1, reference numeral 10 generally denotes a grinding wheel which is constructed according to one embodiment of the present invention, for effecting on-the-spot rolling of grinding rolls as installed on hot-rolling mill stands arranged in a line, while the rolls are engaged or not engaged in a rolling process. The grinding wheel 10 has a circular outer periphery and includes an annular or cylindrical inner abrasive member 12, and an annular or cylindrical outer abrasive member 14 which is disposed radially outwardly of and integrally with the inner abrasive member 12. The inner abrasive member 12 is a vitrified-bond wheel which uses a vitrified bond such as feldspar, pottery stone, refractory clay and other inorganic substances. The modulus of elasticity of the inner abrasive member 12 is selected within a range of 2000-7000kgf/mm², preferably in the neighborhood of 5000kgf/mm², by controlling the proportion of abrasives such as Al₂O₃, SiC, CBN and diamonds, and the above-indicated vitrified bond. For example, GC320K8V and PA220L8V according to the grinding wheel identification of the Japanese Industrial Standards (JIS), or CB170M100VN1 (CONCENTRATION 100) may be suitably used as the inner abrasive 12. The inner abrasive 12 has a working annular front end face 18 which is inclined by an angle ϑ with respect to a plane perpendicular to the axis of the wheel 10, such that the axial distance between the front end face 18 and the rear end face decreases in the radially outward direction. The inner abrasive 12 constructed as described above functions as a first abrasive member of the grinding wheel 10. On the other hand, the outer abrasive member 14 is a resinoid-bond wheel which uses a resinoid or plastic bond such as expoxy resin. The modulus of elasticity of this outer abrasive member 14 is selected within a range of 100-1000kgf/mm², preferably in the neighborhood of 600kgf/mm², by controlling the proportion of the abrasive such as Al₂O₃ SiC, CBN and diamonds, and the resinoid bond. For example, GC220J8BY and WA220J8BY (JIS) or CBNC220J100BY may be suitably used as the outer abrasive member 14. The outer abrasive member 14 has a working annular front end face 22 which is inclined such that the end faces 18 and 22 cooperate with each other to form a straight surface. The radially outer edge of the front end face 22 of the outer abrasive member 14 is rounded to an arc radius of about 5mm. This outer abrasive 14 functions as a second abrasive member which uses the bonding agent (resinoid bond) different from that (vitrified bond) of the first abrasive member 12, and whose modulus of elasticity is lower than that of the first abrasive member 12. The outer or second abrasive member 14 includes evenly distributed short fibers of glass, carbon, Al₂O₃ or other suitable materials, as a reinforcing material for increasing its impact resistance and avoiding deformation due to its thermal expansion. The short fibers are provided in the form of bundles each of which consists of 50-500 fibers, preferably 100-200 fibers, each fiber having a length of 1-10mm, preferably about 3-5mm. Where the fibers are formed of a glass material, the diameter is held within a range of about 5-10 microns. The carbon fibers have a diameter of about 3-15 microns, while the Al₂O₃ fibers have a diameter of about 1-15 microns. In one specific example, dimensions d1, d2 and d3 of the instant grinding wheel 10 as indicated in Fig. 1 are 240mm, 220mm and 120mm, respectively, and the radial thickness of the cylindrical wall of the outer abrasive member 14 is 10mm. The volume of the outer abrasive member 14 is about 21% of the total volume of the inner and outer abrasive members 12, 14. The inclination angle ϑ of the front end faces 18, 22 is selected within a range of about 0.2-1°, and the axial length L of the inner abrasive member 12 is about 48mm. However, the dimensions and configuration of the grinding wheel 10 are not limited to those indicated above by way of example, but may be suitably changed, depending upon various grinding conditions such as the diameter of a roll to be ground, and the operating posture of the grinding wheel 10. The assembly of the inner and outer abrasive members 12, 14 is secured to one of the opposite surfaces of a circular backing plate 23, which has a round center bore. This backing plate 23 consists of the abrasive grains such as Al₂O₃, SiC, CBN and diamonds, which are bonded together by phenol resin. The backing plate 23 has nuts 28 embedded in the other or outer surface thereof, so that a mounting flange 33 is bolted to the backing plate 23, with bolts 30 screwed to the nuts 28. The mounting flange 33 is fixed to an end of a shaft 32 which is rotatably supported by a suitable bearing device, so that the grinding wheel 10 may be used to grind a roll or rolls as mounted on a rolling stand. The inner or first abrasive member 12 per se is shown in the perspective view of Fig. 2. To prepare this inner abrasive member 12, a mass of the selected abrasive grains such as Al₂O₃, SiC, CBN or diamond and a mass of the selected vitrified bonding agent such as feldspar, pottery stone or refractory clay are mixed together, in a suitable proportion. An intimate powdered mixture of the abrasive grains and the bonding agent, which is obtained by a suitable mixing or stirring method, is press-formed into a cylindrical shape, and the formed shape is fired at a temperature in the neighborhood of 1400°C. The fired cylindrical body is then finished to the desired dimensions. The finishing process includes a chamfering to provide the inclined end face 18, and may include roughing of the outer circumferential surface and the rear end face of the fired body, as needed. The thus prepared inner abrasive member 12 is bonded with an adhesive to the inner surface of the backing plate 23, as illustrated in Fig. 3. An epoxy resin adhesive may be suitably used to bond the abrasive member 12 to the backing plate 23. To prepare the backing plate 23, the selected material such as Al₂O₃ or SiC and phenol resin are mixed together into an intimate powdered mixture, in a suitable proportion so as to provide the backing plate 23 with a required value of mechanical strength. The mixture is press-formed into a desired disc-like shape, such that the nuts 28 are embedded in the outer surface of the formed body. The formed body is then fired at about 200°C, and the fired body is finished into the backing plate 23. The finishing process may include roughing of the inner surface to be bonded to the inner and outer abrasive members 12, 14. As illustrated in Fig. 4, a cylindrical mold 34 which has an inside diameter substantially equal to the outside diameter of the backing plate 23 is fitted on the outer circumferential surface of the backing plate 23 to which the inner abrasive member 12 has been bonded. In the meantime, there is prepared an intimate mixture which includes, in a suitable proportion, the selected abrasive grains such as Al₂O₃, SiC, CBN or diamond and epoxy resin as the bonding agent, and short fibers of glass, carbon, Al₂O₃ or other suitable material, if and as needed. The prepared mixture is poured into an annular space formed between the cylindical mold 34 and the inner abrasive member 12, and is left at the room temperature until the epoxy resin is cured for bonding the abrasive grains. Thus, the outer abrasive member 14 is formed as bonded to the inner abrasive member 12 and the backing plate 23. The assembly of the inner and outer abrasive members 12, 14 and the backing plate 23 is removed from the cylindrical mold 34, and the outer abrasive member 14 is finished. The finishing process includes a chamfering to provide the inclined end face 22. Thus, there is produced the grinding wheel 10 which is the integrally bonded assembly of the three members 12, 14, 23. The grinding wheel 10 attached to the shaft 32 is used as indicated in Figs. 5-7. In these figures, reference numeral 40 designates a roll 40 (working roll) which is rotated about a substantially horizontal axis ℓ, on a hot-rolling stand. The grinding wheel 10 is disposed such that an axis "m" of rotation of the wheel 10 is offset by a distance "s" in the vertically downward direction from the axis ℓ of the working roll 40, and such that the rotation axis "m" is inclined with respect to a plane "n" perpendicular to the axis ℓ, by an angle  which is almost equal to the inclination angle ϑ of the end faces 18, 22 of the abrasive members 12, 14. The grinding wheel 10 is supported by the shaft 32, rotatably about its axis "m", such that the end faces 18, 22 are held in pressed contact with the outer circumferential surface of the roll 40, by suitable pressing means. In this condition, the grinding wheel 10 is rotated counterclockwise as indicated by an arrow in Fig. 5, by the roll 40 when the roll 40 is rotated, as also indicated in Fig. 5. The grinding wheel 10 is reciprocated or oscillated in the axial direction of the roll 40 (in the right and left directions as viewed in Figs. 5 and 7). For example, the grinding wheel 10 is rotated at the peripheral speed of 400-1000 m/min. Since the rotating directions and speeds of the wheel 10 and the roll 40 are different and since the wheel 10 is reciprocated relative to the roll 40, there arise frictional sliding movements between the end faces 18, 22 of the abrasive members 12, 14 and the outer circumferential surface of the roll 40, whereby the outer circumferential surface of the roll 40 is ground by the end faces 18, 22. Usually, a plurality of the grinding wheels 10 are arranged in a row parallel to the axis of the roll 40, such that the wheels 10 are spaced apart from each other by a suitable distance. During a grinding operation wherein the grinding wheel 10 is held in pressed frictionally sliding contact with the outer circumferential surface of the working roll 40 in the process of a hot-rolling or cold-rolling operation, the grinding wheel 10 may be subject to a comparatively high degree of impact or shock, due to vibrations of the roll 40 or collision of the wheel 10 with projections on the roughened surface of the roll 40. Further, the frictional sliding movements of the wheel 10 relative to the roll 40 cause a tensile stress and a compressive stress to be exerted to the radially outer and inner portions of the end faces 18, 22, respectively. Therefore, if a grinding wheel consists solely of a vitrified-bond wheel having high heat resistance and high grinding capability but having a comparatively high modulus of elasticity (comparatively low impact resistance), the radially outer portion of the wheel subject to the tensile stress tends to easily chip or crack or be otherwise damaged. In view of the above drawback encountered in the known grinding wheel, the instant grinding wheel 10 has an integral double-layer abrasive structure consisting of the first or inner abrasive member 12 (vitrified-bond wheel) having excellent grinding capability, and the second or outer abrasive member 14 (resinoid-bond wheel) which has sufficiently low modulus of elasticity and accordingly high shock or impact resistance. Namely, the radially outer portion (outer abrasive member 14) of the grinding wheel 10 has improved shock resistance to withstand the tensile stress indicated above, and is therefore effectively protected against chipping or cracking, while the radially inner portion (inner abrasive member 12) assures efficient grinding of the workpiece. In particular, it is noted that the outer abrasive member 14 or the resinoid-bond wheel utilizing epoxy resin as the abrasive bonding agent has the modulus of elasticity as low as about 600kgf/mm², and the cylindrical wall thickness of as small as 10mm, which are combined to provide a synergistic effect of protecting the abrasive member 14 against otherwise possible chipping and cracking. Further, the inner abrasive member 12 which has the radial wall thickness of 50mm enables the grinding wheel 10 to provide a practically sufficient degree of grinding function or capability while assuring improved shock or impact resistance of its radially outer portion (outer abrasive member 14). Moreover, the inclusion of the short glass, carbon or Al₂O₃ fibers uniformly in the outer abrasive member 14 as the reinforcing material further improves the mechanical properties (including the shock resistance) of the radially outer portion of the wheel 10, thereby more effectively avoiding the chipping or other damages of the member 14 due to collision with the irregularities on the surface of the roll 40. Further, the short fibers are effective to increase the toughness and rigidity of the outer abrasive member 14, permitting reduction in the required area of contact with the surface of the roll 40, and protecting the member 14 against deformation due to thermal expansion. In this respect, it is noted that the short fibers exhibit a higher degree of even distribution throughout the mass of the abrasive grains and bonding agent, during preparation of the outer abrasive member 14. Accordingly, the mechanical properties of the abrasive member 14 can be uniformly improved, so that the abrasive member 14 has subtantially no directionality of its properties. The uniformity of the mechanical properties results in further reduction in the chipping or similar damage of the abrasive member 14. For instance, the abrasive member 14 contains bundles of short fibers having a length of 1-10mm, each bundle consisting of 50-500 fibers. In this case, the short fibers are easily uniformly distributed throughout the abrasive member 14, and the evenness of the properties of the abrasive member 14 is significantly enhanced. Referring to Figs. 8-14, other embodiments of the present invention will be described. In these figures, the same reference numerals as used in Fig. 1 will be used to identify the functionally equivalent components, redundant description of which will be omitted, in the interest of brevity and simplification. In the modified embodiment of Fig. 8 wherein a grinding wheel is indicated generally at 42. This grinding wheel 42 has a circular outer periphery and includes an outer abrasive member in the form of an annular vitrified-bond wheel 44, and an inner abrasive member in the form of an annular resinoid-bond wheel 46 disposed radially inwardly of and integrally with, the outer vitrified abrasive member or wheel 44. The inner resinoid abrasive member or wheel 46 has a lower modulus of elasticity than the outer abrasive member 44, because of the use of a resinoid bonding agent, and consequently provides the grinding wheel 42 with improved shock resistance at its radially inner portion. The instant grinding wheel 42 is suitably used such that its axis of rotation "m" is offset from the rotation axis ℓ of the working roll 40, in the vertically upward direction as viewed in Figs. 5 and 6. While a comparatively large tensile stress tends to be applied to the radially inner portion of the grinding wheel 42 in the case, the inner abrasive member 46 is resistant to such a tensile force. In the present embodiment, the outer vitrified-bond wheel 44 functions as the first abrasive member, while the inner resinoid-bond wheel 46 functions as the second abrasive member. Another second abrasive member having a comparatively low degree of modulus of elasticity may be provided radially outwardly of the first abrasive member 44. A grinding wheel 50 according to a further embodiment of the present invention shown in Fig. 9 is different from the grinding wheel 10 of the first embodiment of Fig. 1, in that the outer and inner circumferential surfaces of the inner and outer abrasive members 12, 14, which constitute a boundary or interface of the two abrasive members 12, 14, are formed, with a plurality of annular grooves 52 and a plurality of annular projections 54 which engage each other, while at the same time the interface surfaces of the backing plate 23 and the outer abrasive member 14 are formed with an annular groove 56 and an annular projection 58 which engage each other. Described more specifically, the annular grooves 52 are formed in the outer circumferential surface of the inner abrasive member 12 such that the grooves 52 are spaced from each other in the axial direction of the grinding wheel 10. The grooves 52 have a rectangular cross-sectional shape (as viewed in Fig. 9), and a width of about 5mm and a depth of about 1-2mm. On the other hand, the annular projections 54 are formed in the inner circumferential surface of the outer abrasive member 14, so that the projections 54 may engage the annular grooves 52. The annular groove 56 is formed in a radially outer portion of the backing plate 23 to which the outer abrasive member 14 is bonded, while the annular projection 58 is formed in the corresponding portion of the bonding surface of the outer abrasive member 14, so that the groove and projection 56, 58 engage each other. In the grinding wheel 50 constructed as described above, the outer abrasive member 14 has considerably increased areas of the interface surfaces which contact the corresponding surfaces of the inner abrasive member 12 and the backing plate 23, in the presence of the annular projections 54, 58 which engage the corresponding annular grooves 52, 56. The strength of bonding of the outer abrasive member 14 to the inner abrasive member 12 and the backing plate 23 is accordingly increased. Further, the engagement between the annular grooves 52 and the annular projections 54 prevents a relative displacement of the inner and outer abrasive members 12, 14 in the axial direction of the grinding wheel 50. The increased bonding strength and the prevention of the relative axial displacement cooperate to effectively minimize a possibility of separation of the inner and outer abrasive members 12, 14, which may occur for any of the following casues: difference in the amount of elastic deformation between the two abrasive members 12, 14 upon pressed contact with the roll 40; difference in the thermal expansion coefficient between the abrasive members; vibrations of the roll 40 during a rolling operation on the rolling stand; and collision of the abrasive members with the outer circumferential surface of the roll 40. Even if the outer abrasive member 14 was separated to some extent for some reason or other, the outer abrasive member 14 is prevented from being moved in the axial direction toward the end face 22. Thus, the instant grinding wheel 50 assures safety of operation. Further, since the annular grooves 52 and projections 54 are provided over the axial end portions of the abrasive members 12, 14 remote from the end faces 18, 22, the above-indicated advantages may be offered until the working surface (end faces 18, 22) of the wheel 50 is worn to an intolerable extent during use. Reference is now made to the embodiment of Fig. 10, wherein the annular inner and outer abrasive members 12, 14 of a grinding wheel 60 have tapered boundary or bonded surfaces, i.e., complementally tapered outer and inner circumferential surfaces 62, 64, respectively, such that the diameters of the circumferential surfaces 62, 64 increase in the axial direction toward the end faces 18, 22. Namely, the surfaces 62, 64 are inclined at an angle γ with respect to a cylinder whose axis is parallel to the rotation axis "m" of the grinding wheel 60. In the instant grinding wheel 60, too, an axial displacement of the outer abrasive member 14 relative to the inner abrasive member 12 in the axial direction toward the end face 22 is prevented by the engagement between the tapered outer and inner circumferential surfaces 62, 64, whereby the separation of the two abrasive members 12, 14 and the movement of the outer abrasive member 14 in the above-indicated axial direction are effectively prevented. Moreover, the present embodiment using the tapered surfaces 62, 64 eliminates a complicataed machining operation or a mold to form the annular grooves 52 as provided in the grinding wheel 50 of the preceding embodiment. Accordingly, the cost of manufacture of the grinding wheel 60 is reduced. However, the inclination angle γ of the tapered surfaces 62, 64 should not be excessive, in order to avoid a sudden decrease in the area of the inclined working end face 18 due to wear of the wheel 60, which results a sudden decrease in the grinding capacity of the wheel 60. For avoiding the separation or removal of the outer abrasive member 14 while assuring sufficient grinding capacity of the wheel 60, the inclination angle γ of the tapered surfaces 62, 64 should be held generally within a range of 0.5-20°, preferably within a range of 1-3°. In other words, the taper angle of the tapered surfaces 62, 64 (according to JIS: B0154) should be held generally within a range of 1-40°, and preferably within a range of 2-6°. Referring next to Fig. 11 showing a grinding wheel 70 according to a further embodiment of the invention, the inner and outer abrasive members 12, 14 have outer and inner circumferential surfaces 72, 74, which are tapered like the tapered surfaces 62, 64 of the grinding wheel 60 of Fig. 10, but are formed with annular grooves and projections similar to the grooves and projections 52, 54 provided in the grinding wheel 50 of Fig. 9. This embodiment provides the same advantages as offered by the embodiment of Fig. 9. A grinding wheel 80 shown in Fig. 12 includes the first abrasive member in the form of an annular inner abrasive member 82, the second abrasive member in the form of an annular outer abrasive member 84 bonding to an outer circumferential surface 86 of the inner abrasive member 82, and the backing plate 23 bonded to the rear end faces of the inner and outer abrasive members 82, 84. Like the vitrified inner abrasive member 12 of the grinding wheel 10 of the first embodiment, the inner abrasive member 82 consists of a vitrified-bond wheel whose modulus of elasticity is held within a range of 2000-7000kgf/mm², preferably in the neighborhood of 5000kgf/mm². Further, the outer abrasive member 84 consists of a resinoid-bond wheel which contains evenly distributed short fibers such as short glass fibers, and whose moduls of elasticity is held within a range of 100-1000kgf/mm², preferably in the neighborhood of 600kgf/mm², by adjusting the proportion of the bonding agent of epoxy resin and the abrasive grains, like the outer abrasive member 14 of the grinding wheel 10. The outer circumferential surface 86 of the inner abrasive member 82 is inclined at an angle β with respect to a cylinder whose axis is parallel to the axis of rotation of the wheel 80, so that the diameter of the surface 86 decreases in the axial direction toward a working annular end face 88 of the abrasive 82. The outer abrasive member 84 bonded to this tapered outer circumferential surface 86 of the inner abrasive member 82 has a constant radial wall thickness and a tapered outer circumferential surface 90 which is inclined at the same angle β as the inner abrasive 82. Stated differently, the first or inner abrasive member 82 has an outside diameter (86) which decreases in the direction toward the end face 88, so that the total radial wall thickness of the grinding wheel 80 decreases in the axial direction toward the end faces 82, 92 of the inner and outer abrasive members 82. 84. In this respect, the present grinding wheel 80 is different from the grinding wheels 10, 42, 50, 60 and 70 of the preceding embodiments of Figs. 1, 8, 9, 10 and 11. In the present grinding wheel 90, an angle of an edge 94 of the outer abrasive member 84 adjacent to the working front end face 92 is as large as ( ϑ + β + 90)°. This comparatively large angle of the edge 94 is an additional factor contributing to an increase in the shock or impact resistance of the edge 94, that is, a factor in addition to the use of a resinoid bonding agent to give the outer abrasive member 84 a comparatively low modulus of elasticity, and the use of glass or other short fibers contained in the mass of the abrasive member 84. While the impact resistance of the edge 94 increases with an increase in the angle β of the outer circumferetial surfaces 86, 90, the increase in the angle β results in a decrease in the area of the end face 88, and consequently resulting in a decrease in the grinding capacity of the grinding wheel 80, and a sudden decrease in the area of the end face 88 (sudden reduction in the grinding capacity) as the end face 88 is worn. For assuring a practically optimum compromise between the impact resistance of the edge 94 and the grinding capacity of the grinding wheel 80, the angle β should not exceed 30°, usually about 10°. That is, the taper angle (according to JIS: B0154) of the surfaces 86, 90 should be 60° or smaller, and usually about 20°. Further, the end faces 88, 92 are tapered such that the axial distance or thickness of the grinding wheel 80 decreases in the radial outward direction. The inclination angle ϑ of the end faces 88, 92 is selected within a range of 0.2-1° with respect to a plane perpendicular to the rotation axis of the wheel 80, depending upon the operating posture of the wheel 80. A grinding wheel 98 shown in Fig. 13 is identical with the grinding wheel 80 described above, except that the bonded outer and inner circumferential surfaces of the inner and outer abrasive members 82, 84 have annular grooves and projections, while the bonded surfaces of the outer abrasive member 84 and the backing plate 23 have an annular projection and an annular groove. According to this arrangement, the outer abrasive member 84 has increased strength of bonding with respect to the inner abrasive member 82 and the backing plate 23, and is suitably prevented from being separated or removed from the abrasive member 82 and backing plate 23, or being displaced in the axial and radial directions relative to these members 82, 23. In the illustrated embodiment of Figs. 5-7 of the manner in which the grinding wheel 10 is used for grinding the roll 40 by way of example, the wheel 10 is negatively rotated by the rotation of the roll 40, with the end faces 18, 22 being held in pressed contact with the outer circumferential surface of the roll 40, such that the axis "m" of the wheel 10 is offset relative to the rotation axis ℓ of the roll 40, and inclined with respect to the plane "n". However, the manner of grinding by the grinding wheel according to, the instant invention may be suitably changed, in various aspects such as the operating posture of the wheel. A suitable drive motor or a braking device may be connected to the grinding wheel, so that the wheel is positively rotated or stopped. It will be understood that necessary modifications or adjustments of the grinding wheel may be made in its dimensions and configuration, depending upon the specific manner in which the wheel is operated. While the grinding wheel is used to grind the working roll 40 as installed on a hot-rolling mill stand in the illustrated embodiment of Figs. 5-7, it is to be understood that the grinding wheel constructed according to the invention may be equally suitably used to grind other rolls such as back-up rolls for the working roll 40, and rolls provided on cold-rolling mill stands and other types of machines and equipments. It is noted that the method of preparing the grinding wheel 10 of Fig. 1 has been described above by reference to Figs. 2-4, for the illustrative purpose only. It will be obvious that the grinding wheel according to the invention may be produced by other methods. For example, the outer abrasive member 14 may be formed by bonding with an adhesive a plurality of arcuate abrasive segments to the outer surface of the inner abrasive member 12, such that the arcuate abrasive segments form the outer abrasive member 14. This modification may apply to the outer abrasive members of the other embodiments which include the first and second (inner and outer, or outer and inner) abrasive members. Further, the outer abrasive members 14, 84 of the grinding wheels 60, 80, which have a tapered inner circumferential surface, may be first formed separately from the inner abrasive members 12, 82, and are subsequently fitted on the outer circumferential surface of the respective inner abrasive members 12, 84, with a suitable adhesive such as epoxy resin applied to bond the inner and outer circumferential surfaces of the outer and inner abrasive members. The dimensions and cross-sectional shapes of the annular grooves 52, 56 of the grinding wheel 50 may be suitably modified. For instance, the width of the grooves 52, 56 at their opening is smaller than that at their bottom. Further, the annular grooves and projections 52, 54 having a rectangular cross-sectional shape may be replaced by corrugated or undulated outer and inner circumferential surfaces of the inner and outer abrasive members 18, 22. The same modification may apply to the grinding wheels 70 and 98. While the outer and inner circumferential surfaces 62, 64 of the grinding wheel 60 are tapered over the entire axial length thereof, the front end portions of the surfaces adjacent to the working end faces 18, 22 may be formed as cylindrical surfaces whose axis is parallel to the axis "m" of the wheel. In the grinding wheel 42, the outer first abrasive member 44 and the inner second abrasive member 46 have the cylindrical bonded inner and outer circumferential surfaces. To prevent displacement of the second abrasive member 46 relative to the first abrasive member 44 in the direction away from the backing plate 23, the two abrasive members 44, 46 may have tapered bonded surfaces which are formed such that the inside and outside diameters of the outer and inner abrasive members 44, 46 increase in the axial direction toward the backing plate 23. In the grinding wheels 80, 98 the outer circumferential surface 90 is tapered. However, the inner circumferential surface of the inner abrasive member 82 may be tapered such that the radial wall thickness of the member 82 decreases, i.e., the inside diameter of the inner surface increases in the axial direction toward the end face 88. This configuration is desirable where the radially inner portion of the grinding wheels 80, 98 is more likely to be damaged during a grinding operation, under certain grinding conditions including the operating posture of the wheels. In this case, it is desirable that the second abrasive member 84 of the grinding wheels 80, 98 be positioned radially inwardly of the first abrasive member 82, and have a tapered inner circumferential surface whose inside diameter increases in the axial direction toward the end face 92. If necessary, both of the inner and outer circumferential surfaces of the grinding wheels 80, 98 may be tapered such that the radial wall thickness of the wheels decreases in the axial direction toward the working end face. In the embodiments of Figs. 12 and 13, the outer abrasive member 84 has the tapered inner and outer surfaces which define a constant radial wall thickness over the entire axial length. However, the inner surface of the outer abrasive member 84, and the corresponding outer surface 86 of the inner abrasive member 82 may both be formed as cylindrical surfaces whose axis is parallel to the axis of the wheels 80, 98. It will be understood that the present invention may be embodied with various other changes, modifications and improvements, which may occur to those skilled in the art, without departing from the scope of the invention defined in the following claims.

Claims: A grinding wheel having a circular outer periphery, and a working front end face (18, 22; 88, 92) inclined such that the axial distance between the front end face and the rear end face decreases in the radially outward direction, said grinding wheel comprising: a first abrasive member (12, 44, 82) having an annular shape, characterized by at least one second abrasive member (14, 46, 84) having an annular shape, formed integrally with said first abrasive member and disposed on at least one of corresponding radially outward and inward sides of said first abrasive member, wherein said working front end face is formed by the front end faces (18, 22; 88, 92) of said first and second abrasive members, each of said at least one second abrasive member comprising a mass of abrasive grains and a bonding agent for bonding together said abrasive grains, said bonding agent of said each second abrasive member being different from a bonding agent for bonding together abrasive grains of said first abrasive member, said each second abrasive member having a lower modulus of elasticity than said first abrasive member. A grinding wheel according to claim 1, characterized in that a modulus of elasticity of said first abrasive member (12, 44, 82) is within a range of 2,000-7,000 kgf/mm², while said modulus of elasticity of said each second abrasive member (14, 46, 84) is within a range of 100-1,000 kgf/mm². A grinding wheel according to claim 1 or 2, characterized in that the abrasive grains of said first and second abrasive members (12, 14, 44, 46, 82, 84) consist of at least one of Al₂O₃, SiC, CBN and diamond. A grinding wheel according to any of claims 1 to 3, characterized in that said first abrasive member (12, 44, 82) consists of one of a vitrified-bound wheel, a resinoid-bond wheel and a metal-bond wheel, while each of said second abrasive members (14, 46, 84) consists of one of a resinoid-bond wheel containing one of epoxy resin, phenol resin and polyvinyl alcohol resin as the bonding agent, and a rubber-bond wheel containing synthetic or artificial rubber as the bonding agent. A grinding wheel according to any of claims 1 to 4, characterized in that said at least one second abrasive member consists of a single second abrasive member (14, 84) which is bonded to an outer circumferential surface of said first abrasive member (12, 82), a volume of said single second abrasive being within a range of 5-50% of a total volume of said first abrasive member and said single second abrasive member. A grinding wheel according to one of claims 1 to 5, characterized in that each of said second abrasive members (14, 46, 84) contains evenly distributed short fibers which are selected from the group consisting of glass fibers, carbon fibers and Al₂O₃ fibers. A grinding wheel according to claim 6, characterized in that said short fibers consist of bundles of fibers, each of said bundles consisting of a plurality of fibers having a length of 1-10mm. A grinding wheel according to any of claims 1 to 7, characterized in that said first abrasive member (12, 82) and each of said second abrasive members (14, 84) have bonded circumferential surfaces having recessed and raised portions (52, 54, 72, 74) which engage with each other. A grinding wheel according to any of claims 1 to 8, characterized in that said at least one second abrasive member consists of a single second abrasive member (14) disposed radially outwardly of said first abrasive member (12), and said first abrasive member and said single second abrasive member have bonded circumferential surfaces (62, 64, 72, 74) which are tapered such that diameters of the tapered bonded circumferential surfaces increase in an axial direction of the wheel toward said front end face. A grinding wheel according to claim 9, characterized in that an angle of taper of said tapered bonded circumferential surfaces (62, 64, 72, 74) of said first abrasive member and said single second abrasive member (12, 14) is within a range of 1-40°. A grinding wheel according to claim 9, characterized in that said tapered bonded circumferential surfaces (62, 64, 72, 74) have recessed and raised portions (52, 54, 72, 74) which engage with each other. A grinding wheel according to any of claims 1 to 11, characterized in that at least one (90) of inner and outer circumferential surfaces of at least one of said at least one second abrasive member (84) which is not bounded to said first abrasive member (82) is tapered such that a total radial wall thickness of said first abrasive member and said at least one second abrasive member decreases in an axial direction of the wheel toward said front end face. A grinding wheel according to claim 12, characterized in that an angle of taper of said at least one circumferential surface (90) is 60° or smaller. A grinding wheel according to claim 12, characterized in that said first abrasive member (82) and said each second abrasive member (84) have bonded circumferential surfaces having recessed and raised portions which engage with each other.

Inventors: GOTO TAKAYUKI, HAYASHI KANJI, HENMI YOSHINORI, MATSUSHIMA HISAO, SABURI KOUICHI, TANABE AKIRA, GOTO, TAKAYUKI ADVANCED TECHNOLOGY RESEARCH CENTER, HAYASHI, KANJI HIROSHIMA MACHINERY WORKS, HENMI, YOSHINORI, MATSUSHIMA, HISAO C/O HIROSHIMA MACHINERY WORKS, SABURI, KOUICHI, TANABE, AKIRA
Applicants: MITSUBISHI HEAVY IND LTD, NORITAKE CO LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA, NORITAKE CO., LIMITED
Application year: 1989
Main classification: B24D7
IPC codes: B24D7, B21B28, B24B5