Patent Publication Number: US-2016229024-A1

Title: Resin-bonded grinding disk

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
     This application is a U.S. National Phase application under 35 U.S.C. §371 of International Application No. PCT/EP2014/069835, filed on Sep. 17, 2014 and which claims benefit to German Patent Application No. 10 2013 110 237.9, filed on Sep. 17, 2013. The International Application was published in German on Mar. 26, 2015 as WO 2015/040083 A1 under PCT Article 21(2). 
    
    
     FIELD 
     The present invention relates to a resin-bonded grinding disk, in particular a cutting-off disk or a roughing disk. 
     BACKGROUND 
     Resin-bonded grinding disks are used to machine workpieces by cutting (cutting-off disks) or roughing (roughing disks). They consist, for example, of a resin/reinforcement fabric composite in which abrasive grains are embedded, wherein the abrasive grains effect the subtractive removal of the material from the workpiece. A surface machining of a workpiece is possible with roughing disks. The material of roughing disks is thicker than that of cutting-off disks due to the relatively high lateral load on the surfaces. Roughing disks are additionally always offset to further increase stability. By contrast, cutting-off disks are relatively thin to be able to provide cuts that are as narrow as possible. 
     Known resin-bonded grinding disks are manufactured in a manufacturing mold. The bottom of the manufacturing mold has hitherto been designed with a laminated reinforcement fabric to obtain a surface that is as smooth as possible. A mixture of abrasive grains, resins, and fillers is then poured into the manufacturing mold, wherein the resin-bonded reinforcement fabric can be interlaced with further reinforcement fabrics. A further reinforcement fabric terminates the mixture at the top. The material is then pressed. 
     The main purpose of the reinforcement fabric is to provide stability and thereby also the safety of the grinding disk. Safety is of particular importance, in particular in hand-held machines, since the operator, in contrast to stationary machines, is inevitably located in the immediate vicinity of the grinding disk during machining. Non-optimal guidance of the machine is always to be expected due to manual guidance. Sudden lateral forces, which even the very narrow cutting-off disk must withstand, can therefore arise. The reinforcement fabric is, however, comparatively expensive. 
     SUMMARY 
     An aspect of the present invention is to provide an improved resin-bonded grinding disk which reduces the amount of reinforcement fabric and is thus less expensive to produce. 
     In an embodiment, the present invention provides a resin-bonded grinding disk for use on a hand-held power tool comprising a clamping flange. The resin-bonded grinding disk includes a top side, an underside arranged opposite to the top side, a grinding disk surface area, a central cutout configured to hold the grinding disk in the clamping flange, a first reinforcement fabric arranged on the top side, and a second reinforcement fabric arranged on the underside. The first reinforcement fabric comprises a first reinforcement fabric surface area which substantially corresponds to the grinding disk surface area. The second reinforcement fabric comprises a second reinforcement fabric surface area which is smaller than the grinding disk surface area. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in greater detail below on the basis of embodiments and of the drawings in which: 
         FIG. 1  shows a prior art power tool with an attached cutting-off disk; 
         FIG. 2  shows an arrangement according to the present invention having a power tool according to  FIG. 1  and a cutting-off disk according to the present invention; 
         FIG. 3  shows an arrangement according to the present invention having a power tool according to  FIG. 1  and a roughing disk according to the present invention; 
         FIG. 4  shows an arrangement according to the present invention having a power tool according to  FIG. 1  and an alternative roughing disk according to the present invention; 
         FIG. 5  shows various geometries of the reinforcement fabrics in the grinding disks according to  FIGS. 2 to 4 ; and 
         FIG. 6  shows a pressing mold for the production of a grinding disk according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The quintessence of the present invention is that the grinding disk according to the present invention has as few reinforcement fabrics as possible, with one on the top side and one on the underside of the grinding disk. Each reinforcement fabric initially serves as a support for the introduction of torque from the clamping flange into the grinding disk. In this case, it is important that each reinforcement fabric projects into the region of the grinding disk at which clamping with the clamping flange takes place. In order to pass the torque as far as the radially external regions of the grinding disk, at which machining usually takes place, it is then sufficient for only a single reinforcement fabric to support the transfer of the torque to that location. A second reinforcement fabric is there largely superfluous and can be dispensed with. The minimum requirement for the reinforcement fabric therefore exists, i.e., two reinforcement fabrics radially on the inside, and one reinforcement fabric radially on the outside. In other words, the second reinforcement fabric covers only the radially internal region, but not the radially external region. Depending on the configuration, up to about 35% of the reinforcement fabric can thus be dispensed with per disk. This results in a considerable cost-saving potential. This also includes, in principle, disks in which the surface area of the first reinforcement fabric is slightly smaller than the nominal diameter of the disk, in particular for manufacturing reasons. 
     It is important that the first reinforcement fabric reinforce the disk substantially over its entire area so that the radially external regions are also correspondingly stabilized. It has been found, in particular in the case of roughing disks, that these crumble in the peripheral region if at least one layer of reinforcement fabric is not there provided at least over the entire area. The first reinforcement fabric therefore in particular has a circular shape. By contrast, the second reinforcement fabric must only be arranged in the radially internal region. A circular shape is here not important so that other shapes are also conceivable. For the second reinforcement fabric, it is therefore possible to choose shapes which allow for a waste-free production, for example, rectangular shapes, interlocking shapes, star shapes, or triangular shapes. The surface area is here understood to essentially be the area which is taken up by the disk as seen in the axial direction, without cutouts, for example, the fastening cutout, being included (the calculation uses (D/2) 2 ×π). A diameter of the first reinforcement fabric can here correspond to the nominal diameter of the grinding disk. A diameter of the second reinforcement fabric is much smaller than the nominal diameter of the grinding disk, in particular, at least 10%, for example, at least 20%, or, for example, at least 40% smaller than the nominal diameter. The surface area of the second reinforcement fabric can, for example, also be much smaller, for example, at least 15%, for example, at least 20%, or, for example, at least 50% smaller, than the surface area of the grinding disk. 
     In an embodiment of the present invention, the grinding disk can, for example, only comprise the first and the second reinforcement fabric as reinforcement fabrics. This arrangement is sufficient for a large number of applications. The quantity of reinforcement fabric to be employed is here greatly reduced compared with previous solutions, with the grinding disk being covered over its entire surface with at least one layer. This possibility is applicable to cutting-off disks and roughing disks, in particular to roughing disks which have a thickness of at most 10 mm. 
     In an embodiment of the present invention which is in particular applicable on roughing disks, the grinding disk can, for example, only have the first reinforcement fabric, the second reinforcement fabric, and a third reinforcement fabric as reinforcement fabrics. This variant is in particular applicable for fairly thick roughing disks having a thickness of the roughing disk 9″ of at most 10 mm. Conventional roughing disks of this size have hitherto been produced with much more reinforcement fabric. 
     In the case of the roughing disks, the first reinforcement fabric, i.e., the one with the large area, can, for example, be arranged on that side of the roughing disk which faces the power tool, i.e., the top side. In other words: the second reinforcement fabric, i.e., the one with the smaller area, can, for example, be arranged on that side of the roughing disk on which the disk is in contact with the workpiece to be machined, i.e., on that side of the roughing disk that faces the roughing face, namely, the underside. This is because the reinforcement fabric tends to be obstructive on roughing contact with the workpiece. The reinforcement fabric does not, in contrast, disrupt the roughing operation on the top side. 
     A resin-bonded cutting-off disk is in particular a non-offset and flat cutting-off disk. The thickness of a cutting-off disk, which decisively defines the cutting width, is in particular at most 4 mm, for example, at most 3 mm. 
     The present invention furthermore relates to a method for producing a resin-bonded grinding disk of the abovementioned type. The particular feature of the method is that a surface layer is first laid on the bottom of the pressing mold, in particular a paper fabric or a nonwoven fabric, on which the reinforcement fabric to be laid at the bottom is placed. In particular in the case in which the second reinforcement fabric is laid at the bottom, said second reinforcement fabric does not completely line the bottom, as in conventional grinding disks, on account of its small dimensions. The lining of the bottom is then taken over by this additional surface layer. This prevents the mixture of abrasive grain, resin, and fillers from sticking to the bottom of the mold, thereby making it difficult or even impeding the removal of the finally pressed disk. The surface layer likewise has a circular outer contour and a surface area which largely corresponds to the surface area of the grinding disk. 
     The present invention is explained in more detail below with reference to the drawings. 
       FIG. 1  shows a known hand-held power tool in the form of an angle grinder  1 . Said power tool comprises a housing  2  having handles  6 ,  7  by way of which an operator guides the angle grinder  1  with both hands during a working operation. The angle grinder  1  furthermore has a drive shaft  3  which is mounted in the housing  2 . Fastened to the drive shaft  3  is a grinding disk, in the present case a cutting-off disk  9 ′, wherein the use of a roughing disk is likewise possible. The angle grinder  1  receives electrical energy via a power line  8 . Such a power tool can, however, also be driven by other energy sources, for example, pneumatically or hydraulically. The term housing should be understood broadly and can also comprise internal supporting structures of the power tool. In the context of the present configuration, that axial side of the grinding disk  9  that faces the power tool is denoted as the top side  17 . The other side is the underside  18 . In the case of a roughing disk, the underside  18  is that side with which the disk is in roughing contact with the workpiece to be machined. 
       FIG. 2  shows an arrangement according to the present invention having a power tool, for example, the angle grinder according to  FIG. 1 , and a grinding disk  9  according to the present invention in the form of a cutting-off disk  9 ′. The cutting-off disk  9 ′ is fastened to the drive shaft  3  of the angle grinder  1  in a force-fitting manner via a clamping flange  4 . A drive torque is thereby introduced into the cutting-off disk  9 ′ from the drive shaft  3  at the top side  17  and the underside  18  of the cutting-off disk  9 ′, the driving torque being intended to be transmitted to the entire cutting-off disk  9 ′ and in particular to be conducted radially towards the outside. Consequently, in the central, i.e., radially inner region  19 , there are high stresses within the cutting-off disk  9 ′ in operation, and these stresses must be distributed to the entire cutting-off disk  9 ′. 
     These stresses are primarily absorbed via two reinforcement fabrics  11 ,  12 . According to the present invention, provision is made for exactly two such reinforcement fabrics  11 ,  12  in cutting-off disk  9 ′, the first reinforcement fabric  11  being on the underside  18 , and the second reinforcement fabric  12  on the top side  17 . These two reinforcement fabrics  11 ,  12  project into that inner radial region  19  of the cutting-off disk  9 ′ in which clamping via the clamping flange  4  also takes place. In this respect, the torque is introduced substantially directly into the reinforcement fabric  11 ,  12 . It is possible, however, for the reinforcement fabric  11 ,  12  to be covered on the top side  17  or underside  18  by a thin layer of yet another material so that the clamping flange  4  does not bear directly against the reinforcement fabric  11 ,  12 . 
     The first reinforcement fabric  11  is formed in a circular manner and has a diameter D 1  which corresponds to a nominal diameter N of the cutting-off disk  9 ′. The surface area of the first reinforcement fabric  11  also corresponds to the surface area of the cutting-off disk  9 ′. The second reinforcement fabric  12  is formed in a smaller manner in terms of its diameter and essentially has a diameter D 2  of only 55% of the nominal diameter N of the cutting-off disk  9 ′. The second reinforcement fabric  12  essentially has the purpose to generally support the conduction of the torque from the clamping flange  4  into different regions of the disk. For the further distribution of the torque into the circumferential region, however, it has been found sufficient for this to be supported by only one reinforcement fabric, specifically, the first reinforcement fabric. The advantage compared with conventional resin-bonded cutting-off disks thus resides in the saving of material since only one large layer and one small layer of reinforcement fabric needs to be used rather than two large layers of reinforcement fabric. 
     The reduction to only one reinforcement fabric, which extends as far as the outer circumference, also has the following advantage. Although the reinforcement fabric can in principle introduce stability into the disk, it does not have any abrasive action. The robustness of the reinforcement fabric can much rather have a disadvantageous effect on the cutting operation, for example, the movement of the disk being braked by the fabric. This also in principle applies for roughing. As a result of the reduction in the size of the second disk, only one reinforcement fabric which can “disrupt” the actual cutting operation now bears against the outer circumference. 
     A mixture  10  of synthetic resin, fillers, and abrasive grains is provided between the two reinforcement fabrics  11 ,  12 , as is also known for conventional disks. The thickness B of the cutting-off disk  9 ′ is approximately 2 mm and is suitable for the production of very thin cuts. 
     In hand-held power tools, the cutting-off disk  9 ′ is frequently pushed axially as a result of non-optimal operation, which can create a point lateral force S. This lateral force S creates a bending load on the cutting-off disk  9 ′, the tensile side of which is located on the underside  18  of the cutting-off disk  9 ′. The side to be provided with the first, i.e., the more extensive, reinforcement fabric can, therefore, for example, be on the underside  18 , which represents the axial side (with respect to the drive shaft) of the cutting-off disk  9 ′, facing away from the operator. In contrast thereto, an axial pulling on the part of the operator occurs more rarely so that the reduced reinforcement fabric on the top side  17  is unimportant with regard to faulty operation. Inverted mounting of the cutting-off disk  9 ′ on the angle grinder  1  is, however, in principle also conceivable. 
       FIG. 3  shows an alternative configuration wherein, rather than the cutting-off disk  9 ′, an offset roughing disk  9 ″ is now mounted on the angle grinder  1 . Exactly two reinforcement fabrics  11 ,  12  are here too provided, wherein the first reinforcement fabric  11  corresponds to the surface area of the roughing disk  9 ″, while the second reinforcement fabric  12  has a much smaller surface area. It is here important that the underside  18 , which is in roughing contact with a workpiece to be machined, is provided with the smaller second reinforcement fabric  12 . The second reinforcement fabric  12  is in particular only provided in the radial inner region  19  in which the roughing disk  9 ″ is offset and consequently does not project into the plane E of the machining face. The reinforcement fabric tends to be an obstacle during the roughing operation and therefore should not come into contact with the workpiece. The thickness B of the roughing disk  9 ″ is approximately 8 mm. 
       FIG. 4  shows a development of the configuration according to  FIG. 3 . A third reinforcement fabric is additionally arranged between the first and the second reinforcement fabric  11 ,  12 . This third reinforcement fabric  13  also has a much smaller surface area than the surface area of the roughing disk. The third reinforcement fabric  13  is furthermore only provided in the radial inner region  19  in which the roughing disk  9 ″ is offset. This has the effect that the reinforcing fabric does not project into the then displaced plane E of the machining face even with a partially worn roughing disk  9 ″. The thickness B of the roughing disk  9 ″ is about 9 mm. 
     Various non-exhaustive possible geometries are presented in  FIG. 5   a )- d ), wherein the fabric shapes of the first reinforcing fabric  11  and the second reinforcing fabric  12  are illustrated in a superimposed manner. This illustration applies both for the cutting-off disks and for the roughing disks  9 ″. If a roughing disk were to be provided with an additional third reinforcement fabric, the shape of the third reinforcement fabric can, for example, be the one as is shown in  FIG. 5   a )- d ) for the second, i.e., the smaller reinforcement fabric  12 . 
       FIG. 5   a ) shows the first reinforcement fabric  11  and the second reinforcement fabric  12  essentially as shown in  FIGS. 2 and 3 . Provided in both reinforcement fabrics  11 ,  12  is a fastening cutout  5  through which the drive shaft  3  is plugged during assembly. In accordance with  FIG. 5   a ), both the first reinforcement fabric  11  and the second reinforcement fabric  12  are formed in a circular manner. The second reinforcement fabric  12  has a smaller diameter D 2  than the diameter D 1  of the first reinforcement fabric  11  and thus also has a smaller surface area. 
       FIG. 5   b ) shows an alternative form. The second reinforcement fabric  12  is formed by a rectangle, in the present case, a square. The rectangular shape has the advantage that the corresponding reinforcement fabric can be produced without any waste. In contrast, waste is inevitably produced in the production of circular reinforcement fabrics. Further examples are shown in  FIGS. 5   c ) and  d ) where the second reinforcement fabric  12  is configured as a triangle and as a star, respectively, which can each also be produced in a waste-free manner. It is therefore clear that in particular polygonal shapes are suitable for waste-free production of the reinforcement fabric. 
     It is relevant, however, that the first reinforcement fabric  11  always be formed in a circular manner and covers substantially the entire disk. 
     The production method is explained by way of  FIG. 6 . This is generally based on the conventional method for producing resin-bonded grinding disks, as also forms the basis, for example, for German patent application 10 2011 109 536. The second reinforcement fabric  12 , the mixture  10 , and the first reinforcement fabric  11 , are introduced successively into a pressing mold  14 . A cover  15  is then applied. The arrangement is then pressed via a pressing force F. In conventional disks, however, the second reinforcement fabric  12  completely covers the bottom of the pressing mold  14 ; this is no longer possible with the second reinforcement fabric  12  that is reduced according to the present invention. The risk thus exists of the mixture  10  being able to pass directly onto the bottom of the pressing mold  14  and thus sticking to the pressing mold. It is then harder or impossible to remove the finally pressed disk. In order to improve thereon, a surface layer  16  is laid under the second reinforcement fabric  12  in the pressing mold, representing a barrier for the mixture  10  with respect to the bottom of the pressing mold  14 . The surface layer has a diameter which corresponds to the nominal diameter N of the disk. The surface layer  16  can be formed from a fabric, for example, a paper fabric or textile fabric. A third reinforcement fabric  13  can additionally be laid in the mold during the production of a roughing disk. 
     The present invention is not limited to embodiments described herein; reference should be had to the appended claims. 
     LIST OF REFERENCE NUMERALS 
       1  Angle grinder 
       2  Housing 
       3  Drive shaft 
       4  Clamping flange 
       5  Cutout 
       6  First handle 
       7  Second handle 
       8  Power line 
       9  Grinding disk 
       9 ′ Cutting-off disk 
       9 ″ Roughing disk 
       10  Mixture 
       11  First reinforcement fabric 
       12  Second reinforcement fabric 
       13  Third reinforcement fabric 
       14  Pressing mold 
       15  Cover 
       16  Surface layer 
       17  Top side 
       18  Underside 
       19  Radially internal region of the disk 
       20  Grinding face 
     N Nominal diameter of the disk 
     D Diameter of the reinforcement fabric 
     S Lateral force 
     F Pressing force 
     E Plane of the machining face 
     B Thickness of the grinding disk