Patent Publication Number: US-2011065369-A1

Title: Roughing-grinding disc

Description:
The invention relates to a roughing-grinding disc. 
     A relatively thick peripheral grinding disc is known from CH-PS 434 023, which consists of a plurality of individual discs which are glued to one another all over and reinforced with woven fabric, it being possible for an elastic insert to be provided in the adhesive layer. Multi-section discs of this type have a higher grinding output than a compact disc constructed in one piece. A compact disc is moreover known from CH-PS 434 023, which, in its radial outer regions, in each case, has grinding medium-free zones, which are formed by annular intermediate layers, which can optionally be removed again, so a clear gap is formed between the adjacent regions. These grinding medium-free zones, during peripheral grinding, lead to particularly cool grinding and moreover produce still further chip space, which allows a substantial increase in the grinding output with a disc composition which is otherwise identical. 
     A roughing-grinding disc is known from EP 1 543 923 A1, the diameter of which is greater by at least a factor of 10 than its thickness. Roughing-grinding discs of this type are used on hand-held, pneumatically or electrically driven angle grinding machines. Strong vibrations occur here during grinding use and can cause significant physical damage to the hand-arm system of the user. To reduce vibrations of this type, an annular separating layer is arranged between individual layers in an outer working region, in each case. Within this working region, it has a compact structure. The separating layer primarily has the function of reducing the amplitude of the vibration during grinding. 
     The invention is based on the object of providing a vibration-damped roughing-grinding disc for hand-held use, which is particularly simple with regard to its structure and can therefore be produced particularly simply. 
     This object is achieved according to the invention by the features of claim  1 . 
     The structure of individual flat part discs allows very simple prefabrication of these part discs. As they are flat, there is no risk of distortion as in bent discs, so that they actually rest against one another as closely as possible, in other words rest against one another virtually without an air gap in the unconnected, i.e. unglued outer working region. 
     The flat configuration of the roughing-grinding disc and the attachment of a hub therein make it particularly advantageous to provide an internal thread in the hub, by means of which screwing onto an external thread of an output shaft of a hand-held grinding machine is possible. This leads to the fact that despite the flat configuration, no nut projecting over the roughing-grinding disc is required for fastening on the output shaft of the grinding machine, so flat or virtually flat use of the roughing-grinding disc according to the invention is also possible. This configuration of the hub may also, of course, be used in flat grinding discs which do not have the structure according to the invention. 
    
    
     
       Advantageous configurations emerge from the sub-claims. Further features, advantages and details of the invention emerge from the following description of an embodiment with the aid of the drawings, in which 
         FIG. 1  shows a hand-grinding machine with a roughing-grinding disc according to the invention in grinding use, 
         FIG. 2  shows a roughing-grinding disc according to the invention in a perspective view, 
         FIG. 3  shows the roughing-grinding disc according to the invention in an exploded view before assembly, 
         FIG. 4  shows a part disc of a roughing-grinding disc according to the invention in a side view and 
         FIG. 5  shows a roughing-grinding disc assembled on the output shaft of a hand-grinding machine according to the invention in a side view. 
     
    
    
     As emerges from  FIGS. 1 and 5 , roughing-grinding discs  1  are used on hand-grinding machines  2 , specifically so-called angle-grinding machines. The grinding disc  1 , for this purpose, has a centre opening  3 , in which a hub  4  is inserted. This hub  4  has an internal thread  5 , by means of which the grinding disc  1  is screwed onto an output shaft  7 , which is provided with an external thread  6 , of the grinding machine  2 . 
     The grinding disc  1 , in its basic structure, consists of a plurality, and specifically two to ten, thin part discs  8  with an external diameter D. Each part disc  8 , at its two outer sides, in each case has a reinforcement  9 ,  10 , grinding grain  11 , bound with binding means, generally phenolic resin, being arranged between the two reinforcements  9 ,  10 . The reinforcements  9 ,  10  consist of a woven fabric impregnated with the binding agent of the grinding grain  11 , generally a glass fabric. These part discs  8  are hardened. The part discs  8 , on their outsides, in other words on the exposed faces of the reinforcements  9 ,  10 , have no labels or paper layers or the like, in other words are uncovered. 
     To produce a roughing-grinding disc  1 , a plurality of flat part discs  8  are stacked one above the other, an adhesive layer  12 , generally duromers, being applied in an annular region around the centre opening  3 . This adhesive layer  12  with a diameter d is in each case so thin that when the package consisting of a plurality of part discs  8  is pressed to form a roughing-grinding disc  1 , the adhesive is absorbed in the surface roughness of the part discs  8  located on one another. This results in the fact that the part discs  8  are rigidly connected to one another in the region of the adhesive layer  12  with the diameter d, and that they are not connected to one another outside the respective adhesive layer  12 , but are located closely against one another. “Located closely against one another” does not mean in this context that adjacent grinding discs  1  have a spacing here of precisely 0, but that no practically relevant air gap exists between two adjacent part discs  8 . Thus, with regard to the thickness a of a grinding disc  1  made of n part discs  8  with a thickness b there thus applies: a≈n×b. With regard to the thickness b of the part discs  8  there applies: 0.8 mm≦b≦1.4 mm. With regard to the ratio of the diameter d of the adhesive layer  12  to the external diameter D of the grinding disc  1  there applies: 0.2≦d/D≦0.65. With regard to the external diameter D there applies: 10 mm≦D≦300 mm. The region, in which the adjacent part discs  8  are not connected to one another, forms the working region  13  of the grinding disc  1 . 
     The hub  4  passes through the centre opening  3  of the grinding disc  1  on one side, and specifically on the side remote from the grinding machine  2 , only slightly with a beaded edge  14 , so the roughing-grinding disc  1 , although it is not bent, but is completely flat in design, can be used obliquely as a roughing grinding disc  1 , in other words in the manner described at the outset and shown in  FIG. 1 . However, a surface grind is also possible, in which the roughing-grinding disc  1  is used with its end face  15  associated with the edge  14  of the hub flat or virtually flat on a workpiece  16 . If the roughing-grinding disc  1  is used obliquely in accordance with the view in  FIG. 1 , this takes place at an angle α between the axis  17  of the disc  1  and therefore also the output shaft  7  of the grinding machine  2  relative to a vertical  18  to the surface  19  to be ground of the workpiece  16 . With regard to the angle α there applies: 20°≦α≦60°. If, on the other hand, in the manner mentioned, grinding takes place in a flat manner, with regard to the angle α there applies: α≈0°.