Abstract:
A cutoff disc, having an outer periphery provided with particles which are released during wear, a central opening for passage and clamping on a work spindle for the rotary driving on a grinding hand power tool, and an outer ring region which is provided on an outer edge, the outer ring region extending radially outwardly with a tip and forming a small cutting edge.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a cutoff wheel for hand power tools.  
           [0002]    The present invention relates to a cutoff wheel for hand power tools. Many cutoff wheels for cutoff by grinding are known in the art. One of them is disclosed for example in German patent DE 102 08 818 C1. In this document the cutoff wheel is clamped with a central recess on a working spindle of a grinding power tool and hand guided for workpieces of any type. In particular it can be used for cutoff works, and in some cases also for smoothing of weld or solder seams on metal workpieces or for removal of non uniformities of concrete parts.  
           [0003]    The known cutoff wheels have the disadvantage that due to unavoidable more or less great eccentric position of the periphery of the cutoff wheel with respect to the rotary axis of the grinding hand power tool, in the beginning of the grinding or cutting process only a small region of the periphery of the cutoff wheel engages in the material to be treated. This region of the cutoff wheel which comes first in engagement is overloaded in the case of hard loading, so that individual cutting segments of the periphery can rectify and their cutting action is lost, or in the case of massive overheating of a peripheral region or a soldered segment it is released from the cutoff wheel, and it can not be used any longer. Moreover, the cutting off wheel has a tendency to disturbing vibrations due to the non uniform engagement with the workpiece. Thereby the cutting efficiency and the material removal with this cutoff disc is reduced when compared with an ideally centered cutoff discs, while on the other hand the ideal centering means unacceptably high manufacturing expenses.  
         SUMMARY OF THE INVENTION  
         [0004]    Accordingly, it is an object of the present invention to provide a cutoff wheel which avoids the disadvantages of the prior art.  
           [0005]    In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention, resides, briefly stated, in a cutoff disc for a hand power tool, having an outer periphery provided with particles which are released during wear; a central opening for passage and clamping on a work spindle for the rotary driving on a grinding hand power tool; and an outer ring region which is provided on an outer edge, said outer ring region extending radially outwardly with a tip and forming a small cutting edge.  
           [0006]    When the cutoff disc is designed in accordance with the present invention, it has the advantage that its initial eccentricity with respect to the working spindle of the grinding hand power tool is eliminated after several revolutions during the engagement with the workpiece, a uniform workpiece engagement is provided, a local overheating of the cutoff disc is excluded, and a vibration-free grinding is possible.  
           [0007]    The cutting efficiency and the material removal of the cutoff is increased and the surface life of he cutting disc is significantly improved.  
           [0008]    Since the conventional cutoff discs on their outer edge have a thicker outer ring region up to 2 millimeters which extends radially outwardly to a tip and form a central, relatively thin disc, its thinnest part which is located in engagement of the workpiece is worn relatively fast in a self-centering manner during the first grinding revolutions. Thereby, the above mentioned eccentricity-related disadvantages are quickly eliminated.  
           [0009]    An outer ring on an outer edge of the cutoff disc is composed of a material which is significantly softer and wears faster than the remaining region of the cutoff disc, and therefore the outer ring is removed relatively fast in the self-centering manner and the cutoff disc thereby becomes optimally operational.  
           [0010]    The cutoff discs can be used in pairs for milling of masonry grooves. Thereby the eccentricity-reducing action and the service time of the double running unit are significantly increased.  
           [0011]    When the cutoff disc is formed as a diamond cutoff disc and its periphery is subdivided into tooth segments and tooth gaps, its service life, in particular the connection between the tooth segments and the main blade is improved and the service life of the cutoff disc is increased.  
           [0012]    The tooth segments can carry each a partial ring region which is softer and wears faster than the tooth segment, and this partial ring region can be interrupted on the tooth gaps, so that the cutoff disc has a self-cooling with an improved service life.  
           [0013]    Each part-ring region can be designed roof-shaped with a tip and can form a relatively thin or sharp edge which is smaller than the thickness of the cutoff disc or the main blade. In this case, the partial ring region can be composed of the same material as the toothed segments. Thereby, the eccentricity-reducing action is obtained only by the formation of the outer edge of the cutoff disc.  
           [0014]    The ring region can have a softer bond of its abrasive particles than the remaining region of the cutoff disc. Therefore first a finer chip removal during the engagement with the workpiece is provided than after the wear of the outer ring during engagement with the highly efficient cutting region of the cutoff disc. Thereby the handling of the grinding hand power tools provided with the corresponding cutoff discs is substantially controllable and the accident danger in case of unintentional drop of the machine with the abruptly reacting, aggressive chip removal is excluded.  
           [0015]    The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a view showing a grinding hand power tool with a cutoff disc in accordance with the present invention;  
         [0017]    [0017]FIG. 2 is a view showing a flat side of the cutoff disc in accordance with the present invention;  
         [0018]    [0018]FIG. 3 is a view showing a flat side of a further embodiment of the cutoff disc in accordance with the present invention; and  
         [0019]    [0019]FIG. 4 is a view showing a small side of the cutoff disc of FIG. 3 in accordance with the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    A grinding hand power tool shown on a side view in FIG. 1 is designed as an angle grinder  10 . It has a longitudinally extending machine housing  12  with not identified handle arranged at its rear end, and with an electric cable  13  extending from its end for energy supply of a not shown motor.  
         [0021]    A not shown switching key for turning on and off of the not shown motor is arranged in the region of the handle and is easily acceptable for an operator. The housing  12  at its front end has a work spindle  14  which extends perpendicular to the longitudinal extension of the machine housing  12  and serves for a rotary drive of a cutoff wheel  20  which is clamped in it for joint rotation therewith.  
         [0022]    The cutoff disc  20  has a central opening  24  for setting on the work spindle  14  which extends through the cutoff disc  20 . A clamping nut  18  is screwed on the free end of the work spindle  14 , in particular on its thread  15 . The clamping nut  18  presses the cutoff disc  20  axially to a holding flange  16 , so that the cutoff disc  20  is clamped in a force-transmitting manner for joint rotation with the workspindle  14 .  
         [0023]    The cutoff disc  20  is surrounded by a protective hood  21  in its rear region which faces the electrical cable  13 . Therefore, during operation with the angle grinder  10  the operator can not be subjected to the action of chip and grinding dust or the like.  
         [0024]    The cutoff disc  20  on its outer edge has an outer ring  30 . It has a different binding means composition and grinding means composition when the remaining region of the cutoff disc  20  provided for cutting. The outer ring  30  in a radial direction has a thickness of substantially 5 millimeters and substantially the same thickness as the cutoff disc  20 .  
         [0025]    The cutoff disc  20  has a certain eccentricity of its outer periphery relative to a center point of the central recess  24  due to its manufacture. Thereby, in operation of the angle grinder  10  during the rotation of the cutoff disc  20  a non uniform engagement of its periphery in the workpiece to be treated takes place. This can be also the result of an oval form of the cutoff disc which deviates from the ideal circular shape.  
         [0026]    Since the outer ring  30  is worn relatively fast, for example during several revolutions of the cutoff disc  20  in engagement with the workpiece, the eccentricity of the outer periphery of the cutoff disc  20  is automatically compensated. Thereby, in shortest time, a uniform workpiece engagement without vibration and local overheating of the cutoff disc  20  is provided.  
         [0027]    [0027]FIG. 2 shows a cutoff disc in a plan view on its circular surface. The outer edge  22  can be clearly seen in this drawing. It ends with the outer edge of the cutting segment  26  and is formed by it. The cutting segments  26  are arranged at equal distances relative to one another to form segment gaps  28  therebetween. The cutting segments  26  are composed of a sintered abrasive binder mixture. Each individual segment  26  is connected with the circular main blade  23  in a material-connecting manner, for example by soldering or welding. This connection is relatively sensitive to thermal overloading, so that such a thermal overloading has to be avoided.  
         [0028]    On the outer edge  22  of the cutting segments  26  an outer ring  30  is applied over its width in a ring segment-like manner. Its composition, as described with respect to FIG. 1 is selected so as to be worn out intentionally fast. Thereby, a manufacturing-related deviation of the center of the outer edge  52  and the center of the central recess  24  is compensated after several revolutions of the cutoff disc  20  in engagement with the workpiece. FIG. 3 shows a cutoff disc  200 . Its cutting region  270  is not subdivided into individual segments, but instead is formed as a throughgoing ring which is soldered or welded on a main blade  230  of the cutoff disc  200 .  
         [0029]    Starting from the circular outer edge  220  of the cutoff disc  20 , a prismatically designed outer ring region  300  follows. It forms a relatively sharp-edge, thin and tip-shaped cutting blade  34 . The cutoff disc  20  has a central recess  240  in its center.  
         [0030]    [0030]FIG. 4 shows a small side of the cutoff disc  20 . The prismatic shape of the outer region ring  300  and the cutting region  34  can be clearly seen in this drawing. Due to the prismatic design of the outer ring region  300  with the same material composition as in the cutting region  270 , a same action is obtained only by this geometry, as with the outer ring  30  composed of a softer mixture of FIG. 2. The tip-shaped region  34  of the outer ring region  300  wears relatively fast during cutting. Therefore an eccentricity of the outer periphery  34  or  220  relative to the central point of the central recess  24  is compensated in a very short time.  
         [0031]    It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.  
         [0032]    While the invention has been illustrated and described as embodied in cutoff wheel for hand power tools, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.  
         [0033]    Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.  
         [0034]    What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.