Abstract:
A device for processing welding electrodes with a grinding wheel having a selected grain size driven by a driving motor with a shaft, which runs in a housing, wherein at least one opening is provided in the housing for guiding a welding electrode for processing in a defined position relative to the grinding wheel is characterized in that a recess adapted to the grain size of the grinding material is provided in the range provided for grinding on the surface of the grinding wheel which is coated with grinding material.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This patent application is filed herewith for the U.S. National Stage under 35 U.S.C. §371 and claims priority to PCT application PCT/EP2010/065341, with an international filing date of 13 Oct. 2010 and a Convention priority date of 10 Dec. 2009. The contents of this application are incorporated in their entirety herein. This application is also related to U.S. non-provisional patent application titled Assembly Kit For Upgrading An Electrode Grinding Device And Electrode Grinding Device, filed concurrently herewith. 
     
    
     STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       TECHNICAL FIELD 
       [0003]    The invention relates to a device for processing welding electrodes with a grinding wheel having a selected grain size driven by a driving motor with a shaft, which runs in a housing, wherein at least one opening is provided in the housing for guiding a welding electrode for processing in a defined position relative to the grinding wheel. 
         [0004]    Welding electrodes consist of very hard and high-temperature resistant material, such as tungsten. There are welding electrodes with different cross sections. The welding electrodes have a tip or edge at one end. This shape of the welding electrode depends on the respective application. The tips of the welding electrodes wear out during operation. 
         [0005]    Welding electrodes can be bought without shaping or with a ready-made tip. After use the tip or the shape is worn out. The welding electrodes are then reshaped or disposed of. Due to the precious material this is expensive. 
       BACKGROUND OF THE INVENTION 
       [0006]    It is known to grind electrodes. This is commonly effected manually with open grinding- or separating wheels. Such methods are imprecise and dangerous. Furthermore, there are devices with open grinding wheels known where the welding electrodes are guided through a guiding sleeve with a certain angle relative to the grinding wheel. Such devices are also expensive. In particular, it is expensive to adapt such a device to various types of welding electrodes or for different tips or cutting shapes. In particular, this requires the exchange of the guiding sleeves. 
         [0007]    A device where electrodes can be produced with a plurality (for example  6 ) of different electrode diameters with a plurality of different tip angles (for example 4) with many lengths is a valuable, cost-saving aid. 
         [0008]    DE 100 10 520 A1 discloses a device for processing welding electrodes with a grinding wheel. The grinding wheel rotates in a grinding wheel housing. The device furthermore is provided with an additional housing portion which is adapted to be fixed to the grinding wheel housing and which is provided with at least one opening for guiding a welding electrode for processing in a defined position relative to the grinding wheel. The plane of the grinding wheel is essentially the separating plane between the grinding wheel housing and the additional housing portion. The additional housing portion can be provided with a plurality of adjacent, different openings for receiving different kinds of welding electrodes. The additional housing portion can, however, also be provided with a plurality of adjacent openings having an axis cutting the plane of the grinding wheel under different angles. A radial slit can be formed in the grinding wheel housing extending along the front end of the housing, which is used to receive a welding electrode for cutting at the outer perimeter of the grinding wheel. The grinding wheel of the disclosed device is fixed to a grinding wheel reception which in turn is connected to a driving shaft of a driving motor. The entire device forms a portable unit. 
         [0009]    US 2004/0127149 A1 discloses an assembly where two parallel grinding wheels with different grain size are used. A first grinding wheel rotates in a space between the motor unit and a first housing portion. The second grinding wheel rotates in a second space between the first housing portion and the second housing portion. The housing portions are provided with openings for guiding the welding electrodes. The known assembly enables the use of different grinding wheels without the need of exchange. 
         [0010]    Further to a motor in a motor unit the assembly makes use of further housing portions: a motor flange directly screwed to the motor unit and at least one housing portion provided with openings for guiding the electrodes. The openings extend from the side of the housing portion opposite to the motor in the direction of the grinding wheel rotating between the motor flange and the housing portion. Depending on the amount of grinding wheels further housing portions are added. Here also the openings extend from the side opposite the motor. In other words, the electrodes are always inserted into the openings in a direction towards the motor. Depending on the amount of housing portions the assembly is relatively long and requires a long driving shaft. Several fixing elements, such as screws, nuts, pins etc. are required for fixing the housing portions. 
         [0011]    US 2008/0108284 A1 discloses an assembly where two grinding wheels having a different grain size rotate in practically one plane in a common space. The grinding surfaces of the known assembly are facing opposite directions. A third wheel with a larger diameter is arranged between such grinding wheels. Such wheel is used for cutting electrodes. 
         [0012]    The bore holes or openings for guiding electrodes are produced with high precision regarding the angle. It is understood that the corresponding grinding wheel rotates in a defined position relative to the housing. With different thicknesses or with the use of several grinding wheels this is not ensured anymore. In such a case the grinding angle is not the target value. 
         [0013]    During the production of grinding wheels the unprocessed raw disc is dipped into a bath for application of the grinding means. Accordingly, it is difficult with such a method to produce grinding wheels with a different grain size on the top side and bottom side. The green body is a plane disc. Depending on the grain size the finished wheel is thicker with a rough grain size than with a small grain size. This causes different overall thicknesses. The grinding plane will then not be in the separating plane between the two housing portions for each grain size. Due to pressure of the screw upon tightening the grinding wheel there is a risk of bending the grinding wheel. This is not wanted. 
         [0014]    With such known grinding wheels the best grinding results are obtained in the outer range having the highest velocity of the grinding wheel. The grinding wheel may, however, not be any size because lateral forces and undesired oscillations can occur at high angular rates. Furthermore, large grinding wheels require a large housing thereby rendering the assembly difficult to handle. 
       BRIEF SUMMARY OF THE INVENTION 
       [0015]    It is an object of the invention to provide an easy-to-handle grinding assembly of the above mentioned kind which is suitable for all grain sizes in the same way and which may be manufactured with smaller production tolerances. Furthermore, it is an object of the invention to improve the grinding results. 
         [0016]    According to the present invention this object is achieved in that a recess adapted to the grain size of the grinding material is provided in the range provided for grinding on the surface of the grinding wheel which is coated with grinding material. The recess can be taken into account already during the production of the green body. A deeper recess is required for rough grain size than with a fine grain size. 
         [0017]    Preferably, the diameter of the green body is also adapted to the grain size of the grinding material. Thereby, the same outer diameters are achieved for all grinding wheels. The manufacturing tolerances may then be smaller. The housing diameters are minimized. 
         [0018]    Preferably, the recess extends from an uncoated center range to the edge of the grinding wheel. The center range, which is not provided for grinding has the same thickness in all cases. In such a way a grinding wheel is produced which has the same thickness independent of the grain size. Thereby, the forces effective on the wheel are minimized. The wheel always rotates in the separating plane between the two housing portions independent of the grain size. Thereby the grinding angle is obtained with high precision. The velocity of the grinding wheel is the largest in the outer range. There, the best grinding results are obtained. 
         [0019]    In a preferred modification of the invention it is provided that:
       (a) the grinding wheel is provided with a thinner cutting edge,   (b) a slit is provided in the housing extending perpendicular to the grinding wheel for cutting a welding electrode with the cutting edge, and   (c) the cutting edge forms a plane laying in the plane of the remaining portion of the grinding wheel in such a way that the grinding wheel forms the cutting edge in the range of the circumference without a step.       
 
         [0023]    The thinner cutting edge serves to cut the electrode. A larger range is provided for grinding by forming the cutting edge in the range of the circumference without a step. A separate wheel having a larger diameter is not necessary. Thereby, the assembly is simplified. All wheels have the same diameter. 
         [0024]    In a particularly preferred embodiment of the invention two grinding wheels are provided laying on top of each other and having a different grain size. Thereby, fine grinding and rough grinding can be achieved with the same device without having to exchange components of the assembly. By using grinding wheels having the same thickness it does not matter which grain size is chosen for the grinding wheels. 
         [0025]    Preferably, the cutting edge is provided on the side opposite to the other grinding wheel. Thereby, the larger grinding range having a larger diameter is provided. 
         [0026]    Further modifications of the invention are subject matter of the subclaims. An embodiment is described below in greater detail with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0027]      FIG. 1  is an exploded view of a device for grinding electrodes with two grinding wheels; 
           [0028]      FIG. 2  is a cross sectional view of a device for grinding electrodes with a grinding wheel; 
           [0029]      FIG. 3  shows the head of the assembled device with one grinding wheel in greater detail; 
           [0030]      FIGS. 4(   a )- 4 ( e ) show cross section, side views and a perspective view of a grinding wheel in greater detail; 
           [0031]      FIG. 5  is a cross section of a device for grinding electrodes with two grinding wheels; and 
           [0032]      FIG. 6  is a detailed exploded view of the assembly with two grinding wheels as shown in  FIG. 1  and  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    Numeral  10  in the figures generally denotes a device for grinding welding electrodes made of tungsten. The device  10  comprises a motor with a motor housing  12 , a motor flange  14  screwed to the motor housing  12  and a cylindrical housing portion  16  mounted on the motor flange  14 . The housing portion  16  is connected to the motor and the motor flange in a way which is described below in greater detail. A grinding wheel assembly  18  with grinding wheels  20  and  22  having different grain size rotates in the range between the motor flange  14  and the housing portion  16 . 
         [0034]    The flange is provided with bore holes. The motor flange  14  is screwed to the motor housing  12  with screws extending through such bore holes as shown in FIG.  1 . The housing portion  16  is tightly connected to the motor flange  14  with a screw  13  and a nut  15 . For this purpose the housing portion  16  has a bore hole and the motor flange a receptacle for the nut  15 . 
         [0035]    A disc-shaped recess is provided in the end  26  of the motor flange  14  opposite the motor end. This recess serves to receive the grinding wheel  22 . The shaft  30  screwing the grinding wheel assembly  18  to the motor, simultaneously serves as motor shaft. 
         [0036]    The shaft  30  has an upper portion  28 . Furthermore, the shaft  30  has a bore hole  32  with an inner thread in the upper portion  28 . In addition, an extra-centric pin  34  is fixed to the upper portion  28 . The grinding wheels  20  and  22  of the grinding wheel assembly  18  are provided with a central bore hole  38  and an extra-centric bore hole  40  connected thereto. They can be seen well in  FIG. 4   a  and  FIG. 4   b . The grinding wheels  20  and  22 —or in case of only one grinding wheel as shown in  FIG. 3 , the grinding wheel  20 —are mounted on the shaft  30  and screwed together with a screw  36  in such a way that the central bore hole  38  is aligned with the axial bore hole  32  in the shaft  30  and that the pin  34  extends through the extra-centric bore hole  40  in the grinding wheel  22  on the side of the motor. The grinding wheels rotate about the axis of the bore holes  32  and  38  while the pin  34  engages with the bore hole  40  and transfers the driving power on the grinding wheel assembly  18 . A centering sleeve  37  is inserted from above through the center bore holes  38  of the two grinding wheels  20  and  22 . The upper end of the centering sleeve  37  opposite to the motor end is provided with a receptacle  39  for the screw head of the screw  36 . The centering sleeve  37  ensures that both grinding wheels  20  and  22  rotate about the same axis. The centering sleeve  37  is provided with a projecting nose  41 . The nose engages in the extra-centric bore holes  40  of the grinding wheels  20  and  22 . In such a way the driving power of the motor is transferred from the first, motor-side grinding wheel  22  through the centering sleeve  37  to the second, upper grinding wheel  20 . The centering sleeve  37  is screwed to the shaft together with the grinding wheels  20  and  22  with the screw  36 . This can be particularly well seen in  FIG. 3 . 
         [0037]    In the embodiment shown in  FIGS. 1 ,  5  and  6  with two grinding wheels  20  and  22  the grinding wheel assembly  18  comprises a grinding wheel  20  with rough grains and a grinding wheel  22  with fine grains which is otherwise the same. The grinding wheels  20  have a particularly sharp edge  42 . This edge  42  serves to cut electrodes with improved cutting behavior. The edge is integrated in grinding wheel  20  in such a way that one of its sides lies in the grinding plane. This can be well seen in  FIG. 4   c  and  FIG. 4   d . In such a way one of the grinding surfaces, i.e. grinding surface  44 , is larger on the side of the edge  42 , than the opposite grinding surface  46 . It is understood, that with the use of two grinding wheels, as it is the case in the embodiment shown in  FIGS. 1 ,  5  and  6 , the grinding wheels are arranged in such a way that the larger grinding surfaces are on the outside. Thereby, a larger grinding range is provided. The outer range has a higher local velocity and a larger grinding range. Accordingly, a better grinding result can be obtained. 
         [0038]    The grinding wheels  20  and  22  are made of a green body  48 . The green body  48  is dipped into a bath with grinding material. The grinding material, for example diamond grains of a selected grain size, sticks to the green body. Depending on the grain size different green bodies are used. Each green body has a center range  50  which is not coated. The bore holes  38  and  40  are provided in such uncoated center range  50 . The center range  50  has a standard thickness which is the same for all green bodies independent from the grain size. Accordingly, the wheels will completely lay upon each other in this range if several wheels are used. Furthermore, the green bodies are provided with a wide, area-like recess extending up to the edge. The recess quasi forms an elongated step extending over the entire angular range of the green body. In the plane of the edge  42  the step has a larger outer diameter than in the opposite plane. This can be seen in  FIGS. 4   c  and  4   d . The depth of the recess designated with numeral  52  in  FIGS. 4   c  and  4   d , corresponds to the average thickness of the selected grains. If a fine grain size is selected the recess has a small depth  52 . If a rough grain size is selected the depth of the recess  52  is larger. In each case the depth  52  of the recess is selected in such a way that the thickness of the grinding wheel is essentially the same over its entire range. Then the grinding wheels will smoothly lie on top of each other and always require the same space for rotation independently of the grain size. 
         [0039]      FIG. 4   e  illustrates the proportions of the coated green body according to the equations: 
         [0000]        S   Be,ges   =S   Roh +2&#39; S   Be   ≦S   max    
         [0000]        D   max,S   =D   Roh,S +2× S   Be   ≦D   housing  
 
         [0000]        D   max,S   =D   Roh +2× S   Be   ≦D   housing  
 
         [0000]    with the definitions of the variables as shown in the figures and D housing  being the diameter of the housing. 
         [0040]    If the grinding wheel assembly  18  is installed with the shaft  30  the essentially cylindrical housing portion  16  and—with two grinding wheels—a spacer ring  64  are coaxially mounted on the motor flange  14 . 
         [0041]    The housing portion  16  is provided with a center bore hole  54 . This can be seen in  FIG. 3 . The center bore hole is aligned with the bore holes  38  of the grinding wheel assembly  18  and the rotational axis of the shaft  30 . A disc-shaped recess  58  is provided around the bore hole  54  on the side  56  facing the motor. A recess  62  is provided on the opposite side  60  of the housing portion  16 . Such recesses  58  and  62  have about the same dimensions as the recess on the side  26  of the motor flange  14 . The recesses on the side  26  and the recess  58  form a space in the assembled device. The space serves to accommodate the grinding wheel assembly  18 . A spacer ring  64  is provided between the motor flange  14  and the housing portion  16  in the embodiment with two grinding wheels as shown in  FIGS. 1 ,  5  and  6 . The thickness of the spacer ring  64  corresponds to the thickness of one grinding wheel  20  or  22 . Accordingly, the difference caused by the additional grinding wheel is compensated. Independently from the amount of grinding wheels the same motor flange  14  and the same housing portion  16  with the same recesses  26  and  58  may be used in all cases. The grinding angle will not differ. 
         [0042]    The recess  62  on the upper side  60  serves as accommodating means for the removal of grinding left-overs such as dust and grinding chips. The housing  16 , ring  64  and motor flange  14  also are provided with a longitudinal slit  66  in a radial direction extending over the entire length of the assembly. The longitudinal slit  66  can be seen in  FIG. 1 . The slits  66  in the motor flange  14 , ring  64  and housing  16  are positioned on top of each other. The slit  66  formed in such a way is wide enough to let electrodes pass therethrough. The electrode can be shortened at the edge  42  of the or one of the grinding wheels when the grinding wheel assembly  18  rotates, by cutting the used-up end of the electrode or the newly shaped electrode end. 
         [0043]    The housing  16  and the motor flange  14  are provided with groups  76  and  78  of openings in the form of bore holes. The bore holes extend along the circumference of the housing  16  and motor flange  14  in the direction of the corresponding end faces in the direction of the grinding wheel next to the housing or motor flange, respectively. Each group consists in known manner of a plurality of bore holes with different diameters which is indicated above or below the bore hole by an engraving  80 . This can be seen in  FIG. 6 . The angle between an electrode inserted into the bore hole and the grinding wheel is the same for all bore holes in one group. For example, the bore hole may have a diameter of 1.6 mm and a grinding angle of 22.5 degrees. The grinding angle for each group is indicated by another engraving above the first engraving. For example, four different angles are possible for a grinding. Electrodes having, for example, 6 different diameters may be used. The electrode is guided in the bore hole so well that reproducible results can be obtained without difficulty or risk. 
         [0044]    More grinding angles, further electrode diameters or the use of a grinding surface with different grain size can be introduced by using a motor flange  14  also having such bore holes  78  and using two grinding wheels as shown in  FIGS. 1 ,  5  and  6 . An electrode, for example, can be roughly pre-ground by entering a bore hole in the housing  16 . A grinding wheel  20  having a rough grain size is provided with the grinding surface facing upwards in the drawing. A bore hole in the motor flange  14  is used for fine grinding. The corresponding grinding wheel  22  with a grinding surface facing downwards is provided with fine grains. The bore holes  76  in the housing portion  16  as well as the bore holes  78  in the motor flange were manufactured with the same machine using identical settings. Therefore, the bore holes are identical apart from very small deviations. The grinding surface in the present assembly is always in the same plane. In such a way a particularly small error is made for the grinding angle. In the present example the bore holes  76  are made in such a way that the indicated grinding angle is achieved if the grinding surface is in the plane  60  and the bore holes  78  if the grinding surface is in the plane which lays on wheel thickness below the plane  26 . 
         [0045]    Furthermore, the housing  16  is provided with a group of bore holes extending perpendicular from the upper end to the lower end of the housing  16 . The bore holes of such group also have different diameters corresponding to the diameters of the remaining groups. The bore holes of the group enable the perpendicular grinding of the electrode tips. 
         [0046]    The entire assembly is screwed on a hand-held device. The grinding wheel assembly is positioned directly adjacent to the ball bearing of the motor shaft  30 . This avoids rocking at high frequencies. 
         [0047]    In order to avoid dust, removed material and grinding material or the like entering the motor or the bearings a collision disc  84  is provided. The collision disc  84  is mounted between the motor side grinding wheel  22  and the motor flange with a sleeve  86  on the upper end  28  of the motor shaft and also rotates. The motor side, lower surface of the collision disc  84  is positioned in the range of the bottom of the recess in the end face  26 . A felt ring  88  is arranged around the sleeve  86  which does not rotate. The felt ring  88  avoids further dust, removed material and grinding material to enter the motor or the bearings. The pin  34  extends through a bore hole in the collision disc  84 . In such a way not only the grinding wheel assembly  18 , but also the collision disc  84  is driven by the shaft  30 . 
         [0048]    The present assembly was explained with reference to two precise embodiments, one with one and one with two grinding wheels. It is understood, however, that the assembly may be varied. It is, for example, possible to install a further housing portion similar to the housing portion  16  and to use further grinding wheels in the space formed therebetween. Also, different designs of the bore holes for guiding the electrodes are possible.