ASSEMBLY FOR GRINDING ELECTRODES AND GRINDING WHEEL

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

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

TECHNICAL FIELD

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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

FIG. 1 is an exploded view of a device for grinding electrodes with two grinding wheels;

FIG. 2 is a cross sectional view of a device for grinding electrodes with a grinding wheel;

FIG. 3 shows the head of the assembled device with one grinding wheel in greater detail;

FIGS. 4( a)-4(e) show cross section, side views and a perspective view of a grinding wheel in greater detail;

FIG. 5 is a cross section of a device for grinding electrodes with two grinding wheels; and

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

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.

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.

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.

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. 4a and FIG. 4b. 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.

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. 4c and FIG. 4d. 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.

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. 4c and 4d. The depth of the recess designated with numeral 52 in FIGS. 4c and 4d, 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.

FIG. 4 e illustrates the proportions of the coated green body according to the equations:

S _Be,ges =S _Roh+2'S_Be≦S_max

D _max,S =D _Roh,S+2×S_Be≦D_housing

D _max,S =D _Roh+2×S_Be≦D_housing

with the definitions of the variables as shown in the figures and D_housing being the diameter of the housing.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Claims

1. A device for grinding welding electrodes comprising: a grinding wheel with a grinding range on the surface of the grinding wheel, said grinding range coated with a graining material with a selected grain size;a driving motor and a driving shaft for driving said grinding wheel; anda housing, said housing forming a space, said grinding wheel rotating inside said space and wherein at least one opening is provided in said housing for guiding a welding electrode for grinding in a defined position relative to said grinding wheel,wherein a recess is formed in said grinding range having a selected depth, said depth of said recess being adapted to said grain size of said grinding material.

2. The device of claim 1, wherein said surface of said grinding wheel has an uncoated center range and an edge and wherein said recess extends from said uncoated center range to said edge of said grinding wheel.

3. The device of claim 1, wherein (a) said grinding wheel is provided with a thinner cutting edge,(b) a slit is provided in said housing, said slit extending perpendicular to said surface of said grinding wheel and wherein said slit is provided for cutting a welding electrode with said cutting edge, and(c) said cutting edge forms extends in a plane formed by the remaining portion of said grinding wheel in such a way that said grinding wheel forms said cutting edge in the range of its circumference without a step.

4. The device according to claim 1, wherein two grinding wheels are provided, said two grinding wheels laying on top of each other and having a different grain size.

5. The device of claim 4, wherein said cutting edge is provided on the side opposite to the other one of said two grinding wheels.

6. The device of claim 1, wherein the diameter of said grinding wheel is adapted to said grain size of said grinding material.

7. A grinding wheel for use in a device for grinding welding electrodes, comprising: a grinding range on the surface of the grinding wheel, said grinding range coated with a graining material with a selected grain size, the grinding range having a recess formed therein having a selected depth, said depth of said recess being adapted to said grain size of said grinding material.

8. The grinding wheel of claim 7, wherein said surface of said grinding wheel has an uncoated center range and an edge and wherein said recess extends from said uncoated center range to said edge of said grinding wheel.

9. The grinding wheel of claim 7, wherein (a) said grinding wheel is provided with a thinner cutting edge,(b) said cutting edge forms extends in a plane formed by the remaining portion of said grinding wheel in such a way that said grinding wheel forms said cutting edge in the range of its circumference without a step.