Patent Publication Number: US-2021187631-A1

Title: Cutting section for a drill bit

Description:
TECHNICAL FIELD 
     The present invention relates to a cutting section for a drill wherein the cutting section is connectable to the drill bit via a releasable connection. 
     BACKGROUND 
     The design described in WO 2014/096359 A1 has become established as the design for cutting sections which are connectable to a drill shaft section via a releasable connecting device. The cutting section comprises one or more drill segments, a ring section, an outer push element and an annular stop shoulder at the transition from the ring section to the outer push element; the releasable connecting device is in the form of a combined push and twist connection. The cutting section comprises slot-shaped recesses of T shape which are arranged in the outer push element. 
     During the drilling of substrates composed of reinforced concrete, the problem of jammed drill bits occurs. A cause of the jamming of the drill bit can be an iron wedge which is severed on the inner side of the cutting section and wedges in the inner gap between the drill core and the cutting section. It is known from WO 2017/108461 A1 that, in the case of drill bits having a small internal projection of the drill segments in relation to the drill shaft, the risk of the cutting section of a drill bit becoming jammed in the substrate is reduced. However, a small internal projection of the drill segments leads to a narrow inner gap on the inner side of the drill bit and therefore to disadvantages during the wet drilling with the drill bit. During the wet drilling, a cooling and flushing liquid is required which, as cooling liquid, cools the drill segments and, as flushing liquid, transports drilling debris out of the drill hole. The clean cooling and flushing liquid is supplied here via the inner gap between the drill core and the drill bit. Cooling and flushing liquid cannot be sufficiently transported to the machining site via the narrow inner gap. 
     As measures for improving the supply of the cooling and flushing liquid in the case of drill bits having a small internal projection of the drill segments, WO 2017/108461 A1 describes the use of transport channels on the inner side of the drill shaft or the use of drill shafts having a waved, trapezoidal or zigzag-shaped cross-sectional area. 
     In the case of drill bits having a releasable cutting section, transport channels can improve the supply of liquid. It is disadvantageous to replace the cutting section which is known from WO 2014/096359 A1 and has a circular ring-shaped cross-sectional area by a cutting section having a waved, trapezoidal or zigzag-shaped cross-sectional area. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to further develop a cutting section for a drill bit to the effect that the risk of the cutting section becoming wedged in the substrate during drilling in reinforced concrete is reduced. In addition or alternately, the manufacturing outlay for the production of a cutting section is intended to be reduced. 
     The cutting section is provided for a drill bit and is designed to be connectable to a drill shaft section of the drill bit via a releasable connecting device. The cutting section is characterized by:
         a first closed tubular element which is in the form of a first hollow cylinder having a first waved, trapezoidal or zigzag-shaped cross-sectional area and which has a first hollow cylinder height, a first inside diameter and a first outside diameter,   a second closed tubular element which is in the form of a second hollow cylinder having a second circular ring-shaped cross-sectional area and which has a second hollow cylinder height, a second inside diameter and a second outside diameter, wherein the first outside diameter is smaller than the second inside diameter, and a first outer lateral surface of the first closed tubular element touches a second inner lateral surface of the second closed tubular element, and   one or more drill segments,
 
wherein the first closed tubular element is pushed into the second closed tubular element and the one or more drill segments are connected to the first closed tubular element and to the second closed tubular element.
       

     The cutting section according to the invention comprises a first closed tubular element, a second closed tubular element and at least one drill segment. The first closed tubular element is in the form of a first hollow cylinder having a first waved, trapezoidal or zigzag-shaped cross-sectional area and comprises a first outer lateral surface, a first inner lateral surface, a first lower end surface and a first upper end surface. The second closed tubular element is in the form of a second hollow cylinder having a second circular ring-shaped cross-sectional area and comprises a second outer lateral surface, a second inner lateral surface, a second lower end surface and a second upper end surface. 
     In order to manufacture the cutting section, the first closed tubular element and the second closed tubular element are pushed one into the other and the one or more drill segments are connected to the first closed tubular element and to the second closed tubular element. In respect of the stability of the cutting section, it is advantageous if the drill segments are connected to the first and second closed tubular elements. 
     By separation of the cutting section into the first closed tubular element and the second closed tubular element, an adaptation of the cutting section to the different demands made with regard to transmission of force, transmission of torque and stability in relation to tensile loadings during the removal of a jammed drill bit can be taken into consideration. 
     The cutting section is designed in such a manner that force is transmitted from a drill shaft section via the first closed tubular element to the drill segments and torque is transmitted from the drill shaft section via the second closed tubular element to the drill segments. The first upper end surface of the first closed tubular element forms an annular stop shoulder which is used for transmitting force. A drill shaft section transmits the force to the annular stop shoulder by means of an annular end surface. Torque is transmitted, for example, via pin elements of the drill shaft section which interact with slot-shaped recesses in the second closed tubular element. By separation of the cutting section into the first closed tubular element and the second closed tubular element, the different demands made of the cutting section in respect of transmission of force and transmission of torque can be taken into consideration. 
     In addition, by separation of the cutting section into the first closed tubular element and the second closed tubular element, the manufacturing outlay for producing the cutting section can be reduced. The first upper end surface forms the annular stop shoulder for transmitting force, thus obviating the need for turning. The first closed tubular element and the second closed tubular element are in the form of hollow cylinders having circular ring-shaped cross sections and have a constant material thickness. The first closed tubular element can be produced from a first profiled metal sheet which is formed into a first open tubular element and is connected at first abutting edges in an integrally bonded or form fitting manner. The second closed tubular element can be produced from a second flat sheet metal part which is formed into a second open tubular element and is connected at second abutting edges in an integrally bonded or form fitting manner. 
     The first closed tubular element which is in the form of a first hollow cylinder having a first waved, trapezoidal or zigzag-shaped cross-sectional area permits the design of a cutting section without an internal projection or with a small internal projection of the drill segments on the inner side of the cutting section since the cooling and flushing liquid can be transported in the required quantity to the machining site via the depressions. 
     The first lower end surface of the first closed tubular element and the second lower end surface of the second closed tubular element are preferably aligned flush. The flush alignment of the first lower end surface and the second lower end surface has the advantage that a wide attachment surface for the drill segments arises, at which the drill segments can be connected to the first closed tubular element and to the second closed tubular element. 
     The one or more drill segments are particularly preferably connected to the first lower end surface and to the second lower end surface. The flush alignment of the first lower end surface and the second lower end surface gives rise to a wide attachment surface for the drill segments. If the drill segments are connected to the first lower end surface and to the second lower end surface, the first closed tubular element and the second closed tubular element can be connected simultaneously to the drill segments. If the drill segments are connected to the first and second closed tubular elements simultaneously, the manufacturing outlay can be reduced. Depending on the material thicknesses used, it may be necessary for the first closed tubular element and the second closed tubular element to be additionally connected to each other. Should higher resistance torques be required, the first closed tubular element and the second closed tubular element may be additionally connected to each other. 
     The second closed tubular element preferably has at least one slot-shaped recess, wherein the at least one slot-shaped recess comprises a transverse slot and a connecting slot, and the connecting slot connects the transverse slot to the second upper end surface of the second closed tubular element. The at least one slot-shaped recess is part of the releasable connecting device which connects the cutting section to a drill shaft section of the drill bit. The slot-shaped recess is T-shaped or L-shaped and, in the connected state of the drill bit, permits a relative movement between the cutting section and the drill shaft section. The relative movement between the cutting section and the drill shaft section enables a jammed cutting section to be released from the substrate. 
     The second closed tubular element in the second inner lateral surface particularly preferably has at least one transverse groove which is arranged level with the connecting slot of the slot-shaped recess. The at least one transverse groove is part of the releasable connecting device which connects the cutting section to a drill shaft section of the drill bit. The width of the transverse groove is greater than or equal to the width of the transverse slot of the slot-shaped recess. A matching transverse lug of a drill shaft section engages in the transverse groove of the cutting section. The transverse groove and transverse lug form an additional form fitting connection which prevents the push and twist connection from being unintentionally opened during release of a jammed drill bit and the drill shaft section from being removed from the substrate without the cutting section. 
     In a preferred development, the first closed tubular element is formed from a first material and the second closed tubular element from a second material. The cutting section according to the invention is designed in such a manner that force is transmitted to the cutting section via the first closed tubular element and torque is transmitted to the cutting section via the second closed tubular element. By separation of the cutting section into the first closed tubular element and the second closed tubular element, the choice of the first material for the first closed tubular element and of the second material for the second closed tubular element can be adapted to the different demands made of the cutting section in respect of transmission of force and transmission of torque. In addition, the second material can be adapted in respect of tensile loadings during the removal of a jammed drill bit. 
     The first closed tubular element is preferably in the form of a first formed sheet metal part. The use of a first formed sheet metal part permits the production of the first closed tubular element from profiled metal sheets. The first closed tubular element can be produced from a first profiled metal sheet which is formed into a first open tubular element and is connected at the first abutting edges. Cold forming methods and hot forming methods are suitable as the forming method for the first sheet metal part. The first abutting edges can be connected in an integrally bonded or form fitting manner, with the abutting edges of tubular elements conventionally being connected in an integrally bonded manner by welding. In addition to the integrally bonded connection, the first abutting edges can be connected in a form fitting manner. 
     The second closed tubular element is preferably in the form of a second formed sheet metal part. The use of a second formed sheet metal part permits the production of the second closed tubular element from flat sheet metal parts. The second closed tubular element can be produced from a second sheet metal part which is formed into a second open tubular element and is connected at the second abutting edges. The at least one slot-shaped recess can be produced in the second sheet metal part, for example, by punching or cutting out. Cold forming methods and hot forming methods are suitable as the forming method for the second sheet metal part. The second abutting edges can be connected in an integrally bonded or form fitting manner, with the abutting edges of tubular elements conventionally being connected in an integrally bonded manner by welding. In addition to the integrally bonded connection, the second abutting edges can be connected in a form fitting manner. 
     The second formed sheet metal part particularly preferably has at least one second positive form fitting element and at least one corresponding second negative form fitting element on opposite sides, wherein the at least one second positive form fitting element and the at least one second negative form fitting element are connected in a form fitting manner in the second closed tubular element. The connection of the second abutting edges via second form fitting elements has the advantage that heat which may lead to stresses in the second closed tubular element is not admitted into the second open tubular element. 
     The cutting section according to the invention for a drill bit is provided for connection to a drill shaft section of the drill bit. The invention furthermore relates to a drill bit with a cutting section and a drill shaft section, wherein the cutting section and the drill shaft section are connectable via a releasable connecting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are described hereinafter with reference to the drawing. It is not necessarily intended for this to illustrate the exemplary embodiments to scale; instead, the drawing, where conducive to elucidation, is produced in schematic and/or slightly distorted form. It should be taken into account here that various modifications and alterations relating to the form and detail of an embodiment may be undertaken without departing from the general concept of the invention. The general concept of the invention is not limited to the exact form or the detail of the preferred embodiment shown and described hereinafter or limited to subject matter that would be limited compared to the subject matter claimed in the claims. For given design ranges, values within the limits mentioned will also be disclosed as limit values and will be usable and claimable as desired. For the sake of simplicity, identical reference signs are used hereinafter for identical or similar parts or parts having identical or similar function. 
       In the drawing: 
         FIGS. 1A and 1B  show a drill bit with a cutting section according to the invention and a drill shaft section, which are connectable via a releasable connecting device, in an unconnected state of the drill bit ( FIG. 1A ) and in a connected state of the drill bit ( FIG. 1B ); and 
         FIGS. 2A, 2B and 2C  show the cutting section according to the invention of  FIGS. 1A and 1B  consisting of a first closed tubular element, a second closed tubular element and a plurality of drill segments ( FIG. 2A  showing all and  FIG. 2B  showing the first closed tubular element and  FIG. 2C  the second closed tubular element) in a longitudinal section along the section line A-A in  FIG. 1A . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1A and 1B  show a drill bit  10  which comprises a cutting section  11  according to the invention and a drill shaft section  12 , wherein the cutting section  11  and the drill shaft section  12  are connectable via a releasable connecting device  13 .  FIG. 1A  shows the cutting section  11  and drill shaft section  12  in an unconnected state of the drill bit, and  FIG. 1B  shows the cutting section  11  and drill shaft section  12  in a connected state of the drill bit. 
     The cutting section  11  comprises a first closed tubular element  14 , a second closed tubular element  15  and a plurality of drill segments  16  which are connected to the first closed tubular element  14 . The drill segments  16  are arranged annularly and form a drill ring with intermediate spaces. Instead of a plurality of drill segments  16 , the cutting section  11  can also have an individual drill segment in the form of a closed drill ring. The drill segments  16  are welded, soldered or screwed to the first closed tubular element  14  or fastened to the first closed tubular element  14  using another suitable type of fastening. The drill shaft section  12  comprises a tubular drill shaft  17 , a cover  18  and a shank  19  via which the drill bit  10  is fastened in a tool fitting of a core drill. 
     The releasable connecting device  13  is in the form of a combined push and twist connection, as disclosed in WO 2014/096359 A1. The releasable connecting device  13  comprises a first push element  21  which is integrated in the cutting section  11 , and a second push element  22  which is integrated in the drill shaft section  12 . The first and second push elements  21 ,  22  form a push connection and are additionally secured via a twist connection. The twist connection comprises a plurality of pin elements  23  which are introduced into slot-shaped recesses  24 . The pin elements  23  are fastened to an outer side of the second push element  22 , and the slot-shaped recesses  24  are provided in the first push element  21 . The cutting section  11  can be connected simply and rapidly to the drill shaft section  12  by the operator. For this purpose, the cutting section  11  with the first push element  21  is pushed onto the second push element  22  of the drill shaft section  12  in such a manner that the pin elements  23  are arranged in the slot-shaped recesses  24 . 
     In the drilling mode, the drill bit  10  is driven by a core drill in a direction of rotation  25  about an axis of rotation  26 , wherein the axis of rotation  26  coincides with a longitudinal axis of the tubular drill shaft  17 . During the rotation of the drill bit  10  about the axis of rotation  26 , the drill bit  10  is moved in a feed direction  27  into a workpiece  28 , with the feed direction  27  running parallel to the axis of rotation  26 . In the workpiece  28 , the drill bit  10  produces a drill hole  31  with a drill hole diameter d L  and a drill core  32  with a core diameter d K . The drill segments  15  form a drill ring with an outside diameter which corresponds to the drill hole diameter d L  and with an inside diameter which corresponds to the core diameter d K . 
       FIGS. 2A, 2B and 2C  show the cutting section  11  according to the invention of  FIG. 1  with the first closed tubular element  14 , the second closed tubular element  15  and the drill segments  16  in a longitudinal section along the section line A-A in  FIG. 1A .  FIG. 2B  shows the first closed tubular element  14  and  FIG. 2C  shows the second closed tubular element  15  of the cutting section  11 . 
     The cutting section  11  is produced from the first closed tubular element  14 , the second closed tubular element  15  and the drill segments  16 . The drill segments  16  are connected to the first closed tubular element  14  and/or to the second closed tubular element  15 . The drill segments  16  can be welded, soldered or screwed to the first and/or second closed tubular elements  14 ,  15  or fastened thereto using another suitable type of fastening. 
     As shown in  FIG. 2B , the first closed tubular element  14  is in the form of a first hollow cylinder having a first waved cross-sectional area; alternatively to the waved cross-sectional area, trapezoidal or zigzag-shaped cross-sectional areas can be used. The first closed tubular element  14  comprises a first outer lateral surface  41 , a first inner lateral surface  42 , a first lower end surface  43  and a first upper end surface  44 . The dimensions of the first closed tubular element  14  are defined by a first hollow cylinder height H 1 , a first inside diameter d 1  and a first outside diameter D 1 . The width of the first closed tubular element  14  is produced as half the difference of the first outside diameter D 1  and the first inside diameter d 1  and is referred to as the first width B 1 . The diameter of an inner circle is defined as the first inside diameter d 1  and the diameter of an outer circle is defined as the first outside diameter D 1 . 
     As shown in  FIG. 2C , the second closed tubular element  15  is in the form of a second hollow cylinder having a circular ring-shaped cross-sectional area. The second closed tubular element  15  comprises a second outer lateral surface  45 , a second inner lateral surface  46 , a second lower end surface  47  and a second upper end surface  48 . The dimensions of the second closed tubular element  15  are defined by a second hollow cylinder height H 2 , a second inside diameter d 2  and a second outside diameter D 2 . The width of the second closed tubular element  15  is produced as half the difference of the second outside diameter D 2  and the second inside diameter d 2  and is referred to as the second width B 2 . As shown schematically, the second closed tubular element  15  can be connected at second abutting edges  115  in an interlocking manner with a second positive interlocking element  116  and a second negative interlocking element  117 . 
     The first lower end surface  43  of the first closed tubular element  14  and the second lower end surface  47  of the second closed tubular element  15  are aligned flush. The flush alignment of the first lower end surface  43  and the second lower end surface  47  has the advantage that a wide attachment surface for the drill segments  16  arises, at which the drill segments  16  can be connected to the first closed tubular element  14  and to the second closed tubular element  15 . If the drill segments  16  are connected to the first lower end surface  43  and to the second lower end surface  47 , the first closed tubular element  14  and the second closed tubular element  15  can be connected to each other simultaneously. Depending on the material thicknesses used, it may be necessary for the first closed tubular element  14  and the second closed tubular element  15  to be additionally connected to each other. 
     The cutting section  11  is designed in such a manner that force is transmitted from the drill shaft section  12  via the first closed tubular element  14  to the drill segments  16  and torque is transmitted from the drill shaft section  12  via the second closed tubular element  15  to the drill segments  16 . The first upper end surface  44  of the first closed tubular element  14  forms an annular stop shoulder  49  on the inner side of the cutting section  11  for the transmission of force from a connected drill shaft section. Torque is transmitted from the drill shaft section  12  to the cutting section  11  via the pin elements  23  and the slot-shaped recesses  24 . The second closed tubular element  15  of the cutting section  11  has a plurality of slot-shaped recesses  24  on the second upper end surface  48 . The slot-shaped recesses  24  each comprise a transverse slot  51  and a connecting slot  52 , wherein the connecting slot  52  connects the transverse slot  51  to the second upper end surface  48 . 
     The first closed tubular element  14  can be produced from a first material and the second closed tubular element  15  from a second material. By separation of the cutting section  11  into the first closed tubular element  14  and the second closed tubular element  15 , the choice of the first material and of the second material can be adapted to the different demands made of the first closed tubular element  14  and of the second closed tubular element  15 .