Patent Publication Number: US-2006006002-A1

Title: Working tool for machining mineral constructional components

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a working tool for machining mineral constructional components, mineral foundations, and the like, in particular, for machining with an ultrasonic tool, and having a carrier body provided with at least one cutting element.  
      2. Description of the Prior Art  
      Mineral constructional components, mineral foundations, and the like and foundations, and the like are subjected to drilling, cutting, grinding with suitable power tools such as, e.g., drilling tools, cutting or grinding tools, etc. Both hand-held tools and column-guided tools are used.  
      In particular, with hand-held systems, the pressure forces, which are applied by a user during the operational process, are limited and rarely exceed 200 N. In order to increase an operational efficiency of hand-held systems, it is known to superimpose a rotational movement of a working tool with an auxiliary or additional kinematics. E.g., German application DE4444853A1 of the assignee herein discloses superimposition of a rotational movement of a core drilling bit with ultrasonic oscillations in the direction of a bore longitudinal axis. The proposed system achieves good results. However, the improvement of the machining efficiency is diminished because of economical considerations, e.g., the performance capability of the core drilling bit is reduced in comparison with systems without additional kinematics.  
      German Publication DE 44 26 238 A1 discloses forming a carrier body for a working tool, e.g., a bit body for a core drilling bit of an unalloyed constructional steel with a carbon content less than 0.2% (e.g., of S235JR, material No. 1.0037 (European standard EN 10025, corresponds to steel A252-02 (ASTM)). This material provides for an economical manufacturing of core drilling bit and has good welding characteristics. However, these core drilling bits are not suitable for an ultrasonic drilling because the produced ultrasonic oscillations are strongly attenuated by an unalloyed constructional steel, which leads to an inefficient machining process and excessive heating of the core drilling bit, resulting in a reduced fatigue strength of the core drilling bit.  
      In order to eliminate the foregoing drawbacks upon the use of an ultrasonic machining, German Patent DE 42 07031 C2 suggests to use a chromium-nickel steel. This material has very good characteristics, which makes it suitable for ultrasonic machining. However, this material is in 3-5 times more expensive than an unalloyed constructional steel. Another material that has very good characteristics for an ultrasonic machining is a titanium alloy which, however, is also much more expensive than an unalloyed constructional steel. Therefore, from an economical point of view, neither chromium-nickel steel nor titanium alloy is suitable for manufacturing of single-use working tools.  
      Accordingly, an object of the present invention is to provide a tool for machining mineral constructional components, mineral foundations, and the like that can be used with conventional power tools and, at the same time, has good characteristics for use with an ultrasonic tool, and that can be economically produced.  
     SUMMARY OF THE INVENTION  
      This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a working tool the carrier body of which is formed of an unalloyed hardened steel with a carbon content from 0.2% to 0.8%.  
      The costs of an unalloyed hardened steel with a carbon content from 0.2% to 0.8% are only slightly higher than the costs of a conventional unalloyed constructional steel. However, a working tool the carrier body of which is formed of an alloyed hardened steel with a carbon content from 0.2% to 0.8%, has a small material-dependent attenuation of the ultrasonic oscillations and, as a result, an increased fatigue strength. In addition, the unalloyed hardened steel with a carbon content from 0.2% to 0.8% has good welding properties and machinability. Working tools, which have a carrier body formed of an unalloyed hardened steel with a carbon content from 0.2% to 0.8%, can be used with both conventional power tools and ultrasonic tools.  
      Surprisingly, it was found out that the working tools, the carrier body of which is formed of an un alloyed hardened steel with a carbon content from 0.2% to 0.8%, not only have a smaller attenuation of ultrasonic oscillations and an increased fatigue strength in comparison with tools from un alloyed constructional steel, but also require less power for generation of the ultrasonic oscillations. Furthermore, the working tools, which have a carrier body formed of an un alloyed hardened steel with a carbon content from 0.2% to 0.8%, have, because of a reduced material fatigue, a reduced probability of failure, so that with a probability of fracture the same as with the tools the carrier body of which is formed of an alloyed constructional steel, the inventive working tools can operate with an elongation (expansion) amplitude greater by up to 80% than the tool the carrier body of which is formed of an unalloyed constructional steel. It has also been found that by using an unalloyed hardened steel with a carbon content from 0.2% to 0.8% instead of an unalloyed constructional steel for forming carrier bodies of working tools for use with ultrasonic tools, it became possible to obtain greater ultrasonic amplitude at the same ultrasonic power. As a result, due to an increased fatigue strength of the unalloyed hardened steel with a carbon content from 0.2% to 0.8%, the material-dependent probability of failure of the incentive working tools remained the same as of the tools formed of an unalloyed constructional steel even at a greater ultrasonic amplitude.  
      Preferably, the carrier body is formed of an unalloyed hardened steel with a carbon content in a range from 0.5% to 0.7%, advantageously 0.6%. A suitable unalloyed hardened steel can be, e.g., steel “C60E” (material No. 1.1221, European standard EN 10297-1 corresponding to AISI 1060), which has a carbon content from 0.57% to 0.65%.  
      According to one embodiment of the present invention, the working tool is formed as a core drilling bit having a hollow cylindrical bit body that forms the carrier member. Such core drilling bits are used, in particular, for drilling holes in a reinforced concrete. At the first end of the bit body, there is provided a shank for connecting the core drilling bit with a power drilling tool. At the second, opposite end of the bit body, there are provided cutting elements such as, e.g., sintered diamond segments or cutters of hard metal, and which serve as machining elements. The machining process is effected by rotation of the core drilling bit with a power drilling tool. These core drilling bits form so-called single-use consumer goods, when the bit body is provided with new cutting elements for a new application of the core cutting bit.  
      Instead of an entire hollow cylindrical bit body, often, section of the hollow cylindrical bit body, so-called exchange modules are used, which are provided with cutting elements. An exchange module has a hollow cylindrical bit body section that forms the carrier body and is provided at its first end with a connection surface for connection the bit body section with the hollow cylindrical bit body, and at its second, opposite end is equipped with cutting elements. In order to insure that the core drilling bit retains the advantageous characteristics of the inventive core drilling bit also when the bit is used with an ultrasonic tool, the hollow cylindrical bit body section is also formed of an unalloyed hardened steel with a carbon content from 0.2% to 0.8%.  
      According to a further embodiment of the present invention, the inventive working tool is formed as a drill the stem of which forms the carrier body. Such drills are used for drilling bores, with the stem being provided with a shank at its first end for connecting the drill with a power drilling tool, and having, at its other opposite end, at least one cutting element that forms the machining element. The at least one cutting element can be formed of a hard metal plate or as a drilling head, with the hard metal plate or drilling head being fixedly secured at the second end. The stem is provided on its outer circumference with at least one helical groove for removing the drilling cuttings, so that the drillings or drilling dust, which are produced during a drilling process, are removed. According to an alternative embodiment of the drill, the stem is provided with a longitudinal bore through which a rinsing fluid is fed to the at least one cutting element during the drilling process, or through which drillings or drilling dust, which are produced during a drilling process, can be aspirated from the drilling bore.  
      According to a still further embodiment of the present invention, the inventive working tool is formed as a cutting disc with a disc-shaped carrier body. Such cutting discs are used for cutting the constructional components, mineral foundations, and the likeand foundations, and the likeor for forming slots therein. The cutting disc has a through-opening for mounting the cutting disc on a drive shaft of a power tool. On the outer circumference of the cutting disc, there are provided cutting elements such as, e.g., as sintered diamond segments or cutters having a predetermined shape and formed of a hard metal. The diamond segments or cutters form machining elements.  
      According to another embodiment of the present invention, the inventive working tool is formed as a grinding disc having a substantially disc-shaped carrier body. Such grinding discs are used for machining, grinding, flat surfaces of constructional components. The substantially disc-shaped carrier body has a through-opening for mounting of the grinding disc on a drive shaft of a power tool, and is provided on its bottom with grinding elements, e.g., sintered diamond segments which form the grinding elements.  
      The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The drawings show:  
       FIG. 1 a  longitudinal cross-sectional view of a working tool according to the present invention formed as a core drilling bit;  
       FIG. 2 a  longitudinal cross-sectional view of another embodiment of a working tool according to the present invention also formed as a core drilling bit;  
       FIG. 3 a  longitudinal cross-sectional view of a working tool according to the present invention formed as a drill;  
       FIG. 4 a  plan view of a working tool according to the present invention formed as a cutting disc;  
       FIG. 5 a  plan view of a working tool according to the present invention formed as a grinding disc; and  
       FIG. 6 a  diagram illustrating attenuation behavior of different materials at two different characteristics of ultra-sound. 
    
    
      In the drawings, the same elements are basically shown with the same reference numerals.  
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      A working tool according to the present invention, which is formed as a core drilling bit  11  and is shown in  FIG. 1 , has a hollow cylindrical bit body  12  that serves as a carrier body and is formed of an unalloyed hardened steel with a carbon content from 0.2% to 0.8%, e.g., of C60 E. The core drilling bit  11  has a first end  13  with a shank  15  for connecting the core drilling bit  11  with a drilling tool (not shown), and a second opposite end  14  provided with cutting elements  16  which serve as machining elements.  
      In a core drilling bit  21 , which is shown in  FIG. 2 , at the second end  24  of the hollow cylindrical bit body  22 , there is provided a replaceable exchange module  30  having a hollow cylindrical bit body section  27  that serves as a carrier body and is formed of an alloyed hardened steel with a carbon content from 0.2% to 0.8%. The bit body section  27  has a first end  28  that is formed as a connection surface for connecting the bit body section  27  to the bit body  22  of the core drilling bit  21 , and a second, opposite end  29  provided with cutting elements  26  which serve as machining elements. The exchange module  30  is connected with the hollow cylindrical bit body  22  by a weld seam  31  or, alternatively, can be connected by a solder seam. The exchange module  30  can be separated from the bit body  20  upon wear of the cutting elements  26  and be replaced with a new exchange module with new cutting elements  26 .  
      A working tool according to the present invention, which is shown in  FIG. 3 , is formed as a drill  36  having a stem  37  which serves as a carrier body and is formed of an unalloyed hardened steel with a carbon content from 0.2% to 0.8%, e.g., of C60E steel. The stem  37  is provided at its first end  38  with a shank  40  for connecting the drill  36  with a drilling tool (not shown). At its second, opposite end, the stem  37  is provided with a cutting element  41  that is formed a hard metal plate and serves as a machining element. The stem  37  is provided with helical grooves  42  on its circumference.  
      A working tool according to the present invention, which is shown in  FIG. 4 , is formed as a cutting disc  46  having a disc-shaped carrier body  47  formed of unalloyed hardened steel with a carbon content from 0.2% to 0.8%. The disc-shaped carrier body  47  has a through-opening  48  for mounting the cutting disc  46  on a drive shaft of a power tool (not shown). A plurality of cutting elements  49 , which serve as machining elements, is provided on the outer circumference of the disc-shaped carrier body  47 .  
      A working tool according to the present invention, which is shown in  FIG. 5 , is formed as a grinding disc  56  having a substantially disc-shaped carrier body  57  formed of an unalloyed hardened steel with a carbon content from 0.2% to 0.8%. The disc-shaped carrier body  57  has a through-opening  58  for mounting the grinding disc  56  on a drive shaft of a power tool (not shown). On the bottom  60  of the disc-shaped carrier body  57 , there are provided a plurality of grinding elements  59 .  
      Advantageous characteristics of working tools having a carrier body formed of an alloyed hardened steel with a carbon content from 0.2% to 0.8%, in particular, of C60E and unexpected properties obtained by their use with ultrasonic tools were confirmed by numerous tests. Thus, diagram of  FIG. 6  shows temperature rise of different materials at two different amplitudes. The left column of each column pair shows the temperature rise when the material sample is loaded for 2 min at elongation (ε) of 0.3×10 −3  at an amplitude of 12 μm. The right column of each column pair shows the temperature rise when the material sample is loaded during 1 min at elongation (E) of 0.5×10 −3  at an amplitude of 20 μm. The first column pair show results for a material sample of a titanium alloy (Ti 6 Al 4 V) which is used as a reference material and has a very small temperature under a respective ultrasonic load. The small temperature rise of the titanium alloy corresponds to a small material-dependent attenuation of ultrasonic waves. The second column pair shows, in comparison, the results for a material sample form an unalloyed constructional steel (S235JR) which is conventionally used for manufacturing of carrier bodies of the working tools and which has a high temperature rise at a respective ultrasonic load. The very high temperature rise corresponds to a large material-dependent attenuation of the ultrasonic waves. The third column pair shows results for a material sample of an unalloyed hardened steel (C60E) which is used for manufacturing of the carrier body of a working tool according to the present invention. The temperature rise of this material sample under the respective ultrasonic load is only slightly greater than of the titanium alloy (first column pair) but is substantially smaller than of the unalloyed constructional steel (second column pair).  
      Further tests confirmed these results and showed that the efficiency of the fed power with regard to the produced ultrasonic amplitude with working tools having a carrier body formed of an unalloyed hardened steel with a carbon content from 0.2% to 0.8%, in particular of C60E, is noticeably increased in comparison to the tools having a carrier body formed of an unalloyed constructional steel (S235JR). In addition, with tools having a carrier body formed of an unalloyed hardened steel with a carbon content from 0.2% to 0.8%, in particular of C60E, higher elongation amplitudes are obtained in comparison with an unalloyed constructional steel at the same probability of fracture.  
      Though the present invention was shown and described with references to the preferred embodiments, such are merely illustrative of the present invention and are not to be construed as a limitation thereof, and various modifications of the present invention will be apparent to those skilled in the art. It is, therefore, not intended that the present invention be limited to the disclosed embodiments or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.