Abstract:
A machine tool device, particularly a hand-held machine tool device, includes at least one screw that is configured to secure at least one metal component to at least one additional component in a form-fitting manner. The machine tool further includes an electrical insulating unit that is configured to prevent the conduction of current at least between the metal component and the screw.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2012/057663, filed on Apr. 26, 2012, which claims the benefit of priority to Serial No. DE 10 2011 077 622.2, filed on Jun. 16, 2011 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     There are already known hand-held power tools in which a metallic transmission housing is connected to a cover cap in a form-fitting manner by means of screws. 
     SUMMARY 
     The disclosure proceeds from a power-tool device having at least one screw, which is provided to fasten at least one metallic component and at least one further component to each other in a form-fitting manner. 
     Proposed is an electrical insulating unit, which is provided to prevent conduction of current, at least between the metallic component and the screw. An “electrical insulating unit” is to be understood to mean, in particular, a unit having an electrical conductivity of less than 10 −10  S/cm. This makes it possible, in particular, to prevent electrical current from being conducted from the tool, via the metallic component and the screw, to a user in the case of a flow of current through a tool to which the power-tool device is assigned, for example as a result of damage to a current-carrying conductor by the tool, thereby making it possible to prevent a risk of electric shock to the user. 
     It is additionally proposed that the metallic component be constituted by an internal metallic housing. An “internal metallic housing” is to be understood to mean, in particular, a component of the power-tool device, realized as a housing, that is made of a metal and that, when the power-tool device is in a mounted state, is at least mostly, and preferably completely, encompassed by surrounding components, in particular by surrounding housing parts, and that is therefore located outside of a possible region of contact by a user. It is advantageously possible to prevent the occurrence of a flow of electrical current, from inside the power-tool device to an outer region of the power tool that can be contacted by the user, that can endanger the user. 
     It is additionally proposed that the electrical insulating unit comprise at least one electrically insulating surface coating. A “surface coating” is to be understood to mean, in particular, a material layer, which forms a surface of an element that is different from a main body of the element, and whose material thickness is small in comparison with a material thickness of the whole element. That “the material thickness of the material layer is small in comparison with a material thickness of the element” is to be understood to mean, in particular, that the material thickness of the material layer has a value that is maximally 5 percent, advantageously maximally 1 percent, and preferably maximally 0.1 percent of a value of the material thickness of the element. An “electrically insulating” surface coating is to be understood to mean, in particular, a surface coating that has an electrical conductivity of less than 10 −10  S/cm. Advantageously, an inexpensive electrical insulating unit of simple design can be obtained. Preferably, the at least one screw has the electrically insulating surface coating. Advantageously, therefore, in particular, a coating can be applied to ordinary, commercially available screws, thereby enabling costs to be saved. Moreover, advantageously, in particular in the case of damage to the electrically insulating surface coating, the screw can be easily exchanged, thereby advantageously enabling savings to be made in costs, time and work. In principle, however, it is also possible for the metallic component and/or the further component to have the electrically insulating surface coating. Moreover, the realization as a surface coating makes it possible to achieve an insulating unit for a power-tool device in which it is possible to dispense with a structural redesign of the power-tool device. In principle, it is also possible, as an alternative to an electrically insulating surface coating of the screws, to use screws composed entirely of insulating material. 
     It is additionally proposed that the surface coating be composed of a non-conducting material applied electrolytically. A “non-conducting material applied electrolytically” is to be understood to mean, in particular, a material that constitutes an electrical non-conductor, and that is applied to a substrate, for example a screw, by means of electrolysis. A “non-conducting material” is to be understood to mean, in particular, a material having an electrical conductivity of less than 10 −10  S/cm. It is possible to obtain a resistant layer that, in particular, has a high scratch resistance. Advantageously, it is thereby possible, in particular, to prevent the occurrence of a conductive connection via the screw as a result of damage to the surface coating, which constitutes an electric shock hazard. 
     It is additionally proposed that the at least one screw comprise a smooth partial region. A “smooth partial region” is to be understood to mean, in particular, a region of the screw that does not have a screw thread, and that extends at least over 10 percent, advantageously at least over 20 percent, and preferably at least over 30 percent of a longitudinal extent of the screw, and extends maximally over 90 percent, advantageously maximally over 80 percent, and preferably over maximally 60 percent of the longitudinal extent of the screw. Advantageously, it is possible to increase a distance between an end of the screw, that can be contacted by the user, and a component. Furthermore, advantageously, it is possible to prevent damage to the coating in a region of the screw that can be contacted by the user when the screw is in a screwed-in state, during a process of screwing-in the screw. 
     It is additionally proposed that the smooth partial region adjoin a screw head. In a screwed connection, the screw head is normally fitted on a region that can be contacted by the user. Advantageously, the region that can be contacted by the user can be protected against damage to the coating, and a risk of electric shock to the user can be prevented. 
     It is additionally proposed that the electrical insulating unit comprise at least one additional insulating element, which is provided to be disposed between the screw and the metallic component. An “additional insulating element” is to be understood to mean, in particular, an insulating element constituting an element that is different from the screw and the metallic component. Preferably, the additional insulating element is provided to be disposed between the smooth partial region and the metallic component. This can be effected, for example, by covering the smooth region with a shrink-down tube or with a sleeve of non-conducting material. In principle, however, alternative designs of the additional insulating element are also conceivable, for example a lining of a screw hole in the metallic component, the lining being made of a non-conductor, for example a plastic material. The additional insulating layer advantageously further increases safety for the user and prevents the risk of electric shock to the user. 
     There is additionally proposed at least one insulating rib, which is disposed in a screw hole in the metallic component that is provided to receive the screw. An “insulating rib” is to be understood to mean, in particular, a body made of a non-conducting material that is provided to serve as a spacer between the screw and the metallic component. Preferably, the insulating rib is made of a non-conducting plastic. Preferably, the insulating rib is realized as a cylindrical body having a hole, through which the screw can pass. In a preferred design, the insulating rib is integral with the further component, and realized as a projecting region of the further component. An additional insulating layer can be achieved between the screw and the component, thereby advantageously enabling the safety of the user to be further increased. 
     It is additionally proposed that the metallic component be constituted by a transmission housing, and the further component be constituted by a cover cap. Advantageously, therefore, it is possible to reliably prevent, in particular, a flow of current via a metallic transmission housing, that is in conductive contact with the tool, to a screw that is disposed on the outside of a cover cap and that can be contacted by the user. The risk of electric shock to the user can thus be kept to a low level. 
     There is furthermore proposed a portable power tool, in particular a hand-held power tool, having a power-tool device according to the disclosure. 
     It is additionally proposed that the portable power tool comprise a bevel gear transmission. The portable power tool is realized, for example, as an angle grinder, as a jigsaw and/or, particularly advantageously, as an oscillating hand-held power tool, in which a rotary motion is also converted, via the bevel gear transmission, into an oscillating back-and-forth motion. In the manipulation of such a portable power tools, it is frequently necessary to contact the portable power tool on outer regions that are outside of guide regions specially provided for this purpose, with the result that there is a high probability of contact with screws, in particular screws that connect an internal metallic component to an external housing component. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the figures: 
         FIG. 1  shows a hand-held power tool having an oscillating tool, 
         FIG. 2  shows a schematic detail view of an insulating unit according to the disclosure, in a sectional representation, and 
         FIG. 3  shows a schematic sectional representation through a screw according to the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a hand-held power tool  10  having an oscillating tool  20  that is disposed in a tool receiver  24 . A housing  12  of the hand-held power tool  10  encloses an electric motor unit  14  and a transmission unit  16  that comprises a bevel gear transmission. Via the transmission unit  16  and an output unit  18 , a rotary motion of the electric motor unit  14  is transmitted to the tool  20 . In particular, the rotary motion is reversed, and the tool  20  is made to execute an oscillating working motion in a circumferential direction  50  about a rotation axis  48 . 
     A cover cap  22  is fastened to the housing  12  in a form-fitting manner by means of four screws  30 , of the same type, which are disposed in screw holes  52  that are uniformly distributed around the hand-held power tool  10  in the circumferential direction. The cover cap  22  constitutes an operating unit  26 , which is provided to be gripped by a user for the purpose of guiding the hand-held power tool  10 . In particular, an operating lever  28 , disposed on the operating unit  26 , is provided for this purpose. In cases in which the hand-held power tool  10  is used in a confined space, in particular, the user, in order to guide the hand-held power tool  10  in a precise manner, may grip and guide the operating unit  26  at a region other than the operating lever  28  by the user. 
     The transmission unit  16  has an interior metallic housing in the form of a transmission housing  46 , which is enclosed by the cover cap  22  and the housing  12 , and which constitutes an internal component of the hand-held power tool  10 . The transmission housing  46  is connected to the cover cap  22  and the housing  12  in a form-fitting manner. For this purpose, a respective screw  30  is inserted in one of the four screw holes  52 , which extend from the cover cap  22 , through the transmission housing  46 , and into the housing  12  (cf.  FIG. 2 ). A diameter of the screw hole  52  is dimensioned such that the screw  30 , together with additional elements of an electrical insulating unit  40 , can be inserted without play into the screw hole  52 . In the region of the screw hole  52 , the housing  12  has a thread, which is provided to act in combination with an external thread of the screw  30 , in order to achieve a form-fitting connection between the cover cap  22 , the transmission housing  46  and the housing  12 . The screw  30  comprises a screw head  34 , which is adjoined by a cylindrical screw body. The screw body comprises a smooth partial region  32 , and a region that has an external thread. The smooth partial region  32  extends over 45 percent of a total length of the screw body. When the screw  30  is in a screwed-in state, the screw head  34  bears against the outside of the hand-held power tool  10 , in a recess of the cover cap  22 , where it is partially protected against contact by the user. 
     The electrical insulating unit  40  is provided to prevent a flow of current between the internal metallic transmission housing  46 , via the screw  30 . The electrical insulating unit  40  comprises an electrically insulating surface coating  38  of the screw  30 , which is composed of an electrolytically applied coating of a non-conducting material. The smooth partial region  32  is surrounded by an additional insulating element  44 , in the form of a shrink-down tube, which is disposed between the screw  30  and the transmission housing  46 . The shrink-down tube has been brought, by means of heat treatment, into a state in which it covers the smooth partial region  32  without play, and has a layer thickness of 0.5 mm. The additional insulating element  44  constitutes an additional insulating layer between the screw  30  and the transmission housing  46 , and further prevents damage to the electrically insulating surface coating  38  in the smooth partial region  32  during an operating of screwing-in the screw  30 . An insulating rib  42  is disposed, in the region of the screw hole  52 , in the metallic transmission housing  46 , and constitutes an insulating layer, between the transmission housing  46  and the screw  30 , that is additional to the electrically insulating surface coating  38 . The insulating rib  42  is realized as a projecting region of the cover cap  22 , and constitutes a cylindrical region having a hole, through which the screw  30  is passed. 
       FIG. 3  shows a schematic sectional representation, through a screw  30  according to the disclosure, in a plan view from a direction facing away from the screw head  34 . The screw  30  has a screw core  36 , which is surrounded by the electrically insulating surface coating  38 . A material thickness of the electrically insulating surface coating  38  is 50 μm, and is therefore significantly less than a material thickness of the screw core  36 . In the smooth partial region  32  of the screw  30  that does not have a screw thread, the screw  30  is surrounded by the insulating element  44  that is additional to the electrically insulating surface coating  38 .