Abstract:
The invention relates to a plug ( 10 ) for fastening to hollow or panel-type building materials and to solid building materials. The invention proposes providing the plug ( 10 ) with expansion limbs ( 18 ) that extend longitudinally and that are connected to one another by thin skins ( 22 ) having a corrugation in the peripheral direction. That has the advantage of good screw guidance and a torsionally rigid construction of the plug ( 10 ); especially when fastening to hollow and panel-type building materials, undesirable backwards rotation of the plug tip ( 16 ) is avoided when screwing in an expansion screw by hand. Angled slits ( 32 ) in the plug tip ( 16 ) bring about good adaptation to screws having different diameters and different pitches of thread.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a plug for fastening to hollow building materials and to solid building materials, having the features of the preamble of claim 1. Hollow building materials are understood herein to be, for example, hollow block bricks or panels behind which there is a cavity. Solid building materials are understood to be, for example, concrete or the like. 
     Such plugs are known per se. They are usually made of plastics material and, in a middle region, have expansion limbs extending longitudinally and separated from one another by slits. The expansion limbs are connected to one another at a rear end by a sleeve-like plug end and at a front end by a sleeve-like plug tip. An expansion screw can be pushed through the sleeve-like plug end and screwed into the plug tip. For the purpose of fastening the plug in a solid building material, the plug is inserted in a hole drilled in the solid building material and an expansion screw is screwed into the plug. The expansion screw pushes the expansion limbs apart, that is to say the expansion screw expands the expansion limbs and, as a result, anchors the plug in the hole drilled in the solid building material. 
     In a hollow building material or in a panel, the plug is pushed through a drilled hole so that its sleeve-like plug end is located in the hollow building material. An expansion screw is then pushed through the plug end, guided through between the expansion limbs and screwed into the plug end. Screwing the expansion screw into the plug tip causes the plug tip to move towards the plug end, in the process of which the expansion limbs are expanded. Two possibilities for expansion are known per se. The first is that the expansion limbs bend outwards as the plug tip comes closer to the plug end and, as a result, grip behind the hollow building material in positive manner. The other possibility is that, when the expansion screw is being screwed in, the plug tip twists relative to the plug end, as a result of which the expansion limbs are wound around one another and form a knot-like structure that grips behind the hollow building material. 
     The known plugs have the disadvantage of poor screw guidance; when being screwed in, the expansion screw can emerge to the side through the slits between the expansion limbs. A further disadvantage of the known plugs is their low torsional rigidity, which results in resilient twisting of the plug tip relative to the plug end when the expansion screw is being screwed in. When the expansion screw is being screwed in by hand, the resilient twisting of the plug tip with respect to the plug end causes the plug tip, together with the expansion screw screwed into it, to rotate back again when a screwdriver is released for “grip changing”. The consequence thereof is that the expansion screw can be screwed into the plug by hand only poorly. 
     SUMMARY OF THE INVENTION 
     The invention is based on the problem of avoiding the disadvantages mentioned above. 
     The problem is solved in accordance with the invention. In the plug according in which the expansion limbs are connected to one another in a peripheral direction by an expandable material. For the purpose of expandability, the material can be thinly formed and/or can be corrugated in the peripheral direction of the plug. When the plug is made from plastics material, the expandable material is preferably integral with the expansion limbs and consequently is made from the same plastics material as the rest of the plug. The expandable material in that case is preferably thinly formed as a plastic skin. As a result of the connection of the expansion limbs in the peripheral direction, the plug according to the invention is shaped like a sleeve which is closed in the peripheral direction even in the region of the expansion limbs. As a result, good guidance of the expansion screw is achieved and the expansion screw is preventing from emerging through the side of the plug between the expansion limbs, even when the expansion screw is subjected to a transverse load. A further advantage of connecting the expansion limbs in a peripheral direction is an increase in the torsional rigidity of the plug. The increased torsional rigidity firstly has the advantage that, when the expansion screw is being screwed in, the plug tip rotates together with the screw to a lesser extent, as a result of which the expansion screw can be better screwed into the plug tip. Furthermore, the increased torsional rigidity has the advantage that, when the screwing torque is released, for example when changing grip on a screwdriver, the plug tip rotates back less. As a result, the expansion screw is easier to screw into the plug, especially when it is being screwed in by hand. In addition, the plug according to the invention has the advantage that, when the expansion screw is being screwed in, there is a less pronounced drop in torque after expansion in a hollow building material has begun. In the case of the known expansion plugs, there is a marked drop in the torque once the expansion limbs have begun to bend out or wind around one another when the plug is being fastened to a hollow building material. As a result of the increased rigidity of the plug according to the invention caused by connecting its expansion limbs in a peripheral direction, that effect is, at least, smaller in is disadvantageous because it gives the false impression that the expansion screw or the plug have come away as a result of excessive force and consequently do not have a firm seating in the hollow building material. 
     In an embodiment of the invention, the sleeve-like plug end has a larger transverse dimension than the rest of the plug. This embodiment has the purpose of providing the plug with a good seating in a hollow or panel-type building material, in which essentially only the sleeve-like plug end of the plug is accommodated within the drilled hole and the rest of the plug is in a hollow space. 
     In an embodiment of the invention, a cross-section of the sleeve-like plug end has a sawtooth-like contour. This means that the plug end has radial surfaces, from the outer edge of which a contour line of the plug end extends inwards to the next radial surface in the manner of a helix contrary to the direction in which the expansion screw is screwed in. The radial surfaces are therefore oriented in the direction in which the expansion screw is screwed in. In soft building materials, they form a kind of abutment that presses into the building material and forms an anti-rotation means, which holds the plug in the building material so that it does not rotate when the expansion screw is being screwed in. Of course, the radial surfaces need not be oriented exactly radially. Especially together with the plug end having a larger cross-section compared to the rest of the plug, the sawtooth-like arrangement of the contour of the plug end provides a good anti-rotation means in soft building materials because, when the plug is introduced into a hole drilled in a soft building material, the plug end having a relatively large transverse dimension so compresses the building material in a region surrounding the plug end that the radial surfaces digging into the building material gain a good hold in the building material. 
     In an embodiment of the invention, the sleeve-like plug tip is provided with angled, for example V-shaped, slits, the corner (point) or tip of the slits pointing preferably towards the front or towards the rear end of the plug. As a result of being angled, the slits have one leg that has a pitch in the same direction as the pitch of the thread on the expansion screw and another leg that has a pitch in the opposite direction. The pitch of the slits in the plug tip can differ from the pitch of the thread on the expansion screw, it is merely their direction that is the same or opposite. The legs of the angled slits whose pitch is in the same direction as the thread pitch on the expansion screw serve to engage the turns of thread on the expansion screw; they bring about good adaptation to different screw diameters. The angled slits bring about reliable engagement of an expansion screw of small diameter without the expansion screw coming out of the plug tip when the expansion screw is tightened. At the same time, the angled slits avoid a large increase in torque when screwing in an expansion screw having a large screw diameter. 
     The legs of the angled slits whose pitch is in the opposite direction to the pitch of the thread on the expansion screw bring about axial expandability of the plug tip, as a result of which the axial spacing of angled slits provided in axial succession on the plug tip changes. By that means, adaptation to different pitches of thread on expansion screws is achieved. 
     In an embodiment of the invention, the plug has, within the sleeve-like plug tip, a screw channel for the expansion screw, which screw channel has a cross-section that is other than circular in shape. The screw channel within the plug tip therefore has different transverse dimensions in different directions. This measure also serves to adapt the plug to different diameters of expansion screw. In a development, the screw channel within the plug tip has a flat, for example slot-shaped, screw channel. The screw channel within the plug tip can also have the shape of two slots that cross one another. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained in greater detail hereinafter with reference to an exemplary embodiment illustrated in the drawing, in which: 
     FIG. 1 is a perspective view of a plug in accordance with the invention; 
     FIG. 2 is a side view of the plug in FIG. 1; 
     FIG. 3 is an axial section through the plug in FIG. 1; 
     FIG. 4 is an end-on view, from behind, of the plug in FIG. 1; 
     FIG. 5 is an end-on view, from the front, of the plug in FIG. 1; 
     FIGS. 6-9 are cross-sections along the lines VI-VI to IX-IX in FIG. 2; and 
     FIGS. 10 and 11 show two examples of use of the plug from FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The plug  10  according to the invention shown in FIGS. 1-3 is made from plastics material; it is shaped approximately like a sleeve. The plug  10  has a screw channel  12  (FIG. 3) for an expansion screw (not shown in FIGS.  1 - 3 ), which screw channel  12  passes through the plug  10  axially and has a conical taper at two locations. 
     In its rear region, the plug  10  has a sleeve-like plug end  14 ; in its forward region it has a sleeve-like plug tip  16 , the plug tip  16  being integrally connected to the plug end  14  by means of two expansion limbs  18  extending longitudinally and arranged opposite one another. The expansion limbs  18  define an expansion region  20  of the plug  10 , extending from the plug end  14  to the plug tip  16 . In a peripheral direction, the expansion limbs  18  are connected to one another by an expandable material  22 . The expandable material  22  consists of the same plastics material as the rest of the plug  10 ; the expandable material  22  is an integral constituent of the plug  10 . The expandable material  22  is formed as a thin skin  22 , which connects the expansion limbs  18  to one another in a peripheral direction (cf. the cross-sections of the expansion region  20  in FIGS.  7  and  8 ). The thin skin  22  has a corrugation in the peripheral direction. The thin skin  22  is expandable in the peripheral direction of the plug  10 , both as a result of its corrugation and as a result of its being thinly formed and the expandability of the plastics material; if subjected to excessive force, the thin skin  22  can tear. 
     The sleeve-like plug end  14  has a larger transverse dimension or diameter than the plug tip  16  and the plug  10  in the expansion region  20 , although that is hard to see in the drawing. Furthermore, the sleeve-like plug end  14  has a sawtooth-like contour, as can be seen in FIG.  6 . The plug end  14  has two radial surfaces  24  lying opposite one another and facing in the screwing direction of the expansion screw (not shown in FIGS.  1 - 3 ). Adjacent to the outer edges of the radial surfaces  24  are contour lines or contour surfaces  26 , which extend, contrary to the screwing direction of the expansion screw, helically inwards up to the radial surface  24  located opposite in each case. The radial surfaces  24  serve to secure the plug  10  against rotation in a drilled hole when the expansion screw is being screwed in. 
     Projecting out from the plug end  14 , between the said radial surfaces  24 , are anti-rotation ribs  28 , which extend in the longitudinal direction of the plug. The anti-rotation ribs  28  have a sawtooth-shaped cross-section; their surfaces facing in the screwing direction of the expansion screw also form radial surfaces  30  of the plug  10 . 
     The sleeve-like plug tip  16  is provided with angled slits  32 , the tips or corners  34  of which are directed forwards. The slits  32  are arranged on the plug tip  16  at two locations opposite one another and several (three) slits  32  are arranged on the plug tip  16  spaced axially apart from one another. The angled slits  32  each have legs  36 ,  38 , one leg  36  having a pitch in the same direction as the pitch of the thread of the expansion screw (not shown in FIGS. 1-3) and the other leg  38  having a pitch in the opposite direction. The pitch of the legs  36  does not need to be the same as the pitch of the thread on the expansion screw, it is merely oriented in the same direction. 
     In the region of the plug end  14 , the screw channel  12  has an approximately circular cross-section; in the expansion region  20  it narrows into two slots that cross one another (FIGS.  7  and  8 ); and in the plug tip  16  it is slot-shaped (FIG.  9 ). That enables the screw channel  12  to adapt well to expansion screws of different diameters. 
     The function of the plug  10  according to the invention will be described hereinbelow with reference to FIGS.  10  and  11 : FIG. 10 shows the fastening of an article  40  to a panel-form building material  42 . The plug  10  is inserted into a hole drilled in the panel-form building material  42 . Because of the relatively large transverse dimension of the plug end  14 , the plug end  14  widens the drilled hole and, in so doing, consolidates the building material surrounding the plug end  14 . At the same time, the plug end  14  digs into the building material  42  by means of its sawtooth-shaped contour (FIG.  6 ); the radial surfaces  24 ,  30  form abutment surfaces preventing the plug  10  from rotating together with an expansion screw  44  when the latter is being screwed in. 
     After the plug  10  has been inserted, the article  40  to be fastened, provided with a drilled hole, is held up to the panel-form building material  42 , and the expansion screw  44  is pushed through the article  40  and screwed into the plug  10 . In the process, a screw thread  46  on the expansion screw  44  cuts into the plug tip  16  and the screw thread  46  comes into engagement with the legs  36  of the angled slits  32  having a pitch in the same direction as the screw thread  46  on the expansion screw  44 . The legs  38  of the angled slits  32  having a pitch in the opposite direction enable axial expansion of the plug tip  16  so that the axial spacing between the slits  32  adapts to the thread pitch of the screw thread  46 . In conjunction with the flat, slot-shaped screw channel  12  in the plug tip  16 , the angled slits  32  bring about good adaptation of the plug tip  16  to the diameter of expansion screw used in a particular case and to the pitch of its screw thread  46 . 
     When it is screwed in and tightened, the expansion screw  44  pulls the plug tip  16  towards the plug end  14 ; the spacing between the plug tip  16  and the plug end  14  is reduced. In the process, the expansion limbs  18  wind around one another in knot-like manner so that the expansion limbs  18  of the plug  10  grip behind the panel-form building material  42  in positive manner, which results in good anchoring of the plug  10  even in a panel-form building material  42  of low strength, for example plasterboard. The skins  22  (FIGS. 1,  2 ,  7 ,  8 ) connecting the expansion limbs  18  to one another in a peripheral direction bring about high torsional rigidity of the plug  10 . The skins  22  counteract twisting of the plug tip  16  relative to the plug end  14  when the expansion screw  44  is being screwed in and tightened, and, as a result, they especially prevent extensive backwards rotation of the plug tip  16  on having to release a screwdriver for the purpose of changing grip when the expansion screw  44  is being screwed in by hand. Furthermore, the skins  22  avoid a pronounced drop in the screwing torque of the expansion screw  44  once the expansion limbs  18  have begun to wind around one another. Such a drop in torque would give the false impression that the expansion screw  44  had come out of the plug  10  or the plug  10  had come out of the building material  42  and was only poorly anchored. 
     FIG. 11 shows the anchoring of an article  40  to a solid building material  48 , for example concrete. In this case, the expansion plug  10  is inserted in a hole  50  drilled in the solid building material in a manner known per se, the article  40  is positioned and the expansion screw  44  is pushed through the article  40  and screwed into the plug  10 . The expansion screw  44  pushes the expansion limbs  18  apart and, as a result, anchors the expansion plug  10  in the drilled hole  50 . The pushing apart, that is to say expansion, of the expansion limbs  18  is not impeded by the thin skins  22  connecting the expansion limbs  18  in a peripheral direction because the skins  22  are thin and have a corrugation and are therefore expandable in a peripheral direction. The thin skins  22 , which connect the expansion limbs  18  in the expansion region  20  to form a kind of sleeve, prevent the expansion screw  44  from being able to emerge through the side of the screw channel  12 , between the expansion limbs  18 , when it is being screwed in. Without the thin skins  22 , there is a risk of that happening especially when the expansion screw  44  is loaded in a transverse direction by the article  40 . The flat, slot-shaped screw channel  12  and the angled slits  32  also enable the expansion screw  44  to be screwed into a hard and unyielding solid building material  48 , for example concrete, using comparatively little torque.