Abstract:
The expanding sleeve ( 1 ) of the anchor has an interior bore ( 13 ) and an expander plug ( 15 ) which are conical, with roughly the same cone angle, and designed so as, through the wedge effect caused by the plug ( 15 ) being driven into the sleeve ( 1 ) to cause it to expand. The sleeve ( 1 ) has, at its periphery, an annular weakening groove ( 9 ) intended, during expansion, to shorten its axial expansion length.

Description:
TECHNICAL FIELD 
     The invention relates to an anchor comprising an expanding sleeve and an expander plug; the sleeve comprises an expanding skirt with axial slots and, between the slots, expanding legs which between them form a conical axial bore which converges towards the free ends of the legs; the expander plug is also conical, with the same cone angle as the conical bore of the expanding skirt in which it is fitted; through a wedge effect, brought about by the expander plug being driven into the bore of the expanding skirt, the legs pivot and the skirt expands to anchor itself in the wall of the material which takes it. 
     BACKGROUND ART 
     Such anchors are well suited to materials of the concrete type. In the case of soft material, no problems arise. By contrast, in the case of hard material and because of the firmness of the legs and of the material, it is no longer possible for the plug to be driven far enough into the skirt and its expansion is not great enough to provide adequate anchorage. 
     SUMMARY OF THE INVENTION 
     The invention sets out to solve this problem. 
     To this end, the invention relates to an anchor for hard material having an expanding sleeve with an interior bore and an expander plug which are conical, with roughly the same cone angle, and designed so as, through the wedge effect caused by the plug being driven into the sleeve, to cause it to expand, the anchor being characterized in that it comprises means designed, during expansion, to shorten the axial expansion length of the expanding sleeve. 
     Thus, if the sleeve is functionally shortened, the plug can be driven in more fully and can correctly expand the functional axial portion of the sleeve engaged by the plug. 
     As a preference, the means of shortening the sleeve are designed to be able to drive the plug beyond the expansion end of the sleeve. 
     Advantageously, the shortening means are designed to shorten the expansion length of the sleeve by radially compressing an axial base portion of the sleeve. 
     In the preferred embodiment of the anchor of the invention, the shortening means comprise an annular weakening groove formed at the periphery of the sleeve, beyond which the axial base portion of the sleeve has an interior bore with a cone angle which is at least inflected with respect to that of the plug. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood from reading the following description of the preferred embodiment of the anchor, with reference to the appended drawing, in which: 
     FIG. 1 is a perspective view of the anchor during expansion; 
     FIG. 2 is a profile view of the anchor; 
     FIG. 3 is a view of the anchor in axial section; 
     FIG. 4 is a view of the anchor in axial section after anchorage in soft material, and 
     FIG. 5 is a view of the anchor in axial section after anchorage in hard material. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The anchor comprises an expanding sleeve  1 , of axis  20 , with an expanding skirt  2  extending a portion of the cylindrical body  3 , at the free end of which is formed a head flange  4  for fitting and holding the anchor in an accommodating hole in the support material. The skirt  2  has expanding legs  5  formed between slots  6  extending overall in axial planes of the sleeve. 
     The sleeve comprises an axial base portion  7  which is deformable in radial compression and which extends between the end  8  of the sleeve and an annular weakening groove  9  formed at the periphery of the sleeve. Upstream of the weakening groove  9  there extends, towards the body  3  of the sleeve, an axial gripping portion  10  with peripheral grooves or channels  11  to improve the anchorage of the sleeve in the support material. 
     Formed inside the sleeve is an interior bore with three portions in the continuation of one another. The bore portion  12  of the body portion  3  of the sleeve is cylindrical. The bore portion  13  of the expanding skirt  2 , upstream of the base portion  7  and downstream of the body portion  3 , which extends the cylindrical bore portion  12 , is conical, converging towards the base portion  7  and the end  8  of the sleeve. Finally, the bore portion  14  of the base portion  7 , which extends the conical bore portion  13 , is cylindrical. More generally, and for a reason which will become apparent later on, the cone angle of the bore of the base portion  7  is at least inflected with respect to that of the bore  13 . This cone angle may be smaller, zero (in which case the bore is then cylindrical), or even inverted, in which case the bore then diverges towards the end  8  of the sleeve. 
     The bore  12  of the body portion  3  comprises a tapping  19  extending from the flange  4  to slightly upstream of the regions  18  at which the legs  5  are articulated. 
     At rest, the anchor is externally cylindrical overall. The radial thickness of the expanding legs  5  increases slightly from their region  18  of articulation to the body portion  3  as far as the weakening groove  9 , that is to say over the axial expansion length of the sleeve. 
     The anchor also comprises an expander plug  15 , of conical shape, with roughly the same cone angle as the bore  13  of the expanding skirt  2 . It is slightly chamfered at the front end  16 . At the rear, there is a small strip  17  for retaining the plug. 
     Having described the anchor, let us now tackle its operation. 
     Having previously bored in material  21 , to which a part is to be fixed using the anchor, a hole  22  which is deeper than the axial length of the anchor and has a diameter very slightly greater than that of the cylindrical outer envelope of the anchor, the anchor is inserted into the hole  22  until the flange  4  rests against the surface  23  of the material. 
     Then, using an appropriate tool, the expander plug  15  which was inside the sleeve, retained by the small strip  17  slightly upstream of the articulation regions  18 , is hammered in. As the cone angle of the plug  15  and of the bore portion  13  inside the legs  5  is the same, the legs  5  pivot outwards by a wedge effect about their articulation regions  18 , the skirt  2  expands and becomes anchored in the material  21 . 
     In soft material (FIG.  4 ), the plug  15  can easily be driven in until its chamfer  16  reaches, for example, the end  8  of the base portion  7  of the sleeve, the legs  5 , because of their firmness and rigidity, being driven radially into the material  21  over a thickness which is perfectly adequate to provide satisfactory anchorage. 
     In hard material (FIG.  5 ), the firmness of the legs  5  would have prevented the plug  15  from being driven in and therefore the radial penetration of the expanding legs  5  into the material  21 ′ to a gradually increasing extent along the axis  20 . In any event, the base portions  7  of the legs  5  would have had to bite into the material  21 ′ to an excessive thickness for at least that part of the plug  15  adjacent to its retaining strip  17  to more or less reach the axial portions  24  of the expanding legs  5  which are adjacent to the groove  9  and for these portions  24  to be able themselves to bite into the material  21 ′ to an adequate depth to provide anchorage. 
     The weakening groove  9  will, at the time of driving of the plug  15 , allow the sleeve to be functionally shortened by the base portion  7 , extending beyond the groove  9 . The groove  9 , at the time of expansion, functionally, or virtually, shortens the axial expansion length of the sleeve which then extends only from its head flange  4  to the weakening groove  9 , which thus constitutes the expansion end of the sleeve. 
     When, inside the bore  13 , the plug reaches the position in which the base portions  7  of the legs  5  should be pushed out into the material  21 ′ by the plug, the material opposes this without in any way preventing the portions  24  adjacent to the groove  9 , upstream of the portions  7  in the direction in which the plug is being driven, from being pushed back themselves, because the portions  7  will be able to pivot inwards, about the region of this groove  9 , with respect to the portions  24 . The base portions  7  of the legs  5  thus undergo radial compression. Because of the inflection in the cone angle of the interior bore of the sleeve on each side of the plane of the groove  9  which, from conical ( 13 ), like the plug  15 , here becomes cylindrical ( 14 ), the front end  16  of the plug  15  will even be able to be driven in over a sufficient axial distance beyond the plane of the groove and here reach the front end  8  of the sleeve so as to ensure perfect engagement of the leg portions  24  by the plug  15  as in a soft material; the annular clearance  25  thus created around the plug  15  (FIG.  4 ), with a larger cone angle than the cylindrical bore  14  in which it is located, specifically allows the radial compression of the base portion  7  of the sleeve. 
     Having anchored the anchor, all that is required, in order to secure the part, is for a fixing screw or bolt to be screwed into the tapping  19 .