Patent Publication Number: US-2003223842-A1

Title: Self-drilling screw for use in steel houses

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates to a self-drilling screw for use in steel houses, and more particularly relates to a self-drilling screw used to construct a steel frame employing C-beams, wherein these C-beams are zinc-plated steel plate articles having a relatively small thickness of about 1 mm and used in the so-called “two-by-four” system construction of houses.  
       PRIOR ART  
       [0002] Raw steel beams are combined with each other to form such a steel frame, generally using the so-called self-drilling screws. The shapes and dimensions of self-drilling screws are prescribed in the “KC Standards” (viz., standards established by the Japanese Official Society “Kozai Club”) in Japan.  
       [0003] Exemplified in FIG. 5 is a steel frame  1  constructed using a flathead bolt  2  qualifying as a screw defined in the KC Standards. A plasterboard  4  as a material for finishing the interior of a house may be attached to this frame  1 . A portion of this plasterboard will contact the head  2   a  of such a bolt  2 , and this head is prone to produce a protuberance in the surface of plasterboard  4 , thereby impairing appearance of the finished interior. In view of such an inconvenience, the KC Standards prescribe a self-drilling screw to have a flathead  2   a  as shown in the drawings. If this bolt  2  has a nominal diameter of 4.8 mm, then the thickness of its head has to fall within a range of 1.8 mm to 2.2 mm.  
       [0004] On the other hand, the item B1122 in the Japanese Industrial Standards (viz., “JIS”) relates to a usual self-tapping screw with a head having formed therein a cruciform recess. If its head is 2.15-2.4 mm thick, then nominal diameter for its threaded leg is 2.9 mm. In contrast, the bolt has such a thin flathead (1.8-2.2 mm thick) by the KC Standards, and nevertheless has to drive its thick threaded leg of a diameter of 4.8 mm. Such a nominal leg diameter 4.8 mm is much greater than 2.9 mm by the JIS, as compared with its head so thin as equal to or much smaller than 2.15-2.4 mm (for the JIS&#39;s ordinary self-tapping screws each with a cruciform recessed head).  
       [0005] Correspondingly, a recess  3  formed in such a thin head  2   a  for engagement with a driver bit must be so shallow that the bit will be worn out or damaged soon, failing to tightly fasten the screw. If a motor-driven high-speed wrench or the like rotating at a high speed of 2500 rpm or more is used, then a very troublesome “caming-out” of its driver bit will probably happen.  
       SUMMARY OF THE INVENTION  
       [0006] The present invention was made to resolve the drawbacks inherent in the prior art. Its object is therefore to provide a self-drilling screw adapted for use in steel houses, having such a head as withstanding a torque strong enough for it to reliably tighten the screw, and also protecting a driver bit from “caming-out” trouble, even if the head is made thinner than the conventional thickness as prescribed in the KC Standards.  
       [0007] In order to achieve this object, the present invention will provide a self-drilling screw whose leg with opposite end regions has a screw thread formed by the rolling method, one of the end regions being formed as a drilling portion, with the other end region continuing to a flathead through a neck disposed close to the flathead. A recess formed in the flathead for engagement with a wrenching bit of a screw driver has torque-receiving vanes that extend generally in parallel with an axis of the threaded leg. It is a characteristic structural feature that the neck is formed as a thickened portion of the leg so as to have a diameter larger than a diameter of valleys each present between adjacent crests of thread and smaller than an outer diameter thereof. It is a further characteristic structural feature that the thickened neck extends between a top of the flathead and inner ends of the torque-receiving vanes, with the recess having formed therein a conical bottom that is disposed in the leg&#39;s top region continuing to the thickened neck.  
       [0008] The flathead may have a thickness of about 1.0 mm. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009]FIG. 1 is a front elevation of a self-drilling screw provided in an embodiment of the present invention for use to construct steel houses;  
     [0010]FIG. 2 is a plan view of a head of the screw shown in FIG. 1;  
     [0011]FIG. 3 is a front elevation of a raw rod, viz., a screw blank, going to be processed to give the finished self-drilling screw of the invention;  
     [0012]FIG. 4 is a front elevation of the self-drilling screw shown in use; and  
     [0013]FIG. 5 is a front elevation of the prior art flathead self-drilling screw used in a steel house frame and shown partly in cross section. 
    
    
     THE PREFERRED EMBODIMENTS  
     [0014] Now some embodiments of the present invention will be described in detail, referring to the drawings.  
     [0015] A screw blank  10  comprises a raw leg  11  that has to be rolled to form thereon a screw thread  18 . One of opposite ends of the raw leg  11  continue to a thin flathead  12 , through a neck disposed adjacent to this head  12 . This neck is formed as a thickened portion  13  whose diameter is larger than the raw leg  11 , but smaller than the outer diameter of the screw thread  18 . On the other hand, a recess  14  for engagement with a rotary driver will be dug in the flathead  12 . Preferably, this recess  14  may be of a special and highly sophisticated shape in cross section, as if two equilateral triangles were superimposed with an angular shift of 60 degrees, wherein all the apices are rounded to be arcs as proposed by the present applicant in the Japan Patent Publication No. 7-37805. Thus, the recess  14  has six torque-receiving vanes  15  that extend generally in parallel with an axis of screw (so that peripheral portions of a driver bit will come into a surface contact with each vane, enabling transmission of a strong torque). Such a configuration of the recess in flathead is effective to diminish the possibility of an undesired ‘caming-out’ of the driver bit from said recess  14 , in spite of the strong torque imparted thereto. Further, the thickened portion  13  formed as a neck continuing to this flathead  12  will enhance its mechanical strength, whilst reducing its thickness to about 1.0 mm.  
     [0016] Alternatively, the recess may be a square hole of the IFI Standards, a “Torx hole” of the item No. 116-89 in the JASOF Standards, or any one else, each having longitudinal vanes efficiently receiving a strong torque.  
     [0017] The thickened neck  13  is of a length corresponding to the substantial depth of the recess  14 , thus reaching the inner ends  15   a  of torque-receiving vanes  15 . Consequently, the thickened neck  13  extending down from the flathead a distance to reach the inner end of recess  14 , so that this recess has a conical bottom  16  formed therein and disposed in the leg&#39;s  11  top region continuing to the thickened neck  13 .  
     [0018] As seen in FIG. 1, distal end portion of the leg  11  of screw blank  10  of the configuration described above will be pressed to give a drilling bit  17 , before said leg is rolled to produce on its periphery the screw thread  18  so as to finish the flathead self-drilling screw  20 . This screw thread  18  extends to a basal or upper end of leg  11 , but terminates short of the thickened neck  13 . There is no possibility that the thread rolling process would adversely cause the driver-engaging recess  14  to shrink. Thus, the thickened neck  13  need not be of an excessively large diameter but can be designed to fall within a certain range. This range is defined between a diameter larger than the diameter of leg  11  (viz., diameter of valley portions each present between adjacent crests of thread  18 ) and another diameter smaller than the outer diameter thereof. If the recess  14  is made shallow as in the illustrated case, then the thickened neck  13  may be rendered short considerably but enough to cover the inner ends  15   a  of torque-receiving vanes  15 .  
     [0019] In this case, when the self-drilling screw  20  is used to fasten metal panels  21  and  22  stacked one on another as shown in FIG. 4, the thickened neck  13  can easily be intruded into the upper panel  21 . Consequently, only the thin flathead  12  will be exposed to the exterior of said upper panel  21 , advantageously to the steel frames for building a steel house.  
     [0020] It will now be apparent that the self-drilling screw of the invention has beneath its head the thickened neck of such reduced diameter and height as easily intruding it into the panel being fastened, leaving only its flathead exposed to the outside. However, the driver bit-engaging recess formed in the head may be rendered deep enough to penetrate the thickened neck such that transmission of a strong torque would not give rise to the trouble of “caming-out” when this screw is tightened surely and firmly into thin plates constituting a steel frame. Further, the thickened neck of the screw&#39;s leg does improve the flathead in its strength to such a degree as reducing its thickness to about 1.0 mm, thus protecting plasterboards from swelling out to make ugly protuberances on the steel frame surface.