Abstract:
Disclosed is a fastener comprising a central elongate shank extending between first and second ends. The first end of the shank has a tapered point. The second end a head has an annular shoulder disposed towards the second end. The fastener further comprises an opposed pair of spines extending helically along the shank and a plurality of hooks extending from each of the pair of opposed spines. Also disclosed is a protrusion extending axially with the shank from the head deformable into an anti-friction washer upon impact by a fastener driver.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to fasteners in general and in particular to an improved fastener that is resistant to removal or pull-out. 
     2. Description of Related Art 
     Fasteners, such as nails, are well known for the purpose of securing articles of wood, plastic and the like together. Nails are elongate pin-shaped, sharp objects of hard metal or alloy having a sharpened end and a blunted or flared driving end. 
     Nails are typically driven into the work piece by a hammer, a pneumatic nail gun, or a small explosive charge or primer. A nail holds materials together by friction in an axial direction and shear strength laterally. Fasteners, such as nails, which are applied by an axial force are advantageously quick and easy to use. One limitation of nails, however is their reliance upon the friction between the nail on the wood surface to retain the nail in the material. Accordingly, nails may be prone to being axially displaced within the material which is also known as being pulled out. 
     Screws are also well known fasteners, however it is well known that screws are more difficult and time consuming to apply as they are required to be twisted or torque into the material. In particular, many screws are required to be axially rotated a plurality of times while being driven into the material. This is both time consuming and labor intensive. Screws also typically have a single helical thread extending therearound. 
     Other attempts to provide fasteners having improved pull out performance have provided circumferential rings or ridges around the shank of the nail or spiraled planar surfaces surrounding the shank of the nail, also referred to as screw-shank nails. Such attempts have similarly been limited in the resistance of the nail to pull out as the nail does not engage a surface area of the material into which it is applied that is a significantly larger than the circumference of the nail itself. 
     SUMMARY OF THE INVENTION 
     According to a first embodiment of the present invention there is disclosed a fastener comprising a central elongate shank extending between first and second ends. The first end of the shank has a tapered point. The second end has a head having an annular shoulder disposed towards the second end. The fastener further comprises an opposed pair of spines extending along the path of a double-alpha helix along the shank and a plurality of hooks extending from each of the pair of opposed spines. 
     The plurality of hooks may have sharpened tips oriented towards the second end of the shank. The spines and the hooks may be formed from a planar member defining a double-alpha helix plane around the shank. The plurality of hooks may be curved out of the double-alpha helix plane of the spines. The tips of the plurality of hooks may be disposed to opposed alternating sides of the spines. The plurality of hooks may have flexible tips. 
     The spines may extend radially from the shank. The spines may have a constant angle of inclination about the shank. The spines may include a directional self-tapping blade oriented at an angle corresponding to the angle of inclination about the shank proximate to the first end of the shank. The spines may extend 360 degrees around the shank between the first and second ends of the shank. The spines may extend less than 360 degrees around the shank between the first and second ends of the shank. 
     The fastener may further include a protrusion extending axially with the shank from the head. The protrusion may be frangibly connected to the head. The protrusion may be formed of a more ductile material than the head. The protrusion may be deformable into an anti-friction slip washer upon impact by a fastener driver. The washer may be separable from the head upon rotation of the shank and head. 
     Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In drawings which illustrate embodiments of the invention wherein similar characters of reference denote corresponding parts in each view, 
         FIG. 1  is a side elevational view of a fastener according to a first embodiment of the present invention. 
         FIG. 2  is a side elevational view of a fastener of  FIG. 1  embedded in several boards. 
         FIG. 3  is a front view of a blank for forming the fastener of  FIG. 1  at a first stage. 
         FIG. 4  is a front view of a blank for forming the fastener of  FIG. 1  at a second stage. 
         FIG. 5  is a front view of a blank for forming the fastener of  FIG. 1  at a third stage. 
         FIG. 6  is a side view of a blank for forming the fastener of  FIG. 1  at a third stage. 
         FIG. 7  is a perspective view of a portion of one of the spines having a plurality of hooks of the fastener of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a fastener according to a first embodiment of the invention is shown generally at  10 . The fastener  10  has an elongate central shaft or shank  12  extending between a first or sharpened end  14  and a second or driving end  16 . The fastener  10  includes first and second spines  18  and  20  extending therealong. The first and second spines  18  and  20  are located to opposed sides of the shank  12  and spiral around the shaft along a double-alpha helix path as will be more fully described below. The first and second spines  18  and  20  each include a plurality of protrusions or hooks  30  having pointed ends oriented towards the driving end  16  of the fastener. 
     The shank  12  may have a round cross section, as are common in the art although it will be appreciated that other cross-sections may also be useful, such as, by way of non-limiting example, oval, square or rectangular. In embodiments having a non-round cross section, the cross section shape may twist around the shank in correspondence with the first and second spines such that the location of the spine on the cross-sectional shape will remain constant along the length of the shank. Optionally, the cross section may remain at a constant radial orientation around the shank while the spines twist therearound along a double-alpha helix path. 
     The path of each spine has an angle of inclination, generally indicated at  23  relative to an axis  24  of the shank  12 . The angle of inclination  23  of the spines  18  and  20  is constant along the length of the shank. As illustrated, a path of each of the first and second spines  18  and  20  curves around the fastener by 360 degrees from the sharpened end  14  to the driving end  16  although it will be appreciated that the first and second spines  18  and  20  may twist about the shank  12  by other rotation angles as well. Preferably, the twist of the first and second spines  18  and  20  about the shank will be limited to 360 degrees such that the first or second spine  18  or  20  does not overlap upon itself. Accordingly, the angle of inclination  23  of the spines  18  and  20  will be selected so as to permit each of the spines to rotate around the shank by up to 360 degrees along a double-alpha helix path depending upon the length of the fastener  10 . As utilized herein, a double-alpha helix path is defined as the path of a pair of paths twisting about the central shank in a continuous right-hand spiral with a smooth constant angle on opposite sides of the shank. 
     Each spine  18  and  20  may also include a directional self-taping blade  40  comprising a planar member  42  extending radially from the shank  12 . The planar member  42  is oriented relative to the shank  12  at an angle corresponding to the angle of inclination  23  of the spines  18  and  20  so as to form a path in the material into which the fastener  10  is to be inserted for the first and second spines  18  and  20  to follow. Each directional self-taping blade  40  includes a leading edge  44  being angled away from the sharpened end  14  of the fastener. The leading edge  44  may optionally be sharpened so as to facilitate insertion of the fastener through the material. As illustrated in  FIGS. 4 ,  5  and  6 , the leading edge  44  may be formed between side blade surfaces  48 . The side blade surfaces  48  may be continuations with sharpened tip surface  49  as illustrated. The leading edge  44  may be angled by an angle relative to the axis  24  of the shank generally indicated at  46 . The leading edge angle  46  may correspond to the angle of the sharpened portion of the shank and be selected to facilitate ease of insertion of the fastener into a material as is commonly known. As described above, the directional self-taping blade  40  cuts a path into the material along a double-alpha helix path about a bore formed by the shank  12  for the first and second spines  18  and  20  to follow. 
     The driving end  16  includes a flattened head portion  17  and an annular shoulder  19  as are conventionally known. The fastener  10  may also include a protrusion or nipple  22  extending axially from the head portion  17 . The protrusion  22  may be of a softer material or have less material hardening treatment than the remainder of the fastener such that the protrusion  22  is operable to be sheared off of the head portion  17 . The protrusion  22  may also be attached to the head portion  17  by a frangible portion. Upon impact by a hammer or the like, the protrusion  22  will be flattened and sheared from the head portion  17  so as to form a slip washer  25  on the surface thereof as illustrated in  FIG. 2 . The slip washer  25  formed by the protrusion  22  will reduce the friction between the head portion  17  of the fastener  10  and a driving surface, such as a pneumatic nail gun, hammer, or the like it is driven into a material. It will therefore be seen that the slip washer will therefore reduce the torque imparted to the head portion  17  and will therefore be particularly useful for applications where the fastener  10  is inserted by the use of a nail gun and the like. It will be appreciated that for applications where the fastener  10  is to be driven by a hammer, that the slip washer may not be necessary due to the repeated impacts of the hammer on the head portion  17  of the fastener being for a shorter duration therefore less prone to friction or exertion of a torque on the head. 
     The fastener  10  may be formed of any known means such as machining, forging or casting. The fastener  10  may be formed of any suitable metal, such as, by way of non-limiting example, mild steel, iron, stainless steel, copper, titanium, or alloys. In particular, one method of forming the present fastener  10  may to be form, by pressing, stamping, extruding from a roll of wire or otherwise forming the shank  12  with opposed side plates  50  extending radially therefrom as illustrated in  FIG. 3 . Thereafter, excess material or notches  52  may be removed, by cutting, grinding, stamping, pressing or otherwise so as to form the hooks  30  in the side plates  50  as illustrated in  FIGS. 3 and 4 . The head portion  17  and protrusion  22  may then be formed in driving end  16  by a press or other means as illustrated in  FIG. 5 . Before, after or concurrently with forming the head portion and nipple, the fastener  10  may be twisted about the shank  12  so as to provide the required twist to the first and second spines  18  and  20 . The fastener  10  may also be formed with a twisting side plates  50  thereabout along a double-alpha helix path wherein the spines  18  and  20  and the hooks  30  are formed in the side plates along the double-alpha helix path. Optionally, the fastener  10  may be formed to have the side plates  50  and thereafter the side plates and fastener twisted to follow the double-alpha helix path before the spines and hooks are formed therein. 
     Turning now to  FIGS. 6 and 7 , the hooks  30  and spines are formed of a common side plate  50  as described above. The hooks may be formed to have a rearwardly inclined triangular shape having leading and trailing edges,  37  and  39 , respectively, and first and second distal pointed ends,  34  and  36 , respectively. The spines  18  and  20  and hooks  30  are aligned along and extend radially from the shaft along a longitudinal path  32 . The spines and hooks therefore define a plane  33  extending radially from the shank  12  along the path  32  as illustrated in  FIG. 7 . It will therefore be appreciated that the path of travel  32  and plane  33  follow a double-alpha helix path along the shank  12 . As illustrated in  FIG. 6  (showing the fastener  10  before a twist is applied to spiral the spines) the first pointed ends  34  of the hooks  30  may be displaced to a first side of the plane  33  while the second pointed ends  36  may be displaced to a second opposed side of the plane  33 . The first and second pointed ends  34  and  36  are alternated along the first and second spines  18  and  20 . Additionally,  FIG. 7  shows the alternating protrusion orientation in greater detail wherein the first and second pointed ends  34  and  36  are disposed to alternating sides of the plane  33 . The first and second ends may be arcuately curved out of the plane  33  such that the majority of the protrusions are aligned therewith. The offset to the hooks  30  may be formed during forming of the hooks  30  or at any other time. 
     The trailing edge  39  of the hooks  30  may be inclined from radial to the shank  12  in a direction towards the driving end  16  of the fastener. Once imbedded within a material, the rearwardly inclined hooks  30  will resist pull out of the fastener and the head portion  17  and will resist further insertion of the fastener thus securing the fastener therein. As illustrated in  FIG. 2  wherein the fastener  10  is embedded through first, second, third and fourth boards,  8   a ,  8   b ,  8   c  and  8   d , respectively, the hooks  30  will resist any pull out movement of the fastener as indicated generally at  64 . In any movement of the fastener in direction  64  relative to one of the boards  8   a ,  8   b ,  8   c  or  8   d  will cause the hooks  30  to engage with that board and draw the hooks out of the plane  33  in directions  60  and  62 . This will further serve to embed the fastener within the material as the fastener is attempted to be drawn backwards. Similarly, if any of the boards  8   b ,  8   c  or  8   d  are drawn downward in directions generally indicated at  66 , such as by prying between the boards, the hooks  30  will also be drawn out of plane  33  in directions  60  and  62  to further engage in that board. It will be seen that the first board  8   a  is maintained fixed with the fastener  10  by the head portion  17  which will bear upon the top surface of the first board. Therefore, any movement between the boards  8   a ,  8   b ,  8   c  and  8   d  will cause a corresponding movement between the fastener and at least one of those boards and will therefore further engage the hooks  30  in that board. 
     Thus it will be seen that any attempt to remove the fastener  10  from the boards or to pry the boards apart from each other will server to further engage the hooks  30  within the boards and more securely secure them to each other. Such a fastener may be useful for constructions in locations susceptible to natural disasters and may therefore be useful as a tornado, hurricane or earthquake fastener (T.H.E Fastener). 
     While specific embodiments of the invention have been described and illustrated, such embodiments should be considered illustrative of the invention only and not as limiting the invention as construed in accordance with the accompanying claims.