Fastener with stepped head for composite decking

Abstract

A fastener with a head having a stepped configuration to assist in drawing down a composite material about a fastener to reduce flagging.

I claim:  
     
         1 . A fastener disposed about a longitudinal axis and having a head at an upper end, a tip at the other lower end and a shank extending from the head to the tip about the axis, 
 in cross-section normal to the axis at any respective position along the axis, the head being circular about the axis and of a respective radius,    the radius of the head reducing in a stepped manner towards the tip from an upper portion of the head having a largest radius to a lower portion of the head having a radius less than the largest radius but greater than a radius of the shank so as to present at least two downwardly directed annular shoulders spaced axially from each other,    the upper portion of the head presenting an uppermost downwardly directed annular shoulder merging at a radially inward extent into the lower portion of the head, and the lower portion of the head presenting a lower downwardly directed annular shoulder merging at its radially inward extent into the shank.    
     
     
         2 . A fastener disposed about a longitudinal axis and having a head at an upper end, a tip at the other lower end and a shank extending from the head to the tip about the axis, 
 in cross-section normal to the axis at any respective position along the axis, the head being circular about the axis and of a respective radius,    the respective radius of the head increasing in a stepped manner from where the head merges with the shank away from the tip so as to present on the head two downwardly directed annular shoulders which are spaced axially from each other by a radially outwardly directed side wall of the head.    
     
     
         3 . A fastener as claimed in  claim 2  in which the two annular shoulders comprise: 
 (a) a lowermost downwardly directed annular shoulder merging at its radially inward extent into the shank and merging at its radially outward extent with a lower edge of the side wall; and  
 (b) an upper downwardly directed annular shoulder merging at its radially inward extent into an upper edge of the side wall.  
 
     
     
         4 . A fastener disposed about a longitudinal axis and having a head at an upper end, a tip at the other lower end and a shank extending from the head to the tip about the axis, 
 in cross-section normal to the axis at any respective position along the axis, the head being circular about the axis and of a respective radius,    the respective radius of the head increasing in a stepped manner, from where the head merges with the shank, away from the tip so as to present on the head three downwardly directed annular shoulders which are spaced axially from each other by two radially outwardly directed side wall of the head.    
     
     
         5 . A fastener as claimed in  claim 4  in which the three annular shoulders comprise: 
 (a) a lowermost downwardly directed annular shoulder merging at its radially inward extent into the shank and merging at its radially outward extent with a lower edge of a lowermost radially outwardly directed side wall;  
 (b) an intermediate downwardly directed annular shoulder merging at its radially inward extent into an upper edge of the lowermost side wall and merging at its radially outward extent with a lower edge of a intermediate radially outwardly directed side wall; and  
 (c) an upper downwardly directed annular shoulder merging at its radially inward extent into an upper edge of the intermediate side wall and merging at its radially outward extent with a lower edge of an upper radially outwardly directed side wall.  
 
     
     
         6 . A fastener disposed about a longitudinal axis and having a head at an upper end, a tip at the other lower end and a shank extending from the head to the tip about the axis, 
 the head comprising a first disc portion and a second disc portion each disposed normal to the axis centered on the axis,    the first disc portion disposed below the second disc portion and joining the second disc portion to the shank,    the first disc portion extending radially beyond the shank to define a first shoulder surface directed axially toward the lower end about the shank,    the second disc portion extending radially beyond the first disc portion to define a second shoulder surface directed axially toward the lower end about the first disc.    
     
     
         7 . A fastener as claimed in  claim 6  wherein the first disc has a radially outwardly directed first side surface with an upper edge and a lower edge, the first side wall merging with the first shoulder surface at the lower edge of the first side wall, the first side wall merging with the second shoulder surface at the upper edge of the first side wall, 
 the second disc has a radially outwardly directed second side surface with an upper edge and a lower edge, the second side wall merging with the second shoulder surface at the lower edge of the second side wall.  
 
     
     
         8 . A fastener as claimed in  claim 7  wherein the first and second shoulder surfaces are directed towards the lower end to a greater extent than they are directed radially outwardly, and 
 the first and second side surfaces are directed radially outwardly to a greater extent than they are directed towards the lower end.  
 
     
     
         9 . A fastener as claimed in  claim 8  wherein the first and second shoulder surfaces are disposed at an angle to the axis of between 90 degrees and 60 degrees and the first and second side surfaces are disposed at an angle to the axis of between 0 degrees and 45 degrees.  
     
     
         10 . A fastener as claimed in  claim 8  wherein the ratio of axial extent of the first side surface as measured parallel the axis to the radial width of the first shoulder surface as measured along a radius from the axis is in the range of 1:1 to 4:1, and 
 the ratio of axial extent of the second side surface as measured parallel the axis to the radial width of the second shoulder surface as measured along a radius from the axis is in the range of 1:1 to 4:1.  
 
     
     
         11 . A fastener as claimed in  claim 8  wherein the ratio of the axial extent of the first side surface as measured parallel the axis and the axial extent of the second side surface as measured parallel the axis is in the range of 1:0.66 to 0.66:1.  
     
     
         12 . A fastener as claimed in  claim 9  wherein the ratio of the axial extent of the first side surface as measured parallel the axis and the axial extent of the second side surface as measured parallel the axis is in the range of 1:0.66 to 0.66:1.  
     
     
         13 . A fastener as claimed in  claim 8  wherein each of the first disc and second disc have an axial extent at least equal to ½ of an average radius of the shank over an upper portion of the shank proximate the head.  
     
     
         14 . A fastener as claimed in  claim 6 , 
 the head further comprising a third disc portion disposed normal to the axis centered on the axis,    the third disc portion disposed above the second disc portion,    the third disc portion extending radially beyond the second disc portion to define a third shoulder surface directed axially toward the lower end about the second disc.    
     
     
         15 . A fastener as claimed in  claim 6  wherein the fastener comprises a screw and threads are provided on the shank at least over a lower portion of the shank proximate the tip.  
     
     
         16 . A fastener as claimed in  claim 7  wherein the fastener comprises a screw and threads are provided on the shank at least over a lower portion of the shank proximate the tip.  
     
     
         17 . A fastener as claimed in  claim 8  wherein the fastener comprises a screw and threads are provided on the shank at least over a lower portion of the shank proximate the tip.  
     
     
         18 . A fastener as claimed in  claim 11  wherein the fastener comprises a screw and threads are provided on the shank at least over a lower portion of the shank proximate the tip.  
     
     
         19 . A fastener as claimed in  claim 6  wherein in cross-section through the head normal to the axis at any respective position along the axis, the head being circular about the axis and of a respective radius.  
     
     
         20 . A fastener as claimed in  claim 6  wherein each disc is substantially cylindrical and disposed coaxially about the axis, the respective radius of the first disc being greater than a radius of the shank and the respective radius of the second disc being greater than the radius of the first disc.  
     
     
         21 . Use of a fastener as claimed in  claim 1  to secure a composite wood member to an underlying substrate by driving the fastener from an upper surface of the member to have the tip and a forward portion of the shank of the fastener engage in the substrate, with the head of the fastener to be driven approximately flush with the upper surface of the member.  
     
     
         22 . Use as claimed in  claim 21  wherein the composite wood member is plastically deformable and comprises a mixture of plastic and/or polymer resins and wood fiber.