Patent Publication Number: US-RE42207-E

Title: Masonry anchor device

Description:
BACKGROUND OF THE INVENTION 
     This invention is generally directed to a novel anchor device or fastening member which is particularly suited for use in the attachment of various fixtures and equipment to masonry, concrete, and other hard and/or friable substrates. 
     The prior art in one-piece, masonry tapping fasteners have uniform thread forms throughout the entire length of the fastener. They are typically heat treated to a case hardened metallurgical structure. These masonry tapping fasteners have failed for a variety of reasons, such as stripping out during the installation process, brittle failure while resisting the applied loads, and premature failure due to embrittlement and stress corrosion. As a result, users of these fasteners have been required to use other styles of fasteners that have exhibited better load versus displacement characteristics than that of a masonry tapping fasteners. These fasteners also back out of the substrate with relative ease in applications involving dynamic loads and system vibrations. 
     The present invention provides an anchor device or fastening member which overcomes the problems presented in the prior art and which provides additional advantages over the prior art, such advantages will become clear upon a reading of the attached specification in combination with a study of the drawings. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     A general object of the present invention is to provide a novel fastening member which is particularly suited for use in the attachment of various fixtures and equipment to masonry, concrete, and other hard and/or friable substrates. 
     An object of the present invention is to provide a fastening member which produces a higher torque differential between the tapping torque of the thread and the strip-out torque of the fastening member, thereby resulting in a fastening member that has more inherent reliability, and the capability of being used in a wider variety of substrates versus the prior art. 
     Another object of the present invention is to provide a fastening member which has less overall axial movement per unit load, while resisting withdrawal forces. 
     Yet another object of the present invention to provide a fastening member which imparts higher radial loads on the substrate which results in large spall cones and generally higher pullout values in masonry. 
     A further object of the present invention is to provide a fastening member which provides a more uniform stress distribution at the surface and the upper regions of the substrate. 
     Yet a further object of the present invention is to provide a fastening member which has a higher resistance to dynamic loads, and system impacts and vibrations. 
     An even further object of the present invention is to provide a fastening member which provides an overall more ductile anchorage. 
     Briefly, and in accordance with the foregoing, the present invention discloses a fastening member which is particularly suited for use in the attachment of various fixtures and equipment to masonry, concrete, and other hard and/or friable substrates. The fastening member includes a head and a shank which depends therefrom. The shank has a first threaded portion having a predetermined thread angle and a predetermined hardness, and a second threaded portion having a predetermined thread angle and a predetermined hardness. The first threaded portion is proximate to the head and the second threaded portion extends from the first threaded portion. The thread angle of the first threaded portion is different than the thread angle of the second threaded portion. In addition, the hardness of the first threaded portion is softer than the hardness of the second threaded portion. This provides for a more ductile anchorage when the fastening member is engaged with the substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The organization and manner of the structure and operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, wherein like reference numerals identify like elements in which: 
         FIG. 1  is a side elevational view of a fastening member which incorporates the features of the invention; 
         FIG. 2  is a partial, enlarged side elevational view of the fastening member of  FIG. 1 ; and 
         FIG. 3  is a cross-sectional view of the fastening member along line  3 — 3  of FIG.  1 . 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
     While the invention may be susceptible to embodiment in different forms, there is shown in the drawings, and herein will be described in detail, a specific embodiment with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as illustrated and described herein. 
     The present invention provides a novel anchor device or fastening member  20  which is particularly suited for use in the attachment of various fixtures and equipment to masonry, concrete, and other hard and/or friable substrates (not shown). The fastening member  20  may be a screw. 
     The fastening member  20  includes a head  22  which has a shank  24  depending therefrom. The head  22  may take a variety of forms and is dependant on the application. As shown in  FIG. 1 , the shank  24  includes an unthreaded portion  26  which extends from the head  22 , a first threaded portion  28  which extends from the unthreaded portion  26 , a second threaded portion  30  which extends from the first threaded portion  28 , and a centering point  32  which extends from the second threaded portion  30 . The head  22 , the unthreaded portion  26  and the first threaded portion  28  form a first zone  34  of the fastening member  20 . The second threaded portion  30  and the centering point  32  form a second zone  36  of the fastening member  20 . 
     The threads  40  of the first threaded portion  28  and the threads  42  of the second threaded portion  30  are helical and have a substantially constant major diameter, minor diameter and pitch. As shown in  FIG. 2 , the threads  42  of the second threaded portion  30  have a smaller crest width than the threads  40  of the first threaded portion  28 . As shown, the threads  42  of the second threaded portion  30  have a crest width of approximately two-thirds of the crest width of the threads  40  of the first threaded portion  28 . The threads  42  of the second threaded portion  30  have a smaller volume than the threads  40  of the first threaded portion  28 . 
     Each thread  40  of the first threaded portion  28  has a predetermined thread angle  44 , and each thread  42  of the second threaded portion  30  has a predetermined thread angle  46  which is different than the thread angle  44  of the threads  40  of the first threaded portion  28 . The thread angle  44  of the threads  40  of the first threaded portion  28  is three to seven degrees less than the thread angle  46  of the threads  42  of the second threaded portion  30 . The preferred difference is five degrees. The type of material used for the substrate dictate what thread angle is used. 
     As shown in the drawings, the threads  42  of the second threaded portion  30  are at a relatively sharp thread angle  46 , indicated at forty-five degrees, and the threads  40  of the first threaded portion  28  are at forty degrees thread angle  44 . It is to be understood, however, that other thread angles  44 ,  46  can be used. For example, a fifteen degree thread angle  46  can be used in the second threaded portion  30  and a ten degree thread angle  44  can be used in the first threaded portion  28 ; a thirty-seven degree thread angle  46  can be used in the second threaded portion  30  and a thirty degree thread angle  44  can be used in the first threaded portion  28 ; a sixty-five degree thread angle  46  can be used in the second threaded portion  30  and a sixty-two degree thread angle  44  can be used in the first threaded portion  28 , and the like. The thread angles  44 ,  46  in the first and second threaded portions  28 ,  30  is adjusted based upon the type of substrate with which the fastening member  20  is being engaged. 
     In addition, the head  22 , the unthreaded portion  26  and the first threaded portion  28  which form the first zone  34  of the fastening member  20  have a predetermined hardness as measured on the Rockwell “C” scale, and the second threaded portion  30  and the centering point  32  which form the second zone  36  of the fastening member  20  have a predetermined hardness as measured on the Rockwell “C” scale which is different than the hardness of the first zone  34 . In particular, the threads  40  of the first threaded portion  28  have a hardness as measured on the Rockwell “C” scale which is different than the hardness as measured on the Rockwell “C” scale of the threads  42  of the second threaded portion  30 . The hardness as measured on the Rockwell “C” scale of the components of the first zone  34  is softer than the hardness as measured on the Rockwell “C” scale of the components of the second zone  36 . The components of the second zone  36  are selectively heat treated to provide the higher hardness level than the components of the first zone  34 . The arrangement increases the holding strength when the fastening member  20  is engaged with the substrate. The components in the first zone  34 , and in particular the threads  40  of the first threaded portion  28 , are approximately twenty points softer as measured on the Rockwell “C” scale than the components of the second zone  36 , and in particular the threads  42  in second threaded portion  30 . For example, the components in the first zone  34 , and in particular the threads  40  of the first threaded portion  28 , can have a hardness of twenty-five as measured on the Rockwell “C” scale, while components of the second zone  36 , and in particular the threads  42  in second threaded portion  30 , have a hardness of forty-five as measured on the Rockwell “C” scale. For masonry and other like substrates, it is required that the threads  42  of the second threaded portion  30  maintain at least a hardness of forty-five as measured on the Rockwell “C” scale. For other softer, yet friable substrates, this minimum hardness may not be required, and the minimum hardness differential may be different than forty-five as measured on the Rockwell “C” scale. 
     As such, the threads  42  of the second threaded portion  30  are harder and much sharper than the threads  40  of the first threaded portion  28 . Therefore, the threads  42  of the second threaded portion  30  will cut into the substrate, such as concrete which is brittle, and form a female thread form. Once the threads  40  of the first threaded portion  28  are engaged with the thread form as cut with the threads  42  of the second threaded portion  30 , because the threads  40  of the first threaded portion  28  are softer than the threads  42  of the second threaded portion  30 , the threads  40  of the first threaded portion  28  compress against the substrate and the threads of the first threaded portion  28  are compressed by the walls of the female thread form. The threads  40  of the first threaded portion  28  deform the substrate between the threads of the substrate thus, providing higher installation torque which provides a tactile feel during installation, and less tendency to fracture the substrate. In testing of this fastening member  20  versus the prior art, a twenty-one percent increase in the pullout force from a concrete test block was found. 
     Because the threads  40  of the first threaded portion  28  are heat treated to provide a more ductile, more malleable thread then the threads  42  of the second threaded portion  30 , and because the geometry (that is, wider crest width and higher volume thread) of the threads  40  of the first threaded portion  28  provide a thread form that conforms more closely with the thread form that is tapped in the substrate by the threads  42  of the second threaded portion  30 , the threads  40  of the first threaded portion  28  provide a more uniform stress distribution at the surface and the upper regions of the substrate and provide increased resistance to axial movement during withdrawal loads. This results because of the more intimate fit between the fastening member  20  and the tapped thread form in the substrate throughout the entire length of the fastening member  20 . 
     Because of the friable nature of tapped threads in masonry, and because of the relatively high speed tapping that is typically employed in the installation of the fastening member  20 , it has been observed that the resultant threads tapped into the masonry substrate are not of a true or perfect form, especially near the surface and upper area of the anchorage, where the tapping threads make multiple rotations. These multiple rotations break down the initial thread form produced by the sharper crested, lower volume, harder threads  42  provided in the second threaded portion  30  of the fastening member  20 . Upon tapping the substrate, the tapped threads in an upper zone thereof spall and crush, and the resulting tapped thread is rough and less defined. The wider crested, higher volume, more malleable threads  40  provided in the first threaded portion  28  of the fastening member  20 , tend to fill and conform to these more erratically shaped tapped threads found in the upper zone of the substrate. 
     By contrast, the bottommost thread in the tapped masonry is made in the last revolution of the fastening member  20  and is therefore inherently more defined, and more representative of the thread of the fastening member  20  in that zone. The fastening member  20  of the present invention produces an anchorage in masonry substrates and friable substrates that maintains a tighter, more intimate fit throughout the entire length of the threaded portion  28 ,  30  of the fastening member  20  than the prior art fastening members. This tighter, more intimate fit throughout the entire length of the threaded portion  28 ,  30  of the fastening member  20  improves a variety of performance characteristics over the prior art. This fastening member  20  produces a higher torque differential between the tapping torque of the thread  40 ,  42  and the strip-out torque of the fastening member  20 , thereby resulting in a fastening member  20  that has more inherent reliability, and the capability of being used in a wider variety of substrates versus the prior art. This is especially important in those substrates that are both friable and soft, as in lightweight concrete and light weight masonry units, as well as those substrates that utilize very soft aggregates where fastening member strip-out is frequently encountered. The fastening member  20  has less overall axial movement per unit load, while resisting withdrawal forces. The fastening member  20  resists backing out, when subjected to dynamic loads, and system impacts and vibrations. 
     The dual zone heat treatment provides for an overall more ductile anchorage. The threads  40  of the first threaded portion  28  typically endure more abuse during the installation process, and more stress and movement once installed, but because the threads  40  of the first threaded portion  28  are more ductile, the fastening member  20  bears these more handily than the prior art. In addition, ductility is a requirement of structural fastenings, and in applications that tend to embrittle the fastening member and/or applications where stress corrosion cracking is of concern. 
     The larger thread angle  46  of the threads  42  of the second threaded portion  30 , i.e. larger than the thread angle  44  of the threads  40  of the first threaded portion  28 , produces higher radial loads in the substrate than the threads  40  of the first threaded portion  28 . The increased radial load manifests itself as higher compressive forces imparted into the substrate during the act of withdrawing the fastening member  20 . Higher compressive forces generated in the second threaded portion  30  of the fastening member  20  in masonry has shown to produce large spall cones and higher withdrawal resistance. A five degree differential in the thread angle  44 ,  46  has been calculated to impart a fourteen percent increase in radial loading. The fastening member  20  biases the higher radial loads in the second threaded portion  30  of the fastening member  20 , and lesser radial loads in the upper zones of the substrate, where in many cases, the surface of the substrate is unsupported and prone to premature spalling. 
     A plurality of notches  48  are provided in the threads  42  of the second threaded portion  30 . As shown, three equidistantly spaced notches  48  are provided in each thread  42  of the second threaded portion  30 . As shown in  FIG. 3 , each notch  48  is “V” shaped, however it is to be understood that other shapes, such as a “U” shape can be used. In addition, while three equidistantly spaced notches  48  are shown, it is to be understood that more or less than three notches can be provided and the notches do not need to be equidistantly spaced. The shape, amount and spacing of the notches  48  is dependant upon the type of substrate used. The notches  48  are used to cut the friable substrate during tapping of the female thread in the substrate. 
     While the transition of the thread angle  44 ,  46  from the threads  42  in the second threaded portion  30  to the threads  40  in the first threaded portion  28  is shown as an abrupt change, it is to be understood that this change can be formed by blending the thread angle down along a plurality of the threads  40  in the first threaded portion  28 . 
     While the unthreaded portion  26  is shown in the drawings, it is to be understood that the unthreaded portion  26  can be eliminated and instead, the first threaded portion  28  can extend to the head  22  of the fastener member  20 . 
     While a preferred embodiment of the present invention is shown and described, it is envisioned that those skilled in the art may devise various modifications of the present invention without departing from the spirit and scope of the appended claims.