Patent Publication Number: US-4728238-A

Title: Plastic drive fastener

Description:
This is a continuation of application Ser. No. 159,899, filed June 16, 1980, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     Plastic drive fasteners of various configurations are found in the art classified within the U.S. Patent Office as classes 24/73 and 85/5; more particularly particular reference should be made to the patent to Edwin Grant Swick, U.S. Pat. No. 3,810,279 issued May 14, 1974 and assigned to the common assignee of the present invention. Such fasteners while suitable for many applications have a single inherent problem, namely, the insertion force for installing the fastener in an aperture or bore of a work piece is substantially equal to the force required for removal of the fastener from such an aperture or bore. In some applications it has been found desirable to provide a fastener which can be readily installed but which requires an excessive amount of force to remove same. 
     SUMMARY OF THE INVENTION 
     The present invention is an improvement over the teachings of U.S. Pat. No. 3,810,279 and provides a fastener in which there is provided a one piece member having a head and a shank, the shank including a generally non-circular cross-section which presents a plurality of generally flat axially extending surfaces. Each of the flat surfaces on the shank carry a plurality of axially spaced flexible resilient wing elements; the wings being flexed along their straight line connection with the flat surfaces. Certain wings located on at least one said surfaces being angled to tilt towards said head and being provided with means for substantially increasing the force required for removal of said fastener from an aperture or bore as compared to the force required to introduce said fastener into said aperture. 
     An object of the present invention is to provide a fastener of the type generally described immediately above. 
     Another object of the present invention is to provide a fastener having angled wing elements which are knuckled wherein each wing element is provided with an angularly disposed reinforcing portion on its upper surface which causes said wing elements to flex generally parallel to the flat surface but at a point radially removed therefrom. 
     A further object of the present invention is to provide an economical fastener which can be readily molded in a two-plate mold. 
     Still another object of the present invention is to provide a fastener capable of being utilized with multiplicity of head styles as well as a plurality of differing designs of entry or nose configurations. 
     Other objects will be apparent to those skilled in the art when the specification is read in conjunction with the following drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view of one embodiment of the present invention; 
     FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1; 
     FIG. 3 is an end view taken from the entering end of FIG. 2; 
     FIG. 4 is a fragmentary enlarged cross-sectional view of the improved wing portions of the present invention; 
     FIG. 5 is an elevational view of a prior art drive fastener; 
     FIG. 6 is a fragmentary view of a drive fastener having angled wing elements without the improvement of the present invention; 
     FIG. 7 is a fragmentary view of the present invention; 
     FIG. 8A is a schematic view of wing elements of the prior art; 
     FIG. 8B is an intermediate development of the type shown in FIG. 6; 
     FIG. 8C is a schematic view of the present invention. 
    
    
     DETAILED DESCRIPTION 
     A plastic drive fastener of the improved variety contemplated by the present invention is generally designated by the numeral 10 and includes a head (12) and a shank (14). While the present invention shows the head (12) as being a domed ceiling head, it should be recognized by those skilled in the art that this is merely one showing of a head form. Such a fastener, as contemplated by the present invention, can have a single head (12), as shown, or may include a multiplicity of axially spaced heads of the type normally used to fasten trim panels to automotive door interiors, not shown. 
     The importance of the present invention relates to a plastic drive fastener which can be readily installed into an apertured panel or a bore within a thick panel in which the removal force is far in excess of the force of installation. An embodiement of such a fastener is shown in FIGS. 1 through 4, 7 and 8C. The shank (14) of such a fastener is generally non-circular or polygonal in configuration and provides a plurality of axially extending flat surfaces (16) which in the present embodiement are four in number, however, it should be appreciated that any equal number of flat surfaces will suffice. Extending outwardly from the flat surfaces (16) are a plurality of axially spaced flexible resilient wing elements (18) which are provided with a generally tapered undersurface (20) and a radially extending upper surface (22), as best seen in FIG. 2. 
     Along at least one flat surface (18) are a plurality of certain resilient wing elements (30) which are angularly disposed relative to the axis of the shank (14) and tilt upwardly, as viewed in the drawing, toward the head (12). The initial development work of this fastener was to utilize a tilted wing, as seen in FIG. 6, which had substantially the same configuration as the flexible wing elements (18) that extend radially outwardly. As can be seen in FIG. 6 these elements generally designated (32) flexed along a straight line formed by their juncture with the flat surface (16). The insertion and removal forces of such items were slightly different. 
     Further development resulted in the present embodiement shown in FIGS. 1 through 4 and FIG. 7 wherein a knuckle portion (34) is added to each of the angled wing elements (30) this results in the certain wing elements (30) having a bend line (36), as best seen in FIG. 7, which is generally parallel to surface (16) but radially spaced outwardly therefrom in essence, this creates a short stubby wing element (30) that can be readily inserted into an aperture or bore but which resists with great tenacity the removal of the fastener from the aperture or bore. Tests were conducted on various configurations of wings and the results of such tests are shown in pounds of force required to push the fastener in and to pull the fastener out. The figures are displayed in reference to the wing configurations shown in FIGS. 8A, 8B and 8C, the latter being the embodiement of the present invention. These test results are as follows: 
     
         ______________________________________                                    
FIG. 8A      FIG. 8B       FIG. 8C                                        
IN     OUT       IN     OUT      IN   OUT                                 
______________________________________                                    
24     32        10     18.5     30   75                                  
21     23        11.5   14.5     35   75                                  
20     23        11     16.5     20   70                                  
19     22        10.5   13       25   80                                  
24     21        10.5   15       25   82.5                                
22     21        10     14.5     35   65                                  
22     23        10.5   12.5     25   87.5                                
22     20        10     12.5     20   75                                  
21     19        10     12       22.5 75                                  
20     18        10     12       27.5 72.5                                
AVERAGES                                                                  
21.5   22.2      10.4   14.1     23.8 75.8                                
REMOVAL/INSERTION RATIOS                                                  
1.0          1.4           3.2                                            
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     As will be noted there is a dramatic unexpected result in the device of the present invention as shown in FIG. 8C. 
     In the present disclosure the improved form of resilient wing (30) with its knuckle portion (34) is shown extending in opposite directions from two of the flat wall surfaces (16) of the shank (14) with the radially extending wing element (18) occupying the other two flat opposed surfaces. It will be recognized that the amount of force removal can be controlled for a fastener of this design dependent upon the number of surfaces provided with knuckled angled wing elements (30). Wing elements (30) extending from one or more of the surfaces is all that is required, however, all of the surfaces can utilize such a wing element. Where wing elements (30) or (18) are extending from only one or two surfaces, now shown, it has been found desirable to provide means, such as an axially extending centering rib, not shown, to locate the fastener for optimum operating conditions relative to the cooperating aperture or bore. 
     While the present shank (14) includes four flat surfaces (16) it should be appreciated that the wing element (18) and (30) can extend from and cover the entire width of the flat surface or alternatively the shank (14) can include, if desired, a plurality of axially extending recesses (40) which interrupt and space adjacent flat surfaces for purposes of accepting an axially extending tool. 
     The nose portion (44) in the present embodiement is shown as an arrow-shaped member but it will be appreciated that other configurations are equally usable. The shank (16) can be blunt at the end, rounded, arrow-shaped, or pointed as may be desired. 
     Other embodiements of the present invention will be apparent to those skilled in the art.