CA1039987A

CA1039987A - Composite fastener

Info

Publication number: CA1039987A
Application number: CA252,052A
Authority: CA
Inventors: Charles J. Decaro; Samuel B. Davis (Jr.)
Original assignee: Textron Inc
Current assignee: Textron Inc
Priority date: 1975-05-08
Filing date: 1976-05-07
Publication date: 1978-10-10
Also published as: ZA762749B; AU1369776A; GB1497239A; FR2310491A1; SE7605087L; BR7602931A; AU501560B2; FR2310491B1; CH601683A5; DE2620272A1

Abstract

ABSTRACT
The composite fastener comprises a metal screw and a plastic head. The metal screw includes a threaded shank, a tool engage-able metal head, a scalloped washer adjacent the metal head and a shoulder connecting the washer to the threaded shank. The plastic head encapsulates the metal head and washer and includes a tool engageable portion and a washer portion extending around and in between the scallops and terminat-ing at the shoulder. The tool engageable plastic portion preferably has a cylindrical central section encapsulating the metal head and at least two ribs extending radially outward from the cylindrical section along the washer portion, the ribs forming the tool engageable portion. The ribs may be tapered in either or both of two directions and/or may be structured to shear off at predetermined torques.

Description

FIELD OF THE INVENTION
This invention relates to a composite fastener and, more particularly, to a metal screw in which the metal head and washer are .
encapsulated by a plastic head. ~ `
DE~CRIPTION OF THE PRIOR ART
A number of fasteners having integral plastic fastener heads have been developed for utilization with metal siding, much of which is `
prefinished so that the exposed fastener head must color coordinate with `
the siding. The plastic head furnishes this aesthetic requirement and ~
provides corrosion resistance at the same time. The major drawback ~i ~ ` `-of the presently employed, integral plastic fastener head is that they do ;~ ~ ;
not withstand sufficient torquing and as a result, the plastic heads fre~
quently fail as the power fastener tool either loosens the plastic portion of the head or defaces it, primarily by rounding the corners, in the pro-cess of setting the fastener. Many of these fasteners also require a sealing wa9her and, therefore, the plastic which form9 the head must also form the seal or washer portion of the fastener. Heretofore, the attempts to increase the torque resistance of the plastic headed fastener have been directed to the increased keying of the plastic to the metal head of the fastener which becomes encapsulated by the plastic through molding ,; ;;
techniques . `
As a precaution to rounded off plastic corners, the metal head must be engageable by a tool so that the plastic can be stripped off and the fastener removed by engaging the metal head. The result has been a variety of complex metal head designs which, on the one hand, ~ `
key the encapsulated plastic in place to meet certain torque requirements ; ;
and, on the other hand, provide a tool engageable head in the event the ;~
plastic head is rendered unturnable during setting. Of course, the rounded ~ 2--~.~3~ 7 corners further detract from the aesthetic value of the fastener.
It is further the objective of the builder of metal buildings to minimize the visual appearance of these fasteners so that the continuity of the metal siding and not the siding connections creates the visual impression.
In this regard, large metal heads which provide greater surface area and more means for keying the plastic become self-defeating since the ultimate plastic head becomes enlarged thereby highlighting rather than minimizing the presence of ~he fastener.
We have eliminated the concentration of forces at the plastic corners by eliminating such corners andJ in a preferred embodiment of the ` -invention, utilizing ribs as the tool engaging portion of the plastic heads.
We have also found that it is more important to key the plastic portion to the metal washer or flange rather than the head since when the fastener bottoms out against the workpiece, the forces are transferred to the washer from the head. We have further determined that we can minimize the forces on the plastic washer portion by utilizing a metal shoulder below the metal washer which engages the workpiece after the plastic washer portion is com-pressed. This metal shoulder further minimizes or eliminates the bending moment caused by a fastener installed nonperpendicular to the workpiece. And our composite fastener can be structured so as to provide a tamperproof ~ -fastener in the installed condition.
According to a broad aspect of the present invention, there is -provided a composite fastener comprising a metal screw and a plastic head, ;~
said metal screw including a threaded shank, a tool engageable metal head, a scalloped washer adjacent the metal head and a shoulder adjacent the scalloped washer and joining it to the threaded shank, said plastic head en-capsulating said metal head and washer and including a tool engageable por-tion and a washer portion extending around and between said scallops and terminating at said shoulder.
In the preferred embodiment, the plastic tool engageable portion includes a central section encapsulating the metal head and at least two ribs B ~

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extending radially outward from the central section and extending along the washer portion, said ribs forming the tool engageable portion.
The ribs may be structured to shear off at a predetermined torque leaving the central portion only in the driven condition. ' The invention will now be described in greater detail with reference to the accompanying drawings, in which~
Fig. 1 is an elevation of our composite fastener;
Fig. 2 is a plan view of the fastener of Fig. l;
Fig. 3 is an elevation of a modified form of our fastener;
Fig. 4 is a plan view of the fastener of Fig. 3; `
Fig. 5 is an elevation of a further modified form of our fastener;
Fig. 6 is a plan view of the fastener of Fig. 5; `
Fig. 7 is an elevation of another modified form of our fastener;
Fig. 8 is an elevation of the metal screw blank of our composite fastener;
Fig. 9 is a plan view of the metal screw blank;
Fig. 10 is a bottom view of the metal screw blank; ~
Fig. 11 is a section through our composite fastener in an installed `~
condition;
Fig. 12 is a section taken along section lines XII-XII of Fig. 2; ' Fig. 13 is a section taken along lines XIII-XIII of Fig. 12;
Fig. 14 is a section taken along lines XIV-XIV of Fig. 13; ~.
Fig. 15 is an elevation of still a fur~her modified form of our ,, fastener; ~, Fig. 16 is a plan view of the fastener of Fig. 15; ;
Fig. 17 is an elevation of the fastener of Fig. 15 in the installed condition; and ,~"
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Fig. 18 is a plan view of the installed fastener of Fig. 17. -Our composite fastener, generally designated 10, comprises a metal fastener such as screw 11 and a plastic head 12, Figs. 1 and 2.
The plastic head 12 is normally bonded to the metal 11 by extrusion mold-ing techniques well known to those skilled in the art. ``
The metal screw 11, shown in blank form prior to thread rolling and final point formation, includes a metal head 13 having six ~`
faces 14 intersecting in end to end relationship to form a hex head for `
engagement by a standard wrenching tool, Figs. 8-10. The head 13 may .
also be recessed or slotted to form the engaging surfaces for a driving `~ -tool; the primary consideration on this feature being the ability to remove . ~ , .
the fastener from the installed condition by str;pping the plastic and engag-ing the metal head. The screw 11 also includes a shank 15 terminating in an entry end 16. After thread rolling, the shank 15 includes threads 17.
The entry end 16 is formed as a standard entry point 18, Fig. 1, or can include a cutting groove 20 so as to define a self-drilling and tapping screw, Fig. 3.
Joining the metal head 13 and the shank 15 is a metal washer 19 and a :houlder 22 positioned below the washer 19 and adjacent the shank Z0 15, Figs. 8-10. The ~letal washer 19 is made up of a series of fin-like surfaces, each in the form of a scallop 21. Each scallop 21 extends out~
wardly from a face 14 of the metal head 13. ~djacent scallops 21 come .
together substantially adjacent the metal head 13 so as to form spaces 23 `-between the scallops, Fig. 9. These scallops are also tapered outwardly ~-from each face 14 so that the largest cross section is adjacent the metal head 13, Figs. 11 and 12. This taper places the maximum cross section at the point of the maximum bending moment on each scallop 21 as will be described hereinafter. The scallops 21 can actually be formed from the ~" ' . .

excess metal which is removed during the formation of each face 14.
Immediately below the metal washer 19 is the shoulder 22. / `- ~ -Shoulder 22 is larger in cross section than shank 15 onto which shoulder 22 connects. In the fully driven position the shoulder 22 engages the work-piece 28, Fig. 11. Therefore, shoulder 22 is also of sufficient diameter -and axial extent to eliminate or minimize any bending moment on the scallops 21 which could occur if the shoulder 22 were extremely small and the fastener 10 were installed in a slightly cocked position rather than perpendicular to the workpiece. ;~-The plastic head 12 totally encapsulates the metal head 13 and metal washer 19 and terminates adjacent the shoulder 22t Fig. 12.
The plastic head portion which surrounds the metal head 13 is a cylindrical `~
section 24, Figs. 2, 4, 6 and 13. The plastic head portion which encapsu~
lates the metal washer 19 forms a plastic washer 25 which extends com- `` "
plately aro~md and between the scallops 21 so as to completely fill the spaces 23 between the scallops 21, Figs. 12 and 14. In this manner, you have a continuous communication of plastic from the top of the metal washer 19 to the bottom of the metal washer 19. The plastic extends axially below ~ ~
but radially outward from the shoulder 22. The shoulder 22 acts as a stop ~ -`
fo~ the plastic which abuts the shoulder's radially outward periInetric sur- ~:
face. The plastic which extends axially below the shoulder 22 forms a seal ,~
with the workpiece 28, Fig. 11. , - ;
The fastener is driven by a tool which engages ribs 26 which extend radially outward from the cylindrical section 24 and along the top surface of plastic washer 25. In the present most preferred embodiment, -; `
there are three such ribs 26 equally spaced 120 apart extending outwardly ~ `
to the perimeter of the plastic washer 25, Fig. 2.
In order to further minimize the visual impression of the ;`

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fastener 10, the ribs can be tapered from the top of the cylindrical section 24 to the perimeter of the plastic washer 25. These tapered ribs 27 are illustrated in Figs. 3 and 4 where four such tapered ribs 27 are shown.
The ribs 26 or 27 may be push fit into the mating recess of a driving tool to facilitate installation. The ribs may also be tapered in a second direction as illustrated by ribs 36, Figs. 5 and 6. Ribs 36 are tapered so as to have a maximum cross section adjacent the washer 25. ` -Each rib 36 then tapers upwardly and inwardly from the washer 25 so that the rib walls lessen in cross section. Such a configuration also permits ' the plastic head 12 to be push fit into a driving tool. ~ ;
The push fit can also be accomplished by merely placing projections 37 along the ribs 27 to provide the frictional engagement with the driving tool. Such projections 27 can be utilized with any of the rib configurations previously discussed.
During setting, the composite fastener 10 is driven by a suit-able wrenching tool (not shown) which generally slips over the cylindrical section 24 and engages the driving side surfaces of the ribs 26. As the fastener is driven into the workpiece 28, the plastic washer 25 below the ~'!'"'` ~,' scallops 21 engages the workpiece 28 before shoulder 22. Thereafter, -plastic washer 25 is compressed between the workpiece 28 and the scallops 21 until the shoulder 22 bottoms out on the workpiece 28. Thereafter, the additional torque applied to the composite fastener 10 is primarily trans- ` -mitted to the shoulder 22 and not the plastic washer 25.
The effect of forming notches (corresponding to spaces 23 between scallops 19) along the metal washer on the torquing capability of integral plastic heads was determined. Specifically, metal inserts were tested with and without such notches by clamping the shank of the metal insert into a vise and applying torque to the plastic head of the fastener -7- ~`~

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with a torque wrench. The particular plastic employed was a 30% glass filled nylon base material. The composite fastener with the conventional ~ -metal washer with no notches or spaces fractured on an average of 55 in. ~;
lbs. of torque. The co}~lposite fasteners with the notched metal washer fractured on an average of 140 in. lbs. of torque. In addition to the dif-ference in torque capability, the mode of the fracture was different. The insert with the conventional flange failed when the plastic to metal bond - ~
failed, whereas the notched flange insert failed when the plastic material ; ;
: ... ~.:
fractured. -Our composite fastener 10 can also be designed so as to be ~-tamperproo~. We have illustrated such a design in Figs. 15-18 where plastic head 30 has a central, cylindrical portion 33 and a washer portion ~.
32 as in the earlier embodiments. The ribs 31p of which we have illustrated `~
two; extend outwardly from the cylindrical section 33 and along the washer `~
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32, also as in the earlier embodiments. However, the ribs 31 are struc- `~
tured so as to shear off at a predetermined torque. This can be accom- `
plished by controlling the material and the cross sectional dimension of the ribs 31 and/or by including intentional, weakened areas to initiate the shearing of the ribs 31. Such a fracture of ribs 31 leaves a slightly dis-20 rupted surface 35 along the cylindrical portion 33 and a similarly disrupted surface 34 along the washer portion 32, Figs. 17 and 18. To remove such a fastener requires removal of the plastic head material 30 to expose the !i ~ -tool engaging metal head of the screw 11.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composite fastener comprising a metal screw and a plastic head, said metal screw including a threaded shank, a tool engage-able metal head, a scalloped washer adjacent the metal head and a shoulder adjacent the scalloped washer and joining it to the threaded shank, said plastic head encapsulating said metal head and washer and including a tool engageable portion and a washer portion extending around and between said scallops and terminating at said shoulder.

2. The fastener of Claim 1 wherein said plastic tool engage-able portion includes a central section encapsulating the metal head and at least two ribs extending radially outward from the central section and extending along the washer portion, said ribs forming the tool engageable portion.

3. The fastener of Claim 2 wherein said central section is cylindrical and said ribs are of constant cross section and tapered out-wardly and downwardly from the cylindrical section.

4. The fastener of Claim 2 wherein said central section is cylindrical and said ribs are of a tapered cross section so that a maximum cross section is adjacent the washer portion.

5. The fastener of Claim 2 wherein the ribs include at least one small projection extending outwardly therefrom to form a push fit with a driving tool.

6. The fastener of Claim 2 wherein said ribs are structured to withstand a given torque and thereafter to shear off leaving a tamper-proof cylindrical central section.

7. The fastener of Claim 1 wherein the scallops are tapered outwardly so as to define a greatest cross section substantially adjacent the metal head.

8. The fastener of Claim 1 wherein the tool engageable head comprises six faces joined to form a hex head, each face having a scallop extending outward from a base thereof.

9. A tri-rib composite fastener comprising a metal screw and a plastic head, said metal screw comprising an entry end, a threaded shank joined thereto, six faces joined to form a hex head, a scalloped washer adjacent the hex head with a scallop extending outward from a base of each face and a shoulder joining the washer to the threaded shank, said plastic head encapsulating the metal head and washer and extending around and between said scallops but terminating at said shoulder and having a cylindrical central section over the metal head, a washer section over the metal washer and three equally spaced ribs extending radially outward from the cylindrical section and along the washer section.

10. A connection comprising a composite fastener installed in a workpiece, the composite fastener comprising a metal screw having an encapsulating plastic head, said metal screw including a threaded shank, a tool engageable metal head, a scalloped washer adjacent the metal head and a shoulder connecting the washer to the threaded shank, said plastic head encapsulating the metal head and the washer and extending around and between said scallops and terminating at said shoulder, said fastener having the plastic compressed between the scalloped washer and the workpiece and having the metal shoulder in direct contact with the work-piece.

11. The connection of Claim 10 wherein the plastic head has a cylindrical central section encapsulating the metal head and at least two ribs extending radially outward from the central section along the washer.

12. The connection of Claim 11 wherein the ribs are structured to withstand a given torque so that in a fully driven condition the ribs shear off.