US3541918A

US3541918A - Self-locking fastener

Info

Publication number: US3541918A
Application number: US844959A
Authority: US
Inventors: Thomas B Johnson
Original assignee: THOMAS B JOHNSON
Current assignee: THOMAS B JOHNSON
Priority date: 1969-07-25
Filing date: 1969-07-25
Publication date: 1970-11-24
Anticipated expiration: 1987-11-24

Description

[7 2] lnventor Thomas B. Johnson Droz Ave., Ambridge, Pennsylvania 15003 [211 App]. No. 844,959 [22] Filed July 25, 1969 [45] Patented Nov. 24, 1970 [54] SELF-LOCKING FASTENER 4 Claims, 8 Drawing Figs.

[52] US. Cl 85/46, 151/22 [51] Int. Cl ..F16b 25/00, Fl6b 39/30 [50] Field of Search 85/46; 151122 [56] References Cited UNITED STATES PATENTS 984,969 1/1911 Reinigor 85/46 2,321,378 6/1943 Green 85/46 United States Patent 2,321,379 6/1943 Green 2,353,030 7/1944 Green ABSTRACT: A self-locking fastener is made from a selftapping screw and a resilient washer. The upper surface of each V-thread has a uniform pitch, and the lower edge of each thread root has the same pitch as its upper edge for most of its length but becomes less steep along the upper portion of the thread to thicken the root in that area. Each thread at its upper portion is widened downwardly from the outer edge of its upper surface to form a longitudinally tapered crest extending along the thread from its upper end. The upper end of each thread has a flat end face connecting the upper end of the tapered crest with the screw stem and the upper end of the thread also has a flat top extending away from the upper edge of its end face. The latter is inclined downwardly away from the adjoining flat top face.

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SELF-LOCKING FASTENER Self-tapping screws for fastening sheets of metal and the like together are well known. Their V-threads cut notches in the sheets, through which the threads travel. Ordinarily, it is a simple matter to unscrew the screws by simply reversing them, which means that they may work loose when they are supposed to remain tight. There are many places in which it is desirable to lock the screws so that they cannot work loose. For example, a screw should lock in place when used for the side laps and end laps of roofing and siding sheets for buildings, especially when the light gauges of metal are used where very little movement of the sheets due to vibration and other factors will cause ordinary sheet metal screws to work loose. Also, with building and siding sheets it is important that there be no leakage of water past the screws.

It has already been proposed that self-tapping screws be formed in such a manner that they cannot be unscrewed from the sheets or worked loose, by themselves, but such screws have not been used in locations where sealing of the screw holes is necessary. Furthermore, they are not practical because their construction is such that a different screw must be used for every thickness of sheet, and even where the sheets are supposed to be the same thickness there may be so much variation that some screws will be tight but others cannot be tightened.

It is among the objects of this invention to provide a selflocking fastener which can be used with sheets of considerable variation in thickness, which will securely lock itself in place, which cannot possibly work itself loose, and which will seal the opening through-which the fastener extends.

The preferred embodiment of the invention is illustrated in the accompanying drawings, in which;

FIG. 1 is a side view, partly broken away; FIG. 2 is a cross section taken on the line II-II II-II of FIG.

FIG. 3 is a reduced longitudinal section taken on the line III-III of FIG. 1, but showing the fastenerjoining two sheets;

FIG. 4 is a cross section, looking down, showing the upper ends of the threads just before they pass through the sheets; and

FIGS. 5 to 8 are enlarged fragmentary diagrams showing how the fastener locks itself in the sheets itjoins.

Referring to FIGS. 1 and 2 of the drawings, the fastener consists ofa screw and'a washer. The screw has a head 1 that can be shaped to receive either a wrench or a screwdriver, or both. Extending away from the head is an integral stem 2. For convenience of description claiming, the screw will be described as if it is in a vertical position with the head at the top. The lower end of the stem is tapered for insertion in a preformed opening in sheets of metal or the like that are to be fastened together, or it can be provided with a drill point to drill its own hole through the sheets. The stem is encircled by a plurality of equally spaced V-threads 3. Although one or two threads can be used, it is preferred to use three for greater security and stability.

Each thread has the usual upper and lower surfaces which.

meet along a common outer edge 5 that extends upwardly from the lower end of the thread. It does not extend all the way to the upper end as will be explained presently. The upper ends of the threads are blunt and are spaced from the head a distance greater than the total thickness of the sheets that the screw is to join. The upper edge 6 of the root of each thread has a uniform pitch from end to end. The lower edge 7 of each root has the same pitch as its upper edge for most of its length, but it becomes less steep along the upper portion of the thread, whereby the root is thickened in that area. The outer edge of the upper surface of each thread has the same uniform pitch as the upper edge 6 of the root from its upper end to substantially its lower end, where the thread fades away.

Another feature is that each thread along its upper portion where the root is thicker is widened to form a longitudinally tapered crest 10 that extends along'the thread from its upper end. It is important that this widening extend only downwardly from the outer edge .of the upper surface of the thread. Otherwise, the pitch of that outer edge would not be uniform. This tapered crest preferably terminates below the upper end of the next thread. The upper end of each thread has a substantially flat end face 11 that'connects the upper end of the tapered crest with the stem. Also, the upper end of the thread has a substantially flat top face 12 extending away from the upper edge of its end face. All of the top faces lie in the same plane, which is substantially radial to the stem. Each flat end face 11 is inclined downwardly away from the adjoining flat top face.

To complete the fastener, it is provided with a resilient washer 15 encircling the stem between the head and the upper ends of the threads. This washer, which may be made of rubber or other elastic material, is of such thickness that when the screw is screwed into place as shown in FIG. 3, the washer will be compressed between the head and the top sheet to and tightly around the screw stem, whereby the sheets will be pressed tightly against the flat top faces 12 of the threads and the opening through the sheets will be sealed. The resilient washer may engage the head of the screw directly or it may be spaced from the head by a metal washer 17 that has a large enough opening so that the central part of the resilient washer can squeeze up through the hole. If desired, the bottom of the head itself may be provided with an annular recess that receives part of the resilient washer. It is even possible to enclose the metal head of the screw in a plastic head that has a depending flexible skirt which serves as a resilient washer.

When such a fastener is screwed through a pair of overlapping sheets the action of the threads in cutting the sheets is the same as with ordinary self-tapping screws, as shown in FIGS. 4 and 5, until the thickened upper portions of the threads reach the sheets. Since the lower surfaces of these por-.

tions have a pitch that is less steep than the rest of the thread, they press or tear down the underlying rear edges 20 of the notches formed by the screw threads in the sheets and thereby make the notches wider, as shown'in FIG. 6. After a thread has passed completely through the sheets as shown in FIGS. 6 and 7, its flat top face 12 slides on around against the bottom of the lower sheet 21 while the upper part of the following thread moves forward into engagement with the back or lower surface of the turned down rear edge 20 of the notch. As shown in FIG. 8, continued rotation of the screw will cause this following thread to bend the downturned edge of the notch upwardly again to substantially close the notch. At the same time the same thing is happening at the other two notches. Con-.

sequently, if the screw is reversed, there are no notches for the 5 upper ends of the threads to enter in order to permit the screw to be unscrewed or to work loose from the sheets. Furthermore, the inclined end faces 11 of the upper ends of the threads will ride under the rear edges of the notches even if they have not been bent all the way back to their original positions, so the threads cannot enter the notches even if they are still partly open.

If the rear edge 20 of a notch were bent down no more than the conventional distance, as shown in FIG. 5,-it would be so short that the following thread would not bend it up permanently, so it would spring back down as soon as the thread passed. With this invention, the rear edge portion is bent farther down and is longer as shown in FIG. 6 so that it will be bent up by the following thread and will stay there and not spring back.

It will be seen that the compressed washers will seal the screw holes and'prevent leakage. They also have the big advantage of allowing the same screws to be used with sheets of different thicknesses, because the washers will compensate for those differences. The threads of thescrew do not cut into the lower surface of the bottom sheet, which would be highly undesirable in many cases where the sheet is coated. If the threads were allowed to cut into the sheet they would scour off tighten into place, contrary to those having threads with a change of pitch at their upper ends.

I claim:

1. A self-locking fastener comprising a self-tapping screw having a head and a downwardly extending stem encircled by a V-thread having upper and lower surfaces meeting along a common outer edge extending from its lower end upwardly for most of its length, the thread being provided with a blunt upper end spaced from the head, the upper edge of the root of the thread having a uniform pitch from end to end, the lower edge of the root having the same pitch as its upper edge for most of its length but becoming less steep along the upper portion of the thread to thicken the root in that area, the outer edge of the upper surface of the thread having the same pitch as said root upper edge from its upper end to substantially its lower end, the thread at said upper portion being widened only downwardly from said outer edge to form a longitudinally tapered crest extending along the thread from its upper end,

the upper end of the thread having a substantially flat end face connecting the upper end of the tapered crest with the stem, the upper end of the thread also having a substantially flat top face extending away from the upper edge of its end face, said top face lying in a plane that is substantially radial to said stem, said flat end face being inclined downwardly away from the adjoining flat top face, and a resilient washer on the stem between the head and thread.

2. A self-locking fastener according to claim 1, in which there are a plurality of said threads equally spaced apart with their flat top faces all lying in said plane.

3. A self-locking fastener according to claim 2, in which there are only three of said threads.

4. A self-locking fastener according to claim 2, in which there are only three of said threads, and the lower end of each tapered crest is disposed below the flat top face of the adjacent thread.