WO2011143733A1

WO2011143733A1 - Screw with pull-out resistant thread normal to shank

Info

Publication number: WO2011143733A1
Application number: PCT/CA2010/000747
Authority: WO
Inventors: Mirco Walther
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-05-18
Filing date: 2010-05-18
Publication date: 2011-11-24
Anticipated expiration: 2012-11-18
Also published as: TW201142156A

Abstract

A screw fastener (1) having a head (A), threaded shank (B) and tip end (C) has an upper thread surface(s) extending at an angle x of 0° - 3° from a normal to a longitudinal axis (3) of the screw and an apex angle β at the periphery of the screw in the range between 25° and 45°. The screw exhibits resulting in significantly increased pull-out resistance.

Description

SCREW WITH PULL-OUT RESISTANT THREAD NORMAL TO SHANK

BACKGROUND OF THE INVENTION

The present invention pertains to a screw type fastener utilizable in substrates including lumber, LVL, particle board, wafer board, plastic lumber, cement board, plaster board and similar penetrable products. The screw has a substantially improved pull-out resistance in consequence of the unique thread design.

Self-tapping screws, such that the screws do not require a pilot hole, are typically employed in relation to penetrable substrates such as wood. Typically, the screws have a driving head, a threaded shank and a form of point at the tip of the screw to aid in penetration. While screws having a variety of apertured or notched threads are known for improved thread cutting during penetration, traditional threads have a thread profile which is substantially symmetrical about a normal from the shank access.

A major problem within the housing industry, and in particular wood framed housing, arises from wind uplift during high winds such as generated in hurricanes, typhoons, etc. Wind uplift applies pressure on sheathing materials which may be held to structural lumber by nails or screws. Various nail designs have been developed to improve holding capacity against wind uplift (i.e. against pull-out forces). While it is recognized that screws of a traditional design may well have equal or greater resistance to pull-out during uplift conditions, pull-out remains a problem.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel thread design which increases pull-out resistance, particularly under wind uplift conditions.

In general terms, the invention provides a screw having a head end, an intermediate threaded shank and a pointed end wherein the screw thread has a substantially flat upper surface, by which "flat" means normal to the axis of the screw. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of preferred and exemplary embodiments, with reference to the accompanying drawings which are diagrammatic, and not to scale.

Figure 1 is a side view of a screw according to the present invention.

Figure 2 is a detail of a section of the shank, showing the thread orientation.

Figure 3 is a cross-section of a portion of the screw thread through the center axis, illustrating the generally right angular profile of the thread of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED AND EXEMPLARY EMBODIMENTS The screw of the present invention incorporates standard features of many screws including a driving head A, a shank B and a tip C. The head may have a multiple of shapes adapted for driving, such as wrench flats, slot, Phillips, torques, Robertson and other screwdriver formats. The shank may be fully threaded or only partially threaded over its length, and may contain additional specialized threads for scavenging cuttings or enabling penetration. The tip is usually pointed, and may be adapted with cutting facets to ease penetration.

Unique to the present inventive Eagle Thread™ screw is the thread profile, with the cross-section of the thread comprising a substantially right angle triangle. The base of the triangular profile is parallel to the axis of the shank and the upper face (the face oriented towards the head) is substantially normal or perpendicular to the shank. The lower face of the thread (oriented towards the tip) is inclined from the base of an acute angle of substantially 45° to 65°, thereby providing an apex angle at the outer periphery of the thread of substantially 45° - 25°. This thread profile results in the upper thread face being substantially parallel to the surface of the substrate into which the screw is inserted, assuming it is inserted perpendicularly to the substrate. In any event, the upper thread face is normal to the shank axis and provides a maximum surface area to resist axial pull-out forces. It is believed that the forming of an upper thread surface substantially normal to the shank axis eliminates any camming or sliding effect which may be present during pull-out of a screw having a conventional inclined surface in the order of 25° to 45°. Figure 1 illustrates a screw 1 having an upper head portion A, an intermediate shank portion B partially threaded, and a lower tip portion C, tapering generally to a point with the threads embodying the configuration of the present invention.

In Figure 2, a detail of the thread configuration is shown wherein the screw shank 2 has a central axis 3 with threads 4 formed therearound. The upper thread face 5 is substantially normal or perpendicular to the thread axis 3 (as may be seen in Figure 2), while upper thread face 5 is substantially normal to the screw axis 3 (see Fig. 3), it may vary through an angle a ranging from 0° to 3° from the normal in a direction away from the head portion. The lower thread face 6 is at an acute angle relative to the shank axis and merges with the upper thread face at apex 7, forming an angle β between 28° and 42° (25°- 45°) as may be more clearly seen in Figure 3.

While conventional screws have an upper surface typically in the range of 20° to 30° away from the screw head, the application of a substantially normal upper thread face to a screw thread has significant increase in pull-out resistance, and has particular advantages in applications requiring axial integrity. This is particularly advantageous in applications where wind uplift, such as during hurricanes, applies extreme tension against the screw head and resistance to pull-out is critical. In tests of the present Eagle Thread screw design, it has been found that with an upper thread surface varying between 0° and 3° from a normal to the shank axis (inclined away from the head) pull-out resistance is significantly increased, between 8% and 10% over a conventional screw having an upper thread surface inclined at a conventional 20° to 30° from the normal of the screw axis (away from the head).

For example, a comparative 2" inch screws, both conventional and in accordance with this invention, were embedded in stud grade lumber to the full 1-7/16" depth of the thread with a controlled deformation rate of .1 in/minute. The "Eagle Thread" screw of the present invention exhibited an increase in the order of 10% for pull-out resistance.

The foregoing embodiments have been described in relation to conventional wood screws, the invention can be applied to screws for other applications including, without limitation, metal or plastic applications and even in concrete or masonry with a pilot hole. Minor variation in degrees or length can be made without departing from the scope of the invention as recited in the accompanying claims. Further, while the Eagle Thread™ screw threads of the present invention may be applied to the entire length of the threaded portion, a more conventional or symmetric thread cross-section may be employed over a portion of the threaded length and particularly may be used in the tip portion, having a conical reduction to a pointed end.

Claims

1. A screw fastener comprising:

a head adapted for driving means at an upper end;

an elongated shank extending from the head to a tip at a lower end, the shank having a central axis and having helical threads extending outwardly from the shank over at least a portion of the length of the shank;

the threads having upper and lower thread faces converging at an acute angle at a peripheral edge of the screw thread, the upper thread face being substantially normal to the axis of the shank, and the lower thread face subtending an acute angle of 25° to 45 ⁰ with the upper thread face.

2. The screw of claim 1 wherein the upper thread face slopes away from the screw head at an angle of between 0° and 3° from normal to the shank.

3. A screw fastener comprising a head with drive means at one end;

a shank extending from the head to a tip at the other end, the shank having helical threads and a central longitudinal axis,

wherein at least a substantial portion of the thread forms a substantially right triangle in cross-section with a base parallel to the shank axis, an upper thread face at substantially 90° to the base, and an apex angle between 25° and 45°.

4. The screw of claim 3, wherein the substantially right angle of the triangle is between 90° and 87°.

5. The screw of claim 3, wherein a portion of the threaded length has threads which are generally symmetrical about a normal to the central axis.

6. The screw of claim 3, wherein the tip end of the screw is conical, and the threads of the tip are generally symmetrical about a normal to the central axis.