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1. WO2020109760 - A FASTENER

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[ EN ]

A FASTENER

The present invention relates to a fastener and in particular, but not exclusively, to a screw for use primarily with soft and hardwoods, low-, medium-, and high-density fibreboard, but also with plastics, masonry, and metals, or the like.

Typically, a screw includes a head portion, a shank portion, a tip, and at least one spiral screw thread extending from the tip and at least partially along the shank portion towards the head portion. A fully-threaded screw, or a screw with a non-threaded shank portion having an outer diameter which is less than that of the thread, can allow material, e.g. timber, around the thread or the reduced shank portion to expand and retract, creating undesirable unseating moments. A partially threaded screw with a non-threaded shank portion having an outer diameter which is substantially the same as the thread allows the non-threaded shank portion to sit tightly in the void created by the gimlet thread as it drives through the top piece material to thereby restrict timber movement and securely fix the top piece material to the substrate material. In this manner, the unthreaded shank portion acts as a dowel. However, the dust created by the gimlet thread can build up and become trapped in the thread and/or between the non-threaded shank portion and the material which undesirably increases friction and heat and in turn the torque and energy required to drive the screw into the material. Dust build up can also cause poor seating between the screw head and the material.

It is an aim of certain embodiments of the present invention to provide a screw that includes a dowel-acting shank portion and which allows dust created when the gimlet thread is driven into material to be efficiently extracted from the screw/material interface to thereby minimise the torque and energy required to drive the screw into the material.

According to a first aspect of the present invention there is provided a fastener comprising:

a drive end region, a tip end region, and

at least one screw thread extending from at least proximal the tip end region; and

a dowel portion located between the at least one screw thread and the drive end region, said dowel portion comprising a thread form having at least one substantially flat and axially oriented outer surface extending around the dowel portion and at least one channel extending towards the drive end region.

Optionally, the thread form is arranged in the same direction as the at least one screw thread.

Optionally, the at least one outer surface and the at least one channel have substantially the same width in an axial direction.

Optionally, the width substantially equals half the pitch of the thread form.

Optionally, the thread form comprises a trapezoidal thread form.

Optionally, the fastener comprises a reaming portion located between the dowel portion and the at least one screw thread.

Optionally, the reaming portion comprises a plurality of circumferentially spaced apart cutting elements defining a channel between adjacent ones of the cutting elements.

Optionally, each channel of the reaming portion is substantially the same width as the at least one channel of the dowel portion.

Optionally, at least one channel of the reaming portion communicates with the at least one channel of the dowel portion.

Optionally, the cutting elements define an outer diameter which is substantially the same as an outer diameter defined by the thread form of the dowel portion.

Optionally, the cutting elements are oriented in the same direction as the thread form of the dowel portion.

Optionally, a length of the reaming portion is equal to or greater than a pitch of the at least one screw thread.

Optionally, a length of the reaming portion is equal to or less than a length of the dowel portion in an axial direction.

Optionally, the reaming portion is located adjacent to the dowel portion.

Optionally, the fastener comprises a non-threaded shank portion between the at least one screw thread and the reaming portion.

Optionally, the drive end region comprises a head portion having at least one tapered countersink surface.

Optionally, the countersink surface comprises a plurality of circumferentially spaced apart ribs extending along the countersink surface.

Optionally, each rib is angled with respect to a respective axial plane passing through the longitudinal axis of the fastener.

Optionally, each rib is angled forwardly with respect to an insertion rotational direction of the fastener.

According to a second aspect of the present invention there is provided a method of manufacturing a fastener, comprising:

providing a fastener with a drive end region, a tip end region, and at least one screw thread extending from at least proximal the tip end region; and

providing a dowel portion between the at least one screw thread and the drive end region, said dowel portion comprising a thread form having at least one substantially flat and axially oriented outer surface extending around the dowel portion and at least one channel extending towards the drive end region.

Description of the Drawings

Certain embodiments of the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 a illustrates a side view of a screw according to certain embodiments of the present invention;

Figure 1 b illustrates a first underside view of the head portion of the screw of Figure 1 a; and

Figure 1 c illustrates a further underside view of the head portion of the screw of Figure 1 a.

Detailed Description

As illustrated in the Figures, a screw 100 according to certain embodiments of the present invention includes a threaded portion 102 having a tapered end region 104 which terminates at a pronounced gimlet tip 106. The pronounced gimlet tip 106 allows the screw to start immediately into most building materials without requiring a pre-drilled pilot hole. The threaded portion 102 includes a primary thread 108 which extends along the tapered end region 104 and at least around 50% of the length of the screw. A secondary thread 1 10 is also provided on the tapered end region to provide a twin thread or double start. In particular, the threads start at diametrically opposed sides of the gimlet tip 106 which provides a balanced drive with no ‘kickover’. The threaded portion 102 after the tapered end region 104 defines a single thread. The threaded portion 102 is substantially trilobular in axial cross section which exhibits less insertion torque and, once driven in, the screw resists anti-seating moments so does not work lose. Alternatively, the threaded portion may have a different non-circular cross section, such as oval or elliptical, or it may be substantially circular in cross section.

Each thread has a thread angle of between around 30-60 degrees and aptly around 37-43 degrees. Preferably, the thread angle is around 40 degrees for an M4 screw.

The pitch of each thread is between around 1 mm to 6mm and aptly around 3mm +/-10% for an M4 screw. The helix angle is around 70 degrees relative to the longitudinal axis 128 of the screw. The major diameter of the threaded portion 102 is between around 2mm to 12mm and aptly around 4mm for an M4 screw. The minor diameter of the threaded portion 102 is between around 1 mm to 5mm and aptly around 2.4 mm for an M4 screw.

The screw 100 further includes an optional non-threaded shank portion 1 12 adjacent to the threaded portion 102. The non-threaded shank portion 1 12 also has a trilobular cross section, but may alternatively be oval or elliptical for example. The maximum diameter of the trilobular non-threaded shank portion is between around 1.2 to 7.2mm and aptly around 2.85 mm for an M4 screw. The minimum diameter of the non-threaded shank portion is between around 1.05 to 3.32 mm and aptly around 2.75 mm for an M4 screw. The length of the plain shank portion 1 12 is equal to the total screw length less the head portion length, the dowel portion length, the reaming portion length, and the gimlet thread length, and varies for each length of screw. On a 4mm x 50mm screw, the plain shank portion 1 12 is around 5mm.

The screw 100 further includes a reaming portion 114 including a plurality of annularly spaced apart cutting elements 1 16 for creating a clearance hole in the material as the screw is driven therein. The reaming portion 1 14 is located adjacent to the non-threaded shank portion 1 12. Alternatively, the reaming portion 1 14 may be located adjacent to the threaded portion 102, e.g. for relatively short screws, and would prevent jacking as it is driving the clearance hole. The plurality of cutting elements may be provided by a reaming-type thread form to be at least part-spiral or each cutting element may be substantially linear. Preferably, the cutting elements are oriented in the same direction as the threaded portion 102 to allow for efficient transfer of dust from the threaded portion up between the cutting elements of the reaming portion. However, the cutting elements may be oriented in the opposite direction to the threaded portion. Each cutting element is angled relative to the longitudinal axis 128 of the screw by around 40-60 degrees and aptly around 45 degrees (as viewed from the side as in Figure 1 a). Alternatively each cutting element may be substantially parallel with the longitudinal axis of the screw. The outer diameter of the reaming portion 1 14, i.e. a diameter defined by the outer edge of the cutting elements, is between around 2-10 mm and aptly around 3.5 mm when applied to a 4mm screw. The inner diameter of the reaming portion 1 14, i.e. the diameter of the shank, is substantially the same as the non-threaded shank portion 1 12. The shank and cutting elements of the reaming portion 1 14 are substantially circular in cross section. Aptly, the reaming portion 1 14 may be at least one pitch. Aptly, the length of the reaming portion 1 14 is no less than the pitch of the single threaded portion 102 multiplied by 1.1 such that one complete revolution of the screw reams a 360-degree clearance hole.

The screw 100 further includes a dowel portion 1 18 located between the reaming portion 1 14 and a head portion 120. The dowel portion 1 18 includes a trapezoidal thread form 122 defining substantially flat inner and outer surfaces 124,126 oriented substantially parallel with the longitudinal axis of the screw. Alternatively, the thread form may be a substantially square thread or the like. Preferably, the thread form is oriented in the same direction as the reaming portion 1 14 to allow for efficient transfer of dust from the cutting elements 1 16 to the flute/s defined by the thread form of the dowel portion 1 18. However, the thread form of the dowel portion may be oriented in the opposite direction to the cutting elements of the reaming portion 1 14. The inner and outer surfaces 124,126 have substantially the same length in the axial direction which equates to half the pitch of the trapezoidal thread form. This produces a drive effect which in turn minimises insertion torque and, once driven into the clearance hole created by the reaming portion, acts as a dowel to provide a secure fix. The length of the dowel portion 1 18 is aptly equal to or greater than the length of the reaming portion 114. Aptly, the pitch of the trapezoidal thread form is between around 1.1 mm to 8 mm and aptly around 3.2 mm for an M4 screw. The inner surfaces 124 have substantially the same diameter as the shank of the reaming portion 1 14 and the non-threaded shank portion 1 12.

The outer surfaces 126 of the dowel portion 1 18 have substantially the same diameter as defined by the cutting elements 1 16 of the reaming portion 1 14 such that the outer surfaces 126 of the dowel portion 1 18 engage in the clearance hole started by the threaded portion 102 and finished by the reaming portion 1 14. The thread form of the dowel portion 1 18 is angled at around 60-80 degrees and aptly around 70 degrees relative to the longitudinal axis of the screw (as viewed from the side as in Figure 1 a). The thread form defines a continuous flute to allow dust created by the threaded portion 102 and reaming portion 1 14 to move up the screw/material interface as the screw is being driven into the material and out of the hole created therein. Aptly, the flute communicates with at least one space defined between a pair of adjacent ones of the cutting elements 1 16 of the reaming portion 114 to allow dust to efficiently transfer from the reaming portion to the flute of the dowel portion.

The head portion 120 includes two tapered surfaces 130,132 angled with respect to the longitudinal axis by around 25 and 45 degrees respectively. The head portion has a substantially circular cross section. The head portion includes a drive recess (not shown), e.g. a cross or hex recess, for receiving a suitable driver, e.g. a screwdriver or powered driver bit. The first or lower tapered surface 130 ensures ‘cam-out’ is avoided when the screw is driven about its longitudinal axis 216 into a substrate, whilst maintaining the torsional strength of the screw particularly between the head portion and shank portions.

Whilst a tapered circular head portion is illustrated, this feature may be optional. For example, the screw 100 may not include a head portion as such and instead include a drive recess in the drive end of the screw distal from the tip for a suitable tool to engage with to drive the screw. Alternatively, the drive end of the screw may have a substantially square, hexagonal or the like cross section for a suitable drive socket to engage with to drive the screw.

The second or upper tapered surface 132 includes a plurality of annularly spaced apart ribs 134 each of which extend from the interface with the first tapered surface 130 to the outer edge of the head portion. As illustrated in Figures 1 b and 1 c, six ribs are provided to be circumferentially spaced apart from each other by around 60 degrees. Each rib 134 is angled by around 25 degrees (b) relative to a respective axial plane P such that each rib is oriented forwardly with respect to a clockwise rotation of the screw. With reference to Figure 1 c, length a - b is equal to half distance e which is the maximum diameter of the first tapered surface 130 (minimum diameter of the second tapered surface 132). Length c - d is equal to half distance f which is the maximum diameter of the second tapered surface 132.

As the screw is driven into a material, a tapered countersunk recess is reamed in the material by the ribs which eliminates the need to separately countersink the material prior to inserting the screw. Furthermore, the ribs disperse dust from the material which has been extracted from the screw/material interface via the flutes of the dowel portion 1 18. The forwardly angled ribs 134 capture the dust and efficiently disperse it away from the material to prevent any unseating issues between the head portion and the countersunk recess formed in the material. Alternatively, the ribs 134 may be planar with the longitudinal axis of the screw or may be substantially curved to capture and disperse the dust. The ribs 134 may extend at least partially along the first tapered surface 130 and may terminate at the dowel portion 1 18 such that dust is efficiently transferred from the flute/s thereof to the ribs 134.

As an example, for a 50mm long M4 screw, the tapered end region 104 is around 10mm long and has a taper angle of around 22-30 degrees. The threaded portion 102 from the tip 106 to the start of the non-threaded portion 1 12 is around 30mm long. The reaming portion 114 is around 4.5mm long, and the dowel portion 118 is around 5.5mm long.

The screw 100 is aptly made from hardened carbon steel but may be made from other suitable materials such as brass, stainless steel, hardened plastic, or the like, depending on its intended application. Likewise, the screw thread dimensions and arrangement may be configured to suit a particular application, e.g. the screw may not have a double thread at the tapered end region or may have a twin or triple thread at least partially along the threaded shank portion. Further alternatively, the head portion may be countersunk, round, raised, cheese head, hexagonal, or the like. The drive recess in the head portion may be a cross recess, a slotted recess, a hex recess, or the like, to receive a correspondingly shaped drive tool. The screw may be electroplated, galvanised, or coated with organic treatments to prevent corrosion. The screw may be manufactured by cutting a wire to a predetermined length, providing the head portion to the blank, optionally polishing the blank, machining the thread on the blank by rolling or cutting, and optionally cleaning, e.g. by tumble finishing, and coating the screw.

Certain embodiments of the present invention therefore provide a fastener, such as a wood screw, which is efficient to insert in a material in terms of speed and balance, and which is configured to form a clearance hole in the material for a dowel portion of the screw to engage with to securely fix at least one component to a substrate, such as a decking board to a support member, whilst preventing the two timber components jacking apart and the timber surrounding the screw expanding or retracting which can undesirably create unseating moments. The reaming and dowel portions prevent the screw from‘jacking’ apart two pieces of joined timber, as a fully threaded screw would undesirably tend to do in view of the thread engaged in the top material pulling it away from the substrate. The optional non-threaded shank portion prevents jacking apart before the reaming and dowel portions engage. Dust created from the threaded portion and reaming portion is efficiently transferred up through the screw/material interface and dispersed from the material surface to avoid blocking, frictional losses, unseating issues, and the like.