Patent Description:
A self-tapping screw is a fastening component which is screwed into a pre-drilled hole in a solid material. The hole is drilled with a predetermined diameter, and the screw is configured to form a tapping in the peripheral wall of the hole as it is being screwed in.

The formation of the threads on a self-tapping screw is traditionally done using a rolling process. That is the threads are formed by pressing a shaped tool against a blank (non-threaded rod), and pushing the threaded shape into the blank. The rolling process generates a high concentration of stresses on the screw body. So, sometimes unfavourable bending of the screw can occur (shown in <FIG>). This bending makes installation more difficult and less efficient.

It is therefore an object of the present invention to mitigate the above problems. In particular, it is an object of the present invention to provide screw which can be easily formed during the rolling process with less bending than previous screws. Therefore allowing for reduced installation effort and increased performance of the screw. It is also an objective of the present invention to provide the advantage that a screw with an improved stress distribution may be provided.

The invention is set out in the set of appended claims.

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

Suitably the auxiliary thread extends between <NUM> and <NUM> percent of a length of the longitudinal body.

Suitably the primary thread and auxiliary thread extend parallel to one another around the longitudinal body, such that the auxiliary thread is disposed on an interpitch of the primary thread.

Suitably at least one of the primary thread and/or auxiliary thread are asymmetrical threads.

Suitably, said asymmetrical thread has a first flank which has a planar surface and a second flank which has a concave surface.

Suitably the auxiliary thread comprises excess material from the formation of the primary thread.

Suitably, the auxiliary thread comprises excess material from the rolling of the primary thread.

Suitably, the screw is formed of a metallic material.

Suitably, the auxiliary thread has a crest height that is equal to or less than a crest height of the primary thread.

The crest height of the auxiliary thread is less than the crest height of the primary thread.

According to the invention, the crest height of the auxiliary thread is less than <NUM>% of the crest height of the primary thread.

Suitably, the crest height of the auxiliary thread is less than <NUM>% of the crest height of the primary thread.

Suitably at least one of the primary and/or auxiliary threads has a uniform profile.

In examples, the head portion may comprise a Torx (Registered Trademark) head. In particular, the Torx head may comprise an internal Torx socket and/or an external Torx profile. In some examples, the Torx head comprises both an internal Torx socket and an external Torx profile.

Certain embodiments of the invention provide the advantage that a screw with an improved stress distribution may be provided.

Certain embodiments of the present invention provide a screw which can be easily formed during the rolling process with less bending than previous screws. Therefore allowing for reduced installation effort and increased performance of the screw.

The present intention refers to a screw with a primary thread and an additional auxiliary thread. While the present invention refers to a screw the auxiliary thread concept may be applied to any type of screw an in particular screws formed by a rolling process.

The screw disclosed herein may be a self-tapping concrete screw for insertion into a hole formed in concrete.

Referring now to <FIG> an example of a screw <NUM> is illustrated. The screw <NUM> includes a head portion <NUM> and a longitudinal body <NUM>. The longitudinal body <NUM> is attached to the head portion <NUM> at a first end <NUM>. A second end <NUM> of the longitudinal body <NUM> is configured to be the first part of a screw <NUM> to enter a material in use. The head portion is described below with reference to <FIG>. The longitudinal body <NUM> has a central axis between the first end <NUM> and the second end <NUM>.

The longitudinal body <NUM> has a primary thread <NUM> which helically extends between the first end <NUM> and the second end <NUM> of the longitudinal body <NUM>. In this example the primary thread <NUM> is a symmetrical thread. A symmetrical thread is a thread which has a flank angle (the angle between a flank and the central axis of the longitudinal body <NUM>) that is substantially identical on both sides of a crest <NUM> (see <FIG>, furthest point from the central axis) of the thread. In other examples the primary thread <NUM> may be an asymmetrical thread. It may also be that the auxiliary thread is an asymmetrical thread. According to another example, the primary thread is a symmetrical thread while the auxiliary thread is an asymmetrical thread. An asymmetrical thread is where the flank angle is different on each side of a crest <NUM> of the thread. For example, said asymmetrical thread has a first flank which has a planar surface and a second flank which has a concave surface. For instance, a first flank may be planar and may form a flank angle of between <NUM> and <NUM> degrees and a second flank may have a concave surface.

The primary thread <NUM> may extend substantially the entire length of the longitudinal body <NUM>. That is the primary thread may helically wind around the longitudinal body <NUM> from the first end <NUM> to the second end <NUM>. In some cases there may be a link portion <NUM> between the first end <NUM> and the head portion <NUM> where the link portion <NUM> is not threaded.

The longitudinal body <NUM> further includes and auxiliary thread <NUM>. The auxiliary thread <NUM> is a separate thread to the primary thread <NUM>. In other words, the primary thread <NUM> does not contact the auxiliary thread <NUM>. The auxiliary thread <NUM> helically extends from the first end <NUM> of the longitudinal body <NUM> towards the second end <NUM>. In this example, the auxiliary thread <NUM> extends only partially along the length of the longitudinal body <NUM>. For example the auxiliary thread may only extend along <NUM> to <NUM> percent of the length of the longitudinal body <NUM> and aptly the auxiliary thread extends from the first end. According to another example, the auxiliary thread may only extend along <NUM> to <NUM> percent of the length of the longitudinal body <NUM> and aptly the auxiliary thread extends from the first end. The auxiliary thread <NUM> comprises excess material from the formation of the primary thread. For instance, auxiliary thread <NUM> is formed from excess material from the rolling of the primary thread <NUM> (which is caused by the rolling of the primary thread <NUM>). In this example, the screw <NUM> is formed of a metallic material i.e. stainless steel.

The auxiliary thread <NUM> may helically wind in the same direction as the primary thread <NUM>. In this way the primary thread <NUM> and auxiliary thread <NUM> may extend parallel to one another. For example the auxiliary thread <NUM> may be positioned between two crests <NUM> of the primary thread <NUM> such that the auxiliary thread <NUM> is positioned in the interpitch of the primary thread <NUM>.

The auxiliary thread <NUM> may be a symmetrical or an asymmetrical thread. Moreover any combination of symmetrical and asymmetrical primary and/or auxiliary threads may be used. One of both of the primary and auxiliary threads <NUM><NUM> may be uniform along the length of the winding. That is the thread may have a substantially constant cross-section.

In this example, the crest <NUM> of the primary thread <NUM> is further from the central axis of the longitudinal body <NUM> than the crest <NUM> of the auxiliary thread <NUM> is from the central axis. In other words the primary thread <NUM> may be larger than the auxiliary thread <NUM>.

The auxiliary thread <NUM> provides additional strengthening to the longitudinal body <NUM> of the screw <NUM>, which can reduce unwanted bending. Further, the use of additional material from the rolling process provides an cost effective method of strengthening the screw <NUM>.

<FIG> illustrate an example of a screw <NUM> to which the present invention can be applied. These figures are used for the description of the head portion <NUM> of the screw <NUM> shown in <FIG>.

The head portion <NUM> may be configured to receive a tool in use. In this way the head portion <NUM> is configured to receive an external force so that the screw <NUM> can be inserted into a material, like concrete for example. The head portion <NUM> may have a diameter which is larger than the diameter of the longitudinal body <NUM>.

In this example the head portion <NUM> includes a protrusion <NUM>. The protrusion <NUM> may be a hexagonal shaped protrusion. In other words the protrusion <NUM> has a substantially planar top surface <NUM>, which is perpendicular to the central axis of the longitudinal body <NUM>, the top surface <NUM> being hexagonal shaped. Other examples of the head portion <NUM> may include other shaped protrusions.

In this example the head portion <NUM> includes a cavity <NUM> for engaging with a tool. The cavity <NUM> may be substantially central on the protrusion <NUM>. The cavity <NUM> extending from the top surface <NUM> in a direction parallel to the central axis of the longitudinal body <NUM>. The cavity <NUM> may engage a tool in use. In this example, the cavity <NUM> is a Torx head cavity (cavity with six pointed star cavity). In other examples the cavity <NUM> may be a hexagonal cavity, or other cavity for receiving a tool.

The head portion <NUM> may also include a flange portion <NUM>. The flange portion <NUM> may be adjacent to the longitudinal body <NUM> and the protrusion <NUM> such that it is sandwiched between them. The flange portion <NUM> extends radially around the head portion <NUM> so as to form a lip around the periphery of the head portion <NUM>. This means the lip is configured to sit against the material into which the longitudinal body <NUM> has been inserted during use.

In the example of <FIG> the head portion <NUM> comprises a Torx head <NUM>. In particular, the Torx head <NUM> has an external Torx profile having a six pointed star shaped protrusion <NUM>. Optionally, the Torx head further may comprise an internal Torx socket <NUM>. In another example, the Torx head <NUM> includes an internal Torx socket <NUM> and not a Torx protrusion <NUM>. Instead, the protrusion may be hexagonal, for example. The increased surface contact provided by the Torx head protrusion <NUM> or Torx socket <NUM> reduces screwing effort and facilitates torque transmission. Providing an internal Torx socket <NUM> is also advantageous for access during use of the screw. In particular, where the screw is used in a position having restricted access the provision of an internal Torx socket <NUM> makes it easier for the installer to access the head <NUM> with the tool to rotate the screw.

It will be clear to a person skilled in the art that features described in relation to any of the embodiments described above can be applicable interchangeably between the different embodiments. The embodiments described above are examples to illustrate various features of the invention.

Claim 1:
A screw (<NUM>) comprising:
a longitudinal body (<NUM>) having a first end (<NUM>) and a second end (<NUM>);
a head portion (<NUM>) for receiving a driving force, the head portion adjacent the first end of the body;
wherein the longitudinal body (<NUM>) comprises:
a primary thread (<NUM>) helically extending between the first end (<NUM>) and the second end (<NUM>); and
an auxiliary thread (<NUM>) separated from the primary thread, and helically extending from the first end at least partially towards the second end, wherein the crest height of the auxiliary thread (<NUM>) is less than <NUM>% of the crest height of the primary thread (<NUM>).