Patent Description:
<FIG> illustrates a traditional concrete screw <NUM> including a shank <NUM>, a head <NUM> formed at an end of the shank <NUM>, and a thread <NUM> formed on the shank <NUM>. The screw <NUM> is adapted to be fastened into a concrete structure <NUM> at the masonry (e.g., brick masonry) and/or concrete to join another structure component <NUM> on the concrete structure <NUM>. Before driving the screw <NUM>, a worker uses an electric drill (not shown in <FIG>) to drill a hole <NUM> in the concrete structure <NUM>. The hole <NUM> has a hole diameter slightly greater than the shank diameter of the shank <NUM> but less than the major diameter of the thread <NUM>. Then, with the front end of the shank <NUM> inserted into the hole <NUM>, the head <NUM> is driven to rotate by a tool (not shown) such that the hole wall of the hole <NUM> is cut by the thread <NUM>, and hence the shank <NUM> can be screwed into the hole <NUM> until the head <NUM> gets close to or abuts the structure component <NUM>. However, during the process of the shank <NUM> driven into the hole <NUM>, plenty of concrete debris coming out of stiffened cement mortars (which are not compressed in contrast to rigid wooden fibers) in the concrete structure <NUM> cut by the thread <NUM> worsens the cutting force of the thread <NUM>, retards movement of the shank <NUM> inside the hole <NUM>, decelerates the screw <NUM> and even breaks the shank <NUM>. Moreover, the shank <NUM> driven into the hole <NUM> in the beginning may be shaken or even deviated.

<FIG> and <FIG> illustrates another traditional concrete screw <NUM> including a shank <NUM>, a head <NUM> formed at an end of the shank <NUM>, and first and second threads <NUM> and <NUM> formed on the shank <NUM>. The screw <NUM> is adapted to be fastened into a concrete structure <NUM> on which another structure component <NUM> is fixed. The second thread <NUM> features its major diameter less than the major diameter of the first thread <NUM> and almost equal to the hole diameter of the hole <NUM>. When the shank <NUM> is driven into the hole <NUM>, the second thread <NUM>, which bears against the inner surface of the hole <NUM> and supports cutting, accelerates the screw <NUM> moving inside the hole <NUM>. However, concrete debris neither crushed nor dispersed fast by the second thread <NUM> imposes immense frictional resistances on the shank <NUM> at the time when sunk in the hole <NUM> deeply. Accordingly, the shank <NUM> fails in complete fastening, so that a greater screwing torque must be applied to overcome the resistances and hence probably break the shank <NUM> off. Moreover, the screw-in process of the shank <NUM> driven into the concrete structure <NUM> in the beginning cannot be stabilized by the added second thread <NUM>. Because there is only one contact point between the hole wall and the second thread <NUM> on any cross section of the shank <NUM>, the shank <NUM> newly driven into the concrete structure <NUM> is still shaken such that the screw <NUM> tends to deviate from the drive direction. In addition, since the second thread <NUM> has auxiliary function to aid cutting but the debris cut off by the first thread <NUM> cannot be dispersed efficiently by the settlement of the second thread <NUM> and will keep accumulating between the threads and the hole wall, the hole wall inside the hole <NUM> on retrieval of the screw <NUM> is damaged by interactive frictions between the first and second threads <NUM>, <NUM> and concrete debris directly or indirectly and fails to support pull-out strength through which the screw <NUM> is driven into the hole <NUM> again.

Documents <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT> are documents reflecting the relevant background art, wherein <CIT> describes a screw having a cutting thread with a plurality of spiral cutting edges so as to increase the cutting effect. These documents do, however, not provide a satisfactory solution of the above mentioned problems.

Thus, an objective of the present invention is to provide a concrete screw according to claim <NUM> which is able to efficiently crush concrete debris and evenly disperse concrete debris around a shank of the concrete screw for accelerative movement of the concrete screw which is driven into a concrete structure, kept unshaken in the beginning, not deviated from a drive direction, and fastened stably and robustly.

To achieve this and other objectives, a screw of the present invention is adapted to be driven into a hole with a hole diameter in a concrete structure. The screw, according to claim <NUM>, includes a head, a shank extending from the head and defining a longitudinal axis, a thread, and a plurality of oblique ribs. The shank includes a front segment and a rear segment spaced from the front segment along the longitudinal axis and located between the front segment and the head. The shank has a shank diameter less than the hole diameter of the hole. The front segment includes a front end having a flat end face. The thread is spirally formed on the shank and extends to the rear segment from the front segment. The thread includes a plurality of thread convolutions and has a major diameter greater than the hole diameter. At least three oblique ribs are formed on an outer periphery of the shank and located between any two adjacent thread convolutions of the thread at the rear segment and the front segment of the shank. The at least three oblique ribs are spaced around the shank circumferentially such that the front segment and the rear section of the shank respectively have at least three oblique ribs at cross-section. Each oblique rib has a trapezoid cross section with two lateral sides and a planar top face interconnecting the two lateral sides, and the planar top faces of the plurality of oblique ribs define the rib top diameter. The planar top faces of the at least three oblique ribs defines a rib top diameter less than the major diameter of the thread convolutions and slightly less than or equal to the hole diameter. The plurality of oblique ribs can quickly crush and disperse concrete debris which comes out of a hole wall of the hole cut by the thread when the concrete screw is driven into the hole.

In a form, each oblique rib spirally extends along the longitudinal axis.

In a preferred form, three oblique ribs are designed between two adjacent thread convolutions at the front segment of the shank and spaced <NUM> degrees apart around the shank circumferentially, such that the front section of the shank has the three oblique ribs at cross-section.

In a preferred form, a plurality of notches is designed in the thread convolutions at the front segment of the shank for development of a plurality of teeth on the thread at the front segment.

The present invention will become clearer in light of the following detailed description of illustrative embodiments of this invention described in connection with the drawings.

The illustrative embodiment may best be described by reference to the accompanying drawings where:.

A concrete screw <NUM> according to a first embodiment is shown in <FIG> of the drawings and generally includes a head <NUM>, a shank <NUM> extending from the head <NUM>, and a thread <NUM> formed on the shank <NUM>. The shank <NUM> defining a longitudinal axis X includes a front segment <NUM> and a rear segment <NUM> spaced from the front segment <NUM> along the longitudinal axis X. The rear segment <NUM> is located between the front segment <NUM> and the head <NUM>. The shank <NUM> has a shank diameter D. The front segment <NUM> and the rear segment <NUM> may have an identical shank diameter or distinct shank diameters, respectively. The head <NUM> is used to provide a torque tool (not shown in figures) in combination to apply rotational torque such that the shank <NUM> can be screwed inside a concrete structure <NUM>.

In general, a hole <NUM> should be drilled inside the concrete structure <NUM> with an electric drill (not shown in figures) first for accommodating the shank <NUM> of the screw <NUM>. The hole <NUM> has a hole diameter H which is greater than the shank diameter D of the shank <NUM>. The thread <NUM> is spirally formed on an outer periphery of the shank <NUM> and extends from the front segment <NUM> toward the head <NUM>. In this embodiment, the thread <NUM> extends to the rear segment <NUM> from a front end <NUM> of the front segment <NUM>. The thread <NUM> includes a plurality of thread convolutions <NUM> and has a major diameter C that is greater than both the shank diameter D and the hole diameter H.

The screw <NUM> further includes a plurality of oblique ribs <NUM> formed on the outer periphery of the shank <NUM> and spaced around the shank <NUM> circumferentially. Each oblique rib <NUM> is located between two adjacent thread convolutions <NUM> of the thread <NUM> and spirally extends along the longitudinal axis X. In this embodiment, the front segment <NUM> of the shank <NUM> is provided with the plurality of oblique ribs <NUM> with any two oblique ribs <NUM> parallel to and spaced from each other. Alternatively, the rear segment <NUM> of the shank <NUM> is also provided with a plurality of oblique ribs <NUM>. In this embodiment, three oblique ribs <NUM> are provided between any two adjacent thread convolutions <NUM> of the thread <NUM> at the front segment <NUM> and spaced <NUM> degrees apart around the shank <NUM> circumferentially. Accordingly, there are three oblique ribs <NUM> at any cross section in the front segment <NUM> of the shank <NUM>, and each oblique rib <NUM> has a trapezoid cross section with two lateral sides <NUM> and a planar top face <NUM> (see <FIG>). The plurality of oblique ribs <NUM> have rib tops through which a rib top diameter R is defined. The rib top diameter R is less than the major diameter C and slightly less than or equal to the hole diameter H, that is, not greater than the hole diameter H of the hole <NUM>. Furthermore, an upward extending direction of each oblique rib <NUM> is similar to an upward direction of the thread <NUM> extending toward the head <NUM> (upwardly and slantingly to the upper right). In this embodiment, an inclined angle formed by each oblique rib <NUM> extending toward the head <NUM> relative to a horizontal axis perpendicular to the longitudinal axis X is greater than that of the thread <NUM> extending toward the head <NUM>.

In practice, the front end <NUM> of the shank <NUM> is inserted into the hole <NUM> in the concrete structure <NUM> as shown in <FIG>. The major diameter of the thread convolutions <NUM> at the front end <NUM> is slightly less than the major diameter C of the thread convolutions <NUM> at the rear segment <NUM> for a modest torsion applied on the screw <NUM> in the beginning. Then, the head <NUM> is driven to rotate by a torque tool (not shown in figures), and the shank <NUM> is smoothly screwed into the concrete structure <NUM> when concrete debris coming out of the hole wall of the hole <NUM> cut by the thread <NUM> is crushed by the oblique ribs <NUM> and dispersed around the shank <NUM> evenly. The oblique ribs <NUM> act as the stirrer and grinder that distribute the debris on the shank <NUM> and even mill the debris into smaller pieces. This will mitigate the friction resistance in the whole screw-in process. Therefore, a structure component <NUM> can be fixed on the concrete structure <NUM>. Because the separate oblique ribs <NUM> circumferentially arranged on the shank <NUM> form the rib top diameter R slightly less than or equal to the hole diameter H of the hole <NUM>, there should be three contact planes formed between the hole wall and the three oblique ribs <NUM> at any cross section of the front segment <NUM> of the shank <NUM> which is being driven into the hole <NUM> in the beginning (see <FIG>). Accordingly, the shank <NUM> driven into the concrete structure <NUM> is kept unshaken at first and not deviated inside the concrete structure <NUM> deeply.

The screw <NUM> of the present invention offers benefits over the concrete screw <NUM> in <FIG> as follows:.

<FIG> illustrates the screw <NUM> in a second embodiment. In this embodiment, a taper portion <NUM> extends from the front end <NUM> of the front segment <NUM>, so that the front segment <NUM> of the shank <NUM> can be aligned with the hole <NUM> smoothly.

<FIG> and <FIG> illustrate the screw <NUM> in a third embodiment. In this embodiment, a plurality of notches <NUM> is designed in the thread convolutions <NUM> at the front segment <NUM> for development of a plurality of teeth <NUM> on the thread <NUM> at the front segment <NUM>. When the front segment <NUM> is driven into the hole <NUM> in the beginning, the teeth <NUM> support the plurality of oblique ribs <NUM> to expel concrete debris which is accommodated in the notches <NUM> for less friction on the shank <NUM> but higher speed of the screw <NUM> moved inside the concrete structure <NUM>.

<FIG> illustrates the screw <NUM> in an embodiment of the present invention. In this embodiment, the plurality of oblique ribs <NUM> provided on the shank <NUM> extends from the front segment <NUM> to the rear segment <NUM>, so that at least three separate oblique ribs <NUM> are designed between any two adjacent thread convolutions <NUM> at the rear segment <NUM> of the shank <NUM> for crushing more concrete debris effectively.

Claim 1:
A screw (<NUM>) adapted to be driven into a pre-drilled hole (<NUM>) having a hole diameter (H) in a concrete structure (<NUM>), with the screw (<NUM>) comprising:
a head (<NUM>);
a shank (<NUM>) extending from the head (<NUM>) and defining a longitudinal axis (X), with the shank (<NUM>) including a front segment (<NUM>) and a rear segment (<NUM>) spaced from the front segment (<NUM>) along the longitudinal axis (X) and located between the front segment (<NUM>) and the head (<NUM>), with the shank (<NUM>) having a shank diameter (D) less than the hole diameter (H) of the hole (<NUM>), with the front segment (<NUM>) including a front end (<NUM>) having a flat end face; and
a thread (<NUM>) spirally formed on the shank (<NUM>) and extending to the rear segment (<NUM>) from the front segment (<NUM>) toward the head (<NUM>), with the thread (<NUM>) including a plurality of thread convolutions (<NUM>) and having a major diameter (C) greater than the hole diameter (H);
wherein at least three oblique ribs (<NUM>) are formed on an outer periphery of the shank (<NUM>) and located between any two adjacent thread convolutions (<NUM>) of the thread (<NUM>) at the rear segment (<NUM>) and also at the front segment (<NUM>) of the shank (<NUM>), wherein the at least three oblique ribs (<NUM>) are spaced around the shank <NUM> circumferentially such that the front segment (<NUM>) and the rear section (<NUM>) of the shank (<NUM>) respectively have at least three oblique ribs (<NUM>) at cross-section, wherein each oblique rib (<NUM>) has a trapezoid cross section with two lateral sides (<NUM>) and a planar top face (<NUM>) interconnecting the two lateral sides (<NUM>), with the planar top faces (<NUM>) of the at least three oblique ribs (<NUM>) defining a rib top diameter (R) less than the major diameter (C) of the thread convolutions (<NUM>) and slightly less than or equal to the hole diameter (H), wherein the at least oblique ribs (<NUM>) can crush and disperse concrete debris which comes out of a hole wall of the pre-drilled hole (<NUM>) cut by the thread (<NUM>) when the screw (<NUM>) is driven into the pre-drilled hole (<NUM>).