TECHNICAL FIELD

The present invention relates to a concrete screw adapted for mounting building elements to concrete. TECHNICAL BACKGROUND

When mounting building elements such as railing, pipes and other support structures to concrete foundations metal expanders or special concrete screw may be used. As the concrete is a very hard material a regular screw, such as a wood screw cannot be used as it cannot cut into concrete like it can cut into wood. Usually boreholes are pre-drilled into the concrete, adapted in size to have only the threads of the concrete screws cut into the surrounding concrete. Said pre-drilled boreholes needs to be of the correct size to ensure a secure anchoring in the concrete and that the concrete screw can be inserted into the material without the need to use too much force. There are many problems to overcome when mounting building elements to concrete such as hitting rebars, having too tight fitting pre-drilled boreholes for the screw or having the pre-drilled boreholes clogged up by too much debris from the pre-drilling.

On a building site of a larger scale there might be hundreds or even thousands of boreholes to pre-drill for future mounting of building elements to concrete. This can create a situation where the person drilling does not want to spend extra time drilling each borehole more than absolutely necessary. If the pre-drilled boreholes are too tight for the concrete screws or if there is too much debris from the drilling left in the boreholes which creates the same effect, the mounting of the concrete screws could prove to be difficult or even unsecure as the screws might not be possible to insert fully into the boreholes. If the person performing the mounting tries to overcome this problem by applying too much force to the screw, it can possibly degenerate the material properties of the screw, making the mounting potentially dangerous.

If the pre-drilled boreholes are not a perfect fit for the concrete screw, the problems will be first noticed and of greatest impact at the tip of the screws hitting the bottom of the borehole, this is especially noticeable when the boreholes are drilled downwards as the risk of having too much debris from the drilling left at the bottom of the borehole. Tightly packed concrete debris can act in the same way as a too shallow drilled borehole. A common way of dealing with the concrete debris is to apply pressurized air or a vacuum cleaner or similar to the borehole to make sure the debris is removed. This is however time consuming and therefore a costly process. There are also several concrete screws which have cutting tip portions adapted for widening a borehole on the market. With such a cutting tip portion a too tight borehole becomes less of a problem as the cutting tip portion will widen the borehole automatically if the fit between the screw and the borehole is too tight initially. This also applies to the problem of existing debris, if the debris is spread on the walls of the borehole. WO2014131615 A1 discloses a concrete screw comprising at least one cut-out recess for widening a borehole. Said recess extending, at least in sections, inside the thread base without interrupting the threaded coil. This concrete screw can therefore cut its way deeper into the concrete foundation if the pre-drilled borehole should be too shallow.

A problem with this type of concrete screws however, can be that a widening of the borehole might not always be acceptable as it could risk weakening the concrete structure. As the widening of the borehole happens as the concrete screw is mounted into its final position inspection of the state of the borehole is impossible as the concrete screw is filling up the borehole. Removing the screw for inspection before re-mounting it again would mean adding an additional step to the mounting procedure which would be time consuming and therefore costly. Furthermore, a concrete screw of this type can widen a borehole but it cannot be used in a too shallow borehole to automatically make the borehole deeper, so the depth of the borehole and the existence of potential debris at the bottom of the borehole is still of importance, and may be a problem if the fit is not correct for the applied screw.

Therefore there is a need to come up with an improved concrete screw for mounting building elements to concrete which eliminates drawbacks with prior art. Further, there is a need for a concrete screw which is easy to use without adding additional steps to the mounting procedure. There is also a need for a concrete screw which will achieve reproducible and good results even if the pre-drilled borehole is not fully cleaned from potential debris.

SUMMARY OF THE INVENTION A concrete screw according to example embodiments of the invention is intended for pre- drilled boreholes rather than being screwed directly into a material. Thus, a concrete screw for pre-drilled boreholes are generally distinguished from screws intended for being advanced into a material by itself, i.e. without pre-drilling a hole for receiving the screw.

The object of the present invention relates to a concrete screw as defined in the preamble of claim 1 , and further defined by the features of the characterizing part of claim 1. The purpose of the present invention relates to a concrete screw adapted to be able to be inserted into a borehole where there is debris present after pre-drilling said borehole without being forced to drill the borehole deeper than necessary. The purpose of the present invention is further to create a space for said debris without lowering the grip between the concrete screw and the pre-drilled borehole. Accordingly, the concrete screw is particularly useful for debris already existing in pre-drilled holes, i.e. debris located directly underneath a tip portion of the concrete screw.

The concrete screw according to example embodiments is intended for pre-drilled bores. The concrete screw comprises; a head portion comprising a head member adapted to fit to a mounting tool, a first shaft, substantially uniformly rod shaped having an essentially uniform first diameter, and a second shaft, substantially uniformly rod shaped having an essentially uniform second diameter. The concrete screw further comprises a front section comprising an outer surface and a front end, and threads having an essentially uniform third outer diameter, wherein the threads are arranged on the second shaft and the front section. The concrete screw is characterized in that the outer surface of the front section has a fourth diameter, smaller than the first, second and third diameters, and wherein the threads keep their third outer diameter on the smaller fourth diameter of the front section.

This has the advantage that debris remaining in a borehole after pre-drilling of said borehole for the insertion of the concrete screw does not have to be removed before the insertion of the concrete screw. This is due to the fourth diameter of the front section being smaller than the diameter of the first shaft, second shaft and threads respectively. This smaller fourth diameter creates a space for the debris to fill up. The grip of the concrete screw however is not lowered due to the smaller fourth diameter as the threads keep their outer diameter and thus their grip to the borehole. Further, when getting into contact with the threads of the front section potential debris will move along the threads upwards in the space between the concrete screw and the borehole.

According to one aspect of the invention, the front section is formed as a substantially uniformly shaped rod with the fourth diameter being an essentially uniform diameter. This has the advantage that the concrete screw will be robust and easy to manufacture and have a large space for debris to fill up. The substantially uniformly shaped rod will give an equal support to the threads on the front section making it a mechanically strong device.

According to another aspect of the invention, the front section is formed as a truncated cone with the fourth diameter of the front section being a decreasing diameter, wherein said fourth diameter decreases in a direction towards the front end.

This has the advantage that the concrete screw will have a large space for the debris to fill up and that the debris can easily be relocated within that space due to the truncated cone shape. When getting into contact with the threads of the front section the debris will move along the threads upwards in the space between the concrete screw and the borehole. The truncated cone shape creates a space with a larger volume close to the bottom of the borehole which will lower the amount of force needed to relocate the debris upwards on the threads as there will be less pressure due to tightly packed debris at the bottom of the borehole. According to another aspect of the invention, the outer surface of the front section comprises at least one recess adapted for moving debris in a borehole when the screw is being inserted. Hereby, said debris is moved in a direction from the front side towards the head portion of the concrete screw.

This has the advantage that the risk of packing the debris in the borehole tight against the bottom of the borehole will be lower as the at least one recess will increase the space in which the debris can be relocated and fill up. The at least one recess will also help moving the debris along the length of the concrete screw to avoid pushing and compacting it between the front end of the concrete screw and the bottom of the borehole. To this end, the front section of the screw including the recess will dig into the debris at the bottom of a pre- drilled hole and move it away from said bottom by means of the at least one recess. Thus, the need to clean a pre-drilled hole before inserting the concrete screw in said hole is removed.

According to yet another aspect of the invention, the at least one recess has a semi-circular surface, wherein the intersection of the semi-circular surface and the front end of the front section forms a sharp angle.

This has the advantage that recess will act like a vane and lift the debris from the bottom of the borehole in an efficient way. The sharp angle of the intersection of the semi-circular front end of the front section will create a thin first contact edge towards the debris lifting it from the bottom of the borehole as the concrete screw is rotated down in said borehole. A further advantage with having the recess in a semi-circular shape is that the recess will be easy and therefore cost efficient to manufacture as a grinding disc can simply be rotated against the concrete screw to achieve the desired shape. According to further aspect of the invention, the at least one recess has a slanting surface, wherein the intersection of the slanting surface and the front end of the front section forms a sharp angle.

This has the advantage that recess will act like a vane and lift the debris from the bottom of the borehole in an efficient way. The sharp angle of the intersection of the slanting surface and the front end of the front section will create a thin first contact edge towards the debris lifting it from the bottom of the borehole as the concrete screw is rotated down in said borehole. A further advantage with the recess having a slanting surface is that debris can easily move up on the slope of the recess and be transported to the adjacent parts of the threads and continue to be moved away from the bottom of the borehole by said threads in an efficient manner.

According to yet a further aspect of the invention, the length of the front section is in the range of from about 12% up to about 30% of the length of the threaded parts of the concrete screw.

This has the advantage that the sufficiently large portion of the concrete screw comprises the smaller diameter of the front section which creates an equally sufficiently large space for concrete debris to fill up when the concrete screw is mounted into the borehole.

According to one aspect of the invention, the length of the front section is in the range of from about 20% up to about 25% of the length of the threaded parts of the concrete screw.

This has the advantage that the sufficiently large portion of the concrete screw comprises the smaller diameter of the front section which creates an equally sufficiently large space for concrete debris to fill up when the concrete screw is mounted into the borehole.

BRIEF DESCRIPTION OF FIGURES

Preferred embodiments of the invention will be further described with reference to the accompanying drawings. Figure 1 a shows a perspective view of a concrete screw according to a first embodiment of the present invention.

Figure 1 b shows a perspective view of a concrete screw according to a second embodiment of the present invention. Figure 2 shows a side view of a concrete screw according to a third embodiment of the present invention.

Figure 3 shows a side view of a concrete screw according to a fourth embodiment of the present invention.

Figure 4 shows a side view of the front section of a concrete screw according to the first embodiment of the present invention.

Figure 5a-c shows different side views of the front section of a concrete screw according to the second embodiment of the present invention.

Figure 6 shows a side view of a concrete screw according to a fifth embodiment of the present invention. DETAILED DESCRIPTIONS OF THE INVENTION

Herein embodiments of the invention will be described in detail with reference to the appended drawings. As will be perceived the invention can be modified in various ways without derailing from the scope of the claims. Thus the drawings should be viewed upon as illustrative in their nature and not restrictive. All drawings may not be made to scale. Figure 1 a shows a perspective view of a concrete screw 1 according to a first embodiment of the present invention. The concrete screw is intended for pre-drilled bores. The concrete screw 1 is adapted for mounting building elements to concrete objects or foundations without the need to fully clean out potential concrete debris from the pre-drilled boreholes in said concrete objects or foundations. The concrete screw 1 is further adapted to be able to be mounted in said non-cleaned out concrete borehole and still achieve a secure anchoring of the building elements being mounted. The concrete screw 1 comprises; a head portion 3 comprising a head member 5 adapted to fit to a mounting tool, a first shaft 7, substantially uniformly rod shaped having an essentially uniform first diameter d1 , and a second shaft 9, substantially uniformly rod shaped having an essentially uniform second diameter d2. The concrete screw 1 further comprises a front section 11 comprising an outer surface 13 and a front end 15, and threads 17 having an essentially uniform third outer diameter d3, wherein the threads 17 are arranged on the second shaft 9 and the front section 1 1. The outer surface 13 of the front section 11 has a fourth diameter d4, smaller than the first, second and third diameters d1 , d2, d3, and the threads 17 keep their third outer diameter d3 on the smaller fourth diameter d4 of the front section 1 1. In this embodiment of the invention the outer surface 13 of the front section 11 further comprises a recess 19 adapted for moving debris in a borehole when the screw 1 is being inserted, whereby said debris is moved in an initial direction from the front end 15 towards the head portion 3 of the concrete screw 1.

The recess 19 of this embodiment has a semi-circular surface 21 , wherein the intersection of the semi-circular surface 21 and the front end 15 of the front section 1 1 forms a sharp angle. This intersection of the semi-circular surface 21 and the front end 15 of the front section 11 forming a sharp angle will act as a vane when the front end 15 of the concrete screw 1 engages the potential debris at the bottom of the borehole in which the concrete screw 1 is being mounted into. The sharp angle of the semi-circular surface 21 is achieved by having the centre of the perceived circle from which the semi-circular surface 21 is formed, by a grinding disc or similar, being located towards the head portion 3 of the concrete screw 1 in regards to the front end 15 of the concrete screw, but not further away from the front end 15 than the radius of the perceived circle from which the semi-circular surface 21 of the recess 19 is formed (see figure 4 and the accompanying description for more detail). The diameter reduction of the front section 1 1 , in relation to the first and second shafts 7, 9 of the concrete screw 1 creates a space for the concrete debris of the borehole to fill up and the suitably semi-circular surface 21 of the front section 11 assists in relocating said debris from the front end 15 of the concrete screw 1 to said space around the front section 11. The space for the debris is in other words the volume between the sides of the borehole in which the concrete screw is mounted and the outer surface 13 of the front section 11 of the concrete screw 1. As the debris in the borehole can be relocated to said volume there is no need to clean out said debris and there is also no need to pre-drill the borehole deeper than necessary in relation to the length of the threads 17 of the concrete screw 1 , which threads 17 are the dominating factor for how much load the concrete screw 1 can hold when mounted. The threads 17 of the front section 1 1 keeping their outer third diameter d3 even though the fourth diameter d4 of the front section 1 1 is smaller than the threaded second shaft 9 of the concrete screw 1 give the concrete screw 1 the same load bearing properties as if there would not be any reduction in diameter along the concrete screw 1. These combined features gives a concrete screw 1 with good load bearing properties, whilst typically eliminating the time consuming job of cleaning out debris in the boreholes before mounting the screw 1. The pre-drilling process is also made more efficient as there is no need to drill deeper than necessary to create space for debris as an alternative method of not cleaning out said debris. The embodiment described here may have more than one recess 19; two recesses 19 may very well be arranged on opposite sides of the concrete screw 1 to increase the debris moving effect of the invention. The recess may also have other shapes, e.g. as described in relation to fig. 1 b.

Figure 1 b shows a perspective view of a concrete screw according to a second embodiment of the present invention. This second embodiment of the invention is similar to the first embodiment depicted in figure 1 except for the shape of the recess 19. In this embodiment of the invention, the recess 19 has a slanting surface 23, wherein the intersection of the slanting surface 23 and the front end 15 of the front section 1 1 forms a sharp angle. This slanting surface 23 which also intersects the front end 15 of the concrete screw 1 will act as a vane in the same way as the semi-circular surface 21 of the recess 19 of the first embodiment. However, the debris will in this embodiment be pushed upwards over the slanting surface 23 and onto the threads 17 behind the slanting surface 23 when the sharp angle of the recess 19 engages said debris. The width of the recess may vary but the slanting surface 23 of the recess will always intersect with the front end 15 of the concrete screw 1 to achieve the desired effect of moving the debris away from the bottom of the borehole. Preferably the width of the recess 19 will not be wider than the distance between the threads 17 on the same side of the concrete screw 1 as to keep the load bearing properties of the screw 1.

In both the first and second embodiments depicted in figures 1 a and 1 b, respectively, the length of the front section is about 20% of the length of the threaded parts of the concrete screw 1 , which threaded parts are the front section 11 and the second shaft 9 together. The length of the first shaft 7 is based on a preferred thickness of a building element that will be mounted to the concrete and is usually not inserted into the borehole. The threaded parts of the concrete screw 1 are therefore the factor which decides the load bearing capabilities of the concrete screw 1. The length of the front section 11 may vary in the range of from about 12% up to about 30% of the length of the threaded parts of the concrete screw 1 , and more preferably in the range of from about 20% up to about 25% of the length of the threaded parts of the concrete screw 1. This is a large enough portion to achieve the desired space for the debris in the borehole but will not weaken the mechanical properties of the concrete screw 1 as a whole in a significant way. The recesses 19 depicted in figure 1 a and 1 b both intersects with the front end 15 of the concrete screw 1. This results in that the recess 19 interacts with debris being located under the screw 1. This contributes to ensure that the recess 19 can act as a vane which relocates debris. This typically holds true regardless of the shape of the recess.

Figure 2 shows a side view of a concrete screw 1 according to a third embodiment of the present invention. In this embodiment of the invention the front section 11 is formed as a substantially uniformly shaped rod. The uniformly shaped rod has a fourth diameter d4 being an essentially uniform diameter. In this view it is easily seen that this fourth diameter d4 of the front section 1 1 is noticeably smaller than the first and second shaft 7, 9 of the concrete screw 1 , creating a space for relocated debris to fill up as the screw is inserted into a borehole. The threads 17 of the concrete screw 1 , arranged on the second shaft 9 and the front section 11 have essentially the same outer diameter d3 along the length of the screw 1. However, the end part of the threads 17 arranged at the intersection of the outer surface 13 of the front section 11 and the front end 15 of the front section 13 have a diminishing geometry in width and thickness as the threads 17 elongates towards the front end 15 of the concrete screw 1. This diminishing volume due to lesser thickness and width only occurs in the range from about 40% up to about 80% of a total turn around the perimeter of the concrete screw 1. The threads 17 of the concrete screw 1 having essentially the same outer diameter d3 along the threaded regions of the screw 1 creates a longer active load bearing length than if the threads 17 would extend equally in a radially direction from the different sized diameters d2, d4 of the different parts of the screw 1. This results in a concrete screw 1 with space for debris but without lowering the load bearing properties of the screw 1.

Figure 3 shows a side view of a concrete screw 1 according to a fourth embodiment of the present invention. In this embodiment of the invention the front section 11 is formed as a truncated cone with the fourth diameter d4 of the front section 11 being a decreasing diameter. The fourth diameter d4 decreases in a direction towards the front end 15. This embodiment of the invention is similar to the embodiment of the invention depicted in figure 2 except that the front section 1 1 is formed in the shape of a truncated cone instead of a rod. This creates a larger space for debris to fill up and also decreases the area of the front end 15 of the concrete screw 1. The reduction of the area of the front end 15 also lowers the risk of debris which is not moved from underneath the concrete screw 1 when it is being inserted to get stuck and in the same process get compacted there in between.

Figure 4 shows a side view of the front section 11 of a concrete screw 1 according to the first embodiment of the present invention. The characteristics and functionality of this first embodiment are the same as described in the description accompanying figure 1a.

However, in this view of the first embodiment it is easier to see the semi-circular shape of the recess 19 and the width of the second diameter d2 of the second shaft 9, the third outer diameter d3 of the threads 17 and the fourth diameter d4 of the front section 11 of the concrete screw 1. The sharp angle a of the intersection of the semi-circular surface 21 and the front end 15 of the screw 1 is also easily seen in this side view of the front section 11 of the first embodiment of the invention. This angle a may be altered by changing the radius R of the semi-circular surface 21 of the recess 19 or moving the centre C of the circle from which the semi-circular surface 21 is obtained along the length of the screw 1. To achieve an intersection between the semi-circular surface 21 of the recess 19 and the front end 15 of the front section 1 1 a distance D between the front end 15 and the centre C of the circle from which the semi-circular surface 21 is obtained must be the same as the radius R of said circle or shorter. This distance D and/or radius may be altered within the scope of the invention to achieve a concrete screw 1 with altered properties in regards to the angle a of the intersection of the semi-circular surface 21 of the recess 19 and the front end 15 and the mechanical properties of the concrete screw 1. The intersection of the semi-circular recess 21 and the front end 15 results in that the recess 21 interacts with debris being located under the screw 1. This ensures that the recess 19 can act as a vane which relocates debris.

Figure 5a-c show rotationally different side views of the front section 11 of a concrete screw 1 according to the second embodiment of the present invention. The characteristics of this second embodiment are the same as described in the description accompanying figure 1 b. However, in these views of the second embodiment the shape of the recess 19 and the slanting surface 23 of said recess 19 are shown in more close-up detail. The slanting surface 23 of the recess 19 and the sharp angle a' of the intersection of said surface 23 and the front end 15 of the front section 1 1 is clearly visible and the slanting surface 23 acting as a vane between the lower threads 17 when the concrete screw 1 is rotated in its insertion rotation can easily be understood viewing the figures 5a-c in that order. Figure 6 shows a side view of a concrete screw according to a fifth embodiment of the present invention. The characteristics and functionality of this embodiment are the same as described in the description accompanying figure 2, but with an added feature of a plurality of deformation indicators 25 arranged on the periphery of the first shaft of the concrete screw. The deformation indicators 25 extend in an essentially longitudinal direction along the first shaft 7 of the concrete screw 1. This embodiment is, in addition to the non-need for removing debris in boreholes before mounting a concrete screw in said borehole according to the above mentioned embodiments, adapted to be re-used in multiple mountings of building elements without the risk of using a concrete screw 1 with degenerated mechanical properties. If the concrete screw 1 is new and no force has been applied to said screw 1 then the direction of the deformation indicators 25 will be parallel with the outer periphery of the first shaft 7. If however the concrete screw 1 has been used in a previous mounting procedure where it has been exposed to a momentum/torque, large enough for the material of the concrete screw 1 to have been plastically deformed, the direction of the deformation indicator 25 would be non-parallel in regards to the outer periphery of the first shaft 7 due to the mechanical deformation. Depending on the amount of deformation the direction and distribution of the deformation indicator 25 would be slanting or twisted in appearance when comparing it with the outer periphery of the first shaft 7, giving a clear and efficient indication of mechanical deformation of the material of the concrete screw 1. A user would therefore see and know that the concrete screw 1 has been mechanically deformed and that it would not be able to hold the same amount of load as before the deformation. The concrete screw 1 can then be discarded properly and a new screw 1 should be used in its place. The deformation indicators 25 will hence give a clear visual cue regarding the mechanical properties of the concrete screw 1. The deformation indicators 25 may be provided as a plurality as described above but other variations are also possible. A single deformation indicator 25, or two deformation indicators 25 arranged in a pair, or a plurality or pairs of deformation indicators 25 may also be used. The deformation indicators 25 may be formed as projection on the periphery of the first shaft 7 of the concrete screw 1 , or be formed as recesses, or a combination of both. The projections and recesses may have different shapes, such as triangular, cubical, polygonal, or rounded shapes. The deformation indicator or indicators 25 may also be formed by surface treatment methods, such as painting, applying a rotating wire brush, polishing, embossing or other.

The invention is not limited to the specific embodiments presented. Combinations of features between different embodiments are possible. Accordingly, the drawings and the description thereto are to be regarded as illustrative in nature, and not restrictive.