The present invention relates to a screw for fixing gypsum plasterboards to dry-wall support structures of different materials. Hence the invention is related to the technical field of fixing planar materials as dry-wall panels to support structures in buildings and structures. Fixing gypsum wallboards to support structures in buildings presents problems since the adequately and properly fixing is required for different materials for the support structure. Often in buildings there are different types of the support structure such as metal profiles or wooden studs what requires the use of different types of screws. Different types of screws mean that builders need to carry more than one type of screw causing problems with transport to the site and cartage around a building site.

This also can mean that it can be difficult to carry, enough screws to do a job, requiring more frequent trips to replenish screw supplies. Other problems include the need to provide more storage space for less of one type of screw, to cover more than one type of screws as required. Additionally, having different screws for different uses can cause the use of wrong screws to be used for a particular type of support structures. Inappropriate use of screws can then cause structural problems or problems in the wall surface finishing. Screws for fastening a gypsum wallboard to support structures made of different materials are known. Such screws usually comprising a shank portion having a wood screw thread capable of fixing the gypsum wallboard to a support structure made of a wooden material and a metal screw thread capable of fixing the gypsum wallboard to a support structure made of a metal material.

In use of screws capable of being fastened to support structures of different materials problems arise from the occurrence of different tensioning forces due to the fastening to support structures of different materials. Variations in tensioning forces cause over tightening or under tightening of the gypsum wallboard to the support structure. If over tightened, the head portion of the screw can pierce, sever or tear the paper layer of the gypsum plasterboard, requiring greater finishing than more shallow fixed head portions. Destroying the paper leads to structural problems, since even piercing the paper layer weakens the structural integrity of the gypsum plasterboard. This can result in a loss of the structural integrity of dry-walls and to a loss of strength with which the gypsum plasterboard is mounted to the support structure.

Therefore, it is an object of the invention to provide a screw for mounting plasterboards which overcomes or at least greatly reduces the disadvantages known from the prior art, that is to say a screw to be used in different support structures which provides a sufficient fit of the screw head under differing tension forces caused by the fastening to different types of the support structure materials.

This object is achieved by the screw as it is characterized by the features of the independent claim. Advantageous embodiments become evident from the features of the dependent claims.

According the invention, there is provided a screw for fastening a gypsum wallboard to support structures made of different materials. The screw comprises a shank portion having a wood screw thread capable of fixing the gypsum wallboard to a support structure made of a wooden material and a metal screw thread capable of fixing the gypsum wallboard to a support structure made of a metal material. The screw further comprises a head portion shaped larger in diameter than the diameter of the shank portion so that the shank portion joins the head portion by a curved circumferential wall. The curved circumferential wall has a curvature comprising a step so as to form a circumferentially running edge. This allows for the head portion to fit to the fastened gypsum wallboard independent from the support structure material for different tensioning force.

Hence, the invention provides a head portion having a stepped shape, the step forms an edge to allow for fixedly arrange the head portion at the gypsum plasterboard which provides a sufficient fit of the screw head under differing tension forces caused by the fastening to wood or metal as support structure materials. Hence, the head portion engages in the paper layer without break off the paper layer when the screw is inserted in different materials.

According to an aspect of the invention, the circumferentially running edge has a square curvature. The outwardly extending variant allows for a good grip because of the formed square edge extends outwardly and cuts into the paper layer. Alternatively the circumferentially running edge has a rounded curvature. The rounded curvature might be concavely or convexly formed and is advantageous for paper layers of low strength, i.e. when of a small paper thickness.

In one aspect, the wood screw thread and the metal screw thread begin at a spaced position from the curved circumferential wall joining the head portion and the shank portion. Alternatively, the wood screw thread and the metal screw thread begin at the curved circumferential wall joining the head portion and the shank portion.

According to a further aspect, a portion of the wood screw thread is oriented to provide a reverse thread to cause the gypsum material to be expelled out of the hole while the screw is pulling into the support construction. Preferably, the reverse thread has a length of about 1.2 cm. This length is ideal for the gypsum plasterboard of a thickness of about 1.2 cm, wherein in about includes a length of 1 mm plus and minus.

Advantageously, the head portion comprises a cylindrically shaped portion adjacent the step of the curved circumferential wall to provide a circumferentially running supporting surface at the side towards the shaft portion. The cylindrically shaped portion has a similar contact improving effect compared to the circumferentially running edge at the curved circumferential wall.

Preferably, the screw comprises a further curved circumferential wall arranged in between of the cylindrically shaped portion and the step of the curved circumferential wall, wherein the further curved circumferential wall has a linear shape or a curved shape. Each shape allows for providing a fit of different strength at the same applied force, i.e. for a specific screw position.

In another aspect, the wood screw thread is higher than the metal screw thread. The wood screw thread being twice the height of the metal screw thread allows for the screw to be pulled into a wooden stud without any weakening of the fastening strength due to the presence of the metal screw thread.

Preferably, the wood screw thread is triangular shaped in cross section. The triangular shape provides a sharp outer edge for cutting into the wooden stud. According to another aspect, the width of the cross section of the wood screw thread is smaller compared to the width of the cross section of the metal screw thread.

Further advantageous aspects of the screw according to the invention become evident by the following detailed description of the specific embodiments with the aid of the drawings, in which: Fig. 1 is a side view of a screw according to a first embodiment of the screw according to the invention;

Fig. 2 is a side view of a screw according to a second embodiment of the screw according to the invention;

Figs. 3-5 are side views of a head portion of a screw according to the

invention;

Fig. 6 is a top view of a head portion of a screw according to the

invention;

Fig. 1 shows a side view of the screw of the present invention in accordance with a first preferred embodiment. Without limitation to this specific embodiment, the screw 1 can be used for attaching a gypsum wallboard (not shown) to a support structure (not shown) known from dry wall construction. That gypsum wallboard can comprise at least one core layer of gypsum plaster encased in an outer (frontside and backside) paper layer. The support structure can be a timber or metal frame like structure oriented in any suitable orientation. The current example will cover a dry wall support structure comprising a support member made up of interconnected elongate members. For a wall support structure, the elongate members can be stud members shaped with a massive cross section being made of wood or with hollow channel like cross sections such as profiles being made of metal or steel. As shown in figure 1 screw 1 includes an elongate body with ends comprising a head portion 12 at one end, a shank portion 13 at an opposite or distal end to the head portion 12. In this example, the end of the shank portion 13 opposite to the head portion 12 is simply a pointed shaped end. Shank portion 13 includes an elongate cylindrical body with shank portion ends. The body formed of shank portion 13 has a curved outer surface being provided with at least two spaced threads of a different pitch. A wooden screw thread 20 and a metal screw thread 21 winding in alternating sequence for threads 20 and 21 around in parallel relationship along the curved outer surface to cause the screw when being turned to move in a forward direction into and through the paper layers and then into the support structure. Threads 20 and 21 can be formed as continuous or broken spiral-like or helical protruding designs with there being a difference in height whereby wooden screw thread 20 can be called a high thread of a larger depth dimension and metal screw thread 21 can be called low thread having a lower depth dimension normal to the longitudinal axis of the screw. Head portion 12 is adapted to allow a suitable driving means (not shown) to cause screw 1 to turn or rotate and be driven into whatever the screw 1 is to be fastened to for example the elongate members of the wall support structure to hold the plasterboard in place which might be of a different material according to the invention. Additionally head portion 12 is shaped to have a larger diameter than the shank portion 13 to keep the screw 1 from being driven deeper than the length of the screw and to provide a bearing surface. The screw comprises a curved circumferential wall 28 having a curvature comprising a step so as to form a circumferentially running edge 33. Circumferentially running edge 33 allows for the screw to be grippingly fastened to the gypsum wallboard independent from the tensioning force occurring due to the fastening to different support structure materials. In the present example, head portion 12 has a stepped shape, the step forming an edge to allow for fixedly arrange the head portion 12 at the gypsum plasterboard. This provides a sufficient fit of the screw under differing tension forces caused by the fastening to wood or metal as support structure materials. Thus, the head portion 12 can engage in the paper layer without break off the paper layer when the screw is inserted.

Fig. 2 illustrates a second embodiment of the invention, whereby in difference to the embodiment shown in Fig. 1 , additionally a portion of the wood screw thread 20 and the metal screw thread 21 is oriented to provide a reverse thread 22. Reverse thread 22 causes the gypsum material to be expelled out of the hole while the screw is pulled into the support construction. In the shown example, reverse thread 22 has a length of 1.2 cm.

Alternative head portions 13 are disclosed in Figs. 3-5. In all variants, the shank portion 13 joins the head portion 12 by a curved circumferential wall 28. The curved circumferential wall 28 has a curvature comprising a step so as to form a circumferentially running edge 33. Running edge 33 has a square curvature. In all figures, the head portion 12 comprises a cylindrically shaped portion 121 adjacent to the edge 33 of the curved circumferential wall 28 to provide a further circumferentially running supporting surface 34. The circumferentially running supporting surface 34 additionally allows the screw to be grippingly fasted to the gypsum wallboard independent from the tensioning force for different support structure materials.

As can be seen in Fig. 4, to facilitate turning or driving the screw, head portion 12 also has at least one shaped recess 37 extending from end face 26 having a certain depth 38. For example, recess 37 can be shaped as a 'philips' or 'posi-drive', square or wedge shape etc. for any type of driver or implement such as a screwdriver which can be manually or mechanically operated.

The invention has been described with particular reference to certain embodiments thereof. It will be understood that various modifications can be made to the above- mentioned embodiment without departing from the ambit of the invention. The skilled reader will also understand the concept of what is meant by purposive construction.