Abstract
A gradient insulation screw (1) for adjustable fastening of a roofing membrane (2) on a substrate, in particular a steel sheet (3), the gradient insulation screw (1) comprising a drilling tip (4) with a first direction of rotation; following the drilling tip (4), an assembly thread (7) with a second direction of rotation, which differs from the first direction of rotation; following the assembly thread (7), a first thread-free region (8); following the first thread-free region (8), an adjustment thread (9) with the first direction of rotation, the outer diameter of which is greater than the outer diameter of the assembly thread (7) and the drilling tip (4); and following the adjustment thread (9), a tool holder (10) as well as a system (11) for adjustable fastening of a roofing membrane (2) on a substrate with a gradient insulation screw (1) and a holding element (12) and a method for adjustable fastening of a roofing membrane (2) on a substrate using such a system (11).
Claims
1. A gradient insulation screw (1) for adjustable fastening of a roofing membrane (2) on a substrate, in particular a steel sheet (3), the gradient insulation screw (1) comprising: a drilling tip (4) with a first direction of rotation; following the drilling tip (4), an assembly thread (7) with a second direction of rotation, which differs from the first direction of rotation; following the assembly thread (7), a first thread-free region (8); following the first thread-free region (8), an adjustment thread (9) with the first direction of rotation, the outer diameter of which is greater than the outer diameters of the assembly thread (7) and the drilling tip (4); and following the adjustment thread (9), a tool holder (10).
2. The gradient insulation screw (1) according to claim 1, wherein a second thread-free region (4a) is arranged between the drilling tip (4) and the assembly thread (7).
3. The gradient insulation screw (1) according to claim 1, wherein a preassembly thread (5) with the first direction of rotation is arranged between the drilling tip (4) and the assembly thread (7).
4. The gradient insulation screw (1) according to claim 3, wherein a third thread-free region (6) is arranged between the preassembly thread (5) and the assembly thread (7).
5. The gradient insulation screw (1) according to claim 3, wherein the preassembly thread (5) and the assembly thread (7) have substantially the same outer diameter.
6. The gradient insulation screw (1) according to claim 3, wherein the preassembly thread (5) and the assembly thread (7) have substantially the same core diameter.
7. The gradient insulation screw (1) according to claim 4, wherein the third thread-free region (6) comprises a length in the longitudinal direction of the gradient insulation screw (1) which is greater than the thickness of the substrate.
8. The gradient insulation screw (1) according to claim 1, wherein the first thread-free region (8) comprises a length in the longitudinal direction of the gradient insulation screw (1) which is greater than the thickness of the substrate.
9. The gradient insulation screw (1) according to claim 1, wherein the first thread-free region (8) is followed by a thickening (8a), wherein the thickening (8a) has a diameter which is greater than the diameter of the first thread-free region (8).
10. A system (11) for adjustable fastening of a roofing membrane (2) on a substrate, in particular a steel sheet (3), consisting of a gradient insulation screw (1) according to claim 1 and a holding element (12), the holding element (12) comprising: a holding plate (13); and a hollow shaft (14), which follows the holding plate (13) and which is adapted such that the adjustment thread (9) of the gradient insulation screw (1) can engage in the hollow shaft (14).
11. The system (11) according to claim 10, wherein the inner diameter of the hollow shaft (14) of the holding element (12) is smaller than the outer diameter of the adjustment thread (9), but greater than the core diameter of the adjustment thread (9) of the gradient insulation screw (1).
12. The system (11) according to claim 10, wherein the inner diameter of the hollow shaft (14) of the holding element (12) is greater than the outer diameter of the assembly thread (7) of the gradient insulation screw (1).
13. The system (11) according to claim 10, wherein the gradient insulation screw (1) is made of a material which is harder than the material of the holding element (12).
14. The system (11) according to claim 13, wherein the gradient insulation screw (1) is made of metal and the holding element (12) is made of plastic.
15. A method for adjustable fastening of a roofing membrane (2) on a substrate, in particular a steel sheet (3) using a system (11) according to claim 10, the method comprising: pushing the drilling tip (4) of the gradient insulation screw (1) of the system (11) into the roofing membrane (2) in the direction of the substrate located underneath; screwing the drilling tip (4) of the gradient insulation screw (1) into the substrate in a first direction of rotation; screwing the assembly thread (7) of the gradient insulation screw (1) into the substrate in a second direction of rotation, which differs from the first direction of rotation, until the first thread-free region (8) of the gradient insulation screw (1) is located in the substrate; and rotating the gradient insulation screw (1) furthermore in the second direction of rotation until the holding plate (13) of the holding element (12) of the system (11) rests on the roofing membrane (2).
Description
[0051] The invention is now explained in more detail with reference to the attached drawings. This results in further details and features of the subject-matter of the invention. In the drawings:
[0052] FIGS. 1a to 1c are examples of a gradient insulation screw according to the invention with and without preassembly thread and thread-free region;
[0053] FIGS. 2a and 2b are a schematic side view or a schematic top view of a drilling tip of a gradient insulation screw according to the invention;
[0054] FIG. 3 is a vertical section through a holding element, which can be used together with the gradient insulation screws shown in FIG. 1 in a system according to the invention;
[0055] FIG. 4 is an example of a system according to the invention made of the holding element from FIG. 3 and the gradient insulation screw from FIG. 1B;
[0056] FIGS. 5a to 5d are schematic representations of the individual steps during the assembly of the system according to the invention from FIG. 4, also using the gradient insulation screw from FIG. 1B;
[0057] FIGS. 5e to 5h are schematic representations of the individual steps during the assembly of a system according to the invention consisting of the holding element from FIG. 3 and the gradient insulation screw from FIG. 1c;
[0058] FIGS. 6a and 6b are schematic representations of the forces occurring during the screwing in of the gradient insulation screw for the system from FIG. 4; and
[0059] FIG. 7 is a schematic representation of several systems according to FIG. 4 consisting of gradient insulation screw and holding element in the screwed-in state for an inclined roofing membrane.
[0060] FIG. 1a shows a schematic representation of an embodiment of a gradient insulation screw 1 according to the invention. The gradient insulation screw 1 comprises a drilling tip 4, which is located at one end of the gradient insulation screw 1. In the exemplary embodiment shown in FIG. 1a, the drilling tip 4 is adapted to drill a hole into the substrate by a right-handed rotation.
[0061] An assembly thread 7, which is a left-handed thread in the exemplary embodiment shown here, follows the drilling tip 4. In the present example, the assembly thread 7 has substantially the same core diameter as the drilling tip 4.
[0062] A first thread-free region 8 follows the assembly thread 7 in the embodiment of the gradient insulation screw 1 according to the invention shown in FIG. 1a. In principle, the diameter of this first thread-free region 8 can also substantially correspond to the core diameter of the assembly thread 7 and the outer diameter of the drilling tip 4. In the embodiment shown here, a thickening 8a, i.e., a region having a larger diameter than the diameter of the first thread-free region 8, follows the first thread-free region 8 at the end facing away from the drilling tip. This thickening 8a can also be referred to as a collar. An adjustment thread 9 follows the first thread-free region 8 or the thickening 8a, respectively. The thickening 8a can be helpful during the assembly of the gradient insulation screw according to the invention, because it is prevented thereby that the adjustment thread 9 engages in the steel sheet 3.
[0063] According to the invention, the adjustment thread 9 has an outer diameter which is greater than the outer diameters of the drilling tip 4 and the assembly thread 7. A tool holder 10, with which a rotational movement can be transmitted to the screw, follows the adjustment thread 9.
[0064] In the exemplary embodiment shown in FIG. 1a, the gradient insulation screw 1 comprises, at the end opposite the drilling tip 4, a head, in which the tool holder 10 is arranged. The outer diameter of the head is greater than the core diameter of the adjustment thread 9.
[0065] The embodiment of the gradient insulation screw 1 according to the invention shown in FIG. 1a has been described starting from the drilling tip 4 up to the tool holder 10 with reference to the threads and regions of the screw following one another. However, it is clear to the person skilled in the art that these regions do not necessarily have to follow one another directly. The person skilled in the art also knows additional regions, which can be arranged between the thread-free regions and/or the threads without substantially influencing the function of the screw according to the invention. This is the case in the same way for the other embodiments shown and described.
[0066] FIG. 1b shows a schematic representation of a further embodiment of a gradient insulation screw 1 according to the invention. In this exemplary embodiment of the gradient insulation screw 1, a second thread-free region 4a is located between the drilling tip 4 and the assembly thread 7. In the present exemplary embodiment, the diameter of this second thread-free region 4a substantially corresponds to the core diameter of the drilling tip 4. The longitudinal extension of the second thread-free region 4a, i.e., the extension parallel to the longitudinal axis of the gradient insulation screw 1, corresponds at least to the thickness of a steel sheet. The longitudinal extension of the second thread-free region 4a can, however, also be significantly greater and correspond, for example, to a multiple of the thickness of a steel sheet.
[0067] In the exemplary embodiment of the gradient insulation screw 1 shown in FIG. 1c, a preassembly thread 5 follows the drilling tip 4. Although this is not shown in FIG. 1c, a second thread-free region 4a, as is shown in FIG. 1b, can be located between the drilling tip 4 and the preassembly thread 5. In addition, a third thread-free region 6 can, but does not have to, be arranged between the preassembly thread 5 and the assembly thread 7. The preassembly thread 5, like the drilling tip 4, has the first direction of rotation. In the exemplary embodiment shown here, this is a right-handed thread. In the present exemplary embodiment, the core diameter and the outer diameter of the preassembly thread 5 are each the same over the longitudinal extension of the preassembly thread 5. In connection with the invention, however, it is also possible, for example, for the core diameter and/or the outer diameter to increase over the length of the preassembly thread 5. For example, the core diameter and/or the outer diameter of the preassembly thread 5 can increase from the end which lies closer to the drilling tip 4 to the other end of the preassembly thread 5.
[0068] In the present exemplary embodiment, the core diameter and/or the outer diameter of the preassembly thread 5 and that of the core diameter and/or the outer diameter of the assembly thread 7 are of the same size. In connection with the present invention, however, the core diameter and/or the outer diameter of the preassembly thread 5 can also be smaller than the core diameter and/or the outer diameter of the assembly thread 7.
[0069] In the exemplary embodiment of the gradient insulation screw 1 according to the invention shown in FIG. 1c, a third thread-free region 6 is arranged between the preassembly thread 5 and the assembly thread 7. This third thread-free region 6 enables a simple change of the direction of rotation from the preassembly thread 5 with the first direction of rotation to the assembly thread 7 with the second direction of rotation.
[0070] FIG. 2a shows a schematic side view of a drilling tip 4 of a gradient insulation screw 1 according to the invention. In connection with the present invention, the drilling tip 4 comprises a first direction of rotation. The drilling tip 4 is therefore adapted to drill into a substrate when it is rotated in the first direction of rotation. For this purpose, the drilling tip 4 shown here comprises at least one cutting element.
[0071] A cutting element of the drilling tip is, in the embodiment shown in FIG. 2a, the main cutting edge 16a, which extends radially outwards from the tip of the drilling tip 4 at an angle to the axis of rotation of the gradient insulation screw 1. It could also be said that the main cutting edge 16a is arranged on the lateral surface of the body of the drilling tip 4. The drilling tip 4 may comprise one or more main cutting edges 16a, which form the first opening in the substrate in most applications. A further cutting element may be the secondary cutting edge 16b shown in FIG. 2a. The secondary cutting edge 16b is arranged on the lateral surface of the body of the drilling tip 4 in the embodiment shown in FIG. 2a. The secondary cutting edge 16b enlarges the drilling hole and removes any drill residues. The drilling tip 4 may comprise one or more secondary cutting edges 16b, which are preferably arranged on the outer side of the lateral surface in such a way that they protrude as a projection at least partially in relation to the cylindrical body. FIG. 2a also shows the second thread-free region 4a and the assembly thread 7, wherein in this embodiment the core diameter and the outer diameter of the assembly thread 7 are greater than the core diameter and the outer diameter of the drilling tip 4.
[0072] As can be seen from the synopsis of FIGS. 2a and 2b, the drilling tip 4 may comprise a chip groove 17, which in the present embodiment extends along the at least one main cutting edge 16a and/or the at least one secondary cutting edge 16b. The chip groove 17 extends substantially in the direction of the axis of rotation of the gradient insulation screw and is adapted to assist in the removal of the drilling chips.
[0073] FIG. 3 shows an embodiment of a holding element 12, as can be used together with the gradient insulation screws 1 described in FIGS. 1a to 1c in a system according to the invention.
[0074] The holding element 12 comprises at least two parts, a holding plate 13 and a hollow shaft 14. The holding plate 13 is adapted to rest on the roofing membrane, and thus to hold downwards the roofing membrane and the insulation arranged thereunder. The hollow shaft 14 is adapted such that the adjustment thread 9 can engage in the hollow shaft 14. In the embodiment shown in FIG. 3, the holding element 12 also comprises a connecting element 15, which connects the holding plate 13 and the hollow shaft 14 to one another. While the hollow shaft 14 comprises an inner diameter, which is adapted such that the adjustment thread 9 can engage therein, the connecting element 15—as shown in FIG. 3—may comprise a larger inner diameter. In the embodiment shown here, the end of the holding element 12, which lies opposite the holding plate 13, is adapted to taper in order to simplify the introduction of the fastening system consisting of gradient insulation screw 1 and holding element 12 into the roofing membrane 2 and into the insulating material.
[0075] FIG. 4 shows an example of a system 11 according to the invention consisting of the gradient insulation screw 1 shown in FIG. 1b and the holding element 12 shown in FIG. 3. In the embodiment of the system 11 consisting of gradient insulation screw 1 and holding element 12 shown here, the inner diameter of the connecting element 15 is greater than the outer diameter of the head of the screw 1, so that the head can be moved longitudinally in the connecting element 15, while the inner diameter of the hollow shaft 14 is smaller than the outer diameter of the head. This enables a screwing of the gradient insulation screw 1 into the holding element 12 until the head of the screw rests on a stop at the transition from the inner diameter of the connecting element 15 to the inner diameter of the hollow shaft 14. It is thereby prevented that the screw 1 can be rotated downwards, i.e., away from the assembling person, out of the holding element 12.
[0076] In the embodiment shown, the inner diameter of the hollow shaft 14 is smaller than the outer diameter of the adjustment thread 9 of the gradient insulation screw 1, but greater than the core diameter of the adjustment thread 9 of the gradient insulation screw 1.
[0077] FIGS. 5a to 5d show a schematic representation of the individual steps during the assembly of the system 11 according to the invention from FIG. 4, i.e., of the gradient insulation screw from FIG. 1b and the holding element from FIG. 3, for fastening a roofing membrane 2 on a steel sheet 3. FIG. 5a shows the resting of the drilling tip 4 of the gradient insulation screw 1 on the steel sheet 3 after the pushing in and the screwing of the system 11 into the roofing membrane 2 in the direction of the steel sheet 3 located underneath. The adjustment thread 9 is already located here in the hollow shaft 14 of the holding element 12, i.e., the screwing in of a counter thread into the hollow shaft 14 for the adjustment thread 9 has optionally already taken place beforehand. As already explained above, it is also possible that the counter thread is formed during the production of the holding element 12. Independently of this, the screwing in of the adjustment thread 9 into the hollow shaft 14 can take place before the assembly of the system or during the pushing in and the screwing in of the system 11 into the roofing membrane 2.
[0078] In FIG. 5a, the holding plate 13 is located in the vicinity of the roofing membrane 2 after the initial pushing in, but not necessarily on the roofing membrane 2. The gradient insulation screw 1 is now rotated further in the first direction of rotation, in the example of FIG. 5a in right-handed direction. However, this does not necessarily lead to a corresponding rotation of the holding element 12, since the holding element 12 is held by the insulating material of the roofing membrane 2. For this purpose, the holding force caused by friction can be sufficient. Alternatively, the holding element 12 can comprise projections, which prevent any co-rotation of the holding element 12. With continued right-handed rotation, under slight pressure from above, the drilling tip 4 of the gradient insulation screw 1 penetrates through the steel sheet 3, until the steel sheet 3 is located in the second thread-free region 4a of the gradient insulation screw 1. At the same time, the adjustment thread 9 rotates into the hollow shaft 14 of the holding element 12.
[0079] When the drilling tip 4 and optionally the second thread-free region 4a penetrate the steel sheet 3, this causes an axial movement of the gradient insulation screw 1 in the direction of the substrate. The rotation of the adjustment thread 9 of the gradient insulation screw 1 in the hollow shaft 14 of the holding element 12 in the first direction of rotation has the effect of that the holding element 12 moves axially and relative to the gradient insulation screw 1 upwards, i.e., away from the substrate. When, due to the screwing in, the holding element 12 moves upwards more quickly relative to the gradient insulation screw 1 than the gradient insulation screw 1 moves in the direction of the substrate due to the lowering of the drilling tip 4 and the second thread-free region 4a through the steel sheet 3, the distance between the holding plate 13 of the holding element 12 and the roofing membrane 2 increases. If the drilling tip 4 and optionally the second thread-free region 4a move faster through the steel sheet 3 than the holding element 12 moves away from the gradient insulation screw 1, the distance between the holding plate 13 of the holding element 12 and the roofing membrane 2 decreases. When both movements take place almost equally quickly, the distance of the holding plate 13 from the roofing membrane 2 does not change.
[0080] In the embodiment shown in FIG. 5a, there is a substantial difference between the movement of the drilling tip 4 through the steel sheet 3 and the relative movement between the gradient insulation screw 1 and the holding element 12. The relative movement between the gradient insulation screw 1 and the holding element 12 is a substantially continuous movement that depends on the rotational speed of the gradient insulation screw 1 and the pitch of the adjustment thread 9. In the embodiment shown in FIG. 5a, the speed at which the drilling tip 4 moves through the steel sheet 3 is discontinuous. First, the drilling tip 4 moves very slowly in the direction of the substrate, while the drilling tip 4 slowly starts drilling the steel sheet 3. As soon as a sufficiently large hole exists in the steel sheet 3, the drilling tip 4 and optionally a thread-free region following thereon moves quickly through the steel sheet 3 until the movement is stopped, for example, by a thread. However, this movement does not necessarily have to be the case in connection with the present invention. As already explained above, the drilling tip can also comprise a thread. This thread can be adapted in such a way that the drilling tip moves at least temporarily continuously through the steel sheet. If the gradient insulation screw 1 comprises, for example, a preassembly thread 5, as is shown in FIG. 1c, the gradient insulation screw 1 moves continuously in the direction of the substrate after the drilling tip 4 has been pushed quickly through the steel sheet 3. The speed of this movement then also depends again on the rotational speed of the gradient insulation screw 1 and the pitch of the preassembly thread 5.
[0081] FIG. 5b now shows the situation after the drilling tip 4 has penetrated the steel sheet 3. The assembly thread 7 with the second direction of rotation follows the second thread-free region 4a. In the exemplary embodiment shown here, this is a left-handed thread. This assembly thread 7 with the second direction of rotation prevents the gradient insulation screw 1 from moving further in the direction of the substrate when it is rotated further in the first direction of rotation. Since—as described above—the holding element 12 is held by the roofing membrane 2, the further rotation of the gradient insulation screw 1 has the effect of that the adjustment thread 9 moves in the counter thread in the hollow shaft 14 of the holding element 12. This leads to that, during a rotation of the gradient insulation screw 1 in the first direction of rotation, the hollow shaft 14 of the holding element 12 moves on the adjustment thread 9 in direction of the tool holder 10. This also has the effect of that the holding plate 13 of the holding element 12 moves again away from the roofing membrane 2. When the assembling person sees this, he knows that the drilling tip 4 has penetrated the steel sheet 3 and that he can therefore now change the direction of rotation from the first to the second direction of rotation, i.e., in the example shown here from right-handed to left-handed run.
[0082] By the rotation of the gradient insulation screw 1 in the second direction of rotation, here in the left-handed direction and optionally by slight pressure from above on the gradient insulation screw 1, the assembly thread 7 of the gradient insulation screw 1 now engages in the steel sheet 3 and the assembly thread 7 is screwed into the steel sheet 3 until the steel sheet 3 is located in the first thread-free region 8, as shown in FIG. 5c.
[0083] In this case, the holding plate 13 of the holding element 12 is lowered again in the direction of the roofing membrane 2, since firstly the gradient insulation screw 1 passes further downward through the steel sheet 3 and since secondly, due to the left-handed rotation, the holding element 12 moves in the direction of the drilling tip 4 of the gradient insulation screw 1. This is indicated in FIG. 5c by the arrow next to the holding plate of the holding element 12.
[0084] A possible thickening 8a, which follows the end of the thread-free region 8 facing the adjustment thread 9, can prevent the steel sheet 3 from not being pressed out of the first thread-free region 8 in the direction of the adjustment thread 9 despite pressure from above on the gradient insulation screw 1, e.g., by a battery-operated screwdriver.
[0085] With continued rotation of the gradient insulation screw 1 in the second direction of rotation, as shown in FIG. 5d, the steel sheet 3 remains in the first thread-free region 8 and the holding plate of the holding element 12 is pulled further onto the roofing membrane 2. This further pulling of the holding plate 13 of the holding element 12 against the roofing membrane 2 is represented in FIG. 5d by the vertical arrow. Thereby, a re-entry of the assembly thread 7 of the gradient insulation screw 1 into the steel sheet 3 is avoided, since an opposite direction of rotation of the gradient insulation screw 1, namely a rotation in the first direction of rotation (here: right-handed rotation), would be necessary for this purpose. The continued rotation of the gradient insulation screw 1 in the second direction of rotation is stopped when the holding plate 13 of the holding element 12 is pulled with the desired force onto the roofing membrane 2.
[0086] When using an additional preassembly thread on the gradient insulation screw, the steps of FIGS. 5a to 5d are slightly modified. This is described in the following. FIGS. 5e to 5h show a schematic representation of the individual steps during the assembly of a system 11 according to the invention consisting of gradient insulation screw 1 from FIG. 1c and a holding element from FIG. 3 for fastening a roofing membrane 2 on a steel sheet 3. FIG. 5e shows the resting of the drilling tip 4 of the gradient insulation screw 1 on the steel sheet 3 after pushing in and screwing in of the system 11 into the roofing membrane 2 in the direction of the steel sheet 3 located underneath. The gradient insulation screw 1 is now rotated further in right-handed direction. The holding plate 13 is still located at a certain distance from the roofing membrane 2. With continued right-handed rotation, the drilling tip 4 of the gradient insulation screw 1 penetrates through the steel sheet 3, and the preassembly thread 5 of the gradient insulation screw 1 is screwed through the steel sheet 3, until the steel sheet 3 is located in the third thread-free region 6 of the gradient insulation screw 1. This situation is represented in FIG. 5f. Thereby, the distance between the holding element 12 and the roofing membrane 2 has initially not yet changed, since, due to the right-handed rotation, not only the preassembly thread 5 of the gradient insulation screw 1 moves into the steel sheet 3, but also the adjustment thread 9 rotates relatively to the hollow shaft 14 of the holding element 12 and thus the hollow shaft 14 of the holding element 12 moves on the adjustment thread 9 in direction of the tool holder 10. With continued right-handed rotation, the gradient insulation screw 1 now rotates freely in the thread-free region 6 in the steel sheet 3 and does not enter further into the steel sheet 3. Thereby, the holding plate 13 lifts off further from the roofing membrane 2, as represented by the arrow in FIG. 5f, since, due to the continued right-handed rotation, the adjustment thread 9 of the gradient insulation screw 1 rotates further relatively to the hollow shaft 14. By means of the lifting off of the holding element 12, it is indicated to the assembling person that the direction of rotation should be changed from right-handed to left-handed run.
[0087] By subsequent left-handed rotation of the gradient insulation screw 1 and optionally by slight pressure from above on the gradient insulation screw 1, the assembly thread 7 of the gradient insulation screw 1 now engages in the steel sheet 3 and is screwed in until the steel sheet 3 is located in the first thread-free region 8, as shown in FIG. 5g. Thereby, the holding plate 13 of the holding element 12 is lowered again in the direction of the roofing membrane 2, since firstly the gradient insulation screw 1 passes further downward through the steel sheet 3 and since secondly, due to the left-handed rotation, the holding element 12 moves in the direction of the drilling tip 4 of the gradient insulation screw 1. This is indicated in FIG. 5g by the arrow next to the holding plate.
[0088] As described above, a possible thickening 8a following the first thread-free region 8 can prevent the steel sheet 3 from not being pressed out of the first thread-free region 8 in the direction of the adjustment thread 9 despite pressure from above on the gradient insulation screw 1.
[0089] With continued left-handed rotation of the gradient insulation screw 1, as shown in FIG. 5h, the steel sheet 3 remains in the first thread-free region 8 and the holding plate 13 of the holding element 12 is pulled further onto the roofing membrane 2. This further pulling of the holding plate 13 against the roofing membrane 2 is represented in FIG. 5h by the vertical arrow. As above, a re-entry of the assembly thread 7 of the gradient insulation screw 1 into the steel sheet 3 is thereby avoided, since an opposite direction of rotation of the gradient insulation screw 1, namely a right-handed rotation, would be necessary for this purpose. Here too, the continued left-handed rotation of the gradient insulation screw 1 is stopped when the holding plate 13 of the holding element 12 is pulled with the desired force onto the roofing membrane 2.
[0090] FIGS. 6a and 6b show by way of example a schematic representation of the forces occurring during the screwing in of the gradient insulation screw 1. When the first thread-free region 8 of the gradient insulation screw 1 is located in the steel sheet 3, the holding plate 13 of the holding element 12 is pulled in the direction of the roofing membrane 2 by continued left-handed rotation. As a result, two forces act on the insulating material, at the steel sheet 3 and at the holding plate 13. These forces are illustrated in FIG. 6b with the aid of arrows.
[0091] In FIG. 7, three systems 11 consisting of gradient insulation screw 1 and holding element 12 are represented at three locations of different roof thickness for an inclined roofing membrane 2 after the assembly. Hereby, it can be seen that the interplay of the adjustment thread of the gradient insulation screw 1 and the hollow shaft 14 of the holding element 12 enables various vertical total lengths of the system 11 consisting of gradient insulation screw 1 and holding element 12, without the gradient insulation screws 1 protruding differently far below the steel sheet 3.
