The present invention relates to a roof cladding element with hidden fastening, which roof cladding element has been manufactured of plate material, and which roof cladding elements are adjacently and in succession mountable such that the edges of roof cladding elements will be placed a distance overlapping the edges of the adjacent roof cladding elements, and which roof cladding element includes at least one step mainly transversal with the cladding which step has at least one lock¬ ing recess for locking a roof cladding element at least from one step to the next lower roof cladding element, and which roof cladding element includes at least one attaching shoulder placed at the upper edge of a roof cladding element for fastening of the upper edge of a roof cladding element to the fastening construction of the cladding and for tightening and locking of at least the locking recess next to the lower edge of a roof cladding element to the locking recess placed in the upper part of the next roof cladding element placed lower.

Today known roof cladding elements, from which a cladding equivalent to a profile cladding made of a cladding plate may be assembled, are fastened to battens adja¬ cently and in succession with nails, screws or with some other suitable fastening elements. Frequently these kinds of roof cladding elements are with hidden fasten¬ ing in which case fastening points are placed in locations which are hidden under the adjacent roof cladding element. To ensure the remaining fastened of roof clad¬ ding elements and to increase the tolerance of wind load there are roof cladding elements which include fasteners remaining invisible, through which fasteners adja¬ cent or roof cladding elements in succession are fastened to each other by means of separate fastening elements. These kinds of roof cladding elements/bricks are pre- sented in patent publications US 3,220,150 and US 5,752,355. In addition, from in¬ ternational application WO 2004001155 a brick figured roof cladding element made by forming out of plate material is familiar and in it, there are locking recesses at the points of valleys of the profile in vertical parts of steps forming the brick figure, by means of which locking recesses it is possible to fasten the roof cladding ele- ments in succession to each other by tightening the steps to be mounted one on top of the other of roof cladding elements in succession against each other by means of fold like attaching shoulders placed on the upper edge of the upper roof cladding element.

With present fastening methods it is possible to fasten roof cladding elements long- lasting as such and the finished cladding will be tight and uniform in appearance. Mounting of a cladding made of roof cladding elements fastened in recognized ways requires, however, fastening work of fastening elements such as nails or screws taking much time. For example, joints between roof cladding ele¬ ments/bricks to be fastened to each other in various ways presented in publications US 3,220,150 and US 5,752,355 and others of the same kind are often slowening and hindering mounting because joints need separate fastening elements. A roof cladding element in accordance with publication WO 2004001155 is very fast and easy to be mounted and the roof cladding elements fastened to each other and to fas¬ tening constructions of the cladding remain in place regardless of the loads on the cladding. The problem in a roof cladding element with this kind of locking recesses is, however, the fact that manufacturing of a locking recess used in a roof cladding element by forming from thin metal plate requires a forming tool for a locking re¬ cess to be mounted to a forming tool of steps. This kind of forming tool is complex by construction as well as troublesome to make and therefore relatively expensive by manufacturing costs. Furthermore, since the forming of a locking recess has to be carried out at the time when the forming tool of a step is in place for a moment the forming of a locking recess limits the manufacturing speed obtained with the forming device of a step.

The purpose of the invention is to provide a roof cladding element with hidden fas¬ tening, with which the earlier mentioned disadvantages related to present roof clad- ding elements are eliminated. Especially the purpose of the invention is to provide a roof cladding element, which may be fastened in succession to each other without separate fastening elements between roof cladding elements and which does not in¬ crease manufacturing costs of forming device of a roof cladding element made by forming from a thin metal plate and does not limit the manufacturing speed obtained with this kind of forming device.

The object of the invention is accomplished by a roof cladding element with hidden fastening, the characteristics of which are presented in the claims.

Characteristic to a roof cladding element in accordance with the invention is that a locking recess has been formed to steps of a roof cladding element such that the up- per cladding surface before a step is above the lower cladding surface placed a dis¬ tance after the step, and that viewed from side the step is mainly a straight part of a roof cladding element slanting in regard to cladding surfaces, in which case the lon¬ gitudinal cross section of a roof cladding element on the step area is mainly Z shaped. In this kind of roof cladding element the lowest step of the next, upper roof cladding element placed on the upper most step of the roof cladding element is fas¬ tened due to locking recesses (originating from the Z shape of the cross section of the step area) in the steps to the step of the lower roof cladding element when the roof cladding elements are tightened to each other in longitudinal direction of the slope by means of attaching shoulders on the upper edge of the roof cladding ele¬ ments. Due to this, there is no need for separate visible fastening elements between roof cladding elements. In addition, for example while manufacturing these kinds of roof cladding elements of a thin metal plate strip in a continuous production line based on roll forming a locking recess included in a roof cladding element may be made to a step of a roof cladding element without a separate moulding phase of a locking recess and without a separate forming tool of a locking recess to be mounted to a forming tool of a step. Therefore, the forming tool of a step of a form¬ ing device used in manufacturing of this kind of roof cladding element may be real¬ ized as simply and with same manufacturing costs as a forming tool of a step used in manufacturing of a traditional roof cladding element with straight steps or of a cladding plate. Furthermore, differently from most traditional roof cladding ele- ments without locking recesses these kinds of roof cladding elements may be fas¬ tened in succession such that all fastening elements necessary for fastening of roof cladding elements remain hidden in a finished cladding.

In an advantageous application of the invention, a locking recess measures mainly the width the entire roof cladding element widthwise of a roof cladding element. Due to this, there is no need to form shoulders into the forming tool of a step or some other complex shapes in terms of manufacturing but the forming tool may be very simple to be manufactured. In addition, with this kind of locking recess it is possible to fasten the roof cladding elements reliably to each other as the gripping surface of roof cladding elements measures the entire width of a roof cladding ele- ment.

In the second advantageous application of the invention, the lower edge of the roof cladding element is located between the middle of a step and the lower corner be¬ tween a step and lower cladding surface. In this way, the connecting point of roof cladding elements may be placed invisible under the upper cladding surface placed on the lower cladding surface. Due to this, a finished cladding will be uniform and seamless in appearance.

Next, the invention will be explained in more detail with reference to the accompa¬ nying drawings, in which, Figure 1 illustrates a roof cladding element with hidden fastening viewed diagonally from above, Figure 2 illustrates a longitudinal cross section of a roof cladding element placed in succession in accordance with figure 1 at the connection point of elements, and Figure 3 illustrates functioning principle of the forming device of a step used in manufacturing of a roof cladding element in accordance with figures 1 and 2.

Figures 1 and 2 illustrate a brick figured roof cladding element with hidden fasten¬ ing 1, which has been manufactured of a coated thin metal plate strip in a continu¬ ous production line, which includes an opening device for strip reel, a roll forming device, a press type step forming device and a cutting device. First, a transversal profile of a roof cladding element is formed to the thin metal plate strip to be opened from a reel by forming valleys 2 and peaks 3 with a roll forming device, which comprises a suitable number of forming phases in succession (forming roll pairs). The shape of the transversal profile in this case in accordance with figure 1 symmetrically wavelike such that the valleys 2 and the peaks 3 of the profile are ap¬ proximately of the same width and height. After forming the transversal profile steps 4a and 4b are formed at intervals of the length of a brick to the strip by a step forming device after the roll forming device. The steps are formed on principle pre¬ sented in figure 3 with a forming tool M, which moves between the holding tool P and the counter tool V inclined downwards with respect to the profiled strip N kept at place during forming and to opposite direction with respect to the direction of motion of the strip. In this way the step will be forwards inclined such that viewed from the ridge the upper cladding surface 7a before the step extends for a distance on top of the lower cladding surface 7b after the step, such forming locking recesses 5 a and 5b with the length of the width of the entire roof cladding element. After forming the transversal profile, steps (and locking recesses), the ready roof cladding element strip is cut with a cutting device into roof cladding elements. In this case roof cladding elements are of the length of one space between brick figures (i.e. there are two steps 4a and 4b in a roof cladding element) and their width is greater than the length i.e. roof cladding elements are so-called horizontal elements. At¬ taching shoulders 6 are formed while cutting to the upper edge of roof cladding ele- ments i.e. to the edge of a roof cladding element on the ridge side of the roof in a finished cladding. They are folds formed by cuttings from the upper edge down¬ wards near the upper most step as presented in figure 1. There are attaching open¬ ings 8 in the upper part of attaching shoulders. They are also made, in this case, with penetrating tools mounted to be in connection with the blades of the cutting device or they may be made separately during a separate working phase. A roof cladding of the size of a roof, reminding a brick cladding by appearance is made out of roof cladding elements in accordance with figures 1 and 2 by fastening roof cladding elements to fastening constructions of the roof one horizontal line at the time (usually from the right to the left, but in this case assembling may be car- ried out also in opposite direction) from the eaves to the ridge of the roof. Alterna¬ tively, roof cladding elements may also be fastened a vertical line at the time, pro¬ ceeding from the eaves to the ridge. Roof cladding elements are fastened to the fas¬ tening constructions of the roof (e.g. wooden battens) by fastening openings 8 in at¬ taching shoulders 6 with roof nails or screws. Roof cladding elements may also be fastened with other suitable fastening elements. For example, to battens made of metal they may be fastened with suitable rivets or tin screws. In any case, roof clad¬ ding elements of the next upper roof cladding element row (nearer to the ridge of a roof) in respect to the lower roof cladding element row are mounted in respect to the lower roof cladding elements such that the lowest step 4b in the lower edge of upper roof cladding elements is placed on upper most step 4a of the lower roof cladding element row in accordance with figure 2. Each roof cladding element is fastened by the attaching shoulders 6 in the upper edge of a roof cladding element such that the lowest step 4b in the lower edge of a roof cladding element is tightened against the upper most step 4a of the next lower roof cladding element. In this case, the inclined steps (i.e. locking recesses 5a and 5b) placed one on top of the other of roof clad¬ ding elements in succession lock the roof cladding elements in succession to each other. In addition, attaching shoulders 6 placed in the upper edge of the lower roof cladding element and their fastening elements remain hidden under the lower edge of the upper roof cladding element such that in a finished cladding only attaching shoulders of the upper most roof cladding element row reaching the ridge of the cladding and fastening elements fastened to those shoulders remain visible. Also these are covered when the sheet metal for the ridge is placed on the ridge and ex¬ tends over the attaching shoulders of the upper most roof cladding element row. Since there are no more roof cladding element rows after the lowest roof cladding element row which is nearest to the eaves all roof cladding elements for the lowest row must be fastened with separate additional fastening elements between the lower part of the roof cladding element and the batten (not presented in figures).

A roof cladding element in accordance with the invention may differ in many parts from the presented example application and a roof cladding element may be manu- factored also of other suitable material than a coated thin metal plate. Suitable mate¬ rials are e.g. many plate materials made of copper, aluminium or plastics. Materials may be ready coated or without coating in which case coating may take place after manufacturing of roof cladding elements. The shape of transversal profiles, the number of steps (the brick figure) as well as the number of profile peaks and valleys in one roof cladding element may vary. All profile shapes to which steps similar to application in accordance with figures 1 and 2 may be formed are possible in prin- ciple. The design of steps in roof cladding elements may vary. In the application in accordance with figure 2 the step is a part of a roof cladding element in inclined po¬ sition with respect to horizontal cladding surfaces of a roof cladding element i.e. on the step area the longitudinal cross section of a roof cladding element in Z shaped. Alternatively, the step may be curved in a suitable way inwards or outwards, for ex- ample, or it may be slightly S shaped. In the application in accordance with figures 1 and 2 the lower edge of a roof cladding element (i.e. the cutting point during manufacturing) is placed between the middle of the lowest step and the lower corner between the lower cladding surface after it (in a roof cladding element strip before cutting into roof cladding elements) and the step. For obtaining greater stiffness and strong joint between locking recesses the lower edge may be placed such that it is, for example, c. 3-5 mm after the lower corner between the step and the lower clad¬ ding surface after it (i.e. on the area of the lower cladding surface). At this point the lower edge remains usually invisible in the shadow of the upper cladding surface, since in the application in figures 1 and 2, for example, the upper cladding surface 7a extends due to inclination of the step, c. 7 mm on the lower cladding surface 7b.

Attaching shoulders placed in the upper part of a roof cladding element are parts of a roof cladding element which extend beneath the lowest point of the lower surface of a valley of a transversal profile to the extent that nails or screws mounted in at¬ taching shoulders do not bend the upper edge of a roof cladding element and that locking recesses to be placed one on top of the other of successive roof cladding elements are tightened against one another when attaching shoulders are fastened to fastening constructions of a roof. Therefore, attaching shoulders may be instead of folds made by cutting presented in figure 1 e.g. depressions formed on the upper edge of a roof cladding element which correspond to the folds of a roof cladding element in accordance with figure 1 fastened at its place. In case so-called drill screws are used as fastening elements in attaching shoulders ready fastening open¬ ings are not necessary. In some applications there are depressions made at the point of openings in attaching shoulders, which depressions enable to screw ordinary wooden or tin screws through the plate material of a roof cladding element.

Manufacturing of a roof cladding element may also be carried out in many different ways differing from the presented example application. The production line used in manufacturing must not necessary be continuous as said earlier but the transversal profile of roof cladding elements and steps, attaching shoulders and other details formed in the way described earlier may be formed in some suitable method, for ex¬ ample, to plate objects cut into pieces of suitable size. Therefore, for example the transversal profile of roof cladding elements may be manufactured instead of roll forming by some press type forming device when using formable plate materials. While manufacturing great series a continuous production line based on roll form¬ ing or similar is, however, often more cost efficient than this kind of manufacturing method forming separate objects.

The invention is not limited to the presented advantageous application but it can va¬ ry within the frames of the idea of the invention formed in the claims.