RECESSES AND PROTRUSIONS

The invention relates to a folding device for folding a flat sheet of a foldable material into a sheet displaying a pattern of successive recesses and protrusions in a cross- section .

A sheet folded with such a device, which sheet is for instance manufactured from corrugated board and has a zigzag shape in cross-section, can be applied as connecting

intermediate layer between two plates of a wall element.

A device is known from NL 1015909 C for folding a strip of zigzag-shaped corrugated board from a flat strip of corrugated board, wherein the strip of corrugated board is first provided, as a pre-operation, with folding or bending lines by means of a cutting die. After the cutting operation the strip of corrugated board is moved along a guideway embodied to converge in the direction of movement of the strip of corrugated board. By making use of corrugated board with a natural material weakness, of the pre-cut folding lines and of the tapered or conical form of the guideway the zigzag shape is obtained "as it were automatically" in the strip of corrugated board during transport. Use is made of guide wheels in order to realize a controlled guidance of the strip of corrugated board.

After the pre-operation in the form of the cutting, the strip is in the known device immediately guided along the, over the width, full number of guide wheels, wherein the distance between the guide wheels decreases each time in the direction of movement, in such a way that the peaks and valleys of the zigzag shape come to lie increasingly closer together and the sides thereof become steeper. All this seems possible only if the corrugated board is sufficiently weak, so that the known device is apparently not suitable for folding a strip of corrugated board having no or little material weakness. The known device is further unsuitable for folding cardboard with a truncated zigzag shape in cross- section at peaks and valleys.

It is an object of the invention to provide a folding device using which a sheet with a pattern of successive recesses and protrusions can be folded, wherein the recesses and protrusion have a predetermined, well-defined form. The sheet material for folding has to be foldable, however without requirements in respect of maximum stiffness having to be made thereof.

These objectives are achieved, and other advantages gained, with a folding device of the type stated in the preamble, which according to the invention comprises (i+1) successive folding stations (1; 2; 3), wherein i is a natural number not equal to zero (i=l, 2, 3,...), wherein in each folding station (2, 3) beyond the first folding station (1) , as seen in the direction of transport of a sheet through this folding device (10) , two recesses or protrusions are each time added to recesses or protrusions previously arranged in a prior folding station (1, 2) .

In such a folding device two recesses or protrusions are each time folded into the sheet material in each subsequent folding station, wherein the part of the sheet material to be folded is pulled from sides, transversely of the direction of transport, and in the direction of the recess or protrusion folded in the first folding station. Other than in the known folding device, only one (in the first folding station) or two (in each subsequent folding station) protrusions or recesses are folded per folding station. As a result no or hardly any deformation of the sheet material occurs at positions where it need not be folded. With the folding device according to the invention it is also possible to fold very stiff sheet material.

It is noted that the names protrusion and recess are here chosen arbitrarily.

In an embodiment each of the (i+1) successive folding stations comprises two shafts extending through the folding device substantially above each other and transversely relative to the direction of transport of the sheet, wherein i is a natural number not equal to zero (i=l, 2, 3,...), which shafts are provided with co-acting discs for folding the flat sheet, wherein, for an odd value of i, a first shaft of the i ^th folding station is provided with one disc (i=l) or with i discs (i>l) which co-acts or co-act with (i+1) respective discs on the second shaft in such a way that, in a part of a flat sheet supplied between the shafts, the discs form one (i=l) protrusion or i (i>l) protrusions directed toward the second shaft and (i-1) recesses directed toward the first shaft, and wherein, for an even value of i, the first shaft of the i ^th folding station is provided with (i+1) discs which co-act with i respective discs on the second shaft in such a way that, in a part of a flat sheet supplied between the shafts, the discs form (i-1) protrusions directed toward the second shaft and i recesses directed toward the first shaft, and wherein (i+2) discs of the (i+l) ^th folding station each time lie in the direction of transport in one line with (i+2) corresponding discs of the i ^th folding station.

In a subsequent embodiment the folding device according to the invention is provided with drive means for driving at least one of the shafts.

At least one of the folding stations is for instance provided here with drive means for driving the first and the second shaft in opposite rotation directions.

In another embodiment the folding device comprises at least two folding stations which are each provided with drive means for driving at least one of the first and the second shaft of that folding station, and with control means for controlling the drive means in mutual dependence.

In an advantageous embodiment each of the folding stations is provided with drive means for driving the first or the second shaft of that folding station and with control means for controlling the drive means in mutual dependence, in such a way that corresponding shafts of two successive folding stations have a mutually differing rotation speed.

With a mutually differing rotation speed of

corresponding shafts of two successive folding stations, wherein the rotation speed of a driven shaft is a fraction lower than the rotation speed of the corresponding shaft in the subsequent folding station as seen in the transport direction, it is achieved that the sheet material remains tightly tensioned during the folding process, whereby the occurrence of creases and undesired folds is prevented.

The occurrence of creases and undesired folds is likewise prevented when the folding process is stopped if the rotation speed of a driven shaft is a fraction lower during this stage than the rotation speed of the corresponding shaft in the subsequent folding station, as seen in direction of transport .

In an embodiment the first and second shafts are preferably provided with respective co-acting drive rollers fixedly coupled to those shafts for the purpose of feeding through the sheet between the respective first and second shafts .

Such a drive roller, at least a drive roller on a driven shaft, has a frictional surface of a suitable material, for instance rubber, whereby sufficient grip on the surface of a sheet is obtained to enable feeding through of that sheet between the first and second shaft of the respective folding station in regular manner, while simultaneously forming the respective protrusions and recesses.

In another embodiment the first shaft and the second shaft are provided on either side of the discs with guide rollers for guiding the flat sheet fed through between the respective shafts.

To further facilitate the transport of the sheet between the folding stations a folding device according to the invention is for instance provided between the successive folding stations with guide rollers for guiding a sheet fed through between the respective first and second shafts.

In an embodiment of a folding device the parts of the discs above and below the respective first and second shafts are in an axial cross-section formed as an isosceles

trapezoid narrowing from the respective shaft. A sheet folded by such discs has in a cross-section protrusions and recesses with a truncated zigzag shape.

In order to achieve that the surfaces of the recesses and protrusions are straight, the edge of such a disc on a first or second shaft of a folding station in each case co- acts with a cylindrically formed peripheral body on

respectively the second or first shaft of that folding station .

In an embodiment the discs are manufactured from a plastic material, for instance a polyamide such as nylon, or a PTFE (polytetrafluoroethylene ) .

In a preferred embodiment the folding device is provided with a creasing apparatus for arranging crease lines at positions, corresponding to the folding lines of the recesses and protrusions, in a flat sheet to be supplied to the folding stations.

The folding device according to the invention provides particular advantage when it is configured to fold a flat sheet which is provided as endless cardboard.

The invention will be elucidated hereinbelow on the basis of exemplary embodiments, with reference to the drawings .

In the drawings

Fig. 1 is a perspective view of a part of a folding device according to the invention as seen in the direction of transport,

Fig. 2 is a perspective view of a part of the folding device according to the invention shown in fig. 1 as seen in a direction opposite to the direction of transport,

Fig. 3 shows in axial cross-section a disc of the folding device shown in fig. 1, and

Fig. 4 is a perspective view of a wall element with an intermediate layer manufactured using a folding device according to the invention.

Corresponding parts are designated in the figures with the same reference numerals.

Fig. 1 shows a part of a folding machine with a frame 9 in which three successive folding stations 1, 2, 3 are arranged, each with a first (upper) shaft 11, 21, 31 and a second (lower) shaft 12, 22, 32, the upper shaft 11, 21, 31 of which is in each case provided with a drive motor 13, 23, 33.

Upper shaft 11 of the first folding station 1 is provided with one disc 114 which co-acts with two discs 124 on lower shaft 12.

Upper shaft 21 of the second folding station 2 is provided with three discs 214 which co-act with two discs 224 on lower shaft 22, wherein three of the five discs 214, 224 lie in the direction of transport in one line with the corresponding discs 114, 124 of the first folding station 1.

As shown in detail in fig. 2, upper shaft 31 of the third folding station 3 is provided with three discs 314 which co-act with four discs 324 on lower shaft 32, wherein five of the seven discs 314, 324 lie in the direction of transport in one line with the corresponding discs 214, 224 of the second folding station 2.

In the first folding station 1 fig. 1 further shows two pairs of co-acting drive rollers 115, 125 on respectively first shaft 11 and second shaft 12, between which drive rollers 115, 125 a sheet for folding is fed through. Of these drive rollers 115, 125, which are fixedly coupled to the respective shafts 11, 12, only the rollers 115 coupled to the driven upper shaft 11 are in this embodiment driven by drive motor 13, and rollers 125 on lower shaft 12 can rotate freely .

As also shown in fig. 2, for the purpose of guiding a sheet outside of the parts to be folded shafts 11, 12, 21, 22, 31, 32 are provided on either side of the respective discs 114, 124, 214, 224, 314, 324 with respective guide rollers 116, 126, 216, 226, 316, 326 for guiding the flat sheet fed through between the respective shafts.

Guide rollers between the successive folding stations are not shown.

In addition to the above stated parts, Fig. 2 further shows rollers 117, 127, 217, 227, 317, 327 on respectively the first shafts 11, 21, 31 and second shafts 12, 22, 32 of the first folding station 1, the second folding station 2 and the third folding station 3, which correspond with the edges of the discs 124, 114, 224, 214, 324, 314, positioned

opposite these rollers 117, 127, 217, 227, 317, 327, on respectively the second shafts 12, 22, 32 and the first shafts 11, 21, 31.

Fig. 3 shows an axial cross-section 4 through a disc

114, 124, 214, 224, 314, 324, the parts of which above and below respective shaft 14 are formed as an isosceles

trapezoid 18 narrowing from that shaft, the short parallel side 7 of which co-acts with the above stated rollers 117, 127, 217, 227, 317, 327.

Fig. 4 shows a wall element 40 with two outer flat plates 41, 42 and an intermediate layer 43 of a sheet of corrugated board folded in truncated zigzag shape in cross- section, wherein the truncated peaks and valleys 77 and sides 88 of the zigzag shape respectively correspond with edges 7 and sides 8 (shown in fig. 3) of discs 114, 124, 214, 224, 314, 324.

Not shown in the figures is a creasing machine for arranging folding lines in a flat sheet at positions

corresponding with the transitions between edges 7 and sides 8 of discs 114, 124, 214, 224, 314, 324. Such a creasing machine is per se known, and has as its most important parts at least two rotating shafts, one of which is provided with narrow discs at mutual distances corresponding to distances between the crease lines to be arranged in the flat sheet and the other of which is provided with rollers which co-act with the discs and support the sheet material.

Not shown either is a pre-folding station between the creasing machine and the first folding station, which pre- folding station, just as the folding stations, comprises two shafts extending substantially above each other and

transversely relative to the direction of transport. These shafts are provided with at least a disc which exerts a pressure on a part of the flat sheet bounded by two crease lines so as to pre-fold this part before the sheet is guided through the first folding station.

In the above described embodiment the number of folding stations amounts to three.

The number of folding stations in a folding device according to the invention is of course not limited to three, but is in practical situations determined by the number of desired recesses and protrusions, wherein the maximum

possible number of folding stations will be determined substantially by the maximum available width of the sheet material for folding. For the purpose of folding a length of endless cardboard with a width of 122.5 cm into a length width three protrusions and four recesses and a width of 60 cm, the folding device according to the invention is for instance provided with four successive folding stations.