Duct and method for its manufacture

Abstract

A duct of fiber material and binder agent, at least two fold lines are present lengthwise for providing a foldability of the duct by weakened material along the fold lines. The duct is pushable into a folded state and the material remembers the original shape and return to its original shape when released from a folded state. A method of manufacturing a duct: applying a web of origin fiber material with binder agent to a core and compressing the web by an outside form under the influence of heat against the core, wherein the core and/or the outside form is provided with a number of lengthwise ridges corresponding to the desired number of fold lines, to a third of the original thickness of the sides and at the ridges a tenth to a twentieth of the original thickness, and in that the fiber and binder agent web weighs 1.5-3 kg/m.sup.2.

Claims

1. A duct, the duct being at least partly produced from fibre material and binder agent, the duct making up an elongated flow space in an original and a use state thereof, wherein at least two fold lines are present lengthwise of the duct and define sides of the duct, wherein a foldability of the duct is provided by weakened material along the fold lines, wherein the duct is pushable into a folded state and has a memory of its original shape and state such that it is adapted to expand and return to its original shape and state when released from the folded state, and wherein a main cross sectional shape of the duct is circular in the original state.

2. The duct according to claim 1, wherein the weakened material along the fold line comprises a partial amount of messed and crushed fibre material and a partial amount of intact fibre material compared to the fibre material in adjacent sides of the duct or the weakened material along the fold line lacks fibre material in comparison with the fibre material in the adjacent sides of the duct.

3. The duct according to claim 1, wherein the amount of intact fibres is at least 20-70% in the weakened material along the fold lines compared to the fibre material in the adjacent sides of the duct.

4. The duct according to claim 1, wherein the duct is pushable into an intermediate shape, between the original circular shape and the folded state, the intermediate shape having four sides folded in at least four fold lines.

5. The duct according to claim 4, wherein the cross sectional shape is rectangular in the intermediate shape.

6. The duct according to claim 1, wherein the fibre material with binder agent has a surface weight between 1.5-3 kg/m2.

7. The duct according to claim 1, wherein origin fibre material used for forming the fibre material with binder agent is compressible under the influence of heat so that sides of the origin fibre material are compressed to about a third of an original thickness of the origin fibre material with binder agent.

8. The duct according to claim 1, wherein origin fibre material used for forming the fibre material with binder agent is compressible under the influence of heat so that fold lines of the origin fibre material are compressed to a tenth to a twentieth of an original thickness of the origin fibre material with binder agent.

9. The duct according to claim 1, wherein the duct is laminated on the inside and/or outside with a foil comprising at least one layer of metal and at least one layer of polymer.

10. The duct according to claim 9, wherein the duct is laminated with a foil comprising an outer layer of aluminium, an intermediate layer of a thermoplastic polymer having a melt point lower than polyethylene terephthalate (PET), an intermediate layer of polyethylene terephthalate (PET), and an inner layer of a thermoplastic polymer having a melt point lower than polyethylene terephthalate (PET).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will now be described in detail under reference to the accompanying drawings, in which

(2) FIG. 1 shows an embodiment of a duct according to the present invention in a cross sectional view.

(3) FIG. 2 shows a detail of FIG. 1.

(4) FIG. 3a, b, c shows an embodiment of a duct according to the present invention showing the duct in original state, intermediate state and folded state.

(5) FIG. 4 shows another embodiment of a duct according to the present invention showing the duct in original state, intermediate state and folded state.

(6) FIGS. 5a and b shows an embodiment of an outer form used in a method according to the invention and two embodiments of a core, respectively.

DETAILED DESCRIPTION OF EMBODIMENTS

(7) In FIG. 1 an embodiment of a duct 1 according to the present invention is shown in a cross sectional view showing two fold lines 2 and thicker sides 3 in between the fold lines 2. The duct is produced, at least partly, of fibres and binder agent, which is compressed under the influence of heat into the form shown in FIG. 1. Of course many different cross sections are possible.

(8) In FIG. 2 a closer detail of FIG. 1 is shown where the thickness in the fold line 2 and the thicker side 3 is shown at A-A and B-B, respectively. Lines 4 are indicating fibres and layers of fibres making up the wall of the duct.

(9) In FIG. 3a, b and c an embodiment of an inventive duct is shown in three different states. In the shown embodiment the weakened fold lines 2 are arranged on the outside of the duct 1. In the shown embodiment the fold lines 2 are positioned with 60, 120, 60 and 120, respectively, from each other, around the circular original shape. In FIG. 3a the duct 1 is in its original state, which also may be a use state, having a circular cross section.

(10) In FIG. 3b the duct 1 is in an intermediate state, a use state, having a more or less rectangular cross section. To retain in this intermediate state the duct 1 needs to be supported by some kind of installation arrangement (not shown) which expose the duct to pushing forces along the longer sides.

(11) In FIG. 3c the duct 1 is in a folded state. In order to get there, in the shown case, the duct needs to be pushed and slightly slid into position. To stay in the folded state the pushing forces must be retained. This may for example be provided by means of a suitable bag of a flat shape (not shown). Preferably, the air is evacuated, too, from the bag in order to keep the folded state.

(12) In FIG. 4a, b and c another embodiment of a duct 1 is shown in three different states, in original state, intermediate state and folded state, respectively. In this embodiment the weakening making up the fold lines 2 are provided be means of using less fibres along the fold lines 2. In the shown embodiment this is arranged by means of lengthwise voids 5.

(13) In FIG. 5a one embodiment of an outer form 6 having lengthwise ridges 7 provided on the inside 8 shown in a cross sectional view. The number of ridges 7 will correspond to the number of weakened fold lines 2 provided in the produced duct 1. Two embodiments of a core 9 having lengthwise ridges 7 on the outside 10 is shown in a cross sectional view in FIG. 5b.

(14) An embodiment of a method of producing a duct according to the invention comprises arranging or winding at least one layer of a web of fibres with binder agent around the core 9 until a suitable thickness and density is reached. Preferable the weight is 1.5-3 kg/m.sup.2. The fibres could be glass or stone fibres, for example. The binder agent may be phenol based and the amount is preferably 4-8% by weight. It is also possible to first provide a foil around the core 9 and thereafter winding the web of fibres onto the core 9.

(15) Thereafter the outer form 6 is arranged around the core 9 and the web of fibres and binder agent arranged outside the core 9. The fibres and binder agent are compressed between the outer form 6 and the core 9 under the influence of heat, preferably between 120-200 C. During this compression stage the binder agent will cure and thus bind the fibres together. If a foil was arranged on the core 9 initially this foil could be heat laminated onto the inside.

(16) The compression will be carried out until a residual thickness of the sides 3 are compressed to about a third of the thickness of the origin fibre material with binder agent.

(17) The fold lines 2 are compressed to a tenth to a twentieth of the thickness of the origin fibre material with binder agent.

(18) In order to be able to compress the fold lines 2 more than the sides 3 the ridges 7 are provided on the core 9 or on the outer form 6 or on both the core 9 and outer form 6. The ridges 7 will also break or tear the fibres along their extent weakening the material thus providing the fold lines 2. Either the outer form 6 is compressed towards the core 9 or the other way round where the core 9 is expanding and thus pressing against the outer form 6.

(19) According a further embodiment the method comprises the step of crushing the fibres along the fold lines, further weakening the material in the fold lines. This may preferably be done during a phase of stripping the duct from the core. During stripping means grip the duct and withdraws the duct from the core.

(20) For example, wheels may run along the fold lines, crushing fibres by pressing against the fold lines of the duct. An anvil is preferably arranged on the opposite side of the fold line of the duct. Preferably every wheel has an anvil, the wheel being positioned on the inside of the duct and the anvil on the outside, although the opposite is also conceivable.

(21) At least two fold lines are further weakened by means of this arrangement. In case of six ridges in the core or outer form it is preferred to further weakening four of them in order to push the duct into a rectangular shape, corresponding to the embodiment shown in FIG. 3b.

(22) The fibres that will not be broken or deformed, which are intact, will remember the original state, i.e. the state they were formed into under production, for example circular cross section. In order to provide the memory in the material the amount of intact fibres is at least 20-70% in the weakened material along the fold lines, preferably 30-60% and most preferred 40-50% compared to the amount of fibres in the adjacent sides.

(23) It is also possible to decrease the amount of fibres along the fold lines 2 during production by not adding the same amount of fibres around the periphery but less along where the fold lines are meant to be. This could be made from the outside, inside or both or by for example arranging a rod (not shown) lengthwise at each position to be a fold line 2 providing an embodiment of the duct 1 in accordance with FIG. 4a. The rods are taken out after the compression step.

(24) In order to provide a sealed duct which would withstand fire and heat according to high level class fire requirements the duct may be laminated on the inside and/or outside, preferably at least on the inside but also on the outside. The foil used is preferably comprising at least one layer of metal and at least one layer of polymer.

(25) According to an embodiment a special foil is provided which withstands not only fire and heat but also adhere to the fibre duct even when it is repeatedly folded and unfolded. This foil is also good at withstanding cracking during repeated folding and unfolding. In order to provide the foil with some flexibility it is comprising an outer layer of aluminium, an intermediate layer a polymer having a melt point lower than polyethylene terephthalate (PET), an intermediate layer of polyethylene terephthalate (PET), and an inner layer a polymer having a melt point lower than polyethylene terephthalate (PET).

(26) The layer of PET is providing increased mechanical properties and flexibility. The polymer having a melt point lower than PET is for heat sealing between the layer and to the surface of the fibre duct or itself along an overlapping edge. Preferably the polymer having a melt point lower than PET is polyethylene (PE).

(27) It is also possible to add a layer of reinforcing glass fibres, preferably in the form of a net, between the intermediate layer of polymer having a melt point lower than PET and the intermediate layer of PET, or preferably between the intermediate layer of PET and the inner layer of polymer having a melt point lower than PET.

(28) The present invention is not limited to the embodiments described but can be modified within the scope of the appended claims.