Patent Description:
Within the area of concreting parts of houses and buildings, in particular concreting stairs, it is necessary to use formworks, i.e. a form or a mould, in place to hold in wet concrete until the concrete hardens and sets in the forms.

In the field of concreting parts of houses and buildings, there is a need of a large number of formworks to define the house parts, such as stairs. The formworks are conventionally manufactured on the concreting site in wood or timber boards, and sometimes even metal moulds are manufactured if special considerations applies, i.e. larger number of products, a higher need for precision or higher load on the sides of the formwork. Normally the formworks are made in wood boards, and the forms are applicable only for a relatively smaller number of concrete products. Furthermore, the formwork is often a unique specimen to the specific order of a concrete house part, especially when it comes to stairs. This means that subsequent to the concreting no or only little reuse can be made of the formworks, which are then discarded as an industrial waste product from the concrete construction.

Particularly when it comes to formworks for concreting stairs a need of very specific and unique formworks is identified and in addition, the formworks have to be of an extremely detailed execution as a stair is a complex form due to the many steps, corners, etc..

The use of wood material for producing a stair formwork and the manual construction is both time consuming and rather demanding with respect to dedicated skilled personnel. Additionally, wood formworks, especially large formworks as formworks for stairs, have a heavy weight and thereby a heavy and troublesome load for the skilled person to handle. It also requires storage room for the formworks before and after use for concreting. Furthermore, the wood material is a significant industrial waste production from the concreting process.

<CIT> discloses a cardboard formwork for concreting steps of stairs, comprising a plurality of individual cardboard elements, each of the individual cardboard elements being assembled with mortise-tenon, biscuit and tongue-groove joints. <CIT> discloses another formwork for concreting a support structure for a stair, such as a pillar and beam structure, concreting said support structure in a body of water.

Hence, an improved formwork for concreting stairs would be advantageous, and in particular a more efficient, economically and/or reliable formwork for the concreting industry would be advantageous.

In particular, it may be seen as an object of the present invention to provide a formwork for prefabricated stairs that solves the above mentioned problems of the prior art disclosing the use of manually constructed formworks, typically in wood.

Thus, the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a cardboard formwork for concreting a prefabricated stair, the cardboard formwork adapted for concrete being poured into said cardboard formwork during concreting, wherein:.

The invention is particularly, but not exclusively, advantageous for obtaining an improved and simplified formwork for concreting stairs. Particularly, the use of cardboard instead of wood, normally used in this field, has a significantly simplified manufacturing, lowering production time, improving the working environment due to lower weight and improving the financial expenses of a formwork for concreting a stair.

Furthermore, the invention is particularly, but not exclusively, advantageous for being more environmentally friendly because cardboard can normally be recycled more easily than wood or metal. The cardboard formwork of the invention is a very sustainable variant of a formwork for stairs, as the formwork is exceptionally environmentally friendly compared to prior known stair formworks.

The cardboard of the formwork is preferably made of recyclable cardboard capable of being recycled after concreting as defined by appropriate waste standards, formal or de-facto standards, optionally after light or moderate cleaning/removal of concrete remnant material from the casting. Additionally or alternatively, the cardboard itself is made of recycled material from recycled paper or cardboard to lower the environmental footprint of the invention.

In the context of the present invention, a 'stair' may be understood to have a stair-like structure and shape, as the skilled person or engineer in building construction will readily understand. In particular, it is to be understood that a stair in the context of the invention is defined as having a plurality of steps - thereby a minimum of two steps.

In the context of the present invention, a 'prefabricated concrete stair' may be understood as a stair made of concrete and which is fabricated off-site, that being in contrary to stairs being fabricated on site.

In the context of the present invention, a 'cut' in the cardboard elements may be understood as preferably straight cut into the cardboard, the cut being in any preferred angle, wherein nothing from the cardboard element should be removed after the cut. That being contrary to the cutout defined below.

In the context of the present invention, a 'cutout' may be defined by a plurality of cuts made into the cardboard so as to facilitate a removal of a piece of the cardboard element after the cutout is prepared. Thus, a cutout may generally be defined as a shape that has been cut out from a material, in the present invention the material being cardboard.

In the context of the present invention, 'facing' may be understood as a synonym to e.g. fronting or abutting. Meaning that the cardboard elements facing the concrete constitute the part of the cardboard formwork, which during concreting is in contact with the concrete.

In the context of the present invention, a 'substantial part' may be understood as the most of or the majority of the formwork - Meaning that e.g. <NUM>%, <NUM>%, <NUM>% or preferably <NUM>% to <NUM>% of the formwork is made of cardboard.

In the context of the present invention, 'cardboard' may be understood to mean heavy-duty paper of various strengths and thicknesses, in particular the cardboard is understood as comprising sandwich-elements i.e. a composite structural paper material having layers of cardboard facing each other, for example for obtaining higher strength and/or improved humidity repellent properties for concrete casting or moulding, the layers of cardboard may be oriented in various directions relative to the surface of the cardboard, e.g. parallel to the surface or orthogonal to the surface, or combinations thereof. In particular, a part of the cardboard sandwich-element may have a fluted core, and/or it may have one or more corrugated layers.

Preferably, the cardboard sandwich-element may have an in-plane and out-of-plane compressive strength of at least <NUM>, <NUM> or <NUM> kN/m and/or at least <NUM>, <NUM>, <NUM> kN/m, respectively, to provide sufficient strength for the formwork during the entire casting process, e.g. several hours of casting. Thus, the casting process may last at least <NUM> hours, <NUM> hours, <NUM> hours, <NUM> hours, <NUM> hours, <NUM> hours, <NUM> hours, <NUM> hours, <NUM> hours, <NUM> hours, <NUM> hours, <NUM> hours, <NUM>-<NUM> days, or even longer. Preferably, the cardboard sandwich-element may have a total thickness of at least <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>, or thicker, to provide sufficient thickness for the formwork during the casting process.

Alternatively or additionally, the cardboard sandwich-element may have a humidity repellent surface layer, such as a wax or polymer-coating, facing the concrete stair during casting, or molding, so as to repel or prevent any liquids from the concrete to moisture, or wet, the cardboard formwork during casting, which may negatively influence the strength and durability of the cardboard formwork. It is known within the field of cardboards to define a so-called wet strength including the ability to withstand humid or wet conditions; the wet strength may be increased by appropriate wet strength adhesives for cardboards, such as water resistant adhesives, e.g. glues, paste, or mucilage. The humidity repellent surface layer is preferably chosen for being subsequently recyclable together with the cardboard. Alternatively, the humidity repellent surface layer may be, at least partly, removed prior to recycling of the cardboard formwork.

In an embodiment of the invention, the formwork facing the concrete during concreting of the stair is made entirely of cardboard.

The embodiment is particularly, but not exclusively, advantageous for providing a stair formwork with the exact desired stair design. Many unique designs of concrete stairs are often very advanced to produce in a wood formwork, as the design might have several different proportion and special needs that cannot be made by wood formwork or is very challenging and consuming and demanding to produce. By producing the part of the formwork facing the stair entirely in cardboard, it provides a formwork being able to produce more or less every design a customer potentially wants of their stair, as cardboard is very easy to form in any desired design.

Preferably, the entire formwork is made of cardboard, though in an embodiment of the invention, the substantial part of the formwork is made of cardboard and minor parts are made in other material e.g. some reinforcement part on the outer side of the formwork is made of wood and/or metal. The 'outer side' of the formwork being the part of the formwork not facing the concrete during concreting.

In an embodiment of the invention, the part of the formwork intended for forming the steps during concreting of the stair is made entirely of cardboard.

The embodiment is particularly, but not exclusively, advantageous for providing a stair formwork with the exact desired step design. The steps of the concrete stairs often being the ones most advanced to produce in a formwork, as the steps might have several different proportion and special needs.

In an embodiment of the invention, the stair being concreted in the cardboard formwork is a freestanding stair.

The embodiment is particularly, but not exclusively, advantageous for possibly providing a stair with a lot lower quantity of concrete needed compared to a fully supported stair from beneath, and thereby providing a stair with a lot lower weight and a lot easier to handle.

In the context of the present invention, 'freestanding stair" may be understood to mean a concreted stair only being supported from below at the two ends of the stair when mounted in a building.

In an embodiment of the invention, the assembling of the cut cardboard elements is made as a puzzle-assembly, wherein a cutout of a first cardboard element is fitting a cutout of a corresponding second cardboard element. The embodiment is particularly, but not exclusively, advantageous for providing an easy and rapid, but still sufficient and durable, assembly of the cardboard elements of the formwork for concreting a stair.

In the context of the present invention, a 'puzzle-assembly' may be understood as an assembly wherein two (or more) pieces of cardboard due to their matching cut and/or cutouts are fitting substantially together, preferably fitting ideally, when assembled, so as to form two (or more) interlocking cardboard elements. This means that two adjacent elements are connected in such a way that the elements are locked in at least one direction. One embodiment of an interlocking puzzle-assembly of cardboard elements could e.g. be when a first element is cut to form a protruding part on one of its sides and a corresponding second cardboard element is cut with an inward part on one of its sides, the protrusion and the inward part engaging and fitting substantially together, preferably fitting ideally, to each other.

One cardboard element can fit with a plurality of other cardboard elements, as an interlocking puzzle-assembly can be made on any side of a cardboard element. if a cardboard element is cut in a shape having four sides, the cardboard element potentially being able to interlock with <NUM> other cardboard elements.

In an embodiment of the invention, the assembly of the cardboard elements is made by fixing a cardboard element between at least two other cardboard elements via tension.

The embodiment is particularly, but not exclusively, advantageous for providing an easy and rapid, but still sufficient and durable, assembly of the cardboard elements of the formwork for concreting a stair.

Furthermore, the embodiment is advantageous as the assembly of two cardboards via tension provides an assembly without the need of at least two fitting cuts and/or cutouts as when e.g. a puzzle-assembly is prepared.

In an embodiment of the invention, the assembly of the cardboard elements is made by fixing a cardboard element between at least two other non-cardboard elements via tension.

The embodiment is particularly, but not exclusively, advantageous for providing an even stronger cardboard formwork.

In an embodiment of the invention, the assembling of the cardboard elements is made by inserting at least a first cardboard element into at least a second other cardboard element. The at least two corresponding cardboard elements being cut to allow an insertion, wherein the insertion performs a function of an assembly.

In an embodiment of the invention, the cardboard formwork comprises:.

The embodiment is particularly, but not exclusively, advantageous for providing a formwork for concreting a stair potentially made entirely of cardboard. This embodiment of the invention thereby provide a cardboard formwork having a simplified manufacturing, a lower production time, an improved working environment due to lower weight, improved financial expenses as the only material needed is cardboard and a more environmentally friendly cardboard because cardboard can normally be recycled more easily than wood, or metal. The cardboard formwork therefore being a very sustainable variant of a formwork for stairs.

Furthermore, the embodiment is particularly, but not exclusively, advantageous for providing a stair formwork wherein the at least three main parts of the formwork can easily be changed if any unique design of the stair is demanded. The three pieces can easily be cut in different dimensions, different shapes with different cut and/or cutouts and still be assembled to form a formwork for concreting a stair. This provides a stair formwork that very easily can adopt the exact design of a stair, which a customer might demand.

Additionally, the embodiment is particularly, but not exclusively, advantageous for providing a formwork, which is overall made of three main parts, wherein the three parts are very easy to handle when assembling the formwork.

In an embodiment of the invention, the formwork comprises a baseplate, wherein the formwork is assembled by inserting one or more cardboard pieces of the formwork into the baseplate for stabilizing and supporting the cardboard formwork, the baseplate preferably being positioned at the bottom of the cardboard formwork.

The embodiment is particularly, but not exclusively, advantageous for providing a stair formwork that easily can be manufactured suitable for concreting a large stair construction, which often would need some kind of a reinforcing supporting element. By inserting a baseplate as an extra supporting element at the bottom of the formwork, the formwork provides an even stronger formwork and thereby allowing the stair, which has large dimensions, to be concreted in the formwork. Furthermore, the embodiment is particularly, but not exclusively, advantageous for providing a stair formwork that is stabilized in a unique manner, as the baseplate provide an extra support and stabilizing effect to the formwork.

Additionally, the embodiment is particularly, but not exclusively, advantageous for providing a stair formwork being easily assembled on the baseplate.

In an embodiment of the invention, the cardboard formwork comprises one or more of cardboard support-elements assembled to the base-plate. The embodiment is particularly, but not exclusively, advantageous for providing extra support and stability to the the formwork.

In an embodiment of the invention, the cardboard formwork comprises one or more through-going cardboard elements, the one or more through-going cardboard elements preferably being attached to the side-pieces. The embodiment is particularly, but not exclusively, advantageous for providing an even better stabilization and support of the formwork.

In an embodiment of the invention, the formwork during concreting is constructed with reinforcement plates on one or more of the sides of the formwork, the plates possibly being made of other materials than cardboard, and wherein the reinforcement plates are interconnected via at least one through-going threaded rod.

The embodiment is particularly, but not exclusively, advantageous for providing a stair formwork that easily can be manufactured suitable for concreting large stair constructions, which often would need some kind of a reinforcing support element. The reinforcement elements are providing an extra support at the sides of the formwork and thereby providing an even stronger formwork allowing the stair having large dimensions to be concreted in the formwork.

Furthermore, the embodiment is particularly, but not exclusively, advantageous for proving a stair formwork that is stabilized in a unique manner, as the interconnection of the reinforcement plates via at least one through-going threaded rod provide an extra support and stabilizing effect to the formwork.

In an embodiment of the invention, the cardboard formwork is providing a prefabricated concrete stair having one or more rounded front edges, the rounded front edges being constructed by folding cardboard elements with custom made cuts, so that the cardboard element can form a curvature at the one or more rounded front edges.

The embodiment is particularly, but not exclusively, advantageous for providing a cardboard formwork that provides a concreted stair with rounded front edges, which is a huge demand today - Up to about <NUM>% of the customers request stairs having rounded front edges. Having rounded front edges on a stair leads to the advantage that the stair steps are in the most comfortable shape as possible. A stair with sharp edges have the disadvantage of potentially hurting e.g. the foot or the shin of a person who by accident bumps into the step edge.

Also the rounded front edges provide an aesthetic advantage to the stair.

In the context of the present invention, 'rounded edges' may be understood as edges, which is facing the person walking on the stair, having some kind of rounded form. The rounded form being in contrast to an angular edge, which is often in a rectangular form. The form of the rounded edges can potentially be made in any desired rounded form and with any desired radius of the rounding at the edge of the stair.

In an embodiment of the invention, the curvature for forming the one or more rounded front edges is made with a predetermined radius, the radius being determined by at least:.

The embodiment is particularly, but not exclusively, advantageous for providing a formwork that can easily be adopted to provide any desired shape of the curvature of the rounded edges.

In an embodiment of the invention the number of cuts prepared into the cardboard are in the range of <NUM>-<NUM>, preferably in the range of <NUM>-<NUM>, most preferably in the range of <NUM>-<NUM>.

In an embodiment of the invention, the cuts prepared into the cardboard are made as <NUM>-<NUM> cut, preferably <NUM>-<NUM> cut, most preferably <NUM>-<NUM> cut.

In an embodiment of the invention, the cuts prepared into the cardboard are made in the cardboard only leaving ½-<NUM> of the bottom of the cardboard not being cut through.

The embodiment is particularly, but not exclusively, advantageous for proving a rather specific dimension of the cut into the cardboard. The cut dimension having an operative effect one the cardboard to be folded to form the rounded edge of the stair.

In an embodiment of the invention, the cut are made with an angle in the range of <NUM>-<NUM> degree, preferably in the range of <NUM>-<NUM> degree, most preferably in the range of <NUM>-<NUM> degree.

In an embodiment of the invention, the cuts for forming a curvature are made with a distance from the centre of the curvature. The embodiment is particularly, but not exclusively, advantageous for providing an optimal technique of cutting a cardboard to be folded to form a curvature.

In an embodiment of the invention, the cardboard formwork is providing a stair having one or more string coves. In the context of the present invention, 'string cove' may be understood as one or more of the side edges of the steps having some kind of protrusion. A synonym of a string cove might be a "protruding edge", a "washing edge", a "water stopping edge" or other relevant alternative designations.

The embodiment is particularly, but not exclusively, advantageous for providing a cardboard formwork that provides a concreted stair with string coves on the steps, which is a huge demand today - Up to about <NUM>-<NUM>% of the customers request stairs having string coves. Having string coves on the steps of the stair leads to the advantages that the stair steps can easily be washed without the soap and water flushes over the side edges. The water is kept on the steps within the string coves due to the protrusion of the string coves.

In an embodiment of the invention, a plurality of step-pieces are comprised in the formwork, wherein the step-pieces are being assembled together, preferably by puzzle-assembly.

The embodiment is particularly, but not exclusively, advantageous for providing the possibility of forming a cardboard formwork for concreting a relatively large stair comprising many steps. The more the steps of the stair, the more cardboard step-pieces might be needed to form the formwork.

In an embodiment of the invention, the one or more string coves are constructed by introducing at least one string-cove-piece into the cardboard formwork, the string-cove-piece being an elongated cut cardboard element positioned between a side-piece cardboard element and a step-piece cardboard element of the cardboard formwork. The embodiment is particularly, but not exclusively, advantageous for providing an effective and easy construction of a formwork, which can provide a concreted stair with string coves.

The embodiment is particularly, but not exclusively, advantageous for providing one or more additional pieces of the cardboard formwork e.g. the string-cove-pieces, which are optional pieces - meaning that the cardboard formwork can easily be produced to include one or more string-cove-pieces, if one or more string coves is desired on the stair. If a string cove is not desired on the stair, the formwork can also easily be produced without the additional pieces.

Furthermore, the embodiment is particularly, but not exclusively, advantageous for providing one or more additional pieces, which easily can be customized depending on the desired dimension of the string-coves on the stair. As the one or more string-cove-pieces are elongated cut cardboard elements, preferably without any protrusions or any inward parts, the additional elongated string-cove-piece is very easy to produce in any desired dimension. The string-cove-piece is preferably also being cut to provide a string-cove with rounded edges.

In an embodiment of the invention, the at least one string-cove-piece is inserted into an adapted cutout of the side-piece element and is adjacent to the step-piece element.

The embodiment is particularly, but not exclusively, advantageous for providing a very easy but effective assembly of a cardboard formwork with a string-cove-piece, as the string-cove-piece is straightforwardly inserted into the adapted cutout of a side-piece cardboard element. This assembly being straightforward but in the same time being a very effectively and strong attachment.

In a second aspect, the present invention relates to a method for manufacturing a cardboard formwork for concreting a prefabricated stair, preferably concreting the stair in one piece, the method comprising:.

wherein the folded and assembled cardboard elements facing the concrete constitute a substantial part of the formwork, the formwork being capable of supporting the prefabricated stair during the process of concreting said stair.

The present invention according to the second aspect is particularly, but not exclusively, advantageous for providing a method that may significantly lower production time, improve the working environment due to lower weight and is more environmentally friendly because cardboard can normally be recycled more easily than wood, or metal.

An embodiment of the invention relates to a method for manufacturing the cardboard formwork, wherein the cardboard formwork is assembled as a puzzle, where cuts and/or cutouts of a first cardboard element are fitting a cut and/or cutout of a second corresponding cardboard element, and wherein the first cardboard element can be cut to be assembled with a corresponding second cardboard element.

The embodiment is particularly, but not exclusively, advantageous for providing an easy and rapid, but still sufficient and durable, method of assembling of the cardboard elements of the formwork for concreting a stair.

In an embodiment of the invention relates to a method for manufacturing the cardboard formwork, wherein the cardboard formwork is assembled by fixing a cardboard element between at least two other elements via tension.

Furthermore, the embodiment is advantageous as the method of assembling of cardboard formwork via tension provide an assembly without the need of at least two substantially fitting cuts and/or cutouts as when e.g. a puzzle-assembly is prepared.

In a third aspect, the present invention relates to a computer program being adapted to enable a computer system comprising at least one computer having data storage means in connection therewith to control a cutting apparatus, or cutting system, for cutting cardboard elements for a cardboard formwork according to the first aspect.

Thus, the computer program product, e.g. in the form of computer-aided drawings (CAD) with the appropriate instructions for cuts and cutouts, may enable a cutting apparatus to implement, at least partly, the invention according to the first aspect, the folding and assembling of the formwork preferably being subsequently performed manually by an operator/technician, and/or by a robotic device.

The invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

In the following, the present invention will be described in detail in connection with a preferred embodiment thereof with references to the accompanying figures.

<FIG> schematically shows a formwork <NUM> according to a presently preferred embodiment of the invention. The cardboard formwork is used for concreting a prefabricated stair, wherein concrete is being poured into the cardboard formwork during concreting, and wherein the cardboard formwork is constructed by folding and/or assembling one or more cardboard elements <NUM>, and the one or more cardboard elements are cut with predetermined cuts <NUM> and/or cutouts <NUM> (not shown). Furthermore, the assembled cardboard element(s) facing the concrete constitute a substantial part of the formwork, the formwork being capable of supporting the prefabricated stair during the process of concreting said stair.

Moreover, <FIG> schematically shows a present preferred embodiment of the invention, wherein the cardboard formwork <NUM> comprises one step-piece <NUM> forming the steps of the stair being concreted and two fixing-pieces <NUM> (only one is visible) fixing the at least one step-piece into a desired step-form and wherein the two fixing-pieces is assembled with the step-piece using puzzle-assembly <NUM>, wherein cutouts <NUM> (shown in <FIG>) of the step-piece are fitting the cutouts of the corresponding fixing pieces. Furthermore, the formwork in <FIG> comprises a side-piece <NUM> for forming a side of the stair being concreted. In the preferred embodiment of the invention a second side-piece (not shown) is provided on the out-fronting side of the formwork in <FIG> for forming a second side of the stair being concreted. Also the preferred embodiment illustrated in <FIG> comprises a string-cove-piece <NUM> for providing a stair having one or more string-coves <NUM> (shown in <FIG>). The string-cove-piece being an elongated cut cardboard element positioned between a side-piece <NUM> cardboard element and a step-piece <NUM> cardboard element of the cardboard formwork, and wherein the string-cove-piece is inserted into an adapted cutout <NUM> (shown in <FIG>) of the side-piece element and being adjacent to the step-piece element. Beneath the adjoining of the step-piece and the string-cove-piece a support might be provided (not shown). In the cardboard formwork illustrated in <FIG>, the concrete to be poured into the formwork will thereby be facing the part of the step-piece and side-piece so as to form - by the reverse forming process - a stair with string-coves <NUM> (shown in <FIG>).

Additionally the cardboard formwork illustrated in <FIG> is suitable for providing a prefabricated concrete stair having one or more rounded front edges <NUM> (shown in <FIG>) being constructed by folding the cardboard elements <NUM> with custom made cuts <NUM> (shown in <FIG>), so that the cardboard element can form a curvature <NUM> for forming the one or more rounded front edges of the stair being concreted. The curvature of the one or more rounded front edges are made with a predetermined radius and the radius is determined by at least: the number of cuts <NUM> (shown in <FIG>), the angle of the cuts, and the placement of the cuts on the cardboard element <NUM> forming the rounded front edges.

<FIG> schematically shows two fixing-pieces <NUM> of a cardboard formwork for concreting a stair. The two illustrated fixing-pieces are suitable for fixing at least one step-piece <NUM> (shown in <FIG>) into a desired step-form. The two fixing-pieces illustrated is each made of one cut cardboard element <NUM> and the cardboard is cut to provide a puzzle-assembly <NUM> with a step-piece <NUM> (shown in <FIG>). The shape and design of the puzzle-assembly cutouts can be made in several different shapes and designs. The invention is not limited to the specific design illustrated in <FIG>, which is just one of many different cutouts of the fixing-pieces <NUM>. The one or more cutouts <NUM>, <NUM> and their corresponding fitting parts may together collectively form a puzzle-assembly <NUM> (shown in <FIG>). The cutouts for puzzle-assembly in the illustrated fixing-pieces are made with two relatively large protruding parts <NUM> and furthermore a plurality of relatively smaller protruding parts <NUM>. Depending on the size of the stair to be concreted in the form, the fixing-pieces could have <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>-<NUM>, <NUM>-<NUM> or even more relatively large protruding parts <NUM>, if the stair being concreting has large dimensions and thereby need larger fixing-pieces. In addition, the number of smaller protruding parts <NUM> also depends on the size of the stair to be concreted in the formwork.

When assembling a cardboard formwork with a puzzle-assembly, the protruding parts both the relatively larger and the relatively smaller are all cut in a very specific shape so as to fit substantially with the cutouts (shown in <FIG>) of the corresponding step-piece (shown in <FIG>), and so they have the strongest possible fixing.

In other embodiments of the invention the fixing-pieces <NUM> are not necessarily made with cutouts for a puzzle-assembly, as any other preferred assembly e.g. via tension between at least two other elements or via an attachment made as an insertion of element into another, is also a possible embodiment.

<FIG> schematically shows a step-piece <NUM> of a cardboard formwork <NUM> for concreting a stair when the step-piece is folded and ready to be assembled with the other parts of the formwork. The step-piece <NUM> illustrated is made of one cut cardboard element and the cardboard is cut to provide a puzzle-assembly <NUM> with at least one fixing-piece <NUM>. The shape and design of the puzzle-assembly cutouts <NUM> can be made in several different shapes and designs. The invention is not limited to the specific design illustrated in <FIG>, which is just one of many different cutouts of the step-piece.

The cutouts for puzzle-assembly in the illustrated step-piece <NUM> are made with four relatively large protruding parts <NUM> on each side (only one side is illustrated). Depending on the size of the stair to be concreted in the formwork, the step-piece could have <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>-<NUM>, <NUM>-<NUM> or even more relatively large protruding parts, if the stair being concreting has large dimensions and thereby need a larger step-piece. Also it could comprise relatively smaller protruding parts <NUM>.

When assembling a cardboard formwork with a puzzle-assembly, the protruding parts are all cut in a very specific shape so as to fit substantially with the cutouts of the corresponding fixing-piece <NUM> (shown in <FIG>), and so they have the strongest possible fixing.

In other embodiments of the invention the step-piece <NUM> is not necessarily made with cutouts for a puzzle-assembly, as any other preferred assembly e.g. via tension between at least two other elements or via an attachment made as an insertion of element into another, is also a possibility.

Furthermore, <FIG> illustrates a step-piece <NUM> being cut so as to provide a formwork for a stair, which is to be concreted with rounded front-edges <NUM> (shown in <FIG>).

<FIG> schematically shows a top-view of a step-piece <NUM> of a cardboard formwork for concreting a stair, when the step-piece is not yet folded. The cutouts <NUM> made around the edges of the cardboard is in this illustrated embodiment made to be assembled via puzzle-assembly.

The cuts <NUM> made into the surface of the step-piece (illustrated with dotted lines) is cuts <NUM> into the cardboard, as no cardboard is removed after the cut.

The cuts are potentially performed in both a vertical direction (V) and a horizontal direction (H) of the cardboard, when seeing the cardboard from above as illustrated in <FIG>.

The horizontal H cuts <NUM> are made to form the rounded front edges of the stair <NUM> (shown in <FIG>). The cuts are performed with a specific number of cuts, with specific angles and with specific placements of the cuts into the cardboard element, to form the exact desired rounded front edges on the stair to be concreted in the formwork.

The vertical V cuts <NUM> is made to allow folding the side of the step-piece <NUM> to form a perpendicular folding and thereby allow the puzzle-assembly cutouts <NUM> on the sides of the step-piece to be assembled with corresponding fixing-pieces.

<FIG> schematically shows a string-cove-piece <NUM> of a cardboard formwork for concreting a stair having one or more string-coves <NUM> (shown in <FIG>). The string-coves of the stair are constructed by introducing at least one string-cove-piece <NUM> into the cardboard formwork, and one embodiment of a string-cove-piece is illustrated in <FIG>. The string-cove-pieces in <FIG> is an elongated cut cardboard element to be positioned between a side-piece <NUM> (shown in <FIG>) cardboard element and a step-piece <NUM> cardboard element of the cardboard formwork. The string-cove-piece illustrated is suitable for being inserted into an adapted cutout <NUM> (shown in <FIG>) of the side-piece element and being adjacent to the step-piece element.

Furthermore, <FIG> illustrates a string-cove-piece <NUM> being cut so as to provide a formwork for a stair, which is to be concreted with rounded front-edges <NUM> (shown in <FIG>).

<FIG> schematically shows a side-piece <NUM> of a cardboard formwork for concreting a stair. The side-piece being for forming the sides of the stair being concreted, the side-piece <NUM> is made of at least one cut cardboard element.

The side-pieces illustrated in <FIG> is suitable for attachment and fixation of an elongated string-cove-pieces <NUM> (shown in <FIG>) by inserting the string-cove-piece into the adapted cutout <NUM> of the side-piece <NUM> element.

The side-piece <NUM> is suitable for being attached to a baseplate <NUM> (shown in <FIG>) of the formwork (not shown) either via assembly, via insertion or via tension between two other elements.

<FIG> illustrates a cardboard formwork of a cardboard formwork for concreting a stair comprising a base-plate <NUM>, wherein the formwork is assembled by inserting one or more cardboard pieces of the formwork into the baseplate <NUM> for stabilizing and supporting the cardboard formwork, the baseplate preferably being positioned at the bottom of the cardboard formwork. Furthermore, <FIG> illustrates a cardboard formwork comprising a plurality of cardboard support-elements <NUM> assembled to the base-plate, the support-elements are supporting and stabilizing the formwork during concreting.

<FIG> illustrates five support-elements <NUM> attached to the base-plate <NUM>, the number of support element are variable. A formwork with no, or with <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or more support-elements <NUM> is within the scope of the invention. <FIG> furthermore illustrates the possibility of a cardboard formwork comprising through-going cardboard elements <NUM> attached to the side-pieces <NUM> and for providing an even better stabilization and support of the formwork. Only one through-going cardboard element <NUM> is also a possible variant of the invention. The through-going cardboard elements are preferably engaging with the cardboard support-elements <NUM>.

In addition, it is illustrated in <FIG> that the cardboard support-elements <NUM> are prepared to potentially allow a plurality of through-going treaded rods <NUM> (shown in <FIG>) to interconnect reinforcement plates via a plurality of holes made in the support elements.

<FIG> shows a cardboard formwork filled with wet concrete and comprising reinforcement plates <NUM> being interconnected via through-going threaded rods <NUM>. The cardboard formwork illustrated in <FIG> is a formwork comprising reinforcement plates <NUM> (shown in <FIG>) on two of the sides of the formwork, the plates possibly being made of other materials than cardboard, in <FIG> they are made of wood. The reinforcement plates are interconnected via at least one through-going threaded rod <NUM>, the embodiment illustrated in <FIG> is interconnected via <NUM> through-going threaded rods <NUM>. The number of through-going threaded rods vary depending on the size of the stair being concreted.

<FIG> shows a flow-chart of a method according to the invention for a method for forming a cardboard formwork <NUM> (shown in <FIG>) for a stair, the method comprises:.

The above method according to the invention is performed in this order, possibly one or more steps may be combined as the skilled person will readily understand.

<FIG> shows a prefabricated stair <NUM> concreted in a cardboard formwork <NUM> (shown in <FIG>). The stair illustrated is a preferred embodiment of a prefabricated stair having a plurality of steps <NUM>, having string-coves <NUM> at two of the ends of the steps <NUM> and the steps is provided with rounded front-edges <NUM>.

Furthermore <FIG> illustrate a stair suitable for being supported only at the two ends of the stair <NUM> when mounted in a building construction.

<FIG> shows a plurality of prefabricated stairs <NUM> concreted in a cardboard formwork <NUM> (shown in <FIG>). The stairs illustrated is a preferred embodiment of prefabricated stairs having a plurality of steps <NUM>, having string-coves <NUM> at two of the ends of the steps <NUM> and the steps is provided with rounded front-edges <NUM>.

In short, the invention relates to a cardboard formwork <NUM> for concreting a stair as shown in <FIG>, wherein concrete is being poured into the cardboard formwork during concreting. The cardboard formwork is constructed by folding and assembling two or more cardboard elements <NUM>, and the two or more cardboard elements are cut with predetermined cuts <NUM> and/or cutouts <NUM>. The assembled cardboard elements facing the concrete constitute a substantial part of the formwork, the formwork being capable of supporting the prefabricated stair during the process of concreting said stair.

The invention lowers production time, improves the working environment due to lower weight and is more environmentally friendly because cardboard can normally be recycled more easily than wood, or metal.

The invention can be implemented by means of hardware, software, firmware or any combination of these. The invention or some of the features thereof can also be implemented as software running on one or more data processors and/or digital signal processors.

Claim 1:
A cardboard formwork (<NUM>) for concreting a prefabricated stair (<NUM>), the cardboard formwork adapted for concrete being poured into said cardboard formwork during concreting, wherein:
- the cardboard formwork is constructed by folding and assembling two or more cardboard elements (<NUM>), and
- the two or more cardboard elements are cut with predetermined cuts (<NUM>) and/or cutouts (<NUM>), and
wherein the folded and assembled cardboard elements facing the concrete constitute a substantial part of the formwork, the formwork being capable of supporting the prefabricated stair during the process of concreting said stair.