Patent Description:
As commonly known, a wind turbine comprises among others several turbine blades attached to a hub. The blades interact with the wind making the hub rotate. A generator is coupled to the hub, which generator is driven by the rotating hub.

The turbine blades of nowadays turbines have enormous dimensions in length and width and are becoming even larger in size.

A wind turbine blade comprises a hollow blade shell having a circular cross-section in the area of the root, which root is fixed to the hub, which circular cross-section changes to an airfoil cross-section towards the blade tip. In the inner of the hollow blade shell, preferably in the airfoil cross-section region, one or more webs are arranged, which are fixed to the lower and upper shell parts for reinforcing the hollow shell. The hollow shell itself is usually made of fiber mats, preferably glass fiber mats, which are arranged in several layers, and preferably core elements for example made of wood like balsa wood or formed polymer etc. The blade building material is infused with resin, so that, when the resin is cured, the whole blade building material is firmly embedded in the hardened resin matrix.

Several techniques are known for producing a turbine blade. According to a first technology, two separate shell halves are produced, i.e. a lower and an upper shell half, which are then fixed or glued together along their abutting edges. Another technology is the one-shot technology, where the whole blade is produced as a one-piece blade, wherein all blade building material is arranged in a respective mould and then completely infused with the resin. No matter which technology is used, it is always necessary to arrange the blade building material in the respective half shell mould or the one-shot mould. This involves arranging each separate fiber mat like the glass fiber mats in the respective mould in chordwise direction. If the so-called butterfly technology, in which as mentioned the two separate half shells are produced, is used, each fiber mat corresponds to the half of the circumference of the respective half shell and needs to be manually arranged in the respective half mould. If the one-shot technology is used, each fiber mat corresponds to the whole circumference of the complete shell or blade body, seen in the circumferential direction. Also, this arrangement is done manually. In addition to arranging the fiber mats, it is also necessary to arrange further building material like the core elements or any other reinforcing elements etc., which arrangement is also done manually.

According to another technology, the blade shell is produced by using pre-fabricated preform elements made of a blade building or preform element building material, which comprises fiber mats and a binding agent and, optional, core elements. The binding agent is arranged only locally and is used for fixating the fiber mats to each other, so that the preform element has a specifically defined setup and shape, but still has an open and therefore infusible structure. A number of these preform elements, which have a remarkable width of approximately <NUM>-<NUM> and a length of approximately <NUM>-<NUM>, is used for building a half shell or the whole one-piece shell by finally embedding them in a resin matrix. As also these preform elements require the arrangement of the respective preform building material like fiber mats, the binding agent and, optionally, the core elements, there is a need for and arrangement allowing for simply and quickly producing such a preform element.

<CIT> discloses a mould arrangement showing features of the preamble of claim <NUM>. It comprises a mould element with a form-defining mould surface. This mould element receives preform building material. <CIT> further discloses a first heating means for heating the preform building material from below the mould element. This first heating means is fixedly arranged at the mould element and may preferably be integrated into the mould element. Further, a second heating means is provided, which heats the building material from above, so that the material may be heated from two opposite sides. The second heating means may for example be a radiator like an infrared radiator. In an alternative, also a hot air heating means may be provided as a second heating means. This second heating means is realized by means of a heat isolating foil or plate attached to the mould element for realizing an air channel, through which the air is blown.

It is therefore an object of the invention to provide an arrangement which allows for the simple and fast production of a preform element of a wind turbine blade.

To address this object, the invention proposes a mould arrangement for producing a preform element of a wind turbine blade according to claim <NUM>.

According to the invention, a specific mould arrangement is used for manufacturing preforms. This mould arrangement is adapted in its size to the size of the preform element, and therefore roughly corresponds in its width and length to the width and length of the preform element to be produced. The mould therefore is way smaller than moulds used for producing a complete half shell or the one-piece shell.

The mould arrangement comprises a mould carrier, which is the basic mould construction, on which the production process is performed. On this mould carrier, which is usually arranged on the floor, a plate- or tray-like mould element is arranged. This plate- or tray-like mould element is a thinner element, which is adapted to receive the blade building material. The mould element has a mould surface, on which the preform building material is arranged. This mould surface may be flat or may be curved, corresponding on the requested geometry of the preform element to be built. On this mould surface, the preform building material, i.e. especially the fiber mats, are arranged. This is quite simple and can be done manually, as the dimension of each fiber mat corresponds in maximum to the final width and length of the preform element. Therefore, the workers can easily arrange the one or several fiber mats in respective layers on the mould surface. The same is true for the optionally needed core elements and the needed and locally provided binding agent.

Furthermore, the mould arrangement comprises two separate heating means, which are adapted to heat the building material after its arrangement on the mould surface. A first heating means is arranged below the mould element and is adapted to heat the preform building material from below. It therefore heats the plate- or tray-like mould element and via this mould element the building material. The second heating means is adapted to heat the blade building material from above. This second heating means therefore applies the heat from the opposite direction compared to the first heating element. Therefore, the building material is perfectly heated from both sides and over the whole area, where it is arranged, in order to melt the binding agent, which then wets the fiber mats and, if arranged, the core elements, for fixating them after the binding agent is again cured in order to receive a fixated and stabilized preform element.

It is obvious, that this mould arrangement allows for a simple and fast production of a preform element. As mentioned, it is possible to easily and quickly arrange the building material on the mould surface, as the dimension of the preform building material, especially of the fiber mats, solely corresponds to the final dimension of the preform element. Also, the heating process can be performed very quickly, as a double-side heating is performed, using the first and second heating means, which are arranged on opposite sides of the building material and which allow for a very fast heating process. After the heating is performed, it is only necessary to cool the building material for curing the previously melted binding agent, which is applied as a powder or granulate or is a respective glue, for finally receiving the preform element.

According to a first embodiment, the first heating means comprises one or more pipes extending below the mould element adapted to carry a circulating heating means. The first heating means comprises a pipe arrangement, which is for example in a meandering shape arranged directly below the bottom of the mould element. Preferably, it is arranged as close as possible to the bottom of the mould element or directly fixed to the bottom of the mould element to have an excellent heat transfer. The geometry of the pipe or pipes respectively the pipe arrangement is preferably such that it covers nearly the whole bottom surface, respectively at least an area, on which on the mould surface the blade building material is applied. The pipe arrangement geometry is such that the heat is applied preferably uniformly.

Through the pipe or pipes a heating means circulates. Therefore, the pipe arrangement is connected to or is a part of a circuit, in which the heating means circulates. This circuit comprises a respective means for circulating the heating means and for tempering it to a requested heating temperature.

The heating fluid may either be tempered heating water or tempered heating air. Therefore, the circuit comprises a respective water pump or a respective blowing means for circulating either the heating water or the heating air.

In an alternative to the pipe arrangement, the first heating means may also comprise one or more wires extending below the mould element and is coupled or is to be coupled to a power source. In this embodiment, the heating is performed by using electric current flowing through the wire or wires which are thereby heated. Again, the wire or wires are arranged in a geometry which covers most of the bottom surface of the mould element, again preferably in the meandering shape. Also, these wires are preferably attached directly to the bottom of the mould element for a best heating performance.

As several embodiments are given for the first heating means, also the second heating means can be realized in different ways. For example, second heating means which do not form part of the invention could be a heating blanket adapted to be arranged on the mould element for covering the preform building material. This blanket corresponds in its size at least to the size of the area on which the preform building material is arranged, preferably it is to a certain extend larger, so that the preform building material is completely covered. Preferably, it corresponds to the size of the mould element itself. As it is a blanket, which is flexible, it perfectly adapts to the shape of the underlying structure, here the blade building material and also the mould surface, respectively the mould element, as far as the blanket extends also in these areas. So, also this blanket allows for an almost direct heat transfer. Usually, a vacuum foil used for applying a vacuum for pressing the building material is arranged on top of the building material, to which foil it is referred later, which foil is then directly covered by the blanket respectively on which the heating blanket lies. So, the heating blanket indirectly covers the preform building material, as a vacuum foil is sandwiched between.

As also the dimension of the heating blanket roughly corresponds to the dimension of the preform element to be built, also this heating blanket may easily be applied manually.

The heating blanket may comprise one or more wires to be coupled to a power source. Also, this second heating means in form of the heating blanket is therefore heated by an electric current flowing through the wire arrangement. Again, the wire arrangement respectively its geometry is such that it has for example a meandering shape and covers the whole necessary heating area, while certainly also other geometries are feasible.

Second heating heating means as used in the invention comprise a lid to be attached to the mould element and adapted to cover the preform building material while creating a space between the mould surface and the lid, which space is coupled to a heating air source blowing a circulating heating air in the space. The second heating means is an air heating means. The mould element with the preform building material arranged on the mould surface is covered by a lid. This lid defines a certain space between its lid side facing the mould element and the mould element. In this heating space the tempered heating air is blown, which heats the building material and which is exhausted from the space, as the second heating means is connected to or is a part of a heating air circuit comprising a respective ventilation means and tempering means. The arrangement of the lid at the mould element is certainly such that the space is sealed to the surrounding, so that the heating is solely performed within the space.

As also the dimension of the lid corresponds to the size of the mould element in its maximum, also this lid, which is solely used for covering the building material and for realizing the heating space, may be arranged manually on top of the mould element, so that also, comparable to arranging the heating blanket, this heating means element may easily be arranged. Certainly also an arrangement using a lifting equipment is feasible.

According to the invention, the lid is adapted to create a U-shaped air channel within the space, which channel is coupled at one end to a heating air supply of the heating air source and with the other end to a heating air exhaust, which is connected to the circuit respectively the heating air supply. The coupling may preferably be realized by means of respective pipes, which are connected to the heating air source and to the lid respectively the specific channel end. So, this embodiment defines a U-shaped airflow through the U-shaped space, with the first leg of the channel extending in the longitudinal direction of the mould, at the end of which the channel makes a U-turn to the second leg extending in the longitudinal direction of the mould to the exhaust, with the airflow being directed in opposite directions in the first and the second channel leg.

During the passage through the channel the air cools down, it is warmer at the channel entrance than at the exhaust. To avoid heat differences within the building material, it is advantageous that the flow direction can be reversed in certain intervals. Also, when the heating process comes to an end, it is advantageous if cool air can be circulated through the channel by the air supply, preferably also in a reversing manner, so that a rapid and active cooling is possible.

As already mentioned, the mould arrangement may further comprise a vacuum foil to be arranged on the mould element and adapted to cover the preform building material arranged on the mould surface, and a vacuum pump for evacuating a space between the vacuum foil and the mould surface. As mentioned, the building material comprises several separate fiber mats, the binding agent and, optionally, one or more core elements. These separate items are loosely arranged on the mould surface. For pre-fixing them in order to avoid any shifting during the heating process, a vacuum foil is applied, which completely covers the preform building material and which also extends on the mould element and seals to the mould surface. The space between the vacuum foil and the mould element surface may be evacuated by a vacuum pump, so that the vacuum foil is firmly pressed or sucked against the building material which is therefore fixed in its position towards the mould element. Therefore, any unwanted shifting is avoided. The vacuum pump may be arranged below the mould element within the mould carrier and coupled to the space between the mould element and the vacuum foil by one or more vacuum openings.

As mentioned, the mould carrier is the basic construction carrying the mould element. The mould carrier may either be a wooden construction or a metal construction, which is adapted to carry the mould element, but also all items applied to or on it. This is the first and the second heating means, but also especially the blade building material. The blade building material itself has a remarkable weight of several hundred kilograms, usually of something between <NUM>-<NUM>, so that the mould carrier construction needs to be adapted to carry an overall load of approximately <NUM> ton for example. Also, the mould element may be made of wood or metal. It also needs to be adapted to carry the respective weight of the building material and any other applied item like the vacuum foil or the heating blanket etc. It may also be made of wood or a, preferably reinforced polymer, which has a heat resistance which is sufficient to withstand the heating process, during which the preform building material is heated to approximately <NUM>-<NUM>. Although the mould element is adapted to carry the respective weight, it is also preferable to keep the blade- or tray-like mould element as thin as possible in order to have a good heat transfer from the first heating means arranged below the mould element through the mould element to the preform building material.

The drawings, however, are only principal sketches designed solely for the purpose of illustration and do not limit the invention. The drawings show:.

<FIG> shows a first embodiment of a mould arrangement <NUM> in a shorter cut illustration, as the mould arrangement usually has a size of at least approximately <NUM>-<NUM> in width and <NUM>-<NUM> in length.

The mould arrangement is used for producing a preform element of a wind turbine. It comprises a mould carrier <NUM>, which is either a wooden or a metal construction. In this principal embodiment, the mould carrier <NUM> comprises a bottom <NUM> and two side walls <NUM>. On the mould carrier <NUM> a plate- or a tray-like mould element <NUM> is arranged, which in this embodiment has a slightly bent geometry or cross-section. The mould element <NUM> is either made of wood, metal or a preferably reinforced polymer. It corresponds to the width and length of the mould carrier <NUM> and rests with its longitudinal edges <NUM> on the respective upper edges <NUM> of the side walls <NUM> of the mould carrier <NUM>. The mould element <NUM> may either be firmly fixed to the mould carrier <NUM> or may be removable in order to change it to a mould element having a different cross-section or geometry in order to produce a different shaped preform element.

Below the mould element <NUM> a first heating means <NUM> is arranged. This heating means comprises a pipe arrangement <NUM> comprising at least one pipe <NUM>, which is arranged in a meandering form and extends preferably from one end of the mould element <NUM> to the other end. It is arranged directly underneath the bottom surface of the mould element <NUM>, preferably as close as possible or in direct contact. The pipe arrangement <NUM> is connected to or is part of a circuit, in which a heating fluid is circulating. This heating fluid may either be tempered heating water or tempered heating air. As the heating pipe arrangement <NUM> is arranged directly underneath the mould element <NUM>, it heats the preform building material, which is arranged on top of the mould element <NUM>, from underneath.

The mould element <NUM> has an upper mould surface <NUM>, which, as mentioned, in this embodiment is slightly bent or curved. On this mould surface <NUM>, which defines the final form or cross-sectional shape of the manufactured preform element, the preform building material <NUM> is arranged. This preform building material <NUM> comprises a number of fiber mats, preferably glass fiber mats, which are stacked on top of each other in separate layers, further, optionally, one or several core elements made for example from balsa wood or from polymer, and a binding agent, which is applied as a powder or a granulate but only locally on the mat- and core-arrangement, so that the fiber mats and if provided the core elements are only locally fixed. As <FIG> shows, the building material is only arranged in the concave bent part of the surface <NUM>.

The building material <NUM> is arranged manually on the mould surface <NUM>, as it is easily possible to handle the separate fiber mats, which have a width of for example <NUM>-<NUM> and a length of for example <NUM>-<NUM>, and to arrange them in the correct position on the mould element <NUM> respectively on top of each other. The same is true for the application of the binding agent and the optional core elements.

For fixing the building material <NUM> in its finally arranged position a vacuum foil <NUM> is placed on top of the building material <NUM>. This vacuum foil extends to all four sides over the building material <NUM> and overlaps with the upper surface <NUM> of the mould element <NUM>. The vacuum foil <NUM> delimits a certain space between itself and the mould element <NUM>, in which space the building material <NUM> is arranged. This space is evacuated by means of a vacuum pump <NUM>, which is connected by a respective tubing to the space between the vacuum foil <NUM> and the mould element <NUM>. Due to this evacuation the vacuum foil <NUM> is sucked towards the mould element <NUM> thereby pressing against the building material <NUM>, which is thereby vacuum-fixed.

Furthermore, a second heating means <NUM> is provided. This second heating means <NUM> is a heating blanket <NUM>, in which one or more heating wires <NUM> are integrated, which can be coupled via a cable <NUM> to a power source. The heating blanket <NUM> has a size which corresponds to the size of the mould element <NUM>, so that the heating blanket <NUM> almost or entirely covers the mould element <NUM> and therefore also the arrangement of the building material <NUM> and the vacuum foil <NUM>. As the heating blanket <NUM> is flexible, it perfectly adapts to the shape of the underlying items or construction like to the surface of the vacuum foil <NUM>.

As mentioned, <FIG> is only a principal illustration without any reference to the real dimensions. Certainly, the pipe arrangement <NUM> extends over the whole length or almost over the whole length of the mould carrier <NUM>, the same is true for the mould element <NUM>. Also, the building material <NUM> certainly extends over almost the entire length of the mould element <NUM>, the same applies for the vacuum foil <NUM> and the heating blanket <NUM>.

The first heating means <NUM> and the second heating means <NUM> are adapted to quickly and homogeneously heat the building material <NUM> in order to melt the binding agent, which may then wet the fiber mats and, if provided, the core elements. After finishing the heating, the fluid binding agent cures again and becomes a hardened glue or polymer matrix, in which the fiber mats and, if provided, the core elements are firmly, but locally embedded. The final preform element therefore comprises the fixed mat and core items and has a defined shape and setup, while it is still an open structure due to the mat structure allowing for a resin infusion, when the preform element is used for finally building the blade or the blade part.

To perform the heating, a heating fluid is circulated through the first heating means <NUM> respectively the pipe arrangement <NUM>, which is connected to a circulating means <NUM>, which is adapted to first circulate the heating water or the heating air and therefore comprises a pump or a ventilator, and which is secondly adapted to temper the water or the air. So, the tempered heating water or heating air circulates from the circulating means <NUM> to the pipe arrangement <NUM>, through the pipe arrangement <NUM> and from the pipe arrangement <NUM> back to the circulating means <NUM>, where it is again tempered.

As the first heating means <NUM> is arranged directly below the mould element <NUM>, the heating of the building material <NUM> is heated through the mould element <NUM>. This is easily possible, as the mould element <NUM> is a thin plate- or tray-like element, which is for example made of wood or a thin sheet metal or a, preferably reinforced, polymer. It is adapted to carry the load of the items arranged on it, i.e. the building material <NUM>, the vacuum foil <NUM> and the heating blanket <NUM>, which weight amounts to several hundred kilograms, as only the building material <NUM> may already weigh several hundred kilograms, i.e. something between <NUM>-<NUM>. Nevertheless, the mould element <NUM> is designed as thin as possible in order to have a good heat transfer from the first heating means <NUM> through the mould element <NUM> to the building material <NUM>, which is heated from below.

The second heating means <NUM>, i.e. the heating blanket <NUM> is heated by an electric current flowing through the one or more wires, which are thereby heated. It is only necessary to connect the heating blanket <NUM> to a power source.

Certainly, a respective heating control is provided, which controls the temperature of the heating fluid of the first heating means <NUM> and the temperature of the second heating means <NUM>, in order to control the respective heating to a temperature or temperature interval which is necessary for heating the binding agent for melting it, but which avoids an overheating.

When the heating step is ended, no more heating fluid is circulated and the heating blanket <NUM> is also no longer active. The heated building material <NUM> may cool down, so that the melted binding agent cures and fixes the building material <NUM>. Afterwards, the heating blanket <NUM> is removed, the vacuum pump <NUM> is switched off and the vacuum foil <NUM> is removed, so that the preform element, made from the building material <NUM>, can be removed from the mould element <NUM> by a respective device.

<FIG> shows an inventive mould arrangement <NUM>. The same reference numbers are used for the same or comparable items.

Also, this mould arrangement <NUM> comprises a mould carrier <NUM>, which here only has two side walls <NUM>. Firmly fixed to the side walls <NUM> is the mould element <NUM> with its upper mould surface <NUM>. Also here, the mould element <NUM> is plate- or tray-like made of wood, metal or a preferably reinforced polymer and is adapted to carry the respective load applied on it, while it is also as thin as possible in order to ascertain a good heat transfer.

Also here, a first heating means <NUM> in form of or comprising a pipe arrangement <NUM> with at least one pipe <NUM> is arranged with a meandering geometry directly underneath the mould element <NUM> and preferably directly connected to the bottom surface of the mould element <NUM>. The pipe arrangement <NUM> is again part of or connected to a circuit, in which a heating fluid circulates. This is realized by means of a circulating means <NUM> like a water pump or a ventilator, so that tempered water or tempered air flows through the pipe arrangement <NUM> for heating the mould element <NUM> and through the mould element <NUM> the building material <NUM> arranged on the surface <NUM>.

As mentioned, the building material <NUM> comprises a certain number of fiber mats, preferably glass fiber mats, which are arranged one above the other or overlap each other on the mould surface <NUM>, optionally together with one or more core elements. Also locally, the binding agent is applied to the fiber mat stack and the core elements.

After arranging the building material <NUM> a vacuum foil <NUM> is placed on top of the building material <NUM>, which extends on all four sides over the building material <NUM> and overlaps with the mould element <NUM>. The space between the vacuum foil <NUM> and the mould element <NUM> may then be evacuated by means of a vacuum pump <NUM> for sucking the vacuum foil <NUM> against the building material <NUM> respectively the mould element <NUM> thereby fixing the building material <NUM> in place.

Also here, a second heating means <NUM> is provided, which is an air heating means. It comprises a lid <NUM>, which is placed on top of the mould element <NUM> and is tightly sealed towards the mould element <NUM>. As shown, it extends over the vacuum foil <NUM> at the longitudinal sides, also at the not shown front end a respective sealing is provided, as also a sealing is provided at the shown back end towards a heating air supply <NUM>. The lid <NUM>, which may also be made of wood, preferably light wood, metal or a polymer, can easily be arranged manually or with a lifting equipment on top of the mould element <NUM>, as its width and length correspond to the width and length of the mould element <NUM>.

The lid preferably has a design that make it fit to various or all different preform geometries that can be built on the mould arrangement <NUM>.

As shown, the lid <NUM> delimits a space <NUM> between the lid <NUM> and the mould element <NUM>. In this sealed space <NUM> tempered air is blown by the heating air supply <NUM> and is also exhausted from this space <NUM>. So, in this embodiment a hot air heating of the building elements from above is realized, together with the second heating from below.

As shown, the lid <NUM> comprises a web <NUM> extending towards the mould element <NUM>. By this web <NUM> the space <NUM> can be split into a U-shaped channel, comprising a first channel leg <NUM>, which at the not shown end of the space <NUM> makes a U-turn and communicates with a second channel leg <NUM>. The first channel leg <NUM> is connected to the heating air source <NUM> by a heat supply <NUM> realized with a tube, while the second channel leg <NUM> is connected to the heating air source <NUM> by an exhaust <NUM> also realized by means of a tube. In this embodiment a heating air circuit is realized, in which the heating air circulates. The heating air is tempered in the heating air source <NUM> and blown in the first channel leg <NUM> or sucked from the second channel leg <NUM> in order to circulate it. The respective flow paths in the first and second channel leg <NUM>, <NUM> is shown by the respective arrows P1 and P2.

Also, in this embodiment, a double side heating of the building material <NUM> is realized. It is heated by the first heating means <NUM> from below through the mould element <NUM> and is heated from above by the second heating means <NUM>. Again, the respective temperature of the heating water or heating air of both heating means <NUM>, <NUM> is precisely controlled in order to maintain the heating temperature in a respective temperature interval. After the heating has ended, the lid <NUM> is removed. Also, the vacuum pump <NUM> is switched off, so that the vacuum foil <NUM> may be removed. The melted binding agent may cure or has already cured, so that finally the preform element may be removed from the mould element <NUM>. Further it is possible to use the air supply <NUM> also as a cooling means, as it is possible to blow cooling air, e.g. ambient air into the U-shaped channel. This accelerates the cooling of the preform element.

While the first heating means <NUM> in both embodiments is shown as a pipe arrangement <NUM> through which heating water or heating air, i.e. a heating fluid circulates, it is certainly also possible to use one or more wires, through which an electric current flows for heating the wires. Also, this wire arrangement may for example have a meandering shape and is preferably directly fixed to the bottom of the mould element <NUM>. It is only necessary to connect this wire arrangement to a power source. So, in this embodiment, the heating is done by an electric current, comparable to the heating method of the heating blanket <NUM>.

Claim 1:
Mould arrangement for producing a preform element of a wind turbine blade, comprising a mould carrier (<NUM>) and a plate- or tray-like mould element (<NUM>) arranged at the mould carrier (<NUM>) with a form defining mould surface (<NUM>) adapted to receive preform building material (<NUM>), a first heating means (<NUM>) arranged below the mould element (<NUM>) for heating the preform building material (<NUM>) from below the mould element (<NUM>), and a second heating means (<NUM>) for heating the preform building material (<NUM>) from above, wherein the second heating means (<NUM>) comprises a lid (<NUM>) to be attached to the mould element (<NUM>) and adapted to cover the preform building material (<NUM>) while creating a space (<NUM>) between the mould surface (<NUM>) and the lid (<NUM>), which space (<NUM>) is coupled to a heating air source (<NUM>) blowing a circulating heating air in the space (<NUM>), characterized in that the lid (<NUM>) is adapted to create a U-shaped air channel (<NUM>, <NUM>) within the space (<NUM>), which channel (<NUM>, <NUM>) is coupled at one end to a heating air supply (<NUM>) and at the other end with a heating air exhaust (<NUM>).