LT3143B - Device for the continuous manufacture of slabstock polyurethane foam - Google Patents

Abstract

This invention is for devices for the continuous production of expanded polyurethane plate. Said devices consist of a transporter device (1) and a stirring stem (51) and means (6) for unloading the reaction compound from the stirring stem (51) on the transporter device (1). There is also an initial board (7), a terminal board (8) on the device to move the initial board (7) along the transporter device at the beginning of the production process, making the reaction compound move to increase the thickness of the front part of the foamed plastic being produced, and to move the terminal board, pushing the foamed plastic reaction compound forward to increase the thickness of the terminal part. The operator does not need to enter the machine which produces the foamed plastic, and the initial and the terminal profiles of the foamed plastic blocks obtain optimal results.

Description

The present invention relates to continuous polyurethane foam sheet production units consisting of a conveyor device, a mixing head for mixing polyurethane reaction components including a blowing agent, means for discharging said reaction mixture on said conveyor device and means for driving said conveyor device.

Such a device is inherently known. In practice, different types of foam plastic machines with conventional tilt conveyors, with or without flat support for Maxfoam and Varimax machines, are used. The disadvantage of these known machines for continuous production of foam foam is that they require manual control both at the beginning and end of foam production in order to obtain a suitable front and rear part of the foam board. Without manual intervention by the operator, the front and rear portions of the foam pad slowly decrease during production compared to the sudden formation of foam pads, losing a few feet of foam pad.

In known machines, operators board mounted on a long portion of the reaction mixture, a conveyor, a holding member, a starting board, a reaction mixture, and thus a device.

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When using, for example, the end of a mast, the first it stands on the first conveyor begins by holding onto the foam as well as moving the conveyor.

At the end of the production process, the operators push the last part of the reaction mixture forward and obtain the rear part of the required height.

The disadvantages of known equipment are that in some cases operators have to enter the foam pad machines both at the beginning and end of the manufacturing process and to form the required foam profile. It is clear that this can be dangerous and harmful to their health due to the formation of toxic gases during the foam production process. In addition, the resulting foam profile depends on the qualifications and experience of the operator. In fact, the operator has no direct control over the height of the foam, and the effect of manually adjusting the foam's reaction mixture can only be seen after some time. needed for the foam to reach its final height. Furthermore, the process of blowing out the reaction mixture depends on the composition, and most of all on the amount of blowing agent, so that the composition must be considered when manipulating the reaction mixture to obtain the required foam profile.

It is an object of the present invention to provide a device for continuous foam sheet production which can adjust the foam profile from the beginning to the end of the manufacturing process without the operator entering the foam production machine and obtaining an optimum front and rear foam block profile.

Finally, the device according to the invention is characterized in that it further comprises a start board and a back board; means for positioning said starting board transversely on a conveyor device adjacent to said unloading point of said reaction mixture at the start of the manufacturing process; means for moving the parent board along the conveyor device such that the parent board in the first phase prevents the reaction mixture from moving through said conveyor device, thereby increasing the height of the front of the manufactured polyurethane foam board substantially so that this front has substantially the same height after complete foaming, and such that in the second phase it moves at substantially the same speed as said conveyor device; means for disengaging the parent board from said conveyor device after the front of the fabricated foam substantially retains its shape; means for positioning the end board transversely on the conveyor device at said unloading point of said reaction mixture after said unloading of said reaction mixture is stopped; means for moving said endplate along said conveyor device after said endplate is disposed by pushing the foam reaction mixture forward with respect to said conveyor device, thereby increasing the rear portion of the manufactured polyurethane foam block substantially so that this end portion is substantially the same; height as the part in front of it after full blowing.

The above-described means in the device according to the invention allow mechanical control of the front and rear profiles of the manufactured foam block, such that these profiles are no longer dependent on the operator's manual manipulation. In addition, an important advantage of such mechanical control is that it enables the front and rear profiles to be controlled on a fully enclosed foam production machine, such as the machine disclosed in the same applicant's PTC patent application no. PCT / EP 91/02176.

In a preferred embodiment of the device according to the invention, said means for providing the starting board in motion in said first phase at rest and starting propelling the starting board at substantially the same speed as said conveyor device when the foam reaction mixture reaches a predetermined height.

In a specific example of the device according to the invention, said end-board arrangement means are adapted to position said end-board within a distance of 3 m, and preferably at a distance of 0.5 m from the place of discharge of the reaction mixture.

In another specific embodiment of the invention, said starting board arrangement means is adapted to position said starting board within a distance of 3 m, preferably at a distance of 1.5 m and in a particular case at a distance of 0.5 m from the landing site.

Other details and advantages of the invention will be apparent from the following description of several examples of continuous production of polyurethane foam panels (device according to the invention. This description is provided by way of illustration only and is not intended to limit the scope of this invention.

FIG. 1 is a schematic longitudinal sectional view of a device according to the invention comprising a starting board and means for controlling the starting board;

FIG. 2 is a schematic view of the device shown in FIG. 1, top view;

FIG. Figures 3 and 4 show an embodiment of the original board of Figs. 1 side view in two different positions;

FIG. 5 is a longitudinal sectional view corresponding to FIG. 1, but showing the end board and end board controls instead of the starting board and the starting board controls;

FIG. 6 is a schematic of the device shown in FIG. 5, top view; and

FIG. 7 and 8 are a schematic longitudinal sectional view of a device such as the device shown in FIGS. 1 and 5, but in which the beginning and end boards are the same board;

FIG. Figures 9 and 10 are longitudinal cross-sectional views of the bottom belt anchorage mechanism of the first lower conveyor at two different positions.

In these drawings, the same references are used for the same elements.

a digital or analog continuous production device for polyurethane foam panels according to the present invention comprising, essentially, a conveyor device, a mixing head for mixing components of a polyurethane reaction mixture comprising a blowing agent, means for discharging said reaction mixture onto said conveyor device and said transporter. This machine can be of different types, including tilt conveyor (with or without flat support), Maxfoam or Varimax. However, it is clear that the invention is not limited to any of these types, although the drawings are limited to the Maxfoam machine.

The Maxfoam machine conveyor assembly 1 shown in the drawings consists of a sloping plate 2, a first lower conveyor 3 and a bottom strip 4 disposed along a sloping plate 2 and a first lower conveyor 3. The mixing head shown in position 51 is connected to a channel 5 with a trough. 6 bottom. The reaction mixture fed to the trough 6 foams and flows onto the bottom strip 4 from the start of the sloping plate 2. During its transport by a moving conveyor device 1, the reaction mixture continues to foam and polymerize to form a foam block.

In order to obtain the required block profile at the beginning and end of the manufacturing process, i. i.e., to obtain a foam block having substantially the same height towards the ends of the block, the device according to the invention comprises a starting board 7 and a back board 8 and means for mechanically controlling the movement of these boards 7 and 8.

These control means consist of a means for arranging the starting board 7 at the beginning of the manufacturing process across the conveyor Device 1 at the unloading point of the reaction mixture, i.e. y. 6. Initial board layout arrangements need not be purely mechanical and may require manual adjustment of operators at the start of the manufacturing process before noxious gases are formed, allowing operators to enter the foam production machine without risk.

Further, the control means include means for providing the starting board 7 with movement along the conveyor device 1 such that the initial board 7 in the first phase prevents the reaction mixture from moving through the conveyor device 1 and its speed in the second phase is substantially equal to that of the conveyor device 1. In this first phase, the reaction mixture is deposited on the starting board, increasing the thickness of the front part of the manufactured polyurethane foam board, i. y. so that this front part has the same height as the fully fractured further part.

The starting board 7 may interfere with the foam reaction mixture moving at a lower speed than the conveyor device 1. However, in a preferred embodiment, the starting board 7 is maintained at rest during said first phase. The second phase, in which the starting board 7 moves at the same speed as the conveyor device 1, begins when the foam reaction mixture reaches a predetermined height at the starting board 7. This moment can be defined so that the start of the production process can be repeated each time. in the same way. In addition, said predetermined height can also be adjusted according to the foaming properties of the reaction mixture. Preferably, the conveyor device 1 starts to move synchronously with the movement of the starting board 7.

In a working embodiment, the starting board arrangement means are adapted to position the starting board within a distance of 3 m from the unloading site of the reaction mixture, i. y. from the edge of trough 6. It is desirable that the starting board 3 be located within 0.5 m of the landing location. In this way, the reaction mixture may be sufficiently deposited by means of the starting board 7 to obtain the desired thickness.

The device according to the invention also has means for removing the starting board 7 from the conveyor Device 1 after the foam has been manufactured to obtain a proper shape or, in other words, sufficient dimensional stability.

The starting board removal means shall include a device for accelerating the starting board 7 in the direction of movement of the foam and a device for lifting the starting board 7 after sufficient clearance has been provided between the front of the foam and the starting board.

At the end of the manufacturing process, the end board 8 is positioned across the conveyor unit at the point where the reaction mixture is unloaded by means of its arrangement. These means are partly adapted to position the end board within a distance of 0.5 m from the place where the reaction mixture is unloaded. In this way, the final portion of the reaction mixture can be pushed forward by the conveyor device, increasing the height of the rear portion of the foam block produced. Finally, the device includes means for giving the rear board 8 movement along the conveyor device at a speed greater than the speed of the conveyor device 1. In a typical tilted foam machine, the conveyor device may be stopped at the point where the discharge of the reaction mixture is stopped. In a Maxfoam machine, it is desirable that the conveyor unit stop moving when the last portion of the reaction mixture is applied to the first conveyor belt 3.

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1.

In the device shown in Figs. 1 and 2, the starting board 7 is secured to a support 10 by a first connecting shoulder 9 which can move by the first upper guide 11 by means of the first variable speed motor 12. The first upper guide 11 is straight extending substantially along the conveyor device

In an embodiment not shown in the drawings, this upper guide 11 may be substantially parallel to the conveyor device 1, also above the sloping plate 2, such that the starting board 7 and the first support 10 undergo substantially the same up and down movement. In this case, to compensate for the possible difference in distance between the conveyor device 1 and the first upper guide in the direction of the first connecting shoulder 9, the shoulder 9 may be hinged to both the support 10 and the starting board 7.

11, measured by this joint

When the foam machine is enclosed in a hood, for example, for pressure control during foam production, as shown in PCT patent application no. PCT / EP 91/02176, preferably the first upper guide 11 is straight so that the height of the foam machine is uniform over the entire length. In this case, the first connecting arm may also be pivotally mounted to the first support and to the starting board 7. However, to prevent the starting board 7 from being too high in relation to the speed of the bottom bar 4 when moving on a sloping plate 2, also moving with the inclined plate 2, due to the anticlockwise rotation of the first connecting shoulder 9 around its upper pivot axis 13, the angle α between the first connecting shoulder 9 and the first guide 11 is maintained constant by moving down the inclined plate 2. This is realized in the example shown in FIG. . 1, such that the first connecting arm 9 is movably attached to both the first support 10 and the starting board 7.

The movable links between the connecting shoulder 9 and the support 10 may be formed such that the starting board 7 can move substantially up and down. However, it is desirable that the movable links be made slightly oblique, thereby further reducing the speed of the starting board 7 as it moves on the sloping plate 2, and thus slightly adjusting the speed of the starting board to the speed of the moving bottom bar 4 going down the speed component of the starting board 7. By minimizing the difference in speed between the starting board 7 and the bottom bar 4, the risk of damage to this bottom bar is significantly reduced.

In order to further limit the risk of damage to the bottom strip 4, it is desirable to provide means for reducing the pressure of the starting board 7 on the bottom strip 4. This can be accomplished, for example, by using a counterweight to pull the coupling arm 9 into sliding contact with the support 10 or by creating a constant hydraulic pressure in this contact by tensioning the coupling arm 9 upwards. The connecting shoulder 9 may then be fixedly connected to the starting board 7, or other similar means may be used for sliding contact between the starting board 7 and the connecting shoulder 9 to create an upward force on the starting board 7.

In the example shown in FIG. 1, the connecting shoulder 9 is pivotally connected to the sliding element 14 in the support. However, the downward travel of the connecting shoulder 9 is limited by the angles α or β of the positions I and II of the connecting shoulder FIG. 1.

In position II, the expansion of the foam has stopped and is substantially stable. The motor 12 is then accelerated to form a gap between the front of the foam block and the starting board 7. The means for removing the starting board 7 from the conveyor device 1 include a projection 15 which mechanically lifts the connecting shoulder 9 and the starting board 7 as they pass through. this projection 15. FIG. 2, which comprises a device according to FIG. 1 is a plan view showing that the projection 15 is secured to the upper guide 11 and that the connecting shoulder 9 has two parallel shoulders, both of which are raised by this projection 15. It is clear that mechanical lifting means may also be used, e.g. hydraulic lifting means.

FIG. 3 shows a larger scale of the starting board 7 shown in FIG. 1, but connected by a vertical connecting shoulder 9 with a support 10. In fact, the connecting shoulder 9 may be arranged at different angles depending mainly on the possible space for the different components such as the upper guide 11 and the supporting member 10. The starting board 7 is provided with a roll 16. designed to roll the conveyor device 1, thereby further reducing the risk of damage to the bottom belt 4. To prevent the foam reaction mixture from reaching this roll 16, a bottom barrier 17 is hinged to the base 18 of the starting board 7.

The starting board 7 shown in Figs. 3, further comprises an upper barrier 19 which is also pivotally mounted to the base 18 and which is supported by a spring 20 in an upright position. In this way, the upper barrier 19 may be folded down as shown in FIG. 4 when it touches a vertical barrier, such as when a foam machine is covered by a narrow enclosure.

FIG. 5 and 6 show a rear board 8 and a mechanism for providing this rear board 8 with movement along the conveyor device 1 at the end of the manufacturing process. As can be seen in Figs. 6, the end board 8 is composed of two mutually movable panels 21, 22 partially overlapping each other so that width can be varied. Each plate 21, 22 is pivotally mounted to a separate support 23 and 24 by the crank arms 25 and 26, respectively. Each abutment 23 and 24 may move in a separate upper guide 27 and 28 by means of a second variable speed motor 29, respectively. Each of the upper guides 27 and 28 is secured to the lateral walls 30 and 31 of the slanting plate 2 by clamps 32 and 33 such that the width of the end board 8 is automatically adjusted as the foam width varies.

The means for positioning the end board 8 on the conveyor device 1 include a stop 34 which maintains the end board in the rest position I shown in FIG. 5. As the end board 8 moves to position II, it is lowered downwardly to incline III, pushing the mixture 35 forward until it moves on the inclined plate 2 to form the desired block profile.

it is automatically plate 2. Moving the foam reaction

Like the end board 8, the starting board 3 can also be made up of two sliding panels to automatically adjust the width of the starting board. In addition to this automatic adjustment, the width of the starting board must be adapted to the foam width produced by moving the starting board.

Automatic width adjustment is also possible by means of a starting board and / or end board having a central section, two side rails hinged to this central section, and means for guiding these side rails towards the side walls 30, 31. These guide means may: be formed, for example, by elastic side barriers. They may also have springs or other rigid means. The central portion itself may be composed of different elements, for example two mutually movable plates 21, 22.

Although the description above includes a reference to the starting board 7 and the end board 8, the function of these boards may be performed by the same board 7,8. Such an embodiment is schematically shown in Figs. 7 and 8. In this embodiment, the board 7,8 is secured to the shoulder 9 hinged to the support 10. At the beginning of the manufacturing process, the board 7,8 is lowered from the rest position I to position II on the conveyor device 1 as shown in FIG. 7th

FIG. Table 8 7,8 is shown in position III in which it is raised above the first lower end of the lower conveyor 3. From this position, the board 7,8 is driven along the upper guide 11 by motor 12 back to the start of the conveyor device 1 at the trough 6 and is lowered again to the end of the manufacturing process, from position I to position II. The board 7,8 is then driven along the conveyor device 1 by pushing the reaction mixture forward, increasing the thickness of the back of the fabricated foam board. In this embodiment, the means for lowering and lifting the board 7.8 are, for example, hydraulic, not shown. 7 and 8.

Before production begins, the bottom band 4 is unwound from the feed roller 36, deflected by the slanting plate 2 and the first lower conveyor 3, and secured to the rewinding roller 37. 41 and at the side rollers 42. The horizontal edges of the bottom bar 4 are bent slightly up to the side bars 38.

At the beginning of production, the roller roller 37 tensiones the bottom strip 4 with great force to pull the front part of the foam block with a sloping plate 2. Due to the long length of the bottom strip 4, for example about 30 m, this bottom strip can be narrowed (compressed) horizontally so that it device surface. In order to prevent this from happening, the present invention provides means for securing the bottom strap 4 at the beginning of the manufacturing process to the sloping plate 2 on the first lower conveyor 3.

In the first embodiment, these fasteners consist of a flat weight having a surface such that it cannot fall into the gap between the first end of the first web conveyor 3 and the winding roller 37. There may be additional means for lifting weight when it reaches said gap.

In an exemplary embodiment of the invention, said fastening means comprise a transverse row of bars 43 mounted on a first lower conveyor 3 and means

1-4 for automatic removal of these rods during first turn of lower conveyor 3. The means for this removal ensure the release of the bottom strap 4 from the rods at the end of the lower conveyor 3.

Such a mechanism is shown in Figs. 9 and 10. The lower conveyor 3 is formed by a series of transverse bottom plates which are pivotally interconnected so as to move a wheel around the drive gears 44 of the conveyor 3. 9 and 10 show two adjacent bottom plates 45 and 46, respectively, in a flat position and in a position where these two plates are rotated about a gear 44.

A plurality of rods 43 are pivotally mounted on a transverse axis 47 mounted on a plate 46 such that the rods 43 can pivot from an unloading position in which they are folded down, below the surface of the conveyor, to a position in which they are pivoted backwards. 10. There are also springs (not shown in the drawings) forcing the rods 43 to be in the release position. These springs may act directly on each rod 43, or axis 47 in the case where the axis 47 is pivotally mounted on the plate 46.

To prevent the rods 43 from being turned back by extending the bottom strip 4, at least one shoulder 48 is mounted on an axis 43, and more particularly, on rods 43 whose rotation of the shoulder 48 in a flat position is limited by a stop 49 on an adjacent plate 45. 9. When the rods reach the end of the conveyor 3, they should release the bottom strip 4. As shown in Figs. 10, the release of the bottom bar is achieved by turning the rods 43 backward. Reversing is possible due to the increased distance between the two plates 45 and 46 as they move in an arc around the pinion 44 such that the shoulder 48 can freely pass through the stop 49 and plate 45. When the bottom bar 4 is released, the springs turn the rods 43 position. In this position they lie in notches 50, beneath the surface of the conveyor. As the conveyor 3 continues to rotate, they remain in this position until they are manually lifted by securing the new bottom strap 4 at the beginning of the next manufacturing process.

It is to be understood that the invention is not limited to the examples above and that these examples may be modified in many ways within the scope of this patent application.

In particular, the starting board and its controls could be constructed so that they can also be used to adjust the profile of the front and rear fabricated foam block.

In addition, the same top guide can be used for both the start and end boards. For adjusting the width of the starting and / or end boards, they can be made of two overlapping panels which can be displaced, for example, hydraulically along one another or, as described above, with respect to the end board by connecting these panels to two different sliding upper guides.

The width of the starting and / or rear board can also be optionally adjusted by side hinged fences which are forced to pivot to the side walls or to the side conveyors, for example by means of springs. Such lateral barriers may also be combined with other width adjusting means provided for precise width adjustment, rather than such accurate adjustment requiring other width adjusting means.

Like the end board, the starting board can consist of two panels that are connected to two separate top guides or to the same top guide as the back board.

Claims (20)

DEFINITION OF INVENTION A continuous polyurethane foam sheet production device comprising a conveyor device (1), a mixing head (51) for mixing polyurethane reaction components comprising a blowing agent, discharging said reaction mixture onto said conveyor device (1) and means (44) actuating said conveyor device, characterized in that said device further comprises a starting board (7) and an end board (8), means for positioning said starting board transversely on said conveyor device (1) at the unloading point of said reaction mixture. at the beginning of the manufacturing process, means for providing the starting board (7) with movement of said conveyor device (1) such that the initial board (7) in the first phase impedes the movement of the reaction mixture by said conveyor device (1) thereby increasing the height of the manufactured polyurethane foam board , or rather, so that this one the front portion having substantially the same height as the fully deflated farther and moving in the second phase at substantially the same speed as said conveyor device (1), means for deflecting the starting board (7) from said conveyor means (1) after the front part of the manufactured foam retains its shape, the means for the end board (8) are arranged transversely on said conveyor device (1) at the unloading point of said reaction mixture after the unloading of the reaction mixture is stopped; movement of said conveyor device after positioning said end board (8) to move the foam reaction mixture forward relative to said conveyor device (1) thereby increasing the height of the rear portion of the manufactured polyurethane foam board, more precisely, the part would have a height that I would completely blow out si in front of it. 2. A device as claimed in claim 1, wherein said means for providing motion to the starting board are designed to maintain the starting board (7) at rest during said first phase and to start propelling the starting board (7) at substantially the same speed as said conveyor device. (1) when the foam reaction mixture reaches a predetermined height in front of the starting board (7). 3. A device according to claim 2, characterized in that said device comprises means for actuating said conveyor drive (44) at substantially the same time as said starting board (7) begins to move with said conveyor device (1). A device according to any one of claims 1 to 3, characterized in that the retracting means of the starting board comprises a device for accelerating the starting board in the direction of foam movement and means (15) for raising the starting board (7) the required space is made. 5. A device as claimed in any one of claims 1 to 4, characterized in that said rear board arrangement means are adapted to be arranged on said end board (8) 3 m. distance, and more preferably 0.5 m. at a distance from the place of discharge of the reaction mixture. 6. A device as claimed in any one of claims 1 to 5, characterized in that the starting board arrangement means are adapted to position said starting board (7) .3 m. within a distance, preferably 1.5 m, and in individual cases 0.5 m. within a distance of the place of unloading. Apparatus according to any one of claims 1 to 6, characterized in that said means for positioning the starting board and said means for providing motion to the starting board have a first upper guide (11) extending substantially along the first support (10) of the conveyor device (1). operable to drive said first guide (11), the first variable speed motor (12) to drive said first support (10), said first guide (11), at least one first connecting arm (9) coupled to said first support (10), both with said starting board (7) and means for lowering the starting board (7) down on the conveyor device by means of said first connecting shoulder (9). 8. A device according to claim 7, characterized in that said first connecting arm (9) is movably connected to said first support (10) and / or said starting board (7) such that said flexible connection allows to compensate for the distance between said first members. the difference between the first upper guide (11) and the means (1) of said conveyor when the starting board moves with said conveyor device (D · Device according to claim 8, characterized in that said conveyor device (1) has a sloping plate (2) and a first lower conveyor (3), and in that said sliding connection allows the starting board (7) to move when said starting board moves. sloping plate (2), moving up and down in a direction which reduces possible speed differences between the starting board (7) and the moving conveyor device (1) on the sloping plate (2) due to the downward movement of the starting board (7) on the sloping plate (2) . Device according to any one of claims 1 to 9, characterized in that it comprises means for reducing the pressure of the starting board (7) on the conveyor device (1). Device according to any one of claims 1 to 10, characterized in that said starting board (7) has at least one roll (16) to be rolled by said conveyor device (1) and a lower barrier (17) capable of rotating about a substantially horizontal starting board. (7) an axis for contacting the conveyor device (1) and obliquely disposed between said roller (16) and the foam reaction mixture. Device according to any one of claims 1 to 11, characterized in that said starting board (7) has an upper barrier (19) which is hinged to the base (18) of the starting board (17) so that it can be folded down. when an obstacle is encountered and a spring (20) forcing said upper barrier to be upright. Device according to any one of claims 1 to 12, characterized in that at least said end board (8), and more preferably also said starting board (7) have means for automatically adjusting their width to the width of the foam produced. 14. A device according to claim 13, characterized in that at least said end board (8), and more preferably also said starting board (7) have at least two mutually movable panels (21,22) and means for these boards (21). , 22) to adjust the mutual displacement of the respective board to the width of the foam produced. 15. A device according to claim 14, characterized in that said sliding plates (21,22) partially overlap each other and are each secured by separate connecting arms (25,26) to a support (23,24) movable by an upper guide (23,24). 27,28) in the longitudinal direction of the conveyor device (1), and in that said device has width adjusting means for adjusting the distance between the two connecting arms (25,26), said device having in each case one support (23,24) and one upper guide (27,28) for each of said two plates (21,22), each of said upper guide (27,28) being mounted on one of two transversely adjustable sidewalls (30,31), along the first portion of said conveyor device (1). . 16. A device according to claim 13, characterized in that at least said end board (8), and more preferably also said starting board (7) has a central part, two lateral hinges hinged to said central part, and means , guiding said side gates towards the side walls (30,31), automatically adjusting the width of the respective board to the width of the foam produced. 17. A device as claimed in any one of claims 1 to 16, wherein said starting board (7) and said end board (8) are one and the same board. A device according to any one of claims 1 to 17, characterized in that it comprises a sloping plate (2), a first conveyor (3) following said sloping plate (2) and means for securing a bottom strip disposed along said sloping plate (2). 2) and said first conveyor (3), on a sloping plate (2) on the first conveyor (3) before the production process begins. 19. The device of claim 18, wherein said securing means comprises a transverse row of rods (43) mounted on said first lower conveyor and means for automatically removing said rods (43) upon first rotation of said first conveyor (3). 20. Apparatus according to claim 19, characterized in that said first conveyor (3) is formed by a series of transverse plates that are hinged to each other, wherein said row of rods (43) is pivotally mounted on a transverse axis (47). mounted on one of the two adjacent plates (46) behind the pivot axis of the two plates (45,46) and in that said removal means are provided with springs forcing the rods (43) to rotate from a position in which they extend through the notches between said two plates (45,46) being in the release position, at least one shoulder (48) being mounted on said axis (47) at a fixed angle with respect to said bars (43), and a stop (49) on said shoulder (48) is disposed on the opposite plate. (45) of said adjacent plates (45,46) such that said stop (49) prevents rotation of the sliding rods (43) when said The two plates (45, 46) are substantially in the same plane, limiting the rotation of said shoulder (48), but allowing the pivoting rods (43) to rotate when said two plates (45, 46) are rotated about the first conveyor (3). a pinion (44) such that a greater distance is provided between said axis (47) and said stop (49) than the length of said shoulder (48).