A device of this nature is known from NL-A-9002531. The device comprises a mould and a prestressing device, which is arranged outside the mould, for applying a stress to a set of reinforcement wires which extends through the mould. In this case, the reinforcement wires are engaged on at their ends by combs of the prestressing device. The combs can be moved hydraulically in the longitudinal direction of the reinforcement wires, so that a desired prestress can be imposed on the wires.

The mould comprises a mould base, two longitudinal walls and two end walls which are rigidly connected to one another as a single unit. The device comprises a movement mechanism for moving the mould up and down. During a demoulding operation, a sufficiently set moulded product comes to rest on pin-like bearing members.

During manufacture, the bearing members form part of the mould base but remain in place during the demoulding operation, while the rest of the mould is moved downwards. In this way, the moulded product is held in place while the mould is removed.

During the downwards movement of the mould, the reinforcement wires are held under stress by the prestressing device. In particular, this device is intended for the manufacture of a moulded product which is composed of a plurality of sleepers, which are connected to one another in the longitudinal direction, for rails. After the elongate assembly of sleepers has set sufficiently, it is demoulded under prestress and the sleepers are separated from one another by being sawn through.

A drawback of this known device is that the prestressing device is expensive. This applies in particular when stressing a set of reinforcement wires of a limited length. This requires relatively little prestressing force, an operation which does not require a prestressing device with combs which can be moved hydraulically in the longitudinal direction. A further drawback is that a moulded product may become jammed in the mould.

Consequently, it is not always possible to remove the mould during a demoulding operation. This may damage the moulded product. For example, cracks may form in the moulded product.

The object of the invention is to overcome the abovementioned drawbacks. The particular object of the invention is to provide a device in which there are stressing means which are able to maintain stress on the reinforcement wires during at least a first part of a demoulding operation without there being any risk of jamming.

According to the invention, this object is achieved by means of a device according to claim 1. The mould is composed of a mould base and mould side walls which can be displaced independently with respect to one another. A movement mechanism is provided for the purpose of removing the mould base during a demoulding operation. The device comprises pivotably arranged stressing frames. At least two mutually opposite mould side walls are arranged on such stressing frames. The stressing frames can pivot in such a manner that the mould side walls which are connected thereto can pivot laterally away from a moulded product during a demoulding operation. Delimiting elements, against which the stressing frames are supported in a closed position of the mould side walls, are arranged at a certain distance from the pivot points of the stressing frames.

The mould side walls are provided with suitable cutouts through which reinforcement wires can pass. There are stressing means which act on the reinforcement wires and which, during a manufacturing process and during the removal of the mould base in the course of a demoulding operation, are supported against the stressing frames or the mould side walls which are connected thereto.

Thus, the invention advantageously provides a structure with pivotably arranged stressing frames with mould side walls and tensioning means which interact therewith and which is inexpensive and reliable. During the demoulding operation, the mould base can be removed separately while the set of reinforcement wires remain under stress and the mould side walls remain in place. The fact that the reinforcement wires remain under stress ensures that the moulded product is not liable to shrink while the mould base is being removed. This is

particularly important if the mould base is of profiled design, since that is when the risk of jamming caused by shrinkage is highest. Nor is there any possibility of the set moulded product becoming jammed between the mould side walls, since, during a subsequent step of the demoulding operation, these walls can pivot away laterally as a result of the stressing frames pivoting into an open position. To carry out this operation, it is necessary firstly to eliminate the stress on the reinforcement wires, allowing the stressing frames and the mould side walls which are connected thereto to pivot into the open position.

It is noted that GB-A-1,377,189 discloses a mould with a baseplate and side walls and with pivotably arranged stressing frames for stressing a set of reinforcement wires. However, in this case the mould side walls are not connected to the stressing frames, and the baseplate cannot be removed separately while the reinforcement wires are kept under stress and the mould side walls remain in a closed position. Consequently, it is impossible to carry out demoulding under prestress, and this document deals with a different type of device from that described by the present invention.

Preferred embodiments of the invention are defined in claims 2-10.

The device according to the invention is advantageously used for the manufacture of an assembly of sleeper slabs which are connected to one another. Separate sleeper slabs are known per se for laying rails and are each composed of for example ten sleeper elements which are located next to one another and are connected to one another. In this application, two sets of mutually perpendicular, prestressed reinforcement wires are used to impart additional strength to the sleeper slab. After a moulded product comprising interconnected sleeper slabs has set sufficiently, these slabs have to be separated from one another, for example by being sawn through. Particularly the set of reinforcement wires which lie in the transverse direction of the mould can be stressed in this process with the aid of stressing frames according to the invention and stressing means which interact therewith.

The invention will be explained in more detail with reference to the appended drawing, in which: Fig. 1 shows a cross-sectional view through an embodiment of the device according to the invention; Fig. 2 shows a side view, on an enlarged scale, of Fig.

1, showing only the stressing frames and the mould side wall; Fig. 3 shows a plan view, on an enlarged scale, at the location of the mould side wall in Fig. 1; Fig. 4 shows a cross-sectional view on line IV-IV in Fig. 2; Fig. 5 shows a cross-sectional view on line V-V in Fig.

3; Fig. 6 shows a separate view of a securing element in Fig. 5; Fig. 7 shows a view, on an enlarged scale, of the bottom section of the mould side-wall in Fig. 4; Fig. 8 shows a plan view of a variant with an elongate mould; Fig. 9 shows a plan view of a sleeper slab which is manufactured using the device in Fig. 8; and Fig. 10 shows a cross-sectional view on line X-X in Fig.

9.

The device shown in Fig. 1 has a mould 1 which comprises a profiled mould base 2 and mould side walls 3 which lie opposite one another. The mould base 2 is provided with cutouts 5 in which various types of inserts can be placed and on the underside is strengthened by means of box sections 11. The mould base 2 is supported on a plurality of support pillars 10 which lie next to one another and can be moved up and down by means of a suitable movement mechanism. The mould base 2 can be moved up and down by means of the mechanism between an open position and a closed position, the closed position being shown in Fig. 1.

Stressing frames 14 are arranged at the sides of the mould base 2. A stressing frame 14 comprises a metal section piece which is substantially C-shaped. One end of the stressing frame 14 has a pivot point 16, while the other end is connected to a mould side wall 3. Pivoting of the stressing frame 14 about its pivot point 16 moves the mould side wall 3 between an open position and a closed position. In Fig. 1, the open position is

shown on the left-hand side and the closed position on the right-hand side. In the closed position, the mould base 2 and the mould side walls 3 adjoin one another and define a mould cavity. Approximately next to the centre of the stressing frame 14, there is a delimiting element 20 against which the stressing frame 14 bears in the closed position of the mould side wall 3.

Advantageously, the delimiting element 20 is formed by a pressure rod 21 which extends over the entire width of the device so that two opposite stressing frames 14 are able to make use of the same delimiting element. The forces exerted on the pressure rod 21 by the mutually opposite stressing frames 14 are in this case oppositely directed, which is advantageous for the loads on the pressure rod 21.

The pivot points 16 of two mutually opposite stressing frames 14 are connected to a tension rod 24 which extends over the entire width of the device. In this case too, the forces exerted on the tension rod 24 by the mutually opposite stressing frames 14 are oppositely directed, which is advantageous for the loading on the tension rod 24.

The device according to the invention is intended for the manufacture of concrete moulded products with at least one set of prestressed reinforcement wires. The mould side walls 3 are provided with suitable cutouts 27 for reinforcement wires 30 to fit through. The right-hand side of Fig. 1, shows part of a reinforcement wire 30 of this nature. It can be seen from Fig. 3 that the mould side wall 3 is of profiled design and is provided with six cutouts 27, through which six ends of reinforcement wires 30 project. The reinforcement wires 30 extend between the two mutually opposite mould side walls 3. Stressing means 32 are provided in order to be able to apply a desired prestress to the reinforcement wires 30 (cf. Figs. 3 and 5). The stressing means 32 act on the ends of the reinforcement wires 30 and are supported on the mould side wall 3. As can be seen from Figs. 2 and 3, the mould side wall 3 is connected to two adjacent stressing frames 14. The forces which are exerted on the stressing frames 14 by the stressing means 32 via the mould side walls 3 are absorbed by the tension and pressure rods 24 and 21, respectively.

During a manufacturing process, the mould base 2 and the mould side walls 3 are placed in the closed position. Then, the reinforcement wires 30 are laid in the mould 1 and a desired prestress is applied by means of the stressing means 32. In addition to the abovementioned set of prestressed reinforcement wires 30, it is also possible to arrange one or more further sets of prestressed reinforcement wires in other directions. It is also possible to lay reinforcement meshes and the like in the mould 1. These reinforcement meshes are not prestressed and form part of the so-called"soft reinforcement". In a following step, the mould is filled with concrete. After the concrete has set sufficiently, the demoulding operation begins. The demoulding operation begins with the mould base 2 being moved downwards. In this process, the sufficiently set moulded product comes to rest on a number of bearing members 35. These bearing members 35 are formed, for example, by support pins 36 which are located directly beneath the mould base 2. The mould base 2 slides downwards over the bearing pins 35. During the downwards movement of the mould base 2, the mould side walls 3 remain in the closed position. At the same time, the reinforcement wires 30 remain under stress. Keeping the reinforcement wires 30 under stress ensures that the moulded product is not yet susceptible to deformation which occurs as soon as the stressing means acting on the reinforcement wires 30 are released. This makes it easier to remove the mould base 2 downwards. Particularly in the case of a heavily profiled mould base, deformation of the moulded product would lead to jamming, with the result that it would be impossible to remove the mould base, or else doing so would cause damage.

The reinforcement wires 30 are formed, for example, by threaded rods. The stressing means 32 may then comprise elements which are provided with threaded holes which engage on the threaded rods. It can be seen from Fig. 5 that each stressing means 32 comprises a head 51 which is provided with a threaded hole and is adjoined by a bolt end 52. On the rear side, the bolt end 52 projects through a cutout 53 in a box section 54 which is connected to the mould side wall 3. The box section 54 extends over the entire length of the mould side wall 3. A nut 55 which is supported against the box section 54 is screwed onto

the bolt end 52. Tightening the nut 55 allows the desired prestress to be applied to the threaded rod.

The cutout 27 in the mould side wall 3 is advantageously formed by a slot which is open at the top. Consequently, it is possible to place the reinforcement wire 30 into the slot-shaped cutout 27 from above. The reinforcement wire 30 which has been laid in the cutout 27 is covered on the top side by a securing element 60 (cf. also Fig. 6).

Fig. 4 shows the stressing frame 14 in more detail. The stressing frame 14 is connected to a mechanism for controlling the movement of the stressing frame 14 between an open position and a closed position. Advantageously, the control mechanism is formed by an inflatable body 70. In the inflated state, the body 70 presses the stressing frame 14 upwards into the closed position. The closed position of the stressing frame 14 is also the closed position of the mould side wall 3. This makes it possible to then position and prestress the reinforcement wires 30. By applying a stress to the reinforcement wires 30, the stressing frame 14 is automatically held in the closed position.

It is then possible to allow the body 70 to empty. The result is an advantageous control mechanism which does not continuously store any spring energy. Advantageously, the control mechanisms of the two adjacent stressing frames 14 are activated simultaneously, in order to prevent undesirable deformation of the mould side wall 3. It is also possible to design the control mechanism as an inflatable hose which extends beneath a plurality of stressing frames.

The pivot point 16 of the stressing frame 14 is located sideways of the centre of gravity of the stressing frame 14, with the result that the stressing frame 14, provided it is free to do so, automatically moves into the open position as a result of the force of gravity. The stressing frame 14 is free to do so if the body 70 is not in the inflated state and if the stressing means 32 are not acting on the mould side wall 3 in the stressed state. Advantageously, the body 70 forms a damping means when the stressing frame 14 automatically moves from the closed position into the open position as the result of the force of gravity. This is easy to achieve by allowing air in an inflated body 70 to flow out via a restrictor valve.

To obtain a good seal between the mould base 2 and mould side walls 3, which can move independently of one another, the mould side walls 3 are provided with a flexible sealing element 75 on the underside (cf. Fig. 7). The C shape of the stressing frame 14 is such that the arm with the pivot point 16 is shorter than the arm with the mould side wall 3. This specific embodiment ensures that the mould side wall 3 moves vertically downwards to some extent during the final phase of the movement from the open position into the closed position. This provides a particularly good seal between the mould side wall 3 and the mould base 2.

The device according to the invention is particularly suitable for use in appliances for the manufacture of elongate moulded products made of reinforced concrete. The pivotably arranged stressing frames and the stressing means which interact therewith can then be used for a set of reinforcement wires which are to be prestressed and extend in the transverse direction from one side of the mould to the other. For these reinforcement wires, which are of small dimensions, a relatively low stressing force is required.

Fig. 8 shows an embodiment of an elongate mould which is interrupted in the centre. It can be seen that the mould is substantially composed of a plurality of device elements 80 which are located next to one another and connected to one another as described with reference to Figs. 1-7. In practice, elongate moulds which contain more than twenty-five such device elements 80 are sometimes used. A first set of reinforcement wires 82 which are to be prestressed extends in the transverse direction of the mould, which wires comprise six adjacent threaded rods per device element 80. A second set of reinforcement wires 81 which are to be prestressed extends in the longitudinal direction of the mould and in this case comprises ten bundles of in each case six reinforcement wires.

If the second set of reinforcement wires 81 is of great length, the device comprises at least one prestressing device 84 which can move in the longitudinal direction of the mould. This longitudinally movable prestressing device, which is only indicated highly diagrammatically, is preferably hydraulically actuated. The second set of reinforcement wires 81 extends in

the longitudinal direction from one side of the elongate mould to the other, through cutouts in the end walls 86. The reinforcement wires 81 are in particular provided with an upset head and are held by a comb of the prestressing device 84. By then moving the prestressing device 84 in the longitudinal direction, a desired prestress is applied to the second set of reinforcement wires 81.

The device shown in Fig. 8 is intended to be used for the manufacture of an assembly of a plurality of sleeper slabs 90 which are connected to one another. In this case, each device element 80 corresponds to one sleeper slab which is to be manufactured. Fig. 9 shows a sleeper slab 90 of this nature.

Each sleeper slab 90 is composed of ten sleeper elements 91 which lie next to one another and are connected to one another (cf. also Fig. 10). After a demoulding operation, the plurality of connected sleeper slabs 90 are separated from one another, for example by sawing. This also involves sawing through the second set of reinforcement wires 81 each time. The first set of reinforcement wires 82 projects out of each sleeper slab 90 on both sides. The ends of the reinforcement wires 82 are advantageously used to couple sleeper slabs 90 together while laying rails. The reinforcement wires 90 preferably comprise an end which is provided with a screwthread. Therefore, according to the invention, the screwthread on the first set of reinforcement wires 82 has a dual function, namely that of interacting with the stressing means during manufacture and that of providing a coupling feature when laying rail tracks.

Moreover, the first set of reinforcement wires 82 provides the sleeper slab 90 with additional strength. The second set of reinforcement wires 81 (not shown in Figs. 9 and 10), which extend in bundles through each sleeper element 91, ensure that each sleeper element 91 acquires a suitable compressive stress after demoulding.

For the sake of completeness, it should be noted that the longitudinal direction 87 of the mould shown in Fig. 8 corresponds to the transverse direction 98 of the sleeper slabs 90 or the longitudinal direction of the sleeper elements 91.

The invention can be applied to various shapes and dimensions of moulds. In particular, it is also possible to

arrange a plurality of pairs of mutually opposite mould side walls, which extend in different directions, on pivotable stressing frames and to prestress a plurality of sets of reinforcement wires in these frames.

As an alternative to the embodiment shown, where the stressing means have a screwthread, it is also possible to use other stressing means which act on the reinforcement wires and rest against the stressing frame or the mould side wall arranged thereon. Consideration may be given to stressing means which are provided with a part which clamps securely around a reinforcement wire. To this end, the reinforcement wire may be provided with an upset head.

The invention thus provides a structure with pivotably arranged stressing frames with mould side walls and stressing means which interact therewith, which structure is simple and strong and can be used to apply a desired prestress to a plurality of reinforcement wires in a simple manner, which can also be maintained during part of a demoulding operation, while the mould base can be removed separately from the mould side walls.