EP0008820B1 - Improved apparatus for the manufacture of prestressed products - Google Patents

Abstract

1. Improved installation for the manufacture of elongated prestressed products and especially for prestressed girders from ductile concrete on the tracks of a prefabricating bench, this installation comprising a non-stop drawing mill adapted to allow its movement along the bench and comprising at its rear section drawing dies with openings shaped to the profil of the products to be manufactured and open cross-wise at their lower sections at the level of the tracks to match the breadth of the aforesaid product beads, the said installation being characterized in that the drawing mill comprises at the rear end of the drawing dies a movable blanking plate provided with identations shaped and located to match the prestressed cables so as to enable them to lodge into the indentation during lowering of the plate, and guiding and driving means adapted to enable the said plate to shift between an upper position where the drawing dies are completely cleared off and a lower position where the plate extends near the tracks and blanks the aforesaid drawing dies.

Description

The invention relates to an improved installation for manufacturing prestressed longiform products, in particular prestressed beams, on tracks of a prefabrication bench. It aims to allow, in an installation operating according to a spinning-extrusion process, to produce prestressed products of desired adjustable lengths, having at their ends lengths of cables protruding from said ends.

It is known that prestressed beams are manufactured in the factory on benches of several tens of meters in length comprising several parallel tracks. To meet user demand, these beams must be manufactured at adjustable lengths; moreover, certain specifications stipulate that they must have their prestressing cables which protrude at both ends.

There are several types of manufacturing processes for these products. A first type of relatively old process, which is illustrated by US Pat. No. 3,608,163, consists in equipping the installation with molds arranged along the bench and passing over these molds a machine for pouring concrete, known as " layer ", which presents the length of the products to be manufactured and advances discontinuously, step by step, along the bench. This machine is provided at its two ends with two plates. When it stops, the plates are lowered so as to close sections of molds and the concrete is poured until filling these sections of molds; after a certain drying time, the plates are raised and the laying machine is brought to advance by one step to produce a new series of products in neighboring sections of molds. Under these conditions it is understandable that there is no difficulty in preserving between the aligned products empty intervals where the prestressing cables remain bare. When the products are dry, these cables are cut and we obtain products with cables that protrude at their ends.

However, this type of process has drawbacks which have determined that most manufacturers have abandoned it. Firstly, the products have an invariable length equal to the length of the laying machine and it is not possible to adapt the manufacturing to demand. Furthermore, such a manufacturing process is extremely slow; indeed, on the one hand, the advance of the machine is discontinuous (constituted by a succession of displacements and stops) and, on the other hand, it is necessary to wait after each stop that the products of the current series have dried at least partially before making the following. Finally, this process requires the presence of a battery of molds along the bench and its cost is seriously affected.

It should be noted that, in this type of process, the plates situated at the two ends of the laying machine are controlled to descend and to go up while the machine is stopped: they have the simple function of closing the sections of fixed molds, au- above which the laying machine is located, to prevent the concrete from spreading at the two ends of these sections. These plates are raised before restarting the laying machine and have no use during its movements.

Another manufacturing process, derived from the first, consists in advancing a machine for pouring concrete, continuously, along a bench equipped with fixed molds. This faster process poses a problem in stopping the beams and leaving part of the prestressing cables bare between them. The manufacturers have solved this problem by providing so-called intermediate pieces, which are placed in a fixed position along the molds at the intervals between beams. These spacers fill the mold in these intervals and there is no concrete discharge when the concrete pouring machine passes over them. However, this process, which can be illustrated by US Pat. No. 4,051,216, has several drawbacks: the need for a battery of molds along the bench, long and tedious installation of the intermediate pieces, risk of tearing them off. ci by the machine as it passes, lack of flexibility for length adjustments, delicate removal of these spacers after the concrete has dried, etc.

There is also another manufacturing technique which uses a process known as 'extrusion-extrusion _' ; this process consists in advancing on the tracks of the bench a continuous spinning machine essentially comprising, on the one hand, a vibrating pre-mold having a profile close to that of the products to be produced and open in the lower part, on the other hand, a hopper to pour the concrete in a pasty state into this pre-mold, finally, at the rear and in the extension of the pre-mold, dies having the product profile and open at the bottom at the level of the tracks over widths equal to those of the heels said products (by definition, the heels of the products consist of their lower portion resting on the bench). The products are thus produced by extrusion, in the total absence of molds along the tracks of the prefabrication bench. Such a process is extremely advantageous since it operates without a mold with continuous progression of the spinning machine.

However, the problem of separations between beams with bare sections of cable arises in this type of process with an even greater acuity than in the previous process, because of the very nature of said process, which predisposes the products to deformations. Currently this problem has been solved imperfectly by planning parts dividers similar to those already mentioned for the previous process and which have the same drawbacks.

The present invention relates to an improved installation of the type mentioned above, operating by extrusion-extrusion; an objective of the invention is to satisfactorily solve the problem of separations between beams.

One of the aims of the invention is in particular to benefit from the advantages of the extrusion-extrusion processes, while eliminating the intermediate pieces along the bench, so as to eliminate all the drawbacks relating thereto.

Another objective is to considerably increase the flexibility of adjusting the lengths of products until it is possible to program these without any manipulation on the bench.

Another objective is to achieve these results by a simple modification of existing spinning machines, which does not significantly increase the cost.

To this end, the improved installation according to the invention comprises a continuous spinning machine adapted to be able to move along a prefabrication bench and comprising, at its rear part, dies whose orifices have the profile of the products to be manufacture and are open at the bottom at the level of the tracks over widths equal to those of the heels of said products; according to the present invention, the spinning machine comprises at the rear of the dies, a movable closure plate provided with notches of shape and position corresponding to those of the prestressing cables to allow them to be housed therein for the descent of the plate, and means for guiding and driving means of said plate adapted to allow it to be moved between a raised position where the dies are fully released and a low position where the plate extends to near the tracks and closes said channels.

Thus no accessory is installed in advance on the tracks which remain bare; the spinning machine continuously advances along the bench; when it has progressed by a length corresponding to that of the desired products, the cover plate is lowered by the action of the drive means, the machine continuing to advance at constant speed: in this way the outlet of the concrete is interrupted over an adjustable length (in general of the order of about twenty centimeters for prestressed beams in order to leave about ten centimeters of cables protruding at the end of the two neighboring beams). The plate is then raised and the concrete spinning resumes. When lowering the plate, the prestressing cables are housed in the notches thereof provided for this purpose; these cables are thus left exposed along the interval between beams where the concrete is interrupted. They will be sectioned in a conventional manner once the concrete of the products has hardened.

The control of the shutter plate of the spinning machine can be carried out manually or automatically by equipping these machines with control units, in particular electronic, capable of triggering the various sequences of a work program determined in in order to obtain products at the requested lengths. Note that due to the flexibility conferred by the invention, this program can be managed on a computer as and when manufactured according to stocks and other data.

• la figure 1 est une vue de profil schématique d'une installation conforme à l'invention,
• la figure 2 en est une vue en plan schématique,
• la figure 3 est une vue par l'arrière, en perspective partielle, d'une machine fileuse perfectionnée selon l'invention.

Other characteristics, objects and advantages of the invention will emerge from the description which follows with reference to the appended drawings which present, by way of nonlimiting example, an embodiment of installation in accordance with the invention; on these drawings, which form an integral part of the description:

• FIG. 1 is a schematic profile view of an installation according to the invention,
• FIG. 2 is a schematic plan view thereof,
• Figure 3 is a rear view, in partial perspective, of an improved spinning machine according to the invention.

The prefabrication installation targeted by the present invention comprises a bench B with several tracks, provided at each end with a conventional system for tensioning the prestressing cables (not shown). On either side of the tracks are arranged rails 1 and 2 extending all along the bench.

The installation is equipped with a continuous spinner machine P which can be seen diagrammatically in FIGS. 1 and 2 and the rear part of which can be seen in FIG. 3.

The conventional and well-known members of this machine P will not be described in detail and are simply recalled below: concrete hopper, vibrating pre-mold, dies which can be seen in 3 at the rear of the machine, traction winch of the machine which allows it to roll in the direction of arrow f on wheels 4 resting on rails 1 and 2.

The known operation of this spinning machine is as follows: the machine is immobilized at the start of the tracks and the hopper is filled with concrete; this descends by gravity into the pre-mold; the vibration of the latter allows a uniform filling thereof (its length is of the order of 3 m). When the pre-mold is properly filled, the traction winch is started and, by the push of the concrete contained in the pre-mold, the latter is extruded in the dies 3 (which themselves do not vibrate).

Of course, the prestressing cables were previously placed on the tracks to be embedded in the beams thus extruded.

According to the present invention, a closure plate 5 is arranged at the rear of the machine across the width of the latter. This plate is vertically movable and is linked to two vertical slides 6 and 7 which guide it laterally. Each slide is constituted by a guide cylinder fixed to the frame of the machine and by a movable rod fixed to the cover plate.

In addition, support rollers 8 and 9 are arranged at the lower end of descending supports 10 and 11 secured on the frame at the rear of the dies between two outputs from neighboring dies; the shutter plate 5 which is movable between a raised position where the die outlets are completely free and a low position near the tracks, is thus guided during its descent between the rear face of the die and the support rollers 8 and 9 which exert on this plate a pressure opposite to the pressure of the concrete.

The shutter plate 5 is driven by a vertical cylinder 12, in particular a hydraulic cylinder, which makes it possible to lower or raise it. This cylinder is located on the median axis of the machine.

In addition, the plate 5 is provided at its lower part with notches such as 13, which have a suitable shape and position to form housings for the prestressing cables during the descent of the plate.

This plate is preferably bevelled in its lower part 5a in order to facilitate its penetration into the concrete of the beams during the descent of the plate.

In addition, for each beam, are welded to the plate 5 cheeks such as 14 and 15 which extend towards the rear of the machine in line with the sides of each beam, and follow the shape of these sides; for the purpose of simplification, FIG. 3 shows only the cheeks of a single beam. When the plate 5 is lowered to interrupt the exit of the concrete, these cheeks form a guide for the already cast end portion of each beam and avoid deformations thereof and in particular a flaring of this part.

It is understandable the advantage of the improved installation according to the invention which allows to realize in the best conditions prestressed beams to the desired lengths with prestressing cables protruding at the ends.

Of course, the invention is not limited to the terms of the above description, but includes all variants thereof. It extends in particular to the manufacture by extrusion-extrusion of any elongated product in prestressed concrete.

Claims (5)

1. Improved installation for the manufacture of elongated prestressed products and especially for prestressed girders from ductile concrete on the tracks of a prefabricating bench, this installation comprising a non-stop drawing mill adapted to allow its movement along the bench and comprising at its rear section drawing dies with openings shaped to the profil of the products to be manufactured and open cross-wise at their lower sections at the level of the tracks to match the breadth of the aforesaid product beads, the said installation being characterized in that the drawing mill comprises at the rear end of the drawing dies a movable blanking plate provided with identations shaped and located to match the prestressed cables so as to enable them to lodge into the indentations during lowering of the plate, and guiding and driving means adapted to enable the said plate to shift between an upper position where the drawing dies are completely cleared off and a lower position where the plate extends near the tracks and blanks the aforesaid drawing dies.

2. Improved installation as set forth in claim 1, characterized in that the guiding means for the blanking plate located at the rear of the drawing mill comprise vertical slides to which the said plate is linked, and supporting rollers located at the lower end of lowering supports located at the rear of the drawing dies between two outlets of contiguous drawing dies, so that, during lowering, the blanking plate is guided between the rear face of the aforesaid drawing dies and the supporting rollers exerting an opposite load to the load of the material in the drawing dies.

3. Improved installation as set forth in claims 1 or 2, where the driving means for the blanking plate comprise a vertical jack.

4. Improved installation as set forth in claims 1, ² or 3, characterized in that the blanking plate is chamfered in its lower section so as to make easier its penetration into the material of the girders during lowering of the said plate.

5. Improved installation as set forth in claims 1, 2, 3 or 4, characterized in that, for each girder, bosses welded on the blanking plate extend to the rear of the mill perpendicularly to each girder side and fit the shape of these sides, so as to form a guide for the already casted extreme part of each girder when the blanking plate is lowered.

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