METHOD AND APPARATUS FOR PRODUCING CONCRETE PRODUCTS

Abstract: A method of casting concrete elements comprising one or more longitudinal hollow cores. When casting is started, forming means (4) provided in the apparatus are pushed through openings in a headplate located at the front end of the element to be cast and fresh concrete is pressed against the headplate by means of feeding screws (3) provided in the apparatus. When casting the back end of the element to be cast, the casting apparatus, as well as the feeding screws (3) and the forming means (4) thereof, pass over a part (10) mounted on the casting bed (1) to form the lower part of the endplate of the form. The feeding opening of the apparatus is covered by a covering means (8) and a part (11) provided in the apparatus to form the upper part of the endplate of the form is pushed above the lower part (10) of the endplate of the form. Openings are formed between the upper part and the lower part of the endplate, allowing the feeding screws (3) and the forming means (4) to pass through.

Description: METHOD AND APPARATUS FOR PRODUCING CONCRETE PRODUCTS This invention relates to a method and apparatus for casting concrete elements comprising one or more hollow cores. Slipform casting is a commonly used concrete element casting method. A known slipform machine for casting hollow core stabs is described in patent publication FI 70821. As disclosed therein, the concrete is compacted by the so-called shear compaction method, using oscillatory hollow core forming means. Usually, slipform casting is used for producing a long, continuous casting that, once hardened, is sawn into sections of a desired length. In terms of handling, however, it is more preferable in some cases to produce castings having the correct final length. In patent application FI92 0494, a solution is described in which a headpiece is used to render the front end of the casting compact and give it the right final shape. In this case, no waste part having to be sawn off and discarded, is created at the front end of the casting. From patent publication FI 102 253 (WO 97/7949) a solution is known, in which a wall defining a casting space is placed at the front and back edges of a metal plate forming a part of a composite construction. No form is used in the casting. After the casting, the front side is lifted away. The back side moves back and forth, thus pressing fresh concrete under the vibrating plate during the casting. This known solution has the problem of not being useful for casting pre-stressed elements, since it is not possible to anchor wires to the movable end walls. In the solution, reinforcement rods running in the longitudinal direction along the top surface of the metallic base plate are used instead of pre-stressing wires. The steel plate with reinforcement rods increases the price of the cast product. The characteristics of the method according to the present invention are set forth in Claim 1. The characteristics of the device according to the invention are set forth in Claim 3. The method according to the invention makes it possible to give both the front and the back end of the casting precisely the right final shape. Thus, it is possible to cast elements or beams of the desired length that do not have to be sawn into sections of the right length following the casting. Consequently, no waste parts are produced. In the production of short slabs, the portion of slab end waste parts would be proportionally greater than in the production of long, continuous slabs that are afterwards sawn into sections of the desired length. Therefore, it is particularly important to avoid producing waste parts in the case of short slabs. in the device according to the invention, one end of the concrete pre-stressing ropes can be anchored to a headplate, while the other end thereof can be anchored to the lower part of an endplate forming a part of the form. Because short elements do not always have to be pre-stressed, the invention can also be implemented using non-tensioned wires or reinforcement bars. In a preferable embodiment of the invention, a movable anchor plate is employed that forms either the headplate or the lower part of the endplate. It can be mounted at an appropriate position on the casting bed according to the length of the element to be cast. The method is easy to apply by using a customary slipform machine moving along a casting bed. In this case, an endplate upper part that can be moved by means of the casting machine is fastened to the prior art device. In the following, the invention and details thereof will be described in more detail with reference to the accompanying drawings in which Figure 1 is a side view of the apparatus according to the invention at the beginning of casting, Figure 1a shows the upper and the lower part of the endplate seen from the end of the apparatus, Figures 2 to 5 show the apparatus of Figure 1 at the different final stages of the casting, Figure 6 shows an alternative way of fastening the headplate or the endplate to the sides of the form, and Figures 7a and 7b show a way of locking in place a plate fastened in the way shown in Figure 6. The apparatus according to the invention comprises a slipform machine that moves along a bed 1 (Figurel). It is also possible to use a stationary machine and a movable bed. The casting machine comprises a feed hopper 2 and a number of parallel feeding screws 3 that become wider towards the rear end of the apparatus and the extensions of which form mandrels, i.e. compacting sleeves 4. The shafts of the feeding screws are supported on the machine frame and connected to a drive 5 at their front end. The concrete form is formed by a top plate 6 located above the screws and the mandrels as well as by side plates located on the sides thereof. When the feeding screws push fresh concrete towards the trailing end of the screws, the reaction force of the screws makes the apparatus move on its wheels in the direction shown by the arrow. The compacting sleeves move in relation to the casting machine, for example by rotating back and forth around the longitudinal axis in opposite directions relative to each other, or by traveling back and forth in the longitudinal direction, each compacting sleeve moving in the opposite direction relative to the adjacent sleeve. Thus, the concrete is compacted into its final shape around the sleeves. Moreover, the top plate 6 can be vibrated. All of this is known. A concrete chute 7 is mounted to the casting machine, under the feeding screws. Its upper surface is formed by a number of parallel chutes each of which lies under a feeding screw. The casting machine comprises a bottom shutter 8 that can be pushed under the opening of the concrete hopper to cover the opening. The shutter can be moved for example by means of a hydraulic actuator. At the front end of the casting bed, a headplate 9 is provided that forms a vertical wall in the front end and that comprises openings through which the mandrels 4 can be pushed. A lower endplate 10 is mounted at the back end of the casting bed. In the upper edge thereof arched recesses are provided, shaped in such a way that the screws and the feeding chute of the casting machine can pass over it. Pre-stressing wires can also be anchored to the lower stop in advance. The other ends of the wires are anchored to headplate 9. Further, the casting machine comprises an upper endplate 11 , in the lower edge of which are provided arched recesses, and which can be shifted, at the final stage of the casting, from a position in front of the concrete hopper to a position abutting the end wall of the finished slab. When the upper part of the endplate lies above the lower part of the endplate, the coinciding recesses of both of these parts form openings allowing passage of the feed screws and mandrels. Figure 1a shows a cross-section of the form, perpendicularly to the casting direction, the lower endplate 10 and the upper endplate 11 aligning. The device according to the invention operates as follows: The casting is started by reversing the casting machine into headplate 9 located at the end of the form, into a position where the compacting sleeves 9 pass through the openings in the headplate (Figure 1). The feeding screws feed fresh concrete and press it against the headplate, compacting the front end of the element. Thereafter, the casting machine moves forward along the bed in the normal way and an element is formed on the bed. Approaching the back end of the element, the casting machine moves until the lower endplate 10 is near the outer end of the concrete chute 7, below the chute. Fresh concrete is still flowing from tank 2 of the casting machine onto the feed screws 3, and the screws are rotating (Figure 2). At this stage, the upper endplate 11 is shifted above the lower endplate 10 by means of an actuator. At the same time, the feeding of concrete from the tank 2 is stopped by closing the concrete tank bottom shutter 8 (Figure 3). As the upper endplate 11 is pushed above the lower endplate while the screws are still rotating (cf. Figure 1a), a vertical element end wall is obtained. The back end of the element is compacted in such a way that, while the upper endplate 11 is in the position shown in Figure 3, aligned with the lower endplate 10, the feeding screw 3 still feeds concrete and maintains the pressure at the compacting sleeve 4 which at the same time compacts the concrete into its final shape and density. The precise feeding of concrete at the back end of the slab is controlled by continuously maintaining a steady feed pressure. If the pressure increases too much, the superfluous concrete is discharged through the space between the spiral ridges of the adjacent feeding screws, as well as by sliding backwards through the space between the ridge and the hollow core. The screw continuously transfers concrete to its outer periphery with the result that the concrete is very loose at the feeding screw and is able to fiow if the local pressure increases too much. The casting machine moves further into the position shown in Figure 4 in which the rotation of the screws is stopped whereas the sleeves are still compacting. Finally, the machine moves into the position shown in Figure 5, after which the machine is driven out of the cast slab and away from the position above the lower endplate 10. After this, the casting machine is taken to the front end of the following form to be cast and is reversed into position with the compacting sleeves 4 in the headplate 9, passing through the openings in the headplate. At this stage, the feeding screws are started with the result that the rest of the concrete on the screws falls onto the form. The upper endplate 11 can now be moved to the starting position by means of an actuator, and a new casting can be started. Preferably, the upper endplate is at least 100 to 150 mm wide. If it is this wide, it covers more than one screw ridge. Preferably, the lower endplate is as wide as the upper endplate, so that it covers the rear end of concrete chute at the final stage and, consequently, prevents the fiow of concrete onto the form. The headplate 9 and/or the lower part 10 of the endplate can be removably mounted in the desired position on the bed, to allow for changing the position of the stop according to the size of the slab to be cast. Figure 6 shows a solution in which the headplate is fastened to the sides of the bed. The plate is locked in place by means of a stop slide 12 having holes 13 in its ends. In the sides of the bed, a number of consecutive holes 14 are provided, and the slide is locked in position as desired by pushing a pin through the aligning holes 13 and 14. Pre- stressing wires 15 are tensioned by means of the slide. The holes 13 and 14 do not have to be made in horizontal surfaces but they can also be made in the vertical surfaces of the sides of the slide and the bed. Figures 7a and b show a manner of locking in place the movable stop of Figure 6 in cross-section and from above, respectively. The hole 13 in the slide is oval and its larger diameter is transversal to the casting direction. A circular plate 16 is provided in the hole 13, having a diameter corresponding to the smaller diameter of the hole 13. A pin 17 fitting the holes 14 in the sides of the bed is fastened eccentrically to the plate 16. The top plate 18 is provided with an operating and locking lever 19. Thus, the stop can be moved by turning the plate 16 in the oval hole 13 by means of the lever 19. When the holes 14 have the right spacing with respect to the size of the holes 13 and to the eccentricity of the pin 17, the position of the stop can be changed steplessly. Adjustable locking of the headplate and endplate may be provided in some other expedient manner, and the plates can be locked not only to the sides but also to the end wall of the bed.

Claims: Claims 1. A method of casting concrete elements having one or more longitudinal hollow cores by means of a slipform machine that moves along a bed (1 ), in which method, at the beginning of the casting, core forming means (4) provided in the machine are pushed through openings in a headplate (9) provided at the front end of the element to be cast and forming the front wall of the form, and fresh concrete is pressed against the plate face by means of feed screws (3) provided in the apparatus, after which the casting continues and the feed screws feed fresh concrete onto the bed, the casting machine moving forward on the bed due to the reaction force of the concrete at the same time, characterized in that during the casting of the back end of the element - the casting machine, as well as the feeding screws (3) and the forming means (4) thereof, pass over a part (10) mounted on the casting bed (1 ) to form the lower part of the endplate of the form, the feeding screws remaining, at first, above the lower part of the endplate, - the feeding opening of the feeding tank (2) of the apparatus is shut by a shutting means (8), and a part (11 ) provided in the apparatus to form the upper part of the endplate of the form is pushed above the lower part (10) of the endplate of the form resulting in openings being formed between the upper part and the lower part of the endplate, allowing passage of the feeding screws (3) and forming means (4), - the feeding screws (3) and the forming means (4) are subsequently pulled out of the slab cores. 2. A method as defined in Claim 2, characterized in that, before casting is started, wires forming the reinforcement of the element are fastened between the headplate (9) of the form and the lower part (10) of the endplate of the form. 3. A slipform device movable along a casting bed (1 ) for casting concrete elements, the device comprising a feed container (2), feeding screws (3) supported at the front end of their shafts for feeding fresh concrete, forming means (4) extending from the feeding screws for forming at least one hollow core in the element to be cast, a top wall (6) and side walls of the form, as well as a headplate (9) at the front end of the element to be cast, forming the front wall of the form and comprising openings through which the forming means (4) can be pushed, characterized in that - the device comprises a part (10) mountable on a stationary casting bed (1 ) to form the lower part of the endplate of the form, comprising recesses in its upper edge and over which the casting machine, as well as the feeding screws (3) and forming means (4) thereof, can pass, - the device comprises a part (11 ) mounted in the movable casting apparatus to form the upper part of the endplate of the form, comprising recesses in its lower edge and movable in relation to the casting machine in the casting direction, between a position in front of the opening of the feed tank (2) and a position above the lower part (10) of the back wall, above the back end of the element, at the final stage of the casting, and the recesses in the upper edge of the lower part (10) and in the lower edge of the upper part (11 ) of the endplate of the form are shaped to form openings through which the feeding screws (3) and the forming means (10) can be pushed when the lower part and the upper part align. A device as defined in Claim 3, characterized in that the headplate (9) and/or the lower part (11 ) of the endplate of the form are fastened to the bed in such a way that its position can be changed according to the length of the element to be cast.

Inventors: KANKKUNEN HEIKKI, SEPPAENEN AIMO, KANKKUNEN, HEIKKI, SEPPAENEN, AIMO
Applicants: ADDTEK RES & DEV OY AB, KANKKUNEN HEIKKI, SEPPAENEN AIMO, ADDTEK RESEARCH & DEVELOPMENT OY AB, KANKKUNEN, HEIKKI, SEPPAENEN, AIMO
Application year: 2000
Main classification: B28B3
IPC codes: B28B1, B28B21