METHOD AND APPARATUS FOR MANUFACTURING A CONCRETE PRODUCT AND A CONCRETE PRODUCT SERIES

Abstract: The invention relates to a method and assembly for manufacturing a concrete product series of hollow-core slabs of at least two different sizes, the products having hollow cores of different heights. According to the method, using at least one feeder auger (4), concrete mix is extruded through a delimited cross section acting as a nozzle section, and to the rear end of each feeder auger (4), within the length of the delimited cross section, is adapted a core-forming tubular member (6) serving to shape a hollow core in the product being manufactured. The core-forming member (6) is selected to be a tubular member having its height adjusted to be at the core-troweling portion of the member equal to the desired height of the hollow core in the product, and the members (7) serving to delimit the top surface of the nozzle section are contoured to conform to the shape of the top surface of the selected tubular member (6) so that the height difference between the ingoing end and the outgoing end of the members (7) in the concrete mix flow direction is within a 50 % tolerance equal to the height difference between the top level of the rotational envelope perimeter of the auger (4) and the top level of the core-forming tubular member (6) that trowels the hollow core of the product.

Description: Method and apparatus for manufacturing a concrete product and a concrete product series The invention relates to a method according to the preamble of claim 1 for manufacturing hollow-core slabs of different heights by means of an extrusion continuous- casting machine. The invention also relates to an assembly suited for implementing the method and further relates to a hollow- core concrete slab series that can be manufactured by virtue of the method. During extrusion casting of concrete, the concrete mix is extruded through a mold or nozzle section generally with the help of feeder augers. The casting machine moves propelled by the reaction force of the feeder augers over a casting bed and the finished product remains resting on the bed, whereon it is allowed to harden at least partially. Conventionally, long castings are made that are then trimmed to a length required at the final erection site. The product has a relatively large hollow-core portion that serves to reduce the product weight and amount of mix needed for casting without substantially compromising the product strength. The hollow cores are molded into the product with the help of core-forming members adapted to the auger rear ends. The feeder augers and core-forming members are aligned parallel to the longitudinal axis of the casting bed and the product, whereby the core-troweling or other core-forming member generally is nonrotatable, but may in some machine con- structions rotate with the auger. The function of the feeder augers is to propel the concrete mix past the molding member and the nozzle section and to simultaneously exert a compacting pressure on the mix as it is forced through the molding cross section delimited by the nozzle section and the core-forming members. The core- forming member is generally located so that at least a portion thereof extends into the delimited molding cross section. Various reasons associated with the development of the hollow-core slab extrusion technique have influenced the progress toward current types of cross sections. In the first hollow-core slabs, the hollow cores had a circular cross section, whereby the diameter of the auger and the diameter of the core were determined by the slab thickness, and the number of cores adapted laterally over the slab width was made as large as permitted by the minimum possible thickness of the isthmuses between the cores. Hence, the shape of the cores and the proportional area thereof in the overall cross-sectional area of the slab was limited, and the number of cores had to be selected according to the slab thickness. The most commonly used slab width is 1200 mm and the respective slab heights are standardized as 150, 200, 265, (250), 320, 400 and 500 mm. With these dimensions, circular or almost circular core cross sections give the height-to-core number combinations of 150/8, 200/6, 265/5, 320/4, 400/4 and an obsolete standard of 400/3. Of these cross sections, those of the larger height are the latest additions to the selection, and a 500 mm high slab is still rarely used. Along with advances in the continuous casting technique, some freedom was gained in the shaping of the cores so that initially the deformation of the height-to-width ratio of the core was limited to 1.15, but presently even larger deformation ratios in the cores are possible. While the envelope generated by the tips of the rotating auger flights is obviously circular, it is possible in the concurrent technology to combine such an auger with core-forming members having a noncircular cross section so that a desired shape of the core can be troweled. In fact, it is possible to use hollow cores of different cross-sectional shapes in one and the same slab. Herein, the feeder auger and the core-forming member are mounted on the same shaft thus acting as the core-forming assembly. If the cross section of the core-forming member is made noncircular, the forming member is advantageously mounted in a pivotal manner to the core-forming assembly so as to prevent the forming member from rotating about its longitudinal axis, but instead allowing it to move in some other manner, e.g., so that a compacting motion is attained. Some constructions utilize a mounting technique that allows the core-forming member to perform a limited reciprocating rotation even when the shape of the core- forming member is made noncircular. Prior-art technology is handicapped by needing the feeder auger, the core-forming assembly and the cross section of the nozzle section that define the external dimensions of the cast article to be matched with each other so that the feeder augers will provide a suitable compacting pressure during casting without unduly obstructing the flow of the concrete mix through the cross section of the forming assembly. Hence, conventional continuous casting machines are generally designed for the manufacture of a single hollow-core slab type and size. Herein, it is very difficult to make changes for a different height of slab and hollow core. Normally it is necessary to replace an entire nozzle section assembly or make drastic changes in the construction of the nozzle section. This restricts the main use of concurrent machine constructions to the manufacture of a single slab size and cross section type due to the high costs and loss of time incurred in the modification of the machine assemblies. Frequently, such a modification is even impossible if it would require lateral shifting of the feeder augers. It is an object of the invention to provide an entirely novel type of casting method and machine capable of overcoming the above-described problems of the prior art and to provide a slab casting method that permits a plurality of slabs of different sizes and types to be manufactured on a single machine. The goal of the invention is achieved by way of shaping the top side of the core-forming member so that the shape of the initial end of the core-forming member jointed to the auger rear end is made equal to the circular envelope of the auger rear end, wherefrom it gradually changes toward the other end of the member toward a shape corresponding to the desired core dimensions of the hollow core to be manufactured, whereby also the underside shape of the nozzle section upper wall is made conforming to the varying shape of the core-forming member top surface. Respective gradual shaping may also be made on the underside surface of the core-forming member, whereby also the underside shape of the core-forming member can be made to change from the auger rear end dimension toward the core dimension and the shape of the concrete mix feed trough 5 is then made conforming to the varying shape of the core- forming member underside surface. More specifically, the method according to the invention is characterized by what is stated in the characterizing part of claim 1. Furthermore, the assembly according to the invention is characterized by what is stated in the characterizing part of claim 6. The slab series according to the invention is characterized by what is stated in the characterizing part of claim 12. The invention provides significant benefits By virtue of the invention, a single continuous-casting machine can be advantageously used for the manufacture of slabs of different heights and widths. The isthmus thicknesses of the slabs can be optimized irrespective of a change in the hollow core size, since the variations in the core dimensions are accomplished by way of changing the core height without changing the spacing/number of the cores in the slab lateral direction. To change the slab/core height, only the core-forming member assembly and the top part of the mold nozzle section must be re- placed, which is a relatively uncomplicated operation. Hence, there is no need to realign the locations of the feeder augers when the core dimensions are changed. The aggressive shaping of the compacting beam assembly mem- bers over the nozzle section gives a novel type of means to control the degree of filling over the entire cross section and to achieve a balanced casting process. The top portion of the cast cross section can be subjected to a compacting pressure, whereby the compaction in this region is not solely determined by the compacting effect of mere vibration. The flow channels of concrete mix in the cross section of the product being cast can be kept constant, whereby the feed power exerted by the auger is at all times sufficient for the casting operation. The invention also makes it possible to produce slabs of different widths by way of mounting in the lateral direction a required number of core-forming members and feeder augers. The nozzle section is readily subdividable by means of a mold partition to a desired lateral width, as well as the concrete mix feed hopper, too. The invention is next examined with the help of the exemplifying embodiments by way of making reference to the appended drawings, in which FIG. 1 shows a partially sectioned side view of an embodiment of an apparatus according to the invention; FIG. 2 shows a partially sectioned side view of another embodiment of an apparatus according to the invention; FIG. 3 shows a cross section of a slab manufactured using the apparatus illustrated in FIG. 1; FIG. 4 shows a partially sectioned side view of a still another embodiment of an apparatus according to the invention; FIG. 5 shows a cross section of a slab manufactured using the apparatus illustrated in FIG. 4; FIG. 6 shows a partially sectioned side view of a still another embodiment of an apparatus according to the invention; FIG. 7 shows a cross section of a slab manufactured using the apparatus illustrated in FIG. 6; and FIG. 8 shows different kinds of slab cross sections that can be manufactured by virtue of the invention. By its basic structure, the concrete casting assembly according to the invention has a construction similar to conventional continuous-casting machines. A hollow-core slab is cast onto a casting bed 1 or mold that is adapted to support the travel of the casting machine on wheels 9. The operating controls of the machine are mounted in an enclosure 2 at the rear of the machine. This enclosure houses, e.g., the controls of the feeder augers and reinforcement steel inserters and the operating controls of vibrators possibly adapted to the augers. As these pieces of equipment are a standard outfit on a casting machine, their detailed description will be omitted here- from. The concrete mix is poured into a feed hopper 3 located above feeder augers 4. Plural augers 4 are used in parallel, whereby the number of the augers is equal to the number of hollow cores in the product. Below the feeder augers 4 is mounted a concrete mix flow guide or feed trough 5 that delimits the concrete mix flow channel formed under the auger 4. The shape of the feed trough 5 may be kept unchanged from run to run, or, advantageously, the shape of the trough is always arranged conforming to the shape of the core-forming member. At the rear end of the auger 4 begins the delimited cross section of the flow channel later called the nozzle section. This nozzle section is delimited by the casting bed 1, the sidewalls of the machine and a compacting beam assembly 7 located above the feeder auger 4. The compacting beam assembly 7 is adapted to be movable in the vertical and horizontal directions by means of an electric-motor-driven actuator 8. This actuator device may be adapted to make the trowel beam assembly perform either a slow compacting movement or a vibratory motion at a higher frequency. The appro- priate compaction technique is selected according to the product being manufactured and the properties of the concrete mix being used. To the rear end of the feeder augers 4 is mounted a core- forming member 6. A characterizing feature of the present invention is related to the conforming shaping of the combination formed by core-forming member 6 and the trowel beam assembly 7. In the embodiment shown in FIGS. 1 and 2, the height of the core-forming member 6 is made larger than the largest diametral dimension of the feeder auger 4. Accordingly, the largest outer dimension of the core-forming member 5 must be adapted to mate with the rear end of the auger at their mutual interface. This is implemented by way of making at least the top side 11 of the core-forming member 6 to taper toward the joint with the auger 4, whereby in the illustrated construction the initial end of the core-forming member 6 facing the rear end of the auger 4 is made slanting toward the perimeter of the rear end of the auger. As the concrete mix flow channels must have a well-defined cross section to assure a suitable internal compacting pressure, the shape of the trowel beam assembly 7 is contoured conforming to the shape of the core-forming member 6, which means that the assembly has an upward flaring portion 10 that conforms in the downstream direction of the concrete flow to the increasing cross section of the nozzle section in a manner allowing the core-forming member to flare in the portion of the nozzle section to the desired dimension of the hollow cores being cast. The trowel beam assembly may be mounted in an adjustable or replaceable manner. In FIG. 3 is shown the cross section of a slab manufactured using the above-described embodiment of the continuous-casting machine. In the machine construction illustrated in FIG. 4, the diameter of the core-forming member 6 is substantially equal to the diameter of the feeder auger 4, whereby the trowel beam assembly 7 is made straight in the same manner as the perimeter of the core-forming member. The construction shown in FIG. 6 has the vertical dimension of the core-forming member 6 made smaller than the diameter of the auger 4, whereby the trowel beam assembly must be provided with a slanted portion 12 that conforms to the tapering height of the core-forming member 6. FIGS. 5 and 7 illustrate hollow- core slabs manufactured using these embodiments of the casting machine. As is evident from FIGS. 3, 5 and 7, the core widths as well as the thicknesses of the intercore isthmuses are kept constant, but the height of the cores are varied according to the slab height in order to optimize the slab dimensions. In the implementation of the invention, the shape of the hollow cores can be varied by changing the core-forming members. Obviously, such a change necessitates a simultaneous replacement of the overlying trowel beam assembly into one conforming to the shape of the new core-forming member. The above-described diagrams illustrate a method through which modular core-forming member sets for larger and smaller heights of hollow cores may be obtained by modulating the basic shape of the core-forming member. In this fashion, it is possible to manufacture slabs with standardized size of, e.g., 200/4, 265/4, 320/4, 400/4 and 500/4 on one and the same continuous-casting machine. Herein, the spacing between the core-forming members and the lateral locations of the feeder augers are kept constant, while the thicknesses of the intercore isthmuses as well as of the top and bottom shell portions of the hollow-core slab may be varied and adjusted to desired values in the fashion determined by the shaping of the overlying trowel beam assembly and/or the underlying concrete mix flow guide trough. In the example shown in the diagrams, the intermediate slab size of FIG. 4 may be defined to represent the basic shape of the core-forming member adapted to mate with the diameter of the feeder auger and suited for the manufacture of a 320/4-size slab, for instance. Then, the other modular heights of the hollow cross section shown in FIG. 2 and FIG. 6 respectively represent a 400/4-size and a 265/6- size slab, for instance. The design of the machine must be dimensioned to provide a sufficiently high concrete mix propelling capacity of the feeder auger even at the largest slab cross section and, respectively, a sufficiently low capacity at the smallest slab cross section. In the construction shown in FIG. 2, wherein a larger core-forming member is used, a simple shaping of the nozzle section with a conforming shape of the trowel beam assembly is sufficient to achieve a practicable construction and, in fact, this design may already be found in conventional continuous-casting machines. In contrast, the embodiment illustrated in FIG. 6 has not been possible in prior-art machines. Now, by virtue of invention based on adapting the shape of the trowel beam assembly to conform to the shape of the core-forming members, slabs thinner than the diameter of the feeder augers can be made, which generally has been considered to be out of question. In the illustrated exemplifying embodiment, the nozzle section extrudes a slab 265 mm thick, and yet the compaction space of the concrete mix behaves in a con- trolled manner by virtue of the proper shaping. In terms of full filling of the slab cross section and a balanced casting process, this kind of aggressive shaping of the trowel beam assembly offers a novel method of casting process control. When the shaping of the trowel beam assembly and the core-forming member is arranged in the above-described manner so that the trowel beam assembly is contoured conforming to the shape of the core-forming member, enhanced compaction is attained over the entire cross section of the flow channel and, particularly, at the upper part of the slab shell above the hollow cores. This is because of the dual function of the trowel beam assembly, not only as a concrete mix flow guide and retarder, but also as a backing surface in ramming compaction for the concrete mix to be compacted irrespective of the frequencies and amplitudes used in the compacting movement . By way of adapting the assembly according to the invention also on the underside of the core-forming member as shown in FIGS. 1 and 2 with the help of the contoured concrete mix flow guide trough 5, even still more aggres- sive approaches to the shaping of a hollow-core slab cross section may be attained. Also embodiments different from those described above may be contemplated without departing from the scope and spirit of the invention. The trowel beam assembly can be implemented either using a beam assembly of the kind described above or as a combination of beams or trowel plates that comprises at least a compacting beam set typically followed by a trowel member. Generally, the set of compacting and trowel beams is arranged to be tiltable into different angles and positions so that the inclination of the assembly can be adjusted conforming to the shape of the core-forming member, whereby the height difference between the ingoing and outgoing edges of the assembly in the flow direction of the concrete mix is from 10 to 400 mm, typically in the order of a few centimeters. When casting a slab of a lower height than the diameter of the feeder auger, the ingoing end of the trowel beam assembly can be adjusted even above auger, while the outgoing end is simultaneously located below the top level of the rotational envelope perimeter of the auger. The shape of the trowel beam assembly and the core-forming member may be contoured different from a simple slanted plane, e.g., as an appropriately curved plane. An essential requirement is, however, that the shape of the surface formed by the trowel beam assembly or other part of the nozzle section that delimits the flow channel must be adapted to conform to the shape of the core-forming member so that the height difference between the ingoing end and the outgoing end of the trowel beam assembly is within a 50 % tolerance equal to the height difference between the top level of the rotational envelope perimeter of the auger and the top level of the core- forming member that trowels the hollow core of the slab. Herein, the term core-forming member is used when reference is made to that part of the member over which the concrete is shaped to make a desired core into the slab. In practice, this part is located there where the core-forming member has its largest or smallest outer diameter. The term nozzle section is used when reference is made to the confined cross section that determines the shape of the outer surfaces of the produced article. While the apparatus embodiment according to the invention described above has no means for shifting the position of the feeder augers in the lateral direction, a provision must be arranged for shifting the augers in the vertical direction if the difference between the selected sizes of the core-forming members is substantial. Normally, the lateral dimension of the core-forming members is kept constant even if the height of the members is varied. In FIG. 8 is shown a series of slab cross sections in which the slab manufactured in the basic shape and width has six hollow cores, while the narrower one has only three cores. The narrower slab in this kind of modular series of slabs could be manufactured by way of, e.g., using a partition to delineate the nozzle section during the casting process. The diameter of the auger may vary over its length, whereby diametral dimensions of the core- forming member must be evaluated relative to the largest diameter of the auger, that is, the rotational envelope perimeter of the maximum diameter of the auger.

Claims: What is claimed is: 1. Method for manufacturing a concrete product series of hollow-core slabs of at least two different sizes, the products having hollow cores of different heights, in which method - using at least one feeder auger (4), concrete mix is extruded through a delimited cross section acting as a nozzle section, and - to the rear end of each feeder auger (4), within the length of the delimited cross section, is adapted a core-forming member (6) serving to shape a hollow core in the product being manufactured, c h a r a c t e r i z e d in that - said core-forming member (6) is selected to be a tubular member having its height adjusted to be at the core-troweling portion of the member equal to the desired height of the hollow core in the product, and - the members (7) serving to define the top surface of the nozzle section are contoured to conform to the shape of the top surface of the selected tubular member (6) so that the height difference between the ingoing end and the outgoing end of the members (7) in the concrete mix flow direction is within a 50 % tolerance equal to the height difference between the top level of the rotational envelope perimeter of the auger (4) and the top level of the core-forming tubular member (6) that trowels the hollow core of the product. 2. Method according to claim 1, c h a r a c t e r i z e d in that, for the manufacture of one size of a hollow-core slab, the core-forming tubular member (6) is selected to a tubular member, wherein the height of the core-forming portion is smaller than the largest diameter of the feeder auger (4) and whereby said smaller height is accomplished by means of a downward slanted surface. 3. Method according to claim 2, c h a r a c t e r i z e d in that, for the manufacture of a first size of a product, a core-forming tubular member is selected having a height of the core-forming portion smaller than the largest diameter of the feeder auger, for the manu- facture of a second size of a product, a core-forming tubular member is selected having a height of the core- forming portion equal to the largest diameter of the feeder auger, and, for the manufacture of a third size of a product, a core-forming tubular member is selected having a height of the core-forming portion larger than the largest diameter of the feeder auger. 4. Method according to claim 1, c h a r a c t e r i z e d in that the members serving to define the top surface of the nozzle section comprise an assembly of trowel beams (7) adapted to be movable in at least one direction relative to the product being manufactured in order to achieve the compaction of the product. 5. Method according to claim 1, c h a r a c t e r i z e d in that the nozzle section is delimited lateral- ly so that at least one feeder auger and one core-forming tubular member remain outside the delimited nozzle cross section. 6. Assembly for manufacturing a concrete product series of hollow-core slabs of at least two different sizes, the products having hollow cores of different heights, said assembly comprising - means (1, 7) for forming a nozzle section of a delimited cross section, - at least one feeder auger (4) for extruding concrete mix through said delimited cross section acting as a nozzle section, and - core-forming tubular members (6) adapted to be mountable to the rear end of each feeder auger (4), c h a r a c t e r i z e d in that - said core-forming tubular members at least by their core-forming portions consist of tubular members of two different height, either one of which may be selected to be mounted to the rear end of the respective feeder auger (4) depending on the desired height of the hollow cores to be made in the product, and - the top surface of the nozzle section is delimited by members (7) that are adaptable to con- form to the shape of the top surface of the selected tubular member (6) so that the height difference between the ingoing end and the outgoing end of the members (7) in the concrete mix flow direction is within a 50 % tolerance equal to the height difference between the top level of the rotational envelope perimeter of the auger (4) and the top level of the core-forming tubular member (6) that trowels the hollow core of the product. 7. Assembly according to claim 6, c h a r a c t e r i z e d in that at least one of the core-forming members is selected so that the height of the its core-forming portion is smaller than the largest diameter of the feeder auger. 8. Method according to claim 7, c h a r a c t e r i z e d by a set of core-forming tubular members including at least one size of tubular member having a height smaller than the largest diameter of the feeder auger, then, for the manufacture of a second size of a product, another size of a tubular member having a height equal to the largest diameter of the feeder auger, and for the manufacture of a third size of a product, a still another size of a tubular member having a height larger than the largest diameter of the feeder auger. 9. Method according to claim 6, c h a r a c t e r i z e d in that the members serving to delimit the top surface of the nozzle section comprise an assembly of trowel beams (7) including means (8) for moving the trowel beam set in at least one direction relative to the product being manufactured. 10. Assembly according to claim 6, c h a r a c t e r i z e d by means for dividing the nozzle section in the lateral direction so that at least one feeder auger (4) and one core-forming tubular member (6) remain outside the delimited nozzle cross section. 11. Assembly according to claim 6 or 7, c h a r a c - t e r i z e d by at least one concrete mix feed trough (5) located underneath said feeder augers (4) and having a shape adapted to conform to the shape of the underside surface of the selected core-forming tubular member. 12. A concrete product series comprising hollow-core slabs having hollow cores of at least two different heights, c h a r a c t e r i z e d in that, in the slabs of different sizes, the heights of the hollow cores are varied, while the intercore isthmus thicknesses are kept unchanged.

Inventors: KAJAVA ANTERO, OJANEN PAAVO, SARJA ASKO, SILLANPAEAE TEUVO, KAJAVA, ANTERO, OJANEN, PAAVO, SARJA, ASKO, SILLANPAEAE, TEUVO
Applicants: KAJAVA ANTERO, OJANEN PAAVO, SARJA ASKO, SILLANPAEAE TEUVO, VALKEAKOSKI EXTEC OY LTD, KAJAVA, ANTERO, OJANEN, PAAVO, SARJA, ASKO, SILLANPAEAE, TEUVO, VALKEAKOSKI X-TEC OY LTD
Application year: 2000
Main classification: B28B3
IPC codes: B28B1