METHOD AND SLIPFORMING EXTRUDER FOR CASTING CONCRETE SLABS

Abstract: In a method and an apparatus for casting concrete el­ ements from a concrete mix by means of slipforming mould­ ing, the concrete mix is extruded onto a bed (2) by means of one or more extruder members (8), and is compacted by re­ ciprocating at least one movable wall (6,7,19,20) of the mould in a direction approximately parallel to its plane, the wall hav­ ing tamping splines (21,22) protruding into the mix. Prefer­ ably at least one pair of opposite walls (6,7,20) are reciproca­ ted in a counterphased manner, and the walls may be reciprocated in a direction parallel to the extrusion direction, transverse thereto, or both.

Description: The present invention relates to a method for casting concrete slabs. The invention also concerns an apparatus for implementing the method. The invention can be easily adapted to the manufacture of different kinds of concrete slabs. The invention is especially applicable to the fabrication of hollow-core concrete elements. Finnish patent publications 64072 and 64073 describe a so called shear compaction method for compacting a stiff mix during the casting operation of concrete slabs. These disclosures of the method achieve compaction by means of contradirectional parallel shear displacements in the different zones of the mix within the mould by moving two opposite walls of the mould in a reciprocating, synchronized manner, with the walls moving mutually in the same direction. Vibration is also used for compaction of the mix during moulding by slipforming. The method described in the aforementioned patent publications requires a complicated drive system because the angle of the mould walls relative to the vertical plane changes during compaction, while the shape of the mould is subjected to a continuous periodic state of change. Furthermore, the use of vibration as a method of compaction is a noisy method which in effect wears down the equipment. EP-A-0 174 924 discloses a ram casting machine for concrete slabs having feed means for feeding the concrete mix to be cast, means for extrusion and initial compaction of the concrete mix, at least two mould members and means for reciprocating the mould members in counterphase to each other. EP-A-0 175 930, in addition, discloses a slipforming moulding method including an auger and drive means for driving the auger. The present invention aims to overcome the disadvantages found in prior-art constructions and to present a completely new type of method and apparatus for the fabrication of concrete slabs. According to a first aspect of the present invention there is provided a method for slipforming moulding of concrete elements from a concrete mix, wherein the concrete mix is extruded onto a casting bed by means of extruder members which exert pressure on the concrete mix, and the concrete mix is compacted by reciprocating at least two movable members of the mould in a direction approximately parallel to their planes and in counterphase to each other, characterised in that one of the movable mould members is located on the top surface of the concrete element being moulded and is reciprocated in counterphase to a second movable mould member located on the bottom surface of the element, the mould members being provided with splines protruding into the concrete mix. According to a second aspect of the present invention there is provided an apparatus for the manufacture of concrete elements by a slipforming moulding method, comprising at least one auger for extrusion and initial compaction of the concrete mix, first drive means for driving the auger, feed means for feeding the concrete mix to be cast to the auger, at least two mould members and second drive means for reciprocating the mould members in a direction approximately parallel to their planes and in counterphase to each other, characterised in that one of the mould members is located to contact the top surface of the concrete element being moulded and is arranged to be reciprocated by the second drive means in counterphase to a second mould member located to contact the bottom surface of the element, the mould members having splines protruding from the side which, in use, faces and contacts the concrete mix being extruded and moulded. The invention provides remarkable benefits. In particular, the method in accordance with the invention achieves a high degree of compaction of a concrete mix by means of an uncomplicated apparatus without generating loud noise. In the following, the invention will be examined in more detail by means of exemplifying embodiments. Figure 1 shows a longitudinal cross section of a slipforming extruder for hollow-core concrete slabs in accordance with the invention. Figure 2 shows a cross section of another embodiment of a slipforming extruder for hollow-core slabs in accordance with the invention, especially illustrating the implementation of the transverse movement of compaction in relation to the moulded mix. Figure 3 shows a cross section of two different alternatives of profiles in accordance with the invention for the trowel plate. Figure 4 shows a longitudinal cross section of a slipforming extruder for the fabrication of massive concrete slabs. Figure 5 shows cross-sectional views of concrete slabs which are capable of being manufactured by means of an apparatus in accordance with the invention. Figure 1 illustrates a slipforming moulding apparatus in accordance with the invention, operating according to an auger flight extruder principle with the concrete mix fed from a hopper 1 by means of an auger 8. The auger is followed by a core-forming mandrel 4 for shaping the core into a desired form. The core-forming mandrel 4 is followed by a trowel tube 3 for the purpose of preventing the mix from collapsing during the final phase of the slipforming process. The apparatus moves on a bed 2 supported by wheels 13. The actual compaction is obtained by moving reciprocatingly in the flow direction of the extruder, parallel to the slab surface, a trowel plate 6 and a mix guide plate 7, both of which are provided with splines 21 protruding into the cast mix. The protruding splines 21 are wide in the crosswise direction, probably extending over the entire width of the plate. Hence, in the vicinity of the mold surface, the concrete mix tends to conform to the movement trajectory of the surface, whereby the concrete mix is internally sheared, resulting in a simultaneous compaction under the prevailing pressure. The synchronized reciprocating movement is provided by an auxiliary mechanism 9, in which an eccentric, driven by a motor 10, moves the trowel plate 6 and the mix guide plate 7 in a reciprocating, synchronized manner. The trowel plate 6 is followed by a stationary trowel plate 5 which finally shapes the slab surface into the desired form. Additionally, the apparatus comprises side mold walls 14. The compaction process of concrete mix can also be adapted in accordance with Figure 2 so that the trowel plate 6 and the mix guide plate 7 are moved in a reciprocating, synchronized manner in opposite directions, crosswise to the molding flow direction, and parallel to the plate, by means of the eccentric 9. The compaction process of the concrete mix is most efficient when a combination of trajectories, as shown in Figures 1 and 2, is used. Figure 3 illustrates in a longitudinal cross section the trowel plate 6 and the mix guide plate 7 used in the hollow-core slab extruder shown in Figure 2. Compaction in the crosswise direction to the molding flow direction requires splines 22, shown in Figure 2, to have the acute and narrow part extending to the mix in the crosswise direction. Extruding a massive slab by means of the slipforming method can be implemented in accordance with Figure 4, whereby the extrusion pressure is generated by means of an auger. The actual compaction process is accomplished in a corresponding fashion by moving the trowel plate 6 and the mix guide plate 7 in opposite directions in a reciprocating, synchronized manner by means of the eccentric 9, whereby, in accordance with the invention, both the mix guide plate 7 and the trowel plate 6 are provided with splines 21 protruding into the mix for the improvement of compaction and tamping. In the fabrication of a massive slab, the movement of the mould walls crosswise to the mould flow direction as shown in Figure 2 also improves the compaction of the concrete mix. Thus the described embodiment is capable of the manufacture of hollow-core slabs, massive slabs, beams, and similar concrete products having different cross sections as shown in Figure 5. The frequency of the reciprocating movement varies in the range of 20...1000 reciprocatory cycles per minute, preferably at about 300 cycles/min. The length of the reciprocating movement of the mould walls varies in the range of 0.5...50 mm, and is preferably about 10 mm. The splines 21, 22 of the compacting surfaces are preferably adapted to have the maximum protrusion of the splines in the vicinity of the hopper 1 and then steadily diminishing towards the final end of the slipforming extruder, whereby the finished product will be free of impressions from the splines.

Claims: 1. A method for slipforming moulding of concrete elements from a concrete mix, wherein the concrete mix is extruded onto a casting bed (2) by means of extruder members (8) which exert pressure on the concrete mix, and the concrete mix is compacted by reciprocating at least two movable members (6, 7) of the mould in a direction approximately parallel to their planes and in counterphase to each other, characterised in that one of the movable mould members is located on the top surface of the concrete element being moulded and is reciprocated in counterphase to a second movable mould member (7) located on the bottom surface of the element, the mould members being provided with splines (21, 22) protruding into the concrete mix. 2. A method as claimed in claim 1, wherein the protrusion of the splines (21, 22) from the mould members (6, 7) is greatest at the end nearer the extruder members (8) and diminishes in the flow direction of the extruded concrete mix. 3. An apparatus for the manufacture of concrete elements by a slipforming moulding method, comprising at least one auger (8) for extrusion and initial compaction of the concrete mix, first drive means for driving the auger (8), feed means (1) for feeding the concrete mix to be cast to the auger (8), at least two mould members (6, 7) and second drive means (9, 10) for reciprocating the mould members in a direction approximately parallel to their planes and in counterphase to each other, characterised in that one of the mould members (6) is located to contact the top surface of the concrete element being moulded and is arranged to be reciprocated by the second drive means in counterphase to a second mould member (7) located to contact the bottom surface of the element, the mould members having splines (21, 22) protruding from the side which, in use, faces and contacts the concrete mix being extruded and moulded. 4. An apparatus as claimed in claim 3, wherein the protrusion of the splines (21, 22) from the mould members (6, 7) is greatest at the end of the mould nearest the feed means (1) and diminishes in the direction away from the feed means (1). 5. An apparatus as claimed in claim 3, wherein the mould members (6, 7) are reciprocated in a direction perpendicular to the flow direction of the extruded concrete mix.

Inventors: SEPPANEN, AIMO
Applicants: LOHJA PARMA ENGINEERING LPE OY
Application year: 1987
Main classification: B28B1
IPC codes: B28B1, B28B3