A method and an apparatus for casting concrete products

Abstract: Concrete mass is extruded onto a bed into a space between the bed and a mould, and the mass is compacted. After the compaction, the surface layer of the product is again caused to enter into a plastic state by means of vibration and recesses discontinuous in the casting direction are pressed into the surface layer thus plasticized. The apparatus comprises a mould (2, 3) formed of a cover portion and side walls, as well as means (1, 2, 3) for feeding and compacting the concrete mass. At least one mould wall has a pressing means (5) provided with a vibrator. The pressing means (5) provided with a vibrator is placed after the compaction step (3). The pressing means (5) is provided with discontinuous ridges.

Description: The present invention relates to a method of casting a concrete product by using continuous slide casting, wherein concrete mass is extruded onto a bed and into a space between the bed and a mould, by means of slide casting apparatus travelling along the bed, and the mass is compacted and recesses discontinuous in the casting direction are formed in a surface layer of the product. The invention also relates to slide casting apparatus for casting a concrete product provided with discontinuous recesses in the casting direction, which apparatus comprises a mould, means for feeding concrete mass into the mould, one or more compacting vibrators for compacting the concrete mass, a driving mechanism for driving the feeding means and vibrators and for transporting the mould along a casting bed, and pressing means having a pressing surface arranged to be stationary, in the casting direction, whilst forming the recesses in a surface layer of the concrete mass. The surface prepared by means of conventional methods by slide casting is relatively smooth. The surface smoothness is in fact generally a desired property, when the product to be cast acts as such as a visible part of the structure. However, in the building industry, structures are often used in which the entire structure is formed of an element prepared at a plant and of a portion to be joined thereto and prepared on site. The functioning of such concrete structures in the desired manner requires that the bonding of the element to the portion prepared on site is as strong as possible. For ensuring this, it is advantageous that dowel patterns or recesses are made on the surface of the element. The part to be cast on site then fills these recesses and adheres to the element prepared at the plant. For preventing the mutual sliding of the parts of the structure, the patterns have to be both in the casting direction and in the transverse direction discontinuous, e.g. square or rectangular recesses. A suitable dowel depth is e.g.1-20 mm. A certain concrete product, in which the dowels are specially important, is a so-called casing, club. The casing slab acts as a mould, on top of which is cast a concrete layer required by the total thickness of the slab. The casing slab remains as part of the structure and the load carrying capacity requires a strong grip between the parts. The necessary dowel grooves have previously been generally such that the product has not been cast in a slide casting manner but in a mould on site, whose bottom contains bulges. The bulges have formed recesses on the lower surface of the slab. However, a drawback of the method is that one surface of the slab or the upper surface has to be smoothed separately so that a smooth surface could be made visible on the finished slab. This results in an additional working step in the slab casting. From FI patent publication 61652 is also known a device, by means of which recesses are formed in the sides of the slab by using two successive wheels, whose teeth form the recesses in the side of the slab. Since the concrete mass is compacted between these two wheels, the latter wheel has to be slightly smaller than the wheel operating first, and in addition the speeds of the wheels have to be synchronized by means of a special sliding coupling, which takes into account the changed dimensions of the slab. The device is thus fairly complicated, and it is difficult to make it satisfactorily operative in all conditions. US patent publication 3 740 176 and FI application 878/71 in turn describe devices, in which the recesses are formed either by means of a flexible belt or one gear wheel. However, problems are caused in both these devices by a deformation caused by the compaction of the slab. According to a first aspect of the present invention, there is provided a method of casting a concrete product by using continuous slide casting, wherein concrete mass is extruded onto a bed and into a space between the bed and a mould, by means of slide casting apparatus travelling along the bed, and the mass is compacted and, after the compaction, recesses discontinuous in the casting direction are formed in a surface layer of the product by using vibration to cause the surface layer to enter a plastic state and by pressing the recesses into the surface layer thus plasticized, characterized in that the effect of the vibration occurring after the compaction is sufficiently low and directed in such a way that the surface layer is plasticized only to a depth necessary to permit the pressing of the recesses, whilst the main portion of the product remains in its compacted state. According to a second aspect of the present invention, there is provided slide casting apparatus for casting a concrete product provided with recesses discontinuous in the casting direction, which apparatus comprises a mould, means for feeding concrete mass into the mould, one or more compacting vibrators for compacting the concrete mass, at least one plasticizing vibrator for plasticizing a surface layer of the compacted concrete mass, pressing means having a pressing surface arranged to be stationary, in the casting direction, whilst forming the recesses in the plasticized surface layer, and a driving mechanism for driving the feeding means and vibrators and for transporting the mould along a casting bed, characterized in that the plasticizing vibrator(s) are arranged so that the effect of the vibration occurring after the compaction is sufficiently low and directed in such a way that the surface layer is plasticized only to a depth necessary to permit the pressing of the recesses, whilst the main portion of the product remains compacted. The recesses are formed by pressing. i.e. without removing any of the concrete mass. The slide casting technique requires the use of a fairly dry concrete mass, since the product has to retain its shape after leaving the mould. The pressing of sufficient recesses into such a dry mass after compaction requires the bringing of the surface again into a plastic state, but only to a depth just needed, whereby the cohesion of the entire product after leaving the mould is not in danger. Preferably, when forming dowel grooves during the casting of a concrete slab, they are formed in an upper surface of the horizontal slab. Then, a flat steel plate may be used as a lower surface of the mould and the visible surface of the mould can be made completely smooth. The invention may also be applied when forming dowels in other concrete products that are prepared by slide casting, such as hollow slabs, beams and pillars. A non-limiting embodiment of the invention will now be described with reference to the accompanying drawing, which is a side view of slide casting apparatus in accordance with the invention. A slide casting machine comprises a frame and a driving mechanism 6, which may also be replaced by an external driving device, as well as a funnel and a moulding box 1, via which the concrete mass flows into a slide casting mould. On the upper surface of the mould is, seen from the funnel 1, first located a moulding beam 2, whereto is fixed one or several vibrators. The vibrating moulding beam 2 improves the flowing of the concrete mass into the mould. Next is located a compacting beam 3, which is provided with more efficient vibrators than the previous ones. The compacting beam 3 compacts the product to be cast into its final form, except for the dowel grooves. Next is located a pressure balancing/smoothing beam 4, which is further provided with vibrators, but they are less efficient than those of the compacting beam 3. The smoothing beam 4 has two tasks. It smooths the surface of the product to be prepared, and on the other hand it prevents the surface of the concrete mass from rising after the actual compacting beam 3. When the rising is thus prevented, the pressure needed for the compaction remains under the compacting beam 3. In the application shown in the drawing, the recesses are formed by means of a cylindrical press roll 5, whose surface has bulges. These bulges press the corresponding recesses into the surface of the product. The cylindrical press roll 5 may be replaced with an endless belt travelling around rollers, to which belt are fixed bulges for pressing the dowel grooves. The roll or the belt is rotated at a speed synchronized with the advancement of the machine e.g. by means of a toothed belt or a chain so that the roll or the belt rolls along the surface of the product to be cast and simultaneously presses a regular dowel pattern into the concrete surface. In this connection, a belt refers, except for an entirely flexible belt, also to a caterpillar type construction, which is comprised of plates joined to each other. The roll or the belt may also be replaced with a stamp-type press, which may operate by means of cranks or levers or also hydraulically. The press performs in the pressing direction a to-and-fro movement towards the product and away therefrom. In addition, the movement track of the device is such that it does not drag along the surface of the product as the machine advances, so it presses a sharp pattern. This means that on one hand, during the pressing step, the press remains stationary relative to the casting direction on the surface of the product, moving relative to the casting machine, and on the other hand, when it comes off the product, it returns back to the same position relative to the casting machine. The roll 5 may be vibrated e.g. by vibrating bearing blocks supporting the roll. Similarly, the vibration of the belt is achieved by vibrating the support rollers of the belt. When using a stamp-type press, the vibrator may be placed inside the press itself. The vibrating effects of both the dowel-making device itself and of the balancing beam 4 have been selected such that they are sufficient for plasticizing again the surface of the slab, but only to such a depth that the dowel patterns may be pressed without endangering the shape of the rest of the slab. When the method is applied to making dowel grooves in a hollow slab, the upper surface of the slide mould of the hollow-slab machine is replaced with apparatus as described above. In the hollow-slab extruder, the mass flow into the slide mould is arranged by screws as well as by compacting mandrels located after the screws. Such a machine is described e.g. in Finnish patent publication 70821. In addition to producing dowel patterns in the upper surface of the concrete product, the method and apparatus of the invention may also produce dowel patterns in the side surfaces of a concrete element by installing corresponding devices on the side walls of the slide cast mould.

Claims: A method of casting a concrete product by using continuous slide casting, wherein concrete mass is extruded onto a bed and into a space between the bed and a mould, by means of slide casting apparatus travelling along the bed, and the mass is compacted and, after the compaction, recesses discontinuous in the casting direction are formed in a surface layer of the product by using vibration to cause the surface layer to enter a plastic state and by pressing the recesses into the surface layer thus plasticized, characterized in that the effect of the vibration occurring after the compaction is sufficiently low and directed in such a way that the surface layer is plasticized only to a depth necessary to permit the pressing of the recesses, whilst the main portion of the product remains in its compacted state. The method according to claim 1, wherein the product is a hollow slab. Slide casting apparatus for carrying out the method of claim 1 for casting a concrete product provided with recesses discontinuous in the casting direction, which apparatus comprises a mould (2, 3), means (1) for feeding concrete mass into the mould one or more compacting vibrators for compacting the concrete mass, at least one plasticizing vibrator (4) for plasticizing a surface layer of the compacted concrete mass, pressing means (5) having a pressing surface arranged to be stationary, in the casting direction, whilst forming the recesses in the plasticized surface layer, and a driving mechanism (6) for driving the feeding means and vibrators and for transporting the mould along a casting bed, characterized in that the plasticizing vibrator(s) are arranged so that the effect of the vibration occurring after the compaction is sufficiently low and directed in such a way that the surface layer is plasticized only to a depth necessary to permit the pressing of the recesses, whilst the main portion of the product remains compacted. Apparatus according to claim 3, wherein the plasticizing vibrators comprise (i) a vibrating wall (4) downstream of the compacting vibrator(s) (3) and (ii) the pressing means (5), which is downstream of the vibrating wall (4) and is arranged to vibrate. Apparatus according to claim 4, wherein the compacting vibrator(s) comprise a compacting wall (3) which is upstream of the vibrating wall (4).

Inventors: HARALA OLLI, MONONEN HANNU, NIEMINEN KARI, SUTINEN RISTO, HARALA, OLLI, MONONEN, HANNU, NIEMINEN, KARI, SUTINEN, RISTO
Applicants: PARTEK CONCRETE DEV OY AB, PARTEK CONCRETE DEVELOPMENT OY AB
Application year: 1993
Main classification: B28B1
IPC codes: B28B3, B28B1, B28B11