Patent GB-1376994-A (GB)
Title: Method and plant for manufacturing products of concrete
IPC: B28B3/02
Filed: 1972-01-14
Abstract: 1376994 Compressing and vibrating concrete SVENSK HARDBETONGTEKNIK AB 14 Jan 1972 [14 Jan 1971 6 Sept 1971] 1923/72 Heading B5A [Also in Divisions B3 and B8] Concrete articles such as curbstones, garden stones or roofing tiles are formed under pressure and simultaneous vibration resulting in high density (1000 kg./cm.<SP>2</SP>), and compressive strength of concrete. The moulding is carried out in a continuous sequence of operations at successive stations, Sequence, of operations.-Perforated mould bottoms stored at 1 (Fig. 1), are fed by a conveyer 12 to receive compartmented mould blocks from a store 2. The moulds are vibrated, and filled from a conveyer-fed hopper 23 and conveyed to a press 4 for simultaneous pressing and vibrating. At a station 5, the mould blocks are removed and returned by a conveyer 26 to the store 2. A switch 14 separates groups of articles on to parallel conveyers for (3-4) hours resting at ambient temperature. The parallel groups then pass for 6 hours through a kiln 7 injected with steam. A switch 15 sorts the groups into single file for movement to a station 8 where the articles are removed from the mould bottoms and the bottoms returned to a stacker 11 for removal to the store 1. Each group is arrested by a stop bar 45, which feeds the articles singly through a grinding station 9 (see Division B3), to a loading station 10 (see Division B8). The articles are water-sprinkled during storage. Mould filling.-The aggregate such as stone rich in silica is sieved, and the concrete mixed with only sufficient water for hydration, in a stirring mixer for (10-15) minutes. The concrete is left in the hopper 23 for 20 minutes. At the filling station 3, the release-coated mould is supported on a roller conveyer (18) (Fig. 2, not reproduced). As concrete is fed inameasured quantity from the hopper by feed rollers (24), the roller conveyer (18) is lowered to place the mould on vibrated foundation beams (21). The concrete is smoothed and excess removed, and left in an elevated store for (20-30) minutes before pressing. Pressing.-At the pressing station 4 the mould is supported by a spring-urged roller conveyer 18 (Fig. 3). A shaped presshead 33, 34 (Fig. 3), is lowered hydraulically; the pressure is increased to 1 kp./cm.<SP>2</SP> over 5 seconds, and to (15-30) kp./cm.<SP>2</SP> over 1 minute. The pressure lowers the rollers 18 to seat the mould on to foundation blocks 31 attached to vibrators 30. - Vibration by vibrators 30, 35 is begun after pressing has started, to avoid article disintegration; the vibrations of force (10,000-30,000) kp./cm.<SP>2</SP> dominate the press forces to give fluidity of movement of the concrete constituents. The vibrators 30, 35 are synchronized, and of the centrifugal force type using eccentrics. Immediately before the presshead 33, 34 is released, an hydraulic cylinder 38 is actuated to move the mould block 20 a little, to avoid sticking. For making tiles, the upper surfaces of the tiles are powder or liquid sprayed with silicon or hydrocarbon enamel after pressing. Mould removal.-At station 5, the mould block 20 is removed by a winched, pronged gripper (40) (Fig. 4, not reproduced). Steam hardening .-The kiln 7 (Fig. 1), is at 50‹ C. at the entrance and (120-140)‹ C. at the end, with an overpressure of 0À2 atmospheres.