GB1330636A - Production of prestressed concrete - Google Patents

Abstract

1330636 Moulding prestressed concrete FLOWCRETE Ltd 22 Sept 1970 [30 Sept 1969] 47975/69 Heading B5A In an apparatus for continuous production of prestressed concrete, fluent concrete is fed on to a moulding conveyer 10 from a casting unit 29, the conveyer drive drum 28 being operated synchronously with a pretensioned wire feed drum 37 so that pretensioned wires 31 are fed at the same linear speed as the conveyer 10. The speed of the conveyer may be regulated to ensure that the concrete product 20 has set by the time it reaches a predetermined position with respect to an output location on the conveyer. To form the product 20, a crosshead 33 (Fig. 1) is initially used by means of which a closed loop of pretensioned wire is obtained, passing from reels 32, along the outside conveyer to pulleys 35, back under the conveyer, on to the feeding drum 37 through a guide 36, and from there to the crosshead 33, the wires being tensioned by means of hydraulic jacks 39. A length of concrete is then east around the wires, the crosshead moving with the conveyer, and the product allowed to harden, the conveyer remaining stationary, until it has achieved the desired strength for stress transfer, when the jacks 39 are released allowing the hardened concrete to hold the stress in the wires 31, thus prestressing the concrete product. The crosshead may then be removed and the cycle repeated or, for continuous operation, the product and outer reinforcing wires 31 are threaded through two advancing devices 40, 40A (Fig. 3) having clamps 41 for gripping the concrete product and wire gripping jacks 42, 42A. The advancing devices are hydraulically operated by jacks J1, J2 and are movable longitudinally of the conveyer. The clamps 41 and wire gripping jacks 42, 42A are hydraulically operated. To advance the product along the conveyer during casting, the advancing devices are moved towards each other, the device 40 gripping both the product and the reinforcing wires. When the two devices are adjacent, the device 40 trips a switch 44, causing the device 40A to grip the product and wires, itself being released, the two devices then moving away from each other until the device 40A trips a switch 44A, causing the device 40 to grip the product and wires and releasing the device 40A. The devices then move towards each other again. Thus the devices together serve to advance the product towards the output end of the conveyer and allow fresh wire into the system under tension. The whole control system for operating the devices 40, 40A is hydraulic. Also described (Fig. 2, not shown) is a conveyer in which the conveyer belt (15) is supported on a water film, which may be heated to assist curing of the concrete. The whole conveyer is mounted, in this case, in an insulated, covered trough (11).