Patent GB-849035-A (GB)
Title: Improved method and device for moulding products of concrete or the like
IPC: B28B7/36
Filed: 1958-08-25
Abstract: 849,035. Casting concrete. PRODUKTIONSMETODER A. B. Aug. 25, 1958 [Aug. 27, 1957], No. 27165/58. Class 87(2). [Also in Group X] Concrete articles are first cast in a mould composed of rigid components with the addition of a fluid-tight membrane and then subjected to high external fluid pressure through the membrane and to low internal fluid pressure on the cast, green concrete, the maintenance of the pressure difference enabling the rigid parts of the mould to be removed, leaving the concrete to solidify enclosed in the membrane. The mould sides 1a, 1b are mounted on a base 1c. Pipes 6 pass from inside the mould sides, through valves 7, to flexible pipes 8 which are connected, through valves 9, to a vacuum line 11 and the pipes 6 may be opened to atmospheric pressure through valves 10. The insides of the mould walls may be plain, or may have grooves connected to the pipes 6 to assist in applying high or low pressure to the membrane 2 ; or a wire net may be used instead of the grooves. The top 18 of the mould is connected through a pipe 14 to the vacuum line 11. Before concrete is poured into the mould the valves 7, 9 are opened and the membrane is sucked, by the vacuum so applied, against the rigid mould walls 1a, 1b. Reinforcement 22 is inserted, concrete 21 is poured in, and vibrators 19, secured to the mould sides, are started. The external suction is then removed by closing the valves 9 and opening the valves 10 and the top mould member 18 is fitted with the membrane 23. The valve 15 is opened, applying suction, the mould sides 1a, 1b are removed and the conditions are then that the concrete remains under vacuum within the membrane while it solidifies. Alternatively the valve 15 may be closed and a valve 16 opened to connect the top of the mould with a vacuum pump on a transporter 17, by which the cast concrete may be taken to a place where it is packed with other concrete castings and solidifies, either under a vacuum, or immersed in water. For casting articles such as piles the membrane 2 is inserted in the mould 1a, 1b on a carrier 32, Fig. 4, and forced outwards against the walls of the mould by compressed air through a pipe 34, vacuum then being applied through channels 5 to hold the membrane against the inside surface. The carrier 32 is then removed, reinforcement inserted, and the concrete poured in. The vacuum through the channels 5 is then replaced by pressure and vacuum is applied to the inside of the concrete as before. When cores are used for making cavities, each is made of porous material and surrounded by a membrane which is sucked against the core at the same time as the mould membranes are sucked against the mould sides, the concrete then being poured in. Sand is laid on the top of the concrete ; the vacuum is then removed from the membrane but is applied to the sand and extends thence to the inside of the concrete, the required pressure difference thus being produced to enable the components of the mould to be removed. The mould and cores may be replaced by supporting sand. A link mechanism may be used to move the mould sides inwards or outwards, this being specially suitable for casting I-beams. Membrane-enclosed castings may be transported and placed next to one another on a floor, the row so formed being then enclosed in a comprehensive membrane within which vacuum is applied, the connections by which vacuum is sustained in the individual castings being removed. The membrane may remain permanently, to give the concrete a fluid tight surface ; or a silicon may do the duty of a membrane. Double-layer membranes of plastic material may be used. Wet clay may be used for an impervious covering. Instead of sucking the membrane against a mould side before casting, it may be clamped. The method is also applicable to casting concrete structures in situ (see Group X).