Patent GB-1518795-A (GB)
Title: Production of cementitios board
IPC: B28B11/08
Filed: 1975-09-19
Abstract: 1518795 Fluid-pressure servomotors B P B INDUSTRIES Ltd 19 Sept 1975 [27 Sept 1974] 42165/74 Heading G3P [Also in Division B5] A cementitious boarding 13 produced in a continuous length is transported during setting between opposing edge profile elements 23, 24 that detect and correct any unwanted profiling (e.g. sloping) of the edges of the boarding. As described for producing plaster or gypsum paper-faced boarding the edge profile elements 23, 24 are slidable along guides 50, 51 by pneumatic piston and cylinders 18, 19 which are adjustable in initial spacing by screws 25 engaging a cross-member 16. This member rests, in use, on rollers 15, and is raised and lowered by a piston and cylinder 28/29. In use, the apparatus is controlled pneumatically (see Fig. 3, not reproduced) by air or other gas. Initially, the cross-member 16 is fully raised and the edge profile elements 23, 24 fully retracted by piston and cylinders 18/19. A push button is operated momentarily to actuate the cylinder 29 and lower cross-member 16 at a controlled rate. A supported cam surface 32 operates an upper valve 33 to pass high pressure air through cleaning orifices connecting with the opposing faces the edge profile elements. A lower valve 34 is then operated to stop cleaning and supply low pressure air to the cylinders 18, 19 to move the pistons (and thence the edge profile elements) inwardly. The piston of 18 is of greater cross-section so that it moves quickly to its innermost limit to act as a datum, whereas the piston of 19 moves slowly until it engages the edge of the boarding 13 between itself and the piston of 18. Sensing air is passed through orifices in the faces of the edge profiling elements so that a pressure develops when the orifices are blanked off by the boarding edges, and is used to balance the piston of 19 against the boarding edge. Any irregularity (e.g. edge sloping) of the edges opens a said orifice which operates pneumatic valves to reposition the piston of 19 and thence the edge former 24 for removing the irregularity. If the boarding supply ceases, or has weak or hollow edges, then the piston of 19 is moved to overtravel inwardly, so that the orifice 55 lines up with an overtravel orifice in the guide 51 to shut down the apparatus, with the cross-member 16 raised to its starting position. A similar shut down can be initiated by a press button, which also sends high pressure air through the cleaning orifices. Pneumatic Circuit When the high pressure supply 36 is switched on, piston 28 is drawn upwards while pistons 52/  53 are retracted outwards. Switch 43 is operated momentarily to switch over value 40 and feed high pressure air to the upper end of cylinder 29, and so move piston 28 downwards. The cam 32 operates valve 33, which feeds high pressure air from valve 34 to the orifices 47 for cleaning. When the cam 32 operates valve 34, as shown, the cleaning air supply to valve 33 is cut off, and low pressure air from a regulator 38 is fed via valve 34 to the rear ends of cylinders 18/19 to move the pistons 52/  53 inwards. Piston 52 moves faster than 53, to reach the end of its stroke and provide a datum. Sensing air is fed continuously through the orifices 47 from the supply 36 through restrictors 61 until the orifices are blocked off by the board 13 edges. Pressure between restrictors 62/63 then rises to operate valves 64/65 and feed low pressure air to the front ends of cylinder 19, for equilibrium. Any release of air through an orifice 46 (indicating an uneven board edge contour) drops the pressure between restrictors 62/63, switches over valves 64/65, and vents the front ends of cylinder 19, to cause piston 53 to move forward and the edge former 22 to remould the board edges. A valve 44 operated momentarily raises the piston 28 and sends a blast of cleaning air to the orifices 47. An inlet 56 in the edge former 22 is normally fed with pressure air but is blocked by the support 51. If the edge former overtravels to line inlet 56 with a support bore to atmosphere, then the drop in pressure operates a valve 58, valve 66 and thence valve 40 to withdraw piston-rods 28/52/53.