Patent GB-1413981-A (GB)
Title: Foam producing apparatus
IPC: B01F15/04
Filed: 1972-01-19
Abstract: 1413981 Generating foam R V M STAPLE 19 Jan 1973 [19 Jan 1972] 2500/72 Heading B1C A foam producing apparatus especially for plastics insulating foam comprises a mixing chamber 14 supplied with liquid constituents (e.g. resin, and a mixture of hardener and foaming agent) through lines 13a, 13b from pressurized containers 12a, 12b, and with air through a line 11c. The containers 12a, 12b have equal volumes and the concentrations are adjusted to produce the required proportions when the liquids are mixed in equal volumes. There may be a surge reservoir 33 in the air line. Magnetic or optical level indicators 54 may activate control switch 21 to stop foam production before supply of the liquids fails. The mixing device 14 comprises a rear chamber 60 to which air and one liquid are supplied and which connects through apertured plate 61 with another chamber to which the other liquid constituent is fed. There may be a transparent foam delivery and mixing tube 15. The pressure in the chamber 60 is sensed by a pressure-sensitive switch 64 which closes contacts 64A to energize a relay 18 and stop production in the event of excessive back-pressure in the chamber. Air/liquid regulation-As the mixing device is carried up from ground-level the air pressure in line 11c is reduced to counter balance the fall in hydrostatic pressure in the liquid lines by pressure sensors 26, 27 feeding a comparator 28 which energizes relay 24 to close solenoid valve 25 when the air pressure is greater than that in the liquid line by e.g. 1 lb/sq. inch: the relay 24 is de-energized, and valve 25 opened, automatically when the pressure falls. In a modification, Fig. 2 (not shown), the comparator 28 is replaced by another (34) which gives an output on a line (35) when the air pressure lies above an upper or below a lower pre-determined pressure, and on another line (36) when it is below: the upper pre-determined level. An output on line (35) energizes a relay (37) to operate a DC motor (38) the shaft of which is coupled to the spindle of a pressure-reducing valve (41) in air line 11c, so that as the pressure in liquid line 13a falls the pressure in line 11c is reduced. When the device is lowered a signal is also produced on line (36) and energizes a relay (39) which reverses the polarity of supply to motor (38) and hence the direction of operation of the valve (41). In another modification, Fig. 5 (not shown), the air pressure is regulated by a pressure-reducing valve (52) in the air line near the mixing chamber, adjusted so that its output pressure is approximately equal to its control pressure, which is derived from line 13a or 13b through a large bore connection (56). The valve (52) may be of conventional diaphragm type with its control spring removed and replaced by the liquid pressure.  Liquid/liquid proportioning-Flow rate sensors 16a, 16b feed a comparator 17 which energizes relay 18 to close solenoid valves 22a, 22b, 25 if the flow rate on either of lines 13a, 13b is more than 10% greater than in the other. Relay 18 may be reset by releasing control switch 21. In a modification, Fig. 3 (not shown). the flow rate sensors are thermistors (42, 43) arranged in adiacent areas of a bridge (44) the other areas of which are equal resistors (47), the measure of flow rate being the cooling effect of the liquid flowing over the thermistors. The bridge output is fed to a comparator (49) analogous to the comparator 17.