Patent GB-1409996-A (GB)
Title: Curing of surface coatings
IPC: B23K26/082
Filed: 1974-03-28
Abstract: 1409996 Drying VIANOVA KUNSTHARZ AG 28 March 1974 [28 March 1973] 13880/74 Heading F4G [Also in Division G3] A method of curing surface castings by irradiation with infra-red radiation emitted by a maser comprises monitoring the temperature of the radiation emitted by that part of the surface being cured on which the maser beam is incident and controlling the curing process in dependence thereon and apparatus for the method comprises a mirror which is movable about two mutually perpendicular axes and directs the maser beam on to and scans the beam over a surface coating to be cured and an infra-red thermometer which receives after reflection by the mirror radiation from that part of the surface which is irradiated by the maser beam and means for controlling the curing process in dependence on the temperature. A beam from a maser is directed by a fixed mirror 7 on to a mirror 2 which is movable about two axes at right angles. Thermal radiation from the heated surface is directed by the mirror 2 to a telescope 4 and to an infra-red thermometer 5 which modulates the maser beam to maintain the surface temperature at a predetermined value. Light from a lamp 6 passes from a condenser 8 and an annular mirror 9 through the telescope 4 to the mirror 2 to illuminate an annulus on the surface around that irradiated by the maser beam. The maser beam scans the paint surface by an appropriate movement of the mirror 2. The thermometer provides a signal which is converted to a voltage which is proportional to the temperature of the surface and this is compared with a voltage corresponding to a predetermined temperature of a temperature programmer. The amplified voltage difference changes the frequency of an oscillator which controls the speed of scanning of the maser beam. Alternatively the control may be by an external amplitude modulator or by an internal modulator. In a modification an external digital optical switch producing a continuous number of irradiation pulses of various durations is used to change the output of the maser beam or an internal modulator in the resonator of the maser is used as a switch. A temperature programmer controls the curing and controls a number of current sources I 1  to I 4  and timing circuits which are connected to a charging capacitor C and an electrometer amplifier E to produce a voltage Ua and is compared in the control amplifier with the voltage produced by the thermometer when amplified. The capacitor is charged to a predetermined value a timer T is switched in the voltage remains constant for the preselected time then the next timer is switched in for the next voltage L is a control logic for the programmer. The movements of the mirror 2 may be controlled by a digital electronic store which controls electronic driving means for the mirror 2. Co-ordinates are transferred from an input device 102 to an intermediate digital memory 101 by an address counter 106 and a decoder 107. A digital comparator 103 compares co-ordinates at the memory output with a co-ordinate counter 104 recording the position of the laser beam. When a difference exists the counter 104 adjusts until the comparator 103 registers equality. The counter 104 is stopped and the next co-ordinates are fed from the memory 101, the address counter 106 and decoder 107 being stepped forward by one unit. The state of the counter 104 determines the mirror drive means 108 and the position of the mirror 2. The elements 201-209 control the movement of the mirror about its other axis. The data can be read from punched tape, cards, magnetic tape or provided by hand. Two dimensional scanning of the beam is used when a large area is irradiated by the maser beam.