Patent GB-860437-A (GB)
Title: Apparatus for exposing sheet material to radiation
IPC: G03B27/30
Filed: 1957-03-07
Abstract: 860,437. Heating by incandescent lamps; tubular electric incandescent lamps. MINNE SOTA MINING & MANUFACTURING CO. March 7, 1957 [March 7, 1956; Feb. 19, 1957], No. 7685/57. Classes 39 (2) and 39 (3). [Also in Group XVI]. A machine for exposing a sheet to intense radiation, comprises a support, e.g. a drum, on which the sheet is supported adjacent the radiation source so that it can be progressively irradiated from one edge to an opposite edge. by releasable means which hold the sheet in the neighbourhood of those edges without exerting pressure on the area of the sheet there between. The sheets may have a rough thermo-plastic coating fused by the radiation into a smooth continuous coating or a layer of heatsoftenable resinous material containing a " blowing agent " and inked so that the inked pattern absorbs more energy and causes the blowing agent to release gas thereby thickening the layer at the inked portions. The source is an infra-red gas-filled elongated quartz envelope 10, Fig. 1, containing a tungsten filament and at 2400‹K gives a 100 watts per inch of filament length. The centre areas of the lamp may be masked to equalise radiation along its length and an elliptical reflector 11 concentrates a narrow band of radiation on the drum and is slotted to decrease its efficiency near the centre of the lamp. Fumes are removed through an exhaust 39 by a fan 38. The sheet is held on a rotatable drum 13 by resilient fingers 24, 19 at the leading and trailing edges and the lamp is energised on rotation of the drum before the leading edge of the sheet reaches the lamp and is de-energised when the trailing edge has passed the lamp. The resilient fingers 19 are mounted on a bar 18 Fig. 2, extending the length of the drum and supported at its ends on radial arms 17 pivoted on the shaft 15 of the drum. The fingers 19 are forced on the drum by a cam 20 pivoted at 21 on the arms 17 when a lever 22 integral with the cam 20 is pulled manually away from a stop 40. Resilient fingers 24 for the leading edge of the sheet extend into a recess 23 in the drum and beneath them is a flat cam 26 with end shafts 27 pivoted in the recess 23. When a hand bar 29 with arms 30 fixed to the shaft 27 is pushed down, the cam 26 raises the fingers 24. Fixed to one shaft 27 is a cam arm 31 against which abuts a cam follower arm 32 pivoted at 34 to the drum. Inside the arm 17 is fixed a cam follower 35 abutting on a cam arm 33 integral with the arm 32. As the drum rotates the arm 32 is freed from the cam arm 31 and the fingers 24 move down to grip the sheet. Control cams 41, 42, Fig. 3, are fixed to the drum shaft 15 to rotate therewith, and control cams 43, 44 are fixed to a bushing 16 on the arm 17. In each cam is a peripheral recess 51-54 receiving cam followers 61-64, which actuate switches. On starting, the sheet is inerted beneath the fingers 24 and a foot switch is depressed to start the fan and a motor rotating the drum 13-clockwise. The cam follower 61 is almost immediately forced down over the periphery of the cam 41 and operates a switch supplying motor current so that pressure on the foot switch can be removed. On further slight rotation of the drum, the cam follower 62 falls into a recess in cam 42 and energises the lamp 42, removing motor control from the cam 41. During treatment the operator smooths the sheet over the drum and then operates the lever 22 to press the fingers 19 on the sheet. The bar 18. arm 17, and bushing 16 now rotate with the sheet. Just after the clamped trailing edge passes under the lamp cam follower 63 passes into recess 53 on the cam 43 and extinguishes the lamp. On further rotation of the drum, cam follower 64 enters recess 54 in cam 44 and control of the motor is restored to cam 41; and the motor is stopped when the drum has completed one rotation and the cam follower 61 slides into recess 51 of cam 41. The sheet may then be removed manually and another sheet inserted. A thermistor mounted adjacent the reflector may be used to compensate the rise in temperature of the device during use and to provide uniform energy level of radiation during one or more exposure cycles. A cam on the shaft 15 also operates a rheostat to cause a decrease in its resistance and a lowering of lamp voltage as the periphery of the drum moves past the heating lamp.