GB1484181A - Monitoring welds - Google Patents

Abstract

1484181 Testing welds photo-electrically FRANCE ARMED FORCES MINISTER OF 22 Oct 1974 [23 Oct 1973] 45729/74 Heading G1A The quality of a weld is tested by measuring the infrared radiation it emits immediately after it is formed. In Fig. 1 two flanges 3a, 3b are being welded to a plate 4 by passing a high electric current between wheels 2a, 2b. The wheels move along the flanges, producing a weld 5 a zone 6 of which is viewed by mirrors M1, M2. The infrared beams are directed by these mirrors to a chopper 10 and then alternately to detector 18. The detector and the optical elements are mounted to move with wheels 2a, 2b so as to always view a zone just behind the wheels. The sum of the two beams is found at 16 by storing and adding the detector signals corresponding to the beams, while the difference is found by storing and subtracting at 15. The sum and difference may be thresholded, displayed, or recorded to indicate weld quality. The sum indicates the presence of defects such as inclusions, while the difference is a measure of the correction of the weld position; the wheel path may be controlled by the difference measurement. The chopper may rotate rapidly, in which case the two detector signals which are summed or subtracted will represent two views of the same zone 6; however, if the chopper rotates slowly, one of the mirrors M1, M2 should be displaced along the line of the weld to ensure that the signals still represent views of the same zone. In another embodiment, Fig. 2 (not shown), the beams are received by separate detectors whose outputs are summed and subtracted.