TORCH DESIGN TO REDUCE FATIGUE ASSOCIATED WITH ARM AND SHOULDER MUSCLES IN WELDING PROCESS OF AIR CONDITIONING FACTORY

Abstract

Inappropriate hand tools cause fatigue at work. The objectives of this study are to design new torch as principles of ergonomic for reducing fatigue on shoulder muscle using EMG monitoring results on shoulder of welder and to study the efficiency of new torch to weld copper capillary tube at air conditioning factory.  This quasi- experimental study was carried out with 9 subjects who had no history that may affect to fatigue on arm, hand and shoulder. Anthropometers were used to measure body dimension of subjects and directed to design new torch for reducing shoulder level, angle between arm and trunk and angle to twist the wrist while welding. Percentile5^th of elbow height was 87 centimeters, Percentile5^th of inside grip diameter was 3.8 centimeters and percentile 95^th of hand breadth was 10 centimeters. Handle length, handle diameter and distances between middle handle to the end of torch are 12, 3 and 25 cm. respectively with curve end is new torch design shape. The EMG of deltoid muscle activity was measured and would be represented as mean of RMS EMG by electromyograph for 20 minutes and circle time of welding per piece of copper tube of all subjects were measured from time records in video camera. All results which were measured while welding by using existing torch and new torch were compared statistically. The results of this study demonstrated that while subjects were welding by using new torch, deltoid muscle activity and circle time for welding per piece were significantly less than while using existing torch (P< 0.05). The experimental concluded that new torch designed as principles of ergonomic can reduce fatigue shoulder muscle and can increase efficiency of copper capillary tube welding.