Abstract
The study of relation between the base metal roughness and its torsional strength of mild steel brazed joint has been investigated in this experiment. To obtain some experimental data, some specimens (16φ×105mm) of mild steel rods (SS 41) and BAg-8 filler metal were prepared.The surface of each specimen was identically polished by various emery papers (No 60, 240 and 600 esh), and other specimens were machined by milling cutter or ground by WA 60, WA 80 grinding wheels. These specimens were brazed with BAg-8 filler metal (wt=0.1g) using the 35KW resistance furnace operated in hydrogen atmosphere, and machined according to the scheme of Fig 1. The torsional strength test of these sepcimens was carried out by a 50Kg-m torsional strength testing machine shown in Photo. 1. The torsional test of these specimens gave the results as follows:1) The torsional strength of specimen polished by No. 600 mesh emery paper (Rmax=0.6 micron) was very high, its value being 34.1 kg/mm2 at the joint clearance 0.12 mm, but that of the specimen polished by No. 60 mesh emery paper (Rmax = 15 micron) was lower, its value being 30.9 kg/mm2 at the joint clearance 0.15mm.2) The torsional strength of specimen ground by WA80 grinding wheel (Rmax=0.8micron) was excellent, its value being 35.5Kg/mm2 at the joint clearance 0.18mm, but that of the specimen ground by WA60 grinding wheel (Rmax=1.6 micron) was poor, it value bieng.32.2Kg/mm2 at the joint clearance 0.11mm.3) In general, the torsional strength of brazed joint with a smooth surface was greater than that of one with a coarse brazing surface due to the effect of residual stress of filler metal at the brazed joint.4) As regards the relation between torsional strength and joint clearance, the torsional strength of specimen with 0.12-0.3mm joint clearance was very high among the specimens polished by emery papers and those of specimens with other joint clearance were lower, and also, that of a specimen with 0.15-0.25mm joint clearance was high among the specimens machined or ground.
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