New Tin Free Steel for Cans Weldable without Edge Grinding

摘要

The shells of 18-liter metal cans, pails, and similar containers for paints, chemicals, and other products are commonly manufactured by welding chromium plated tin free steel (JIS G 3315) using a copper wire type electric resistance seam welder. In comparison with tinplate, tin free steel is superior in paint coating adhesion and is economically advantageous, but the welding of conventional tin free steel is difficult due to the large electric resistance of its hydrated chromium oxide coated layer. The narrow available welding current range (ACR, defined as the range between the lower limit current for securing sufficient bonding strength and the upper limit current for small splash formation) has made it impossible to weld the finished tin free steel surface, and it has therefore been necessary to remove the coating from the weld area by grinding immediately before welding. Consequently, the composition of the can making line is complicated with tin free steel, involving a grinder and suction pick-up device for the grinding scrap, and the productivity of the can making process is poor. Finally, where edge grinding is concerned, paint coating adhesion is deteriorated at the ground surface by the loss of the coated layer, and it has been pointed out that welding is unstable because uniform removal of the chromium layer is difficult.