Optimization of Parameters for Tinning 1-Inch Uranium Hexafluoride Cylinder Valves

摘要

A laboratory investigation of parameters for tinning 1-inch aluminum bronze (Copper Development Association Alloy 636) valves for uranium hexafluoride cylinders has been conducted at the Portsmouth Gaseous Diffusion Plant. The purpose of the study was to establish a solder type, a tinning temperature range, and an exposure time which would best limit solder penetration into the aluminum bronze in the threaded inlet region of the valve, a phenomenon that leads to cracking and subsequent valve failure. Of three solder types tested, a 50:50/lead:tin composition (grade 50A solder ASTM B 32) proved superior to high lead and high tin solders. The optimum tinning temperature range was found to be 600 to 650 deg F. The degree of embrittlement increased as temperature increased - an indication that control of temperature during tinning may be a critical factor in the prevention of valve failure. After exposure of the valve body to molten 50A solder at 600 to 650 deg F for as much as 120 seconds, no evidence of liquid metal penetration was found. Since this time span greatly exceeds normal (approximately 20-second) exposures, minor variations in exposure time should not greatly affect the results of tinning. A recommended tinning procedure incorporating the experimental findings and ensuring the necessary temperature controls is given in the appendix.