Hi All Is it possible to repair porosities in a Phosphor Bronze casting? The cast is of an impeller. Can ECuSn-A (5% Sn) , ECuSn-C(8% Sn) be used ? Inspection Engineer BE (Metallurgy) ASNT Level II RT,LPT,MPT HPL, India Ananda.Sarkar@hpl.co.in 09232396661

Ananda Sarkar Phosphor Bronze impeller can be repair welded successfully - free from porosity -with precautions as follows: Copper - Tin alloys are susceptible for hot cracking under stressed condition. High pre-heat, High Heat input, slow cooling should be avoided (if the impeller is already under stressed condition). For GTAW or GMAW or even SMAW, it is preferable to use a joint design of wider Single V - 70-80 degreee to allow for fusion and penetration (Copper alloys have high thermal conductivity than steel). Base metal must be thoroughly clean and free of mositure. Do not allow moisture to set in during welding - as it will develop porosity. For Phosphor bronze pre-heat should be maintained at 232 deg cent during welding and during passes. E Cu-Sn-A or ECUSN-C with DC + should give good weldabiity for repairs. This should give porosity free deposits and slag can be easily removed. After welding, if exces metal has been deposited in impeller, dynamically re-balance impeller will be needed (already suggested by Debasis). If only a small weld deposit had been made, then u can run the pump and see if pump develops high radial vibration. Trust this is of help to you C.V.Srinivasan Nishi Engineers Pvt Ltd India March 18 E-mail: nishi @vsnl.com >Dear Ananda, >My suggestions are as follows : > >(1) As impeller will be needing an accurate Dynamic >Balancing - better to avoid any repair weld patches and >better try to rectify surface pores by light grinding >smears. > >(2) If at all welding rectifics is reqd. you may follow the >following steps : >** Clean the weld area. Ensure all DP traces are well >removed >** Preheat wel area & adjacents to 400F preferably by coil >cooperheats and maintain >** Preferably weld by AWS5.7 ECuSn-A by GTAW using lowest >current AC or DC RP / backstep staggered weaving techniques >** Controlled asbestos cooling slowly . After cooling only >remove slags. > >note : AWS 5.6 ECuSn-C is harder and stronger than AWS5.7 >ECuSn-A and thus chances of incipient crackings are bit >higher. Also ECuSn-A is used for castings. > >Pl. give small trials an ensure own. >regards >DM / mail back at debumitra2004@rediffmail.com