A number of issues need to be considered.
- It is essential to remove all sharp corners to avoid local spots of high dilution when welding, otherwise cracking may occur.
- Bottoms of excavations should be rounded to reduce shrinkage stresses at the root and their end profiles should be inclined at an angle of 45° to the casting surface.
- Butt joints in cast iron should be wider than those used for steels. The preferred included angle is 60-75° for MMA (SMAW), MIG/MAG (GMAW) V-joints and 20-30° for U-joints and may well be up to 90° for TIG (GTAW) and oxy-acetylene welding.
- Wherever possible in heavy sections a double-V joint or double-U joint is preferred to minimise distortion and welding stresses. More information on distortion can be found in Job knowledge for welders 34: Distortion - prevention by design
- Where a crack exists and cannot be removed completely, it is recommended that a hole is drilled at the end of the crack before welding commences to reduce stress concentration.
Joint design for welding cast iron requires care. If in doubt, contact an experienced practitioner.
Further information on welding of cast iron is available in:
Welding of cast irons - a guide to best practice
C.L.M.Cottrell, 'Welding cast irons', published by TWI, Abington, Cambridge, UK, 1986 and available from Woodhead Publishing, Abington, Cambridge, UK. e-mail: sales@woodhead-publishing.com
ISBN 0 85300 176 6
Guide for Welding Iron Castings - ANSI/AWS D11.2-89, American Welding Society, Miami, Florida, USA. e-mail: info@aws.org
ISBN 0 87171 295 4