Technical Knowledge Database

Welding Image

Welcome to the Weldability Sif Technical Knowledge Database. We frequently answer technical questions while assisting customers with selecting and using our products in their applications. You can search these questions using the form below.

Displaying KnowledgeBase Entry 1418:

Sif offer several options of filler materials, depending on desired results. Your biggest challenge with Cast Iron is preventing cracking during cooling. Due to the gain-structure of Cast Iron there are lots of fissures to fill with the consumable, and this often involves “peening”, hitting with a hammer, on less ductile filler rods. Suitable Sif brazing alloys – SifSilCopper 968 and Sifphosphor Bronze 8 – are more ductile and therefore flow into the fissures better without peening, adhering and cooling more consistently and avoiding separation cracks. But these are brass/bronze in colour, so the repair is very visible.

For colour-match and matching of mechanical properties, the best method is to use Super Silicon No 9, which can be utilised – without flux – in TIG, by grinding a 4mm No9 rod into a point on a bench-grinder. That point will then melt into the weld-pool. This is the method preferred by many professional Cast Iron restorers.

And finally, where you prefer to weld, not braze,, are happy to peen, and want to use a TIG rod that feels more familiar, then a CuNi rod, like SifAlloy No73, 30% Nickel, can be used. Colour difference will be noticeable, and the deposit will be less ductile, but higher strength.

For the last 2 options, pre-heating the component to “hand-hot”, 50-60C, and controlled-cooling after welding is recommended, to avoid cracking. Cooling can be better controlled by wrapping the component, or at least the joint, with a medium-duty welding blanket.
Disclaimer: This information is provided 'as is' and we accept no responsibility for the accuracy or validity of this information.