Casting crack deficits repairing process
1) Cleaning
1,Burn the cracks or gaps on the castings with oxyacetylene flame to remove the water and oil; you can also use high temperature furnace to heat the castings at 150℃ for more than 1 hour. Cleanness is very important for cast iron welding
2,Grind the castings alongside the cracks or gaps with grinders; The length of grooves should not exceed the cracks but the grooves should be deeper than the cracks or the gaps. In theory, the grooves should be as small as possible to avoid possible secondary crack.
3,Clean the grooves with wire brushes and rinse the grooves and surroundings with acetone or alcohol.
2) Welding
1, Choose cast iron electrodes ENi-CI (Ni99) 3/32’’ or 1/8’’ according to the size of the cracks or gaps
2, Fixtures: If possible, fix both sides of the cracks with U type fixtures to ensure the cracks with not expend and there will be no new cold cracks after welding
3, Welding methods: Do not sway the welding electrodes nor stop before completing one pass of welding; If the groove is too long, you can weld segment by segment; Slow cooling should be applied after each welding pass and restart welding after heat affected zone cool down to below 100℃； The weld piece and molten pool should be hammered heavily after each pass of welding.
4、When the welding is completed, second time grinding & welding can be applied if there is still small cracks.
Notes: As castings have high carbon content, cracks can happen easily after welding, please don’t be surprised about this. You can repeat above measures and repair until no cracks can be found.
At the same time ENi-CI pure Nickle cast iron electrodes are highly suggested as the weld bead is more machinable.
