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Cast Iron Welding

Cast iron is obviously a metal - right? Well, sort of. It is heavy and castable and resists heat, but its missing one really important quality, and that is malleability. Cast iron is not very malleable, which means that it will break rather than bend when it is abused.

Broken parts are a common problem with antique stoves and because cast iron is brittle it is also difficult to weld properly. Poor cast iron welding may introduce more damage than it is attempting to fix!

I use oxy-acetylene ("gas") fusion welding, which means that I melt cast iron into a ground-out trough called a V-groove. After the V-groove is prepared and the pieces are aligned on the welding table they are preheated to "black-heat" temperature (just below "red hot). This ensures that the entire casting is expanded, then the weld slowly progresses until completion. The piece may then be fired up to a dull red heat and allowed to cool very slowly for a long time. This produces a stress free repair that is as workable as the original material and can be machined and drilled easily to reshape the surface so that the weld is undetectable when finished.

I can also straighten warped or twisted castings (usually top sections) by heating the damaged area to red heat and slowly applying pressure with screw clamps to force the piece back into shape.

photo 1: cast iron stove panel before
                            repair photo 2: cast iron stove panel
                            "V-groove"-d ready for welding photo 3: cast iron stove panel after
                            repair
Before repair
 V-grooved part ready for welding
After repair

This sequence of photos shows the repair of a crack in the back panel of a large Box Heater. The crack is about 18 inches long with a fork at the top and a piece missing at the bottom. Photo 2 shows the reverse or inside surface of the casting, which has been ground out (i.e. V-grooved) in preparation for welding. Photo 3 shows the restored panel after it has been filed smooth. NOTE: This stove has been in use for 15 years with no further problems.

cast iron repair photo 1
cast iron repair photo 2
Photo 1
Photo 2

These photos illustrate the repair of an ornate High Shelf Support, which is missing its lower left section. Photo 1 shows the piece as received, with a paper pattern taken from the right side and reversed. Photo 2 shows the roughed-in cast iron. Note that the high relief has been embossed with a bead of weld.

cast
                              iron repair photo 3
cast
                              iron repair photo 4
Photo 3
Photo 4

Photo 3 shows the piece after grinding, and in Photo 4 the piece is finished.

kootenay door before repair
kootenay door after repair
Before
After

Another typical problem shown above: a door with the hinge pin broken off  and the piece is missing! Repair involved using the pin off a scrap door and welding it on to the broken door.  In this instance, the owner wanted to preserve the original nickel, so I simply dressed the weld with fine emery paper and buffed the cast iron, which you see in the "after" photo.

Note: I have written a technical paper on cast iron welding for beginners, which was published by THE ANTIQUE STOVE ASSOCIATION (1986) and reprinted more recently in THE ANTIQUE STOVE EXCHANGE quarterly fall 2002 and winter 2003 issues.

Canadian Antique Stoves
PO Box 673, Kaslo, BC, Canada, V0G 1M0
Phone 1-250-353-9648