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Cast Iron Crack Repair
by Lincoln's Cast Iron Expert, Joe Kolasa
Joe Kolasa |
Within the walls of The Lincoln Electric
Company are some of the brightest minds in welding, but we wouldn't be The
Welding Experts® if it weren't for the expertise of our customers. Learn
with us from questions submitted by real customers and answered by the real
experts. |
Question
In an earlier "Ask
the Experts" article, Joe Kolasa recommends stick welding cast iron
with either Softweld
55Ni or Ferroweld.
That got me thinking about welding my cast iron dutch oven that has a crack
in it. Before I start, I have several questions:
- Since the oven is 1/4" thick, is Ferroweld the better choice?
- Will either rod work with AC current?
I have a 25-year-old
AC-225 "buzz-box"
- What about weld prep / preheat?
I’m concerned about
the thermal cycling that the oven will undergo during use, so I suspect that
a complete penetration weld is called for. Obviously the braze material will
have to be ground off, but what else is necessary?
- Should the welds be short sections to control heat input?
How about one-inch long sections - even through I know more starts and stops
equals more opportunity for weld defects!
- Would you recommend drilling a small < 1/8" hole at the tip
of the crack?
I want to try to keep it from running as the iron
heats up
Answer
I would choose 1/8" Softweld
55Ni. This rod can be used on AC Polarity but DC+ is preferred.
As far as the rest of your questions, let’s start at the beginning. Follow
these steps to repair the crack…
- Locate the cracked area using a commercial dye penetrant or rub with
kerosene and then chalk over the crack. The kerosene will absorb through the
chalk to show how long the crack really is. Sometimes it’s difficult
to see the crack with the naked eye.
- Once the crack is located, drill a 1/8” hole at the end of the
crack.
- Clean and grind the area 2 inches at each end of the crack to prevent
them from continuing further. If you’re using a grinder, heat the bevel
with an oxidizing flame to burn off carbon before welding.
- Grind, chip, machine or saw the crack to create a bevel. Gas cutting
or arc gouging can be used on casting that is preheated for welding. Be sure
to get the bottom of the crack. On sections more than 3/16” thick, bevel
the edges so the root of the joint is 1/8” to 3/16” wide. If the
crack extends through the section, leave about 1/8” gap and 1/16”
land.
- Preheat entire casting slowly and evenly to remove surface oils and
dirt.
- At least 500 degrees; not more than 1200 degrees.
- Make sure you maintain your temperature from start to finish.
- Preheat the entire casting, not just the area to be welded.
- Weld the cast iron using low currents for minimum penetration
Make 1-inch to 3-inch welds to limit heat input. Immediately strike (or peen)
the face of each weld with a small ball peen hammer to relieve stresses in
the weld. Skip weld – move around the cracked area – do
not keep heating the same area. Run your beads in the same direction.
- Cool very slowly!! Oven or furnace cooling is preferred. Drop 50
degrees every hour until room temperature. Bury in dry sand, wrap in fireproof
blanket – anything to slow the cooling rate. Air cooling is too fast!
Note: For machineable welds, use Softweld 99 or Softweld 55. Ferroweld deposits
are not machineable.
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