Cast iron repair

[PTfan]

I have a 2 1/2" thick casting that cracked in half. It is a rocker arm for a punch and seems to have been abused a little. I have already V grooved out almost half way on one side. I was planning to V groove out the other side then drill and tap studs into the V groove preheat peice in oven to 500deg.. Then make with one pass with nickel rod to cover V groove and then fill in the rest with mig, put back in oven and post heat for a few days. After the peice cools I was going to place 3/8" plates on eather side of arm and drill holes through plate and casting to give more strenght. Any opinions welcome please.

[dyn88]

you are going to need to mig with Ni wire. Also You dont need to post heat for much longer than 1 hour per inch of thickness. I however would preheat to 1000 to burn off any contaminates then bring down to 700 before weld. Slow cool is neccassary to prevent cracking, either wrap in ceramic blanket or in fiberglass insulation(peel off the paper it smokes and stinks badly). Lastly after slow cool another heat cycle will insure against premature failure. probably around 1000 again with slow cool. Ive repaired just about every part of our four slide in this fashion and none of the parts failed again yet.(those old machines dont like running to fast, and you can never oil them enough) All this may seem like over kill but if the part is no longer atainable than you only want to repair it once. Also you wont need to pin the assembly.

[Paul Seaman]

PTfan:
Dyn88 is on the money, if this is a crack then you'll need to drill the end of the crack to prevent it from starting a new crack after the repair. If this is a clean break obviously no drill stop is required.

My .02
Peace,

[PTfan]

So pre heat to 1000 slow cool to 700 weld up then heat back up to 1000 then wrap up in insulation let cool down for 2 to 2 1/2 hours.

Have you ever heard of samwiching plates on both sided to relieve some presure of the casting?

[dyn88]

sorry heat to 1000 to burn off any impurities let sit to 700 weld area then heat at 700 for 1 hour per thickness after that wrap in insulation and let sit till next day(depending upon mass of item may still be warm). then repeat cycle (w/o weld) at 1000 at least once but we do twice(almost like double temper, if it were tool steel). We never use plates but we gouge entire repair area. in the end the whole of the crack or two pieces will be joined by all weld(100% penetration). I said it before but it may seem like a lot of time and work but the repair will probably never fail if care is taken to ensure cleanliness and heat. #1 cause of premature failure is thermal shock!!

[HAWK]

PTfan,

Dyn88 has you covered in detail on the cast repair. My concern is if the rocker arm endures regular stress, it may be better to braze than to weld. Either way will get you some use from the casting.

[dyn88]

Ive never had good luck with braze on a working impact part. But Im sure HAWK has some good tried and true methods.

[HAWK]

dyn88,

Success rate for brazing and Ni welding is about the same for short term use in smaller parts. However, in larger castings subject to chronic rhythmic impact brazing seems to last longer.