Cast Iron Dilemma
Cast Iron Dilemma
(OP)
I have a "1 off" class 40 casting that has a partial drilled hole (17/32) in the wrong location. The correct location only moves the hole about 100 thousands from the incorrect location, and I need the entire depth of the hole to be threaded. The partial drill is at most .25” deep and the final depth will be 1.25”. What would be the best method to fill this partial hole so that a new one may be drilled and completely threaded? The suggestions I’ve received are brazing in new cast iron with some special brazing rod we’ve obtained, or mechanically plugging the hole with a tight press fit. I was hoping someone in here might be able to shed light on some other ideas, or tell me if the two options I’ve got wont cut it. There are many concerns about the cast iron becoming too brittle if we were to braze in new material, and concerns that a plug, even if only a partial depth, will not support the loads. Replacing the casting is not an option at this point. Can anyone help?
Thanks
Thanks





RE: Cast Iron Dilemma
For us to be able to help you on the decision we will need to know some more information, what type of loads will the threaded area see, will it be cyclic or repeat loading?
I'm not very familiar with cast iron, but I know that you have not given enough info for a good answer. My personal thought would be to go with the press fit as it shouldn't effect the mechanical properties of the cast iron. However don't rule out brazing. In my last company we brazed a great deal of steel hubs to steel stampings and the break away loads were in the 10-23k lb range.
Alan M. Etzkorn

Product Engineer
Nixon Tool Co.
www.nixontool.com
RE: Cast Iron Dilemma
Based on your situation you can attempt to plug weld the mis-drilled hole based on its size and depth. I would not braze, I would use either a cast iron weld rod or a high nickel electrode (Ni-Rod 55). Was the casting exposed to oil that would require a high temperature bake out?
Extreme care must be used to weld cast iron. From what I have seen, you need to work with small beads and avoid excessive penetration of the weld rod into the cast iron base metal. The reason for this is to mininze dilution so the formation of high carbon martensite (brittle material) in the heat affected zone of the casting is minimized.
Preheat of 600 to 800 deg F is benefical for gray iron castings. However, to avoid generating thermal stresses that could potentially crack the casting, the entire casting should be preheated in this temperature range. If this is not possible, do not preheat and use a low interpass temperature (less than 300 deg F temperature) between weld passes. As I stated above use small beads to avoid cracking the adjacent base metal. Take your time.
Your second option of using an inteference fit plug would not work because in the process of re-drilling the new hole, you would be relieving the residual stresses that hold the plug in place (based on your new hole location).
You might have a third option without the need for weld repair. If appearance is not critical, you might want to consider drilling the new 17/32" diameter hole at the correct location and machine a tapered shoulder around the entire circumference of the hole to the depth (0.250") and width that consumes the mis-drilled hole. Basically, you would have a counter-sunk arrangement of the new bolt hole with a 0.250" reduction in wall thickness of the casting along the base of the shoulder. If you decide this is feasible, make sure you radius the corner of the shoulder to reduce stress concentration.
RE: Cast Iron Dilemma
hope this helps
RE: Cast Iron Dilemma
RE: Cast Iron Dilemma
RE: Cast Iron Dilemma
RE: Cast Iron Dilemma
RE: Cast Iron Dilemma
thanks