Until about 10 years ago, I used to send my inline 6 cyl race cranks to Industrial Metal Heat Treating in Newark NJ for Tufftriding, a type of nitriding process. I think the process was licensed from the Kolene company. The cranks were finish ground before treatment and only required a light polish and straigtening before use. Usually they were not out by more than about 0.006" and I used the hammer peen method to get them straight within a couple of tenths. These cranks are about 30" long, weight about 80 lbs and are fairy stout with 3" mains and 2 3/4" rods, but are a somewhat soft steel. Additionally, the tuftride process put the surface of the metal in compression, increasing the fatigue life. I think the EPA made things too difficult for this process to be economical, as I am no longer able to find anyone that runs it. I have since tried Ion nitriding, but wound up with two cranks bowed more than 0.020 that I could not straighten with hammer peen. I don't want to use a press to straighten the cranks post treatment as I think it would weaken the cranks from a fatigue standpoint. Anyone have any experiance with a good, fairly low temperature surface hardening process, that would also help fatigue life and not bow a long item like a crank?
Look for where aircraft cranks are done. Not positive , but I think all such cranks must be nitrited. Boy, was that a fun job. Threading out heavy hot cranks from below your feet and all in one breath or brave the worst cat box smell one could imagine.
Actually; the last place I had the cranks done was an aircraft crank place in Texas called Rick Romans. Did a real nice job on the grinding, all journals +/- 0.00005 of my target diameters and straight. Shipping back and forth to PA is pretty expensive now though. They used a nitride process. Looking to see if I can find someone closer if possible.
I gotta' say, I'm impressed that you could *tell* that they were +/- 0.00005!! How do you do that? Bob
Have you considered hard chrome plating? Suggest you talk to a shop that does this. I have no experience in this but have heard/read about.
That would require considerable work, perhaps more than one might desire. The crank must be ground undersized for the hard chrome to be applied, then reground after plating. Hard chrome doesn't deposit uniformly-----in fact far from it. It tends to migrate to sharp edges and ignores inside corners. In order to get a full covering that is deep enough to regrind, it would require a large amount deposited oversize to insure that inside corners were filled. It's a very hard surface, though.
TiAlN (Titanium, Aluminum, Nitride) PVD (Poly Vapor Deposition) Laser Hardening (really wouldn't recommend that for a crank, makes the surface too hard - 90-92 HRC - would probably result in stress cracks.) There are many others too.
TiAlN and PVD will give a surface of 70-72 HRC about 20 microns deep, I've not had either deform a part as long as the growth is taken into account.
Someone please tell me what I am missing in this thread. The OP said he could straighten a crank that was out by 0.006 to within "tenths" with a ball peen hammer. Is that a normal procedure for straightening heat treated crankshafts?
Bob (drawing total blank) Swinney
Robert Swinney wrote:
Yep, It is how crankshafts have been straightened for a LONG time. Cast iron, Forged Iron and steel all are straightened that way. You use a set of V block, a good dial indicator and a hammer and brass drift. Or if it's larger a lead mallet. A good crank man can get the shaft dead straight with a few hits.
Greetings Steve, It has been my experience that peen straightening is accomplished by peening the shaft. It's like peening a sheet of copper. If you hammer on just one side of the sheet the sheet will start to curve. So the straightening of the shaft is not accomplished by bending the shaft with an impact but instead by changing the length of one side of the shaft to make it curve in the desired direction. Since this curve is the opposite of the curve present in the bent shaft the net result is a straight shaft. ERS
email@example.com (Eric R Snow) wrote in
You are correct.
There is also a carbide plasma impregnation coating out there, but I don't know the technical name. They shoot a carbide-fed plasma at a steel part at tremendous velocity and it actually imbeds the carbide into the steel. The nascar crowd was using it for a while for brake rotors (may still be). Of course, this would require grinding afterward.
We've used that for collets in heavy turning applications. Lately we've been using this:
The plasma impregnation will peel off after some time. So far that hasn't happened with the Carbinite process. I'm sure it will wear out over time, but they claim it can be reapplied. Hands down the Carbinite is a better product in a production environment.
I can't help with a process, but can recommend a heat treater.
A very big company, but I've received excellent advice and service on small jobs from the NH plant. They did do some nitriding for me, but the parts were very small and distortion wasn't an issue. I don't know what sort of nitriding process they use.