Material selection for machinery pins
Material selection for machinery pins
(OP)
Hi All,
I am new and posted previously but not sure if it was clearly posted.
I am looking for some advice on material and treatment to make 25mm pins out of that are loaded in shear on a tractor driven mulcher. Below is some pictures of previously failed pins.
I have a standard machine shop and furnace.
4140? 1045? flame hardened by hand with oxy-acet and water jet?
They need to be very hard on the surface as the existing ones show signs of wear and were not touched by a centre punch.
Thanks in advance for your advice
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I am new and posted previously but not sure if it was clearly posted.
I am looking for some advice on material and treatment to make 25mm pins out of that are loaded in shear on a tractor driven mulcher. Below is some pictures of previously failed pins.
I have a standard machine shop and furnace.
4140? 1045? flame hardened by hand with oxy-acet and water jet?
They need to be very hard on the surface as the existing ones show signs of wear and were not touched by a centre punch.
Thanks in advance for your advice
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RE: Material selection for machinery pins
There are no links to the five attachments,
desertfox
RE: Material selection for machinery pins
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RE: Material selection for machinery pins
RE: Material selection for machinery pins
How long have the pins that failed been in service?
I think I would go with the 1045 steel, however if the pins have not lasted very long I would try to find out why they have failed, your cross section picture shows a brittle and quite rapid failure but its hard to see any surface detail.
desertfox
RE: Material selection for machinery pins
You need full cross-sectional strength for that pin, and 4140 should give it to you. Also consider having the pins nitrided after the previous HT.
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: Material selection for machinery pins
If 4140 or 4340 won't work, there is a problem with the design. Heck, like desertfox said, 1045 should be plenty strong for a typical application. It's not a spaceship, go with 1045 and if that breaks, you better look at the overall design. Stronger pins like 4140 might just cause it to fail somewhere else.
I suspect a problem with the original pins.
RE: Material selection for machinery pins
This machine works very hard in a rough environment and hits rocks and all other things that should be avoided.
Indeed, pin failure is desirable as the point of failure before anything else.
The original pins were made by the mulcher manufacturer and appear to be forged, with the head as integral and turned later then presumably case hardened.
The pin case was very hard and showed signs of wear. Given this, I would like to have the 4140 pins a bit harder than they presently are (case). What would you recommend?
Or is another steel better to achieve this but still maintain the same (suitable) shear strength.
Is 4140 supplied in the H/T state needing re-hardening and tempering?
Thanks for your help guys, I really appreciate it.
Regards, Iain.
RE: Material selection for machinery pins
Hardened at what temp?
Tempered at what temp?
RE: Material selection for machinery pins
RE: Material selection for machinery pins
Assuming that this pin is intended to shear to prevent a much more expensive failure elsewhere, I don't like the looks of that break. Like desertfox said, it looks more like brittle failure than a shear overload. That leads me to believe that the pin itself was faulty, or was designed too hard/brittle to begin with.
RE: Material selection for machinery pins
In short, be wary of high strength steels in fatigue applications with a large stress range. High strength steel works well in high load applications as long as long as the range of stress due to fluctuating loads is small. When the K value of max/min stress gets low (less than 0.4 or so) or goes into the negative range of reversing loads then high strength steel is no better than plain A36 and can actually perform worse due to the reduced ductility not allowing the pin to locally deform to equalize the stresses.
Have you investigated some sort of bushings between the pin and the mounting clevis? Using multiple pins? Some sort of damper between the attachment mounting arm and the pin, similar to a suspension?
You may have already though of all this but I have seen problems before where the bigger/better/harder/stronger mindset makes people forget about what they are trading off for the increased hardness/strength.
http://www.linkedin.com/in/gregtirevold
RE: Material selection for machinery pins
Look at this site:-
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for the heat treatment.
desertfox
RE: Material selection for machinery pins
The subject pin doesn't have any stress raisers in the loaded area, so the fatigue strength will rise with the ultimate strength, at the levels of strength involved here. The fatigue strength should be ~50% of the ultimate.
Note that nitrided Nitralloy 135 Mod. is/was frequently used for highly stressed gears in helicopters, and gear teeth have significant bending stresses. 1045 can't be nitrided.
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: Material selection for machinery pins
We used them under some very difficult drive conditions where these pins worked very well.
http://www.connexusa.com/HTML/shear.html
RE: Material selection for machinery pins
Refer to the attached chart for an example of how "notches" or corrosion can de-rate the endurance limit for even high strength steel.
http://www.linkedin.com/in/gregtirevold
RE: Material selection for machinery pins
You might well be confused now with the different advice however it seems to me that either material for the pin would be suitable with the correct heat treatment.
The 4145 would certainly be stronger and with nitriding after heat treatment give better wear, but in one of your earlier posts you indicated that the pin should fail in preference to anything else, in that case you might well be better off talking to the OEM and find out what material they used.
What you will find if you do a google search is that hitch pins in 1045 steel are common.
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RE: Material selection for machinery pins
I have asked my supplier what temperature my current stock of 4140 was tempered at and for some reason he cant track this lot but says it would definately fall in the range of
570-650 degrees C.
Is this ok?
Regards, Iain.
RE: Material selection for machinery pins
Look at this site tempering at that temp is fine:-
http://www
desertfox