the response to my previous post from all over the world has been just phenomenal to say the least....i've had probably 20 emails from blokes offering advice, to words of encouragement, to leads on appropriate books to refer to.....
here are a couple......
from aaron in australia:
Hi Matt,
Read you post on hardening. It is frustrating when you approach a craftsman and ask to understand more of what makes their skills so appreciated & important to be passed on & not lost to our 'progress'. Not all are like what you have encoutned though, good luck finding others who get it.
Just a note, a quick dip into my old Mech Eng text books & most gear/splines are case-hardened not fully hardended. The reason being you want the surface (i.e 0.05mm) to have high wear resistance, but needs overall strength to withstand bending & torsional loads. Full harden steels can become brittle and may get a fracture.
Case Hardening of a gear tends to be by induction coil to surface is evenly heated quickly to above the point that ferrite starts to form (approx >800c for most carbon steels) but the internal is kept below the Eutectoid temp (<727C for most Carbon Steels). As you normally need to heat quickly and accurately this is not simple to do this via flame heating (but not impossible).
When quenched the outside surface will form the Martensite struture you need for hardening. Some tempering will control the hardness, but not a major issue (IMHO) for your requirements.
I will scan if I have any literature on heating gears like this.
Sorry for the long-winded tech filled crap, but thought it might assist to understand what needs to be achieved for the sproket to work optimally
Just another thing.. Read you welded the sproket after annealing them? Did you re-anneal the finished sproket? The carbon steel in each sprocket may be different and the Heat Affected Zone (HAZ) may have formed martensite (the harden form of steel) & can get weld fractures at the joints. Tis unlikely, but thought it best to tell you while on the topic of heat treatments.
I am sorry, I haven't provided a solution to what you need to do, but though would pass on some info to you to help achieve the goal. Will dig my old books again & speak with my old toolmakers at work (they are the helpful type)
Cheers,
A
from Marcel in Amsterdam:
Hello Matt,
This weekend we have in Amsterdam a rusty swap meeting, all bikers coming together, live music, parts market.
So not much at home. for the moment.
to Hardening your sprocket, it will be like this in short terms,
going to around 900 degree temparture ( slowly bringing it up in temp.) , for the size of the sprockets a holding time 30 minutes at 900 degree
then wait just a few seconds, and cool it in harderning oil ( special oil, up to 1000 degree)
after that it needs tempering, getting out some stress. mostly done arround 500 - 600 degree temp. hold it for 30 minutes
then slowy cooled down in air to normal 25 degree.
what whe also do is, when whe want some extra hardness after the hardening proces, put it in a freezer at -80 degree, for at least 6 hours
The only thing is at my company , whe do the hardening process in a furnace. with controlled temparture, bring it up exactly how we want it to be.
and cool it at the right moment.
If you want to do this by torchflame, you need at least some extra torches to get a constant heated surface.
But it will not be the same character as with a furnace hardening
On this quest i come back on this monday, ask my colleagues what's best to do.
I also added some explanation about hardening end tempering i found in englisch.
The company i work for is not situated in Australia, but i found a company who does a simulary job as whe do. Heat treatments
It's called Heat Treatment Australia, maby they can also help you.
Best regards,
Marcel
and from the always insightful Pete from Occhio Lungo:
If you just need case hardening, not through hardening, you have some choices. The simple route is to use Kasenit or something similar. Just follow the instructions on the can, heat it up, quench in water, dip it in the Kasenit (I think it is just a carbon powder), then heat and quench. Basically, you need carbon for the heat treatment to make the steel hard. Some steels don't have much C, but Kasenit will deposit onto the sprocket. I wrote up a quick article on my site about it last year when I hardened some pushrod ends.
(in the old days, blacksmiths would use bits of bones and horns to coat the metal!)
Another option is to carburize the part. But that requires a trip to the heat treat shop, and they'll heat it up and coat it with carbon. Then cook it properly to give whatever case hardness you want. My last part was Rockwell C 62, which is pretty darn hard. .060" minimum thickness. That left me plenty of material so that I could grind off .010" to make the part perfectly round again. You probably don't need that much for a sprocket.
By the way, I've run a lot of sprockets with teeth that weren't hardened. They last for a while, but you'll want to make sure that everything is straight and true. Crooked sprockets wear out fast and break chains too.
this fine publication was recommended to me and i did a hunt for it......
these are photos of the copy i secured...1946 issue...its in the post on the way to me...
so after the last week of lots of talk on the subject, i have a possible direction for the work at hand. i've a little more reading to do and some hunting of materials then ill do another post with what my approach and method will be so bear with me for a bit.....
thanks for all the well wishes and all the infos blokes.....its why i write this blog...
mm
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