willy wrote:
So all in all - any tufftriding/nitriding to a crankshaft is wasted money?
willy, in no way is it a waste of time.
The reason for hardening any mechanical part is to increase wear resistance.... resistance to abrasion... resistance to scratching.... However you'd like to say it, it makes the journel last longer between grinds.
Even 0.005" is beneficial. It will help.
I should have done this in my first post, in this thread,,,, just so we're all on the same page... those of us
with qualifications have been using terminology that we understand, but is often missused or miss understood by everyone else... Anyone who either knows me or has read many of my posts knows that I don't believe in with holding info.,., this stuff isn't some "big scary secret" ... or a "dark art"... (bloody hell I learnt it at TAFE doing my trade.... I was just awake in class .... No offence Matt
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When we're talking about Mechanical Properties of steel (or anything for that matter), we're basically talking about their make up, their characteristics, and their suitability for different applications.
HARDNESS refers to resistance to denting, scratching and abrasion. Hard materials are brittle... this means that they don't cope well with impact or shock.. as hardness goes up, embrittlment almost parodies it..
THOUGHNESS refers to how well a material resists shock, bending and twisting. If you belt a lump of hardwood with a hammer, you'll put a dent in it, but its not going to shatter,, if you belt ya mums porcelain dinner plate with a hammer it will shatter.... the hardwood is tougher than the plate... and the plate is harder than the hardwood (its not going to scratch or dent) but it won't deal with shock the same way hardwood would.. wood... could a wood chuck.... ok I'll stop
ELASTICITY refers to a materials memory.... a highly elastic material will return to its original shape after its bent, twisted or struck
TENSILE STRENGTH is pulling stress.... how hard you can pull on something before it rips in two.
SHEAR STRENGTH is resistance to sideways, or a stress bought about by a sliding action between to parts .... think of a set of shears or tin snips... they
shear materal..... a material with "high shear stregth" will be harder to
shear.... things like dowels are subject to shear stress.
MALLEABILITY is directly related to plasticity... The correct definition is "The plastic respons to compressive force"... Malleable materails are soft. Think Plasticine,,, its extremely malleable... Lead and Gold are highly malleable as far as metals go.
COMPRESSIVE STRENGTH Is resistance to crushing stress... Materials with high compressive strength can with stand compression and crushing without changing shape. Cast Iron has good compressive strength,, concrete has good compressive strength.... Hard materials will have better compressive strength,, but,, they are more brittle.
DUCTILITY relates to tensile stregth.... to a how a material copes with pulling... ductile materials change shape when pulled
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Now, when we are talking about mech properties of steel.... it gets a little more interesting.... or becomes so boring that everyone starts falling asleep
Metal isn't just metal... see... as you no doubt already know or have already worked out if you didn't know, there are many different types of steel with different elements in them. Steel always has at least Carbon and Iron in it. Steels that are only Iron and Carbon are called "Plain carbon steel".... mild steel is a plain carbon steel....
Now all that stuff I just wrote about "Mechanical Properities" comes into play....
With plain carbon steel, it has limited Mech Properties... its usually tough-ish (remember,,,, tough = resistance to twists, bends and shocks) but not a lot else.... Plain carbon steels with higher amounts of carbon in them are harder... with any steel, the more carbon in it "generally" the harder it is, or the harder you can make it. Mild Steel (MS) only has about 0.15-0.2% carbon. If you want to case harden it, you can't just "throw it over a flame and quench it"... you need "Pack Harden" (basically pack it in a steel box with charcol and barium carbonate,,, or normal salt will work too... thats the "old school blacksmith method" these days box hardening is done differently)....
Now..,.,.,.,.,. Alloy steels.....
First off.... Alloy
DOES NOT MEAN ALUMINIUM, but if you weren't from a steel working trade you probably wouldn't know that so we'll forgive you
... Alloy means a mixture... so when we "alloy a steel" we mix other elements in with it. Why? To change its make up and provide a more desireable steel for what ever application....
I mentioned earlier that putting more carbon in a steel makes it easier to harden???? Thats great,,,, but what do we know about hard materials??? They're brittle,, they don't like shock, twisting or bending.... so... what if we need a Hard material, that
is shock resistant???? We alloy it with elements like Nickel, Chrome, Vanadium and Silicon etc.... What these elements allow you to do, is harden the material, without it becoming brittle.... now obviously, each one of these elements also introduce other mechanical properties to the steel as well... so you need to think about whats getting used where and how much of it.... I won't go into what elements do what... well, not unless you really want me too, but I doubt anyones even read this far!
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What happens when we harden a steel.....
It gets hard.
Ask a vague question get a vague answer.
There are sooooooooooooooot many different types of hardening... what method you use depends on the steel you have, how hard you want it, and how deep you want it (depth of penetration). I won't go list an explain all the different types, because again, I doubt anyone has read this far
BUT to be reeeeeaaaaaallly general, you could say that there are two groups of hardening.... Case Hardening and Through Hardening....
Case Hardening is where a hard skin is developed. The depth of penetration depends on the material used, and the method of hardening (and then the finer details in the hardening opperation). Most hardened parts you encounter are case hardened. Its by far the common type of hardening.
The appeal of case hardening is that its only the skin that gets hard... the core remains tough.... so you get a wear resistant material thats still tough..... the best of both worlds,,,, its not going to scratch, and it will cope with twisting, bending and impact... BUT, the deeper the case, the more you start trading off your Toughness.. So if its too deep it can still crack.
The other appeal is that its far quicker and cheaper than through hardening.
Through Hardening.... alright... someone else like David might know of some more applications for Through Hardening,, but about the only place I have encounted through hardening is in my trade... With steel, when it gets hot, it grows or changes shape... when you machine it, it relieves and changes shape......... some steels are more affected by heat changes more than others.... By through hardening a suitable steel, you make it diamentionally stable. We use it on Plastic Injection Dies because they go from being hot enough to melt plastic, to cold enough to re-solidify it very quickly, and they need to remain stable to within a 0.01-0.02
mm (0.000397-0.001") tolerance.
These Dies aren't subject to twisting or bending. So you don't need to worry about the fact that they are 65+ HRc the whole way through. But they do crack sometimes if they are dropped (and yeah,,,,, I "might" have seen that once..... I swear it wasn't me
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The only only other time you find through hardening that I know of, is measuring instruments (and again, its for size stability)... and things like files.
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Alright..... so knowing that little bit about metals and mechanical properties..... lets have a look at a crank shaft for a second....
What do we know about cranks????
They have journels for bearings..... which are subject to friction which can lead to scratching, scoring and abrasion.... (yeah yeah,,, I know they "float on oil".... but what about start up?? No oil pressure then.... what about cornering so hard that your oil pick up goes dry?? No oil then.... what about when the motor is newly rebuilt and even after you've cleaned the hell out of it there are still microscopic swarf particals floating around your oil ways??? It will cause friction then.... What about when you change gears and wear a little off your synco hub which then goes into the oil ways????? I think you're getting the idea
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.... So they have journels for bearings..... which are subject to friction which can lead to scratching, scoring and abrasion
They are subject to twisting forces (torsion)
They are subject to shock (Like David said, every time a cylinder fires, its like the crank is being hit with a hammer)....
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Ok,,,, so..... we have a bearings runing on the
surface of the journels,.... and then the core of the crank and the webs which are subject to twisting.....
The only part, that needs to be resistant to wear, is the
surface of the journal..... the rest of it needs to be able to deal with twisting and impact/shock......
So we want a
...... "hard" surface on the journal for wear resistance ...... and a............
........... "tough" core to cope with the shock and torsion.
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Not a waste of time at all. Its a great thing. Just don't get confused about what it does and why its there
that 0.022" is plenty. If it was through hardened it wouldn't cope with the torsion and shock, it would crack.
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Clear as mud???
See, not so scary.... (appart from the spelling mistakes
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