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Hardening...

(and tempering)

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Wolfie04/11/2010 12:17:57
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OK do these two always go together. I know nothing about this. To harden something you heat it up right?? Doesn't that make it brittle? Whats tempering??
Andrew Johnston04/11/2010 12:42:52
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Hi Wolfie,
 
As always in engineering the answer is yes, no, but!
 
For high carbon steels, to harden parts you heat them above the critical temperature and then cool rapidly by quenching in water, brine or oil. As you correctly say, that makes the material hard, but brittle. Tempering is the process of heating the part to a much lower temperature and then quenching. This trades off hardness against toughness. So somehing like a cold chisel will be tempered at a higher temperature than a hand scraper, as the chisel needs to withstand shock loadings, ie, less hard and tougher.
 
I recommend the book WPS1 by Tubal Cain, which has a good explanation of the complex processes that are happening when hardening and tempering steels.

Materials other than carbon steel harden by other processes. Materials like copper and some stainless steels harden by being mechanically strained, which is a PITA when you are trying to cut them. Other alloys can be precipitation, or age, hardened. This involves heating parts to moderate temperatures and letting them soak, allowing some of the alloying elements to migrate within the lattice structure and harden the material. An example of precipitation hardening is aluminium alloy rivets for aircraft. Before use these are heat treated and then have to be kept cool and used within a certain time. After fitting and forming they age harden over time.
 
Regards,
 
Andrew
 
 
 

Edited By Andrew Johnston on 04/11/2010 12:44:06

Wolfie04/11/2010 22:21:22
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WPS1 is that the title??
Andrew Johnston04/11/2010 22:33:09
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Sorry, dumb use of abbreviations on my part.
 
WPS1 = Workshop Practice Series Book1 - Hardening, Tempering & Heat Treatment
 
Regards,
 
Andrew
 
PS: on a note from another thread; I do know Sutton Bank, been there a few times, but never flown there due to the rotten weather. I did get as far as getting in a glider, but then the tug pilot wimped out 'cause the cloudbase was only 300 feet. It's a bit of challenge towing a glider trailer up Sutton Bank itself. Real bummer if the car in front stops!
John Olsen04/11/2010 22:43:39
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Hi Andrew,
 
How do you find those long trailers in traffic? I ask because my steam launch is 30 feet long, designed to just fit the maximum length allowed behind the towball here. Beam is 6 feet, so it is not all that wide, but it will be a fair length back to the end. It will of course be a little heavier than a normal glider.
 
regards
John
NJH04/11/2010 23:58:53
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A major problem I found when towing glider trailers was missing a turning - it could mean a long ride in the wrong direction until you found a sufficiently large space to turn around!
Generally though even quite big trailers tow well .
 
Regards
 
Norman 
Wolfie05/11/2010 09:13:20
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LOL as a local lorry driver (ex anyway) I've been up and down Sutton Bank many many times with an artic.
 
On 2 occasions I've had to turn one round on Sutton Bank too You're right about missing a turning, I've driven for miles looking for a side road to reverse into.

You're right about the weather up here too lol. 
NJH05/11/2010 09:47:00
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Whoops !  - sorry wrong button - posted in error. Is there no way to delete a posting once made?

Edited By NJH on 05/11/2010 09:49:04

Gordon W05/11/2010 15:07:15
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Sutton Bank, well to get somewhere near topic, me and my mate ,back in the 50's,when we had no sense, built a tandem with 3 speed hub gear and a derailleur system fitted to that, to give very high gears. Set off from the hairpin on the bank to see how fast we could go, the moped speedo showed 80mph, probably wrong. Still doing 40 at Thirsk, according to nice policeman who stopped us. Of course the roads were much quieter then.
Wolfie06/11/2010 11:04:07
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Its 10 miles from the bank to Thirsk lol
 
Back on topic - ordered the book!

Edited By Wolfie on 06/11/2010 11:05:02

Andrew Johnston06/11/2010 11:33:13
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I'm sure you'll find the book informative, although the physics/chemistry of iron/carbon alloys is pretty complex, and will probably require several readings!
 
Actually I think coming down Sutton Bank with a trailer was worse than going up. At least on the way up the only thing you're likely to lose is traction; a disadvantage of front wheel drive cars. On the way down, it's bottom gear, brakes, and 'oh #@*& we're sliding with the wheels locked'.
 
John: Generally modern glider trailers tow pretty well. Older ones are much more of a mixed bag. Weight balance and distribution is critical. I find I need about 50-70lbs of downforce on the hitch, plus weight in the front of the car to retain steering. Even if the balance is correct, weight in the back of the trailer can lead to instability. Ultimately the car is the most important factor; it needs to be heavy for stability. I used to drive Citroens, which had self-leveling suspension, a real joy for towing. Now I have a Peugeot, and while it's a good tow car I need to pay more attention to weight and balance. Set up properly, the biggest danger is forgetting you've got the trailer on the back! In the UK we have a speed limit of 60mph for braked trailers. I normally stick to 55-60, as faster really hammers the fuel consumption. I've towed through quite a lot of towns and cities, before bypasses were built. The main issues are that it is more difficult to change lane, because of the length, and you need to be careful about the back of the trailer swinging out when turning at junctions. I've even been through the centre of Edinburgh with a trailer, due to a slight navigational error coming off the Forth road bridge. I don't know what your steam launch weighs. I estimate my single seat glider and trailer weigh about 1400lbs in total. My new two seat glider and trailer is well over a ton. There is a myth (?) that glider trailers are longer than permitted by UK law, but a 'blind eye' is turned as they are classed as an indivisible load. I've added a picture of your scribe picking up a mate who had made a navigational error in Scotland and was consequently in the middle of nowhere. This particular trailer is about 13 metres long. Real pain to turn round on narrow country lanes. We entertained a whole restaurant full of pensioners while turning it round in a hotel carpark, having missed the turn off to 6 miles of single track road up to where the glider was.
 
Regards,
 
Andrew

Edited By Andrew Johnston on 06/11/2010 11:33:46

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