TIL: Today I Learned... (1 Viewer)

Galbreath34

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Sometimes you just learn something strange you'd like to share but there is no good place.


TIL: The subreddit /r/marijuanaenthusiasts is actually about trees, dendrology and getting trees identified from pictures. It has this name becase /r/trees was already taken by marijuana enthusiasts who didn't want to give up the name.
 

Sandman

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I learned to be a little more patient when heat treating aluminum. I had a stack of 7075 plates that a 100* bend. Thinking I could save time, I took them out of the oven 6 at a time for quenching. Since they were nested together it took too long for the water to reach every piece.
The top and bottom plates are usable. The four in the middle warped pretty badly.
Oops. :covri:
I took some cinnamon rolls out of the oven too soon once, so I understand what you saying.
 

bigdog

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Bill Parcells once told his QB Phil Simms that if he didn't throw at least 2 interceptions in a particular game he wasn't trying hard enough. Said he wasn't taking enough chances.
 

saintmdterps

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Skip buying replacement spools for your string trimmer. Take off the empty spool and attach zip ties to the spool holder on the end of the shaft. Cheaper and more durable :9:
 

staphory

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staphory

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This for work or for fun? I just get skittish around SCC issues with T6 7075, but if it's not under applied stress and a corrosive environment, it's not a big deal.
It is for work and goes on naval aircraft.
I'm required to use the material called for and heat treat to T6. It meets hardness requirements as measured with a Barcol hardness tester. Additionally it has passed a conductivity test. There's nothing else I can do to the thing.
Solution heat treatment is as much art as science. With a little luck thrown in.
In any case, it's really just an over engineered dust cover. Not structural at all. It just keeps aircrew from dropping things inside the console. No real reason to be .063 thick or as hard as it is. We just do what Jacksonville says.
As far as stress concerns go, lots of parts that are under stress loads are 7075-T6. BAE and McDonnell Douglas (Boeing) apparently like it that way. Job security I guess.
 

Saint_Ward

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It is for work and goes on naval aircraft.
I'm required to use the material called for and heat treat to T6. It meets hardness requirements as measured with a Barcol hardness tester. Additionally it has passed a conductivity test. There's nothing else I can do to the thing.
Solution heat treatment is as much art as science. With a little luck thrown in.
In any case, it's really just an over engineered dust cover. Not structural at all. It just keeps aircrew from dropping things inside the console. No real reason to be .063 thick or as hard as it is. We just do what Jacksonville says.
As far as stress concerns go, lots of parts that are under stress loads are 7075-T6. BAE and McDonnell Douglas (Boeing) apparently like it that way. Job security I guess.
Well, if they're not being replaced due to cracking (well, SCC related cracking, not regular fatigue based), then it's all good. If they're cracking (again SCC style, not Fatigue), well, then the likely solution is T7X.

And yeah, if it's for work, you follow the paper work. No issues there. This is just my wheel house.

They probably do T6 in this case, just because it's less time in the furnace. Why spend more money to make it T7?
 

staphory

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Well, if they're not being replaced due to cracking (well, SCC related cracking, not regular fatigue based), then it's all good. If they're cracking (again SCC style, not Fatigue), well, then the likely solution is T7X.

And yeah, if it's for work, you follow the paper work. No issues there. This is just my wheel house.

They probably do T6 in this case, just because it's less time in the furnace. Why spend more money to make it T7?
I think aluminum requires a certain amount of cold working to get above T6. We aren't set up for that.
 

Saint_Ward

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I think aluminum requires a certain amount of cold working to get above T6. We aren't set up for that.
Today You Learned....lol.

So, T7 is overaged.. meaning, similar to T6 (artificially aged), but in the oven for longer. It reduces strength a bit, but fixes the Stress Corrosion Cracking (SCC) issues that come up with some 7000 series Aluminum. Most commercial aircraft skin uses the T7 condition.

Now, T8 is with the cold work. You have to solutionize it, like you're doing T4 (which, counts the natural aging you'd get after a couple days at room temperature.. ), then give it a 1.5-3% stretch (approx.) to induce cold working. this gives you T3 (basically T4 with cold work). Then artificially age it similar to a T6, but you end up with T8.

Interestingly enough, some plate or bar products get the Stretch after solution, and are just aged to T6. They don't count the stretching in the mechanical properties, even though you probably are getting something closer to a T8 condition. I haven't done it, so I'm not sure if the stretching is after quench, before natural aging, or after natural aging. It's mostly used to relieve stresses, so when you machine it, it won't move on you. We used to call it potato chipping, when we were machining plate.

Aluminum Temper designations are confusing, because they aren't exactly intuitive.

http://www.aluminum.org/sites/default/files/AEC presentation 160224.pdf slides 23 - 25 are mostly what I'm talking about.

But yeah, heat treating Al is pretty easy in terms of equipment. You can do it in air. Solution is around 1000F, and artificial aging is around 300-500F.

Which, BTW, for those of you with Aluminum bake ware, it's the reason they usually say don't cook them over 350-400F.. it's not just the coating that goes bad, the Aluminum can lose about 70-80% of its strength.
 

Saint_Ward

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Bishop

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Phylicia Rashad had never won an Emmy for her 8 year role as Claire Huxtable. She was only nominated twice...
 
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Bill

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Today I learned that the city of Atlanta was once known as Marthasville.

Well that certainly explains a lot of things.
 

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