EPIC nuts/studs loosening thread (reposting stupid stuff without reading = warning)
08-07-2009, 05:33 PM
#561
And the higher end shops use Inconel... can FR, AMS, and TiAL show their research and prove that one is better or do people just spend more money on shiny polished stainless?
When I got my manifold a brazilian years ago, I picked mild steel for two reasons: First, people I trusted suggested it would have better thermal cycling behavior compared to SS and Second, it was cheaper. I didn't give a rats *** if it was shiny.
When I got my manifold a brazilian years ago, I picked mild steel for two reasons: First, people I trusted suggested it would have better thermal cycling behavior compared to SS and Second, it was cheaper. I didn't give a rats *** if it was shiny.
Pic of mani?
Travis,
The problem is with the expansion of the cast iron side of the connection, the turbine housing mounting flange. When using studs it doesn't matter if they are in an iron, stainless, mild, chrome moly, or titanium manifold because if the manifold expands and contracts, the studs aren't being stretched. The expansion that effects studs is in the turbine flange.
This, of course, only applies to studs and not to bolts. Bolts have the expansion of both the thickness of the turbine flange AND the thickness of the manifold flange to compensate for.
The problem is with the expansion of the cast iron side of the connection, the turbine housing mounting flange. When using studs it doesn't matter if they are in an iron, stainless, mild, chrome moly, or titanium manifold because if the manifold expands and contracts, the studs aren't being stretched. The expansion that effects studs is in the turbine flange.
This, of course, only applies to studs and not to bolts. Bolts have the expansion of both the thickness of the turbine flange AND the thickness of the manifold flange to compensate for.
The bolts/studs ("fasteners") will also warm up, and expand, so there is no issue. It's differential expansion which hurts you
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08-07-2009, 07:12 PM
#566
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We all have failing studs because use (mild) steel not stainless. Read up on THIS:
https://www.miataturbo.net/forum/t35874-20/#post433903
These guys run 304 and it works for them and they tell me normal steel will fail:
https://www.miataturbo.net/forum/t35874-9/#post424085
I do agree that Inconel is the win, but it is insanely expensive.
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08-07-2009, 08:29 PM
#568
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I think you're on 15 types of crack here. Sorry. :-) I'm not sure how what's on the end of a threaded shaft (a nut or a bolthead) will make much difference to how much the middle of the shaft gets stretched.
The bolts/studs ("fasteners") will also warm up, and expand, so there is no issue. It's differential expansion which hurts you
If you have a stud you only have to worry about the red area of thermal expansion. That is the iron only unless I am missing something. Please try to explain how the manifold material would matter if you were using studs.
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08-07-2009, 09:48 PM
#571
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08-07-2009, 09:57 PM
#572
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No, bringing home Machinery's Handbook for a little light reading is FTW, I think.
Stainless Steel - High Temperature Resistance
Stainless Steel - High Temperature Resistance
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08-07-2009, 10:59 PM
#573
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Five minutes on Engineering ToolBox and I built the table below. Why is Corky such a genius for knowing this?
1. note regular steel expands like a quarter less than stainless steel
2. also note mild steel has a significantly better coefficient of heat transfer than stainless so it doesn't hold the heat the same way.
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08-07-2009, 11:11 PM
#575
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The fact that the red area is half the depth of the sum of the mani and turbo flanges suggests that the stud needs to have TWICE the CTE of the flange material in order to "keep up".
I think what happens is that because the stud is the same material, the flanges grow and stretch the stud past its plastic deformation limit, and the stud then stays stretched so it stays loose when it all cools back down.
I think what happens is that because the stud is the same material, the flanges grow and stretch the stud past its plastic deformation limit, and the stud then stays stretched so it stays loose when it all cools back down.
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08-08-2009, 04:06 AM
#579
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The fact that the red area is half the depth of the sum of the mani and turbo flanges suggests that the stud needs to have TWICE the CTE of the flange material in order to "keep up".
I think what happens is that because the stud is the same material, the flanges grow and stretch the stud past its plastic deformation limit, and the stud then stays stretched so it stays loose when it all cools back down.
I think what happens is that because the stud is the same material, the flanges grow and stretch the stud past its plastic deformation limit, and the stud then stays stretched so it stays loose when it all cools back down.
Also, doesnt need twice the CTE is its got only half the material that is expanding.
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08-08-2009, 04:50 AM
#580
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Can someone explain to me why the thermal expansion rate matters? The only measurement I can see that has any weight in the material decision would be yield strength. The studs are heated, which drops yield strength, and then they stretch (plastic deformation). I have proven that this is the problem. It isn't excessive thermal expansion which reduces the torque load, it's plastic deformation.
So if it's not stainless steel, what material do we get studs out of that can handle the stress?
So if it's not stainless steel, what material do we get studs out of that can handle the stress?
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