EPIC nuts/studs loosening thread (reposting stupid stuff without reading = warning) - Page 30 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 08-08-2009, 06:23 AM   #581
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thermal expansion rate is the rate at which a material shrinks or expands depending on temperature change. Studs and flanges will be at roughly the same temperature at any given time, however if they're different material they'll expand differently. If the flange expands faster, it'll stretch the stud. If the stud expands faster it won't keep the two flanges tight together. Therefore, you want roughly the same expansion rates in both materials, however the different sizes is also taken into consideration, I'm not sure what TravisR did about that, or how this new hardware corrects it.
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Old 08-08-2009, 09:34 AM   #582
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Quote:
Originally Posted by JasonC SBB View Post
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".
Sorry but that is not correct at all.
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Old 08-08-2009, 09:49 AM   #583
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Originally Posted by ZX-Tex View Post
Sorry but that is not correct at all.
FTW Have no idea why I thought that was so funny.

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(From M.net)The length of the portion of the stud which can stretch is illustrated with the red line. The total thickness of the flanges is the green line.

The fact that it 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" as the flanges grow in thickness with temperature.

I think what happens is that when the stud has the same CTE as the flanges, 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. Voila leaky joint.
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(From m.net) Sorry man but that is not right at all.
For the double win <Edit

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thermal expansion rate is the rate at which a material shrinks or expands depending on temperature change. Studs and flanges will be at roughly the same temperature at any given time, however if they're different material they'll expand differently. If the flange expands faster, it'll stretch the stud. If the stud expands faster it won't keep the two flanges tight together. Therefore, you want roughly the same expansion rates in both materials, however the different sizes is also taken into consideration, I'm not sure what TravisR did about that, or how this new hardware corrects it.
Well, actually did soemthing pretty damn dorky. I went in and done a FEA transient heat transfer simulation, and tried to equalize the stud expansion ratio with the flange expansion ratios so that it never exceeds the plastic limit of the stud at temperature... (can that be any more freaking complicated?) To do this, I was loosing alot of joint stiffness with the 316Ti, so I'm looking at a bad boy stainless that has about 3 times the strength of the 316Ti at temperature, and the right expansion rate to keep up with the differences in flange temperature to stud temperature. (There was a difference believe it or not.)

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I am calling BS on your metal doctor, or you - whoever came up with this.
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.
It says right there in your post that low carbon steels get brittle if repeatedly heated below 1650. Chromium is what makes stainless ... stain-less. There are high carbon stainlesses, but i don't know the list off the top of my head. Alot of the cheap stainlesses I believe do have quite a bit of carbon, but the expensive stainlesses replace some carbon with titanium to increase its high temperature properties.
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Old 08-08-2009, 09:58 AM   #584
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Originally Posted by TravisR View Post
(There was a difference believe it or not.)
Yes I completely believe it. Hell I expected it which is why I brought it up. Glad you did that analysis. I am sure the delta-T between the flanges and the studs varied a bit, but what was the max delta-t you saw in your model? I'm curious. Was it during the cruise to WOT transition, or vice-versa?
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Old 08-08-2009, 10:47 AM   #585
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I'm re running the analysis in higher resolution to see if I can get this a little bit better. This is a transient time analysis. SO we can see temperature at any point in time. The analysis is basically going from starting your car to redline max boost in 0 seconds. Then the analysis just begins calculating the temperature of each solid. I will tell you this at 3 thousands of a second there is already a 100*F temperature variance between wall, and the coldest parts. I'll post pictures too I suppose. Flanges were modeled after Garrett T3 flanges from the website, and the turbo was simulated by a large chunk of iron basically, with a stainless header simulated by a long oval tube the same size as the T3 inlet. So it is a little simplified, but a solid representation I believe.

Flow parameters, 1400*F @ 200ft/s and outlet parameter is a pressure exit at 14.7lbs.
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Old 08-08-2009, 11:01 AM   #586
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Quote:
Originally Posted by TravisR View Post
I'm re running the analysis in higher resolution to see if I can get this a little bit better. This is a transient time analysis. SO we can see temperature at any point in time.
Yeah sorry should have stated my question better. I was wondering, looking at the delta-t for various time steps during the transient event, what the max delta-t was between, say the 'average' bolt/stud temp in the grip region and the 'average' flange temp in the stud region. 100F is totally believable IMO.

Not trying to make work for you, just wondering what kind of delta you saw during the transient.

When I was in college working on the FSAE car, I did a transient thermal brake rotor analysis (FDM) in Excel of all things. But it worked! It plotted brake rotor temperatures as a function of radius as the car drove around a virtual race track. It took about 2-3 laps before the temperatures 'averaged' out, though at any given point in the lap they were continuously changing depending on whether the brakes were being applied or not.
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Old 08-08-2009, 12:45 PM   #587
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Default Ok so the rerun of the analysis

This is 200*F and I've seen higher in the simulation. Man that looks rough! Both flanges are 200*F ahead of the studs. Which if you buy studs made from any material on the grade or class system they are more then likely expanding slower then cast, and definitely stainless. Couple that with the flanges high temperature already of about 800-1000 degree average temperature and you have a strong chance of dangling turbo.

Stretchy stretchy.
Attached Images
File Type: jpg D200f.jpg (4.3 KB, 247 views)
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Old 08-08-2009, 01:02 PM   #588
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We know that TEC(stainless) > TEC(cast).
Question is:

TEC(stainless) * deltaT < or > TEC(cast) * deltaT+200

Still I don't think this expanding is the issue. 304-something has been proven te work with Garret flanges under race applications.

Truth is, most of us were shipped steel studs, not stainless from BEGI/FM and replacing it over and over again with steel. I've yet to see properly chosen (not HomeDepot) and installed stainless studs fail.
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Old 08-08-2009, 01:21 PM   #589
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316ti (which is the upgrade to 316, and the huge upgrade to 304) is half as strong at 1200F as it is at room temperature. What you have to do is calculate the induced expansion and see if it exceed the plastic deformation limit. Unless you just barely torque the 316 or 304 they arn't going to last forever, because you will stretch them out from preload. It will just take a little longer to do. Right now the bolts are being stretched an additional .002in for just the stainless flange. Now that alone is 44800psi (.0016 normalized strain). Which is more then what the bolt could nearly be loaded to at room temperature. Put any torque on it at all and its OVER.

What I intend on finding (and think I have) is a bolt which is much stronger at these elevated temperatures, so that from the start the joint can be properly preloaded. Then as it heats up its still got the "stretch" to take the thermal expansion, and it itself has enough expansion built in to handle the temperature differentials.

Lots of edits sorry!

Last edited by TravisR; 08-08-2009 at 01:45 PM. Reason: EDIT EDIT EDIT
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Old 08-08-2009, 01:36 PM   #590
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Quote:
Right now the bolts are being stretched an additional .002in for just the stainless flange
Is that because of the +200F and taking into consideration that the expand themselves as well?
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Old 08-08-2009, 01:43 PM   #591
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Yea, they do expand, but the 316 fasteners are still 200*colder. So 316 is like the best cast scenario. With stainless hardware at least the cast iron isn't really hurting you. Its probably coming out even, because its hotter, but it doesn't expand as fast so your more then likely just dealing with the stainless plate when you run 316 fasteners. With a steel fastener you mise well not try, because they will never take the abuse, and you'll even end up with warped flanges if you use some good grade 8 adamantium. The bolts may hold it together for sometime while the center of the flange expands. After too many cycles of this you end up with an egg shaped flange AND broken bolts. 2 for 1.
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Old 08-08-2009, 05:45 PM   #592
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Would strapping a car to a dyno and using some temperature sensitive paint or maybe just a IR temp reader help to confirm any of the temperatures from the model?

I know someone with a bottle of this stuff (Brake Temperature Paint Genesis Brake Temperature Paint [MD-GEN-GB1000] - $79.85 : MotoDelta Motorsports, Speed - Safety - Reliability) and was considering putting some of it on the manifold, stud end, nut, and turbine housing before heading to the track. Although, without video under the hood I'd only get max temp which is why I mentioned the dyno.
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Old 08-08-2009, 05:53 PM   #593
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An IR gun would probably work. The important thing is to do a good solid long pull. The images you seen were also on the inside rather then the outside, so you might have to be pretty quick to catch it.
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Old 08-08-2009, 06:11 PM   #594
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IR doesnt measure on metal I read. Needs tape or paint, both wont survive there.
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Old 08-08-2009, 07:26 PM   #595
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You could probably pick up some of that brake caliper paint and it would do fine. There's also header paint. You wouldn't have to go nuts, just a couple of sprays on key areas for measurement. It'll crack off in just a few runs. Never lasts.
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Old 08-08-2009, 07:53 PM   #596
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You could put a small hole into the stud and put in a thermocouple. You could probably get several and read them all fairly easily.

I have paint that'll hold up, no problem. But you need some ridiculous high tech equipment to read it, and it only starts behaving at Mach 15 temperatures. :-) We we doing experiments inside the nozzle of the main motor for the space shuttle.

The trouble with the IR guns (there's a calibration issue, but it's not too bad) is they typically have a pretty wide view angle. But you could log a bunch of thermocouples or whatever with a measurment computing USB box, another megasquirt, or whatever.
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Old 08-09-2009, 03:33 AM   #597
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After I re-read my post I realized my mistake. That's what happens when I get a thought and type within 10 seconds.

We have a thermal camera at work with VGA resolution. I've used it to troubleshoot clogged condensers. I'll check if it can read up to 1200*F or so, then I'll borrow it for the next guy who does some dyno tuning around here.
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Old 08-09-2009, 08:01 AM   #598
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Are we actually sure about it just being thermal trouble still though?
Corky is pretty good with his stuff and believes the thermal is not helping but not affecting the stretch its a force applied while its hot. Forces so far marked for investigation are exhaust movement, engine movement or both given the apparent 1G movements seen by most on track.
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Old 08-09-2009, 08:28 AM   #599
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Given that usually a first session is fine, and problems become worse the next session, and each session thereafter indicates that heat cycling is a major issue. Normal steel doesn't hold under those circumstances and forms crystals and becomes weak.
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If high-carbon steel is heated much above the absorption point, its strength is injured, its fracture looks dull, and it is said to be "burned." Such a condition may be impossible to remedy. However, low-carbon steel escapes injury at high heats in most instances, but becomes brittle if heated repeatedly below 1650 F. It is restored to its elasticity if heated above 1G50 F.

The crystalline structure of a piece of steel as affected by heat is determined by the five conditions as follows:

(1) Temperature, (2) duration of heating, (3) mass, (4) rapidity of cooling, and (5) whether or not steel cools without being rolled, hammered, or otherwise subjected to pressure or impact.
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Old 08-09-2009, 05:31 PM   #600
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Alright, so i can have people with these fasteners in a week or so, but you have to de-thread your current assemblies. People with the standard M8 hardware and the upgraded M10 hardware will have to ream the threads out. The new hardware is inch size rather then metric. The M8 size is 5/16 and the M10 size will use 3/8's. The fastener assemblies will be a bolt, with a nut on the end. No washers necessary due to how I selected the materials. The more you abuse your exhaust manifold the tighter these fasteners get. They use these bolts on nuclear reactor steam pipes. We should be good to go.

Price is $80.00 for the M10(3/8) size, and $70.00 for the M8 (5/16th) size shipped. You get 4 bolts, and 4 nuts. There is a possibility of a switch to metric, but I am waiting on quotes. These are off the shelf parts for getting them out there quick. I expect all assemblies to be bolt and nut anyways because this just gives the fastener more life.

If there is one volunteer who we can fully expect to kill their car at a road course and wants to try these for everyone else that would be great. I'm a little uncomfortable selling a fix all regardless of how sure I am without some testing.
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