compression by different thermal expansion

[pardal]

Hi all bolt people:

My task to do is to generate a compression force between two plates when they rise it's temperature from ambient to 480°C
This 300 mm diameter round Sae 1010 plates 38 mm thick, will hold a stack of about 100 each Sae 1070 1mm thick to be flattened .
This, can be called sandwich, will be hold by a 40 mm round SAE 4140 threaded bar heat treated as a 12.9 grade bolt.
To build up a increasing compression , I intent to put a spacer over one plate and under the nut that will tighten all the array , this spacer shall be of a material with a different thermal expansion from the others components.
I thought on a aisi 304 hollow bar as it have a thermal exp coefficient about 17E-6 micro mm/meter/°c
and the carbon and alloy steel had about 10e-6 .
My concern is about the behavior of all this array at the 480 C temperature, it will be about 4 hour since this temp is reached.
The task to cope, is to avoid a loss on the compression, so all the 1070 plates are gathered side by side , so they will last flattened when this force is released, of course that it will happen after the eat treatement.
Any comment will be granted.
You can reach me at k281969@hotmail.com
but keep your post here for mutual benefits.
Pardal

 

[ishvaaag]

So you will be wanting mainly to keep some defined minimum force acting on the array of sheets plus padding all along the heat treatment process, starting from an initial situation. This is an analysis on the effect of temperature the axial stiffness (mainly) that one should be able to ascertain through some worksheet or spreadsheet work.

If what compressed and what causing the compression have the same coefficient of thermal expansion, the initial compression force won't vary. If what compressed expands more, the force will increase, and if it is what causes the compression, the compression force will diminish.

 

[RiBeneke]

I have not encountered a procedure like the one you are describing.

Your combination of materials for the differing expansion seems correct. However I wonder why you need to create more compressive force on the bolts than the force that could be achieved with the initial tightening before heating.

The bolts of grade 12.9 are not likely to keep their strength at temperatures above 500 deg C which is s normal stress relieving temperature, so it may be better to use larger low grade bolts.

I am not sure that heat and pressure will flatten thin 1mm plates. If the heating and cooling is not uniformly distributed throughout the thickness, you may actually cause warping. Would a roller-straightening process not work here ?

 

[pardal]

Hi Ishvaaag and Ribeneke:
Thanks both you for your comments.

To Ishvaaag:

If what compressed and what causing the compression have the same coefficient of thermal expansion, the initial compression force won't vary.

> of course , that's why I want different thermal expansion

If what compressed expands more, the force will increase, and if it is what causes the compression, the compression force will diminish

> The plates a fixtures to hold it have a less expansion coef., and the spacer had more so if the spacer is confined between less thermal expansion , it will generate a compression force at all the array , thus it will absorb any play at the fixture, so it will ensure the flattening of plates
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To RiBeneke

I have not encountered a procedure like the one you are describing

> Hope it is so, I always try to develop new method doing any thing, " I do BRAINSTORMING"

Your combination of materials for the differing expansion seems correct.

> I do agree.
However I wonder why you need to create more compressive force on the bolts than the force that could be achieved with the initial tightening before heating.

> Because I do not know the array under heat treatment behavior, in this way I can compensate any loosening.


The bolts of grade 12.9 are not likely to keep their strength at temperatures above 500 deg C which is normal stress relieving temperature, so it may be better to use larger low grade bolts.

> Here my knowhow is poor , the only restriction is that the bolt could not be more than 40 mm diameter and its length no more than 700 mm nuts included.
Why should I use a low grade material, which one?


I am not sure that heat and pressure will flatten thin 1mm plates. If the heating and cooling is not uniformly distributed throughout the thickness, you may actually cause warping.
> I did a test and it works good. I got a 0.1 mm deviation from flatteness. It is enough for me

Would a roller-straightening process not work here ?
> No it can not be used, the plates have an irregular profile .


The method I'm developing will ensure that the work will be done well , and it can be performed by heat treatment workers , whit no specials skill.

Thanks again

Pardal.










You can reach me at k281969@hotmail.com
but keep your post here for mutual benefits.
Pardal

 

[ishvaaag]

Well, I suggest you make a list of the stack thicknesses and areas and coeffs of thermal expansion alfa(T), plus that of the rod or rods, and E(T) of the same if the variation of the modulus of young in the range of temperatures vary significantly. I may find somewhere the data for (some of) the steel(s) but surely only with more difficulty for your special materials. Since in nature your setup finds an equilibrium and no more than expansion and axial stiffness laws are required to -basically- describe your problem, a worksheet in Mathcad should find the solution.

If you provide data enough, I may try to solve the thing.

Respect using common steels instead of high strength is because many lose the high strength when heated above particular temperatures due to physical change in the structure of the steel (hence the bolts softening the pressure), whilst the ordinary steels show proportionally less degradation.

 

[pardal]

This 16 april I will send to heat treatment the array only tighten by 9 each 5/8" by 8" , I will see what happen then .
Thanks again.

Now my concern is how to assembly all the array, I had been working 4 hours to assembly 3 diferent plates totalising 47 plates.
It is a huge work to do.
This task was done by my self, but I shall desing the fixture in such a way IT CAN BE DONE BY NON SKILLED WORKER.

THIS HISTORY WILL LAST A LONG TIME FROM NOW.

.








You can reach me at k281969@hotmail.com
but keep your post here for mutual benefits.
Pardal