Heat transfer times ? 2

[tollie]

The problem
:To get .005 thick nickel cylinder 12.75 dia.X 80" long on a Steel cylinder .625 thick ,O.D.being.005-.008 bigger than the I.D. of the Nickel cylinder. Steel cylinder has been cooled with dry ice.Constant heat being applied to the nickle sleeve.
What is the possible time span to slide the nickel on? Can it be done?

Tollie

 

[metengr]

Sounds too complicated and problematic with regard to distortion. For only 0.005" thick, why don't use a nickel plate over the steel OD surface????

 

[IRstuff]

Is this for school?

TTFN

 

[tollie]

The nickel sleeve is a etched screen that will have a vacuum pulled thur it. It comes with a .005 tol.on the I.D.

 

[tollie]

The company I work for has been working on the delvopment of this product for sometime now.I have been thru many experiments with this, that have lacked good engeering basis.No school projects here, just hard knocks

 

[tollie]

The shell or steel cylinder being cooled with dry ice should have the dia. reduced by about .012-.015.Without heating the screen the cold is transferd very quickly, srinking the screen.So,Is it possible to calulate how much heat is needed to maintain the dia. of the screen?

 

[metengr]

The biggest problem I envision with your process is proper fixturing of the outer nickel sleeve. The linear coefficient of expansion for annealed nickel is reported to be 7.28 X [10]-6 in/in deg F versus 7.3 X [10]-6 in/in/deg F for the steel cylinder.

You are going to have to keep the nickel sleeve stationary while attempting to insert the steel cylinder.

One other question - can you longitudinally split the nickel sleeve, fit it over the steel cylinder and braze the seam?

 

[tollie]

My thoughts are to supend the steel shell with the dry ice in it .Fixture the screen to hold it square to the shell in side a movable oven . Heat the screen as it is slid over the shell.
It's lenght of time and heat concentration that I'm not sure of. The screen at only .005 thick has no mass to hold any amount of heat.

 

[tollie]

The selling point of the product is that it is a seamless very smooth surface.The holes in the screen are very tiny.The screens are used in the printing industry for printing.

 

[btrueblood]

You could hook up a welding power supply and pass enough current thru the nickel sleeve to keep it hot while slipping it on. Calculation left to the user.

 

[MintJulep]

Cool the cylinder with something colder? Liquid Nitrogen perhaps?

Perform the opeation with the screen immersed in a bath of hot something?

 

[ko99]

tollie,

It's very difficult to predict this analytically. As was said, the screen will lose it's heat and shrink quickly and non-uniformly. Perhaps you can find a way to *very* rapidly slide the screen in place, but you'd have more control over the process if you can find a way to keep the screen hot during installation.

Instead of an oven, perhaps you could wrap the outside of the screen in a flexible heater that slides along with it, such as

http://www.watlow.com/literature/specsheets/files/heaters/colflx1003.pdf

Wrapping and unwrapping the heater is labor intensive, but perhaps this could be streamlined by adhering the heater to the inside of a larger tube (lower TCE and more mass) which in turn fits over the screen. This tube can be split longitudinally to open and close over the screen. A thermal gap filler could be attached to the heater to insure contact with the screen, such as

http://www.fujipoly.com

ko (

http://www.ecooling.biz)

 

[panduru]

btrueblood seems to have the right kind of approach.

The heating has to be done in real-time, that is, heat the sleeve as you go, as ko99 suggests.

What should concern you is not the amount of time required or the quantity of heat, but how to maintain the sleeve at a constant temperature by replenishing the heat lost.

Also, it will become necessary to heat the sleeve in such a way that there is no temperature gradiant over its length. That means a simple heating blanket would not do.

 

[tollie]

Panduru,
As a matter of fact ,the next attempt my fearless leaders want to try is a blanket.I can not see enought heat being transfered to the portion of the screen that comes into contact shell to keep the screen dia. expanded with a blanket.The shell becomes a heat sink when the screen comes in contact with it.Ko99has had good thought with this by lining another tube with the heat blanket and splitting.
The welding supply idea has come up too,again what happens when the screen comes into contact with the shell.Up the amps to fry me at the other end of the screen? May be too shocking for me.
Is it possible to calulate the possible heat loss and amount of heat to keep up?
To throw another wrench into the matter,the screen after it is on can not have any defects. Just handling has been an issue.The stuff is very easily wrinkled.
I would like to greatly thank everyone for their thoughts on this matter.
Tollie

 

[IRstuff]

I don't see that the heating will degrade, but that the cooling will degrade. Consider that the sleeve is only 5 mils and that you can apply continuous heat. The cylinder, on the other hand, will be continually heated during the operation with no way to maintain its cooled temperature. The more you try to maintain the heat on the sleeve, the quicker the cylinder warms up.

If the operation can't be completed in a short time, the cylinder will warm up too much and expand.

TTFN

 

[tollie]

Irstuff
This is true ,timing would be critical, the operation would have to take place quickly.I have in the past, had bearing journals that were shrunk on a tube with no welding done,Much to my dismay wrong location.By putting dry ice in the tube and heating the journal,I was able to move to a new location.Using the same theory, The problem comes not having enough mass in the screen to store the heat.The iced tube, the screen is going on, sucks the heat out of the screen very quickly.So, how can we matain enought heat in the screen to get on? Quick enough,before thermal expansion of the tube it's goes takes place. Another aspect is, condensation on the tube. Enough heat must be applied deal with the frost that may accumulate.Can calulations be done to see if this is even possible?
Tollie

 

[MintJulep]

This is why I suggested doing the operation in a hot bath. The large thermal mass of the cylinder will not change temperature that quickly. The hot bath will moderate the temperature change of the screen, because the bath and screen will be at the same temperature.

 

[tollie]

MintJulep
Can you elaborate on your idea a litte more.?Would you cool the Cylinder before the bath? How hot of a bath do you think will be needed.?? We did rap the screen in a hotwater blanket once.This only accomplished a mess of ice on the cylinder though.
Tollie

 

[timbones]

Does the nickel cylinder have to be in direct contact with the steel?

Just thinking outside the box here but, perhaps you could fit a cylinder made of an insulating material on to the cooled steel cylinder first. Then slide the heated nickel cylinder on after that. You might even be able to remove the sandwhiched insulating layer after you have the whole thing together.

Tim

 

[tollie]

Timbones
The nickel cylinder ends up a srink fit on the steel cylinder.The steel being.005-.008 bigger than the I.d. of the nickel sleeve.Out side the box is good ,Cause I been trapped in it with no way out.I have had some sucess with another method.We buy the screen measure the I.D.on a gauge .Then build the steel cylinder to .001 over the I.D. With some fixtures and a good come a long ,I have been able to pull the screen on .The promlem comes when the screen has to be changed due to damage or imperfection. The tolerance on the screen I.d is .006 .We have not been able to drag one on with more than .001 interference.Less than that the screen is loose.
Tollie