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Heat transfer times ?
2

Heat transfer times ?

Heat transfer times ?

(OP)

   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

RE: Heat transfer times ?

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????

RE: Heat transfer times ?

Is this for school?

TTFN



RE: Heat transfer times ?

(OP)
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.

RE: Heat transfer times ?

(OP)
  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

RE: Heat transfer times ?

(OP)
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?

RE: Heat transfer times ?

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?

RE: Heat transfer times ?

(OP)
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.

RE: Heat transfer times ?

(OP)
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.

RE: Heat transfer times ?

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.

RE: Heat transfer times ?

Cool the cylinder with something colder?  Liquid Nitrogen perhaps?

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

RE: Heat transfer times ?

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  (www.ecooling.biz)

RE: Heat transfer times ?

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.

RE: Heat transfer times ?

(OP)
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

RE: Heat transfer times ?

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



RE: Heat transfer times ?

(OP)
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

RE: Heat transfer times ?

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.

RE: Heat transfer times ?

(OP)
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

RE: Heat transfer times ?

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

RE: Heat transfer times ?

(OP)
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

RE: Heat transfer times ?

I think that chilling the cylinder will have a problem with ice build up from humidity in the air.

I would heat the screen in a heated tube (hundreds of degrees).  The tube ID would be the size you want the expanded screen diameter to be.  Then have a track  with a carriage that aligns the cylinder and screen.  Then slide them together quickly (seconds).

RE: Heat transfer times ?

(OP)
Sreid
  Yes,On a hot humid day,lots of frost builds up.We have wrapped the shell in shrink wrap to prevent this build up.Removing the wrap just before the attempting to install the screen.
 Your plan of using a tube to support the screen and heat it is a good one. This idea maybe of some help.
  But I come back to the calulations.People can spend lots of time and money on ideas that fail.Where if it was thought about mathematicaly failure would have been evident.Money would have been saved and my life not so tormented. I like calulations that support ideas and theories. It gives an inspiration of hope that something can be achieved.
                               tollie

RE: Heat transfer times ?

I hear you - even rough calculations could shed some light on the possibility of success.  Someone on this forum may prove me wrong but I think your problem is beyond the scope of a set of formulas.  

A transient CFD analysis can determine the rate of temperature change of the sheet and tube in some of the scenarios we discussed, at least if they are at fixed positions. It's much harder to add the effects of moving the sheet over the tube.

ko  (www.ecooling.biz)

RE: Heat transfer times ?


If timbones could think out of the box, may I have the previlege of kinda thinking "inside the cylinder" please?

Is everyone's presumption that the inner steel cylinder is a solid cylinder and not a hollow cylinder, correct, in the first place?

If it is, is it really necessary? Would it not be possible to use a thin (just thick enough for the purpose) hollow inner cylinder?

My initial thinking was that, if at all necessary, this thin hollow cylinder could have threads inside and a solid cylinder could be threaded into it after the sleeve has been shrink-fit.

.

RE: Heat transfer times ?

Nice idea, pandura, tho it seems like the inner cylinder isn't the real problem.  I figured it was a hollow thick-walled tube that could have dry ice inside it during the whole process but that was probably wishful thinking...

I like ko99's idea of clamping a heater around the screen.  

RE: Heat transfer times ?

Still seems like a more complicated process than necessary.  The screen is supposedly etched and is supposedly used for printing.  

So why can't the nickel be plated on the cylinder and etched in place using the inverse of the printing process?

TTFN



RE: Heat transfer times ?


@IRstuff:
Because, I suppose, the etching process is flat, not rotary.

RE: Heat transfer times ?

(OP)
The product is a vacuum roll. The nickel screen would be a cover on the roll. The in side tube would be a 5/8 wall tube 12.75 dia.This has many holes drilled around the O,D, that the vacuum is pulled thru. The tube is bored ,honed and O.D. ground.The roll controls web tenison on converting machinery for the paper,film and foil industry.The screen provides micro holes that will not deform a coating or the very thin materail being coated.It also has a provides a fine finish 16rms maybe.
 The operation to install the screen will be somewhat complex. If it was easy ,it would have already be done by now .This is what brings me here to maybe find brains better than ours.
                         Tollie

RE: Heat transfer times ?

How big are the holes in the cylinder and the sheath?

TTFN



RE: Heat transfer times ?

So how are competing products fabricated?  

Is this process sufficiently cost effective, even it if worked?  This sounds both labor and capital intensive and is not readily amenable to batch processing.

TTFN



RE: Heat transfer times ?

(OP)
I'm not sure of the size of the holes but they might be .005 .Screens are made on a mandral then the holes are etched into the screen.This is a bought item for us. The holes in the shell the screen goes on, there maybe 10's of thousands .093 holes depending on the size of the roll.
 There is one roll maunfacture that has been sucessful in doing this .How they do it ?? We do'nt know
 The converting machinery is somewhat custom.Vacuum rolls are used to control tension between operations.As coatings and the substrates get thinner and machines go faster.The rolls have to be able to handle the materails without destorting the products.This cover or screen would be highly desired for thin flim coating.
 

RE: Heat transfer times ?

OK... I get the idea.  

My personal druthers would be to start with the cylinder with its holes, use something like the wax for a lost wax process to temporarily fill in the holes.  Deposit the nickel.  Etch the nickel.  Lose the wax.

TTFN



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