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 ?
RE: Heat transfer times ?
TTFN
RE: Heat transfer times ?
RE: Heat transfer times ?
RE: Heat transfer times ?
RE: Heat transfer times ?
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 ?
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 ?
RE: Heat transfer times ?
RE: Heat transfer times ?
Perform the opeation with the screen immersed in a bath of hot something?
RE: Heat transfer times ?
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 ht
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 ?
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 ?
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 ?
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 ?
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 ?
RE: Heat transfer times ?
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 ?
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 ?
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 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 ?
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 ?
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 ?
I like ko99's idea of clamping a heater around the screen.
RE: Heat transfer times ?
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 ?
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 ?
TTFN
RE: Heat transfer times ?
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 ?
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 ?
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