Heat Shrink Analysis

[Phamjt]

I was assigned a task of researching the capability of heat shrinking two metal parts (Rod and Sleeve/Hub) together instead of the current process of welding them. Unfortunately I am an intern and I have very limited knowledge on tolerancing and none on heat shrinking.

From what I was able to find through the machinery handbook and Shingey's Mechanical engineering design textbook I am able to calculate the tolerances using the FN5 table for force/shrink fits.

With a diameter of 1.125 for the hub if it was heated up we should get 0.033" interference in the tightest fit. Would it be reasonable to heat the hub up to around 0.005" or are there more factors I should consider? The hub is Ansi 1045 steel so with the coefficient of thermal expansion I should be able to use this formula: Total deformation = αL(delta T)

My calculations so far have primarily been based off of this example as the problem seems similar:

http://docplayer.net/41324995-Shigl...sign-tutorial-3-16-press-and-shrink-fits.html

 

[desertfox]

Hi Phamjt

The one thing you do need is the external forces which act on the interference joint, the interference fit should be based on the external forces the original joint was designed for.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[RolMec]

Hello Phamjt,

adding to above, the structure of the design / calculation process would be
1. define load / forces to be transmitted
2. define external shapes / dimensions of all parts related
3. define a minimum play to assemble the parts in heated state
4. define the assembly process (type of heating, type of connection) and in relation to this the applicable friction factor
--> design calculation with the aim to arrive at a commonly used shrink fit (in metric e.g. r6/H7)

The calculation might be a recursive one, as the resulting required temperature might be beyond the permitted heating temp. for your materials / the diameter of the connection would need to be altered.

Talking w/o a sketch..
when changing from a welded design to a shrink fit, this change influences the shape of the respective parts. E.g. the "hub", instead of just to provide the space for a weld, now needs to provide sufficient "compression volume", i.e. wall thickness.

I feel it would be a wise decision if you'd sought the support of an experienced mechanical designer to run along at least for this time.
Kind regards

Roland Heilmann
Lpz FRG

 

[Phamjt]

Hello,

I really appreciate the guidance on what areas I should focus on before determining whether or not this method is capable or not.
Unfortunately I do talk to a few of the more experienced engineers at my workplace however they don't have much expertise in heat shrinking. Majority of what I am able to learn is through research online before talking to the head engineer to look over my calculations.

As for the design the assembly will be making a steering cylinder and with some formula's I found online I can calculate the tangential stresses and stress concentration factor. Most likely this would also involve induction heat shrinking but I would need to research that more after I work out some calculations.

Thanks again for the advice!

 

[GregLocock]

You might look at Loctite 6 series goop instead of heat shrinking.

Cheers

Greg Locock


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[MechyMarco]

Phamjt,
Bust open your machine design text again. It goes over everything you need. Make an excel calculator where you can factor in things like internal/external pressure. Calculate your stresses and make sure you're safe. Then do a simple thermal expansion calc to figure how hot you need to make your hub to slide over your shaft. Easy peasy.