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coollx
06-13-2009, 08:54 PM
I'm intrigued by the idea of shrink fitting and want to get some experience shrink fitting metal parts but have a few questions.

1. Would using a hot plate that has a high temperature setting of about 400 degrees work well as a heat source?

2. When using a hot plate do you simply put the part to be heated on top of it, or do you need to place something between the part and the plate?

3. Also when using a hot plate to heat a large part, could you or should you use a temperature stick to insure the appropriate spot on the part is heated to the correct temperature?

4. Is it acceptable to lightly press or drive one part into a heated one or does it compromise the benefit of shrink fitting?

I appreciate any feedback

Thank you

Dom

chief
06-13-2009, 09:39 PM
A hot plate will work but it will take longer due to the heat dissipation to the atompsphere, a kitchen oven woulf be better. Nothing wrong with a temp. stick.
Rather than driving the part try to heat one part and cool the other,ie.
a shaft sleeve, heat the sleeve in the oven and put the shaft in the freezer.

deltap
06-13-2009, 10:27 PM
400 F seems a bit too hot especially for bearing work. I use a temp stick 250 or 300 to check. Cone heaters work well for bearings but a torch will work in a pinch if used carefully. A bearing should slide on quickly by hand when hot enough. Hold in place against shaft shoulder until it cools and shrinks tight. Our company requires use of 2500 # of force with a hydraulic portapower against inner race to make sure bearing is seated against shoulder as they sometimes come away from a bit from the shoulder when they cool. We use heat from oxy-acetelene torch to install aluminum impellers on steel shafts. Impeller is heated in the hub area and the torch is kept moving to heat evenly. Bore is 2 to 5 inches depending on size of impeller. I have heated the impeller in the hot sun for an hour or so with good results as it heats the whole impeller. If the parts are sized right force should not be required to seat the parts.

Mark Hockett
06-13-2009, 11:20 PM
I have used the electric hot plate method for years while working in the auto repair industry rebuilding transmissions. I set the hot plate on high, place the bearing directly on the hot plate coils and place a small drop of oil on top of the bearing race. When the oil starts to smoke the bearing is ready to install.

oldtiffie
06-13-2009, 11:36 PM
Try here too:
http://www.google.com.au/search?hl=en&q=shrink+fit+tolerance&btnG=Search&meta=

http://www.google.com.au/search?hl=en&q=shrink+fit+calculation&meta=&aq=4&oq=shrink+fit

Carld
06-14-2009, 01:38 AM
If your doing a heat shrink don't plan on heating one part and pressing the other one into it. It won't work.

The last place I worked made large rollers and we heat shrunk the roller to the shaft. We always used a .004" interference fit for everything from a 3" shaft up to a 6" shaft. Be sure the bore is heated way oversize and drop the shaft in fast. Don't freeze the shaft as it just makes the roller shrink faster if it touches it.

Have a stop set up so you can drop the shaft in the bore quickly to the length you want because things start shrinking fast and you don't want it half way in and lock up.

Large parts will allow you more time but small parts will shrink so fast you may not get them all the way together.

We got the rollers to a straw or light blue color. I used a telescopic gauge to measure the bore before I droped the shaft. You gotta be fast to do that, there's no time to dilly dally around when measuring a hot bore. Sometimes I used my calipers.

I used to heat the cam gear on the 855 Cummins cam to 300 deg F and drop them on. I have an electric baking oven I used for that. I also use the oven to heat my welding rods to dry them out.

lakeside53
06-14-2009, 02:12 AM
I have used the electric hot plate method for years while working in the auto repair industry rebuilding transmissions. I set the hot plate on high, place the bearing directly on the hot plate coils and place a small drop of oil on top of the bearing race. When the oil starts to smoke the bearing is ready to install.


That works well if you have steel cages on your bearings (most transmission bearings are..). If the cages are PA (nylon) - 200F is pretty much you can do. The bearing manfs list the max temp data for the bearings.

I use a convection oven to heat the casings, and a digitally controlled heat gun for the bearings. An induction heater best.. but...

lazlo
06-14-2009, 11:53 AM
That works well if you have steel cages on your bearings (most transmission bearings are..). If the cages are PA (nylon) - 200F is pretty much you can do. The bearing manfs list the max temp data for the bearings.

I use an industrial hot plate to heat bearings and small to medium sleeves (up to about 4") -- works great.

Most bearing manufacturers say not to go above 250 F (120 C):

http://www.ntnamerica.com/industrial_mountings.htm

Randolph
06-14-2009, 02:24 PM
In my years of working in a rolling mill for a major producer of flat rolled products I many times had the job of over seeing the assembly of rolling mill components --- the biggest ones being shear pin couplings which were shrunk onto their shafts. Some of the shafts were 30" in diameter and were also keyed in place using two tapered keys. The greatest single piece of wisdom I ever heard concerning shrink fits was this ----

"Never begin the assembly of a large shrink fit until you have readily available all the tools required for its dissassembly. The worst thing which can happen is that your parts seize together before being fully in place."

I have had that advice pay off more than once

Steve Steven
06-14-2009, 03:06 PM
I make a small tool that has a threaded adaptor srunk-fit to a hydraulic jack shaft. THe shaft is .862 dia, I cut the bore of the adaptor to .860-.861 and heat it up till its about 600 deg and drop it on, it fits easily and shrinks fine. The joint is is compression, and an internal shoulder in the adaptor limits how much it can move anyway.

Steve

Quetico Bob
06-14-2009, 03:33 PM
Have not tried the hot plate idea but have had good luck with the female part in the oven at 450 for 1/2 to an hour and throwing the male in a snow bank or freezer. Depending on size of part, + .001 - + .003 on male.

If you need to line up the male you will only have a few seconds to do so. Try to design a flange on one side of the male so it has a stop once dropped in place. Usually any axial force side.

Carld is correct, had a piece stop on me half way through once, tried to press while still hot but it was like instant super gall mega unmovable weld crazy glue thing happening. Ended up spending good half day making to new parts, all part of the fun while learning.;)

Cheers, Bob

lynnl
06-14-2009, 03:49 PM
I recently shrunk new sleeves (17-4 SS) onto my tiller tine shaft, which was 1.250. Turned it down about .065" on the ends where I was sleeving it, and bored the sleeves for about .004" interference.

The sleeves dropped right on, but I'd heated the sleeves to a faint red with propane torch. Of course I left the sleeves oversize for subsequently turning down to size.

I probably should've put the bearings, which were inboard of the sleeves, because I had a tough time getting them on over the new sleeves. I considered that beforehand, but rejected the idea. Oh well, it's a done deal now.

Carld
06-14-2009, 10:16 PM
:D Bob, I know the pain. Most the time I can cut the shaft off and bore it out and start over. Sometimes I have to make both parts over again. :mad: Yep, I have tried to press the seized part in or out and it never comes out.

Shaidorsai
06-14-2009, 10:26 PM
It is the temperature difference between the two parts that counts. When faced with a bearing that can be heated only to a limited temp, say 250F and an interference fit that requires a 350 degree temp difference to slip on, you have to cool the mating part to make up the difference. The coldest stuff I have ever had to use is dry ice in alcohol or acetone. This gets parts down below -140 F. I seem to recall that there is a table in Machinery's Handbook that gives the required temp difference for shrink fitting various materials to themselves and one another by class of fit.

J Tiers
06-15-2009, 01:09 AM
A lot of the shrink fit has to do with the mass of the parts..... You can get away with lots of stuff if your parts will stay red hot for several minutes.....

it's those small parts, and fits that are way down a shaft, that are a problem..... the part won't stay hot for long anyway, and it wants to grab even more since it's cooled by the other part.

Then also you have the parts out in the open, and one is cooling as it heats the other, not to mention losing heat out into the air.

Looks easy with a marine engine crankshaft, or the like. But try that at small scale, and you've got trouble coming.

Usually you want to heat considerably hotter to compensate for teh inevitable cooling. Hopefully you CAN do that, without ruining parts.