Shrink fit

[Gordon]

I am trying to shrink fit a steel cylinder into an aluminum sleeve. Drawing called for .001 to .002 press fit. I put the aluminum sleeve in my toaster oven at 200* but it was still a very tight fit. I think that the temp was too low. Any input on temp for shrink fit.

Gordon

 

[Cogsy]

If your aluminium part doesn't have any other material on it (seals, bearings, etc.) then you can get it as hot as you like, short of it becoming plastic or melting. No reason not to get it up as hot as your oven will go. But if it's thin then the aluminium will cool very quickly when exposed to the cold steel. In my experience of shrinking crank bearings into dirtbike cases, if it's not lined up exactly and won't just drop-in instantly then it will freeze within 2 to 4 seconds and need a press to go all the way home.

 

[Gordon]

If your aluminium part doesn't have any other material on it (seals, bearings, etc.) then you can get it as hot as you like, short of it becoming plastic or melting. No reason not to get it up as hot as your oven will go. But if it's thin then the aluminium will cool very quickly when exposed to the cold steel. In my experience of shrinking crank bearings into dirtbike cases, if it's not lined up exactly and won't just drop-in instantly then it will freeze within 2 to 4 seconds and need a press to go all the way home.

So the steel part should just drop in to the aluminum? 2 to 4 seconds does not give me time to even walk over to the arbor press. I have never done this and the plans call for more shrink fit parts.

Gordon

 

[Cogsy]

Sorry, I mean 2 to 4 seconds once it contacts the steel. You do want to be as quick as you can once you get it out of the oven but it gets critical once the two parts come together.

For the dirtbike cases I would heat the case to around 150 C (no hotter because the crank seals couldn't handle it) and freeze the bearings to -20 C overnight in the freezer. Once I was ready to go, the bearing was sat onto the bore and at the very slightest tap with a hammer handle the bearing would fall to the bottom of it's seat - as long as it was near perfectly lined up. If it wasn't lined up I needed to give it a few raps with the hammer handle and it would invariably freeze in place long before it seated.

What size is the bore in the aluminium? I can work out the amount it will grow to give you an idea of how hard it will be to get the cylinder in.

 

[Gordon]

The bore is 15/16" . The drawing calls for .001 to .002 press fit. Is there some formula to determine how much the ID will expand? I would assume that there is a point where more heat has a diminishing affect. That is like perhaps 400 F is not going to expand much more than 300 F. Sorry us yanks have never wised up to the much superior metric system.

 

[Cogsy]

There is a (fairly) simple formula based on the change in temperature and the coefficient of thermal expansion for the material (which changes depending on the material). Until you get close to melting point, the relationship holds so 400 will expand more than 300.

I did the sums based on 350 F and got an expansion of the bore of about 0.003 inches. So in theory the cylinder would drop in but in practice, almost as soon as the steel touches it it will be cooling down to an interference fit again. If you heat it to 450 F then you will have about 0.0045 expansion so it should go in relatively easily.

 

[Gordon]

There is a (fairly) simple formula based on the change in temperature and the coefficient of thermal expansion for the material (which changes depending on the material). Until you get close to melting point, the relationship holds so 400 will expand more than 300.

I did the sums based on 350 F and got an expansion of the bore of about 0.003 inches. So in theory the cylinder would drop in but in practice, almost as soon as the steel touches it it will be cooling down to an interference fit again. If you heat it to 450 F then you will have about 0.0045 expansion so it should go in relatively easily.

So apparently my main problem was just not getting it hot enough. I have them together at this point and I do not want to take them apart or remake them to find out at this point. The parts went together with a LOT of pressure on the Arbor press so I would assume that my heating to 200 did almost nothing. Thanks for the input.

 

[bobm985]

You can cool the liner in a mixture of dry ice and either acetone or MEK, about -100 degrees F., and measureable shrinkage. Wear gloves and use tongs. Should drop right in the hot sleeve.

 

[Richard Hed]

You can cool the liner in a mixture of dry ice and either acetone or MEK, about -100 degrees F., and measureable shrinkage. Wear gloves and use tongs. Should drop right in the hot sleeve.

MEK? Isn't that the explosive dehydrant? That's too dangerous to use in any case!

 

[Noel Gordon]

Placing you steel liner in your freezer for 8 hours plus heating the ali it will just fall in....trying to heat the ali in a toaster or in your cooker is simply not hot enough,,,you need to buy a small gas heating torch THEN you will find everything happens so easy.. Keep trying..

 

[stanstocker]

MEK? Isn't that the explosive dehydrant? That's too dangerous to use in any case!

MEK is Methyl Ethyl Ketone. It's a very common solvent, the explosive air mix ratio is well past the point where you would leave the area due to the irritation caused by breathing. If you've ever used the water thin liquid plastic model solvent / plastic weld you've used MEK. Many serious scratch builders of styrene models buy MEK by the gallon. It's about like acetone in terms of health issues, I wouldn't breath the fumes for 8 hours a day every day, or bathe in it, but small occasional exposure to minor fumes or a small bit on the skin is not a big deal.

It, like some other common chemicals including acetone and sulfuric acid, is on a precursor list for drug manufacturing. No big deal in the quantities a small shop person is going to buy at a big box store, but if you need 55 gallons of it you'll need to fill out some forms. Odds are MEK is somewhere in some explosives manufacturing process stream, but then lots of things are (like charcoal, ammonia, all sorts of things you use all the time). It also can be used to smooth old convertible plastic rear windows that have gotten all scratched up and nasty, a friend used it on his MG back in the 70's.

Cheers,
Stan

 

[Richard Hed]

MEK is Methyl Ethyl Ketone. It's a very common solvent, the explosive air mix ratio is well past the point where you would leave the area due to the irritation caused by breathing. If you've ever used the water thin liquid plastic model solvent / plastic weld you've used MEK. Many serious scratch builders of styrene models buy MEK by the gallon. It's about like acetone in terms of health issues, I wouldn't breath the fumes for 8 hours a day every day, or bathe in it, but small occasional exposure to minor fumes or a small bit on the skin is not a big deal.

It, like some other common chemicals including acetone and sulfuric acid, is on a precursor list for drug manufacturing. No big deal in the quantities a small shop person is going to buy at a big box store, but if you need 55 gallons of it you'll need to fill out some forms. Odds are MEK is somewhere in some explosives manufacturing process stream, but then lots of things are (like charcoal, ammonia, all sorts of things you use all the time). It also can be used to smooth old convertible plastic rear windows that have gotten all scratched up and nasty, a friend used it on his MG back in the 70's.

Cheers,
Stan

I'm not sure if it was MEK or some other similar material, but we used it to mix solid propellants (explosives if under pressure). It was dangerous enough to have to be covered and it drew the water out of your skin/lungs/eyes, etc. At the end of the mix, it had to be recovered and not allowed into the air. It was used like we might use water to dissolve sugar and salt, flour in bread but then baked out. In small quantities, I suppose, like many chems. it is not so dangerous.

 

[davidyat]

Cogsy,
You mentioned dirt bike restoration. This got my attention. Did you ride off road? In the early 70's, I raced a Yamaha 175 MX in California Mojave Desert organized events. My only claim to fame was that I finished a point to point desert race called Barstow to Vegas. 165 miles with NO roads! This was the Indy 500 of desert races. Just to finish this brutal race was an accomplishment. A couple of pictures of me taken during an actual race.

Grasshopper

 

[Richard Hed]

Cogsy,
You mentioned dirt bike restoration. This got my attention. Did you ride off road? In the early 70's, I raced a Yamaha 175 MX in California Mojave Desert organized events. My only claim to fame was that I finished a point to point desert race called Barstow to Vegas. 165 miles with NO roads! This was the Indy 500 of desert races. Just to finish this brutal race was an accomplishment. A couple of pictures of me taken during an actual race.View attachment 118651View attachment 118652
Grasshopper

I'm jjust curious, didn't you have to get a gas fill along the way? How did you do that? What about dringking water, food? how didded you do that?

 

[Richard Hed]

So apparently my main problem was just not getting it hot enough. I have them together at this point and I do not want to take them apart or remake them to find out at this point. The parts went together with a LOT of pressure on the Arbor press so I would assume that my heating to 200 did almost nothing. Thanks for the input.

I know that one has to do this very quickly and that it seems that 5 seconds is a very short time--but imagine if you had 5 seconds to save your life or someone elses, and imagine that it only takes 1-2 seconds to do so. You have time to spare--or do you? You going to walk to save yourself? You going to run or hop like a frog? You're going to act quickly, precisely and effeciently and there is no problem. In this case of your shrink fit (I hope we are not talking about yours or my psychiatrist here), you have a couple extra seconds, enough to position the thing and slide it on. Goo luck!--Oh, and have all your stuff prepared before hand (I know you already know this, but just saying . . . .), have your path as short as possible with no obstructions, plenty goo light, etc. etc. etc. Practice in your mind what you are going to do. (My psychiatrist says that's actually about 80-90% as goo as actually DOING it.)

As an after thot, I realized that you can have some glass wool handy, (use the paper side) in order to help keep the hot alum hot as you take it to the other part. But you can also keep your "frozen" steel in a foam container to help keep it cool as you are working. Every little bit helps no matter how little. It always adds up.

 

[davidyat]

Richard,
The way it worked was this. I rode with a club. If you broke down during any race the club would tow you back to your camping area. Typical races on a Sunday were 65 to 80 miles broken up into two loops. Your gas would last 1 loop. You came into the pits, your club would gas you up, clean your goggles, give you some water and send you on your way. You drank about a quart of Gatorade before the race started. If you want to see what it was like, find the movie, "On Any Sunday" and go to part 18. I remember racing along side a few of the people in the movie, even the guy who raced with his dog between his legs. They were really good and passed me a lot in races! Here's a photo of that guy and his dog.

For the Barstow to Vegas race there were 3 gas stops. My Dad and I would drive my van to Barstow. Camp overnight and on the Saturday after Thanksgiving, I would start the race. My Dad would drive to gas stop 1 and wait for me. Then after the club gassed me up, Dad would drive to gas stop 2, then gas stop 3. I raced 4 times and only finished once. If I didn't come through a gas stop, Dad would wait til the club towed me to the gas pit and we would load up the bike and drive to Vegas and drown my sorrows.
Grasshopper

 

[rklopp]

Just remember 6 and 13. Typical machine steels expand at the rate of 6 millionths of an inch, per inch, per degree F. Aluminum expands about twice as much: 13 millionths of an inch, per inch, per degree F. Therefore, a one-inch steel shaft will expand 6 ten-thousandths for every 100 degrees F temperature increase. An aluminum shaft will increase 1.3 thousandths under the same 100 degree F temperature increase. A two-inch shaft will expand twice as much, and a quarter-inch shaft will expand one-fourth as much. It's all proportional to size.

While it may seem that if you want to shrink-fit an aluminum hub on a one-inch steel shaft, you just have to make the aluminum bore 0.001" smaller than the shaft and heat it less than 100 degrees F more than the shaft, think about how hard it can be to fit a 1.000" shaft in a 1.001" hole even when you don't have to do it fast and with hot parts. Thus, you need to heat more than you think and it's best to provide a way to guide the parts into position quickly, such as by putting a pilot on the shaft, or holding the shaft in the lathe tailstock while you slide the hub off of a smaller, preheated pilot shaft held in the lathe chuck.

Shrink fits are much easier on large parts, because the heat transfer is much slower. This is because the surface-to-volume ratio is much more favorable on large parts. Small parts lose heat quickly, and, as soon as the hub and shaft contact, the hub loses heat to the shaft, the hub shrinks and the shaft expands, and at some point they lock together.

You do not gain much besides frost and dew by chilling the shaft. It's a whole lot easier to increase the temperature by 300 degrees F than it is to decrease the temperature the same amount. I would avoid heating aluminum much above 400 degrees F to avoid ruining the age-hardening.

 

[SailplaneDriver]

Here is a shrink fit calculator. Plug in the data and it will tell you more than you want to know including required pressure to fit the parts for a given temperature differential.

https://amesweb.info/press-fit/interference-fit-calculator.aspx

 

[TSutrina]

I am trying to shrink fit a steel cylinder into an aluminum sleeve. Drawing called for .001 to .002 press fit. I put the aluminum sleeve in my toaster oven at 200* but it was still a very tight fit. I think that the temp was too low. Any input on temp for shrink fit.

Gordon

have you done the calculation??? Aluminum 6000 series 13.0x10^-6 in/(in*F) cast 13.7 to 9.0 x10^-6 in/(in*F) stainless steel 10.4 to 8.3 to 6.4 cast x10^-6 in/(in*F) steel 8.3 to 8.0 x10^-6 in/(in*F) example air 80F measured and steel temp heat aluminum to 250F Say 1 inch OD steel ID Al 1in x (1 + 13x10^-6 in/(in*F) * (250 - 80)F) = 1*(1 + 13*170 x10^-6) in = 1 + 2210 x10^-6 = 1.00221 in

heat the aluminum to 200F Al ID x (1 + 9.0 x 10^-6 *(200-80)) = ID * (1 + 0.00108) = 1.00108*ID cool steel by ice OD x (1 + 8.0x10^-6 x(32-80)) = OD x (1-0.000384)=0.999616*OD will work for about .0013 oversize steel 1 inch diam cylinder

Gordon have pushed steel motor stators into aluminum housing. Did it for a OD the size of a 1 lb coffee can. Cocked the iron so had to remove it and start again. Typical approach is to put it into an oven but the insulation would not take that heat. You can by doing using the above calculation determine the temperate where the steel can be pushed out. For motors a torch is used to heat the aluminum. Must be heated uniformly. we used a record player to have a slow but constant speed. The aluminum just dropped off the stator sitting on a block. The steel is a poor conductor so it is always cooler then the aluminum but difficult to calculate.

 

[Cogsy]

Cogsy,
You mentioned dirt bike restoration. This got my attention. Did you ride off road? In the early 70's, I raced a Yamaha 175 MX in California Mojave Desert organized events. My only claim to fame was that I finished a point to point desert race called Barstow to Vegas. 165 miles with NO roads! This was the Indy 500 of desert races. Just to finish this brutal race was an accomplishment. A couple of pictures of me taken during an actual race.
Grasshopper

I just rode dirt bikes in the dirt in my youth. I had a nice (to me) 1974 125 Elsinore that I wish I'd never got rid of (very sort-after and valuable here nowdays). But most of my repairs were on later years 90's-2000's 2-strokes. I still have the last model KX250 2-stroke they made taking up room in my shed. It's been a long time since I rode it but I'm hoping for one more blast before I gt rid of it.