Shrink fits and retaining compound?

[oxford]

Has anyone ever heated a piece of 6061 aluminum to expand for a shrink and use a retaining compound like Loctite 609? I have a steel tube approx. 1" diameter and 7/8" long that I need to "press" into a piece of 6061. The steel piece has a slight taper to it, I didn't make it and didn't realize it until after I already bored the hole in the aluminum. There is about a .0015 interference at the max but I would also like to put some retaining compound on this to make up for the taper on the end.

I could just press it in normally but I would prefer to heat the aluminum to expand it some but I don't know how the heat will react with the Loctite. Technical data on it says 300 degrees f but I assume that is for when cured. I am thinking that I would heat to aluminum block to no more than 300 degrees f for this. Does anyone have an experience with this?

[Doozer]

If you heat Loctite, of course it melts and releases.
When it cools back down and solidifies, it will hold
again. So as long as you don't scorch the hell out
of it and burn it brown, it should cool down and
hold just fine.

-D

[QSIMDO]

Do I remember correctly that you need the primer with 609 and aluminum because aluminum is a non-reactive metal?

[Forrest Addy]

Treat it as a thermal expansion problem where you work a little math and save yourself pointless guesswork. Thermal expansion is entirely predictable and tables of rates of thermal expansion for different materials abound on Google.

The 1" dia slug is carbon steel which expands 6.5 millionths per degree F per inch for most lean alloys.

The expansion rate of the aluminum part with the interferance fitted bore varies somewhat with alloy but 11 millionths/inch.degree F will serve for this calculation.

The diameters are 1" dia and there is 0.0015 interferance at room temperature.

If the steel slug stayed at room temp how much temperature increase would expand the alumunum ring by 0.0015 to relieve the interferance?

0.0015 / 0.000011 = 136 degrees F temp rise + 70 degrees F room temp = 206 degrees F aluminum part temp

Add some heat to expand for assembly clearance. I suggest warming the aluminum to 300 degrees F, dry, apply LockTite to the steel part and assemble quickly.

[lakeside53]

If you heat Loctite, of course it melts and releases.
When it cools back down and solidifies, it will hold
again. So as long as you don't scorch the hell out
of it and burn it brown, it should cool down and
hold just fine.

-D

Are you sure Loctite retains its properties once heated? It is a form of anaerobic cure epoxy and none I've ever seen are worth beans once heated above their "melt" point.

[garyhlucas]

Two things. A company I know used to put big herringbone steel gears onto 3" steel shafts. The shaft went into the fridge between the beer. The gear went on the $5 hotplate from a yard sale. When the beer was nice and cold and the hotplate couldn't get the big gear any hotter they dropped the shaft right through! One time it didn't go all the way due to a nick. It took a 200 ton press to move it! Second thing. Loctite cures because metal ions are the catalyst that starts the chemical reaction. I used one of their pipe thread sealers and couldn't get it to cure on stainless steel. It turned out that the temperature at the jobsite was below the minimum storage temperature for the loctite!

[oxford]

Thanks for the replies. I did heat up the part for the shrink and used the retaining compound. The tech sheet for 609 did mention shrink fits but didn't give many details on it. The only thing I can say is the excess Loctite that came out the top did set up very fast, whether the heat effected the Loctite's holding power, I am still not really sure.

[Juiceclone]

the actual shape of the item has as much to do with its expansion as the formula ... a ring will expand/shrink along it's circumference not across the diameter and that change will cause a greater diameter than predicted. where a solid bar can exp/shrink across the diameter and. behave more like the exp rate the formulas predict. There are actual circumstances where heating a piece will make the bore smaller because the rest of the mass of the metal is forcing the expansion inward......crazy...

[toolznthings]

Do I remember correctly that you need the primer with 609 and aluminum because aluminum is a non-reactive metal?

Yes, you are correct.

[oldtiffie]

The situation the OP has as I see it is a frustrum of a cone within a cylinder - or vice-versa?

Heating and pressing is normal enough but be sure that the cone does not get "off centre" to the cylinder - or vice-versa - or else solving a problem may result in creating another problem that could easily be avoided and done without.

[Paul Alciatore]

That is not true. The expansion across a hole will be exactly the same as the expansion across a circle of the same diameter drawn on a solid piece of the same material. The amount of change is only dependent on the distance between the two points you are measuring between.

Strange things can happen if there are unrelieved stresses in the part before heating, but that is another thing.

the actual shape of the item has as much to do with its expansion as the formula ... a ring will expand/shrink along it's circumference not across the diameter and that change will cause a greater diameter than predicted. where a solid bar can exp/shrink across the diameter and. behave more like the exp rate the formulas predict. There are actual circumstances where heating a piece will make the bore smaller because the rest of the mass of the metal is forcing the expansion inward......crazy...

[PStechPaul]

the actual shape of the item has as much to do with its expansion as the formula ... a ring will expand/shrink along it's circumference not across the diameter and that change will cause a greater diameter than predicted. where a solid bar can exp/shrink across the diameter and. behave more like the exp rate the formulas predict. There are actual circumstances where heating a piece will make the bore smaller because the rest of the mass of the metal is forcing the expansion inward......crazy...

I think this is incorrect. As long as the temperature of the heated part is consistent throughout, which would be the case for a highly heat-conductive material like aluminum, all linear dimensions will increase by the same percentage. The circumference is just PI times the diameter, so it will also increase at the same rate. The force fit clearance is based on diameter, anyway, and there is no easy way to measure circumference of the hole or the shaft. A ring will expand along the circumference according to the same temperature coefficients, so a 1" steel ring with 100 degrees temperature rise will expand to PI*100*6.5*10^-6 or 0.002" circumference or 0.000650" diameter.

The aluminum expands about twice as much so the hole will now be about 0.0011" larger which just about provides a clearance fit. As mentioned above, 136 F makes this 0.0015". If the shaft is not quickly inserted, or if it binds, it will expand and create the tight press fit before the position is established. So enough extra heat would be advised so that the clearance allows time for positioning.

[oldtiffie]

If you have a look at a good reference such as Machinery's Hand Book (MHB) or the internet (Wikipedia included) you will see that changes to a heated (or cooled) metal object have temperature coefficients of expansion that are both liner and volumetric.

So be careful as to which you care to use - and how you use it.

Perhaps its best to try it out on real samples that represent your job - just to be sure.

http://en.wikipedia.org/wiki/Thermal_expansion

https://www.google.com.au/?gws_rd=ssl#q=temperature+coefficient+of+expansion

See MHB "Thermal Properties of Materials" page 402 onwards. See Tables 8, 9, and 11.

See the note at table 9 which says: "Expansion of Various Substances between 32 and 212 deg F - Expansion of Volume = 3 x Linear Expansion"

My MHB is Edition 27.

"Off the cuff" answers and undue haste may not be in somebody's best interests.

[RWO]

Do I remember correctly that you need the primer with 609 and aluminum because aluminum is a non-reactive metal?

It depends on the alloy. 6061 has enough copper in it such that you do not need a primer. Pure alum like 1100 does require a primer.

RWO

[lakeside53]

Yes. I never prime mag alloy chainsaw cases before 242 or 271 Loctite. Never an issue.