SHRINK FIT

[askjall]

HELLO,

(1) DOES ANYONE KNOW OF OTHER RESEARCH ON SHRINK FITTING? I AM LOOKING FOR A BOOK I CAN BUY (OTHER THAN MACHINERY HANDBOOK)WITH A LOT OF INFORMATION ABOUT SHRINK FITTING - HISTORY, EXPERIMENTS, FORMULAS, ETC.

(2) I RECENTLY DID A PERFORMED A SHRINK FIT EXPERIMENT WITH 6061 ALUMINUM:

15 INCH DIAMETER X 0.25 INCH DISC WITH 6 HOLES SPACED EVENLY 1.5 INCHES IN FROM DISC PERIMETER. EACH HOLD HAD A DIAMETER OF 0.373 INCHES (REAMED).

I WANTED TO SHRINK FIT 6 SHAFTS WITH A DIAMETER OF 0.375 INTO THE HOLES.

I HEATED THE ALUMINUM PLATE UP TO APPROX. 600F ON A PROPANE TANK.

AFTER I PERFORMED THE SHRINK FIT AND I LET THE PARTS COOL FOR ONE HOUR I BENT THE SHAFTS - NOW THE SHRINK FIT IS LOOSE - I CAN'T PULL THE RODS OUT, BUT I CAN WIGGLE THEM. ANY IDEA WHY?

THANK YOU

 

[ctopher]

I'm not 100% clear about your process and what you are trying to accomplish. You want to press fit rods into 'sheet metal', or press the rods into the holes and let them expand tightly into the holes?

Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 08
ctopher's home (updated Aug 5, 2008)
ctopher's blog
SolidWorks Legion

 

[handleman]

You "bent the shafts". Do you mean that your bent them by grabbing one end that was cantilevered out from the plate and bending it, using the shrink fit to hold it on the other side? If so, I'm guessing you wallered out the dang hole. Were they loose before you bent 'em?

-handleman, CSWP (The new, easy test)

 

[askjall]

IN RESPONSE TO CTOPHER:

I WOULD NOT CALL IT SHEET METAL, NO I DO NOT WANT TO PRESS FIT - I WANT TO SHRINK FIT RODS TO THE 0.25 INCH PLATE.

IN RESPONSE TO HANDLEMAN:

YES - I BENT THE SHAFTS BY GRABBING AND PULLING THEM TO SEE HOW STRONG THE FIT IS - I WAS HOPING THE FIT WOULD HOLD PERMANENTLY.

THEY WERE NOT LOOSE BEFORE I BENT THEM.

 

[drawoh]

askjall,

Aluminium 6061 gets its strength from being heat treated. I doubt this survived being heated to 600[°]F. Annealed 6061 is weak.

Handleman's explanation works for me.

JHG

 

[vc66]

WHY ARE YOU YELLING?

V

 

[drawoh]

Oh, and please turn off your caps lock.

Thank you.

JHG

 

[ctopher]

Can you show a pic? I'm not understanding the 'shrink rods to plate" part.

Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 08
ctopher's home (updated Aug 5, 2008)
ctopher's blog
SolidWorks Legion

 

[handleman]

You are confused. The shrink fit has nothing to do with whether or not the plate will hold up against bending. No matter how tight you make your shrink fit if you continue to use 1/4" aluminum as your base you will continue to waller out the hole. You might get some improvement by thickening your plate to 1/2" or so.

-handleman, CSWP (The new, easy test)

 

[unclesyd]

I don't think you will ever get a shrink fit with a 0.375 hole in an 0.25 Al plate. The 0.25 plate is even too thin for a threaded connection unless you can use the backside.

You might want to look at a drive pin for your application. This depends on load that is going to be applied to the pin.

http://www.groov-pin.com/grooved pins/gpins_knurl.htm

It would help a great deal if you could describe the end use of this component.

 

[askjall]

thank you all.

what if i ran this same experiment with stainless steel - do you think the shrink fit would hold then? or do you still think i have to increase the housing dimension?

 

[MotorVib]

My Machhine Design book by Robert L. Norton had a section on it and some equastion that I have used a number of fits.

The Gear people out there might now more abut this.

I always used the same equastions for both press fit and shrink fits, but I always had the question in the back of my mind was that a valid assum. It has work on 1,000's of units but I always had the question.

Chris

"In this house, we obey the laws of thermodynamics." Homer Simpson

 

[drawoh]

askjall,

You have addressed my objection. You have done nothing about anyone else's.

It all depends on how much force you will be putting on this thing. Is there any reason you cannot tap holes? An alternate design would be to have a half inch shoulder on your shafts and threads and a nut on the opposite side?

What are you trying to accomplish?

JHG

 

[unclesyd]

Can you use something like this type rivet nut or something similar?

http://www.hansonrivet.com/w68.htm

http://www.pemnet.com/fastening_products/pdf/AE_pg12.pdf

 

[KENAT]

askjall, there are lots of threads and even a FAQ or too about 'push fits' and the like generally take a look.

Also, in your OP you don't actually give the tolerance on the holes/shafts - this is what is critical in these types of fits.

Sure you have a nominal .375 shaft and .373 hole but if the tolerance is +-.001 then you could have a line fit.

As to bending the pins, you need to do a simple stress analysis to look at the Brunnelling of the pin in the AL and check this is OK. Simplistically, I think by having an interference fit all you're doing is making sure the pin contacts the plate all over the interface instead of at a point/line.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at

http://eng-tips.com/market.cfm?