[868RM]

Does anyone know if liquid nitrogen is too cold for shrinking the wing bolts. I am concerned about messing up the heat treat properties. Thanks Ron

 

[FLTENG]

I found that dry ice worked very well.

 

[ChiefPilot]

Does anyone know if liquid nitrogen is too cold for shrinking the wing bolts. I am concerned about messing up the heat treat properties. Thanks Ron

I really don't think you need it, and I'm not sure it would really help all that much anyway given the relatively minuscule reduction in diameter it would offer. A brass set for your rivet gun (low-to-moderate air pressure) combined with some light grease is all you really need to tap the interference fit bolts home.

 

[Bavafa]

I used dry ice in alcohol and it helped tremendously. The bolt went in with a lite tab on them and shortly later it started tightening up just in time to get the nut on it.

 

[868RM]

dry ice

Thanks I will try to find some dry ice. There is plenty of liquid nitrogen around but not much dry ice. I will look some more.

 

[LAMPSguy]

Dry Ice

Try at your largest local grocery store. Dry ice is often available in the front near the checkout counters.

 

[RV6AussieNick]

Liquid nitrogen

If you have liquid nitrogen handy i'd use that, it's a lot colder, just don't burn yourself.

Like the other guy said you probably wont need it, either grease or sealant (pro seal) will work well when tapping the bolts in.

One negative with cooling parts is, as they normalise in temp they attract condensation, that can lead to corrosion later on, that is why sealant is a good idea.

Use a wood or brass drift so you don't mar the cad plating finish.

Good luck with what ever you decide..

 

[krw5927]

Can't mess up heat treat properties by getting too cold. Once the bolt gets back to room temp the properties are exactly the same as before.

There's probably a point where the bolt would become more brittle and whacking on it with a hammer may not be wise, but I doubt that would be at liquid N2 temps.

 

[longranger]

...There's probably a point where the bolt would become more brittle and whacking on it with a hammer may not be wise, but I doubt that would be at liquid N2 temps.

I'm a bit skeptical about the last (blue) part of this statement. I'm only a lowly intrumentation engineer, and I know nothing of the metallurgy of Van's wing bolts (other than assuming they are some alloy of high-strength carbon steel) but in several decades of working around liquid rocket test stands I've never seen anything intended to be exposed to cryogenic temperatures (-150F or below) made of carbon steel, due to the loss of ductility at those temperatures. Even with stainless, only certain alloys are used. I know there have been cases of car/truck frames failing in the range of -50 to -100F.

Probably a moot point though, as the bolt at -320F (boiling point of nitrogen) the bolt probably wouldn't require a hammer...

 

[DanBaier]

Just a little Boelube on bolts that had been kept in the freezer worked for me.

Dan

 

[az_gila]

I really don't think you need it, and I'm not sure it would really help all that much anyway given the relatively minuscule reduction in diameter it would offer. A brass set for your rivet gun (low-to-moderate air pressure) combined with some light grease is all you really need to tap the interference fit bolts home.

A 100F reduction in temp of a 3/8 bold will give about a 0.0003 reduction in diameter.

It should help a little...

 

[Dennis Fox]

Dry Ice and 91% Alcohol

Dry Ice and 91% Alcohol Worked for me, But be advised, its a 2 person process. I put the chunks of dry Ice in a Styrofoam cup (tall enough to cover the bolts with mixture)

added the alcohol, as the bubbling slows down (alcohol coming up to temp of - 400*) using tongs or pliers drop the bolts slowly in the slurry and Waite 10 to 15 min (bubbling slows down again) use the pliers to get 1 bolt shake off the left over slurry hand the bolt to your buddy in the plane (he better be waring gloves) install the bolt in the hole toward the front and use rivet gun to push the bolt in. (cannot swing a hammer in those close places). all 20 bolts installed in 2 hrs.

 

[868RM]

alcohol

Dennis, I am not a chemist, but I think -400 f is too cold. Cryogenic treatment starts around -300 f is what I'm told. I tried several grocery stores with no luck. A wal-mart about 20 mi. away has dry ice. Two other wal-marts did not carry it. I have help lined up for sat., dry ice bolts & boea lube lined spars, assembly with no galling is the current plan. Thanks for the help. Ron

 

[fixnflyguy]

Cold Bolts

In the big jet plane maintenance business, we use nitrogen every day for this process, but usually for large diameter bushings,ect. We also use dry ice and alcohol. The reality is, both will work, neither will hurt the bolt or plane, the nitrogen will hurt you if not wearing gloves, and you dont need either for an RV ! The fit should be be close tolerance(hole and bolt about the same size), and not transition (hole smaller than bolt). The factory VANS ream job on my -4 was perfect. I dab the bolt hole with wet primer, and a plastic hammer taped it in. Back up the other side with a bucking bar if needed. You wont hurt the threads, as they are slightly smaller than the shank. Grease is also a good measure, as it will help seal out moisture. The problem with the nitro or dry ice, is that there is little mass on a bolt that size, and the second it enters the spar structure, the bolt transfers the cold and it returns to size...unless you really work fast. good luck.

 

[Bavafa]

Dennis, I am not a chemist, but I think -400 f is too cold. Cryogenic treatment starts around -300 f is what I'm told. I tried several grocery stores with no luck. A wal-mart about 20 mi. away has dry ice. Two other wal-marts did not carry it. I have help lined up for sat., dry ice bolts & boea lube lined spars, assembly with no galling is the current plan. Thanks for the help. Ron

If I am not mistaking, the dry ice and 91% pure alcohol will bring the temp down to -197.x and not -400.

I could not find such pure alchohol yet with 75% alcohol it worked just as described and like a charm.

 

[Captain Avgas]

Does anyone know if liquid nitrogen is too cold for shrinking the wing bolts. I am concerned about messing up the heat treat properties. Thanks Ron

Here's a technical document on shrink fitting with liquid nitrogen.
http://www.liquidnitrogenservices.com.au/shrinkfit.htm

It states that the original mechanical properties of carbon steel high strength bolts will return once the bolt is at ambient temperature again. It does state however that the chilled bolt should not be subjected to "severe blows or shock".

My guess is that the Vans wing bolts are such small diameter that they will gain temperature at a very fast rate once they are removed from the liquid nitrogen. I wouldn't be surprised if they were back to "dry ice" temperatures within 4 or 5 seconds which is probably the time it will take you to get the bolt started in its hole.

 

[ArVeeNiner]

Just grease them up and go tap tap tap with a very light pull of the trigger on a rivet gun. Turn down the pressure. That's how I did it and it was a piece of cake.

Here is my write up: http://www.vansairforce.com/community/showthread.php?t=77978