Syleng1
Well-Known Member
Dry ice is easier to work with. Most welding gas supply stores sell it. Bring a small cooler and welding gloves. That stuff is nothing to mess with. Freezer burn on bare skin in 0.0001 sec. lol!
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Ex120-2 boom pin and bushings
- Thread starter Syleng1
- Start date
skyking1
Senior Member
I have a few years of experience working with liquid nitrogen, building landing gear parts for Boeing and others. It gets about 200 degrees colder than dry ice, and I am comfortable working with it.
Syleng1
Well-Known Member
That’s cool! I’ve never played with Nitrogen in liquid form. Having done pins and bushings for part of my living for almost 25 years now on heavy equipment the freezer works just fine. I always pop the bushings in the freezer for 24 hrs and pre heat the bore with a small torch to the point where you can no longer touch it with a light glove. Not blue or discolor. Just hot. Then the bushings drop right in. .002” interference fit is typically what I’ve encountered. Sadly once the bore has been machined, bored and remachined I am not sure of the expanded rate changes. But it always has worked. Lol!
Send so pictures of the liquid stuff at work. I’d be interested in seeing that!
Nige
Senior Member
This pin fell in under its own weight after being soaked overnight in liquid cold @ -320F and once everything was nicely lined up. To remove it probably needs something comfortably excess of 100 tons. Big pins like this are easier, they retain the cold. The smaller the pin diameter the less time you have to work with during the installation before it warms up.
Provided the stuff is readily available in your area I'd say that once you've tried it you would never consider doing pins or bushes any other way.
Provided the stuff is readily available in your area I'd say that once you've tried it you would never consider doing pins or bushes any other way.
skyking1
Senior Member
Thanks Nige for that example.
1) pins only shrink so much. There is a mathematical formula for it, so big pin = big shrink
2) bushings are really awesome, as they are a ring of thin metal and they shrink significantly more than a solid pin.
When I was doing it we had aluminum tools to drive them in and set them, because they were not very long and might push out as they warmed up. Long bushings don't do this, like the ones in our gear. You would pull them off the wire, slap them in with your gloved hand, and double back in a few moments with the driver to insure they remained seated.
The parts were titanium scissors on the main gear of the B747 as shown in this picture, and also the nose scissor linkage. This pair of parts is what keeps the wheels from turning sideways on the strut.
1) pins only shrink so much. There is a mathematical formula for it, so big pin = big shrink
2) bushings are really awesome, as they are a ring of thin metal and they shrink significantly more than a solid pin.
When I was doing it we had aluminum tools to drive them in and set them, because they were not very long and might push out as they warmed up. Long bushings don't do this, like the ones in our gear. You would pull them off the wire, slap them in with your gloved hand, and double back in a few moments with the driver to insure they remained seated.
The parts were titanium scissors on the main gear of the B747 as shown in this picture, and also the nose scissor linkage. This pair of parts is what keeps the wheels from turning sideways on the strut.