Joe Michaels
Diamond
- Joined
- Apr 3, 2004
- Location
- Shandaken, NY, USA
The ongoing thread about the stuck chuck plate on Chippinchunk's LeBlond 13" lathe raised the idea of using dry ice to shrink the spindle and help break the bind.
Dry Ice is commonly used for chilling parts for shrink fits, as well as in certain situations, to break bound fits loose. My local welding supply sells dry ice in the form of chips, which is a handy form for use in shrink fitting of parts. Years ago, on a powerplant turbine erecting job, some body-bound dowels needed to be shrunk before being set in reamed/honed holes. The turbine erecting super was an old millwright with plenty of tricks and he was quite happy to teach people like myself- a green young engineer- what he could. He got a quantity of denatured alcohol (shellac thinner is a common version of this), and some steel pails. In those days, the dry ice came in the form of cakes rather than chips. He put the dowels, which were fairly hefty pieces of steel in their own right, and poured in the alcohol. The dry ice was broken into smaller chunks and dropped into the alcohol. As it was explained to me, the alcohol served as an excellent medium for heat transfer (or removal as the case was). Had the dowels simply been put into a box with the dry ice, it would have been a longer time to get them chilled down, and frost would have formed on the steel pins. The alcohol had a low enough freezing point that it remained liquid. The result was a fairly rapid chilling of the dowels.
At the powerplant, we had some large wicket gate bushings to be chilled for shrink fits. The method used was to build an insulated box out of rigid foam insulating board, along with plywood and framing lumber. The wicket gate bushings (made of a self-lubricating bronze called "Lubron") were placed in the insulated box along with cakes of dry ice. It took a good while to get the bushings chilled down since air was the heat transfer medium rather than a liquid.
A few years back, we needed to shrink some large cast iron valve guides to install in an Alco 539 diesel engine's cylinder head. These guides are many time larger than what would be found in an automobile engine. We were rebuilding the Alco cylinder heads in my buddy's shop, which is a good 25 miles from the welding supply. We agreed that since I had an account at the welding supply, I would swing by and get 25 lbs of dry ice chips. I brought a cooler and got the dry ice chips. My buddy had his own method for chilling the valve guides. Neither of us, or the railroad, was going to shell out the bucks for denatured alcohol. My buddy said an oldtimer had told him about using kerosene as the heat transfer fluid. He had plenty of that in his parts washing tank. We got a pail of kerosene and plunked in the valve guides and the dry ice. The effect was surreal. The kerosene bubbled and CO2 came off it, and we heated the cylinder head with a rosebud to help increase the temperature differential.
After maybe 20 minutes time, we pulled the first valve guide. The added benefit was the low temperature of the dry ice had thickened the kerosene so it clung to the valve guide. No frost issues, and a nice lubricant for the fit. By the time we got to the last of the valve guides, the dry ice had turned the kerosene into a grease, which was bubbling like a pot of stew from the dry ice.
About the time we got done with the cylinder head valve guide installations, I was wiping my hands and picking up my tools when there was a hell of a bang about like a 10 gauge shotgun going off. I jumped and started looking around, wondering if we'd overdid things with the shrink fit, maybe had a head crack. My buddy- a notorious practical joker- was standing behind me when I jumped and he burst out laughing as he saw me checking the cylinder heads for cracks. He stopped laughing and said that while I was finishing up, he'd taken some of the left over dry ice pellets and put them in a 2 liter plastic bottle with a little water, capped it up and left it under the shop window where I was working. He then had time to sneak back in and watch the results. I admitted he'd gotten the better of me, and he suggested, since it was my cooler with the dry ice pellets, that I take the rest home and "have a little fun" with my wife.
I arrived home and found my wife and daughter watching some mindless program or other on television. Wife asked how the job had gone, was happy to hear it went well, and I told her about the prank my buddy had pulled. Wife said she wanted to hear the "bang" for herself. I got a 2 liter plastic bottle out of the recycling bin, put in some dry ice pellets and water and put it under the window near where my wife was sitting watching television. I came back in. Bottle went off with a nice bang. Wife was so engrossed in her program she never heard it. She asked after awhile when I was going to let off the dry ice "explosion". I said I'd done it, but she was so wrapped up in the BS on the television that she'd been oblivious to it. She went back to her program. I went back to the recycling bin and got a couple of 2 gallon plastic jugs along with a mess of assorted plastic bottles from soda and detergent. The devil was loose in me as I scooped hefty amounts of dry ice pellets into each of the plastic jugs and bottles. In went some water, on went the caps, and I slipped back into the house and went into my office. A few minutes later, all hell broke loose on all sides of our house as I'd planted the bottles and jugs all around the outside of the house. It sounded like a combination of small arms fire and light artillery. Wife and daughter let out a collective scream while I split my sides laughing. I told them that since the first explosion of a 2 liter pop bottle did not get their attention, I upped the ante and mounted a good broadside. Wife called me a few choice names, said my buddies and I were overgrown kids, and said boys seem to like to blow stuff up. She went on about how the fusillade startled her, and I could not stop laughing, damned near pissing my pants. I told her I'd spent a day rebuilding locomotive cylinder heads and was entitled to let off a little steam. I also said it was a shame to waste the remaining dry ice pellets, so was entitled to have a little fun. Wife shrugged and finally agreed.
The local welding supply also sells liquid nitrogen. They rent Dewar flasks to transport the liquid nitrogen in. It is quite a bit colder than the dry ice and makes a real good means of chilling parts for shrink fits. I've used liquid N2 on some jobs for shrink fits, but for the most part, dry ice does the trick.
At one of the hydroelectric plants, we were faced with some large straight dowels which had been driven into reamed blind holes. We had to get those dowels removed as we were fitting a new mating part, and would wind up line reaming for oversized dowels. All the usual tricks were tried to remove the dowels, which, to add to the problems, were hardened (or surface hardened). No "touching" them with a drill, no tapped holes for pullers. I was asked to take a look and see what I could come up with. Discovering the dowels to be file hard, I had the mechanics "spot anneal" the ends of each dowel with a brazing torch. This softened things to where we could drill and tap holes for pullers. The dowels would not move, despite putting a puller with a hollow ram porta power on them. I got a call to come take another look. This was when I suggested the dry ice/heat method. The crew opened the hole in each dowel to maybe 3/4" diameter and then packed in the dry ice chips. They heated a ring around each dowel on the turbine part the dowels were fitted into. I had them give the dowels a few good smacks with a 3 lb hammer, and then put the Vise Grips to the dowels. Out they came. Everyone was amazed at what a little bit of dry ice in the right places accomplished. I had the other ace up my sleeve, and that would have been to get liquid nitrogen and pour it into the holes drilled in the ends of each dowel. The dowels were oriented horizontally, so making some sort of dam or cap to keep the liquid nitrogen in the dowels would have been necessary. The dry ice pellets worked out handily.
As I have learned over the years, a combination of temperature differential and impact will often break a hard fit or bind when heavy force such as from pullers or porta powers won't break things loose. Dry ice is usually available in most cities. The local welding supply, aside from the dry ice and liquid nitrogen, does quite a trade with entertainers who use the dry ice for special effects, and with people who make custom ice cream at parties using the liquid nitrogen. As I've posted here in other threads, I carry the coefficient of thermal expansion for steel around in my head, and often run rough calculations as to how much something will grow (or shrink) for a given set of dimensions and temperature change. I've designed a lot of assemblies that went together with shrink fits, and the force or "hoop stress" which can be developed in a hub or walls of a bore from a shrink fit can be quite significant.
Dry Ice is commonly used for chilling parts for shrink fits, as well as in certain situations, to break bound fits loose. My local welding supply sells dry ice in the form of chips, which is a handy form for use in shrink fitting of parts. Years ago, on a powerplant turbine erecting job, some body-bound dowels needed to be shrunk before being set in reamed/honed holes. The turbine erecting super was an old millwright with plenty of tricks and he was quite happy to teach people like myself- a green young engineer- what he could. He got a quantity of denatured alcohol (shellac thinner is a common version of this), and some steel pails. In those days, the dry ice came in the form of cakes rather than chips. He put the dowels, which were fairly hefty pieces of steel in their own right, and poured in the alcohol. The dry ice was broken into smaller chunks and dropped into the alcohol. As it was explained to me, the alcohol served as an excellent medium for heat transfer (or removal as the case was). Had the dowels simply been put into a box with the dry ice, it would have been a longer time to get them chilled down, and frost would have formed on the steel pins. The alcohol had a low enough freezing point that it remained liquid. The result was a fairly rapid chilling of the dowels.
At the powerplant, we had some large wicket gate bushings to be chilled for shrink fits. The method used was to build an insulated box out of rigid foam insulating board, along with plywood and framing lumber. The wicket gate bushings (made of a self-lubricating bronze called "Lubron") were placed in the insulated box along with cakes of dry ice. It took a good while to get the bushings chilled down since air was the heat transfer medium rather than a liquid.
A few years back, we needed to shrink some large cast iron valve guides to install in an Alco 539 diesel engine's cylinder head. These guides are many time larger than what would be found in an automobile engine. We were rebuilding the Alco cylinder heads in my buddy's shop, which is a good 25 miles from the welding supply. We agreed that since I had an account at the welding supply, I would swing by and get 25 lbs of dry ice chips. I brought a cooler and got the dry ice chips. My buddy had his own method for chilling the valve guides. Neither of us, or the railroad, was going to shell out the bucks for denatured alcohol. My buddy said an oldtimer had told him about using kerosene as the heat transfer fluid. He had plenty of that in his parts washing tank. We got a pail of kerosene and plunked in the valve guides and the dry ice. The effect was surreal. The kerosene bubbled and CO2 came off it, and we heated the cylinder head with a rosebud to help increase the temperature differential.
After maybe 20 minutes time, we pulled the first valve guide. The added benefit was the low temperature of the dry ice had thickened the kerosene so it clung to the valve guide. No frost issues, and a nice lubricant for the fit. By the time we got to the last of the valve guides, the dry ice had turned the kerosene into a grease, which was bubbling like a pot of stew from the dry ice.
About the time we got done with the cylinder head valve guide installations, I was wiping my hands and picking up my tools when there was a hell of a bang about like a 10 gauge shotgun going off. I jumped and started looking around, wondering if we'd overdid things with the shrink fit, maybe had a head crack. My buddy- a notorious practical joker- was standing behind me when I jumped and he burst out laughing as he saw me checking the cylinder heads for cracks. He stopped laughing and said that while I was finishing up, he'd taken some of the left over dry ice pellets and put them in a 2 liter plastic bottle with a little water, capped it up and left it under the shop window where I was working. He then had time to sneak back in and watch the results. I admitted he'd gotten the better of me, and he suggested, since it was my cooler with the dry ice pellets, that I take the rest home and "have a little fun" with my wife.
I arrived home and found my wife and daughter watching some mindless program or other on television. Wife asked how the job had gone, was happy to hear it went well, and I told her about the prank my buddy had pulled. Wife said she wanted to hear the "bang" for herself. I got a 2 liter plastic bottle out of the recycling bin, put in some dry ice pellets and water and put it under the window near where my wife was sitting watching television. I came back in. Bottle went off with a nice bang. Wife was so engrossed in her program she never heard it. She asked after awhile when I was going to let off the dry ice "explosion". I said I'd done it, but she was so wrapped up in the BS on the television that she'd been oblivious to it. She went back to her program. I went back to the recycling bin and got a couple of 2 gallon plastic jugs along with a mess of assorted plastic bottles from soda and detergent. The devil was loose in me as I scooped hefty amounts of dry ice pellets into each of the plastic jugs and bottles. In went some water, on went the caps, and I slipped back into the house and went into my office. A few minutes later, all hell broke loose on all sides of our house as I'd planted the bottles and jugs all around the outside of the house. It sounded like a combination of small arms fire and light artillery. Wife and daughter let out a collective scream while I split my sides laughing. I told them that since the first explosion of a 2 liter pop bottle did not get their attention, I upped the ante and mounted a good broadside. Wife called me a few choice names, said my buddies and I were overgrown kids, and said boys seem to like to blow stuff up. She went on about how the fusillade startled her, and I could not stop laughing, damned near pissing my pants. I told her I'd spent a day rebuilding locomotive cylinder heads and was entitled to let off a little steam. I also said it was a shame to waste the remaining dry ice pellets, so was entitled to have a little fun. Wife shrugged and finally agreed.
The local welding supply also sells liquid nitrogen. They rent Dewar flasks to transport the liquid nitrogen in. It is quite a bit colder than the dry ice and makes a real good means of chilling parts for shrink fits. I've used liquid N2 on some jobs for shrink fits, but for the most part, dry ice does the trick.
At one of the hydroelectric plants, we were faced with some large straight dowels which had been driven into reamed blind holes. We had to get those dowels removed as we were fitting a new mating part, and would wind up line reaming for oversized dowels. All the usual tricks were tried to remove the dowels, which, to add to the problems, were hardened (or surface hardened). No "touching" them with a drill, no tapped holes for pullers. I was asked to take a look and see what I could come up with. Discovering the dowels to be file hard, I had the mechanics "spot anneal" the ends of each dowel with a brazing torch. This softened things to where we could drill and tap holes for pullers. The dowels would not move, despite putting a puller with a hollow ram porta power on them. I got a call to come take another look. This was when I suggested the dry ice/heat method. The crew opened the hole in each dowel to maybe 3/4" diameter and then packed in the dry ice chips. They heated a ring around each dowel on the turbine part the dowels were fitted into. I had them give the dowels a few good smacks with a 3 lb hammer, and then put the Vise Grips to the dowels. Out they came. Everyone was amazed at what a little bit of dry ice in the right places accomplished. I had the other ace up my sleeve, and that would have been to get liquid nitrogen and pour it into the holes drilled in the ends of each dowel. The dowels were oriented horizontally, so making some sort of dam or cap to keep the liquid nitrogen in the dowels would have been necessary. The dry ice pellets worked out handily.
As I have learned over the years, a combination of temperature differential and impact will often break a hard fit or bind when heavy force such as from pullers or porta powers won't break things loose. Dry ice is usually available in most cities. The local welding supply, aside from the dry ice and liquid nitrogen, does quite a trade with entertainers who use the dry ice for special effects, and with people who make custom ice cream at parties using the liquid nitrogen. As I've posted here in other threads, I carry the coefficient of thermal expansion for steel around in my head, and often run rough calculations as to how much something will grow (or shrink) for a given set of dimensions and temperature change. I've designed a lot of assemblies that went together with shrink fits, and the force or "hoop stress" which can be developed in a hub or walls of a bore from a shrink fit can be quite significant.