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| Posted by: cannon ® 10/27/2006, 05:01:03 Author Profile eMail author Edit |
I am intending to join 2 overlapping pieces of hollow bar, by means of shrink fittting the parts, being;
a large tube 212 x 170mm (therefore 21 mm wall); a smaller tube 125 x 71mm (therefore 27 mm wall); a joining ring being the i/d of the larger tube, with a bore the same as the o/d of the smaller tube and 76mm thick My solution would be to not only shrink fit the parts tightly enough to resist tensile forces, but to add a mechanical lock as well. The lock on each join would be a groove or increase in diameter,(male or female)50% of the total distance of the overlap of the parts which will be 76mm.(38mm) According to my copy of Machinery's Handbook, the allowance for shrink fitting steel parts should be .002-.003" per inch or diameter (don't know what that might be in microns or whatever.)
To assemble, I propose to heat the ring to slip it over the small tube, allow to cool, then heat the outer tube to expand it, to allow the ring to slip inside, etc. I can heat to 700c As well as asking for comment on the pure mechanics of the proposal, what degree of expansion would I theoretically expect to achieve by heating the ring/tube to 700c ?
The tubes and ring are from carbon steel spec 20MnVS6, from Atlas Speciality Metals (Aust) and I can post the data sheet. Tensile is "500 -700 Mg Pas" which works out to be 32 to 38 tons per sqare inch. I'd like to work on the low side for safety. If I get a bite on the problem, I'll post a sketch or the project. Anybody game ??
Modified by cannon at Sat, Oct 28, 2006, 03:00:23 |
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Posted by: randykimball ®  10/28/2006, 17:04:26 Author Profile eMail author Edit |
The only input I have is that this is the way they used to put the steel tires on steam locomotives. I have seen it done and it worked well. The tires (yes they call them tires) are thick metal rings that get replaced according to ware. They heated them to around "orange" range and they basically fell on the hubs. When cooled.. well, they stayed on pretty darned well, and took plenty of hammering track joint abuse. I "think" they had to cut them off. I know you have to watch that the heated part stays round during the process or it can get hard to fit to the mate without some forces to overcome the shape interferences. To figure the expansion try this... C = circumfrence in feet
C (.0000063) D = NC then convert your NC back to your diameter to get your expanded diameter. I'm betting Kelly has a caluclator for this somewhere. I don't know it that helps any, but it is a vote of support, at the very least. good luck, The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them. Modified by randykimball at Sat, Oct 28, 2006, 17:38:53 |
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| Posted by: cannon ® 10/28/2006, 19:13:54 Author Profile eMail author Edit |
Thanks Randy.
I did see the "tire on loco wheel" situation on the net somewhere, and I've had some experience with the concept, on a small scale, but never this big. Who is Kelly that has the calculator? cannon |
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| Posted by: cannon ® 10/30/2006, 02:33:24 Author Profile eMail author Edit |
So Randy....
Is there no one out there that could assist with the rest of my questions in my original post? When I consider the postings for the guy putting a pulley on a supercharger, I thought I might have been given more info than so far. That's in no way meant to be a crit, just expessing some dissapointment so far. Come back?? cannon |
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| Posted by: randykimball ® 11/02/2006, 17:22:45 Author Profile eMail author Edit |
Sometimes we post questions about a lost art... I seriously doubt there all that many "out there" that have much experience with this kind of a shrink fit. I have done some and likely have as much expereince or more than most in this area but still do not consider myself enough of an expert to posion your project with my ignorance. .. and we can't make anyone answer the questions posted, all are answered at the free will of those that happen to read the posts. Most likely no one with the required expertise read the question. ... sorry... it happens.. often. This just means you will be a leading expert when you figure out how to accomplish the task well. One of the sad losses with the advancement of technology is the going of those whom had vast knowledge in the black arts. Black arts being those that you learned by doing and from the masters that simply can not be learned any other way as well. The most clear example is the black smith.... ( in my mind's eye I see a wise old gentleman with thick arms hammering away at a project with the skills gained by many years of practice .. I wish I could go back and learn some things from him! .. such people "forged America".) ...and I assume this is where both these terms came from. I strongly suggest you worm your way through the Machinery's Handbook, as I'm betting it gets as close as anything to answering your questions. Additionally, I'd seek out an older addition, back around 10 to 12, when these were still well practiced skills. The Machinery's Handbook is the strongest glue I know of working to maintain these skills. A few years ago I was ask if I could re-babbit the bearings of an old turn table that could not be replaced nor undated to modern bearings. Guess what, the Machinery's Handbook told me exactly how. As it turns out in the end, the tuffest chore was obtaining babbit stock, (I finally found some raw stock in an old junk dealer's shop). The book even told me how to use strips of white pine to determine when the babbit and bearing housings were the right temperature to pour. It explained how to put paper around the shaft and between the bearing housing layers. The results were near perfect. The paper burned away and left perfect fit bearings. I'd have never figured it out, and the method was amazing to see work. I now understand well why babbit bearings were so popular for so long. ... they are renewable. The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them. Modified by randykimball at Thu, Nov 02, 2006, 19:04:59 |
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| Posted by: Kelly Bramble ® 10/28/2006, 19:47:16 Author Profile eMail author Edit |
Well, no calculator, however I'll put it on the list. Cannon, also see /manufacturing_spec/press_fit_force.htm |
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| Posted by: Kelly Bramble ® 10/30/2006, 08:15:14 Author Profile eMail author Edit |
Observations: 1. I doubt you will be able to heat it to 700 degress C without melting or effecting the strength of the material. You should read the spec. sheet and see the melting temperature and consult with your supplier about heat treating effects at thie temperature... 2. Thermal interfearance fits are normally used for fatigue (prevent movement under changing load) - thermal interface requirements. Not, to absorb significant amounts of shear, tensile, torque or compression load normal to the interfearance line. 3. Handling and processing thermal interfearance fits is always a challenge, requires special equipement, trained personnel, and failure normally results in scrapping the parts.
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| Posted by: cannon ® 10/31/2006, 18:32:21 Author Profile eMail author Edit |
Dear Both
Thanks for all the info. I have discovered that a joint of this type with sizes given will hold 130 bar of pressure, which is 70% of fail pressure and that is without the proposed steps. Please now remove my postings from your site. Again, thanks Cannon |
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Posted by: Administrator ®  11/01/2006, 09:08:39 Author Profile eMail author Edit |
"Please now remove my postings from your site. Again, thanks
Cannon" How are others going the learn from your questions? |
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