I am pressing a 30 inch O.D. x 2.75
I am pressing a 30 inch O.D. x 2.75
(OP)
I am pressing a 30 inch O.D. x 2.75 inch thick steel sleeve into a mating steel cylinder, that has an average of (-.023 inch) diameter interference. This will be a field installation and I am using 12 each equally spaced 1/2-13UNC jacking studs/nuts (120ksi U.T.S) to pull this thing together (studs go through thru-holes in a flange on the sleeve and are threaded into holes in the mating hub. Nuts on the other end of the studs are tightened to draw the sleeve in). I have calculated a total installation force required of 162,320 pounds. I have used a friction coeficent of (.18) for this press force calculation. I based this calculation on the method described in Shigley's Machine Design text.
To determine the torque required on each jacking nut, I have used 1/12 of the total press force required and used a coef of friction of (.2). Based on other equations in Shigley, I have calculated an installation torque of 223 Ft lbs to draw the sleeve into position. This is a sum of thread torque plus torque to overcome friction between the face of the nut and flange.
NOW FOR THE QUESTION - It has been well discussed that 75-80% or more of fastener torque is lost in friction and does not result in useful axial bolt loading. So I fear that the installation bolt torques that I have calculated will not really provide the sleeve installation force that I have calculated. I am suspicious that the coef of friction values that I have used may be superficially low, but I can not find justification in the literature to use a higher value, or what the higher value should be. Please advise or comment that my approach is legitimate or outline a more appropriate method.
Thanks in advance for advice or referrals.
tc7
To determine the torque required on each jacking nut, I have used 1/12 of the total press force required and used a coef of friction of (.2). Based on other equations in Shigley, I have calculated an installation torque of 223 Ft lbs to draw the sleeve into position. This is a sum of thread torque plus torque to overcome friction between the face of the nut and flange.
NOW FOR THE QUESTION - It has been well discussed that 75-80% or more of fastener torque is lost in friction and does not result in useful axial bolt loading. So I fear that the installation bolt torques that I have calculated will not really provide the sleeve installation force that I have calculated. I am suspicious that the coef of friction values that I have used may be superficially low, but I can not find justification in the literature to use a higher value, or what the higher value should be. Please advise or comment that my approach is legitimate or outline a more appropriate method.
Thanks in advance for advice or referrals.
tc7





RE: I am pressing a 30 inch O.D. x 2.75
Man, I really have nothing to offer, other than these questions:
Are you sure your 75%-80% torque loss is figured correctly for 1/2-13UNC fasteners?
Can you press fit the sleeve in, rather than torque it down?
RE: I am pressing a 30 inch O.D. x 2.75
What are the materials and coatings for all parts? Will the screws be simultaneously tightened? If not, then standard torque/force relationships will not apply.
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: I am pressing a 30 inch O.D. x 2.75
I'm not sure if my suggestion will be practical for a field installation, or for the size of the components, but here goes.
First freeze the sleeve for about thirty minutes -- a bed of dry ice should do well.
Heat the cylinder as UNIFORMLY as possible just prior to sleeve insertion.
Insert the sleeve as quickly as possible --- I have had the good luck of the pieces sliding together by hand with very little effort.
I have used this method on smaller cylinders and sleeves with negative interference. It works quite well if you don't waste any time after you have started the installation.
Hope this helps,
ietech
RE: I am pressing a 30 inch O.D. x 2.75
Please disregard my suggestion above won't work on something that large. I misread your dimensions as 30" long x 2.75" dia without reading carefully, I gotta slow down a little.
ietech
RE: I am pressing a 30 inch O.D. x 2.75
Sleeve is unplated ASTM A514, (110-130ksi UTS, 100 ksi YS)
(by the way the sleeve wall thickness is 0.65", not 2.75 as originally posted).
Cylinder is unplated ASTM A514 with wall thickness of 2.75.
Studs are unplated ASTM A193 Grade B7, (125 UTS).
Nuts are unplated ASTM A194 Grade 2H, (Rockwell C24-38).
I will use some form of lube or antisieze on sleeve and nuts.
I will not be able to tighten all nuts simultaneously. Will use a cross pattern or, just go around the circumference loading each nut up to the installation torque (or some value less than the thread shearing torque) for as long as it takes.
tc7
RE: I am pressing a 30 inch O.D. x 2.75
From practical experience, putting a good solid lubricant anti-seize on the threads and between the nut and washer will allow a nut to pull bolts in tension to failure. Without the solid lube, dry bolts will fail in torsion with an unknown tension value. Lesser lubricants create results in between the two extremes (light oil adds roughly 15% to the tension achieved).
Your interference is fairly high, which indicates you want a good grip after assembly - during operation of the equipment. The planned interference will also cause dry steel materials start to gall, which greatly increases your friction factor during assembly. Lubricants will reduce friction, helping with assembly, and reducing or eliminating galling, but they will also reduce the grip. With a reduced grip, the sleeve may walk out of position during operation. Some Lock-tite or Belzona type products will add lubrication during assembly and increase grip after they set up.
Heating the sleeve or cooling the cylinder is a common method used to assemble parts like yours, and it avoids all the problems discussed above. It’s easy to calculate the temperature difference needed. Remember to install hard stops to assist with axial location, and a method to hold the part up against the stops while cooling, because loose parts will tend to back off a bit as they cool. You also need to have insulated gloves and appropriate slings, etc.
Good Luck! Paul
RE: I am pressing a 30 inch O.D. x 2.75
Bob Setree
Robert Setree
www.advanced-grinding.com
RE: I am pressing a 30 inch O.D. x 2.75
I agree that the diameter interference is extreme. The fact is we have been forced into a situation where we must attempt to use an out of tolerance sleeve that has been delivered to us, rather than send back to the vendor. Therfore I need to show that the designed in jacking provision either can or cannot withstand the additional interference load before I resort to a shrinking technique or before I declare the sleeve is not salvagable.
Thanks for thinking about the problem.
tc7
RE: I am pressing a 30 inch O.D. x 2.75
RE: I am pressing a 30 inch O.D. x 2.75
The problem I see with your method is getting the sleeve to
go on square if the bolts you are tightening down are not done simultaneously.
Is it not possible for you to have one large screwed rod
with one nut on which passes through the center of the sleeve and connects rigidly in the mating part, you could then use a one piece round collar to press home the sleeve
and thus eliminate any out of squareness.
regards desertfox
RE: I am pressing a 30 inch O.D. x 2.75
If you use fine thread fasteners you will have more pulling strength available. It will take about 15,000 lbs. pull to break a ½ NC grade 8 cap screw, and about 17,800 lbs, pull to break a ½ NF grade 8 cap screw.
RE: I am pressing a 30 inch O.D. x 2.75
Is the 15,000 lb. breaking load on the UNC which you cited based on field experience? or on calculation? I can calculate ~14,800# causing yield, and ~17,000# causing rupture.
Also, I'm calculating ~150 ft lbs. torque causing the yield failure at 14,800#. Is this close to max torque values for a 1/2-13UNC in your experience?
I'm also finding that bolt tensile failure during torque-up is far more likely than thread shear failure.
I hope you can comment.
Thanks,
tc7
RE: I am pressing a 30 inch O.D. x 2.75
Good luck
RE: I am pressing a 30 inch O.D. x 2.75
RE: I am pressing a 30 inch O.D. x 2.75
better late than never?
You commented, "I'm also finding that bolt tensile failure during torque-up is far more likely than thread shear failure."
I worked with one M.E. who said they made tests that proved a nut length equal to the bolt diameter would fail the bolt in tenison rather than shear the nut. Machinery's Handbook has a very in-depth article on this subject and Tool and Mfg Engineering handbook is also helpfull. Shigley is well reputed but Machinery's Handbook also has a very good section on interference fits including both shrink and force fits and resulting retention of both types of assembly. One advantage of Machinery's Handbook is that it tends to lean toward more empiracle evaluation rather than just pure theory.
Simultaneous bolting at 180 degrees would certainly help but even if you bolt simultaneously at 120 degrees, I suspect as others have that severe galling will result with such a heavy interference. A simple test would be to use a hydraulic press with the same materials but with a nominal 2" dia using proportional wall thickness, inteference, etc. If you can actually press the pieces together without gall/welding, then you have a good chance of the real article working.
By now it is probably history so this is all academic.
tc7 are you there? What happened?
Jesus is THE life,
Leonard
RE: I am pressing a 30 inch O.D. x 2.75
We even extracted units to confirm that we could do it by the same process and that there was no galling or other damage.
It seems my torque calcs were way conservative and I attribute this to not really knowing the real friction values ( i guess you never do!) and I believe the average interferences were not all as bad as originally reported to me. It was interesting to me to see the amount of flex and conforming the cylinder experienced during the process.
Thanks for asking.
-T