I would like to ask if anyone could please help me select a suitable material for a plane sleeve bushing used in a unique application I am working on.
I need a plain sleeve bushing that will preferably be self lubricating and provide good life in a slow moving, intermittently oscillating application, where the bushing rocks back and forth very slowly and intermittently.
The bushing ID is 1/8" and the bushing OD is 3/16". I am using the bushing as a small cam-follower roller. The cam is rotated manually by hand via a small lever, so the motion is very slow and intermittent. However, the loads are fairly high for such a small bushing, and with the oscillating movement, and the fact that the bushing can only be lubricated once at assembly (and even that will be difficult), I am worried about wear. I want the product to be maintenance free and provide years of service.
I could really use the advice of someone who specializes in Tribology, to recommend the most suitable material and/or lubricant for the bushing, and/or someone who has had real world experience with a steel bushing oscillating on a hardened shaft. I am thinking of using some drill-rod as the bushing material, as I mention below, and I am interested if that may be a viable option.
The maximum load on the bushing will be 7,168 PSI, plus I guess I should have some type of small safety factor. The average bushing sweep angle will be about 42.25 degrees, at an average cycle speed of about 1 to 3 Hz. I think the average surface speed would be 0.46 to 1.4 FPM. The device will always be operated at room temperature, and be in a very clean household environment with no dust or dirt. There is also no chemical exposure & it does not come in contact with food. The bushing will rotate on a hardened steel dowel pin meeting ASME B18.8.2 standards, I can either use plain ground finish, or black oxide finish. I could also go with a 303 stainless shaft if needed. In this application as a cam-follower, the bushing oscillates on a stationary shaft. I could possibly put a very small amount of lube on the bushing at assembly, but never again after that point.
The motion will always last for only a few seconds and then stop. It may last 1-3 seconds on average, say two or three times per minute, and then the rest the time the device is at a standstill, with a static load on the bushing, of about 4,266 PSI, which could also be considered the "average" bushing load, but the maximum will be 7,168 PSI. The load changes as the cam is rotated. It might be used intermittently, for a "total" of about 27 minutes per day, ( i.e., the device is activated a few seconds at a time, a few times per minute, adding up to27 minutes of total intermittent start / stop use, over the course of around 3 hours, each day). Say 9 minutes per hour, with a "turn on" time of 3 seconds, and a rest period of 27 seconds, for 3 hours. If I can get 1,642 hours of service life, the product will last 10 years.
I won't need much running clearance, since the device always operates at room temperature, and since heat from friction will not be enough to cause any significant dimensional changes to the bushing, the speeds are too slow and intermittent. However, I would like to keep the maximum clearance between the bushing ID and the shaft at .004" or less. So, if I start out at a clearance of .003", this only gives me .001" for wear. Maybe I could get away with .002" of wear for a maximum clearance of .005", but I am not sure. I could possibly start out with a smaller clearance, and this would help give me more wear. Ideally, I need something that can provide years of service under these conditions, with very low wear rates.
I tried some plastic bushings frombut found that they were so slippery, that there was sliding between the cam and the bushing OD, because the friction between the cam and bushing OD, was less than the friction between the roller ID and the shaft. Therefore, the roller did not roll on the shaft. This caused the cam to wear a flat spot on the bushing OD. I then tried the "FB" series bushings from but since they are a wrapped or spit bushing, it seems when the bushing seam lines up with the cam, the cam spreads the bushing apart at the seam. Plus the seam causes a little noise, and bumpiness when it rolls on the cam curve.
I thought of pressing the above mentioned bushings into a steel tube, to solve the aforementioned problems, but then the bushing OD becomes about 1/4". I am working in such a confined space, that I cannot really make the cam any smaller at all, because the minimum radius of curvature becomes to small. Therefore, I really need to stay with a bushing that has a 3/16" OD.
I also thought of putting some "belt dressing"on the plastic bushing OD, to insure that the friction between the cam and roller OD is always greater than the friction between the roller ID & shaft, in order to eliminate sliding between the cam and bushing OD, but I just don't know how long it would last, and I need the product to be maintenance free.
Since the plastic bushings seem to be to slippery on the OD, and I cannot press them into a metal tube to make the OD less slippery, since the OD will then be too big, I figure I must need some type of metal roller.
I have not been able to find a stock bushing that meets the requirements, so I am hoping someone can recommend a bushing material I can machine or fabricate the bushings from. The bushings from Igus and/or Peer would have lasted plenty long, but they just would not work due to the problems mentioned above.
I am thinking of trying to use some 3/16" OD drill rod fromfor this cam-follower roller bushing. It's held to close OD tolerance, and I can just cut to length and drill the center hole out. I could then possibly lube it once, and put it in service.
Would drill rod provide both the needed load capacity and decent wear resistance ? Perhaps I can shoot for .001" or .002" running clearance, and then that will leave at least .002" for wear. Do you think I could get a decent service life ?
I will be using a standard 1/8" OD hardened dowel pin as the bushing shaft. It is hardened to Rockwell RC60, and has a surface finish of 8 micro-inch or better.
I can get the drill rod in A2, D2, M-2, 0-1, S-7,or W-1. Which grade would be best ? I am thinking of using W-1.
What type of lube would you recommend ? I can only lube once at assembly, and then never again. I guess the ideal lube would be a high pressure lube that is good for pivoting motion, and that will stay in place, and last. I also have to be very, very, careful not to get any lube on the bushing OD, which looks difficult.
Would a dowel having a black oxide finish help at all, since black oxide has lubricating properties, and it could possibly help retain lube ?
Lastly, would this be just about as quiet as a standard bronze bushing ?
I would really appreciate, and be grateful for any advice or suggestions anyone might have. It seems there must be a cost effective material out there I could make the bushing from, that would provide decent life, and provide quiet and maintenance free operation (it is after all something that is just oscillated manually by hand, and is not driven by a motor constantly). I don't have any way to quickly simulate years of service in a test, but I need to have a reasonable amount of confidence in the material and/or solution. Thank you very much for your help.