Needle bearing thrust washers...carried over

[CharlieDaTuna]

Because  of this statement made by vinceb in a response on the Gamo Gate..

“The reason I'm asking is that needle thrust bearings can indeed be designed for impact loads with intermittent rotation, Timken specifically states that some of their needle thrust bearings are suitable for shock-loaded applications. Perhaps the most common example is the needle strut bearing used in many front-drive vehicles with McPherson strut suspensions. In this application, they obviously get shock loaded.”

 Well according the Service engineering Department that I talked to today, they say that statement is incorrect and that it is not a Thrust Needle Bearing but rather a Sprerical Bearing that is used it suspension systems. Also, there is all the difference in the world between shock and high impact.  Read on.

I thought perhaps I might be wrong. So…. I did about 2.5 hours research on the internet last night and could find absolutely no data regarding impact on thrust bearings or any other bearings for that matter.  Not one bit of impact data anywhere. Although I had been a regional TSA for both Ford Motor Company as well as GM and thought I was fairly knowledgeable about bearing application, I did learn a lot. I looked at all kinds of bearings including Ball Bearings, bearing sets, tapered bearings, Roller Bearings, Sleeve Bearings, Pillow Block Bearings and thrust bearings and many others but my emphasis was on needle thrust bearings.  I didn’t know as much as I thought I did and a lot has changed over the last 40 years. But the principles have not. At 1:30 this morning I finally gave it up but I was far from finished.
Note…. Copied from one of the articles….Common motions include linear/axial and rotary/radial. A linear bearing allows motion along a straight line, for example a drawer being pulled out and pushed in. A rotary bearing or thrust bearing allows motion about a center, such as a wheel on a shaft or a shaft through a housing. Common kinds of rotary motion include both one-direction rotation and oscillation where the motion only goes through part of a revolution, such as with a hinge. Other kinds of bearings include spherical bearings such as ball joints are used in some automotive suspensions and some computer mice.
Gene stopped by this morning and after discussing it (and by the way, Gene just so happens to have an extended working knowledge about bearings and bearing applications and testing) I decided to contact a couple of major bearing companies to determine just what bearing impact data they had available.

I first contacted Timken in Dayton and was put in contact with a guy in the Service Engineering Dept. I asked him whether or not he could provide me with some impact data in the application of thrust bearing and needle thrust bearings in particular. He asked me what I was talking about and that bearings are not designed for impact. There was no such data that he was aware of. Bearings are designed to reduce friction during rotation whether it’s a support bearing, a pillow bearing, a sprerical bearing, as well as several other bearing that he mentioned and not designed to absorb impact. That would be self defeating and  wouldn’t make sense especially with thrust bearings or bushings of any kind. Then he started asking me questions about what I was trying to accomplish and prehaps he could help me out.

I asked him if needle thrust bearings were ever used in high impact suspension systems in the automotive industry. He said that they were not but what is used is Spherical Bearings.

After telling him about applying a needle thrust bearing in an airgun and after ten minute conversation he said that what I was trying to accomplish was impractical and that no bearing made by Timken or any other bearing manufacturer, needle thrust or otherwise is designed for that kind of application and abuse and as far ashe could tell by the discussion, it’s actually self defeating as well as self distructive. I asked him about using a thrust washer and his response was “I was going to suggest that but didn’t because we sell bearings and figured that you would figure it out anyhow”. We both laughed. I had the feeling that there was someone standing or sitting there with him and they were having a good laugh.

Well the guy at Timken beat me up pretty good but I wanted just one more crack at it so I called Boca Bearings in Florida.

I was able to talk to a fella in the Technical application Dept. there and after going through the whole thing again, the responses in effect, all the same. This person did get into some of the application dynamics explaining how and why bearing work the way that they do under various applications and conditions. We talked extensivly about thrust and tapered bearing and about that fact that most thrust designed bearings are designed to have a predetermined measured thrust factor (measured in inch pound and in larger application, foot pounds) and although some needle thrust bearing can handle a high thrust, they of course not designed for and cannot handle high impact.

I got into the application in the springer airgun and he stated that no bearing, needle or other wise would be a choice under those conditions. And then he asked me a question…. And it couldn’t have been a better question to ask. He asded (Do any of the springer airgun manufactures use them??) I of course said “no”. His response was “I wouldn’t think so.”

Just thought I would pass this on…and I still maintain…as does major bearing manufactures…. needle thrust have no place in a springer as some might suggest and a couple of others support. My personal feeling is that a couple of people can’t be right and the rest of the world wrong. That said, it’s the owners gun to do with as he pleases and if elects to bypass logic, the airgun industry and bearing manufactures, that’s his choice.

[Splash]

Now I may not know much,but I do have real good common sence. If there is a bearing that can withstand the shock loads of a springer, it still would not work any better than 2 properly polished and lubed SS washers, so why bother with them. Also if they were so good the higher end springers would already have them in there. I know that I would not have one in mine and I doubt the people that have them in theirs will get there gun replaced when they get trashed, because it came apart. Thats just my oppinion take it or leave it.

Mike

[Gene_SC]

Thanks Bob for taking the time to do your home work and pass it on to all of us. I spent over 20 years in the heavy transmission and differential businessfor big rig trucks and medium trucks OEM's. I spent many hours with Rockwell, Spicer, Fuller and Borg Warner with warranty issues and the thrust bearings were being used in some of the larger applications and were failing. Millions of dollars was spent on warranties to replace these components because of premature fatigue of thrust bearings. As you were told the thrust bearings are made to sit between to rotating surfaces and not to absorb impact. They were designed to float. Most of the ones I have dealt with would sit on a ridge which centered the baring between the two surfaces. Tapered Timken bearings would be used at each end of shafts with shims to set a pre-determined preloads. Due to wear on the tapered bearing they would lose there preloads and the two shafts would start pounding the thrust bearings between them. Causing them to break up and eventually passing through the gears and other bearings. This would cause seizing of bearings, bearing cups and complete failure. So the big boys learned there lessons and pretty much stopped using thrust bearings all together in there transmissions and differentials applications and started using steel thrust washers and in other applications two thrust washers with a fiber washer in between them. This all makes sense to me because I saw the failures and what the cause of the failures were. Just my own on hands experience. Gene

Hey Bob/Charlie:  I wouldn't use a needle bearing thrustwasher as I feel that the benefit over polished spring ends/seats or flat washers, properly lubricated, wouldn't be worth the risk of damage if and when things do go south.  

Just a quick question though.  Would the bearing actually be subject to impact (as in the truck transmissions after wear opened up the tolerances) or only increased load as the spring preloads the bearing which should prevent pounding (impact).  Would the bearing be subject to pounding when the piston bounces off the compressed air column during the firing cycle (assuming it actually does bounce) or does it remain under a varying load throughout the entire shot cycle?  In any case, I agree with you, needle bearing thrust washers are an un-necessary hazard to spring piston airguns.

[CharlieDaTuna]

Hey Tom I'm glad that you brought that up. I didn't try to publish everything that was discussed cuz I couldn't remember it all and in addition to that, if I could, it would just about fill a book.

When talking to both Boca and Timken the subject of the what amount of pre-load was on the bearing considering the preload on the spring and the bearing under the tophat. When I informed them that it could be anywhere from 50 to 75 pounds applied uncocked by the main spring and when cocked again depending on the spring, anywhere from 160 to over 200 pounds pressure when compressed to within 1/2 inch of coil bind.

They both made statement to the effect that this was way beyond the design of that or any type of thrust bearing and went on to say that because of the weight of the piston and tophat (I explained that a topp hat was as used in a springer) that the acceleration and momentum when it hit bottom, the impact  would be extremely high. And you are doing this to a needle bearing that is very small, about .750 inches in diameter with very small needles in a very small cage being very thin.    One also said, and when mentioned I realizes it to be true, there would likely also be a double impact because of bounce although the second one not nearly as severe. Regardless, tht bearing is taking a tremendous impact  beating. :0

Another way to maybe understand just how much energy is developed and applied to a thrust bearing during (same only different) the cycle is to think about a side cocker or under lever cocker. If you have cocked the gun and are loading a pellet into it and the beartrap fails while your finger is in there, the energy developed  can very easily take your finger off with just one impact and the very reason so much extra care must be takes when loading them.  

Again, a much more efficient way to resolve the isse is to use a stainless steel or a polished grade #8 washer between the tophat and p[iston  if a tophat is used and polished double washers if no tophat is used. That said, there will always be someone that buys into someone elses "answer" simply because they don't understand or know the "facts" or alternatives.