Shock Resistant Cartride Bearings

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drewdevitt

Күн бұрын

Пікірлер: 14

@ankushatyalkar8035 5 жыл бұрын

Please make a video on aerodynamic bearing. Very less video's are present in this area

@dongchen7940 5 жыл бұрын

Why the radial pad has a "significantly" larger radius than the shaft? Is the air gap that big?

@Molb0rg 5 жыл бұрын

no, air gap is quite small (small fraction of mm, 1/100th or something in the area). the whole thing is big as it contains the pad which distributes air and holds mounting and the porous pad, so as the outer shell is the damping thing, and the whole thing is a cartridge meant to be removable as I may guess (for replacement repair, be suitable as modification to something) so in general it also all takes space etc. compared to actual bearings of that size and load, it about the same in size and in all that

@dongchen7940 5 жыл бұрын

@@Molb0rg Thanks for the reply. I am talking about the picture at 00:16. It seems the gap between the graphite and shaft is bigger than 0.01mm.

@Molb0rg 5 жыл бұрын

@@dongchen7940 you mean in the corners of pads? yes, I see. For me, it looks like they used pads which are a match to a slightly bigger diameter than the shaft is, or it may be wear and tear from that testing stuff - may imagine corners and some parts of pads getting in contacts while the stuff hit. There may be other reasons for those gaps to exists as well. But that size gaps do not have the meaningful bearing capacity - that I quite certain, but not sure it goes significantly deeper than edges - hard to tell. But for the stuff to work the gaps between rotor and pads have to be small enough to restrict airflow becaus of viscosity of air, and thus hold the pressure, if gap isn' small enough it can't work. from here www.loadpoint-bearings.co.uk/about/how-air-bearings-work "An air bearing may comprise of a sleeve separated from a plain shaft by a small gap, typically 5-50 um" here pdf, from the guys, plot at page 2 www.newwayairbearings.com/wp-content/uploads/2018/03/Damping-Stffness-a-primer-copy.pdf - 5-20 microns

@dongchen7940 5 жыл бұрын

@@Molb0rg Thanks for the reply. Yes, you are right. I also read the newway documents before and recalled the air film stiffness will drop greatly as thickness increase. That's why I initially asked this question. I am experimenting with DIY graphite air bearing in my home shop. I found the flat one is not difficult to make since it is easy to lap graphite to a couple wavelength flatness. But I found it difficult to make the cylindrical one. Do you know a way to lap a cylindrical graphite bearing?

@Molb0rg 5 жыл бұрын

@@dongchen7940 that's interesting, do you have any videos posted? or my interest is more about - the porosity of material - which one you take? I guess the answer may depend on that(material) and tools you have. As an example, you may have insufficient porosity and thus airflow and thus you may have higher demands for precision, higher than you would need in case of sufficient porosity and airflow. They call it graphite, but yeah it does no look like it, and is some composite mix I guess. Considering the gaps can be up to 0.05mm(from the links above) it should be well within the reach of a typical lathe. Plus considering the shaft is more thought than pads then if there are some minor mismatch in pads it may work out after some scratching and wear of a pad in "wrong" spots(and I guess some lapping stone may make it happen in a better way). in general, stuff depends on material - how it machines, how it cuts and grinds and the tools/ways you have to work with it. I see you subscribed to RobRenz, he has good videos about making precision OD/ID and I guess it possible to work in the direction, you do not need the precision he talks about in those videos but principles in general work in a similar way. The precision of shaft plays probably a bigger role, concentricity/roundness of if. Another aspect is - with a bigger surface of a pad, it has higher chances of it to work if there is not enough airflow - so it probably easier to achieve results on a bigger diameter compared to 1cm one. Tolerances you mention are way overkill for the kind of application, as with such precision even no porosity at all(no airflow) will act as a hydrodynamic bearing. My current position on all that is - the material(porosity) is the key here. Seen some mentionings of how much air goes through a bearing in a working state, but a random(not the best) one as an example "A gas bearing with 0.5 square foot (6 x 12 inches of face area), fed 60psi compressed air and loaded with 2,500lbs will have a film thickness of .0002 " (from the second link in comment above, page 3) so it means porosity should be capable of airflow 1L@4bar per 16cm2 per minute - that's a minimum requirement for the porosity of a material, and it probably should do few times of that. (and back to the gap, even in the high-performance case about 5um gap). Not sure about the dependency of airflow from the gap, but gap few times of that may require at least a few times of the flow. So I guess the first thing to check if the material you use meets the basic requirements. So few times the flow to work, few times of the high-performance gap and we may easily have basic minimum like 10L@4bar per 16cm2 - and if it does not do that you may have problems just because of low performance of the material.