>These days I don’t ride on the beach, thats what finally killed the old >bearings, not the 5 years, hard riding or the trip over the lake district. Just >plain old salt water.
Sand (silicon powder) isn’t very good for bearings either. Sealed bearings are
sealed only in the sense that periodic lubrication is not required or nor is it
desirable. Dirt will enter sealed bearings and shorten their life some. However,
sand with its larger and harder silicon particles will grind bearings down to
uselessness in a matter of days or weeks. I’m quite sure that silicon is harder
than steel on the hardness scale (simply the ability of one material to scratch
a softer material - not strength - for example, diamond is the hardest material,
but there may be materials stronger than it).
Can anyone provide a hardness scale for these materials for comparison?
>of days or weeks. I’m quite sure that silicon is harder than steel on the >hardness scale (simply the ability of one material to scratch a softer material >- not strength - for example, diamond is the hardest material, but there may be >materials stronger than it). > >Can anyone provide a hardness scale for these materials for comparison?
Hardness is very, er, difficult to quantify. There are a number of scales, some
of which rely on the sort of comparison you sugested, and some of which attempt
to be more quantifiable. For example, a common scale uses a chart of what will
scratch/be scratched by what. Trouble is, on the most common scale the
difference between 1 and 2 in actual units is greater than that between 2 and
10. Other scales scratch things in known ways and measure the size and depth of
the scratches.
If you get a flawless crystal of it, diamond is about as strong as anything
gets, btw Both its hardness and its strength can be thought of as deriving from
the very highly linked structure of the constituent carbon atoms. (Also the
reason why carbon fibre is high strength.)
I’ll read my data books (if I remember) at work. I’m not actually sure where
sand would fall wrt properly hardened bearing races (hardness is not something I
often consider - more into strength, stiffness and toughness myself), but sand
will certainly be abrasive to cheap bearings.
regards, Ian SMith
|\ /| Opinions expressed in this post are my own, and do
|o o| not reflect the views of Amos, my mbu puffer fish.
|/ | (His view is that small snails are very tasty.)
Amos now on the web at http://www.achrn.demon.co.uk/amos.html
If I am not mstaken, most really good chemistry periodic table of elements give
a rating of hardness for the elements. This is of course relative to the type of
crystal that is formed. ie carbon forms three structures (negating
buckministerfullerene) resulting in three different substances and hardnesses,
one of which, is graphite, a very good lubricant. Try looking in a good
chemistry book; it couldn’t hurt!