Polyurethane can be cast to have a variety of hardnesses. It can be rock
hard, or cushiony soft. You need to get the durometer value of the
material to know for sure. The lower the number the softer. Durometer is
usually defined as a "Shore" value.
Without an additive polyurethane is not normally tacky or gummy, unless
it was mixed wrong (i.e. never cures). There are some additives that can
be used to prevent full curing of the polyurethane, but you don't want
it for something going over a dirty surface. If you need a replaceable
tack surface there are brush-on and spray-on materials that will provide
for this. The tack can usually be removed with alcohol or acetone, and
reapplied. Check out art supply stores for starters.
Alcohol will actually melt polyurethane. I use rubbing alcohol to clean
the polyurethane wheels on my minisumos and they get a slight tack to
This quickly disappears as dust is picked up by the wheels. I've
discovered that the 99% alochol makes the wheels too clean, and they
pick up dust faster than when I clean them with rubbing alcohol (which
is 70% alcohol and has some mineral oil).
This is correct. Alcohol may swell or attack polyurethane, as the
material is made from alcohol. But I was thinking drugstore isopropyl
alcohol, which is one third water. (I prefer the kind without mineral
oil.) Most polyurethanes shouldn't be too attacked by this solution,
though these days there are different polyurethane mixes (some even
water-based) so it's always a good idea to test any possible solvents.
"Polyurethanes are formed by reacting a polyol (an alcohol with more
than two reactive hydroxyl groups per molecule) with a diisocyanate or a
polymeric isocyanate in the presence of suitable catalysts and
additives." - Alliance of The Polyurethane Industry
Irrelevent. The point is there is no single type of "polyurethane," or
single method of casting or applying polyurethane. "Water based
polyurethane" is precisely the definition of a Minwax product: " Water
Based Polyurethane for Floors." I'm not going to argue what the
definition of "is" is.
Those in the medical field well know to be careful about the use of
alcohol as a cleaner or disinfectant with some types of
polyurethane-based components, such as catheters. Companies specifically
tout the additives they use to provide alcohol-resistance.
OK, technically you're correct. But it's not alcohol like when cured.
So? Try to remove _any_ of them post cure by applying alcohol and you'll
find that you are wasting your time and your alcohol.
Some time you might want to visit an aircraft plant and show them how to
dissolve cured polyurethane with alcohol since you are so absolutely
certain that it is alcohol soluble.
As for the medical warnings, that seems to be the only field in which such
degradation is known and I find myself wondering why that is.
Would be nice if it were so. Ever try to get polyurethane off of aircraft
parts? If alcohol would do the job a lot of people would be very happy.
The strippers that they have to use are _nasty_ stuff. Alcohol doesn't
The slight tack was there to begin with--what you're doing is getting off
all the crud that it picked up.
It probably depends on the additives that are in the polyurethane. You
can get polyurethane coated wire to make coils for earphones and
whatnot. If you read the directions for the wire, after you've made
your coil, you brush on some alcohol. This cause the polyurethane
coating to melt slightly and fixes the wire in place.
Depends on the state of cure. The polyurethane that we used on propeller
blades, after curing for a month in the shop (which "by the book" meant it
was completely cured) would clean right off of fiberglass with a selective
stripper. When the blade came back from five years in the field that stuff
wouldn't touch it.
I've just been out looking at wheels today - for the purpose of running
on a fibreglass pultrusion (smooth...shiny) to turn an encoder
Nylon is slippery
Poly wheels are ok - not 'tacky' but much better than nylon
Poly boat rollers are good
Rubber wheels are better
Natural rubber is best of all
I'm not sure of the hardness you need, but you want a wheel that will not
deform too much under the weight of the robot. It has to be large enough in
diameter and wide enough at the cross section so that with the hardness of
the rubber tire, there is enough surface area to move the robot without
slipping "under normal conditions," and not so much that turning becomes
impossible or too power intensive.
The "tacky" feel is typically "molecular friction."
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