VAN DE GRAAFF GENERATOR BELTS
(c)1996 William J. Beaty
NOTICE: even an indetectable amount of oil on the
belt can interfere with roller charging and can cause
the generator to stop working. It's a good idea to
scrub a new belt in detergent and water, rinse thoroughly,
then handle it with gloves or with extremely clean
hands when dry. Scrub your rollers as well. Never
spray any "WD-40" lubricant on any part of a VDG
machine!!!
Recommended belt materials:
- Grey neoprene rubber (hard to find!)
- Balloon rubber (use big balloons from a party store)
- "Dynaband" exercize belt, made of rubber in various colors
- "Dental Dam" latex rubber from dental suppliers, see the yellow pages.
Certain other (ahem) specialty stores have dental dam rubber or even
large latex sheets. Try McMaster-Carr #8611K11 Latex Sheet 0.006 inch
thick. Try sporting goods stores for "Theraband" latex bandage.
- "incontinence sheet", rubber bed sheet. Try a "surgical supply"
store.
- Cut up some disposable latex (thin brown rubber) gloves. Use
cyanoacrylate (crazy glue) to make your belt.
- Large rubber bands (or normal rubber bands, if your VDG is extremely
small,) or other brown, gum-rubber sheets.
- Glue: use rubber cement, or the strong glue which is supplied
with bicycle tire-patch kits. Crazy glue is suppose to work too.
- Yellow sign-tape from hardware stores, the kind that says "wet
paint." The more impressive VDG will have yellow tape that reads
"POLICE LINE" or "CRIME SCENE" ! (From Archie Mcphee,
http://www.mcphee.com)
- Polyethelene garbage bags, cut crosswise into belt-like strips
- Urethane industrial belts. N. Simmons reports that these can be
ordered
in custom sizes from Pyramid, Inc., Newton, IA, phone 515-792-2405
Make sure they understand that you want NO kind of antistatic coating
or additives in the belt material.
- Another source is http://www.durabelt.com
- People on the PHYS-L discussion list recommend spandex cloth, with
the ends of the belt bonded with crazy glue.
If you're building a VDG from scratch, take a look at my TRIBOELECTRIC
SERIES page. This will give you hints about materials to try as the belt
and the roller. A polyethelene roller used with a rubber belt is
traditional, but I doubt it is the ultimate combination.
Rubber belts can be made from rubber strips glued end-to-end. Rubber
cement will work OK. Much better is the glue used in innertube tire
repair kits (bicycle shops have this.) Note that this glue has toxic
fumes and probably shouldn't be used by kids except with adult
supervision. I've heard that cyanoacrylate "crazy glue" works well, but
have not tried it myself yet.
If you use a thick material, it helps to eliminate the glued lump:
before gluing, "feather" the ends by filing or sanding the material into a
taper. If done perfectly, a glued tapered joint will have no lump at all.
Another hint: cut the ends of the strip diagonally, so the glue joint will
be a diagonal stripe across your belt. Then instead of going
"thump-thump-thump" over the rollers, the glue joint will make a smooth
quiet sweep. I have it in my head to try freezing the rubber in dry ice
w/alcohol, or liquid nitrogen, and then grinding with a belt sander, but I
don't know if this will actually work.
Very thin belt material doesn't require feathering, but it's less sturdy.
Belts made of thin balloon-rubber have a limited lifetime because the
ozone and nitrides being generated by the corona-combs will attack the
rubber chemically, making it brittle so it becomes full of holes.
If possible, avoid black rubber or brightly-colored rubber because
sometimes the coloring makes the rubber conductive. To test for this, on
a low-humidity day try rubbing your belt material on hair, fur, etc. Hairy
arms do nicely. If it becomes charged and will attract the hair, the
material is OK. If it will not charge up, either the material is
conductive and the excess charge leaks away, or the air is too humid and
your test is spoiled because *everything* is slightly conductive from the
adsorbed surface water. How to test the air humidity? Try rubbing a
balloon on your arm hair and check for attraction. If rubbing a balloon
doesn't electrify its surface and make hair rise, the weather is too
humid, so therefor you cannot easily test your belt material.
There are a couple of companies which sell VDG replacement belts for
various classroom generators:
SCIENCE FIRST
95 Botsford Pl.
Buffalo, NY
800-875-3214
716-874-0133 phone
716-874-9853 fax
info@sciencefirst.com
WABASH INSTRUMENT CO.
(WINSCO)
PO Box 707
300 Olive St.
Wabash, IN 46992
phone: 219-563-8406
CENCO www.cenconet.com
SARGENT-WELCH
800-727-4368
.