Re: Van Der Graaf Rollers (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Sun, 05 Oct 2003 18:39:35 -0300
From: Antonio Carlos M. de Queiroz <acmq@xxxxxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Van Der Graaf Rollers

High Voltage list wrote:

> From: Daniel Reinders <danreind@xxxxxxx>

> I'm wondering how bulbous the rollers of a Van Der Graaf machine should be
> to keep the belt on track?  I've had a nylon and a pvc roller (1.5" diam)
> lathed out with a slight bulge, approximately accomplished by lathing out at
> 10-15 degrees from the centerline.  But my 6" Theraband wants to fold over
> in two, which means I could get by with a 3" band I suppose but only by
> compromising my charging rate.  Also what shape is most appropriate for the
> roller - are we talking quasi-circular over the full length, or can the main
> portion be flat with just the ends being strongly tapered?

In my Van de Graaff generators, I tappered straight cuts at 2 degrees
only, for about 1.5 cm from the ends of the rollers. The Theraband
belts still eventually slip, but at this point the speed is so high
that there are other mechanical problems, as the belt flying away from
the rollers due to centifugal force.
In a medium machine, I would recommend to make the belt tension
adjustable, by mounting  at least one of the rollers on independently
adjustable  (vertically) bearings. In this way you can adjust the
tension and the parallelsim of the rollers.

Nylon and PVC are poor materials for a friction-excited VDG. Nylon
doesn't work at all, unless the air is desert-dry, and for long time.
PVC is somewhat better. Teflon is perfect, working even if wet.

Antonio Carlos M. de Queiroz