RE: Static Discharges from PE etc... (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 16 Jan 2004 11:04:29 -0500
From: "Mccauley, Daniel H" <daniel.h.mccauley@xxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: RE: Static Discharges from PE etc...


Dave,

My first job out of school was with Anheuser-Busch working on their
bottling and packaging conveyor systems.
Typical practice is using static-dissipative polyethylene or similar
plastic which quickly dissipates any
charge built up on the material due to passing packages etc...  Although
the static-dissipative PE is much more
expensive than standard PE, it works extremely well.

Dan


> HV List
>
> I ran into a very interesting "Van de Graff" type problem while
> working on package conveying systems about 12 years ago.
> After installing a carton conveying system, personnel kept
> complaining of getting "intense" shocks off of conveyor
> body, even though I was responsible for the power / control
> design, and everything was correct (and double checked)
> for compliance to applicable codes (IEEE, NEC, local electrical
> code).  I even had AC utility voltage leakage measurements
> (ground to frame) performed, voltages of << 1VAC/DC
> were observed.
>
> People started complaining of upstream machine jams, etc.
> I went to site to investigate.  Pan of steel conveyor had a
> polethylene wear surface (!!!) and a synthetic cotton belt
> with metallic "alligator" style splice in it.  Belt was perhaps
> 6" wide, moving at 100 FPM.  Static charges were building
> up on alligator clip + surrounding belt to level that you
> could hear loud SNAPPP over the nearby running machinery
> and BRIGHT ARCS measured better then 8" long were
> reaching out to contact around the PE wear surface to the
> converyor frame.  The charges were causing the cartons
> to literally "stick" to the side guide metallic rails and physically
> jam the upstream machines (could not manually move 20
> cartons end to end, the attractive force was that great!!!!).
>
> I strongly recommended shutting the conveyor down and
> removal of the PE wear surface ASAP, due to personnel
> safety risk, potential damage to product, and possible
> conveyor bearing damage.  After these mods were
> performed, manufacturing operations returned to normal.
> Our Mechanical Engineering brethren had successfully built
> an extremely efficient Van de Graff generator, and didn't
> even know it.  Names of personnel, company, location and
> date of occurence shall remain anonymous, to avoid
> embarassment to the guilty parties...   :^D
>
> This is a true story, I was responsible for the original EE
> design of this conveying system, and the resolution
> to this debacle.
>
> Regards
> Dave Sharpe, TCBOR/HEAS
> Chesterfield, VA. USA
>
> High Voltage list wrote:
>
> > Original poster: Steven Roys <sroys@xxxxxxxx>
> >
> > ---------- Forwarded message ----------
> > Date: Thu, 15 Jan 2004 09:55:19 -0800
> > From: Jim Lux <jimlux@xxxxxxxxxxxxx>
> > To: High Voltage list <hvlist@xxxxxxxxxx>, hvlist@xxxxxxxxxx
> > Subject: Re: Van de Graaff generator safety question (fwd)
> >
> > You can run a chain much faster than a belt, for one thing,
> because the
> > mecahnical dynamics are better.  (Chains aren't as
> "stretchy")  ALso, if
> > you want to run parallel chains, it's much easier to do
> than using a big
> > wide belt.
> >
> > There are some other schemes similar to pelletrons that
> appear in the
> > literature, such as a belt carrying metal plates.
> >
> > In my recollection, Pelletrons charge by induction, as
> opposed to using
> > brushes or charge spray bars.  Perhaps this is a more
> "efficient" way of
> > getting charge on the belt, although, as Antonio points out, the
> > fundamental limit is the surface charge density on what
> ever is carrying
> > the charge.
> >
> > Chains might also be more consistent, making field control
> as you move up
> > the column easier, so the field gradients are smaller.
> >
> > At 09:58 AM 1/15/2004 -0700, High Voltage list wrote:
> > >Original poster: Steven Roys <sroys@xxxxxxxx>
> > >
> > >
> > >
> > >---------- Forwarded message ----------
> > >Date: Wed, 14 Jan 2004 14:57:06 -0200
> > >From: Antonio Carlos M. de Queiroz <acmq@xxxxxxxxxxxxxxxx>
> > >To: High Voltage list <hvlist@xxxxxxxxxx>
> > >Subject: Re: Van de Graaff generator safety question (fwd)
> > >
> > >High Voltage list wrote:
> > > >
> > > > From: Dr. Resonance <resonance@xxxxxxxxxx>
> > > >
> > > > Yes, we built one about 12 years ago.  Current
> increase, as compared to a
> > > > belt, is approx 1,200%.
> > >
> > >This doesn't seem possible. The belt in a regular VDG
> operates already
> > >close to the limit of charge density that would cause ionization of
> > >the air. The conductive sections of a pelletron chain would at most
> > >operate at this same density. The current is always directly
> > >proportional to the area per second of charge transport
> surface that
> > >reaches the terminal. For a given belt speed, it's very
> difficult to
> > >get something better than what a belt can give.
> > >
> > >Antonio Carlos M. de Queiroz
>
>
>