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

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Mon, 19 Jan 2004 10:02:33 +0200
From: gtyler <gtyler@xxxxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Static Discharges from PE etc... (fwd)

It already exists!

----- Original Message -----
From: "High Voltage list" <hvlist@xxxxxxxxxx>
To: <hvlist@xxxxxxxxxx>
Sent: Monday, January 19, 2004 1:55 AM
Subject: Re: Static Discharges from PE etc... (fwd)


> Original poster: Steven Roys <sroys@xxxxxxxx>
>
>
>
> ---------- Forwarded message ----------
> Date: Sat, 17 Jan 2004 13:51:25 -0800
> From: Jim Lux <jimlux@xxxxxxxxxxxxx>
> To: High Voltage list <hvlist@xxxxxxxxxx>
> Subject: Re: Static Discharges from PE etc... (fwd)
>
> Similar circumstances occur when moving pellets of material through
tubing,
> especially if it's done by blowing them. This is where the spark that
blows
> up the grain or flour silo comes from. A friend who used to work in a
bakery
> said that they used to get flour explosions when the static
dissipation
> apparatus failed in the storage silos. Loud and muffled boom,
overpressure
> vent opens, etc.
>
> I've had first hand experiences with incidental static charging along
these
> lines, one with a special effect rig that was blowing several cubic
meters
> of popcorn into a set, another with a machine that pulled and trimmed
> lengths of plastic film off a bulk roller. The first generated very
> impressive sparks from the blower to ground (or the operator (ouch!)),
the
> second glowed most impressively in the dark.
>
> Vollrath, and others, have built electrostatic generators using such
> techniques as blowing dust.
>
> A friend once wondered if you could do it with steam.  Superheated
steam is
> a gas (insulating) and you could vent it through a condensing nozzle
to form
> small particles, which could carry charge, much like a Kelvin water
dropper.
> He was theorizing that it might be a way to power something floating
at a
> high voltage, among other things.
>
> ----- Original Message -----
> From: "High Voltage list" <hvlist@xxxxxxxxxx>
> To: <hvlist@xxxxxxxxxx>
> Sent: Saturday, January 17, 2004 1:20 PM
> Subject: Re: Static Discharges from PE etc... (fwd)
> >
> > ---------- Forwarded message ----------
> > Date: Sat, 17 Jan 2004 14:45:51 -0500
> > From: David Sharpe <sccr4us@xxxxxxxxx>
> > To: High Voltage list <hvlist@xxxxxxxxxx>
> > Subject: Re: Static Discharges from PE etc... (fwd)
> >
> > Hi Dan!
> >
> > High Voltage list wrote:
> >
> > > Original poster: 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
> > > ----------------------------
> >
> > The PE material used was virgin grade, and used as a "wear surface".
> Since
> > PE has similar self lubrication characteristics as PTFE, improved
conveyor
> > material wear life was assumed.  Another reason why this situation
> escalated
> >
> > into a major issue, the conveyor belt had metallic fibers in it to
> > "dissappate"
> > (read equalize) the charge.  Lets see, metal over metal with a PE
> insulator
> > the width of the converyor, 15 feet long (180") conveyor, with belt
> > (electrode)
> > width of 6" .  Assuming wear surface was 20 mil thick PE (phi ~2.0)
and
> > actual active capacitor area is 1/3 total would approach
> >
> > Cest(pf) = 0.224 * k * A / d
> > C          =  0.224 * 2.0 * (6 * 180/3) / 0.02
> > C           ~ 8000pF
> >
> > If you assume 15kVDC / inch (high humidity) environment, and 8"
discharges
> > (maximum);
> >
> > V = 8* 15  = 120kV.
> >
> > E = 0.5 * C * V^2;  with these values stored E is >50J...  < OUCH >
> >
> > Even if the actual capacitance is 1/4 what is represented here;
clearly a
> > dangerous and potentially (NO PUN) lethal condition exists.
> >
> > With the attractive force being presented to cartons and actual
jamming
> > (and damage) to upstream machines, I have no doubt that these values
are
> > close to what was seen in field...
> >
> > Regards
> > Dave Sharpe, TCBOR/HEAS
> > Chesterfield, VA. USA
> >
> > >
> > > > HV List
> > > >
> > > > I ran into a very interesting "Van de Graff" type problem while
> > > > working on package conveying systems about 12 years ago.
> >
> > <<SNIPP>>
> >
> >
>
>
>