| Zugriffsnummer | 11883 |
| Dokumenttyp | Bericht |
| Sprache | Deutsch |
| Titel | Vermeiden der Entzündung faserförmiger Beschichtungsstoffe (Flock) beim elektrostatischen Beflockungsprozess |
| Autor(in); Institution |
Pidoll, Ulrich von; 3.33, Physikalische Zündvorgänge, PTB-Braunschweig
|
| Quelle/Jahr | (1999), 29 S. |
| Schriftenreihe | PTB-Bericht PTB-ThEx-9 |
| Herausgeber(in) |
Physikalisch-Technische Bundesanstalt
|
| ISSN | 1434-2391 |
| ISBN | 3-89701-441-6 |
| Berichtsnummer | PTB-ThEx-9 |
| Verlag | Bremerhaven: Wirtschaftsverl. NW |
| Freie Schlagworte | flock ; ignition ; minimum ignition energy ; sparks ; arc discharges ; flock machine ; safety requirements |
| Zusammenfassung | The fires which recently occurred in flock machines in America have shown that today's knowledge of the ignitability of flock clouds on flock machines is not sufficient. This is why it has been investigated within the scope of a research project which minimum spark energy is required to ignite flock whirled-up on flock machines. The first step taken for this purpose consisted in measuring the minimum ignition energy of more than 60 commercial flock samples on a minimum ignition energy apparatus optimized for high spark energies. It turned out that the minimum ignition energy of flock depends on fiber diameter, fiber length, fiber material, type and quantity of the chemical preparation compound and on the fiber color. Average flock has a minimum ignition energy of about 150 mJ. The lowest value of approx. 80 mJ was obtained for the finest commercial ground cotton flock. If the fines content can accumulate, it is, however, possible that even much lower values can be reached. In a second step it was tried to ignite the most ignitable flock samples by sparks and arc discharges from flock machines. It turned out that the single sparks of DC flock machines which are not ignition-optimized ignited the most ignitable flock samples only at discharge energies above 1300 mJ. Such discharges can occur only during failures of large DC facilities. DC arc discharges proved to have a low ignition capability as their strong shock wave seems to separate the flammable flock from the ignition source. A fire could be observed only in the case of compressed flock or flock particles hanging together on other reasons. In contrast to the behaviour of DC, weak AC arc discharges even ignited the least ignitable flock samples unless a current limiting resistor was provided in the discharge circuit. When a sufficiently large current limiting resistor was used, the AC arc discharges ignited only flock samples with minimum ignition energies lower than the energy dissipated in a single AC half-wave. The use of adhesives with a flash point clearly above the working temperature leads to no significant change concerning the minimum ignition energy of flock clouds. On the contrast, types of adhesives with a flashpoint below the working temperature can lead to a drastically fall off concerning the minimum ignition energy of flock clouds due to the highly flammable adhesive vapours. If such adhesives are applied, therefore, further measures concerning explosion protection shall be taken. The observations and measured data led to proposed safety measurements which sufficiently prevent the ignition of flock clouds by flock machines. The results obtained will be incorporated in future European standards. Es wurde untersucht, welche Funkenenergie mindestens erforderlich ist, um aufgewirbelte Textilfasern (sog. Flock) an elektrostatischen Beflockungsmaschinen zu entzünden. Im ersten Schritt wurde die Mindestzündenergie von mehr als 60 handelsüblichen Flockproben bestimmt. Der Niedrigstwert von ca. 80 mJ wurde für den feinsten handelsüblichen Mahlflock aus Baumwolle erhalten. In einem zweiten Schritt wurde versucht, die zündwilligsten Flockproben durch Funken und Lichtbögen von Flockmaschinen zu entzünden. Der Einfluß von Klebstoffdämpfen wurde ebenfalls untersucht. Aus den Beobachtungen und Meßwerten wurden Schutzmaßnahmen abgeleitet, die eine Entzündung von Flockwolken an elektrostatischen Flockmaschinen ausreichend sicher verhindern. |
| Rechteinformation | 1999, Physikalisch-Technische Bundesanstalt |