Charring is the oxidation of hot-melt adhesive due to prolonged and repeated heating. Charred adhesive will not dissolve nor can it be re-melted. Charred hot-melt will clog hoses, filters, nozzles and damage equipment. Charring is inherent and can only be reduced but not completely eliminated.
Hot-melt heated for a long period of time will degrade and begin to gel. As the hot-melt degrades it loses its thermoplastic nature and will not flow. Eventually the gel settles to different areas of the tank and hardens to create char. Char tends to build up at the bottom of hot-melt tanks insulating heating elements. This condition causes heaters to stay on longer and burn hotter, which creates the black material we all recognize as char. The higher the temperature and the longer hot-melt is heated the faster char will form.
Additional causes of hot-melt char are contaminants introduced into the system such as corrugated dust, paper and other airborne contaminants from the plant environment.
If not removed, char will continue to form and will work its way from the hot-melt pot, into the hoses, through the filters and into the nozzles. In each of these areas it has the potential to negatively affect production.
Preventative maintenance procedures can slow the formation of char. These practices include: maintaining constant level of adhesive in the pot, keeping the lid closed, running hot-melt at recommended temperature range, cleaning tanks on regular schedule and reducing heat when lines are down.
How much does downtime cost? Many companies estimate downtime costs, and they can run as little as $100 per minute or as much as $2,000 per minute. In any case downtime is costly and downtime due to char can be minimized by a preventative maintenance program as outlined below
APPLIED Adhesives suggests the following:
- Check filters and change them on a regular basis. See our complete line of inline filters, quick-change filters and tank filters.
- Purge and clean hot-melt hoses and tanks on a quarterly basis with hot-melt purge liquid (SAF-T-PURGE 200)
- Replace or clean nozzles on a regular basis. Select nozzles from the APPLIED inventory or soak with DISSOLV-X to clean and reuse.
Since charring is temperature related, new low temperature and heat stable hot-melt adhesives can lower the rate of char. We suggest:
- Low Temperature Hot-Melt (examples: Technomelt 250A,Technomelt 100D)
- Heat Stable Metallocene Based Products (examples: SUPRA 200, SUPRA 106M)