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Adds Mayle, "Make sure you close the main material valve after draining the container. Operators have been known to load their handliner from a kettle melter and then helplessly watch the thermoplastic run right on the ground."

Kettle thoughts
Mayle notes that thermoplastic has been used in this country since the late 1950s with continuing good results. That material contains binder, pigments, fillers, and glass beads which turn to liquid when heated. There are two types of thermoplastic: hydrocarbon and alkyd. Hydrocarbon is made from petroleum-derived resins and alkyd is made from wood-derived resins.

He offers this advice when heating the material in a melter. Calibrate the kettle's material temperature gauges periodically (weekly is suggested) by using a reference thermometer. Fill the melter to 30% capacity. After the thermoplastic becomes liquid, gradually add the remaining material to fill the melter to capacity.

Mayle advises transferring thermoplastic from the melter to the handliner 30 minutes after its temperature reaches operating range (400˚F to 430˚F). During transfer, thermoplastic should pass through a 1/4-inch mesh screen. Add more thermoplastic when two-thirds of the liquefied material has been used. The new material will be ready for transfer 30 minutes after reaching operating temperature range. Cease agitation during cool-down after the thermoplastics' temperature cools to 275˚F.

"Do not hold thermoplastic above 400˚F for more than six hours, and it should never exceed 450˚F," Mayle says. "Granular thermoplastic can be reheated a maximum of three times and block material only twice. A color change in the thermoplastic indicates the material is overheated and beginning to scorch. Schedule the melter for cleaning if charred or burned particles remain on the screen after transfer and completely flush the system when changing from alkyd to hydrocarbon or vice versa.