New source of big pelletizing dies has hot ideas for temperature control. (Compounding).

For 163 of its 166 years, Borsig was a German builder of heavy machines like compressors and heat exchangers. Three years ago, Borsig began working with KnightHawk Engineering in Houston, an expert in troubleshooting pelletizing dies. Together they used KnightHawk's die expertise and Borsig's knowledge of metallurgy and CFD (computational fluid dynamics) to develop an underwater pelletizing die with four novel features.

First, single-pass heating channels for oil or steam reportedly ensure uniform heat transfer across the die for consistent pellet quality. They also help prevent freeze-offs. Second, so-called "thermal-stabilization cavities" are located inside the die surrounding each hole and each cluster of holes. These buffer cavities transfer heat through conduction, convection, and radiation. They are said to minimize thermal interaction between the die's heating fluid, the polymer, and the water against the die face. Third, a specially designed melt inlet channel reduces pressure drop across the die and increases production. Last, new hard-facing metallurgy reportedly maintain sharper outside edges on die orifices to permit cleaner knife cuts. The harder metal also saves money on resurfacing, Borsig says.

Borsig's new pelletizing dies are designed for big lines: They start at 20,000 lb/hr and go up to 200,000 lb/hr. The first was delivered in late 2001 to a resin producer in Texas for pelletizing HMW-HDPE (MI 0.05) at 65,000 lb/hr. The customer's pellet quality leapt from 65% to 95% size uniformity, Borsig says. That resin producer has ordered a second Borsig die for other HDPE resins, Tel: [phone], www.borsig.de