This page contains a Flash digital edition of a book.
processing feature | High-temperature compounding Preventive maintenance is crucial for high-tempera-

Above: Gala says that mechanical seals require less mainte- nance and

endure faster speeds and higher


Right: Gala’s Heat Flux Die Plate is

designed to reduce or eliminate die-hole freezing

He adds that another technology that is beneficial for high-temperature processing is a mechanical seal to prevent water from entering the pelletizer motor. Compared to radial shaft or lip seals, mechanical seals require less periodic maintenance and better endure faster speeds and higher temperatures, says Tate. While everyone wants to minimize

downtime, it is particularly important to reduce the polymer wasted during downtime when running expensive engineering resins, comments Tate. He claims that Gala’s EAC (Electronically Ad- vanced Cutter) technology increases uptime and reduces blade and die-face wear. The system incorpo- rates automated blade advance, periodic blade sharpening, and blade monitoring. Underwater pelletizers have an advantage for

high-temperature resins with low viscosities that can cause problems when trying to draw a strand. “The temperature difference from the molten material to the cooling water, which is at 80-90°C in these applications, creates a skin around the molten material, and low-viscosity materials are then easy to cut,” notes BKG’s Simon. Underwater pelletizers are closed systems, which

can be an advantage compared to open, strand systems for some materials in which evaporation of volatile components may be an environmental risk. Underwater systems also offer the general benefits of throughput, automation, and a smaller footprint. Underwater systems are broadly used with polyam- ides, and are increasingly used with PEEK, PPS, and PSU, for example. Some grades of LCP have been run successfully in small-scale and larger commercial systems, but other grades of LCP remain a challenge, note suppliers.

18 COMPOUNDING WORLD | December 2012

ture processing because there is less tolerance in all aspects of the process. Because the cycle from room temperature to processing temperature is more extreme, expansion and contraction of metal parts is also more significant, and regular maintenance should be done at shorter intervals. This maintenance should include tightening barrel bolts, checking alignment, and checking that elements on the screw shaft are tight, says Entek’s Benjamin. If gaps develop between the screw elements, polymer could leak through onto the shaft, which would make pulling the screw more difficult. “These are all mainte- nance items that processors should normally do, but they may need to be done more frequently,” he recommends. Cleaning is also important. While

standard, commercial purge compounds may not work well in high-temperature processes, a few high-temperature purge com- pounds are available. For example, Sun Plastech’s Asaclean purging compound comes in high-tempera- ture grades. Asaclean SX is designed

to clean in the temperature range of 300-390°C (570-735°F). Asaclean PX is

designed to clean at temperatures up to 420°C (788°F) with low levels of smoke and processing odour. Some use neat resin as a purging compound between different grades of that resin. When making extreme colour changes, the most

effective technique is still to pull the screw and clean it, says Solvay’s Desio. With PEEK in particular, adds Berstorff’s Winkelmann, mechanical cleaning of screws and barrel borings is necessary. It takes special training and care to clean and

operate a high-temperature processing line. Not only is it hot, but there can be a fire risk because processing can be close to the auto-ignition temperature of materials. Operators must be comfortable working with high-temperature equipment and must take appropri- ate precautions. Training and documentation of procedures are critical.

Click on the links for more information: ❙

Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68
Produced with Yudu -