Pelletizers | machinery
Perfecting your pellets
A well cut pellet is important for many reasons. Prime among these is performance. A consistent pellet means a more consistent bulk density, which pays off for processors in terms of smoother feeding and more even melting. However, consistency in pellet size and shape also conveys an impression of quality. “Appearance is everything,” according to Chris Case,
vice-president of market development at Reduction Engineering Scheer (recently acquired by Dover subsidi- ary Maag). “You could have a perfectly compounded product, but if the Gaylord [bulk container] is full of mis- shapen pellets or fi nes, your customer will judge it as unacceptable.” Obtaining a good pellet cut demands the use of
well-maintained cutting equipment and the selection of the correct settings for the polymer. Variables such as temperature and heat-transfer rate affect pellet quality. “Compounders should apply statistical process control to the pelletizing step, just as they do for the compound- ing processes upstream of pelletizing,” suggests Case. The two basic types of pelletizers - strand and
die-face - each provide specifi c advantages and disadvantages. Strand pelletizers are easy to use, maintain and change over but require manual handling of strands and have a larger footprint, while die-face pelletizers are typically more highly automated, closed systems and offer a smaller footprint. Throughput, cost, and uptime are also important considerations when in choosing the best technology for a particular situation.
Strand developments Reduction Engineering Scheer says that replacing the strand pelletizer water bath with a waterslide – a combination of a trough with a water spray system – is proving a popular option today. Advantages include more effective cooling, greater options for changing the cooling variables (by using the sprayers and a tempera-
www.compoundingworld.com
Perfectly cut pellets help processors maintain consistency in part
production. Jennifer Markarian looks at some of the latest
innovations in pelletizing technology
ture-control system), reduced overall length of the cooling system, and semi-automated feeding of strands into the cutter, says Case. Another option that is gaining ground is the use of a
strand conveyor, which is placed between the waterslide and the cutter. “If you are running multiple polymer types that need different cooling rates, the conveyor gives you more room for this variation,” explains Case. A strand pelletizing technology variation that has
been available for a few years is Reduction Engineering Scheer’s cooling conveyor, which uses a stainless-steel or plastic mesh belt to carry strands while water is sprayed on them. Most recently, the company intro- duced a cooling conveyor designed for cooling very hydroscopic materials, such as bio-based plastics and highly fi lled metal compounds (certain polymers used in the medical industry that could be water soluble are also well-suited for this design). The conveyor belt employs a thin sheet of solid
stainless steel to carry the strand while cool water under the belt provides the majority of the cooling capability by transfer of heat through the thin layer of metal. Fans placed over the conveyor bring the temperature down an additional few degrees, explains sales manager John Sly, who says a few lines are already in commercial use.
January 2016 | COMPOUNDING WORLD 29
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