MAINTENANCE | PURGING COMPOUNDS
Above: The need to
perform screw pulls differenti- ates com- pounding purging from injection moulding
Chem-Trend says companies are interested in
CPCs that are easy-to-use, provide an effective and efficient cleaning of the screw/die, and are recycla- ble in a closed loop system. Processors are chal- lenged with becoming more sustainable and utilising a recyclable CPC is a great way for a company to reduce their footprint. A recyclable CPC is also beneficial from an economic standpoint because it allows companies to utilise the purge scrap rather than send it to landfill. Ultra Purge 3615 has been specifically designed for the compounding and masterbatch industries, according to Chem-Trend. The company says the product is 100% chemical — meaning no abrasive components are present. It is a self-emptying technology that makes screw pulls and material changes fast and easy and is said to result in a screw free of any type of residue after just one purge cycle. This also makes machine shutdowns/ startups easier as there are no remnants left to degrade and show up as carbon.
Closing the loop Ultra Purge 3615 is also recyclable and can be used in a closed loop system. A 2022 study performed by Fraunhofer Institute showed that recycling Ultra Purge with up to 5% virgin resin does not affect the chemical and physical properties of the final product. According to Reeder, companies also need to consider the basics when purging their machines. “First and foremost, when performing a colour change make sure the hopper, feed throat and conveying system has been cleared of all previous colorant,” he says. “All CPCs have unique procedures to maximise their performance. Make sure to use the CPC manufacturer’s recommended procedures.” The market for purging compound is strong, according to US company RapidPurge. “Obviously,
48 COMPOUNDING WORLD | December 2023
it ebbs and flows along with the larger market for resin,” says Joseph Serell, President and Owner of the company. “However, over the past 20 years the growth rate has been somewhat stronger than the resin market itself. This seems to remain the case.” Serell says that, fundamentally, purging com- pound is a cost saving product. “As operating costs increase, such as resin and electricity, purge com- pound has become increasingly important as a cost reducing product,” he says. “A small amount of purge compound can eliminate a large amount of scrap.” Serell also says that new developments in purge compounds have generally been evolutionary as opposed to revolutionary. Purge compound producers are continually looking for more effective resin carriers, scrubbing minerals and surfactants (and their combinations), but the primary driver of new developments is the need to offer improved solutions to customers at a better overall price – as opposed to radically new technol- ogy for new applications. As new resins are developed, new purge compounds are as well. This is especially the case for the newer super engineer- ing resins that are processed at high temperatures and there are now a number of purge compounds that are effective and safe at temperatures of 700˚F (371˚C) and above. Purging compounding machines does not differ
greatly from purging most standard profile extrud- ers. “The key to getting the interior of the machine clean is to get the cleaning mechanism of the purge compound into contact with the surfaces of the metal in the machine,” says Serell. “This sounds simple but is not always so. This is
easier to accomplish with injection moulding machines because friction and pressure can be generated with the reciprocating screw. Compound- ers must take a different course,” he says. “Firstly, mechanical purging compounds rely on scrubbing minerals to remove resin and contaminants from the interior surfaces of the machine. To benefit from the scrubbing minerals, purge compound makers often add a foaming agent to their products. This helps expand the cleaners to the metal surfaces and increase pressure within the machine.” Foaming agents are also employed with chemical purge compounds for the same reason. “Chemical purge compounds also rely on heat and time to be activated. So, it is generally recommend- ed to allow the chemical purge to soak for any- where from 5-30 minutes,” Serell says. “Whether using a mechanical or chemical purge compound, the most important tip is to follow the manufac- turer’s instructions completely. Not all products are used the same way, so following the supplier’s
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IMAGE: CHEM-TREND
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