by Purging Compounds: A Key Tool for Manufacturers to Improve Product Quality
PCs are specially formulated polymer materials that are added to thermoplastic resins during compounding or extrusion processing. When exposed to heat during processing, PCs undergo a controlled decomposition which results in the liberation of gases such as nitrogen. This helps flush out any residual contamination from previous production runs or cleaning processes from the barrel and die areas of extruders and injection molding machines.
PCs typically consist of base polymers blended with chemical blowing agents that decompose at optimum processing temperatures. Commonly used base polymers include polyolefins like polyethylene and polypropylene which have high melt flow rates to help push contaminants out of the processing equipment. Calcium carbonate or sodium bicarbonate are some popular blowing agents incorporated into PCs.
How Purging Works
During initial heating and melting in the extruder or injection molding machine, the blowing agent in the PCs starts to decompose in a controlled manner. This leads to the release of gases like nitrogen which creates millions of tiny bubbles or pores within the purging compound melt.
The bubbles act like tiny balls that effectively help scrape and displace any residues stuck to the barrel walls or crevices in the die areas. Meanwhile, the high melt flow rate of the base polymer allows the PCs to quickly push accumulated contaminants ahead.
As the heavily foamed purging compound melt is extruded or injected, it expands and fills up cavities while simultaneously forcing out trapped impurities through vents and auxillary openings. Multiple passes may be required to thoroughly clear build-ups depending on the level and type of contamination.
Common Types of PCs
Purging compounds come in different formulations tailored for specific resin applications and processing conditions:
– General Purpose: Suitable for purging most thermoplastics like polyolefins, nylons, PET and PBT. Cost-effective for light-moderate contamination clean-up.
– Aggressive: Formulated for stubborn residues and heavy contamination removal during production changeovers involving color, filler or additive system changes.
– Heat Resistant: Incorporate specialized blowing agents that decompose at higher temperatures suitable for engineering resins like polycarbonate, PPE/Noryl, and LCP.
– Compatible: Designed with chemically matching base polymers to minimize potential interaction with the next production resin. Helps prevent carryover contaminant issues.
Benefits of Regular Purging
Consistent purging brings multiple advantages compared to skipping this important cleaning step:
– Reduced down time and easier changeovers by eliminating tedious manual cleaning procedures between product runs.
– Improved product quality and purity with minimal risk of residue transfer between grades affecting properties or color.
– Lower rejection rates as purging removes sources of cosmetic defects, lap shear issues from contaminant build-up inside sprue bushings and gates.
– Increased uptime through better equipment protection against internal corrosion and part surface degradation from contaminants over many cycles.
– Consistent production and reduced variability as machines are uniformly cleaned to original baseline conditions for each job.
– Extended time between preventive maintenance intervals since purging cuts down on residue accumulation inside moving parts and components.
So in summary, using PCs on a planned schedule enables processors to quickly and efficiently clean thermoplastics equipment to like-new conditions for shifting to the next product. This translates directly into better operational efficiency, higher productivity and enhanced product quality control.
*Note:
1.Source: Coherent Market Insights, Public sources, Desk research
2.We have leveraged AI tools to mine information and compile it
