Purging Compounds: Your Key to Clean Molds
Mold and die casters have long relied on purging compounds to clean their tooling and reduce waste. These specialized thermoplastics play a crucial role in producing quality parts efficiently. This article explores the different types of purging compounds and how they can maximize your productivity.
What are Purging Compounds?
Purging compounds are high-quality thermoplastics specially formulated to clean injection molds and extrusion dies. They are similar to the resins being processed but have properties optimized for cleaning rather than part production. When used correctly, purging compounds can purge scrap resin from the tooling and injection system between parts, eliminate debris, and minimize contamination to improve quality.
There are two main categories of purging compounds - melt and solvent. Melt purging compounds are thermoplastics that melt like the production resin during the cleaning cycle. Solvent purging compounds contain cleaning agents that soften residues for removal. Both play an important role in many applications.
Choosing the Right Type
The type of purging compound needed depends on the material being purged and machine/tooling capabilities. Melt purging works well for most thermoplastics like polycarbonate, nylon, and polypropylene on reciprocating screw machines. Solvent purging is preferred when very small amounts of contamination cannot be tolerated, such as in medical or food contact applications.
Melt purging compounds are available for virtually all common resins, including specialized grades for engineering plastics like PBT and LCP. Selecting a purging compound with similar melt properties as the production resin helps achieve the best cleaning results. Solvent purging compounds contain cleaning agents tailored for specific resin families.
Optimizing the Purging Process
To purge effectively, use the correct amount of compound, high temperatures, and proper technique. Most injection presses can hold 1-3 times the shot capacity of the tool in purging compound. Too little won't clear debris, while excess is wasted. Match purging conditions to the normal processing window whenever possible.
Using a melt purging compound, inject it into the heated mold at production pressure and pack/hold times. This melts and encapsulates residues for easy removal. Solvent purging may require soaking or additional physical agitation. Multiple cycles or continuous purging may be needed for tough applications. Purging at scheduled downtimes helps prevent defects related to material contamination.
Maximizing Efficiency
Purging reduces waste and increases tool uptime by minimizing defects related to residue buildup and contamination between parts. This improves part quality and consistency. Regular purging also helps reduce maintenance costs by keeping molds and barrels cleaner.
Advanced purging systems like closed-loop purging compound recyclers further boost efficiency and reduce material costs. These systems automatically reuse expensive purging compound shot after shot with minimal waste. When coupled with automated purging timed to production schedules, they maximize efficiency and minimize operator involvement in purging.
Purging Compound Selection Guide
With many formulations available, selecting the optimal purging compound requires understanding your specific application demands. This quick reference guide summarizes common types for different material families:
- Polycarbonate: General purpose melt purging grades effectively clean at molding temperatures. Solvent purginghandlesstubbornresidues.
- Nylon: Melt purging compounds match production nylon grades for efficient cleaning. Solvent types designed for tougher random copolymers.
- PP & PE: Melt purging compounds match the various grades processed. Solvent types designed for film/fiber applications.
- PBT & LCP: Specialty high-temperature melt purgingcompounds withstand processing conditions formostengineeringresins.
- PS & ABS: Recommended melt purging compounds contain blending agents for complete solubility.
- Medical/Food contact: Solvent purging types approved for critical applicationsrequiring stringent cleanliness.
With the right purging compound selection and process optimization, molders and extruders can leverage purging to improve production efficiency, part quality consistency, and tool up-time. Regular purging plays a fundamental role in reliable plastics manufacturing.
In Summary
This article provided an overview of purging compounds, their different types, applications considerations and how choosing the proper formulation and process optimizes their cleaning ability. Purging is a core part of quality plastics production that resin and tool makers should not overlook. Implementing a systematic purging procedure tailored to each tool and application delivers big returns in waste reduction, higher yields and reduced defects. Purging keeps molds and dies performing at their best for minimal long-term maintenance costs.
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