by Purging Compounds: A Solution to Remove Trapped Air and Moisture from Plastic Parts
Introduction
With injection molded and cast plastic parts becoming more integral to modern products, eliminating air and moisture trapped inside these parts is crucial to ensure optimal quality and performance. Purging compounds have emerged as an effective solution commonly used in manufacturing to resolve this issue. This article provides an in-depth look at purging compounds, how they work, their various types and applications.
Purging Mechanism
When molten plastic is injected into a mold cavity, small pockets of air or moisture can become trapped inside the plastic part. Over time, these contaminants degrade plastic properties like strength, dimensional stability and appearance. Purging compounds work by being injected after regular production runs to push out any trapped air or moisture while filling all empty spaces inside the mold. Their specialized properties enable them to displace contaminants without leaving any residues behind. Most purging compounds are thermoplastic materials formulated to have lower melt viscosities than production resins so they can easily flow into microscopic voids.
Types of Purging Compounds
Purging compounds come in different types suited for specific production plastics and applications:
– General Purpose: Suitable for common thermoplastics like polypropylene, polystyrene and nylon. Used for basic air/moisture removal in transparent as well as opaque parts.
– Optical Grade: Same formulation as general purpose but contain no residues or contaminants that could cloud transparent plastic parts. Ideal for headlight lenses, disc drives etc.
– Flow Improvers: Enhanced flowing properties allow penetration into tightly packed injection molded parts. Effective for purging deep, narrow injection molded syringes.
– Moisture Scavengers: In addition to displacement, absorb and chemically bond with residual moisture inside parts. Required for applications sensitive to moisture like medical devices.
– Thermally Conductive: Added carbon or boron nitride particles increase thermal conductivity for heat sink and LED applications requiring efficient heat dissipation.
Purging Process
Typically, the production resin is first purged from the injection molding machine through a series of cleaning cycles using the selected purging compound. This prepares the machine and tool for actual part purging. Parts are then injection molded using the purging material instead of the regular resin. Multiple cycles may be required for thorough purging depending on part geometry and level of contamination. Finally, the purging compound is cleaned out before resuming production runs. Purging is performed periodically or whenever changes in production resins necessitate it.
Applications
Purging finds application across diverse industries where plastic parts are injection molded, blow molded or thermoformed:
– Automotive: Purging eliminates air traps in sensor housings, switch assemblies, fluid reservoirs impacting performance reliability.
– Consumer Goods: Removes moisture from food packaging, air pockets from blow molded containers ensuring dimensional stability.
– Electrical/Electronics: critical for enclosures, connectors to prevent dielectric breakdowns due to moisture.
– Medical: mandatory for tubing, syringes and implantable devices by safely evacuating air/moisture reducing particulate matter.
– Optics: Clears microscopic bubbles/particles from lenses, filters and precision parts used in LEDs, lasers.
Benefits and Best Practices
Purging delivers multiple manufacturing advantages by thoroughly eliminating internal voids and contaminants:
– Improved Part Quality: Residuals degrade plastic over time leading to loss of mechanical properties, discoloration.
– Enhanced Yields: Eliminates rejects caused by entrapped air in critical surfaces affecting performance.
– Consistent Dimensions: Purging removes moisture influencing stability of wall thicknesses, hole sizes.
– Extended Equipment Life: Prevents buildup of residue preventing mold/machine damage during production runs.
For best results, manufacturers incorporate regular planned purging aligned with tool/equipment PM schedules. Automation via purging stations streamlines the process. Proper selection of purging material type and multiple injection cycles further optimize contaminant removal from even complex plastic components.
Conclusion
As molded plastic components grow increasingly technical, purging compounds play a key role upholding reliability and consistency expectations in manufacturing. Their application ensures air and moisture trapped during production processes are fully evacuated, delivering defect-free parts essential for a wide range of industries. With advanced purging methods and formulation expertise, manufacturers can further enhance part quality and yields.
*Note:
1.Source: Coherent Market Insights, Public sources, Desk research
2.We have leveraged AI tools to mine information and compile it
