Odor Control Methods for POM Injection Molding

POM (Polyoxymethylene, Acetal) is widely applied for precision mechanical gears, wear-resistant structural components with high hardness, low friction coefficient, stable dimension and excellent fatigue resistance. However POM features poor thermal stability and decomposes into irritant formaldehyde under high molding temperature, excessive shear friction and prolonged thermal retention, polluting workshop environment and triggering bubble, silver streak and brittle crack on finished products. Systematic odor control covering raw material pre-treatment, temperature setting, process optimization, mold venting, equipment maintenance and site management improves working condition and production yield.

1. Raw Material Selection and Pre-drying to Reduce Gas Generation Source

Low-odor modified virgin POM blended with heat stabilizer and formaldehyde scavenger is prioritized to restrain thermal decomposition and volatile emission; recycled crushed material is minimized or forbidden because repeated high-temperature shear breaks polymer chain, brings extra impurity and aggravates odor during secondary molding. POM owns low water absorption yet adsorbs surface moisture, dust and slight grease; absorbed water accelerates molecular cleavage and gasification under high barrel temperature. Raw material is dried at 70~80℃ for 2~3 hours before molding to remove surface adsorbed moisture and stored under sealed dry condition away from greasy and corrosive gas to cut odor inducement from contaminated feedstock.

2. Sectional Barrel Temperature Control to Prevent Overheat Decomposition

Excessive temperature is the primary cause of POM degradation and odor emission. Critical decomposition temperature of POM is low with maximum allowable temperature below 210℃; barrel is set by segmented heating: rear zone 200~205℃, middle zone 195~200℃ and nozzle 190~195℃. Barrel temperature is reduced by 10~15℃ during temporary shutdown and standby to avoid long-term detained melt carbonization and persistent formaldehyde release. Remaining degraded material is purged by full idle shot before mass production, mold change and material switching; screw and barrel are disassembled periodically to clear accumulated carbon deposit which catalyzes fresh POM degradation and continuous odor emission.

3. Injection Process Optimization to Cut Shear-induced Thermal Decomposition

Normal barrel temperature with severe workshop odor is mainly caused by excessive shear heat from high injection speed, high screw rotation and over high packing pressure leading to instantaneous local overheating and decomposition. Low-speed medium-pressure stable plasticizing is adopted: injection velocity is segmented and reduced to avoid frictional overheat from rapid melt flow; screw rotation speed and packing pressure are properly lowered to minimize compression-induced thermal degradation inside mold. Stable production cycle avoids frequent intermittent shutdown and fluctuating temperature accelerating POM aging and aggravating odor.

4. Mold Vent Improvement for Timely Exhaust of Decomposed Gas

Trapped decomposed gas accumulates inside cavity and overflows intensively during mold opening to form pungent odor alongside bubble and burnt mark. Continuous vent slot along melt flow is opened on parting line with depth 0.01~0.02mm; breathable steel and exhaust ejector pin are embedded at rib, boss and melt convergence blind corner plus extra overflow well to exhaust internal gas promptly. Hot runner temperature is precisely regulated to eliminate detained degraded material and local overheating inside hot nozzle; vent groove dirt is cleaned regularly to avoid blocked exhaust and concentrated odor release.

5. Daily Equipment Maintenance to Eliminate Persistent Hidden Odor Source

Screw abrasion, barrel scratch and nozzle carbon deposit induce continuous raw material retention and degradation after long-term production with regular cleaning and maintenance schedule. All deteriorated residual melt is fully purged before restart after long downtime and mass production starts only after transparent stable melt output. Crushing workshop adopts fully closed operation for POM granule and powder with centralized sealed storage of fine powder prone to thermal volatilization. Once white fog and bubble appear on finished parts indicating partial POM decomposition, temperature is lowered immediately and barrel cleaned to stop batch gas generation and defective production.

6. Workshop Ventilation and Terminal Exhaust Treatment

Local air exhaust hood is installed beside mold parting line and injection nozzle to extract volatile formaldehyde instantly during mold opening; workshop fresh air circulation system keeps continuous air convection to avoid concentrated irritant gas accumulation. Activated carbon adsorption device is equipped for large-batch high-odor production to absorb volatile organic gas and further optimize on-site working environment.

Full-chain odor management integrating low-odor raw material, precise temperature control, shear reduction, optimized venting, regular equipment maintenance and workshop ventilation drastically reduces POM thermal decomposition and formaldehyde emission, eliminates pungent workshop odor and cuts bubble and crack defects to realize eco-friendly high-yield POM injection molding.