The molding technician at Precision Components Inc. attempted to solve a filling issue by setting the barrel temperature to 230°C, which he believed would enhance flow for a thin-walled POM gear. The machine produced a strong odor within minutes of operation. The POM material underwent thermal breakdown, which resulted in formaldehyde gas emissions and the production of black specks that contaminated the entire production run. The lesson required six hours of operational shutdown time, together with complete barrel cleaning and the disposal of 500 kg of Celanese Hostaform C 9021 material. The material reached its melting point at 166°C. The technician had exceeded the safe processing limit by 64°C when he operated the device.
The scenario demonstrates why knowledge of POM melting temperature goes beyond being a technical requirement. The process control parameter functions as a critical requirement that determines whether production operations will succeed or fail. The engineers who need to understand POM for precision component manufacturing must learn how to distinguish between melting point and processing temperature and the thermal decomposition threshold.
The guide presents you with essential temperature information required for secure processing of POM. We present the essential distinctions between POM homopolymer and copolymer melting patterns together with processing ranges for major branded grades which include Hostaform and Ultraform and Delrin and the safety thresholds that protect against thermal degradation. You will learn the specific temperature settings for your application at the end which will help you prevent expensive errors that occur when POM thermal limits are exceeded.
What Is POM and Why Melting Temperature Matters
POM Material Overview
POM (polyoxymethylene), which people refer to as acetal, functions as a semi-crystalline thermoplastic material that exhibits strong stiffness properties together with reduced friction and outstanding dimensional stability. The material’s semi-crystalline structure creates a sharp melting transition. POM maintains solid properties until it reaches its melting point when it changes to a flowable melt state which happens within a short time.
The sharp melting behavior of this material creates both beneficial effects and restrictive limitations. POM achieves precise tolerances during heating processes although its processing requirements need exact temperature management. Processors cannot rely on gradual softening. The process requires operators to keep barrel and mold temperatures within designated limits so they can maintain continuous flow without causing thermal degradation.
Why Melting Temperature Is Critical
The difference between POM’s melting point and its decomposition temperature is surprisingly small. The safe processing range for POM copolymer extends to 50°C according to its specifications. The processing range for POM homopolymer stands at 10°C which is narrower than that of other materials. The polymer chain breaks down when you exceed these limits which results in formaldehyde release, an irritant gas that becomes potentially explosive at certain concentrations.
For production engineers, understanding these temperature boundaries is essential for:
- Setting barrel zone temperatures that achieve flow without degradation
- Optimizing mold temperatures for part quality and cycle time
- Troubleshooting defects like black specks, voids, and dimensional instability
- Selecting the right POM grade for applications with elevated service temperatures
POM Melting Temperature Overview
Melting Point Ranges by Type
POM exists in two main chemical structures: homopolymer and copolymer. Each has distinct melting characteristics that drive processing behavior.
POM Homopolymer (POM-H)
- Melting Point: 175–185°C
- Typical Value: ~181°C for DuPont Delrin grades
- Structure: Highly regular crystalline chain with repeating -CH₂O- units
- Crystallinity: ~70–80%
The regular molecular structure of POM-H creates a higher melting point than copolymer grades. This higher melting point enables slightly better high-temperature resistance in service but requires higher processing temperatures and creates a narrower safe processing window.
POM Copolymer (POM-C)
- Melting Point: 160–175°C
- Typical Value: ~165–166°C for most commercial grades
- Structure: Trioxane copolymerized with 1,3-dioxolane, introducing -CH₂CH₂O- units
- Crystallinity: ~60–70%
The comonomer disrupts perfect crystalline regularity, lowering the melting point. However, this same disruption improves thermal stability during processing, giving POM-C a wider processing window and better resistance to thermal degradation.
Key Thermal Properties Comparison
| Property | POM-H (Homopolymer) | POM-C (Copolymer) |
|---|---|---|
| Melting Point | 175–185°C | 160–175°C |
| Glass Transition (Tg) | –60°C to –50°C | –60°C to –50°C |
| Heat Deflection Temp (1.8 MPa) | 110–140°C | 95–110°C |
| Vicat Softening Point | ~174°C | ~150°C |
| Max Service Temperature | 90–105°C | 80–100°C |
| Decomposition Temperature | >240°C | >240°C |
| Thermal Conductivity | 0.23–0.31 W/m·K | 0.23–0.31 W/m·K |
Temperature Effects on Properties
Crystallization Kinetics: POM crystallizes rapidly upon cooling. At mold temperatures of 80–100°C, crystallization completes within 5–10 seconds. This rapid solidification enables short cycle times but requires consistent mold temperature control to achieve uniform shrinkage and dimensional stability.
Shrinkage Behavior: POM exhibits higher shrinkage than most engineering plastics, typically 1.8–2.5% depending on grade and processing conditions. Mold temperature directly affects shrinkage. Higher mold temperatures increase crystallinity, resulting in greater shrinkage but better mechanical properties.
Mechanical Property Retention: POM maintains excellent mechanical properties up to its heat deflection temperature. Above HDT, stiffness drops rapidly as the polymer approaches its glass transition region. For structural applications, keep continuous service temperatures at least 10°C below the HDT for the specific grade.
POM-H vs POM-C: Processing Temperature Comparison
Processing Temperature Ranges
The practical difference between POM-H and POM-C manifests most clearly in processing parameters. The following table summarizes typical temperature settings for injection molding:
| Parameter | POM-H (Delrin) | POM-C (Hostaform/Ultraform) |
|---|---|---|
| Melt Temperature | 195–215°C | 185–210°C |
| Optimal Melt | 205–210°C | 200°C |
| Mold Temperature | 80–120°C | 80–100°C |
| Nozzle Temperature | 200–210°C | 190–200°C |
| Processing Window | ~10°C | ~50°C |
| Pre-Drying Temp | 80–100°C | 80–100°C |
| Drying Time | 3–4 hours | 3–4 hours |
Critical Safety Limits
Maximum Safe Temperature: 240°C
Both POM types begin thermal decomposition above 240°C. Decomposition releases formaldehyde gas, which:
- Causes eye and respiratory irritation
- Creates black specks and degradation products in molded parts
- Can form explosive mixtures with air at certain concentrations
- Requires immediate ventilation and purging if detected
Never exceed 230°C in normal processing, even briefly. For POM-H, stay below 220°C to maintain margin against the narrower processing window.
Practical Processing Implications
POM-H Processing Challenges:
- Narrow processing window requires precise temperature control
- Higher melt temperatures increase energy consumption
- Greater risk of degradation if barrel temperatures drift
- Preferred for applications requiring maximum mechanical properties
- Best suited for experienced processors with tight process control
POM-C Processing Advantages:
- Wider processing window forgiving of temperature variation
- Lower melt temperatures reduce energy costs
- Better thermal stability during extended residence times
- Preferred for high-volume production and general-purpose molding
- Better suited for processors requiring consistent, trouble-free operation
When to Specify Each Type
Choose POM-H when:
- Maximum tensile strength and stiffness are required
- Part design assumes higher modulus material
- Operating environment is dry and controlled
- Dimensional stability at elevated temperatures is critical
- Centerline porosity can be managed through design or is not a concern
Choose POM-C when:
- Processing consistency and yield are priorities
- Chemical resistance to bases or hot water is required
- Thick sections require machining after molding
- Long-term thermal stability in service is important
- General-purpose mechanical properties are sufficient
Branded POM Grades: Melting Points and Processing Data
Celanese Hostaform Series (POM-C)
Hostaform is Celanese’s POM copolymer brand, widely specified in European automotive and industrial applications. All Hostaform grades share the same base melting point with variations in flow characteristics and additive packages.
| Grade | Melting Point | Melt Temp Range | MFR (g/10min) | Key Characteristics |
|---|---|---|---|---|
| C 9021 | ~166°C | 190–210°C | 2.5 | Standard grade, general purpose |
| C 27021 | ~166°C | 190–210°C | 7.0 | Easy flow, thin-wall parts |
| C 9021 GV1/20 | ~166°C | 190–210°C | 2.3 | 20% glass fiber, high stiffness |
| MT2U06 | ~166°C | 190–210°C | 2.6 | Medical grade, USP Class VI |
| SlideX CO313 | ~166°C | 190–210°C | 2.7 | Low friction, wear resistant |
Hostaform Thermal Stability:
- Maximum processing temperature: 230°C for stabilized grades
- Heat deflection temperature (unfilled): ~104°C at 1.8 MPa
- Continuous service temperature: up to 100°C in air
- Resistance to thermal and oxidative degradation validated for automotive underhood applications
Processing Recommendations:
- Optimal melt temperature: 200°C
- Mold temperature: 80–100°C (higher for gloss, lower for cycle time)
- Drying: 3–4 hours at 120°C, moisture ≤0.15%
Real-world example: A German automotive supplier specified Hostaform C 27021 for a fuel system component requiring thin-wall molding. The team reached their goal of filling 0.8 mm wall sections by maintaining a melt temperature of 200°C and a mold temperature of 90°C which allowed them to produce 500,000 pieces with unbroken 35-second cycle times. The copolymer grade which provided a broader processing window enabled them to achieve precise tolerances even when the barrel heating system experienced slight temperature changes.
BASF Ultraform Series (POM-C)
BASF Ultraform is the German chemical giant’s POM copolymer offering, extensively used in European OEM specifications and valued for its consistent quality and comprehensive technical documentation.
| Grade | Melting Point | Melt Temp Range | MFR (g/10min) | Key Characteristics |
|---|---|---|---|---|
| N2320 | 166–167°C | 190–230°C | 9.0 | Standard injection molding |
| N2520 XL2 | 166°C | 190–230°C | 7.0 | Heat-stabilized, HDT 116°C |
| W2320 | 166°C | 190–230°C | 13.0 | Very easy flow |
| H2320 | 166°C | 190–230°C | 4.0 | High molecular weight |
| S2320 | 166°C | 190–230°C | 9.0 | Standard, easy processing |
Ultraform Thermal Properties (per ISO 11357):
- Melting point measured by DSC: 166–167°C for standard grades
- Vicat softening point: 145–160°C
- HDT/A (1.8 MPa): 90–116°C depending on grade
- Maximum service temperature in air: ~100°C
Safety Warning: BASF explicitly warns that Ultraform POM may decompose and release formaldehyde when processed above 240°C. Adequate ventilation is mandatory, and strict temperature control must be maintained.
Processing Guidelines:
- Recommended melt temperature: 200°C (optimal)
- Mold temperature range: 60–120°C (90°C optimal)
- Injection pressure: 800–1,200 bar (80–120 MPa)
- Regrind usage: Up to 30% recommended
Polyplastics DURACON Series (POM-C)
DURACON is Polyplastics’ POM copolymer brand, dominant in Japanese and Asian automotive supply chains, particularly for Toyota, Honda, and Denso specifications.
| Grade | Melting Point | Melt Temp Range | MFR (g/10min) | Key Characteristics |
|---|---|---|---|---|
| M90-44 | ~166°C | 190–210°C | 9.0 | Standard injection grade |
| M25-44 | ~166°C | 190–210°C | 2.5 | Extrusion grade, high viscosity |
| M270-44 | ~166°C | 190–210°C | 27.0 | High flow, thin-wall |
| GH-25 | ~166°C | 190–210°C | — | 25% glass fiber reinforced |
| WR-01 | ~166°C | 190–210°C | 9.0 | Weather resistant, UV stabilized |
DURACON Processing Notes:
- Standard melt temperature: 190–210°C
- Mold temperature: 60–80°C for standard molding, up to 120°C for high-gloss surfaces
- Drying: 3–4 hours at 80–100°C
- Higher viscosity grades (M25) require higher melt temperatures for adequate flow
DuPont Delrin (POM-H)
Delrin is the original acetal homopolymer brand from DuPont, still widely referenced in North American specifications and available as both semi-finished shapes and resin pellets.
| Grade | Melting Point | Melt Temp Range | MFR (g/10min) | Key Characteristics |
|---|---|---|---|---|
| 500P | ~181°C | 205–215°C | 18.0 | General purpose |
| 100P | ~181°C | 205–215°C | 2.5 | High viscosity, toughest |
| 900P | ~181°C | 205–215°C | 50.0 | Low viscosity, fast cycling |
| 527UV | ~181°C | 205–215°C | 18.0 | UV stabilized |
Delrin Processing Considerations:
- Higher melt temperatures required due to higher melting point
- Narrower processing window demands tighter temperature control
- Greater tendency toward centerline porosity in thick sections
- Superior mechanical properties justify processing complexity for demanding applications
Processing Parameters by Method
Injection Molding
Injection molding is the most common processing method for POM. Temperature control is critical across all barrel zones.
Barrel Temperature Profile:
| Zone | POM-H | POM-C |
|---|---|---|
| Feed zone | 170–180°C | 160–170°C |
| Compression zone | 190–200°C | 180–190°C |
| Metering zone | 200–215°C | 190–210°C |
| Nozzle | 200–210°C | 190–200°C |
Mold Temperature Guidelines:
- Standard parts: 80–90°C
- High-gloss surfaces: 100–120°C
- Fast cycle times: 60–80°C (may reduce surface quality)
- Thick sections: 90–100°C (reduces internal stresses)
Critical Parameters:
- Injection pressure: 80–120 MPa (typically)
- Hold pressure: 40–60% of injection pressure
- Screw speed: <0.3 m/s peripheral speed
- Back pressure: 5–15 MPa (low, to minimize shear heating)
- Residence time: <10 minutes maximum
Extrusion
POM extrusion requires careful temperature control to prevent degradation during the longer residence times typical of extrusion processes.
Temperature Profile:
- Feed zone: 160–170°C
- Compression zone: 170–185°C
- Metering zone: 185–200°C
- Die: 190–210°C
Considerations:
- Use gradual temperature transitions to avoid overheating
- Monitor melt pressure for degradation indicators
- Keep screw speed moderate to minimize shear heating
- Use streamlined die designs to eliminate stagnation areas
Blow Molding
Blow molding of POM is less common but used for specific hollow part applications.
Temperature Settings:
- Parison temperature: 190–210°C
- Mold temperature: 15–40°C (rapid cooling required)
- Melting temperature in extruder: 180–200°C
Challenges:
- POM’s rapid crystallization can limit blow molding window
- Uniform wall thickness requires precise parison programming
- Part design must accommodate POM’s shrinkage characteristics
3D Printing (Emerging Technology)
POM 3D printing is an emerging application with specific thermal requirements.
Recommended Settings:
- Nozzle temperature: 200–220°C
- Bed temperature: 100–130°C
- Chamber temperature: 50–70°C (enclosure recommended)
- Print speed: Moderate to slow (20–40 mm/s typical)
Challenges:
- POM’s shrinkage and warpage make bed adhesion critical
- Limited availability of POM filament compared to ABS or PLA
- Post-processing annealing may be required for dimensional stability
Troubleshooting Temperature-Related Issues
Degradation and Black Specks
Symptoms: Black or brown specks in molded parts, pungent formaldehyde odor, reduced mechanical properties
Causes:
- Barrel temperature set too high (>240°C)
- Excessive residence time (>10 minutes)
- Dead zones in hot runner systems
- Contaminated regrind
Solutions:
- Reduce barrel temperatures by 10–20°C
- Increase injection speed to reduce residence time
- Purge machine thoroughly before restarting
- Check hot runner system for temperature uniformity
- Limit regrind to 30% maximum
Incomplete Filling (Short Shots)
Symptoms: Parts not filling completely, especially in thin sections
Causes:
- Melt temperature too low
- Mold temperature too cold
- Insufficient injection pressure
- Material viscosity too high for part geometry
Solutions:
- Increase melt temperature gradually (5–10°C increments)
- Increase mold temperature
- Increase injection pressure or speed
- Consider higher-flow grade (higher MFR)
Warpage and Dimensional Issues
Symptoms: Parts warping after ejection, inconsistent dimensions, internal stresses
Causes:
- Uneven mold cooling
- Mold temperature too high
- Insufficient cooling time
- Non-uniform wall thickness
Solutions:
- Optimize mold temperature uniformity
- Reduce mold temperature slightly
- Increase cooling time in cycle
- Review part design for uniform wall sections
Sink Marks and Voids
Symptoms: Surface depressions (sink marks) or internal voids in thick sections
Causes:
- Insufficient packing/hold pressure
- Melt temperature too low (reduces packing effectiveness)
- Inadequate gate size
- Excessive shrinkage in thick sections
Solutions:
- Increase hold pressure and time
- Slightly increase melt temperature to improve flow
- Optimize gate design for adequate packing
- Use rib design instead of thick solid sections
Surface Defects (Silver Streaks)
Symptoms: Silver streaks, splay marks, or surface delamination
Causes:
- Moisture in material (most common)
- Overheating causing volatile release
- Excessive shear heating
- Contamination
Solutions:
- Ensure proper pre-drying (3–4 hours at 120°C)
- Check dryer operation and desiccant condition
- Reduce melt temperature if overheating suspected
- Reduce injection speed to minimize shear heating
- Check material for contamination
Real-world example: An injection molder in the medical device industry experienced intermittent silver streaking in Hostaform MT2U06 components. The investigation discovered that the material dryer failed to achieve its designated 120°C temperature because of a defective heating element. The parts that used material dried at 80°C showed splay marks. The defect rate decreased from 8% to below 0.5% after we repaired the dryer and established a moisture content verification protocol that targeted ≤0.15% moisture content.
Safety Considerations
Thermal Decomposition Risks
POM thermal decomposition is a serious safety concern that all processors must understand and mitigate.
Decomposition Threshold: >240°C
Decomposition Products:
- Formaldehyde gas: Colorless, pungent odor, irritant to eyes and respiratory system
- Other volatile compounds: Dependent on specific grade and stabilizer package
- Solid degradation products: Black or brown char that contaminates parts and equipment
Health and Safety Hazards:
- Eye irritation and damage at elevated concentrations
- Respiratory tract irritation
- Potential carcinogenicity of formaldehyde (classified by IARC)
- Explosion risk: Formaldehyde-air mixtures can be explosive at certain concentrations
Workplace Safety Requirements
Ventilation:
- Adequate exhaust ventilation at barrel and die areas
- Local exhaust at hopper and purge points
- Avoid recirculating air systems in processing areas
Monitoring:
- Temperature alarms on all barrel zones
- Regular visual inspection for smoke or discoloration
- Formaldehyde detection systems for high-volume operations
Emergency Procedures:
- Immediate shutdown and ventilation if decomposition suspected
- Purge procedures for removing degraded material
- Personal protective equipment: Safety glasses, appropriate respiratory protection
Material Handling:
- Keep POM pellets away from open flames or ignition sources
- Store in cool, dry conditions
- Use grounded containers to prevent static buildup
Processing Safety Best Practices
- Never exceed 240°C on any barrel zone
- Monitor residence time — purge if material sits idle >10 minutes
- Use copper-free systems — copper alloys catalyze POM degradation
- Avoid stagnation zones in hot runners and dies
- Train operators to recognize decomposition signs (odor, smoke, black specks)
- Maintain emergency purge procedures and practice them regularly
Sourcing POM with Verified Thermal Properties
The Yifuhui Sourcing Advantage
For international buyers sourcing POM for temperature-critical applications, Yifuhui provides:
- Certified branded grades: Celanese Hostaform C 9021, C 27021; BASF Ultraform N2320, W2320; Polyplastics DURACON M90-44 — all with documented melting points per ISO 11357
- COA verification: Every batch includes Certificate of Analysis with melting point data, MFI, and thermal properties traceable to manufacturer specifications
- 25 kg MOQ: Trial quantities for process validation without volume commitment
- Processing guidance: Technical support for temperature settings based on grade and application
- Port of Shanghai logistics: 7–14 day lead times to major international destinations
Documentation Package Requirements
Every POM shipment for processing applications should include:
- Manufacturer-issued COA: Melting point, MFI, density, and key thermal properties
- Material Safety Data Sheet (MSDS): Thermal decomposition hazards and safety procedures
- Processing guidelines: Recommended temperature settings from the manufacturer
- Compliance certificates: FDA, RoHS, REACH as applicable to your industry
Verifying Thermal Properties on COA
When reviewing COA documentation for POM grades, verify:
- Melting point matches manufacturer specification:
- Hostaform C 9021: ~166°C
- Ultraform N2320: 166–167°C
- Delrin 500P: ~181°C
- MFI is within specification range: Deviation >10% from nominal may indicate off-spec material
- Lot number format is consistent with manufacturer’s numbering system
- Test methods are specified: ISO 11357 for melting point, ISO 1133 for MFI
Conclusion
The POM melting temperature function serves as an essential measurement that determines material properties and production methods for achieving final usage results. The POM copolymer (POM-C) begins to melt between 165 and 166 degrees Celsius, whereas the POM homopolymer (POM-H) starts melting at 181 degrees Celsius. The combination of POM’s low melting points and its precise melting behavior creates both advantages and limitations for processing.
The safe processing temperature range for POM-C extends from 190 degrees Celsius to 210 degrees Celsius whereas POM-H needs a temperature range of 205 degrees Celsius to 215 degrees Celsius. The two POM materials should maintain operation below 240 degrees Celsius because that temperature causes thermal decomposition which leads to formaldehyde gas emissions. The mold temperature range of 80 to 100 degrees Celsius produces optimal part quality while higher temperatures create better surface gloss and lower temperatures decrease cycle time.
When sourcing POM from China, verify that your supplier provides manufacturer-issued COA documentation with melting point data traceable to ISO 11357 testing. The 25 kg MOQ available from qualified distributors enables proper process validation before production commitment, reducing the risk of costly temperature-related processing failures.
Frequently Asked Questions
What is the melting point of POM plastic?
The melting point of POM plastic material reaches its determined value. POM copolymer (POM-C) melts at approximately 165–166°C. POM homopolymer (POM-H) melts at approximately 175–185°C, with DuPont Delrin grades typically around 181°C. The ISO 11357 DSC testing method determines the melting point of each grade, which has a slight variation between different grades.
What is the temperature difference between POM-H and POM-C melting points?
POM-H melts approximately 15–20°C higher than POM-C (181°C vs. 166°C typical). The elevated melting temperature necessitates higher operating temperatures which extend from 205 to 215 degrees Celsius compared to 190 to 210 degrees Celsius operating temperatures. POM-C enables wider processing capabilities because its melting point decreases while thermal stability remains intact.
What temperature should I set my injection molding barrel for POM?
The barrel temperature settings for POM copolymer (Hostaform, Ultraform, DURACON) should establish feed temperature at 160°C and metering temperature at 210°C while setting nozzle temperature between 190 and 200°C. The feed temperature for POM homopolymer (Delrin) should be set at 170°C while the metering temperature should reach 215°C and the nozzle temperature should remain between 200 and 210°C. The temperature in all zones must remain below 240°C.
Can POM be processed at 230°C?
The processing of POM copolymer grades permits operation at 230°C for short durations, although 200°C serves as the best temperature. The maximum temperature for POM homopolymer should remain below 220°C. At 230°C, processors need to maintain exact temperature control while providing enough ventilation and keeping residence time at a minimum.
What happens if POM overheats during processing?
The operational hazards which arise from POM excessive heat during its processing require evaluation. POM begins to decompose at temperatures above 240°C which results in formaldehyde gas release and the formation of black or brown degradation products. POM which experiences overheating results in production of black specks through reduced mechanical strength and increased safety risks. The processing work must stop immediately because decomposition activities need to be investigated.
What mold temperature is best for POM parts?
The standard temperature range for POM molding operations requires mold temperatures between 80 and 100 degrees Celsius. The use of higher mold temperatures which range between 100 and 120 degrees Celsius leads to better surface gloss while it creates longer production cycles. The use of lower mold temperatures which range between 60 and 80 degrees Celsius provides quicker production cycles but it causes decreased surface quality together with increased warpage risk.
Do different POM brands have different melting points?
The melting point of all POM-C grades which include Hostaform, Ultraform, DURACON, KOCETAL and FORMOCON exists within the range of 165 to 166 degrees Celsius. All Delrin POM-H grades reach their melting point at about 181 degrees Celsius. The differences between brands are in flow characteristics (MFI), additive packages, and processing behavior, not base melting point.
How do I prevent POM degradation during processing?
The barrel temperature needs to remain below 240 degrees Celsius with 230 degrees Celsius as the preferred maximum temperature. The material needs to stay in the system for less than 10 minutes. The material requires 3 to 4 hours of pre-drying at 120 degrees Celsius. The system requires proper airflow to function correctly. The melt contact areas in the system should not contain any copper or brass materials. The barrel zones require implementation of gradual temperature changes.
