POM-H Graphite5 is a specialized engineering thermoplastic that combines the excellent mechanical properties of acetal homopolymer (POM-H) with the self-lubricating characteristics of graphite fillers. This composite material has become increasingly important in precision CNC machining applications where low friction, dimensional stability, and wear resistance are critical performance requirements. Unlike standard acetal grades, the graphite addition transforms the polymer matrix into a bearing-grade material capable of operating in demanding environments without external lubrication.
The material designation refers to a polyoxymethylene homopolymer base resin compounded with approximately 5% graphite particles. This specific formulation strikes a balance between the inherent strength of POM-H and the tribological benefits of graphite. Engineers and product designers frequently select POM-H Graphite5 for components that must maintain tight tolerances while experiencing sliding contact, reciprocating motion, or rotational wear. This comprehensive guide examines the material’s composition, performance characteristics, and best practices for CNC machining.
Chemische Zusammensetzung und Mikrostruktur des Materials
POM-H Graphite5 belongs to the acetal resin family, which is known for its high crystallinity and exceptional mechanical strength. The homopolymer variant offers superior mechanical properties compared to copolymer grades, making it the preferred base resin for demanding engineering applications.
Base Polymer Matrix
The homopolymer acetal matrix consists of repeating oxymethylene units (-CH2-O-) that form highly crystalline structures. This molecular architecture provides the material with its characteristic stiffness, creep resistance, and dimensional stability. The homopolymer designation indicates that the polymer chains are composed entirely of oxymethylene units without comonomer interruptions, resulting in higher crystallinity and improved mechanical performance compared to acetal copolymers.
Graphite Filler System
The graphite component in POM-H Graphite5 is typically a fine-particle synthetic graphite dispersed uniformly throughout the polymer matrix. At approximately 5% loading by weight, the graphite particles create a continuous lubricating film at the wear interface during sliding contact. This filler system reduces the coefficient of friction from approximately 0.35 for unfilled POM-H to around 0.15-0.20 for the graphite-filled grade. The graphite particles also improve thermal conductivity, helping to dissipate frictional heat away from critical contact zones.
Additive Package
Commercial POM-H Graphite5 formulations may include small amounts of stabilizers, antioxidants, and processing aids. These additives protect the polymer from thermal degradation during processing and extend the service life of finished components. The specific additive package varies among manufacturers, but typical formulations include hindered phenol antioxidants and heat stabilizers at concentrations below 1% by weight.
Mechanical Properties and Performance Characteristics
POM-H Graphite5 exhibits a unique combination of mechanical properties that make it suitable for precision components operating under load and motion. Understanding these properties is essential for proper material selection and component design.
Tensile and Compressive Strength
The material maintains most of the structural strength of unfilled POM-H while gaining improved wear characteristics. Typical tensile strength values range from 60-70 MPa, with elongation at break between 15-25%. The compressive strength is particularly notable, with values around 100-110 MPa at 10% deformation. These properties allow POM-H Graphite5 components to withstand significant static and dynamic loads without permanent deformation.
Impact Resistance and Fatigue Behavior
POM-H Graphite5 demonstrates good impact resistance, with Izod impact values typically ranging from 5-8 kJ/m² at room temperature. The material also exhibits excellent fatigue resistance, capable of withstanding millions of load cycles when stresses remain below the endurance limit. The graphite filler slightly reduces impact strength compared to unfilled POM-H, but the trade-off is acceptable for most bearing and wear applications.
Wear and Friction Properties
The primary advantage of POM-H Graphite5 lies in its tribological performance. The material achieves a dynamic coefficient of friction of approximately 0.15-0.20 against hardened steel under dry running conditions. The wear rate against steel counterfaces is typically 10-20 times lower than unfilled POM-H. Table 1 summarizes the key mechanical properties of POM-H Graphite5 compared to standard POM-H.
| Eigenschaft | POM-H Graphite5 (Typical Values) | Unfilled POM-H (Typical Values) | Prüfnorm |
|---|---|---|---|
| Zugfestigkeit | 62 MPa | 70 MPa | ISO 527 |
| Bruchdehnung | 20% | 35% | ISO 527 |
| Compressive Strength (10% Def.) | 105 MPa | 110 MPa | ISO 604 |
| Izod-Schlagzähigkeit (mit Kerbe) | 6 kJ/m² | 8 kJ/m² | ISO 180 |
| Dynamic Coefficient of Friction | 0.17 | 0.35 | Pin-on-Disk |
| Wear Rate (vs. Steel) | 0.5 x 10⁻⁶ mm³/Nm | 8 x 10⁻⁶ mm³/Nm | Pin-on-Disk |
Physikalische und thermische Eigenschaften
The physical characteristics of POM-H Graphite5 influence both its processing behavior and its performance in end-use applications. Thermal properties are particularly important for components operating in elevated temperature environments.
Dichte und Wasseraufnahme
POM-H Graphite5 has a density of approximately 1.42 g/cm³, slightly higher than unfilled POM-H due to the graphite content. The material exhibits very low moisture absorption, typically less than 0.2% when immersed in water for 24 hours. This low moisture uptake contributes to excellent dimensional stability, as the material does not swell or shrink significantly with changes in ambient humidity.
Thermal Stability and Operating Temperature Range
The continuous service temperature for POM-H Graphite5 ranges from -40°C to +100°C, with short-term exposure possible up to 140°C. The heat deflection temperature at 1.8 MPa is approximately 110°C. The graphite filler improves thermal conductivity to about 0.5 W/m·K, compared to 0.3 W/m·K for unfilled POM-H. This enhanced thermal conductivity helps dissipate frictional heat in bearing applications, reducing the risk of localized overheating and premature failure.
Electrical and Chemical Resistance
POM-H Graphite5 retains the excellent chemical resistance of acetal homopolymer. The material resists attack by most organic solvents, weak acids, and weak bases at room temperature. However, strong acids and oxidizing agents can cause degradation. The graphite filler slightly increases electrical conductivity compared to unfilled POM-H, but the material remains essentially an electrical insulator with surface resistivity above 10¹² ohms per square.
Anwendungen und Branchenfälle
POM-H Graphite5 finds applications across numerous industries where low friction and wear resistance are critical. The material’s combination of mechanical strength and self-lubricating properties makes it an economical alternative to metal bearings and bushings.
Automotive Components
In the automotive sector, POM-H Graphite5 is used for seat belt mechanisms, window regulator slides, gear shift components, and throttle body bushings. The material’s low friction properties eliminate the need for grease fittings in many applications, reducing maintenance requirements. Components machined from POM-H Graphite5 often replace metal parts to reduce weight and eliminate corrosion concerns. For instance, precision components such as CNC-bearbeitete Schaltwippen benefit from the material’s dimensional stability and wear resistance.
Industrielle Maschinen und Anlagen
Industrial applications include conveyor system rollers, guide rails, cam followers, and wear pads. The material’s ability to operate without external lubrication makes it ideal for food processing equipment where lubricant contamination must be avoided. Textile machinery, packaging equipment, and material handling systems frequently incorporate POM-H Graphite5 components. The material also serves well in Montageblöcke and alignment fixtures where dimensional accuracy must be maintained over extended service periods.
Medical and Precision Instruments
The medical device industry uses POM-H Graphite5 for surgical instrument handles, drug delivery mechanisms, and diagnostic equipment components. The material’s biocompatibility, combined with its low friction and wear characteristics, makes it suitable for devices that require smooth, reliable operation. Precision instruments, including Präzise CNC-Kamerateile, benefit from the material’s dimensional stability and consistent performance across temperature variations.
CNC Machining Considerations for POM-H Graphite5
Machining POM-H Graphite5 requires specific techniques to achieve optimal surface finish and dimensional accuracy. The material machines similarly to unfilled POM-H but presents some unique challenges due to the abrasive nature of the graphite filler.
Werkzeugauswahl und Geometrie
Carbide tooling is recommended for machining POM-H Graphite5 due to the abrasive graphite particles. High-speed steel tools may exhibit accelerated wear, particularly in production environments. Positive rake angles of 10-15 degrees help produce clean cuts and prevent material smearing. Sharp cutting edges are essential to achieve good surface finishes, as dull tools tend to generate heat and cause localized melting.
Cutting Parameters and Speeds
Table 2 provides recommended cutting parameters for common machining operations on POM-H Graphite5.
| Bearbeitung | Schnittgeschwindigkeit (m/min) | Vorschubgeschwindigkeit (mm/Umdrehung) | Schnitttiefe (mm) |
|---|---|---|---|
| Drehen | 150-250 | 0.10-0.25 | 1-3 |
| Milling (Roughing) | 100-200 | 0.05-0.15 mm/tooth | 2-4 |
| Milling (Finishing) | 150-250 | 0.03-0.08 mm/tooth | 0.2-0.5 |
| Bohren | 50-100 | 0.05-0.15 | N/A |
Chip Control and Cooling
POM-H Graphite5 produces short, broken chips during machining, which aids in chip evacuation. However, the graphite particles can create fine dust that may be irritating if inhaled. Adequate ventilation or mist cooling is recommended. Coolant is generally not required for machining, but compressed air can help clear chips and maintain temperature control. If coolant is used, water-soluble types are preferred over oil-based fluids, which may cause swelling of the polymer.
Design Guidelines and Tolerances
Proper component design is essential to maximize the performance of POM-H Graphite5 parts. The material’s low moisture absorption and high dimensional stability allow for tight tolerances, but designers must account for the material’s relatively high coefficient of thermal expansion.
Dimensional Stability and Tolerances
POM-H Graphite5 can be machined to tolerances of ±0.025 mm in controlled environments. The coefficient of linear thermal expansion is approximately 90 x 10⁻⁶ per °C, which is higher than metals. Components operating across wide temperature ranges require careful tolerance analysis to prevent binding or excessive clearance. For critical applications, machinists should allow parts to stabilize at room temperature before final inspection.
Wall Thickness and Feature Design
Minimum recommended wall thickness for POM-H Graphite5 components is 1.5 mm for injection-molded parts, but CNC machining allows for thinner sections down to 0.5 mm in localized areas. Sharp internal corners should be avoided, with minimum radii of 0.5 mm recommended to prevent stress concentration. Threaded features should have a minimum of 75% thread engagement for optimal strength. The material’s excellent machinability permits complex geometries, including the Schraubenkopf-Typen commonly used in fastening applications.
Vergleich mit verwandten Materialien
Understanding how POM-H Graphite5 compares to other engineering plastics helps designers make informed material selections. Several alternatives offer different balances of properties.
POM-H Graphite5 vs. POM-C with PTFE
Acetal copolymer with PTFE filler is a common alternative to POM-H Graphite5. While both materials offer low friction, PTFE-filled grades typically achieve lower coefficients of friction (0.10-0.15) but exhibit higher wear rates under high loads. POM-H Graphite5 generally provides better wear resistance under boundary lubrication conditions and maintains lower friction at higher sliding velocities. The graphite-filled grade also offers better thermal conductivity, making it superior for high-speed applications.
POM-H Graphite5 vs. Nylon with Molybdenum Disulfide
Nylon grades filled with molybdenum disulfide provide similar self-lubricating properties but differ significantly in moisture absorption. Nylon absorbs up to 8% moisture by weight, causing dimensional changes and property variation. POM-H Graphite5 maintains consistent properties regardless of humidity, making it the preferred choice for precision components in environments with variable humidity. Table 3 summarizes the key differences between these materials.
| Eigenschaft | POM-H Graphite5 | POM-C with PTFE | Nylon with MoS2 |
|---|---|---|---|
| Feuchtigkeitsaufnahme (24h) | 0.2% | 0.2% | 1.5-2.0% |
| Reibungskoeffizient | 0.17 | 0.12 | 0.20 |
| Max Continuous Service Temp | 100°C | 95°C | 90°C |
| Maßstabilität | Ausgezeichnet | Ausgezeichnet | Gut |
| Wear Resistance (High Load) | Ausgezeichnet | Gut | Gut |
Tuofa CNC: Precision Machining of POM-H Graphite5
Tuofa CNC Germany specializes in precision CNC machining of engineering plastics, including POM-H Graphite5. Our manufacturing capabilities ensure that components meet the most demanding specifications with consistent quality and reliability.
Advanced CNC Machining Capabilities
Tuofa CNC operates state-of-the-art 3-axis and 5-axis CNC machining centers capable of producing complex POM-H Graphite5 components with tolerances as tight as ±0.01 mm. Our machining expertise extends to producing components for diverse industries, including the Präzision von Klemmenblöcken applications that require excellent electrical insulation and mechanical stability. We employ specialized tooling and machining parameters optimized for graphite-filled polymers to achieve superior surface finishes and dimensional accuracy.
Qualitätssicherung und Prüfung
Every POM-H Graphite5 component produced by Tuofa CNC undergoes rigorous quality inspection using coordinate measuring machines and optical measurement systems. We verify critical dimensions, surface finish, and material properties to ensure compliance with customer specifications. Our quality management system follows ISO 9001 standards, and we provide comprehensive documentation including material certificates and inspection reports. For applications requiring traceability, we maintain complete batch records linking raw material lots to finished components.
Fazit
POM-H Graphite5 represents an excellent choice for engineers seeking a machinable plastic with exceptional wear resistance and low friction characteristics. The material combines the strength and dimensional stability of acetal homopolymer with the self-lubricating benefits of graphite filler, making it ideal for bearings, bushings, guides, and precision components across automotive, industrial, and medical applications. Its low moisture absorption ensures consistent performance in varying environmental conditions, while the material’s machinability allows for tight tolerances and complex geometries. When selecting POM-H Graphite5 for your next project, consider the operating temperature range, load conditions, and counterface material to optimize component design. With proper machining techniques and design considerations, POM-H Graphite5 delivers reliable, long-lasting performance in demanding applications.