Delrin (Acetal POM-C) Homopolymer – Technical Material Specification
Comprehensive technical specification for Delrin (Acetal POM-C) Homopolymer, covering properties, Canadian stock sizing, machinability, defects, and handling for fabrication and machining operations.
Material Overview & Common Uses
Delrin (Acetal POM-C) Homopolymer is a high-crystalline engineering thermoplastic known for its excellent mechanical strength, stiffness, low friction, and dimensional stability. It is widely used in precision mechanical parts such as gears, bearings, bushings, conveyor components, and valve seats. In Canadian fabrication shops, it is common for jigs, fixtures, and wear strips due to its resistance to moisture and chemicals. POM-C grade offers improved thermal stability and reduced centerline porosity compared to POM-H, making it suitable for tight-tolerance machining.
Core Technical Properties & Sizing
| Property | Value |
|---|---|
| Density | 1.41 g/cm³ (ASTM D792) |
| Tensile Strength | 69 MPa (ASTM D638) |
| Elongation at Break | 25% (ASTM D638) |
| Flexural Modulus | 2.8 GPa (ASTM D790) |
| Hardness | Rockwell M94 (ASTM D785) |
| Coefficient of Friction | 0.20 (against steel, dry) |
| Continuous Service Temperature | -40°C to 100°C (short peaks to 140°C) |
| Water Absorption | 0.2% (24 hr immersion, ASTM D570) |
| Standard Canadian Sheet Sizes | 48" x 96" (1220 mm x 2440 mm) and 60" x 120" (1524 mm x 3048 mm) |
| Thickness Range | 1/16" (1.6 mm) to 4" (101.6 mm) in 1/16" increments up to 1", then 1/8" increments |
| Rod Diameters | 1/4" (6.35 mm) to 12" (304.8 mm) in 1/8" increments up to 2", then 1/4" increments |
| Tolerance (Sheet thickness) | ±0.005" for < 1/2", ±0.010" for 1/2" to 1", ±0.020" for > 1" |
| Tolerance (Rod diameter) | ±0.002" for < 1", ±0.005" for 1" to 3", ±0.010" for > 3" |
Machinability, Tooling & Feeds
Delrin machines very well with standard HSS or carbide tooling. It produces a fine, powdery chip and does not require coolant, though air blast or mist is recommended for chip evacuation.
| Operation | Spindle Speed (SFM) | Feed | Depth of Cut (in) |
|---|---|---|---|
| Turning | 800–1200 | 0.005–0.015 IPR | 0.050–0.150 |
| Milling | 600–1000 | 0.004–0.012 IPT | 0.020–0.100 |
| Drilling | 300–600 | 0.002–0.008 IPR (peck cycle for deep holes) | N/A |
Use sharp tooling with positive rake angles to avoid melting or stringy chips. Avoid excessive clamping pressure to prevent distortion. For tapping, use spiral point taps with 50–70% thread depth.
Common Defects & Quality Control
| Defect | Description | QC Method |
|---|---|---|
| Centerline porosity | Voids in thick rods | Visual inspection, ultrasonic testing for critical parts |
| Surface scratches | From handling or storage | Visual inspection; reject if depth exceeds 0.005" |
| Warpage | Residual stress from extrusion | Check flatness on granite table; reject if deviation >0.010" across 48" |
| Discoloration (yellowing) | Thermal degradation | Visual comparison to standard; reject if non-uniform |
| Cracks, bubbles, delamination | Obvious material flaws | Visual and acetone wipe test |
| Stress cracking | Chemical attack or residual stress | Acetone wipe test: apply a drop of acetone; if cracking occurs within 1 minute, reject |
Dimensional checks should be performed after 24-hour stabilization at 23°C/50% RH. Use a micrometer for thickness and a pin gauge for hole diameters. Reject material with visible cracks, bubbles, or delamination.
Storage, Handling & Racking Guidelines
Store Delrin sheets and rods flat on a clean, dry surface away from direct sunlight and heat sources. Ideal storage temperature: 15–25°C. Avoid stacking heavy loads on top of sheets to prevent warpage. Use vertical racks for rods with padded supports to prevent bending. Keep material covered with a breathable tarp to reduce dust accumulation. Do not store near solvents or strong acids. For long-term storage, wrap in polyethylene film to minimize moisture absorption. Rotate stock using FIFO to avoid age-related embrittlement.