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420px-Polyoxymethylene.svg

The Accuhaler is made of a material called POM, or Polyoxymethylene, a thermoplastic polymer which also goes under the names acetalpolyacetal and polyformaldehyde. It is used in precision parts requiring high stiffness, low friction and excellent dimensional stability.

"It is similar to nylon but is stiffer and has better fatigue
and water resistance - nylons, however, have better impact and abrasion resistance. It is rarely used without
modifications: most often filled with glass fiber, flame retardant additives or blended with PTFE or PU. The
last, POM/PU blend, has good toughness. POM is used where requirements for good moldability, fatigue
resistance and stiffness justify its high price relative to mass polymers, like polyethylene, which are
polymerized from cheaper raw materials using lower energy input." From Cambridge Engineering Selector

List of PropertiesEdit

[Taken from Cambridge Engineering Selector].

Mechanical PropertiesEdit

  • Density: 1.39e3 - 1.43e3 kg/m^3
  • Young's Modulus: 2.5 - 5 GPa
  • Yield Strength (Elaqstic Limit): 48.6 - 72.4 MPa
  • Tensile Strength: 60 -89.6 MPa
  • Compressive Strength: 74.9 - 124 MPa
  • Fatigue Strength at 10^7 cycles: 21.9 - 34.2 MPa
  • Fracture Toughness: 1.71 - 4.2 MPa.m^0.5

Thermal PropertiesEdit

  • Melting Point: 160 - 184 °C
  • Maximum Service Temp:  76.9 - 96.9 °C
  • Thermal Conductivity: 0.221 - 0.36 W/m.°C
  • Specific Heat Capacity: 1.36e3 - 1.43e3 J/kg.°C
  • Thermal Expansion Coefficient 75.7 - 202 μstrain/°C

Processibility (higher is better, 5 is max)Edit

  • Castability: 1 - 2
  • Moldability: 4 - 5
  • Machinability: 3 - 4
  • Weldability: 4 - 5

DurabilityEdit

  • Flammability: Highly Flammable
  • UV Radiation: Poor
  • Water: Excellent

For more detailed properties, see PDF in Dropbox.

CostEdit

Designsite.dk lists the price as 'high cost', and indeed it can be found on Alibaba for $1300 - $2500/Ton, which equates to £0.90 - £1.74/kg (assuming a short US ton is in mind (907kg), and the current exchange rate of $1 to £0.6332. This puts the total price of the material at ............. (We need some scales).

Similarly, CES puts the price at £1.41 - 1.56kg. This is actually not that high compared to other polymers (see comparison charts below.

ProductionEdit

  • According to designsite.dk, the production of Acetal requires the equivalent of about 2 1/2 kg of oil (raw material and energy).
  • Embodied Energy in Primary Production: 85.4 - 94.4 MJ/kg
  • CO2 Footprint: 3.85 - 4.26 kg/kg
  • Water Usage: 138 - 413 l/kg

ProcessingEdit

End of Life Edit

  • Designsite.dk says that incinerating releases mainly carbon dioxide and water, and that the heating value is equivalent to 1/4kg of Oil. 
  • Warrengin, a moderator on the Core77 forums , has this to say: "You don't see acetal (Delrin is just a brand name) recycled very often because it's not produced in the quantities like those of commodity resins like HDPE, LDPE, PP, PS, etc. However, you should always mark your parts to identify the material so that it doesn't contaminate other materials when the product is disassembled. The symbol for acetal is POM (stands for polyoxymethylene)."
  • It is recyclable, though, Recycle Mark 7 (Other).
  • Embodied Energy, Recycling: 33.2 - 36.7 MJ/kg
  • CO2 footprint: 2.61 - 2.88 kg/kg
  • Recycle Fraction in current supply: 0.5 -1 % (comparable to other polymers, although Polystyrene, Polypropylene and Polyethylene are higher, PE being 7.5 - 9.5 %)
  • Combustion CO2 1.43 - 1.5 kg/kg
  • Can go in Landfill
  • Doesn't Biodegrade
  • Non-Toxic

Comparing to other PolymersEdit

  • Cost vs Elastic Modulus
  • Cost vs Fatigue Strength
  • Cost vs Fracture Toughness
  • Embodied Energy: Initial Production vs Recycling
  • Moulding Energy vs Extrusion Energy
  • CO2: Initial Production vs Extrusion
  • CO2: Recycling vs Moulding