Polyoxymethylene (acetal)

STANDARDISO 29988FORMBar, sheet, moulded partTrade nameDelrin (homopolymer)

A rigid, dimensionally stable, low-friction engineering plastic. Used for small valve trim parts, bushings and stem bearings; good in water and oils.

HARDNESS: Rockwell M51–M88
Rm · MPa (typical): 44–66
TEMPERATURE: −40 … +100 °C
COST

Representative sample of POM: machined bar specimen — REPRESENTATIVE IMAGE

Design

Polymer; defined by its structure and filler type rather than chemical composition.

Mechanical properties

TYPE · CONDITION	Rm MPa	Elongation at break %	Hardness	Coefficient of friction	Water absorption %
Unfilled, typical	44–66	—	Rockwell M51–M88	0.11–0.35	0.2–0.8

Typical values (the standard gives no minimum values); they vary with grade and filler. Converted from US units.

Service temperature

−40 °C+100 °C−200−1000100200300400500600700800

−40 … 100 °C.

Physical properties and heat treatment

DENSITY: ≈ 1.41 g/cm³

Media suitability GENERAL TREND

Water

Steam

Mineral oil

Fuel, aliphatic HC

Ozone, outdoor

Dilute acid

Caustic

Ketones, esters

Emsal assessment. The final choice is made from corrosion tables, taking concentration, temperature, chloride content and flow velocity into account.

Strengths and weaknesses

Strengths

High rigidity and dimensional stability
Low friction and wear
Can be machined precisely

Weaknesses

Degrades in acids (especially strong ones)
Low UV resistance
Difficult to bond

Manufacturing and use

ECONOMY: Low to medium.
MANUFACTURING METHODS: Injection moulding · Turning from bar
TYPICAL VALVE PARTS: Bushing · Stem · Small ball and disc

Used in 2 Emsal products

084Threaded high-pressure ball valveSeal
130Flanged gate valveGate guide

Source: ISO 29988. Values compiled and verified by Emsal Vana; for binding values, refer to the current edition of the standard and the material certificate.