Engineering plastics

Delrin (Acetal)

Also: POM, POM-H, acetal, acetal homopolymer, polyoxymethylene, Delrin 150, Delrin 570 (glass-filled), Delrin AF (PTFE-filled), Tecaform AD, Celcon (copolymer), Hostaform (copolymer), Acetron GP (copolymer), Tecaform AH (copolymer)

Delrin is acetal homopolymer: the stiffest, most machinable general-purpose plastic, with low friction and good fatigue life. Values for natural extruded stock.

ASTM D6778 (POM molding and extrusion materials)UL 94 HBFDA 21 CFR 177.2470 (food-contact grades)

Sourcing Delrin parts or stock?

Attach a drawing (PDF or STEP) or describe the part; a U.S. shop that fits quotes it.

At a glance

Delrin (Acetal) typical properties
Density	1.41 g/cm³ (0.051 lb/in³)
Tensile strength	69-76 MPa (10-11 ksi) at yield
Yield strength	69 MPa (10 ksi) tensile yield (plastics neck rather than fracture; yield is the design number)
Hardness	Rockwell M 92-94 (Shore D 85)
Elongation	25-40% at break
Modulus of elasticity	3.1 GPa (0.45 Msi) tensile; 2.8 GPa (0.41 Msi) flexural
Thermal	Melts at 175 °C (347 °F); Tg about -60 °C (-76 °F); continuous service 82-90 °C (180-195 °F), copolymer to 100 °C (212 °F); HDT 120 °C (250 °F) at 1.82 MPa
Composition	Polyoxymethylene homopolymer, (CH2O)n, with thermal stabilizer; copolymer adds a few percent ethylene oxide comonomer

Typical values, Natural extruded rod and plate, unfilled homopolymer, dry, 23 °C (73 °F). Confirm against the mill certificate and the purchase spec.

MachinabilityExcellent: The best-machining engineering plastic: clean chips, good finish, holds ±0.05 mm (±0.002") in stable shops. Sharp tools, air or water-soluble coolant, and let it cool before final measurement.
WeldabilityFair: Acetal resists solvents, so it cannot be solvent bonded. Ultrasonic, hot-plate and spin welding work for molded parts. Adhesives need a plasma, flame or acid etch of the surface first; mechanical fastening is the norm.
FormabilityPoor: A crystalline polymer with a narrow melt window; it is not thermoformed or bent in practice. Parts are machined from stock or injection molded.
Corrosion resistanceGood: Resists fuels, oils, alcohols, most solvents, weak acids and bases. Attacked by strong acids, oxidizers and chlorine; homopolymer also loses strength in hot water and alkalis, where the copolymer is the better choice.

Delrin is the trade name for acetal homopolymer (POM-H), a highly crystalline thermoplastic that machines like brass and holds tolerances better than any other commodity engineering plastic. It is the default plastic for machined gears, bushings, rollers, cams, valve bodies and small precision parts because it is stiff, dimensionally stable, absorbs little water and has a naturally low coefficient of friction against steel.

The homopolymer is a little stronger and stiffer than acetal copolymer (Celcon, Hostaform, Acetron GP). The copolymer trades a few percent of strength for better resistance to hot water, alkalis and chlorinated water, a slightly higher continuous service temperature, and freedom from centreline porosity. Large-diameter homopolymer rod (roughly above 50 mm, 2") can carry porosity along its axis, which shows up as leaks in pressure parts and as a rough finish at the centre of a turned face. Buy a porosity-free grade, buy copolymer, or design the bore to remove the centre.

Two hard limits: acetal is attacked by strong acids and oxidizers (chlorine above a few ppm, concentrated bleach, pH below about 4), and it must never be laser cut or overheated. Above about 230 °C (450 °F) it depolymerizes and releases formaldehyde, so it is cut by machining, sawing or waterjet, and molded or machined rather than lasered.

Heat treatment

Not heat treated for properties. Stock shapes are stress relieved by the producer; for parts with heavy one-sided machining or tight tolerances, anneal at about 150-160 °C (300-320 °F) in air or oil, hold about 30 minutes per 6 mm (1/4") of thickness, and cool slowly, then finish machine.

Tempers and conditions

Natural (white) homopolymer
Black (UV-stabilized)
Porosity-free extruded rod
Glass-filled 20-30% (Delrin 570)
PTFE-filled bearing grade (Delrin AF)
Copolymer (Celcon, Hostaform, Acetron GP)
FDA / medical grades

Stock forms

Round rod
Plate and sheet
Tube
Square and rectangular bar
Molding pellets

Relative cost

Tier 2 of 5. Around 2-3x HDPE per pound and a little more than nylon; homopolymer costs slightly more than copolymer. Machining time is low, so finished parts are often cheaper than in other plastics.

Typical applications

Gears, sprockets and racks
Bushings, bearings, rollers and wear pads
Valve bodies, pump parts and fittings
Snap-fit and spring features in molded parts
Conveyor and packaging machine components
Electrical insulators and connector bodies
Fuel-system and automotive interior parts

Process compatibility

How Delrin takes each process, and what to specify. Each process links to its own guide and to the shops that do it.

Delrin (Acetal) process compatibility
Process	Rating	Notes
CNC Machining	ExcellentExcellent	The plastic of choice for tight-tolerance machined parts; chips cleanly and holds size. Can Delrin be machined?
CNC Milling	ExcellentExcellent	Fast at high spindle speeds with sharp carbide; deburrs easily by hand or vibratory bowl.
CNC Turning	ExcellentExcellent	Excellent finish from rod; large diameters may show centreline porosity, so specify porosity-free stock for seals and pressure parts.
Swiss Machining	GoodGood	Small precision pins, bushings and inserts from ground rod; low tool wear and no smearing.
Injection Molding	ExcellentExcellent	A major molding resin: gears, clips, housings; shrinkage about 2%, so allow for it in tolerances and warp.
Waterjet Cutting	GoodGood	The right way to profile plate without heat; a slightly frosted edge, finish-machine if the edge matters.
Laser Cutting	Not recommendedNot recommended	Do not laser cut acetal: it depolymerizes and releases formaldehyde, and the edge chars. Machine, saw or waterjet instead. Can Delrin (acetal) be laser cut?
FDM 3D Printing	PoorPoor	Prints badly: warps, bonds poorly to the bed and to itself. Machine it or print nylon or PETG as a stand-in.
SLS 3D Printing	Not recommendedNot recommended	Not an SLS material; laser-sintered nylon (PA12) is the usual substitute for prototypes.
Vibratory Finishing	GoodGood	Removes burrs and softens edges on molded and machined parts without scratching.
Bead Blasting	FairFair	Gives a uniform matte texture; use fine media and low pressure to avoid embedding grit in a bearing surface.
Anodizing	Not recommendedNot recommended	An electrochemical oxide process for aluminum; it does nothing to a plastic. Color acetal by buying black or pigmented stock.
Plating	Not recommendedNot recommended	Acetal is not a plating-grade plastic; adhesion is poor even with etching. Use ABS or a PC/ABS blend for plated plastic parts.

Compare Delrin

Delrin vs Nylon Delrin vs UHMW

Design and sourcing tips

Say which acetal you mean: "Delrin 150" or "acetal homopolymer" for stiffness and fatigue, "acetal copolymer" for hot water, chlorinated water or alkaline service.
For pressure-tight or sealing parts turned from rod above about 50 mm (2"), specify porosity-free stock or copolymer, or the part may weep through centreline porosity.
Allow for thermal expansion: about 100-120 um/m·K, ten times steel. A 300 mm part grows about 0.5 mm over a 40 °C swing, so leave clearance in metal housings.
Keep tolerances realistic: ±0.05 mm (±0.002") is achievable on small features, ±0.1-0.13 mm (±0.004-0.005") is normal. Tighter costs money and drifts with temperature.
Never specify laser cutting, flame polishing or any process that heats acetal past about 230 °C (450 °F): it releases formaldehyde.
Press fits and snap fits work well, but keep strain under about 2-3% for a lasting fit; acetal creeps less than nylon but is not a spring.

Frequently asked questions

What is the difference between Delrin and acetal?: Delrin is a brand of acetal homopolymer, originally from DuPont and now Celanese. "Acetal" covers both the homopolymer and the copolymer (Celcon, Hostaform, Acetron GP). The homopolymer is about 10% stiffer and stronger; the copolymer resists hot water and alkalis better and has no centreline porosity. Most shops treat them as interchangeable for general parts.
Can Delrin be laser cut?: No. Heating acetal above about 230 °C (450 °F) depolymerizes it into formaldehyde gas, which is toxic and corrosive to the machine. Laser shops refuse it. Profile acetal plate by CNC routing, milling or waterjet.
Is Delrin food safe?: Natural, unpigmented acetal grades are available that comply with FDA 21 CFR 177.2470 and are used in food-processing machinery. The compliance belongs to a specific grade, so ask for a food-contact grade on the RFQ and keep the certificate with the part.
Does Delrin absorb water?: Very little: about 0.2-0.25% at 50% relative humidity and under 1% saturated, compared with about 2.5% and 8% for nylon 6/6. That is why acetal holds size in humid or wet service where nylon parts grow.
What is centerline porosity in Delrin rod?: Extruded homopolymer rod cools from the outside in, and the last material to freeze at the axis can be left with voids. In rod above about 50 mm (2") the centre can be porous enough to leak under pressure or to machine with a rough finish. Porosity-free grades, copolymer rod and compression-molded shapes avoid it.

Processes that commonly use it

CNC Machining CNC Milling CNC Turning Swiss Machining Screw Machining Gear Cutting Injection Molding Overmolding Vibratory Finishing

Related materials

Nylon 6/6 UHMW Polyethylene (UHMW-PE)PEEK PTFE (Teflon)HDPE (High-Density Polyethylene)Polycarbonate (PC)

Where to verify these values

Celanese (formerly DuPont) Delrin product and design guide data sheets
Ensinger TECAFORM AD (homopolymer) and AH (copolymer) stock-shape data
Mitsubishi Chemical Advanced Materials Acetron data
ASTM D6778; ASTM D638 (tensile) and D790 (flexural) test methods

Delrin (Acetal)

Delrin is acetal homopolymer: the stiffest, most machinable general-purpose plastic, with low friction and good fatigue life. Values for natural extruded stock.

ASTM D6778 (POM molding and extrusion materials)UL 94 HBFDA 21 CFR 177.2470 (food-contact grades)

At a glance

Delrin (Acetal) typical properties
Density	1.41 g/cm³ (0.051 lb/in³)
Tensile strength	69-76 MPa (10-11 ksi) at yield
Yield strength	69 MPa (10 ksi) tensile yield (plastics neck rather than fracture; yield is the design number)
Hardness	Rockwell M 92-94 (Shore D 85)
Elongation	25-40% at break
Modulus of elasticity	3.1 GPa (0.45 Msi) tensile; 2.8 GPa (0.41 Msi) flexural
Thermal	Melts at 175 °C (347 °F); Tg about -60 °C (-76 °F); continuous service 82-90 °C (180-195 °F), copolymer to 100 °C (212 °F); HDT 120 °C (250 °F) at 1.82 MPa
Composition	Polyoxymethylene homopolymer, (CH2O)n, with thermal stabilizer; copolymer adds a few percent ethylene oxide comonomer

Typical values, Natural extruded rod and plate, unfilled homopolymer, dry, 23 °C (73 °F). Confirm against the mill certificate and the purchase spec.

MachinabilityExcellent

The best-machining engineering plastic: clean chips, good finish, holds ±0.05 mm (±0.002") in stable shops. Sharp tools, air or water-soluble coolant, and let it cool before final measurement.

WeldabilityFair

Acetal resists solvents, so it cannot be solvent bonded. Ultrasonic, hot-plate and spin welding work for molded parts. Adhesives need a plasma, flame or acid etch of the surface first; mechanical fastening is the norm.

FormabilityPoor

A crystalline polymer with a narrow melt window; it is not thermoformed or bent in practice. Parts are machined from stock or injection molded.

Corrosion resistanceGood

Resists fuels, oils, alcohols, most solvents, weak acids and bases. Attacked by strong acids, oxidizers and chlorine; homopolymer also loses strength in hot water and alkalis, where the copolymer is the better choice.

Process compatibility

How Delrin takes each process, and what to specify. Each process links to its own guide and to the shops that do it.

Delrin (Acetal) process compatibility
Process	Rating	Notes
CNC Machining	ExcellentExcellent	The plastic of choice for tight-tolerance machined parts; chips cleanly and holds size. Can Delrin be machined?
CNC Milling	ExcellentExcellent	Fast at high spindle speeds with sharp carbide; deburrs easily by hand or vibratory bowl.
CNC Turning	ExcellentExcellent	Excellent finish from rod; large diameters may show centreline porosity, so specify porosity-free stock for seals and pressure parts.
Swiss Machining	GoodGood	Small precision pins, bushings and inserts from ground rod; low tool wear and no smearing.
Injection Molding	ExcellentExcellent	A major molding resin: gears, clips, housings; shrinkage about 2%, so allow for it in tolerances and warp.
Waterjet Cutting	GoodGood	The right way to profile plate without heat; a slightly frosted edge, finish-machine if the edge matters.
Laser Cutting	Not recommendedNot recommended	Do not laser cut acetal: it depolymerizes and releases formaldehyde, and the edge chars. Machine, saw or waterjet instead. Can Delrin (acetal) be laser cut?
FDM 3D Printing	PoorPoor	Prints badly: warps, bonds poorly to the bed and to itself. Machine it or print nylon or PETG as a stand-in.
SLS 3D Printing	Not recommendedNot recommended	Not an SLS material; laser-sintered nylon (PA12) is the usual substitute for prototypes.
Vibratory Finishing	GoodGood	Removes burrs and softens edges on molded and machined parts without scratching.
Bead Blasting	FairFair	Gives a uniform matte texture; use fine media and low pressure to avoid embedding grit in a bearing surface.
Anodizing	Not recommendedNot recommended	An electrochemical oxide process for aluminum; it does nothing to a plastic. Color acetal by buying black or pigmented stock.
Plating	Not recommendedNot recommended	Acetal is not a plating-grade plastic; adhesion is poor even with etching. Use ABS or a PC/ABS blend for plated plastic parts.

Design and sourcing tips

Say which acetal you mean: "Delrin 150" or "acetal homopolymer" for stiffness and fatigue, "acetal copolymer" for hot water, chlorinated water or alkaline service.

For pressure-tight or sealing parts turned from rod above about 50 mm (2"), specify porosity-free stock or copolymer, or the part may weep through centreline porosity.

Allow for thermal expansion: about 100-120 um/m·K, ten times steel. A 300 mm part grows about 0.5 mm over a 40 °C swing, so leave clearance in metal housings.

Keep tolerances realistic: ±0.05 mm (±0.002") is achievable on small features, ±0.1-0.13 mm (±0.004-0.005") is normal. Tighter costs money and drifts with temperature.

Never specify laser cutting, flame polishing or any process that heats acetal past about 230 °C (450 °F): it releases formaldehyde.

Press fits and snap fits work well, but keep strain under about 2-3% for a lasting fit; acetal creeps less than nylon but is not a spring.

Frequently asked questions

What is the difference between Delrin and acetal?

Delrin is a brand of acetal homopolymer, originally from DuPont and now Celanese. "Acetal" covers both the homopolymer and the copolymer (Celcon, Hostaform, Acetron GP). The homopolymer is about 10% stiffer and stronger; the copolymer resists hot water and alkalis better and has no centreline porosity. Most shops treat them as interchangeable for general parts.

Can Delrin be laser cut?

No. Heating acetal above about 230 °C (450 °F) depolymerizes it into formaldehyde gas, which is toxic and corrosive to the machine. Laser shops refuse it. Profile acetal plate by CNC routing, milling or waterjet.

Is Delrin food safe?

Natural, unpigmented acetal grades are available that comply with FDA 21 CFR 177.2470 and are used in food-processing machinery. The compliance belongs to a specific grade, so ask for a food-contact grade on the RFQ and keep the certificate with the part.

Does Delrin absorb water?

Very little: about 0.2-0.25% at 50% relative humidity and under 1% saturated, compared with about 2.5% and 8% for nylon 6/6. That is why acetal holds size in humid or wet service where nylon parts grow.

What is centerline porosity in Delrin rod?

Extruded homopolymer rod cools from the outside in, and the last material to freeze at the axis can be left with voids. In rod above about 50 mm (2") the centre can be porous enough to leak under pressure or to machine with a rough finish. Porosity-free grades, copolymer rod and compression-molded shapes avoid it.