Polyoxymethylene (POM), also known as Homo-Polymer acetal

About Delrin
This is the “Homo-Polymer” grade of Acetal and Delrin® is DuPont’s trade name for it. It has excellent load-bearing qualities in both tension and compression. It will absorb minimal amount of moisture and are resistant to a wide range of solvents. The service temperature range is -29º to 85º C, intermittent at 93.3º C. It has high yield strength at elevated temperatures. Properties include low friction (very slippy), high wear resistance and ease of fabrication.

 

 

 


Advantages:

    Good abrasion resistance
    Good mechanical strength
    Low coefficient of friction
    Pretty good heat resistance
    Good electrical and dielectric properties
    Low water absorption

Disadvantages

    Susceptible to being attacked by both strong acids and oxidizing agents
    Is not readily available in a flame-retardant grade
    Typically very difficult to bond


How it performs
Delrin® offers high tensile strength, stiffness, and creep resistance, and significantly outperforms many other polymers on impact resistance, allowing for thinner and lighter part design.   In addition it offers outstanding low and high temperature performance, good colour ability, and good mating with metal and other polymers. It provides dimensional stability in high precision moulding and flexibility of design.

What it’s used for
Typical applications include high performance engineering components (e.g. gear wheels, ski bindings, fasteners, crash pegs on motorcycles). It is also widely used in the automotive and consumer electronics industry.

Applications include:

    Mechanical gears, slide-ways and guiding elements, housing parts, screws, nuts, fan wheels, pump parts, valve bodies.
    Electrical Engineering: insulators, bobbins, connectors, parts for electronic devices etc.
    Vehicle: Fuel sender unit, Light stock (including shifter for light, turn signal), power windows, door lock systems, articulated shells.
    Medical: insulin pen, Metered dose inhalers (MDI)
    Furniture: hardware, locks, handles, hinges.
    Construction: Structural Glass - pod holder for point
    Packaging: aerosol cans, vehicle tanks.

What not to use it for
In areas where very high wear is needed, it has very good resistance but there are better materials such as Nylon and UHMWPE. Areas where strong chemicals are around, this may be the job of its close relative The Co-Polymer Acetal.

Machining characteristics
Delrin® rod is excellent for machining using traditional methods such as turning, milling, drilling etc. The material is free-cutting, but does require sharp tools with a high clearance angle. It usually leaves little or no burrs. The use of soluble cutting lubricant is not necessary, but is recommended. Because the material lacks the rigidity of most metals, care should be taken to use light clamping forces and sufficient support for the work piece.

Machined Delrin® can be dimensionally unstable in comparison with metals, especially with parts that have large variations in wall thicknesses. It is recommended that such features are ‘designed-out’ e.g. by adding fillets or strengthening ribs. Annealing of pre-machined parts before final finishing is an alternative. A rule-of-thumb is that in general, small components machined in Delrin ® suffer from less warping.

Gluing and bonding
Delrin ® is typically very difficult to bond. Special processes and treatments have been developed to improve bonding. Typically these processes involve surface etching, flame treatment or mechanical abrasion. Typical etching processes involve chromic acid at elevated temperatures. Once the surface is prepared, a number of adhesives can be used for bonding. These include epoxies, polyurethanes, and cyanoacrylates.

Epoxies have shown 150-500 psi shear strength on mechanically abraded surfaces and 500-1000 psi on chemically treated surfaces. Cyanoacrylates are useful for bonding to metal, leather, rubber and other plastics. Solvent welding is typically unsuccessful on it, this is due to its excellent solvent resistance.

Food applications suitability
Delrin® can be used to replace metal in automated food processing equipment, with the potential to produce lighter, lower-cost and corrosion-resistant components.  Its low-friction properties make it an ideal material for improving the speed at which high-adhesion foods can be fed through a processor. It meets the U.S.  FDA standards, is USDA approved, and is not UV stabilized.

Wear resistance
Delrin ® combines lubricity and wear resistance with the stiffness and strength needed in parts designed to replace most metal parts.

Chemical resistance
Acetal resins are sensitive to acid hydrolysis and oxidation by agents such as mineral acids and chlorine. Delrin ® is also susceptible to alkaline attack and is more susceptible to degradation in hot water. Thus low levels of chlorine in potable water supplies (1–3 ppm) can be sufficient to cause stress corrosion cracking to develop, a problem which has been experienced in both the USA and Europe in domestic and commercial water supply systems.

Other Trade names (also known as):

    Ticona Hostaform, Celcon ®
    Pom H
    BASF Ultraform®

Size range, colours, and availability
Delrin ® is naturally opaque white, due to its high crystalline composition, but it is also available in black. Rods are available in diameters ranging from 10mm to 200mm.

Why should you choose this material
Its a high performance, easily machine-able engineering plastic.  Because of its high strength, slippery-ness and resistance to impact and fatigue, it is much more economical and easier to machine than most metals .

Why not to choose this material
Delrin ® has been approved for some food applications, but it is not a suitable choice for food storage as it is easily attacked by acidic foods.

Summary
Basically there are two types of Acetal, Co-Polymer grade and Homo-Polymer grade. Delrin ® rod is the name usually given to the homo-polymer grade. Both grades are incredibly similar but have a few differences. Homo-polymer grade is generally used for more “mechanical/strength” applications, Co-Polymer grade works best in “chemical” applications. They are both engineering thermoplastics used in precision parts requiring high stiffness, low friction and excellent dimensional stability. Typical applications for injection-moulding  include high performance engineering components such as small gear wheels, ski bindings, fasteners, knife handles, and automotive lock systems. This material is widely used in the automotive and consumer electronics industry. From auto parts to innovative new medical devices as well as most industrial solutions.