Today's KNOWLEDGE Share:Acetals vs nylons

Today's KNOWLEDGE Share

Acetals vs nylons

Acetals – sometimes also known as polyoxymethylene (POM) – like nylons, are semi-crystalline thermoplastics, and some of their characteristics overlap, such as their fatigue resistance, chemical resistance, and wear resistance with a sharp melting point. Both are used for small components such as #washers, #discs, and #spacers.

One of the most popular properties of acetals is their ease of machining compared to various other engineering plastics, including nylon, as well as such as HDPE and UHMW. Acetals tend not to deflect away from or grab machining tools and they also chip nicely, making them ideal if an application requires the material to be machined.

There are distinct differences between nylons and acetals:

nylon offers superior tensile strength and bending stiffness

nylon can also handle higher loads and higher temperatures

nylon is susceptible to #UVradiation unless special additives are incorporated

nylon reacts poorly to changes in humidity, which cause it to swell and lose #tensilestrength

nylon is a #selflubricating material

acetal provides higher impact resistance and cold resistance

acetal is suitable for moderate loads.

acetal has much better wear resistance and #chemicalresistance

acetal has greater dimensional stability and resists moisture and humidity

acetal is shiny, while nylon appears dull in comparison

Like #nylon, #acetal comes in different formulations, though not so many, of which the main two are acetal copolymer (acetal-C) and acetal homopolymer (acetal-H).

The differences are slight: H has better mechanical properties than C, including higher strength and stiffness, better creep resistance and higher hardness rating. However, C has the better chemical properties, hydrolysis resistance, higher continuous allowable service temperature in air and less outgassing.

One of the biggest differences between C and H is centreline porosity, which is a characteristic of H but not C. Centreline porosity is caused by gasses trying to escape during the cooling process after extrusion or compression. It can appear as small bubbles in thicker rods or a white line down the middle of each cut edge of a sheet.

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