Acetal polymers are used in a variety of applications from bushings and gears to rollers and gaskets. They are valued for their exceptional mechanical properties, dimensional stability, and low coefficient of friction, which is why they are used for a wide range of applications. Two primary variants are acetal copolymer and acetal homopolymer, also known as Delrin. While they are often used interchangeably with success, there are some important differences between these two thermoplastics. Here, we’ll look at the characteristics of both, and how they differ.
Acetal Copolymer: A Versatile Choice
Acetal copolymer, or polyacetal and polyoxymethylene (POM), is a semi-crystalline thermoplastic produced by copolymerizing formaldehyde with other monomers.
Key Properties of Acetal Copolymer
- Chemical Resistance. Superior resistance to hydrolysis, strong alkalis, and thermal oxidative degradation, making it suitable for applications involving exposure to harsh chemicals and high temperatures.
- Reduced Porosity. Minimal centerline porosity and higher density, which ensures consistent mechanical properties and low risk of voids.
- Dimensional Stability. Excellent dimensional stability, which is critical for precision components requiring tight tolerances.
- Glass Reinforcement. Can be chemically bonded to glass fibers for added strength.
- Durability. Low coefficient of friction for high wear and abrasion resistance.
Common Applications
Acetal copolymer is often used for applications where strength, stiffness, and low surface friction are essential, as well as in environments with temperature or humidity fluctuations.
- Medical Devices. Acetal copolymer is the ideal plastic in components requiring high chemical resistance and dimensional stability.
- Food Processing Equipment. With acetal copolymer’s resistance to hydrolysis and chemicals, it is ideal for parts exposed to cleaning agents and varying temperatures.
- Automotive Fuel Systems. Acetal copolymer’s robust chemical resistance is why it is used for fuel system components.
Delrin: Superior Strength and Rigidity
Delrin is the widely-used brand name for acetal homopolymer. This material is synthesized through the polymerization of formaldehyde, resulting in a uniform molecular structure. Because it is similar to acetal copolymer, Delrin material properties are similar; however, a major difference is that Delrin’s uniform crystalline structure improves its ability to bear cyclic loads without deforming.
Key Properties of Delrin
- High Mechanical Strength. Approximately 10% to 15% higher mechanical strength than acetal copolymers, making it suitable for load-bearing applications.
- Stiffness and Creep Resistance. Enhanced stiffness and creep resistance to ensure components maintain their shape under prolonged stresses, including high temperatures and humidity.
- Flex Fatigue Resistance. Superior resistance to repetitive stress and flexing, extending the lifespan of parts subjected to cyclic loading.
It is important to note that Delrin has lower chemical resistance than acetal copolymer. It is also prone to a phenomenon called centerline porosity, in which the middle of a piece may become more porous after cooling, making it more susceptible to bacterial or mold growth in some applications.
Common Applications
- Gears and Bearings. Delrin’s strength and wear resistance is ideal for high-precision gears and bearings.
- Fasteners and Snap-Fit Components. Applications requiring high stiffness and the ability to withstand repeated assembly and disassembly use Delrin.
- Automotive Safety Systems. Critical safety components in vehicles that require mechanical reliability use Derlin.
Comparing Acetal Copolymer and Delrin: Key Differences
When evaluating acetal copolymer and Delrin for an application, several critical differences emerge:
- Mechanical Properties. Delrin offers higher tensile strength, stiffness, and impact resistance compared to acetal copolymers, making it ideal for structural applications requiring robust mechanical performance.
- Chemical Resistance. Acetal copolymers exhibit better resistance to hydrolysis and strong alkaline environments, making them better for applications with water and chemical exposure.
- Centerline Porosity. Delrin is more prone to centerline porosity, where voids form during cooling, potentially compromising mechanical integrity. Acetal copolymers offer more uniform material consistency and higher density.
- Thermal Stability. Delrin maintains its mechanical properties over a broader temperature range, providing better performance in extreme temperatures than acetal copolymers.
Make an Informed Decision With W.S. Hampshire
The choice of acetal copolymer vs. Delrin is a common one for many applications. While the two thermoplastics share many properties and characteristics, they have some differences that make them more or less suitable for certain applications. It’s important to be aware of how both materials and components made from them behave in the real world.
At WS Hampshire, our experts can help you assess the requirements of an application to determine the best material options. We are a full-service, custom, non-metallic materials fabricator, and we produce high-quality OEM components and parts for various industries. Contact us to learn more about our capabilities and range of materials.