|Medical Design & Manufacturing||Minneapolis, MN||November 8-9, 2017|
Acetal is a well known thermoplastic material known chemically as “PolyOxyMethylene” or POM for short. Acetal is available in 2 types of resin formats. Copolymer acetal (POM-C), available in numerous tradenames from several raw material manufacturers and Homopolymer acetal (POM-H), known commonly as Delrin®. So what’s the difference you ask?
For starters, Acetal copolymer is slightly cheaper than Delrin®. Acetal copolymer is also free of the center line porosity that is inherent in Acetal Homopolymer. Due to its lower crystallinity than the homopolymer, Acetal copolymer offers excellent dimensional stability and maximum continuous use temperature up to 180°F (80°C). Copolymer acetal grades are FDA, USDA, NSF, and 3-A Dairy compliant and available in wide variety of colors. A few other advantages acetal copolymer has over the homopolymer variety are the following:
- Due to its higher level of cyrstalinity, copolymer has better dimensional stability.
- Better impact and wear resistance (especially in wet environments)
The main difference in Acetal Homopolymer, or Delrin® is the fact that Delrin® comes with an inherent low density center known commonly as “center line porosity”. The larger the cross section, the larger the center line porosity. Delrin® offers slightly higher mechanical properties than acetal copolymer, but most of its mechancial properties come within 10% of acetal copolymer. Another feature worth mentioning is the fact that Delrin® offers lower chemical resistance than acetal copolymer. Delrin® is availabe in natural and black colors. A few advantages Delrin® offers over acetal copolymer are the following:
- Greater tensile and impact strength at room temperatures and below.
- Greater stiffness, with higher flexural modulus at room temperature and elevated temperatures.
- A bit harder, giving Delrin a better coefficient of friction in applications where water and moist environments don’t come in to play.
So what does all this mean? In most applications, Acetal Copolymer and Delrin® can be used interchangeably due to the fact that most of the material properties fall within 10% of each other. Just keep in mind that when specifying Delrin®, you will always have the center line poroisty issue to deal with which has its pluses and minuses depending on the specific application.
If you need CNC Machined or Stamped Acetal Copolymer or Delrin® parts, give us a call or send us a message on our contact page.
A common question we get asked from time to time is, “What is the difference between a thermoset and a thermoplastic?” Here is a brief description to illustrate the distinction between the 2 categories of engineering plastic materials. A clearer understanding of why plastic materials react the way they do will help you make an informed decision as to what category of plastics is ideal for your application.
In a nutshell, the main difference between a Thermoplastic and a Thermoset is whether or not it can be melted down and recycled. A general rule of thumb is that Thermoplastics can be heated up to a certain temperature, depending on the material’s glass transition point, and can then be melted down for recycling or perhaps extrusion or injected into a mold for injection molding. As thermoplastics cool, they begin to harden into the desired shape without any chemical curing being performed to increase the strength of the material. Once a thermoplastic has cooled, it can now be machined or fabricated using common machining methodologies.
Thermosets on the other hand are cured and hardened into a specific shape, generally through the application of heat and pressure. Curing thermosets, (also known as vulcanizing), is an irreversible chemical process whereby the polymers in the material create permanent connections called “crosslinks” with the materials molecular chains. The crosslinking that occurs in a thermoset creates a very rigid material when cured. Once cured, thermosets are unable to be reprocessed or melted for reusability. While both materials exhibit their own beneficial characteristics, thermosets exhibit several advantages over thermoplastics including mechanical properties, thermal stability, as well as overall durability.
PEEK, also known as Polyether ether ketone, is a semicrystalline thermoplastic used in numerous high-end engineering applications. PEEK exhibits excellent mechanical and chemical resistance characteristics, especially in dealing with high temperature applications. PEEK’s glass transition temperature lies around 289 Fahrenheit, while its melting point is around 662 Fahrenheit. What this equates to is that PEEK is an ideal candidate for applications requiring a non-metallic material that needs to be resistant to thermal degradation.
Since PEEK is such a robust material, it makes it suitable for many demanding applications, such as valves, bearings, cable insulation, and piston parts. A few of the more common markets where PEEK is used extensively are the Aerospace, Medical, and Chemical Process Industries. The main disadvantage of PEEK is its relatively high price. Next time you have a project or application that requires quality CNC machined parts or components, look no further than InsulFab Plastics.