Delrin Homopolymer versus Copolymer Acetal
Have you noticed the little plastic gears in your watch, the working parts in a garden hose nozzle, audio and video cassette moving parts, food slide components, timing screws and pumps parts, or perhaps even acoustic guitar picks? If you have, then you have seen perhaps the most versatile plastic known as Acetal (polyoxymethylene or POM). It is an extremely durable and strong plastic material, so it is no surprise to see it being used for so many different things. Used as a regular replacement for many aluminum or metal parts, or the similar plastic materials, like Polyamide Nylon or Rigid Polyester. It is the next step up from HDPE, a common plastic used in food processing. Because of the uniform molecular structure of Acetal, it can be used for different applications that might require a plastic material to be more rigid, have good mechanical properties and have a low coefficient of friction.
The battle between Delrin and Acetal
Both Delrin and Acetal materials are thermoplastic. What this means a material can be softened by being heated and when cooled becomes hard again, and will retain the new shape. Because of this characteristic it is able to be molded in to many different types of objects, like the few listed above. While some thermoplastics are ‘formable’, Acetal is definitely not to reshape with heat after it is made into a sheet or rod. A crystalline, rather than amorphous type resin is used to make acetal. Because of the uniform molecular structure of Acetal, it can be used for different applications that would require a plastic material to be more rigid, have excellent mechanical properties and have a low coefficient of friction. Both of these resins are produced in Natural (White) and Black, also there are some colors are available on special order; there is also the Delrin AF (a PTFE filled Delrin) is a mid to dark brown color.
There are two basic grades of Acetal
You need to know some of the differences, Acetal versus Delrin. There are two main types of Acetal; one is a copolymer and the other a homopolymer. Ticona is one manufacture that makes a widely known copolymer called Celcon, BASF produces a high quality copolymer, H2320. Likewise DuPont makes Delrin, a popular brand name and the most commonly used Homopolymer. Standard mill shapes include: Acetal Sheet, round rods, flat sheets and some tube and profiles are also produced.
They may be close, but not the exactly
Yes, the copolymer and homopolymer acetal are very similar and they look the same, they do have some large differences in properties and this makes them unique in their own way. For example the copolymer will perform better than the homopolymer in these areas; thermal, impact, wear and chemical resistance. As you investigate the copolymer characteristics, you will discover that it has a lower water absorption rate. You may find this to be important if you plan on using with moist functions such as faucets, impellers, pump parts, valve and valves stems than the homopolymer acetal will. Now, when you review the homopolymer, which has a higher crystallinity, this will increase some properties and make it stronger, with improved mechanical strength and creep resistance, than its brother, the copolymer. Chemical resistance is one of the areas Acetal materials sometimes have a weakness, specifically oxidizing agents and strong acids. Other than these types of chemicals, Acetal is pretty much resistant to a wide range of solvents and commonly used chemicals.
Delrin Versus Acetal
One visual difference, and possibly a significant performance difference, between the copolymer and homopolymer is center line porosity. The homopolymer (Delrin) resin is known to be susceptible to having center line porosity, a section in the center of a rodt, it will be seen as a small circle found at the center. As for slab or sheet, it will appear as a white stripe down the center or middle (of the thickness) of the extruded or compression molded sheet material. This porosity is caused by the gasses trying to escape during the cooling processes. If a large rod is to have the middle or center machined out, then Delrin is an excellent choice. Copolymer Acetal does not have this ‘soft center’ or porosity.
Homopolymer Delrin and Copolymer Acetal are easy to machine
Both of these resins can be excellent choices for machining and mechanical type applications. Tight tolerances may be maintained during the cutting and machining process. The materials are considered to be self lubricating, and make very good dry slide wear strips. Both of these resins are FDA and 3A (Dairy) compliant.
You may wish to consider Acetal, either Delrin Homopolymer or Copolymer Acetal for your next engineering plastic applications. Contact us via Email for additional assistance, or call us at 866-832-9315
Topic: Delrin Versus Acetal in Sheet and Rod
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