Higher impact strengths at room temperature levels and low temperature levels. Tensile strength is around 10-15% higher than similar copolymers. Slightly higher continuous usage temperature level than copolymer (95° C vs. 90° C). Slightly more difficult than copolymer acetals, hence providing the homopolymer acetals a lower coefficient of friction.
POM Acetal Copolymer (Ultraform®, Celcon®) resins are made by numerous companies such as BASF and Ticona. Acetal copolymers have the following advantages over homopolymer: Improved dimensional stability over similar homopolymer solutions due to its lower level of crystallinity. Better chemical resistance with high pH (fundamental) solutions.
Polyoxymethylene (POM), also known as acetal, polyacetal, and polyformaldehyde, is an engineering thermoplastic used in precision parts requiring high stiffness, low friction, and excellent dimensional stability. As with many other synthetic polymers, it is produced by different chemical firms with slightly different formulas and sold variously by such names as Delrin®, Celcon®, Ramtal, Duracon®, Kepital®, and Hostaform®.
Lower centerline porosity than homopolymer in extruded shapes.In most cases, Acetal homopolymer and Acetal copolymer can be interchanged because numerous resin properties are within
approximately 10% of each other. The chemical composition, regular molecular structure and high degree of crystallinity of Delrin® acetal resins result in a unique combination of outstanding characteristics not found in metals or most other plastics:
Delrin® Plastic Materials Supplied by DuPont Performance Polymers
Typical physical properties are shown in the accompanying table. Maybe the most substantial difference between homopolymer and copolymer acetal relates to the phenomenon referred to as centerline porosity. It is most popular in extruded parts, especially thick slab and big diameter rod stock. Visually, it is a whiter shaded area around the center portion of a rod, which extends down the entire length.
DuPont Delrin® is a homopolymer acetal which offers an excellent balance of properties that bridge the gap between metals and plastics. Delrin® shapes possess high tensile strength, creep resistance and toughness. It also exhibits low moisture absorption, it is chemically resistant to hydrocarbons, solvents and neutral chemicals. These properties along with its fatigue endurance make Delrin® shapes ideal for many industrial applications.
In slab form, porosity appears as a line along the center of each cut edge. Sometimes, the piece may seem laminated or glued together. Excessive centerline porosity is unfavorable for the following factors: Cosmetic – irregular color appearance in completed parts. Compromises structural stability. Present routes for leak of gas and liquids. Provide areas where the germs can grow in food processing applications.
Acetal Copolymer vs Delrin ® Acetal Homopolymer
The cause of the porosity is shrinkage. Throughout the extrusion procedure, the outdoors skin of the shape cools before the interior area. As the interior product cools, there is a matching decrease of volume. Because the total volume change of the shape is limited due to the solidified skin, spaces form to compensate for the loss of interior volume.
Here are a couple of charts explaining the physical properties by Dupont explaining the benefits of using Dupont Delrin® Homopolymer:
The Acetal copolymers have the following benefits over homopolymer: Improved dimensional stability over equivalent homopolymer solutions due to its lower level of crystallinity. Lower centerline porosity than homopolymer in extruded shapes.In most cases, acetal homopolymer and copolymer can be interchanged due to the fact that numerous material residential or commercial properties are within around 10% of each other. Perhaps the most significant distinction between homopolymer and copolymer acetal relates to the phenomenon understood as centerline porosity.
One popular method to machine the Acetal materials is to turn rod in a lathe. Here is a typical process in the video: