Why Use Dupont Delrin Instead of Copolymer Acetal Rod

Is Dupont Delrin the same as Acetal CoPolymer?

The best answer is NO, but both have similar properties.

The Copolymer Acetal is the common name for one of the largest families of thermoplastics, with a chemical name of POM or PolyOxyMethylene. Acetal comes in two standard grades: the first is the Copolymer acetal, or POM-C. The second type is homopolymer acetal, or POM-H; in the industry this is called Delrin®, which is a resin produced by Dupont. These two types of acetal has its very own set of advantages and drawbacks, and yet they are similar in many aspects.Machined Acetal Rod Part

Why You Might Choose Acetal Copolymer

The Acetal copolymer type has many unusual qualities and exhibits outstanding performance at a slightly lower cost than the Dupont Delrin® brand material. Acetal copolymer has uniform consistency throughout the material, with no center line porosity. It also has a reduced stress level, as well as  a very high dimensional stability, it can also be used with a continuous temperature of 180° deg; F (80 deg; C).  The copolymer acetal grades meet the FDA, USDA, NSF, and 3-A Dairy compliant. Acetal copolymer materials are stocked and available in a wide variety of sizes, and also can be supplied in a variety of standard and special colors, including: natural, black, blue, red, yellow, green, brownish, and also grey (some may require minimums).

Some Important Factors Of Delrin Homopolymer:Chemical make up of Dupont Delrin Materials

The Dupont Delrin grade of material has a better dimensional stability as a result of a low level of crystallinity. The resistance to temperatures give Delrin better resistance to hot water and also many chemicals, especially high pH (standard). The Delrin has a lower coefficient of friction and a very low water absorption, especially in wet environments.

Dupont Delrin Acetal Homopolymer

The Dupont Delrin® 150SA is the most recognized form of the acetal homopolymer grades, and it offers a higher mechanical strength than acetal copolymer, but is known to have reduced density at center, and it is referred to as porous center line. This is especially true in thicker or large cross-sections. The Dupont Delrin® rods and sheeting materials are likewise somewhat less chemical resistance compared to copolymer acetal rod and plate. For instance, Delrin® is ideal for small and thin walled bushings and molded parts, and can provide excellent toughness and rigidity, typical of homopolymer acetal. Dupont Delrin® is produced and stocked in natural and black colors. The most common version of  the Dupont Delrin is the Delrin 150SA Sheet and Rod material, extruded from this Dupont resin.

Various other advantages over copolymer acetal are:Dupont Delrin and Copolymer Acetal Rods

Acetal Copolymer has a greater consistency or tolerance control, with a higher flexural modulus at higher temperature and raised temperature applications. It has a slightly higher tensile and a higher wear resistance at room temperature levels and also better wear at lower temperatures. The Copolymer Acetal is a bit harder,  and thus gives the homopolymer Acetal a reduced coefficient of friction.

A great choice for many demanding applications, Dupont Delrin® 150SA round rod and sheeting can be compared favorably to the acetal copolymer. And is some applications these two Acetal materials could be exchanged without loss of performance due to the fact that most physical properties are within approximately 8 % of each other. Perhaps the most notable difference between the Dupont Delrin® rod and copolymer acetal rod is the soft center of Delrin, commonly known as centerline porosity, which is an unfortunate issue with the Homopolymer Delrin®. This centerline problem is most obvious in a thick plate, and at the center of large diameter Delrin rod stock. Visually the Delrin centerline is clearly obvious around the center section of a rod, which extends through the entire rod length. In the Dupont Delrin sheeting material, the porous center is visible in a line along the center of the thickness, and along the full edge of a sheet. In most cases, the sheeting might even look laminated or glued together. In some cases the excessive porosity at centerline is unwanted for the following factors:

  • Can compromise the mechanical and engineering integrity
  • Aesthetically – inconsistent color in look on a finished part
  • Can present a path for leakage of water, gas and liquids
  • Can provide areas where microorganisms can grow in food handling applications

The reason for this center line issue is actually a normal outgassing of the Delrin resin during manufacturing. As the material proceeds through the extrusion process, the exterior of the sheet cools prior to the inside, trapping any outgassing from the resin. As the interior material cools, there is an equivalent reduction of volume. Because of the volume change of the form is restricted as a result of the solidified skin, gaps form to make up for the loss of interior volume. In most applications, the Dupont Delrin Sheet and Rod works well, even when factoring in the center line issue.