Differences Between Acetal and Delrin: Unraveling Distinctions

For projects requiring materials characterized by a low coefficient of friction, tensile strength, and rigidity, Acetal and Delrin emerge as optimal choices. While both materials possess distinctive properties, it’s essential to discern the differences between Acetal and Delrin for their correct utilization. This article aims to explore and compare the two, offering comprehensive insights.

Acetal Overview

Acetal polymer, also known as POM (polyoxymethylene), constitutes a plastic material composed of multiple monomers forming repeating CH2O units. Referred to as polyacetal, polyformaldehyde, or polymethylene glycol, Acetal exhibits metal-like properties, making it a viable substitute for certain metals in plastic machining and various manufacturing processes.

Acetal Properties

Regardless of being a copolymer or homopolymer, Acetal plastics share several key properties:

  • Recyclability, liquefying at temperatures ranging from 162°C to 175°C
  • Excellent heat resistance
  • High electrical resistivity
  • Low water absorption
  • Low coefficient of friction
  • Superior strength and rigidity
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Types of Acetal

Two primary types of Acetal exist, each with distinct characteristics: copolymer acetal (POM-C) and homopolymer acetal (POM-H). POM copolymers feature diverse monomeric units in the repeating CH2O structure, providing excellent dimensional stability, chemical, and abrasion resistance. On the other hand, Acetal homopolymer, marketed under the well-known trade name Delrin®, maintains the integrity of the repeating CH2O units.

Overview of Delrin

Delrin plastic is the tradename for acetal homopolymer produced by DuPont. It has recurring CH2O units, which can be elongated and shortened to form different products. It is a common plastic in plastic machining due to its tensile strength and injection molding due to its high flow rates, leaving aside its other properties.

Properties of Delrin

Compared to acetal copolymer, Delrin has better mechanical properties. However, it also lacks a few other things. Below are the properties of Delrin.

  • A low-density center or center line porosity
  • Chemical resistant
  • Great stiffness and higher flexural modulus at room and elevated temperature
  • High tensile and impact strength
  • Hard with a low coefficient of friction
  • High creep resistance
  • High flow rate
  • Recyclable

Delrin Varieties

Due to its adaptability in forming various products while retaining its homopolymer structure, Delrin is available in multiple grades, each offering unique properties and applications. The following are common Delrin grades that may be beneficial for your project.

  • Delrin 150
  • Delrin AF 100 (13% PTFE Filled)
  • Delrin (30% Glass Filled)
  • Delrin AF DE588
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All Delrin grades are highly machinable, making them ideal materials for various projects. Their properties position them as suitable substitutes for other machining materials in rapid prototyping.

Is Delrin Equivalent to Acetal?

No, Delrin differs from acetal. Acetal refers to polyoxymethylene (POM), a category of semi-crystalline plastics widely used in plastic machining. Delrin specifically denotes acetal homopolymer, characterized by consistent repeating CH2O units. Thus, comparing acetal plastic to Delrin is unfounded; instead, the focus should be on acetal copolymer vs. Delrin. Delrin and acetal possess distinct properties, with Delrin exhibiting higher tensile strength and greater thinness, making it preferable for certain applications.

What Sets Acetal Copolymer Apart from Delrin?

Distinguishing Features of Acetal and Delrin

Delrin and various acetal copolymers share a common lineage, yet they exhibit distinct characteristics, each with its own set of advantages and applications. Below, we explore the disparities between these two materials.

  • Composition: While Delrin remains a homopolymer, preserving repeating units with end caps, acetal copolymer introduces other monomers at different chains every 70-100 units. Consequently, these molecular distinctions impact the crystalline nature of both materials. Delrin boasts a sizable crystalline structure due to the organized stacking of the polymer, whereas the copolymer disrupts such organization.
  • Hardness: The contrast in hardness between Delrin and acetal is subtle but significant. Delrin registers a hardness of 86 Shore D, surpassing POM copolymers with a hardness of 85 Shore D. As a result, Delrin exhibits greater resistance to impacts and abrasion, along with a lower coefficient of friction that facilitates easy sliding over other components.
  • Chemical Resistance: Acetal copolymers display enhanced resistance to hot water and strong caustic solutions with a higher pH value compared to Delrin. This makes them preferable for manufacturing parts intended for use in such conditions. Nevertheless, Delrin also demonstrates chemical resistance and remains unaffected by fungi, insects, or other organisms.
  • Temperature Tolerance: Delrin outperforms acetal in temperature tolerance, boasting an operating range of (-40 °C to 120 °C) without brittleness at low temperatures and high impact resistance. However, it can withstand a peak temperature of 175 °C. Copolymers feature a higher operating temperature range of 100 °C and can temporarily function at around 140 °C. Both materials are unsuitable for high-temperature applications.
  • Flexural Yield Strength and Tensile Strength: Examining flexural yield and tensile strength is crucial when comparing acetal and Delrin. Delrin demonstrates a yield strength of 11,000 psi, while acetal has a yield strength of 9,500 psi. Additionally, Delrin exhibits a tensile strength of 13,000, surpassing acetal’s 12,000. Both materials are robust and suitable for structural models, but Delrin’s superior strength makes it more apt for parts with structural applications.
  • Porosity: Delrin features a less dense or porous center, allowing for the inclusion of small bubbles or voids, enabling gases and liquids to seep into the material. In contrast, copolymers lack porosity, making them more suitable for parts where porosity is undesirable, such as in the food and medical industries.
  • Application: Both materials find extensive use in industrial and mechanical applications, albeit with limitations. Delrin excels in parts requiring a robust POM material, while acetal is more suitable for applications demanding a chemically resistant POM material. They are employed in injection molding, plastic machining, 3D printing, and the production of gears, bearings, bushings, rollers, fittings, electrical insulators, and other components in various industries.
  • Cost: POM materials, including common copolymers, are cost-effective, typically ranging from $1500 to $2500 per ton. Conversely, Delrin commands a higher price due to branding and superior mechanical properties compared to other acetal variants.

Acetal vs Delrin

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When to Choose Between Them

Based on the properties of both materials, you should be able to guess when to choose either. Below are when to use both materials in rapid prototyping.

  • Heavy Loads: Both materials have high tensile strength and yield strength. However, Delrin is the better choice for making parts that apply constant heavy loads over long periods due to its higher tensile and yield strength. Also, it would be best if you chose Delrin grade when working with parts exposed to repeated impact.
  • Friction: Delrin has a lower coefficient of friction. Therefore, it is the better option when making parts that undergo back-and-forth or rotating sliding motion against another metal or plastic. When used, there is no need for lubrication.
  • Dimensional Stability and Lightweight: When it comes to dimensional stability and lightweight, consider using acetal copolymers. They have a crystalline structure that reduces dimensional stability, and the plastic material disrupts the organization of a large crystalline structure by not conforming to an organized slacking of the polymer.
  • Chemical Resistance: This is a major distinction in the acetal vs Delrin comparison. Use acetal here as they are less susceptible to acidic or basic chemicals. The high resistance to chemicals will ensure that the part is not susceptible to industrial solvents, lubricants, agricultural.
  • Temperature and Flammability: Avoid using both types of plastics in making parts that you will expose to long-term temperatures greater than 90°C. Also, avoid long-term immersion in hot water (>60°C). Besides, both materials are highly flammable and should not be used in applications requiring flammability ratings above HB.

Choosing Between Acetal and Delrin: Key Considerations in Plastic Part Manufacturing

Crafting plastic parts from Delrin or acetal involves weighing their individual properties. Below are guidelines for selecting the appropriate material, particularly in rapid prototyping.

  • Heavy Loads: Both materials boast high tensile and yield strength. Yet, for components enduring constant heavy loads over extended periods, Delrin stands out due to its superior tensile and yield strength. Opt for Delrin when dealing with parts exposed to repetitive impacts.
  • Friction: Delrin exhibits a lower coefficient of friction, making it the preferred choice for parts undergoing back-and-forth or rotational sliding against other metals or plastics. The use of Delrin eliminates the need for lubrication.
  • Dimensional Stability and Lightweight: When prioritizing dimensional stability and lightness, consider employing acetal copolymers. Their crystalline structure reduces dimensional stability, disrupting the organization of a large crystalline structure and preventing conformity to an organized slacking of the polymer.
  • Chemical Resistance: A crucial factor in the acetal vs Delrin dilemma lies in chemical resistance. Opt for acetal when dealing with applications susceptible to acidic or basic chemicals. The heightened resistance to chemicals ensures the part remains impervious to industrial solvents, lubricants, and agricultural agents.
  • Temperature and Flammability: Exercise caution when employing either plastic in parts exposed to prolonged temperatures exceeding 90°C. Additionally, refrain from subjecting them to prolonged immersion in hot water (>60°C). Both materials exhibit high flammability and are unsuitable for applications requiring flammability ratings surpassing HB.

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