Understanding Polyoxymethylene: The Versatile POM Plastic

Share On:

Polyoxymethylene (POM), known as acetal, or polyacetal, is an engineering thermoplastic widely used across industries like automotive, electronics, medical devices, and consumer goods due to its superior strength, stiffness, and dimensional stability. Known for its fulfilling mechanical and thermal needs, POM is a go-to polymer. In this article, the various properties of POM, its endless applications, and the advantages it provides for manufacturers searching for cost-efficient and dependable materials will be discussed. Whether you’re a curious enthusiast, a design engineer, or a product developer, this article will explain why POM is a favorite amongst many and helps fulfill the needs of modern manufacturing.

What is POM and How is it Used in Engineering Plastic Applications?

Contents show

Polyoxymethylene (POM) is a very efficient thermoplastic engineering-strong material known for its strength and stiffness as well as for its high resistance to chemicals and external wear. POM, or Acetal as it is commonly known, is used for a blend of industrial and consumer products because of its durability and very low friction. POM’s high-tech engineering properties make it the material of choice for many industries, including automotive, electronics, and medicine. POM is most commonly associated with precision parts like gears, bearings, and fasteners where dimensional accuracy as well as flawless mechanical movement is of utmost importance.

Defining POM: Also Known as Acetal

POM, or Polyoxymethylene, is a high-performance polymer used in manufacturing. It has excellent strength, stiffness, and dimensional stability. It has a low friction coefficient and is very wear-resistant, which makes POM a perfect candidate for mechanical components with tight tolerances. POM is also durable and resistant chemically, enabling it to function well under harsh conditions in many industries.

Key Properties of POM Material

Polyoxymethylene, or POM, is a polymer that has been a game changer in the domain of modern engineering and technology, and it is due leveler of its wide variety of features and chemical benefits. Following is a list explaining the reasoning why POM is favored in engineering:

High Strength and Stiffness

POM polymer has high tensile strength. For its different formulations and grades, the tensile strength value varies from 60 to 80 MPa which is considerably a broad range. With these features, it fulfills the requirements for many structural applications which require long service life.

Low Friction and High Wear Resistance

POM is a preferred polymer POM for components of gears, bearings, and sliding parts due to its low friction coefficient (0.1-0.3 when in contact with metal surfaces) and high wear resistance. These miniature loads reduce the energy consumed due to friction forces and render the parts suitable for sustainable operating life under oscillating loads.

Dimensional Stability

Precision components that ensure tight dimensions are usually subjected to certain environmental conditions, and because of the low moisture absorption rate (which is around 0.2-0.4%), POM can maintain its geometrical shape and size. It makes POM applicable to components that need stable dimensions.

Thermal Resistance

POM grade impact variant polymer, owing to its high energy good order and lower heat deformation resistance, is better able to retain its structure under the impact of temperatures ranging from -40 to 120 degrees. It is also highly thermally deformed, which renders the polymer reliable in many cases where there is exposure to heat.

Mechanical Resistance

Solvents, oils, and other chemicals, including fuels and weak acids, are no match for POM’s resistance. Due to its unresponsiveness in severe environments, it is widely used in automotive fuel systems, industrial-grade machinery, and chemical processing apparatus.

Having a dielectric strength of usually over 15 kV/mm, POM offers great electrical insulation which is useful for high-powered electronic parts.

The durability of materials against cyclic loading is denoted as fatigue endurance. In this regard, POM is remarkable as it has a high resilience to repeated stress cycles, making it perfect for dynamic applications like springs, clips, and actuator parts.

In combination, these properties enable POM to be classified as a truly high-performance material in the automotive and consumer electronics, medical devices, and precision machinery industries.

Common Applications for Injection-Molded POM

Automotive Components

Parts of a motor vehicle are made from POM plastic because the material’s low frictional and high wear resistance is, proportional to POM consumable and acetal polymer fuel system components, parts of the gear mechanism, and even fasteners used within acetal polymers. As a motor vehicle parts fed, exposed to chemical and mechanical stress, put into, POM increases the efficiency, and reliability experience of the automotive vehicles. Industry claims suggest that the automotive industry consumes some 30% of the world’s POM production.

Consumer Electronics

POM is commercialized in the manufacture of switches keyboards, gears printers, and many other parts due to its precision and durability. Its mechanical strength permits devices to be made smaller economically because stronger, more efficient devices are produced. Consumer electronics manufacturers increasingly rely on POM for creating lightweight yet durable components in response to the miniaturization trend across the sector.

Medical Equipment

Used for manufacturing medical devices, POM is biocompatible and exhibits good dimensional stability and resistance to repeated sterilization processes. It is used in systems for delivering drugs such as inhalers and insulin pens, as well as in cases and gears of precise diagnostic instruments. Medical applications account for an expanding share of the global POM market due to rising demand for healthcare innovations.

Industrial Machinery

POM is used in the construction of industrial components such as mechanical gears, conveyor belt systems, and precision parts. Acetal resin provides reduced creep deformation which enhances the reliability of machinery in contrast to other materials. Minimal maintenance and longer lifespans of equipment are benefits for factories using components made out of POM.

Electrical and Telecommunication Equipment

As a result of low moisture resistance and stable dielectric properties, POM is optimal for the fabrication of switch components for telecommunication infrastructure. Its ability to withstand damaging conditions makes POM useful in supporting the ever-growing demands of global connectivity. POM’s excellent electrical insulation properties provide durability for housing and connector components.

In modern engineering and manufacturing that require exceptional precision, durability, and efficiency, POM continues to be a critical material in meeting the needs of various industries.

Exploring the Mechanical Properties of Polyoxymethylene

Exceptional Mechanical Properties of POM

Polyoxymethylene (POM) has outstanding mechanical properties suited for harsh engineering applications. Its tensile strength and stiffness provide high dimensional stability under mechanical loads. POM’s low friction and wear resistance make it ideal for durable components such as gears, bearings, and conveyor belts. Moreover, its fatigue resistance allows prolonged performance during repeated stress cycles, thus making it more versatile in engineering and manufacturing. These factors result in POM’s extensive applications for producing reliable, high-precision components.

How POM Exhibits High Stiffness and Rigidity

The semi-crystal polymer, POM, derives its high stiffness and rigidity from the crystalline molecular structure due to the orderly arrangement of polymer chains into an organized lattice with enhanced intermolecular interactions. Crystallinity, or the degree of order within a material, contributes highly to the mechanical strength of POM and falls between 70% to 85%. The crystalline structure is responsible for the high elastic modulus approximately ranging from 2.8-3.8 GPa depending on the formulation and grade of the polymer.

The high melting point (175 degrees Celsius) and glass transition temperature of POM (-60 degrees Celsius) allow it to maintain its thermal structural integrity. The described attributes aid in reduced deformation from loads compared to other thermoplastics. Reduced creep tendency of POM helps retain its rigid form even when precision applications such as cyclic stress are applied which is essential to automotive and industrial sectors.

An exceptionally low moisture absorption rate of under 0.22 \% further assists its rigidity by avoiding significant swelling or dimensional changes even in humid conditions. Along with these intrinsic properties, the addition of tailored additives like glass fibers or fillers can increase POM’s stiffness even further to meet the requirements of high-end engineering applications that need both strength and accuracy.

The Impact Strength and Abrasion Resistance of POM

Polyoxymethylene (POM) is a highly valuable thermoplastic due to its remarkable impact strength making it a preferred choice in most applications that require materials that are mechanically durable and tolerant against mechanical internal stresses. The resilience of POM to sudden forces is connected to its substantial toughness coupled with high crystallinity. For example, a standard grade of POM homopolymers has average impact strength and values of about 6-8 kJ/m² as measured by ISO 179, which is important for components such as gears, bearings, and clips, which work in dynamic and load-bearing environments.

POM also has superb abrasion resistance which is very important in POM applications that involve repetitive friction contact. With a low coefficient of friction (approximately 0.2-0.3), POM exhibits reduced wear on contacting surfaces, greatly increasing the life span of the components. This trait is enhanced even more in lubricated POM grades and those reinforced with PTFE (polytetrafluoroethylene) that are known to yield lower friction forces and greater resistance against abrasive forces.

The combined traits and features of POM allow it to be a highly versatile and suitable thermoplastic in high-performance engineering applications such as parts for conveyor belts, precision automotive components, and industrial machinery. These properties guarantee proper functioning under ever-present mechanical stresses and dynamic conditions making them highly useful in applications that require robust materials like construction and manufacturing.

How Does the Polymerization Process Affect POM Homopolymer?

The Role of Formaldehyde in POM Production

As the main ingredient in the creation of polyoxymethylene homopolymer (POM) polyoxymethylene, formaldehyde serves a building block purpose. The production process of POM begins with a carefully controlled catalytic reaction sequence that converts formaldehyde into trioxane, which is a cyclic trimer of formaldehyde. For industrial purposes, trioxane serves as a useful source due to its stability and high purity.

During the stage of polymerization, trioxane is turned into polyoxymethylene through ring-opening polymerization which can be either anionic or cationic with the help of one or more specific initiators. This process enables the formation of high molecular weight polymers which have long chains of polyoxymethylene and high tensile and thermal strength. In addition, the length and distribution of the polymeric chains can be modified which determines the material’s suitability in harsh environments.

Research has shown that industrial production of POM can achieve greater than 95% yield of polymer with extremely low waste product levels, which renders the process economical and eco-friendly. In addition, the extensive usage of POM across industries is due to improvements in POM fabrication process energy efficiency and scalability brought about by catalyst technology advancements.

Differences Between Homopolymer and Copolymer POM

Polyoxymethylene (POM) is most commonly found in two base forms polyoxymethylenes, whose parts differ markedly depending on their use: homopolymer and copolymer.

Structural Composition

The structure of Homopolymer POM consists of single acetyl units, with each repeating unit differing highly, resulting in a highly crystalline material as a result. This intrinsic homogeneity drives superior mechanical strength and stiffness. On the other hand, copolymer POM reduces the crystallinity of POM by incorporating comonomers into the polymer chain, benefitting the resultant POM’s thermal stability and resistance to degradation.

Thermal Properties

Homopolymer POM usually has a higher melting temperature, closer to 175 °C, compared to that of copolymer POM of 162 – 170 °C, depending on the degree of crystallization. Superior thermal resistance supports the use of homopolymer POM for high-temperature applications, but copolymer POM outperforms its counterpart during extensive heat exposure due to better thermal degradation resistance, making it desirable for high-temperature machined components.

Mechanical Performance

The mechanical type POM materials possess superior tensile strength and hardness, making them ideal for precision parts like gears and bearings. Its rigidity enables outstanding dimensional stability. In contrast, copolymer POM is more amenable to impact and, as a result, better able to survive repeated stress and load cycles.

Chemical Resistance

Both homopolymer and copolymer POM have high resistance to chemicals like oils, fuels, and solvents. However, copolymer POM has better resistance to hydrolysis and acids. This is useful in regions that suffer from high moisture and chemical contact over some time, for example, automotive fuel systems and industrial fluid handling systems components.

Processability

Due to reduced crystallinity and lower melting temperature, copolymer POM is generally easier to process. This copolymer also has better flow properties during injection molding, decreasing the risk of defects like voids and warping that occur due to the trapped air. While more rigid homopolymer POM is easier to process, tighter control of processing conditions may be needed.

Comparative Data Summary

Property	Homopolymer POM	Copolymer POM
Melting Point	~175°C	~162-170°C
Tensile Strength	Higher	Moderate
Impact Resistance	Moderate	Higher
Thermal Stability	Moderate	Higher
Chemical Resistance	High	Higher (esp. hydrolysis)

Understanding these differences allows engineers and designers to select the most appropriate POM variant for their specific requirements, optimizing durability, performance, and cost-efficiency in a wide range of applications.

What Makes POM Stand Out as a Thermoplastic Material?

Good Dimensional Stability and Low Friction of POM

In my view, POM is unique because of its remarkably low friction and exceptional dimensional stability. These features are very useful in the field of precision engineering, where parts are required to retain their shape and size when subjected to different heat and mechanical stress. With POM’s low friction coefficient, it is ideal for wear and smooth operation which is perfect for gears, bearings, and other moving parts in harsh working environments. These features improve operational and reliability across various industries.

Properties of Polyoxymethylene That Enhance Performance

PAM-AO demonstrates its key properties polyoxymethylene (POM) demonstrates several features that carved its appreciation in countless POM applications. One is its high moisture, in addition to being low, gives assurance for retention of dimensional stability in hostility of humid or wet environments. For example, pores moisture absorption is often reported in the literature as 0.2% at equilibrium. This value greatly increases the reliability of POM uses which are with water exposures. Furthermore, POM’s toughness and stiffness render it a structurally strong polymer that undergoes considerable loads without experiencing deformation. Also, POM demonstrates outstanding fatigue resistance which enables it to withstand repeated stress cycles without failing. This feature is very important in various uses such as automotive POM fuel systems and conveyor belts.

In addition, POM is resistant to various chemicals such as hydrocarbons, solvents, and weak acids or bases increasing the longevity of the polymer in chemical processing or medical device applications. Degradation of the polymer is minimized and its service life is maximized.

The material is effective even at various temperatures, usually from -40°C to 100°C for most standard grades, while some modified grades are able to withstand even greater temperatures. Because of this, it is suitable for difficult conditions like those found in automotive under-the-hood parts. Lastly, POM’s wonderful machinability accounts for why it is still the most favorable material for complex components with accurate tolerances, aiding in innovation across manufacturing and engineering industries. All these traits illustrate why many sectors still trust POM to deliver on high-performance and durable requirements.

How is POM Processed for Various Industrial Uses?

Injection Molding Techniques for POM

The injection molding procedure is dominant in the industry owing to the high degree of POM feature accuracy that can be obtained. The POM pellets are heated to a temperature between 190°C to 230°C depending on the grade of the POM to bring it to a form suitable for injection molding. The temperature must be monitored closely because excessive heating causes overcooking and loss of formaldehyde gas.

Like other injection molding processes, POM injection molding takes place in cycles, which involve four major steps: filling the injection mold, packing it, cooling down, and ejecting the finished piece. In contrast to other nylons, POM requires greater mold temperatures, which are kept from 80° to 120°C. Crystallization is important to achieve the desired mechanical properties. The required injection pressures also depend on the size and complexity of the part being produced. W90AMPA108 and W150AMPA110 are the prevalent injection pressures.

POM components exhibit an average shrinkage percentage of 2-3%, which can pose a challenge during ideal mold designing. In order to limit the impacts of shrinkage, design features such as uniform wall thickness and strategically positioned gates are provided. Moreover, vents are required to allow for any gas trapped within the part structure to escape, so that the pieces produced do not have defects.

Progress in CAD technology has made it easier to optimize flow channels, cooling durations, and material allocation, which subsequently improves cycle times and part repeatability. Ongoing advancements in technology have also unlocked the potential use of multi-cavity molds, resulting in higher production efficiency for POM components in the automotive and electronics industries. One example is overmolding which combines POM with elastomers to create multi-functional parts for specialized applications.

The proliferation of refined techniques has allowed injection molding to become the default manufacturing method of POM. This, in turn, has resulted in the widespread adoption of POM for the production of gears, bearings, housings, and other mechanical parts like precision instruments.

Grades of POM: Choosing the Right Material for Your Needs

Polyoxymethylene (POM) comes in two principal grades—homopolymer POM (POM-H) and copolymer POM (POM-C)—which have different properties for different uses or applications. The selection of the appropriate grade is based on specific requirements such as mechanical properties, thermal stability, and a chemical’s compatibility with the material.

Homopolymer (POM-H):

Again, a familiar example of POM-H would be the Delrin ® brand of POM. POM-H grade polymers are preferred in high-stiffness applications, such as tensile strength and dimensional stability. It has great fatigue resistance and creep performance, which is essential for precise mechanical components like POM bearings and gear. POM possesses excellent dimensional stability. POM is also undergoing polymerization which is why POM has homopolymer grades, so it is highly crystalline. Because of this, wear-resistant, abrasion-resistant, and high melting points (175°C) of POM is expected. With all these advantages, POM-H has lower chemical resistance when compared to copolymer grades, particularly against acidic environments.

Copolymer (POM-C):

POM-C is known for its superior resistance to a range of chemicals such as acids and bases and a lower tendency to develop centerline porosity during molding. It keeps its strong mechanical properties, but its stability improves in thermally or chemically volatile environments. Like POM homopolymer grades, POM-C has a melting temperature which is lower than 162-168 °C. For these reasons, POM-C is widely used in modern plumbing parts, fuel systems components, and industrial machinery parts where environmental resistance and durability are critical.

Reinforced and Modified Grades:

Specialized variants of POM are available in addition to standard POM-H and POM-C grades such as for more advanced engineering applications. For example, POM reinforced with glass fibers has greater stiffness and strength for bearing loads. Impact-modified grades are designed with additives that make them more resistant to impact and thus are appropriate for components that experience shock or cyclic loading. Lubricated grades, which are treated with PTFE or silicone, have low friction and increased dirt resistance and are therefore ideal for dynamic use, such as in sliding parts and in conveyors.

Important Issues Related to Material Choices

After determining the details that refer to the POM grade, operational temperature range, load expectations, chemical exposure, and durability requirements need to be evaluated. In addition, certain characteristics may be defined by regulations, which may differ from industry to industry. When such characteristics are integrated with the basic features of POM-H, POM-C or their modified forms, the desired results in terms of component performance and service life are achieved.

Due to the advanced capabilities of POM, thorough attention to detail within material selection proves POM’s vast ability to aid several industries and engineering issues all within one material.

Applications for Injection-Molded POM Include Various Industries

The mechanical properties of strength, stability, and low friction incumbent POM with a great deal of prowess, and as such, it is employed in injection molding extensively within multiple sectors such as:

Automotive: Fuel system parts, gears, door locks, and seatbelt systems.
Consumer Goods: Everyday items such as zippers and buckles further underline the applicability of acetal plastic within appliance parts.
Industrial Machinery: Conveyor belt parts such as bearings, and rollers.
Medical Devices: Dentists’ tools and parts of insulin pens.
Electrical and Electronics: Housings, connectors, switches of devices.

With this multitude of applications, low out-of-pocket expenses for high-quality products are what makes POM ultimately desirable.

Frequently Asked Questions (FAQs)

Q: How does polyoxymethylene (POM) differ from other engineering plastics, and what gives rise to its nickname ‘acetal’?

A: POM or acetal is one of the most widely used engineering thermoplastics featuring high strength, low friction, exceptional dimensional stability, and high stiffness. The term ‘acetal’ is more commonly used because it derives from acetal groups. Highly specialized polymers such as these have a far greater range of use than simpler ones due to their excellent mechanical attributes.

Q: What remarks can be made about POM’s key features and components?

A: One key component of POM is that it is marked by elevated strength, hardness, and rigidity in addition to possessing good dimensional stability, low friction, and moderate wear resistance. The resultant polymer has fairly high melting, strong chemical resistance, and good electrical properties too. Unsurprisingly, these attributes render POM exceptionally useful for the vast majority of modern engineering tasks.

Q: How is the compound provided and fabricated?

A: Due to ease of handling and processing, POM is provided in granulated granules. The principal method of processing is injection molding, although it can be treated using several other methods. Similarly, granules of POM must be treated with care, as at high temperatures POM loosely decomposes. Anything from heat to methods themselves needs to be adjusted properly to achieve a desired outcome.

Q: What are some of the common POM Applications?

A: POM is used throughout the industry for many reasons. Typical applications for injection-molded POM are found in automotive components, consumer goods, sanitation fittings, and mechanical parts, which sheds light on the importance of acetal plastic in contemporary manufacturing. Medical apparatus, conveyors, and zipper parts are other industry applications. These applications utilize POM’s superior strength, dimensional stability, and resistance to wear and chemicals.

Q: Are there different grades of POM available?

A: Different grades of POM are available to suit application needs. These grades can be separated into homopolymers and copolymers, which differ in some of their characteristics. Some grades are designed to optimize thermal stability, chemical resistance, or mechanical properties. The choice of POM grade depends on the specific needs of the application.

Q: How does POM compare to other engineering thermoplastics?

POM excels in many applications owing to its unique set of characteristics relative to other engineering thermoplastics and acetyl resins. POM has an exceptionally high strength-to-stiffness ratio, excellent dimensional stability, and remarkably low friction, making it outperform many other thermoplastics. Although not as strongly resistant to severe acids or bases as some other polymers, POM does offer good chemical resistance. Its large range of tolerable conditions combined with resistance to cycloalkanes and alcohols makes it a perfect candidate for applications where other plastics struggle.

Q: What are the thermal properties of POM?

A: The melting point of POM (homo)polymer is very high when compared to many other thermoplastics. It is approximately 175 degrees Celcius for homopolymers. POM also retains strong mechanical properties over a wide range of temperatures, making POM endure for use in thermal versatile applications. However, POM’s processing temperatures make it vulnerable to POM’s thermal degradation sensitivity, which has to be managed during manufacturing.

Q: Is it Possible to Use POM where there is contact with food?

A: Some grades of POM are authorized for food contact applications. They comply with the FAD and other international safety regulations. When implementing POM in food contact applications, the right grade must be selected, and every step of processing and handling must pass the safety evaluation.

Reference Sources

1. Differently branched polymeric blends: Rheological analysis through shear and elongation of linear/pom-pom polystyrene blends

Authors: M. G. Schußmann, S. Lyu, V. Hirschberg
Published: March 1, 2023
Journal: Journal of Rheology

Highlights:

The research examined the rheological properties of two types of polystyrene: linear and pom-pom-shaped.
It has been observed that the pom-pom structure aids in elongational strain hardening, which is advantageous for processing capabilities.
The interplay between shear and elongational flow was studied, and it was found that the addition of pom-pom polymers has a pronounced influence on flow behavior.

Methods:

All of the experimental results were obtained from rheological testing, which were then fit into constitutive models such as Doi-Edwards and molecular stress function (MSF) models (Hirschberg et al., 2023).

2. Brittle Fracture and Elongational Viscosity of 10 Polystyrene Pom-Poms with the Hierarchical Molecular Stress Function Model.

Authors: V. Hirschberg, M. G. Schußmann, Marie‐Christin Röpert, M. Wilhelm, M. Wagner
Published: April 5, 2023
Journal: Rheologica Acta

Key Findings:

A model is proposed for estimating the elongational viscosity and brittle fracture of pom-pom polymers.
The materials’ complex flow behavior was characterized by the hierarchical molecular stress function model.
This study demonstrates the effect of molecular architecture on the mechanical properties of pom-pom polymers.

Methodology:

The research consisted of a theoretical model which was tested with real-world observation data. (Hirschberg et al., 2023, pp. 269–283).

3. Predictive/fitting capabilities of differential constitutive models for polymer melts—reduction of nonlinear parameters in the eXtended Pom-Pom model

Authors: R. Pivokonský, P. Filip
Published: 2014-07-04 (note: This paper is older than 5 years but is included for context)
Journal: Colloid and Polymer Science