Polyoxymethylene (POM) or acetal/Delrin® is one of the most important modern thermoplastics used in engineering and manufacturing. POM supports a broad range of industries due to its unique mechanical characteristics, chemical resistance, and dimensional stability. In this article, we will examine the attributes that make POM peculiar regarding its composition, performance characteristics, and its applications. We will analyze the advantages of POM’s competitive materials, how it limits competing materials, and discuss the most important factors impacting selection of POM in engineering design. With the help of this blog, we aim to change the perception regarding material selection that engineers and manufactures have by explaining the use of POM further in-depth.
What is POM Material and How is it Made?
Production-grade acetal or polyoxymethylene (POM) is a type of plastic best known in the industry for its strong mechanical attributes and resistance to deformation across varying temperatures outside its crystalline structure. Due to its enduring nature, low friction, and susceptibility to wear, POM is ideal for polymerization into chains using formaldehyde or its derivatives. The two common forms of POM are homopolymer and copolymer, the latter of which is preferred due to improved thermal and chemical durability. Its manufacturing involves polymerized precision and subsequent molding or extrusion, giving it the ability to create complex geometrical structures with high precision.
Understanding the chemical composition of polyoxymethylene
Polyoxymethylene (POM) also known as acetal has repeating units of oxymethylene (-CH2O-) in its structure. A POM backbone comes from formaldehyde or trioxane, which through polymerization becomes a highly crystalline thermoplastic. Purely oxymethylene copolymers result in homopolymers of high rigidity and mechanical strength, but increased thermal degradation. Copolymers introduce comonomers that disrupt molecular structure regularity which increases thermal stability, and hydrolysis resistance, making available all sorts of consumer and industrial applications. Where there are changes to molecular structure, there are properties. Hence, types of POM changes.
The manufacturing process of POM: From acetic anhydride to granulated form
Polyoxymethylene (POM) production starts from formaldehyde synthesis, generally produced from methanol through catalytic oxidation. For the basic type of POM homopolymer, formaldehyde is produced using anionic or cationic catalysis. This process builds highly crystalline polyoxymethylene chains. POM copolymer production involves combining trioxane (stable formaldehyde trimer) with ethylene oxide, count as comonomers which helps ease degradation and increase thermal stability.
After the material has been polymerized, it undergoes stabilization through end-capping processes. This is done in order to avoid chain scission during processing and use. The polymer is then put into an extruder and turned into granules which are then commercially distributed. The granules can be utilized as the base material for injection molding, extrusion, or machining, enabling their use in engineering applications like automotive parts or even consumer products.
Differences between POM homopolymer and copolymer
Due to the differences in structures of Polyoxymethylene (POM) homopolymer and copolymer, each provides unique features which affect performance in applications.
1. Chemical Structure: POM homopolymer’s skeleton consists of repeated units of formaldehyde. It possesses a rigid and highly crystalline structure. On the other hand, POM copolymer has certain units known as comonomer units. This comonomer breaks some degree of crystallinity making it less sensitive to thermal degradation (C6H10O2)n.
2. Applications that require high enduring structural performance use Stringent POM Homopolymer due to its strength, rigidity, and hardness. Co-Polymer impacts Positive Impact Resistance and Toughness, albeit with modest reductions in structural performance.
3. Thanks to prevention of chain unzipping in homopolymers, POM Copolymer is superior in thermal stability enabling reduced risk of deterioration at high temperatures.
4. As POM Copolymer possesses a wider range of porosity, versatility in manufacturing processes, and more favorable mechanical properties than the under narrowed POM Homopolymer, its processing and usability become higher.
Because of these factors, engineers can strategically select which POM would be more appropriate based on the intended application’s functional and environmental requirements.
What Are the Key Properties of POM Plastic?
Polyoxyethylene or POM possesses multiple unique mechanical traits along with temperature and chemical resistance, granting it unmatched value across engineering applications. The key values include:
1. Extremely Durable and Stiff: Significantly large amounts of stress or pressure do not affect the rigidity or tensile strength of POM.
2. Self-lubricating and wear resistant: Systems powered by repetitive motion and those that bear significant loads are protected from friction and durability issues by the material’s self-lubricating attribute.
3. Retains shape and size: POM is critical in precision components due to its retaining of form under differing environmental conditions.
4. Thermal Stability: The thermal stability of the material allows it to maintain its operational effectiveness up to 120°C without notable loss in performance.
5. Chemical Resistance: An added advantage that increases POM’s longevity and durability in extreme environments is its wide-range solvent, fuel and chemical resistance.
6. Moisture Resistance: POM retains its physical properties in humid conditions due to its minimal water absorption and strength.
All of the above properties make POM a material of choice for the construction of gears, bearings, fasteners, and other enduring and precise engineering components.
Mechanical properties: Strength, hardness, and rigidity
Due to its remarkable attributes, Polyoxymethylene (POM) is one of the most widely used thermoplastics in challenging tasks due to its mechanical strength. Each grade offers tensile strength between 60 and 70 MPa. This value secures reliable structural performance of POM under attack forces. The Rockwell hardness of POM ranges from M80 to M90 which indicates that it has high surface strength, resisting deformation and possibly wearing down due to prolonged usage. POM also possesses good stiffness which means it bends less when loads act on it. Its flexural modulus is between 2,600 MPa and 3,200 MPa. This means that POM is able to endure substantial loads while maintaining intact structure. Because POM is able to maintain structural integrity and true shape during still and dynamic conditions, flexibility in applications is achieved.
Dimensional stability and low friction characteristics
Polyoxymethylene (POM) has outstanding precision geometry and dimensional stability which is essential for high level industries. Advanced two or more machine parts that are fitted closely together as one unit to achieve high levels of refinement in defined space require precision geometry, such as measuring instruments. This is possible through low thermal expansion, dimensional hygroscopicity, and turnable hi-precision engineering alloys bound by POM. But even more important, the low coefficient of friction with steel pays for itself in applications with sliding or turning parts like gears and bearings. Resulting with high savings in energy and wear from downtimes in the mechanical systems.”
Chemical resistance and temperature range of POM
Polyoxymethylene (POM) features outstanding chemical resistance to hydrocarbons, fuels, and oils along with a wide variety of solvents and other neutral chemicals. On the other hand, strong acids, oxidizing agents, and halogenated hydrocarbons are capable of damaging its molecular structure. As for temperature, POM performs between -40 °C to 120 °C (-40 °F to 248 °F), with some specific grades extending their operational efficiency to beyond these limits. This thermal resilience, alongside a moderate level of chemical and moisture attack, guarantees reliability within demanding industrial conditions.
How Does POM Compare to Other Engineering Thermoplastics?
Of all engineering thermoplastics, POM has superior compressive strength, low co-efficient of friction, and wear resistance making it very suitable for manufacturing high precision parts. While Nylon’s share similar mechanical strength, POM leads in situations lacking consistent moist environments because of its reduced water absorption sensitivity. Compared to polypropylene and ABS, POM demonstrates higher fatigue endurance and creep resistance, though it may be more thermally versatile than polycarbonate. These attributes make POM appealing in areas demanding endurance, precision, and robust chemical resistance.
POM vs. other high-performance plastics: Advantages and disadvantages
Compared to other high performance plastics, POM (Polyoxymethylene) has a few unique strengths and weaknesses. Its sliding friction is very low, a quality POM possesses that is beneficial in devices that contain moving parts such as gears, bearings, and conveyor systems. Moreover, POM excels in maintaining precise measurements and is dimensionally stable under mechanical stress straining which makes it beneficial in manufacturing. Its chemical resistance to fuels, solvents, and weak acids also make POM suitable for harsh industrial environments.
That said, POM has some disadvantages when compared to some other advanced plastics. For example, Polyethylene Oxide Modified POM has a much lower operating temperature range than PEEK and PPS which can sustain higher thermal loads. POM is effective in moisture absorption but not as effective as Polycarbonate in UV resistance which makes POM less effective for prolonged outdoor applications without containment additives. In addition, its notch sensitivity can result in stress cracking in some high-impact situations which may be better served with Nylon plastics due to their greater toughness.
POM is known for its efficacy in application scenarios that require a compromise between strength, precision, and durability. However, it does require careful consideration for uses that require thermal resistance, UV stability, or impact strength due to those factors being critical.
Comparing POM homopolymer and copolymer: Which to choose?
Fulfilling the needs of POM copolymer and homopolymer requires choosing between the two. The difference lies on the specifics of the application. POM homopolymer provides higher fatigue and damage tolerance along with having greater strength and stiffness which allows it to withstand significant mechanical load occurring in precision parts. Nevertheless, it does suffer in high temperatures or chemically aggressive conditions.
In addition, POM copolymer has better thermal stability and greater resistance to chemical deterioration, especially in cases when acids or moisture are present. It also shows decreased porosity which improves dimensional stability in some sensitive applications. Although this material has somewhat lesser homopolymer mechanical strength, its range of properties enables usage under much harsher operating conditions. In the end, the decision comes down to whether one needs precise mechanical performance (homopolymer) or superior environmental durability (copolymer) for an application.
What Are the Most Common Applications of POM Material?
Polymer of Metal, or just POM, is incredibly common in the automobile industry, used for bushings, gears, and seat belt mechanisms. It’s also put to use in the construction of different consumer products such as zippers. The reasons for POM’s extensive use include its low friction, excellent machining capabilities, toughness, and resistance to harsh environments.
Typical applications for injection-molded POM parts
Parts made of injection-molded POM (polyoxyethylene) are used in a wide range of industries because of their unrivaled mechanical strength, low friction, high dimensional stability, and durability. It is utilized in precision gears in automotive systems such as fuel system parts, and other critical systems which involves safety features like seatbelt mechanisms. POM can also be found extensively in home appliances for manufacturing durable moving components such as handles, latches, and levers. It is also used in the making of electric and electronic parts including connectors and switches where it assures high reliability. Because of its low cost, ease of machining, and versatile features, POM is perfect for use in fasteners, bushings, and even components of medical devices which require precision and long-lasting strength.
POM in automotive and consumer goods industries
The automotive and consumer goods industries benefit Polyoxymethylene (POM) or acetal due to its exceptional mechanical and thermal benefits. For the automotive industry, POM is extremely useful for its low friction, dimensional stability, resistance to fatigue, and so much more in every vehicle. This means its incredibly useful in the production of fuel system components, housing for sensors, gear mechanisms, and many more things. Because of these reasons, vehicles are much more capable when under harsh environments and wear.
In consumer products, POM is preferred due to its rigidity, lightweight, and resistance to chemicals. These properties make it possible for POM to be used in the manufacturing of zippers, kitchen tools and even toothbrushes. POM products are extremely durable and maintain a high level of performance even with repeated use. Additionally, POM’s aesthetic properties such as smooth surface finish also make it appealing for the crafting of long-lasting and high-quality consumer products.
Specialized uses of POM in medical and food-grade applications
Due to its biocompatibility, mechanical strength as well as resistance to repeated sterilization processes, POM is used in medical and food grade applications. POM is frequently used in medical devices to manufacture precision parts for catheter clips, parts of insulin pens and even handles for surgical instruments. These components require a high level of accuracy and durability. Its low moisture adsorption along with high resistance to chemicals make it suitable in situations where high hygiene is crucial.
The two regulations, the FDA and EU certifications, POM complies with, ensures safety on the use of food-grade materials. This is the reason POM is used for parts of food processing machines, conveyors, milk pumps and even POS devices as they are in constant contact with food, and POM’s wear resistance properties help retain its shape. Furthermore, the absence of serration on POM’s surface greatly decreases the possibility of contamination and reduces the effort needed to clean it. This makes POM especially valuable in preserving the quality of food products.
How is POM Processed and Manufactured?
Automobile industries primarily make use of POM because of its low friction characteristics and sensitivity towards harsh environments. Most manufacturers offer POM granulated polymer resins with a mouth temperature of 170 to 230 degrees Celsius. With the right extruding machines, it’s easy to create intricate and detailed components with injection molding or extrusion techniques. During the process, high quality control guarantees the durability and product specifications.
Injection molding techniques for POM plastic
Advanced techniques focus on achieving high efficiency and precision in the injection molding of POM plastics. These practices include avoiding thermal degradation by ensuring appropriate flow into the mold cavities, as well as maintaining appropriate melt and mold temperatures. Depending on part geometry and required cooling rates, mold temperatures usually range between 80 to 120 degrees Celsius. To fill the mold uniformly and reduce the formation of voids, high injection pressures which often range between 700 to 1500 bar, are used.
For successful material processing, mitigating resin material degradation through controlled drying is critical. This often necessitates a moisture level lower than 0.2% prior to processing. Given the mildly abrasive nature of POM, the use of wear-resistant steel molds is highly suggested. For added precision, SVG or sequential valve gating can be incorporated for complex or large molds. SVG offers balance cavity filling and reduction of potential weld lines.
Other processing methods: Extrusion and blow molding
1. Extrusion: This process is common in many industries. It is especially useful in the manufacturing of POM (polyoxyethylene) profiles, sheets, tubes, and other uniform cross-sectioned goods. Firstly, POM resin has to be melted before being forced through a screw-driven extruder shaped die. Critical parameters are keeping the barrel temperatures between 180°C to 210°C, and maintaining a constant screw speed. The shear thermal stability is important as staying at high temperatures for too long destroys the polymer system. Cooling is usually done immediately after extrusion using water baths or cooling rollers. This happens to ensure the material retains shape and dimensions after solidifying. For long and continuous products, like POM, this technique is efficient as extrusion achieves unrivaled precision and consistency.
2. Blow Molding: Another common way of processing POM is by blow molding, specifically for hollow parts such as tanks, bottles, and ducts. It starts with the extrusion or injection molding of POM parison, which is then blown out with air until it fills up the mold cavity. Melt strength should be sufficient to prevent deformation during inflation. Like extrusion, blow molding is performed at barrel temperatures between 180 °C and 210 °C. Both cooling time and mold surface temperature need to be controlled to avoid warping while maintaining uniform wall thickness. Blow molding is typically performed on light-weight, strong pieces having thin walls.
Tips for working with POM in manufacturing
1. Proper Drying: Ensure that POM is properly dried before processing in order to minimize moisture content. Having too much moisture will affect mechanical strength due to pores, surface anomalies, and lower overall strength. It is best to dry at 80 °C for 2 to 4 hours.
2. Temperature Control: Avoid thermal degradation by controlling the processing temperature. Within its processing range, POM has excellent thermal stability, but overheating POM will rapidly degrade it and emit formaldehyde fumes.
3. Tooling and Mold Design: Implements such as vents with polished surfaces should be used in order to limit friction and the risk of snagging. Parting line shrinkage must also be considered as POM has a shrinkage ratio of 1.8 – 2.5%
4 .Flow Behavior: Ensure even wall thickness on all sections of parts to eliminate stress concentrations and enable easy material flow. Internal corners must also be free of sharp edges. Gates and intakes must be positioned for even distribution during filling.
These recommendations help to improve the manufacturability and longevity of POM in its many use cases while ensuring that POM can be produced and processed in an efficient manner.
What Are the Environmental Considerations for POM?
POM, or Polyoxymethylene, raises a number of problems for the environment over the course of a recycling life cycle. In the case of POM, in addition to its value as a durable material, it is also considered useful because of its recyclability. However, the production of POM involves the use of formaldehyde and if not managed, can emit harmful emissions. In addition to that, POM is non-biodegradable which makes it hard to dispose of at the end of its useful life. POM waste can be mitigated through recycling initiatives and reduction of redundant materials resulting in less environmental footprint. Emissions created during the processing and disposal of POM need to be contained to minimize environmental impact.
Recyclability and sustainability of polyoxymethylene
Mechanized recycling of POM demonstrates potential where it is shredded into smaller components for reconstruction and remanufacturing into new products. This method improves resource conservation while facilitating a circular economy in remanufacturing. Moreover, injectable POM chemical precursors are being advanced further in the driven lesions of chemical recycling enabling high-quality material to be re-synthesized. But there are still concerns so far as energy and emissions during processes that focus on recycling. With POM, greater focus should be to reduce formaldehyde emissions during production and processing of POM while ensuring material optimization.
Environmental impact of POM production and disposal
The impact on the environment from making POM and throwing it away has to do with how it is made and how it is managed at the end of its life. During the process of making POM, formaldehyde, which is used as a raw material in POM production, is released. If there is no proper mechanism for controlling formaldehyde, it may cause air pollution. There is a necessity to control formaldehyde emissions using advanced technologies and better production processes. Also, POM’s not being able to biodegrade makes throwing it away a problem because it will remain sitting in landfills and the environment for long periods which is harmful ecologically. To combat these issues, there is a need for recycling strategies such as mechanical and chemical processes to prevent wastage and conserve materials which addresses POM’s tendencies. These recycling techniques do consume a great deal of energy, which can offset environmental progress unless renewable energy resources are employed. POM’s footprint on the environment needs to be diminished with sustainable changes in production, recycling, and emission control.
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Frequently Asked Questions (FAQ)
Q: What are the typical mechanical properties of acetal homopolymer?
A: An example of an acetal homopolymer is Delrin from Dupont which has better mechanical properties such as high tensile strength, moderate stiffness, and good abrasion resistance. Because of these properties, it is used for strong engineering applications.
Q: In what form is polyacetal plastic typically supplied?
A: Polyacetal plastic is usually supplied in bulk as granules, making it easy to inject mold into the desired shape through the application of heat and pressure.
Q: What are some common POM applications in engineering?
A: POM is used in the fiend of injection molds for automotive and consumer electronic parts as well as for precision gears because of their high strength and exceptional dimensional sterility.
Q: How did the development of POM contribute to modern engineering plastics?
A: The development of pom marked a great achievement in the history of engineering plastics considering the new material possessed superior mechanical properties along with ease of machining which made it advantageous for newer industrial applications.
Q: What challenges are associated with bonding acetal polymer?
A: Due to the low surface energy of the acetal polymer, bonding becomes problematic. Typically, some special adhesive or mechanical means of fastening is used to assemble acetal parts.
Q: Is it possible to machine POM using conventional techniques?
A: POM can be processed using conventional techniques such as turning, milling, and drilling. Its ease of machining combined with good dimensional stability may be highly beneficial for the creation of precision intricate components.
Q: How does Hermann Staudinger impact the context of polymers like POM?
A: The German chemist Hermann Staudinger, who won the Nobel Prize in Chemistry, greatly expanded the methods of polymers which greatly contributed to the modern materials such as POM.
Q: What characteristics of POM make it suitable for demanding applications?
A: POM is known for high strength and excellent abrasion resistance, as well as its inherent opacity in white. In addition to the high-performance engineering applications, POM is known for its superb dimensional stability, making POM an ideal choice.
