Polyoxymethylene is used primarily in injection molding for the production of molded parts. The thermoplastic has excellent physical, chemical and mechanical properties. Therefore, polyoxymethylene is predestined for the production of high-quality precision parts.

Polyoxymethylene chains are assembled from individual chemical building blocks known as monomers. As with other polymers, the type and sequence of the polyoxymethylene chains determine the physical, chemical and mechanical properties of the finished plastic.

Polyoxymethylene can be synthesized as a homopolymer or copolymer from different monomers.

The great advantage of polyoxymethylene is that it remains dimensionally stable over a wide temperature range and is characterized by great hardness, rigidity and strength. Above a temperature of about 160 °C degrees, polyoxymethylenes, like other thermoplastics, begin to melt and become soft. The maximum application temperature is about 110 degrees Celsius in continuous use. Operating temperatures of up to about 140 °C are also possible for short periods.

Up to this temperature, polyoxymethylenes exhibit high abrasion resistance, a low coefficient of friction and high heat resistance. Another advantage is that polyoxymethylenes absorb little water and can be dyed into almost any color.

The density of polyoxymethylene is around 1.4 g/cm³, depending on the manufacturing process. Above the temperature of 220 °C, POM begins to decompose thermally. This forms toxic formaldehyde, which is easily identified by its pungent odor.

Is POM (polyoxymethylene) food safe?

Polyoxymethylenes can only be classified as food-safe to a limited extent. Acidic substances with a pH value below 2.5 must not be filled into polyoxymethylene containers. Also, only certain catalysts are to be used in the production process. The melt index must be below 50 g/10 min..

POM has high thermal resistance

POM can only be used under certain temperatures. In the long term, POM can be used at maximum application temperatures of 100 °C to 110 °C; for short periods, polyoxymethylenes can also be exposed to temperatures of up to 140 °C without damage. The glass transition temperature is -60 °C . The melting point of polyoxymethylenes is between 160 °C and 180 °C, depending on the composition. Above 220 °C, thermal decomposition sets in.

The mechanical robustness of POM (polyoxymethylene)

Polyoxymethylenes exhibit quite high shrinkage, which must be taken into account when casting precision parts. The shrinkage is independent of the casting direction and therefore the risk of distortion and cracking in the workpieces produced in this way is very low.

The chemical properties of POM mean high resistance

POM has a high chemical resistance to organic solvents such as oils, gasoline, diesel, aromatic compounds or alcohol. There is also high resistance to dilute alkalis. However, polyoxymethylenes are not resistant to acids with a pH value below 4. Due to their high UV sensitivity, POM has only limited resistance to weathering and is therefore not suitable for long-term outdoor use. One advantage of polyoxymethylenes is their very low water absorption of 0.05%.c

Polyoxymethylenes, like other polymers, are produced by linking individual chemical building blocks. The properties of the finished polymer can be influenced by the type and quantity ratio of the individual monomers. Depending on the individual building blocks used, two different polyoxymethylene groups can be distinguished:

• POM Acetal Homopolymer
• POM Acetal Copolymer
  
  

Production process with only one chemical building block: POM Acetal Homopolymer

In the production of POM acetal homopolymer, only one chemical building block (monomer) is used. Formaldehyde is usually used, but trioxane can also be used. The production is carried out in anionic or cationic chain polymerization, depending on the chemical building block used. In this process, after addition of a suitable initiator, the molecular chains are built up by linking the individual monomers. The ends of the molecular chains are protected by esterification, which serves to stabilize them. The linking of only one chemical building block results in a very high-quality plastic with excellent mechanical properties and electrical insulation capability. Due to its chemical structure, pure POM is opaque white in color.

Several substances are involved in the production of POM acetal copolymer

A completely different plastic is produced by adding a second chemical building block during synthesis. This is incorporated statistically into the molecular chain. This manufacturing process produces so-called POM ESD.

ESD stands for electrostatic discharge. These plastics increase the operational safety of electrical equipment because they safely dissipate electrical charges. POM acetal copolymer is electrostatically conductive. It is also made from trioxane, but oxirane or some other substances are added in varying amounts during production. Since these additives are randomly incorporated into the molecular chain during the reaction, they thus provide the desired electrostatic properties. The molecular chain ends are also protected by esterification in this product variant.

The further processing of polyoxymethylene is similar to that of other thermoplastics. All machining techniques are suitable for further processing of polyoxymethylene. These include:

• Milling,
• sawing,
• drilling.

Compared to other plastics, polyoxymethylene is characterized by very good machinability.

If polyoxymethylene is to be painted, it must be treated with a suitable plastic primer due to its surface properties. Pretreatment of the surface by plasma etching is also possible. Polyoxymethylene is suitable for all common welding processes. Unlike many other plastics, POM cannot be bonded in the conventional way. Bonding of polyoxymethylene is possible by prior surface pretreatment, so-called pickling. We will be happy to help you select suitable pickling agents. Special POM adhesives based on epoxy resins are also available. If you have any questions on this subject, we will be happy to assist you. Do not hesitate to get in contact with us.

Due to a low surface energy, POM is difficult to paint. If this is desired, a special surface treatment must be applied before the paint is applied. However, we recommend coloring POM directly during production.

Polyoxymethylene can be molded directly into the desired shape by injection molding or extrusion. 3D printing has proven to be cost-effective for the production of prototypes and small series. Suitable POM filaments are available for this purpose in white-opaque natural color as well as already dyed.

GOOD TO KNOW

Polyoxymethylene is usually supplied naturally opaque white or black colored, as it is most cost-effective to produce in these two variants. However, in order to be able to produce models and prototypes in the colors projected later, it can be practical to color POM yourself. Special products are available on the market for this purpose.

Due to their mechanical and physical properties, polyoxymethylenes are particularly suitable for the production of precision workpieces by injection molding. The following workpieces and semi-finished products can be manufactured from POM, for example:

• Gears and slip clutches - dimensional stability and high abrasion resistance make POM the privileged plastic for these components.
• Plain bearings and guide elements - are subject to particular mechanical stress and must be highly resistant to abrasion.
• Housing parts can either be constructed from POM sheets or are injection molded directly into the appropriate shape.
• Sleeves, screws and bolts made of POM serve as lightweight and inexpensive connecting elements not only in model making.
• Drip tips for e-cigarettes are the mouthpieces that are also made of polyoxymethylene and can withstand the resulting temperatures.
  
  

Did you know?

Polyoxymethylene is also used for the manufacture of a special sports equipment. The bolts used in the sport of paintball are also made of POM. This is one of the most important parts of the marker, the actual weapon in this action-packed sport.

POM (polyoxymethylene) can be used for blanks and sheets

Polyoxymethylene is available in sheets of various thicknesses. These are usually produced by the casting process. These sheets are used in model and prototype construction as molds and housing parts and can be easily shaped into the desired form by sawing and milling. The sawing out of flat molded parts is also possible without any problems. Due to the limited possibility of bonding, sheets made of polyoxymethylene are usually welded or screwed together. This is also possible with special plastic screws.

The use of POM for thermoplastic semi-finished products

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The advantageous thermal properties of POM are ideal for the production of round and hollow rods.

Polyoxymethylene round bars are available in different diameters for construction. Please note the desired electrostatic properties of the different polymers.

Hollow rods made of POM (polyoxymethylene) have the advantage of being lighter while offering similar stability and are therefore preferable to solid material for certain applications. It is also important to consider the different electrostatic properties of copolymer and homopolymer.

The mechanical properties of polyoxymethylene make it a popular raw material for gears

When it comes to precisely manufactured and durable plastic gears, polyoxymethylene is the ideal material. This is because, in addition to great hardness and strength, it also exhibits outstanding abrasion resistance. Shrinkage of the plastic plays a decisive role in production and must definitely be taken into account.

Due to its high resistance, POM is also suitable as a component of pipes

POM pipes are available in different diameters and wall thicknesses and are used wherever light and stable structures are to be erected in areas that are not critical to weathering. Of course, we will be pleased to meet your individual production requirements. Please do not hesitate to contact us by mail or telephone.

Are you looking for special precision components made of polyoxymethylene? Let our services convince you! Through our years of experience as a traditional company in the field of plastics manufacturing, we know the needs of our customers. We offer them reliable supply chains, great expertise and cost-effectiveness in manufacturing. As we have an overview of the complete manufacturing process of our products at any time, it is possible to intervene individually. We develop our products in close consultation with our customers and have often been able to contribute to targeted improvements in important details.

Contact us today to work with our experts to plan, produce and ultimately implement your next project. Many years of expertise and continuous training of our employees always guarantee you the best solution for your polyoxymethylene projects.