Polyacrylic Rubber (ACM)

Polyacrylic Rubber (ACM) is a specialised synthetic elastomer made from acrylic ester monomers, which are created through the polymerisation of acrylic monomers. It is best known for its excellent resistance to hot oils, high temperatures, and oxidative ageing. This makes it a popular choice for moulded rubber components used in demanding automotive and industrial environments.

ACM offers a stable balance of flexibility, strength, and heat resistance. It performs well in continuous operating temperatures of around 150–175°C, with short-term capability even higher, depending on the compound. One of ACM’s biggest advantages is its resistance to prolonged exposure to transmission fluids, engine oils, and automatic gearbox lubricants. It can withstand these conditions without hardening, shrinking or degrading over time.

This synthetic rubber is not suitable for applications involving water, steam, or strong acids. However, it performs extremely well in powertrain seals, gaskets, diaphragms, and other static moulded components. It is especially effective in applications that demand long-term performance under heat and oil exposure. ACM has low permeability and reliable compression set characteristics.

Polyacrylic Rubber (ACM) offers a strong balance of heat and oil resistance. It sits between more basic elastomers like NBR and high-performance materials such as FKM. Compared with NBR (Nitrile Rubber), ACM rubbers deliver far superior resistance to high temperatures, hot oils, oxidation, and ageing. NBR remains more flexible and performs better in low-temperature conditions. However, it cannot match ACM’s long-term stability when exposed to engine and transmission fluids. As a result, ACM is often selected where NBR would degrade too quickly under heat.

When compared to FKM (Fluoroelastomers), ACM does not reach the same levels of chemical resistance, temperature capability, or fuel resistance. FKM is the premium option for the harshest environments. However, ACM provides a more economical alternative that still offers robust heat and oil resistance for many moulded applications. For high-volume automotive components, such as seals, gaskets, and diaphragms, ACM delivers excellent performance at a significantly lower cost than FKM.

Polyacrylic Rubber (ACM) offers reliable compression set performance, particularly in applications involving prolonged exposure to heat and oils. Compression set refers to a material’s ability to return to its original shape after being compressed. This property is critical for seals, gaskets, and other moulded components. It ensures they maintain effective sealing force over long periods.

ACM is engineered to deliver good compression set values at elevated temperatures, typically outperforming standard oil-resistant rubbers such as NBR. Even after extended ageing in hot engine oils or transmission fluids, ACM retains its elasticity. It maintains this flexibility well enough to preserve an effective seal. This makes it especially suitable for static sealing applications where a consistent clamping force is required over long service periods.

ACM does not match the outstanding compression set resistance of premium rubbers like FKM. However, it still provides a dependable balance of resilience, heat resistance, and cost efficiency. ACM retains its shape and sealing integrity under continuous heat and fluid exposure. This makes it a practical choice for many automotive and industrial applications. It also provides long-lasting performance in demanding environments.

Polyacrylic Rubber (ACM) is widely used in applications that require strong resistance to hot oils, high temperatures, and oxidative ageing. Its combination of durability, stability, and cost efficiency makes it especially popular in the automotive industry. It is also widely used in general industrial environments where components are exposed to heat and lubricants.

In automotive applications, ACM is commonly found in powertrain and transmission systems. It performs reliably even when in continuous contact with engine oils, ATF fluids, and gearbox lubricants. Typical ACM moulded components include shaft seals, gaskets, diaphragms, valve body seals, O-rings, and hose components. Its ability to maintain sealing force at elevated temperatures makes it ideal for static and semi-static sealing duties.

ACM is also used in industrial machinery, pumps, and hydraulic equipment where hot oils and long-term heat exposure can degrade other elastomers. Its low permeability, resistance to oxidation, and stable compression set performance contribute to long service life in these environments.

ACM is not suitable for applications involving water, steam, fuels with high aromatic content, or strong acids. However, it excels in oil-rich, high-heat conditions. As a result, ACM remains a go-to material for moulded components that need dependable thermal and fluid resistance. It offers this performance without the higher cost associated with advanced fluorinated rubbers.

Polyacrylic Rubber (ACM) is primarily suited to static and semi-static sealing applications. In these applications, components are compressed in place. They are also exposed to heat and hot oils over long periods. Its formulation is optimised for thermal stability, oil resistance, and ageing performance, rather than high mechanical stress or repeated flexing.

In dynamic applications, the rubber is subjected to continuous movement, bending, or rapid deformation. In these conditions, ACM generally performs less favourably than elastomers like FKM or EPDM. This is because ACM has relatively lower tear strength, reduced abrasion resistance, and limited flexibility at low temperatures. As a result, it is more prone to cracking or fatigue when used in highly dynamic environments.

ACM can still be used in low-to-moderate dynamic applications. This is possible provided the movement is not excessive and the operating conditions remain within the material’s performance window. When oils, heat, and ageing resistance are the dominant considerations, ACM performs very well. This includes applications such as transmission seals, valve body seals, or shaft gaskets. In these environments, ACM continues to offer reliable performance.

While ACM excels in static sealing roles, its use in demanding dynamic applications is more limited. For components that require frequent flexing or high mechanical stress, alternative elastomers with higher dynamic durability are generally preferred.

Polyacrylic Rubber (ACM) does have some particular processing requirements, but it can be moulded effectively using all common techniques. This includes compression, injection and transfer moulding. The key is maintaining precise control over cure temperatures, timing, and mould conditions. These methods are well-suited to polyacrylic rubber moulding, as long as precise control over cure temperatures, timing, and mould conditions is maintained.

ACM typically relies on peroxide or amine curing systems. This means it often needs longer, carefully managed cure cycles compared to general-purpose elastomers. Whether the part is produced through compression or transfer moulding, the mould must reach the correct temperature. It must also maintain that temperature throughout the process. This ensures full crosslinking and helps avoid issues such as scorching or under-curing.

In injection moulding, ACM’s naturally higher viscosity means mould flow and venting must be well designed. This is to prevent air pockets and ensure complete cavity fill. Good venting, smooth mould finishes, and appropriate release agents help achieve consistent, defect-free components across all moulding methods.

ACM compounds should also be stored in cool, stable conditions to prevent premature curing and maintain their processing window.

At Kea-Flex, these material-specific requirements are built directly into our moulding processes. Our team carefully manages cure cycles, optimises mould venting and flow. We also use controlled material handling procedures to ensure every ACM component meets its intended performance standard. This approach allows us to produce reliable, high-quality products tailored for demanding environments.