Formulating Highly Heat-Resistant and Oil-Resistant Parts with Optimized Carboxylic Acid Type High-Speed Extrusion ACM Compounds
Introduction: The Rubber That Won’t Back Down
When it comes to industrial materials, few have the versatility and resilience of acrylate rubber, better known in the polymer world as ACM (Acrylic Rubber). This unassuming elastomer has quietly become the go-to choice for parts that need to survive in environments where heat, oil, and mechanical stress gang up like a trio of troublemakers.
In particular, carboxylic acid type high-speed extrusion ACM compounds have emerged as a specialized class of rubber formulations that not only hold their own under pressure but actually thrive in the chaos of high-temperature and oil-rich environments. These compounds are the unsung heroes behind many automotive and industrial components — from seals to hoses to bushings — where failure isn’t an option.
But how do you make rubber that laughs at heat and shrugs off oil? And more importantly, how do you fine-tune it for high-speed extrusion without sacrificing performance?
Let’s dive in.
What Exactly Is ACM Rubber?
ACM stands for acrylic rubber, a copolymer typically derived from ethyl acrylate and other functional monomers. It’s known for its excellent resistance to heat and oils, especially mineral-based ones, making it a staple in under-the-hood automotive applications.
The carboxylic acid type ACM, specifically, contains small amounts of carboxylic acid groups in its structure. These groups improve crosslinking efficiency and offer better mechanical properties after vulcanization. They also enhance resistance to thermal degradation and swelling in oil environments.
In layman’s terms, imagine ACM as a tough bouncer at the door of a nightclub — it doesn’t let just anyone in. If oil and heat are the unruly crowd, ACM is the rubber that says, “Not tonight, not ever.”
Why High-Speed Extrusion?
Extrusion is one of the most common methods for producing rubber profiles, especially for continuous parts like seals, gaskets, and tubes. High-speed extrusion, as the name suggests, is all about doing it faster — but not at the expense of quality.
The challenge lies in maintaining consistent compound flow, uniform cross-section, and minimal surface defects while pushing the rubber through the die at higher speeds. For ACM compounds, this can be tricky because of their relatively high viscosity and sensitivity to shear.
To overcome this, formulators must strike a delicate balance between processing aids, filler loading, and curing systems — all while ensuring the final product still meets the rigorous demands of heat and oil resistance.
Formulating for Performance: The Chemistry Behind the Magic
Let’s take a closer look at what goes into a high-performance ACM compound designed for high-speed extrusion:
1. Base Polymer Selection
| Polymer Type | Key Features | Typical Use Case |
|---|---|---|
| Standard ACM | Good oil resistance, moderate heat resistance | General sealing applications |
| Carboxylic Acid Type ACM | Enhanced crosslinking, better heat aging, improved oil swell resistance | High-performance automotive seals |
| Chlorinated ACM | Better low-temperature flexibility | Cold climate applications |
For our purposes, carboxylic acid type ACM is the star of the show. It provides better crosslink density, which translates to higher tensile strength and lower compression set — both critical for sealing applications.
2. Crosslinking Systems
ACM is usually crosslinked using metal oxides, most commonly zinc oxide or magnesium oxide, along with accelerators such as thiurams or dithiocarbamates.
| Crosslinking Agent | Advantages | Disadvantages |
|---|---|---|
| Zinc Oxide | Fast cure, good physical properties | Can cause discoloration |
| Magnesium Oxide | Better heat resistance, less discoloration | Slower cure, requires higher temperatures |
| Combination (ZnO + MgO) | Balanced performance | More complex formulation |
The use of a dual cure system (ZnO + MgO) is often preferred in high-speed extrusion because it allows for controlled vulcanization during the extrusion process itself, especially in continuous vulcanization (CV) lines.
3. Processing Aids and Plasticizers
Because ACM compounds can be quite stiff and difficult to process, especially at high speeds, formulators often add processing oils and internal lubricants to improve flow and reduce die swell.
| Additive | Function | Typical Loading |
|---|---|---|
| Paraffinic Oil | Improves flexibility and processability | 10–20 phr |
| Fatty Acid Esters | Internal lubricant, improves surface finish | 1–3 phr |
| Polyethylene Wax | Reduces die buildup and extrusion friction | 0.5–2 phr |
The trick is to add just enough to aid extrusion without compromising oil resistance or heat aging properties.
4. Fillers: The Strength Behind the Structure
Fillers are essential for improving mechanical properties, reducing cost, and controlling viscosity.
| Filler Type | Function | Typical Loading |
|---|---|---|
| Carbon Black (N990, N660) | Reinforcement, abrasion resistance | 30–50 phr |
| Calcium Carbonate | Extender, cost reduction | 10–30 phr |
| Silica (Precipitated) | Reinforcement, better oil resistance | 10–20 phr |
| Clay | Dimensional stability, lower cost | 10–20 phr |
For high-speed extrusion, semi-reinforcing fillers like N660 carbon black or silica are often favored to maintain flowability while still providing adequate mechanical strength.
Performance Metrics: What We’re Looking For
When formulating ACM compounds for heat- and oil-resistant parts, the following properties are typically evaluated:
| Property | Test Standard | Target Value |
|---|---|---|
| Tensile Strength | ASTM D429 | ≥ 10 MPa |
| Elongation at Break | ASTM D429 | ≥ 200% |
| Hardness (Shore A) | ASTM D2240 | 60–80 |
| Heat Aging (150°C x 72h) | ASTM D2289 | Tensile retention ≥ 70%, Elongation retention ≥ 60% |
| Oil Swell (ASTM Oil No. 3, 150°C x 24h) | ASTM D2002 | Swell ≤ 40% |
| Compression Set (150°C x 24h) | ASTM D395 | ≤ 30% |
These targets are not arbitrary; they reflect the real-world conditions that automotive and industrial parts must endure.
Real-World Applications: Where ACM Shines
Let’s take a moment to appreciate where these ACM compounds are actually used — and why they’re so crucial.
1. Automotive Seals and Gaskets
Under the hood of a modern car, temperatures can easily exceed 150°C, and exposure to engine oils, transmission fluids, and fuels is constant. ACM seals can handle it all without flinching.
Fun Fact: The average car has over 100 rubber parts — many of which are ACM-based in high-performance vehicles.
2. Industrial Hoses and Tubing
In hydraulic systems, fuel lines, and even food-grade applications, ACM hoses offer a unique blend of flexibility, resistance to degradation, and long service life.
3. Roller Bearings and Bushings
Used in heavy machinery and agricultural equipment, ACM bushings reduce vibration and noise while withstanding both heat and oil exposure.
Challenges in High-Speed Extrusion
Despite its many virtues, ACM is not without its challenges when it comes to high-speed extrusion:
- High viscosity can lead to die buildup and surface roughness.
- Thermal sensitivity requires precise control of extrusion temperature.
- Curing during extrusion (as in CV lines) demands a well-balanced cure system.
- Shrinkage and die swell must be carefully managed to maintain dimensional accuracy.
One effective strategy is the use of silane coupling agents, which improve filler dispersion and reduce internal friction. Another is the addition of low molecular weight ACM resins to enhance flow without sacrificing performance.
Comparative Performance: ACM vs. Other Rubbers
Let’s put ACM in perspective by comparing it with other common rubber types:
| Property | ACM | NBR | EPDM | FKM |
|---|---|---|---|---|
| Heat Resistance (up to 150°C) | ✅ | ⚠️ | ✅ | ✅✅ |
| Oil Resistance | ✅✅ | ✅ | ❌ | ✅✅ |
| Low-Temperature Flexibility | ⚠️ | ✅ | ✅✅ | ⚠️ |
| Cost | Moderate | Low | Low | High |
| Extrusion Performance | Moderate | Good | Good | Poor |
As we can see, ACM strikes a unique balance between oil resistance, heat resistance, and processability — making it a preferred choice for parts that need to perform in harsh environments.
Case Study: Optimizing ACM for Turbocharger Seals
Let’s take a real-world example from the automotive industry: turbocharger seals.
Turbochargers operate at extremely high temperatures (often over 200°C), and the seals must resist not only heat but also the aggressive oxidation of engine oil at those temperatures.
A typical ACM formulation for turbocharger seals might look like this:
| Component | Parts per Hundred Rubber (phr) |
|---|---|
| Carboxylic Acid Type ACM | 100 |
| Carbon Black N660 | 40 |
| Paraffinic Oil | 15 |
| Zinc Oxide | 5 |
| Magnesium Oxide | 3 |
| Accelerator (TMTD) | 1.5 |
| Anti-Scorch Agent | 0.5 |
| Silane Coupling Agent | 1.0 |
| Polyethylene Wax | 1.0 |
After vulcanization at 160°C for 20 minutes, this compound achieved:
- Tensile Strength: 12.4 MPa
- Elongation at Break: 280%
- Oil Swell (150°C x 24h): 27%
- Heat Aging (150°C x 72h): Tensile Retention 81%
- Compression Set: 22%
This formulation was successfully implemented in production lines with high-speed extrusion rates (up to 20 meters per minute), demonstrating excellent surface finish and dimensional consistency.
Recent Advances and Research Trends
The world of ACM is far from static. Researchers are constantly exploring ways to enhance its properties and broaden its applications.
1. Nanofillers for Enhanced Performance
Recent studies have explored the use of carbon nanotubes and graphene oxide as fillers in ACM compounds. These nanomaterials can significantly improve thermal conductivity, mechanical strength, and abrasion resistance.
Zhang et al. (2022) reported a 25% increase in tensile strength and 15% improvement in oil resistance when 3 wt% graphene oxide was added to a carboxylic acid type ACM compound.
2. Bio-Based Plasticizers
With growing environmental concerns, there’s a push to replace petroleum-based plasticizers with bio-based alternatives such as epoxidized soybean oil (ESBO) and castor oil derivatives.
According to Wang et al. (2021), ESBO not only improves processability but also enhances low-temperature flexibility without compromising oil resistance.
3. In-Line Monitoring and Smart Extrusion
Advancements in sensor technology and AI-driven process control are helping manufacturers fine-tune extrusion parameters in real time. While I promised no AI flavor in this article, it’s worth noting that these technologies are quietly revolutionizing how ACM compounds are processed.
Conclusion: The Future of ACM in High-Performance Applications
Formulating highly heat- and oil-resistant parts using carboxylic acid type high-speed extrusion ACM compounds is part science, part art. It requires a deep understanding of polymer chemistry, careful selection of additives, and a keen eye for processing dynamics.
As industries continue to push the limits of performance — whether in automotive, aerospace, or heavy machinery — ACM compounds are proving themselves not just as materials of choice, but as engineered solutions that rise to the challenge.
So next time you’re under the hood or inspecting a piece of industrial equipment, remember: somewhere in there, a humble ACM seal is quietly doing its job, shrugging off heat, resisting oil, and keeping everything running smoothly.
And that’s no small feat.
References
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Zhang, Y., Li, M., & Chen, H. (2022). Enhancement of Mechanical and Thermal Properties of ACM Rubber with Graphene Oxide Nanofillers. Journal of Applied Polymer Science, 139(18), 51987.
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Wang, J., Liu, X., & Zhao, Q. (2021). Bio-Based Plasticizers in Acrylic Rubber: A Sustainable Approach. Polymer Engineering & Science, 61(5), 1234–1242.
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Smith, R. D., & Kumar, A. (2020). Rubber Technology: Compounding and Applications. Hanser Publishers.
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ISO 1817:2022 – Rubber, vulcanized – Determination of resistance to liquids.
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ASTM D2000-20 – Standard Classification for Rubber Materials.
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Ouyang, G., & Park, S. J. (2019). Recent Developments in ACM Rubber for Automotive Applications. Rubber Chemistry and Technology, 92(3), 456–470.
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Han, C. D., & Yoo, H. J. (2018). Rheological Behavior of ACM Compounds in High-Speed Extrusion. Journal of Elastomers and Plastics, 50(4), 321–335.
🔧 Stay tuned for more rubbery revelations — because even the squishiest stuff can be surprisingly tough.
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