Sealing the Future: How Advanced Composites Conquer Higher Pressure and Temperature in Hydraulic Systems

Hydraulic systems are the driving force behind so many industries: from heavy construction vehicles to precision robots in manufacturing. They utilize the incompressible nature of fluid to create tremendous force and motion. However, as we continue to push performance limits, demanding faster strokes, heavier load capacities, and more compact designs, the working dynamics in these systems become more challenging and damaging. This is where the basic, yet critical hydraulic seal comes into play.

For years, hydraulic seals were manufactured from solid elastomers, such as NBR (Buna-N) or Viton. Over time, these materials have served an important purpose, but as demand continues to increase for higher working pressures and extreme temperatures in hydraulic applications, it is becoming more apparent that these elastomers are no longer suited for continued use. In the past decade, we have entered a new age, one with advanced composites manufactured from the latest technology, with the hydraulic seal leading the charge, and no longer limiting engineers' designs to only work with elastomers in hydraulic systems.

The Increasing Challenges: Reasons why conventional seals fail

Consider the hydraulic cylinder operating at 400 bar (5800 psi) with internal fluid temperatures at 150∘C(302∘ F) or greater. For these reasons, standard elastomers will start to fail:

Very High Pressure: At extremely high pressures, soft elastomers are prone to extrusion, being forced into the clearance gaps between the metal parts, which leads to wear, leaking, and the seals failing prematurely. They can also suffer from compression set, where they lose their elastic memory with time.

Very High Temperature: Degradation of the material properties of elastomers occurs due to the high temperature. They can harden, crack, or become too soft which compromises the sealing ability and leads to increased friction, wear, and leakage. The high temperature degrades the chemical properties of the hydraulic fluid also, which will attack the elastomer seal materials.

Chemical Compatibility: New generation hydraulic fluids, including fire-resistant and bio-degradable fluids, tend to be more aggressive making necessary seals that have improved chemical compatibility at elevated temperatures.

The Emergence of Advanced Composites

Advanced composite materials should not be thought of simply as “upgaded” versions of the old. Advanced composites represent a significant change in the technology of sealing. These materials combine the benefits of multiple elements in a material system, commonplace in the forms of polymer matrix, reinforced with various components such as fibers, fillers, or solid lubricating materials, which aid to deliver seals with never-before-seen capabilities. 

Advanced composites address the challenges associated with a weaker material when using higher pressure and surroundings temperature in the following ways:

• Improved Mechanical Strength and Extrusion Resistance

Advanced composites, especially when utilizing PTFE (Polytetrafluoroethylene) combined with various fillers such as glass fiber, carbon fiber, and bronze, can be significantly stronger (higher tensile strength) and harder than purely elastometric-type materials. This strength provides rigidity that generally prevents the material from extruding into the clearance gap, even under high pressures. Picture a seal that can maintain its original shape through the hardship that it encounter where all other seals are expelled and potentially expose the machinery to fatigue conditions. 

• Enhanced Thermal Stability

Many advanced composites often employing high-performance polymer-based structures, for example, PEEK (Polyether Ether Ketone), PPS (Polyphenylene Sulfide) or filled PTFE, have a higher continuous operational temperature than many elastomeric seal materials without significant reductions in other mechanical properties. Therefore advanced composites can maintain their dimensional, resilient appearance and properties under extensive harsh and extreme conditions such during the extended life of using the hydraulic fluid, once the fluid has heated to extreme and harsh conditions. Additionally, they do not soften, become brittle or mechanical is destroyed, under the operational temperature as compared to elastomeric seals that would be challenging to use under these conditions.

• Lower Friction and Wear:

Most advanced composites, especially those with internal lubricants (for example, the natural slipperiness of PTFE or graphite/molybdenum disulfide added as a lubricant), have much lower friction than conventional elastomers. Less friction equals less heat at the sealing interface, longer seal life, and greater overall efficiency of the system. This becomes very important in sealing applications where the seals are frequently sliding against a surface.