Abrasion in Sealing Technology

Definition, Causes and Countermeasures

In sealing technology, abrasion is the progressive loss of material caused by frictional contact. Typically, it affects the seal itself (for example the sealing edge) and/or the mating surface — the metallic surface on which the seal runs. Wherever components move relative to one another and require a contact pressure to seal, abrasion can occur.

How can abrasion be identified during operation or on disassembly? Common indicators include a worn or “thinned” sealing edge, score marks (elongated scratches) on the seal or on the mating surface, and detectable particles in the medium — for example through an oil analysis. Furthermore, depending on the system, abrasion also leads to rising leakage, because the sealing geometry loses its defined contact line.

In tribological terms (tribology = the science of friction, lubrication and wear), abrasion is the result of wear mechanisms. Two mechanisms dominate in sealing contacts: abrasive wear (grinding action) and adhesive wear (material transfer during direct contact). However, in practice both often occur together, and the operating conditions determine which one prevails.

Distinction from similar damage patterns

In failure analysis, abrasion is frequently confused with other damage patterns because several effects can occur at the same time. Two important distinctions, therefore, are extrusion and thermal damage.

As a result, extrusion and overheating are rarely true alternatives to abrasion — they are amplifiers of it. For diagnosis, therefore, the key questions are where the damage begins and which operating conditions match it in time.

How abrasion develops: tribological fundamentals in the sealing contact

Seals wear because sealing requires a defined contact pressure. As soon as motion is present, this normal force generates friction, and friction in turn generates heat. Heat then alters both the condition of the material and the lubricating capacity of the medium. Consequently, abrasion is usually the result of a chain reaction of contact, friction, temperature and material response.

The type of motion is decisive. For instance, reciprocating motion (a back-and-forth stroke, e.g. in a cylinder) creates contact conditions different from those of rotational motion (shaft) or slow, microscopic relative motion (micro-movement). In addition, contact time matters: a sealing contact that is loaded for long periods and only rarely moved can show wear patterns different from those of a highly dynamic contact.

Likewise, the quality of lubrication strongly influences the wear rate. A stable lubricating film partly or fully separates the surfaces. With insufficient lubrication, however, the proportion of solid-body contact increases, and friction, temperature and material removal rise with it. In hydraulic systems the oil film can help; by contrast, in pneumatic applications or under dry-running conditions, lubrication is often lower and abrasion appears more quickly.

Load, speed and temperature also act together. As speed rises, frictional power tends to increase, and so does the temperature. Higher temperatures may soften or harden the seal material, depending on the compound, and they alter the viscosity of the lubricant. For this reason, wear data are only comparable when the test conditions are clearly defined — pressure, speed, temperature, surface roughness and level of contamination.

Abrasive vs. adhesive wear (in brief)

Abrasive wear arises when hard particles or rough surfaces act like an abrasive. A common distinction is two-body abrasion (a hard “counter-body” scratches directly) and three-body abrasion (loose particles roll or slide between the surfaces). In sealing systems, three-body abrasion is very typical because particles are carried along in the medium or on the surface.

By contrast, adhesive wear is based on local “sticking” within the micro-contact. Material can be transferred or torn out, especially when the lubricating film breaks down and the surfaces come into direct contact. This phenomenon occurs more often with insufficient lubrication, an unfavourable material pairing or at high temperatures.

Main causes and typical amplifiers in hydraulics and pneumatics

In practice, contamination is one of the most frequent drivers of abrasion. Particles enter the system from several sources: from manufacturing and assembly (chips, dust), through ingress from the outside (ambient dust, splash water carrying solids), or from internal component wear (metallic and polymer abrasion). Once these particles reach the sealing contact, they act like grinding grains and produce score marks as well as material loss.

Misalignment, side load and tilt are further typical causes. They prevent the contact pressure from being distributed evenly. As a result, a local overload develops at the sealing edge, where temperature and wear rise sharply. Often, the damage then appears as one-sided abrasion or score marks aligned with one direction of relative motion.

Equally important is the mating surface. Unsuitable surface roughness or damage (corrosion, run-in marks, defects in hard coatings) increases the abrasive effect. At the same time, the material pairing influences the tendency towards adhesive wear. Because elastomers, thermoplastics, PTFE-based materials and composite solutions respond differently to pressure, temperature and lubrication, the choice has to match both the medium and the type of motion.

For troubleshooting, a brief, systematic check that addresses the key “W” questions is often helpful:

• What rubs against what (seal against rod/shaft/running surface), and where is the heaviest material loss?
• Which type of motion is present (stroke, rotation, mixed motion), and how fast?
• Which particles are possible (origin, hardness, size range), and how are they transported?
• Which operating conditions act simultaneously (pressure–temperature–speed), and when did the change occur?
• How is the guidance designed (clearance, alignment, side forces)?

Practical example: hydraulic cylinder at the piston rod

A common failure path begins with dirt ingress at the piston rod. Particles accumulate around the wiper and the rod seal — exactly where the sealing contact does its work. With every stroke, the particles are dragged along and act as a grinding agent. As a result, score marks appear on the rod and on the seal, leakage rises, and even more particles enter the oil. Consequently, the process becomes self-reinforcing, because every additional bit of abrasion produces new particles.

Detection, consequences and countermeasures

Abrasion can often be detected early through indirect signals. For example, if leakage rises slowly, friction torque changes, or the operating temperature in the sealing area increases, abrasion is a likely cause. In hydraulic installations, moreover, particle monitoring and oil analysis provide additional evidence, since an increase in certain particle classes can indicate progressive wear.

The consequences extend well beyond the seal itself. Sealing performance drops, bypass leakage rises, and overall efficiency declines. In addition, score marks on metal surfaces can run in and damage replacement seals more quickly. At the same time, the overall particle load in the system grows, putting further stress on valves, pumps and bearings, which ultimately raises the probability of failure.

Effective countermeasures address the root causes and combine several levers. In many cases, cleanliness and filtration provide the largest benefit, because they reduce the abrasive content directly. Equally important, however, are stable guides — so that side loads do not cause local overpressure — and a suitable mating surface with the right roughness and an adequate bearing-area structure.

Finally, if abrasion recurs or the boundary conditions are complex, specialised tribological and sealing-technology consulting is often advisable in order to confirm the causes and countermeasures reliably.