Abrasion and Wear

Definition and Distinction (Wear vs. Abrasion)

Wear describes a progressive change in surfaces and geometry that occurs under mechanical load in contact with relative motion. In sealing technology, this means that a seal or its mating surface becomes measurably “different” in operation: the sealing edge loses material, the profile changes, or the surface is damaged. The key word is “progressive” — wear develops over time and over operating cycles.

Abrasion is a common form of wear. The mechanism removes material through rubbing, scratching, or particle contact. In sealing points, abrasion often occurs when hard particles (for example, dust, metal chips, or wear debris already generated) become caught between the seal and the mating surface, or when a rough mating surface acts like an abrasive tool.

In practice, the first question is therefore: where is material being lost — on the seal or on the mating surface? How is the contact established (with or without lubrication)? And what does the material loss mean for the function? Typical consequences are rising leakage, higher friction, and a shorter service life.

The technical framework for all this is tribology. Tribology is the science of friction, wear, and lubrication. As a discipline, it helps treat abrasion not as an isolated defect but as the result of an entire contact system.

Tribosystem: Where Abrasion Forms in Dynamic Sealing Points

Abrasion rarely forms “out of nowhere” — it forms within a tribosystem. A tribosystem consists of two contact partners and everything that acts between and around them. In dynamic sealing points, these elements are typically:

• Body 1: the seal (for example an elastomer, PUR, or PTFE seal)
• Body 2: the mating surface (for example a piston rod, cylinder bore, or shaft)
• Intermediate medium: fluid or lubricant (for example hydraulic oil), including any particles
• Environment: temperature, humidity, contamination, installation condition

In hydraulics and pneumatics, abrasion typically shows up where a sealing lip or sealing edge runs continuously over a surface in relative motion. Common pairings are the rod seal against the piston rod, the piston seal against the cylinder bore, and the wiper against the rod. The wiper plays a special role here, because its job is to keep contamination out — which means it is itself heavily exposed to particles.

The type of motion shapes how a lubricating film can build up. Reciprocating motion (linear) often produces varying lubrication conditions, especially at the reversal points. Rotation, by contrast, tends to build a more stable film, but it also generates continuous sliding paths. Oscillating motion sits in between and can cause local load peaks. In addition, sliding speed matters, because it co-determines the lubricating-film thickness.

The loads in the contact zone are decisive. Beyond the installation pressure, system pressure, side loads, and misalignment all act on the seal. Side loads shift the contact zone and locally raise the surface pressure. As a result, the lubricating film can break down, and the contact tips from a load-bearing fluid film into boundary or dry running. Boundary running means that only very thin layers and surface asperities still carry the load. Dry running means that practically no lubricating film remains. In both cases, the risk of rapid abrasion rises sharply.

Mechanisms and Influencing Factors (Understanding Causes)

Wear at seals can be grouped into a few basic mechanisms. In practice, these mechanisms often overlap, but the classification helps with cause analysis.

Abrasive wear occurs when hard asperities or particles remove material. In sealing points, this is particularly relevant, because even small particles in the lubricating film can act as micro-abrasives. Adhesive wear tends to appear when the lubricating film cannot carry the load. In that situation, contact points stick together briefly and are sheared off again during sliding. Fatigue wear shows up as cracks and pit-outs that result from cyclic loading — for example, during pressure cycles and at reversal points. Tribochemical wear occurs when frictional contact and chemical influences jointly alter the surface, for example through media constituents, additives, water content, or elevated temperature.

For sealing technology, material choice is also central. Elastomers conform well, but they react sensitively to lubrication breakdown, particles, and certain media. PUR (polyurethane) is often abrasion-resistant, yet it can also fail quickly under poor lubrication or high temperature. PTFE has low friction, but its wear behavior depends heavily on fillers, mating surface, and lubrication. Therefore, the right question is not only whether a material is “hard” or “soft,” but which combination of material, surface, and medium actually allows stable operation.

The mating surface itself is also a typical root cause. Roughness, score marks, waviness, hardness, and coatings together determine whether the seal slides over a “friendly” surface or over one that behaves like a cutting tool. Even isolated score marks can locally overload a sealing edge and trigger abrasion. In addition, temperature and fluid chemistry shift material properties — through softening, embrittlement, or altered friction values. In practice, these are often the factors that turn a previously stable state into an unstable one.

One critical aspect is non-linear tipping effects: small changes in particle load, surface condition, or lubrication can be enough to shift the contact from predominantly fluid friction into boundary friction. As a result, wear no longer rises gradually but in sudden jumps.

Two-Body vs. Three-Body Abrasion (Particles in the Contact)

With abrasion, the question is how the abrasive body acts. This distinction is particularly useful for sealing points, because it points directly to root causes such as surface defects or contamination.

Two-body abrasion occurs when the mating surface itself “grinds away” the seal. An overly rough or damaged rod then acts like sandpaper. Three-body abrasion, by contrast, occurs when particles get between the seal and the mating surface. The particles roll or slide along and remove material. In hydraulic systems, this case is common, because particles can come from external contamination, from metal wear, or from the seal’s own wear debris.

The problematic cycle is typical: first, small score marks or particles appear; then more abrasion follows; and this abrasion in turn produces fresh particles. Therefore, wipers, filtration, and clean assembly are not side topics but direct levers against three-body abrasion.

Diagnosis and Assessment: Symptoms, Measurement Variables, Test Approaches

Abrasion typically shows up as a combination of functional change and visible damage pattern. In the application, the first thing noticed is often that leakage slowly rises or that friction force increases. A rise in friction force points to deteriorated lubrication, particle ingress, or an unfavorable surface condition. Visible signs typically include score marks on the rod or bore, polished traces in the contact zone, or a sealing edge that looks thinned and frayed. When fatigue is involved, pit-outs or cracks appear in addition.

For assessment, useful measurement variables either capture material loss or capture functional change. In practice, the following variables are most commonly used:

A systematic failure analysis sensibly starts with the visible findings and then traces them back into the tribosystem: which mating surface is in place, which particle sources are plausible, and when could lubricating-film breakdown occur (at reversal points, on cold start, at low speed, during pressure spikes)?

Useful test approaches include model tests such as pin-on-disk (a standardized sliding pair for measuring friction and wear values) or abrasion tests with defined particles. Such tests are useful for comparing materials or surfaces. However, their transferability is limited, because real sealing contacts involve geometry, elasticity, pressure deformation, and varying lubrication. Therefore, test results should always be cross-checked against the actual sealing point.

In the end, abrasion is usually not a single “material defect” but the result of surface, particles, lubrication, load, and motion all acting together. When the causes are unclear or the sealing point is safety-critical, specialized tribological and sealing-engineering consultation may be advisable.