DIN 3760

Definition and Context of DIN 3760

DIN 3760 is a German standard for radial shaft seals (RSS). A radial shaft seal is a ready-to-install rotary seal that seals a rotating shaft against a stationary housing. It keeps lubricants such as oil or grease inside while at the same time helping to keep contamination out. The sealing principle is usually based on an elastomer sealing lip (an elastomer is a rubber-like material) that is pressed against the shaft with a defined force by a garter spring.

Normatively, DIN 3760 primarily defines designs, nominal dimensions, and tolerances. In practice, this is the basis for assigning geometries unambiguously and making components interchangeable. By itself, however, this is not enough for a service-life-secure selection, because suitability always depends on the actual operating data — such as rotational speed, temperature, medium, and contamination.

Internationally, DIN 3760 is technically aligned with ISO 6194-1, which describes rotary lip seals with elastomer sealing elements. For design in sealing technology, what remains decisive is that standards primarily structure geometry, while the application must be secured through operating conditions.

What Is a Radial Shaft Seal?

A radial shaft seal is used wherever a shaft rotates and the housing is stationary — for example, in gearboxes, electric motors, pumps, or axle drives. It seals radially, that is, perpendicular to the shaft axis, through the contact between the sealing lip and the shaft surface. For this contact zone to work stably, it needs a suitable mating surface and a defined contact force, which is frequently generated by a tension spring.

Standard vs. Design

DIN 3760 mainly answers the question of which design and which dimensions a seal has, and how it is toleranced. The standard does not automatically answer whether this seal will reach the required service life in a specific machine. For that, additional factors must be assessed — for example:

• Medium and additives (oil type, grease, possible chemical influences)
• Temperature and heat dissipation
• Rotational speed and circumferential speed
• Concentricity, eccentricity, and assembly errors
• Contamination, moisture, pressure pulsations

Even small deviations in shaft surface or assembly can place a heavier load on the sealing edge and thereby trigger leakage or increased wear.

Designs According to DIN 3760 (A/AS/B/BS/C/CS) and Their Meaning

DIN 3760 distinguishes designs in particular through the outer casing (elastomer-covered or metallic) and through the S suffix. In practice, the S stands for an additional dust or protection lip on the air side — that is, the side facing the environment.

The choice of design influences how sensitive the seal is to housing-bore quality, how well it seals statically in the housing, and how robust it is against assembly conditions.

Outer Casing and Stiffness: A vs. B vs. C

In sealing technology, the outer casing matters particularly because the static seal between seal and housing arises here. An elastomer casing can often compensate better for micro-leakage at the seat, whereas a metallic casing depends more strongly on housing tolerance and surface quality.

The “S” Suffix: AS/BS/CS

The AS, BS, and CS variants have an additional dust or protection lip beyond the main sealing lip. This second lip reduces contamination ingress to the main lip and improves protection against splash water or dust. It does not replace a pressure seal. With higher differential pressure or strong pressure cycles, other sealing concepts or additional design measures are often required.

Typical Application Limits and Operating Conditions

Radial shaft seals according to DIN 3760 are frequently used in low-pressure applications. As reference values, in practice up to about 0.5 bar and circumferential speeds up to about 12 m/s are often cited. Such values are not guarantees, because they depend heavily on material, lubrication, temperature, shaft condition, and installation situation.

For design, what matters is when the sealing lip still runs stably within the lubricating film. Excessive circumferential speed, insufficient lubrication, or an overly rough mating surface raise friction and temperature at the sealing edge. As a result, elastomer aging accelerates, and early leakage can be triggered.

Why “Low-Pressure / Pressureless” Is Often Cited

A radial shaft seal seals primarily through lip contact and the very thin lubricating film that forms there. When pressure rises significantly, the lip geometry can deform unfavorably, which can cause leakage or increased wear. Pressure pulsations act additionally as a dynamic load and can cause the lip to “pump”. Under such operating conditions, standard designs are often not sufficient, which is why design adaptations or alternative sealing systems are frequently considered.

Design Requirements and Selection Notes (Shaft, Housing, Material)

In many cases, the service life of a radial shaft seal is determined by the quality of shaft and housing. The standard helps with assignment, but tightness and wear depend heavily on fits, surfaces, and material. The mating surface on the shaft is the functional sealing surface. If it is too soft, too rough, or runs geometrically irregularly, the sealing lip can wear faster.

Shaft and Housing: Fits, Roughness, Hardness

Frequently cited reference values are a housing bore of H8 and a shaft of h11. For the shaft surface, a fine range of Ra of about 0.2–0.8 µm is often recommended. In addition, a sufficient shaft hardness is cited — for example, ≥ 45 HRC (HRC = Rockwell hardness) — so that the mating surface remains wear-resistant against the sealing lip.

Beyond these key values, real kinematics decide: concentricity deviations, eccentricity, and assembly offset increase dynamic lip movement. As a result, friction rises, and the sealing edge can be overloaded thermally and mechanically.

Materials at a Glance: NBR, FKM, PTFE

Material selection answers the question of which medium and which temperature can be reliably covered. In practice, these groups are frequently distinguished:

Which compound fits in detail depends on the specific oil, additives, temperature profile, rotational speed, and contamination level. These factors also determine whether a dust lip makes sense and whether additional protective measures are needed.

Designation Logic (Short Example)

Product designations often follow the logic standard + design + dimensions + material. A form such as “DIN 3760-AS … –NBR” means: design according to DIN 3760, design type AS with an additional dust lip, and NBR as the elastomer material. The exact dimensions define the shaft diameter and the housing seat so that the seal fits correctly.

For demanding applications such as high contamination, elevated pressure, large eccentricity, or high temperatures, a specialized design review is sensible, so that the radial shaft seal fits the application and the expected service life.