Loeser LF 500

A rotary shaft seal (lip seal, RWDR) works by a rubber lip pressing against the rotating shaft surface. When the shaft surface has a circumferential grinding pattern — circumferential scratches from cylindrical grinding — the helix-angle of the grinding marks can act as a micro-pump, drawing oil from the wet (oil) side to the dry (air) side along the spiral groove path as the shaft rotates. This is called 'oil pumping' and causes shaft seal leakage even on a new, correctly installed seal. DIN 3760 and ISO 6194 specify that the shaft surface under the lip seal must have a longitudinal (axial-direction) surface texture — produced by longitudinal finishing — to eliminate the spiral groove oil-pumping tendency. The Loeser LF 500 is specifically designed to produce this DIN 3760-compliant longitudinal texture.

DIN 3760 (Rotary shaft seals — technical requirements) specifies shaft surface Ra 0.2–0.8 µm for the shaft running surface under the lip seal, with the additional requirement that the surface texture must be dominantly longitudinal (axial direction) with no spiral marks or circumferential lay. Rmax (maximum peak height) is often additionally specified at < 6.3 µm to prevent individual grinding burrs from cutting the seal lip. Too smooth (Ra < 0.1 µm) causes adhesive wear of the seal lip (insufficient oil film). Too rough (Ra > 1.0 µm) causes excessive seal lip wear from surface asperities. The Loeser LF 500's Ra 0.2–0.8 µm range with longitudinal texture is exactly the DIN 3760 target window.

Yes. Case-hardened steel (58–62 HRC) is one of the primary materials for gearbox and differential shafts requiring seal surface finishing. The Loeser LF 500 uses aluminum oxide or silicon carbide abrasive belts rated for hardened steel finishing. CBN abrasive belt options are available for high-hardness materials or high-volume applications where longer belt life reduces consumable cost. The key consideration for hardened shaft finishing is avoiding thermal damage — the LF 500's controlled contact pressure and oil mist cooling prevent abrasive belt finishing from generating significant heat (unlike grinding), making it inherently safer for hardened shafts than grinding-based finishing operations.

Many gearbox and motor shafts have two or more lip seal seats at different positions along the shaft — for example, a front seal and a rear seal at different axial positions on the same shaft. The Loeser LF 500's CNC-programmed traverse stroke positions and dwell zones allow independent finishing of each seal seat zone. The CNC program specifies: traverse start position (axial), traverse end position, traverse speed, contact pressure, and number of finishing passes for each seal seat zone independently. Between seal seats, the contact tool can be retracted (no contact) during the rapid traverse to the next zone. Multiple seal seat finishing is handled in a single workpiece setup.

The Loeser SZ series (SZ 250, SZ 600) uses short-stroke oscillating superfinishing stones applied to journal bearing surfaces — producing circumferential or cross-hatch textures at Ra < 0.05 µm for bearing and tribological contact applications. The Loeser LF series uses traversing abrasive belts or stones applied in a longitudinal (axial) direction — producing a longitudinal texture at Ra 0.2–0.8 µm specifically for rotary shaft seal surfaces. The two products serve different surface texture requirements: SZ for ultra-smooth bearing surfaces (negative Rsk, high bearing ratio), LF for DIN 3760 seal surfaces (longitudinal lay, moderate Ra). A complete shaft finishing cell for an automotive gearbox output shaft might include both: SZ superfinishing on the bearing journal seats, LF longitudinal finishing on the oil seal seats.