Ein technischer Leitfaden zur Analyse von Linearführungslager-Ausfällen, der behandelt, wie man Laufbahn-Verschleißmuster liest, Kontaminationsschäden erkennt, normales Ermüdungsabblättern von vorzeitigem Versagen unterscheidet und Schäden für Lieferanten-Garantieansprüche dokumentiert.
Reading Wear Patterns: What the Raceway Tells You
Linear bearing failure rarely occurs without warning. The raceway surface records the history of operating conditions - if you know how to read it. When a bearing is returned for failure analysis, the first step is to examine the raceway under 10x–30x magnification. The pattern, location, and depth of wear reveal the root cause with surprising specificity.
Even, Symmetrical Wear Track
A uniform wear track across the full circumference of the outer raceway, with no localized damage, indicates normal end-of-life fatigue. The bearing has reached its rated L10 travel distance. This is the expected failure mode - the bearing was correctly specified and properly maintained. Replace with the same part number.
Offset or Elliptical Wear Track
If the wear track is shifted to one side or forms an ellipse rather than a circle, the bearing experienced uneven loading. Common causes: misalignment of the shaft relative to the housing (angular deviation > 0.5°), or an oversized shaft that presses the ball complement asymmetrically. Measure the shaft diameter at the wear location - if it exceeds the H7 tolerance band, the shaft is oversized and must be replaced or reground.
Wide, Fuzzy Wear Track
A wear track that is wider than the ball diameter, with diffuse edges, indicates the bearing operated with excessive internal clearance. This happens when a zero-clearance bearing (C0) is used in an application that requires preload, or when the bearing has lost preload due to ball wear. The balls skid rather than roll, broadening the contact path. Replace the bearing and verify the clearance class specified on the drawing.
Contamination Damage Signatures
Contamination is the second leading cause of premature linear bearing failure (after inadequate lubrication). The damage signature depends on contaminant type:
Hard Particle Contamination (Abrasive)
Hard particles - typically grinding swarf, metal chips, or mineral dust - embed in the bearing surfaces or circulate between the balls and raceway. The signature is a series of shallow, parallel scratches aligned with the direction of travel, often visible on both the raceway and the ball surfaces. Under magnification, the scratches have raised edges (burrs), confirming abrasive rather than adhesive wear.
Remedy: Improve the sealing arrangement. For environments with airborne particulates, specify double-lip contact seals (2RS type) rather than standard shields. Add a wiper or scraper to the shaft entry side to remove debris before it enters the bearing zone.
Corrosive Contamination
Water, acidic fluids, or humid environments cause corrosion damage. The signature is reddish-brown staining (rust) on the raceway, concentrated at the ball contact points where the protective lubricant film is thinnest. Advanced corrosion produces pitting - discrete voids in the raceway surface that rapidly propagate fatigue cracks.
Remedy: For humid environments, specify stainless steel (AISI 440C) bearings instead of standard GCr15. Verify that the lubricant has corrosion inhibitors. If the operating environment involves washdown, use bearings with integrated contact seals and a stainless steel housing.
Fatigue Spalling: End-of-Life vs Premature
Spalling - the detachment of surface material from the raceway - occurs when subsurface fatigue cracks propagate to the surface. All bearings eventually spall at end of life, but premature spalling (before 50% of rated L10) indicates one of three conditions:
- Overload: The applied load exceeded the dynamic load rating (C). Check whether the application has added weight or increased acceleration since the bearing was specified. A bearing rated for 2,000 N that sees 4,000 N peak loads will spall at 15–20% of rated life.
- Inadequate hardness: If the raceway hardness measures below 58 HRC, the case is too soft to support the Hertzian contact stress. This indicates a heat treatment defect. Request a hardness test report for the replacement lot.
- Lubricant film breakdown: If the lubricant viscosity is too low for the operating load, the elastohydrodynamic lubricant (EHL) film is thinner than the surface roughness, causing metal-to-metal contact. Verify the lubricant viscosity matches the application's specific load and speed parameters.
Documenting Failure for Supplier Claims
When returning a failed bearing to the supplier for warranty analysis, include: (1) the bearing with seals intact, (2) photographs of the raceway at 10x magnification, (3) the operating hours or travel distance at failure, (4) the application description (load, speed, environment), and (5) a sample of the lubricant used. Without this data, the supplier's analysis will be inconclusive and the claim will likely be denied.