There are a number of factors which could cause an unexpected rise in gear failures. You should start by looking at what is different since the number of failures increased. Are you using a different lubricant? Has the operating environment changed? Is there a cross contamination issue? Has your lubrication routine changed?
Oil analysis is recommended and should include elemental analysis and analytical ferrography. These two tests can provide great insight into the potential cause of the failures. Elemental analysis will offer clues as to which contaminant is inducing the failure, along with which metals are being worn. Analytical ferrography can help indicate which type of wear is being produced. Abrasive wear will typically appear as metal particles with curls, spirals or loops, while adhesive wear will usually be seen as larger platelets or chunks with striations or tempered colouring. Surface fatigue wear will generally look like flat plates with jagged edges. The size of these particles can indicate the severity, with the larger the particles, the more severe the wear. Corrosive wear will resemble extremely fine particles that are too small to distinguish individually.
You should also conduct a visual inspection of the gearing and internal gearbox surfaces. Identify where on the gear tooth the wear is occurring to get a better idea of which types of particles you should be looking for in the analytical ferrography. If there is excessive wear on the pitchline, you should have more surface fatigue wear as this is where you see rolling friction. If there is more wear above or below the pitchline, you should see more abrasive and/or adhesive wear particles.
Finally, you should review your maintenance procedures. Are you following the best practices for inspections and top-up? Are you storing your lubricants correctly? Once you know what is happening inside the gearbox to cause the failures, you can investigate and identify where contaminants are entering the system and take measures to address this.
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