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    GEAR FAILURES

    9.0 Monitoring gear tooth damage

    Click on photograph to enlarge 
    Figure 9a
    Typical gear tooth pitting records obtained with marking blue and transparent adhesive tape
    Figure 9b
    Making a resin cast to record gear tooth surface condition
    Figure 9c
    Photos show an early cast and one after 9 months operation.  Two resin casts taken from the same tooth at intervals of running time and showing that the pitting of the teeth is reducing and is therefore only of the initial or corrective type and thus no cause for major alarm.
    Main Characteristics
    Cause 
    Note 
    Possible Confusion with
    Other Types of Damage    		 
    CommentParticularly when tooth pitting occurs relatively early in the life of a gear pair it is useful to monitor the progress of the pitting to see whether it shows signs of healing or is becoming progressively worse. Some means of recording the condition of the tooth surfaces is therefore required.

    One of the simplest techniques is to degrease the gear teeth in situ with a rag and solvent, wipe them dry and then coat them lightly with marking blue. A length of transparent adhesive tape can then be pressed against the tooth surfaces and a blue print of the damaged, areas will be retained on the tape when it is peeled off. If a free length of the tape is left attached, which is still fully adhesive, the tape can then be stuck on a record card for the gear set with information on the date at which it was taken. By taking tape prints of this kind at intervals, a direct visual comparison of the pitting history can be made and the process of pitting can be readily monitored.

    Alternatively if access to the gears is very good, the tooth condition can be recorded with resin casts. The tooth space to be checked is dammed at each end with modelling clay and a two part setting resin poured in to the space. When this has set it is levered out to provide a permanent solid model recording the tooth condition.