Gear problem

In flawless gear boxes relatively prominent tones appears at gearmesh frequency, i.e. number of cogs multiplied with the rotational speed (RPM frequency) of the gear box. When the gear box has been used for a while the level of the gear mesh component decreases as the edges of the cogs are slightly rounded. Continued wear increases the level och gear mesh again. The level is also affected by the alignment of the pinion axles.

Source of vibration Exciting frequency Dominating direction Amplitude Spectral characteristic Comments
Bad gear mesh X times number of cog Radial, axial Constant, sometimes with variations Narrow band Often with 1X on each side of gear mesh frequency
Eccentric pinion 1X, gear mesh Radial   Narrow band Wheel may be balanced but mounted on anunbalanced rotor. 1X sideband around gear mesh frequency.
Bad alignment 2X, gear mesh Axial Constant Narrow band 1X side band around gear mesh
Out of true, unbalance or damaged cog 1X and gear mesh Radial for cut cogs and axial for one or two arrow cogs Constant Narrow band 1X side band around gear mesh
Production fault Gear mesh “Ghost frequency” normally not synchron with 1X Radial, axial Constant Narrow band Production fault due to gear mesh fault in the production machine drive can give “ghost frequencies”.
Problem with planetary gear box Very dependent on gear box geometry Radial Constant Narrow band It is common with side bands around gear mesh frequency with an interval as the planets rotational frequency.

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