What are the failure modes of the gear drive?
Tooth surface wearTooth wear is mainly due to dust and debris into the hard tooth surface caused by abrasive wear; the second is because each tooth surface friction running in wear. After the wear profile lose the right shape (Figure 342), the shock and noise produced during operation. Abrasive wear is difficult to avoid in open transmission. The use of closed transmission to improve the surface finish and maintain good lubrication, can prevent or mitigate this wear and tear.
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Pitting corrosionWhen the gear teeth are working, the contact stress produced by the working surface increases from zero to a maximum value, that is, the contact stress on the tooth surface varies according to the pulsation cycle. Repeated action in high contact stress, the fatigue crack will produce fine surface of gear, the crack spread to the tooth surface of the metal particles and the formation of peeling pits, namely fatigue pitting, meshing situation continues to deteriorate the development that scrapped. Practice shows that fatigue pitting firstly appears on the root surface near the joint line (Figure 3-43). The pitting resistance of the gear surface is mainly related to the hardness of the tooth surface, and the higher the hardness of the tooth surface, the stronger the pitting resistance is.Soft tooth surface (HBS = 350) gear tooth surface pitting often due to failure. In the open transmission, because of the rapid wear of the tooth surface, pitting corrosion is not enough to appear or expand, that is, it is worn off, so there is no pitting phenomenon.Through the calculation of the fatigue strength of the tooth surface, in order to take measures to avoid tooth surface pitting; also can improve the tooth surface hardness and smoothness, improve the viscosity of lubricating oil and additives, reduce the dynamic load and other measures to improve the contact strength of tooth surface.
Tooth surface gluingIn high speed and heavy load transmission, the lubrication failure is often caused by the increase of meshing temperature, which results in the direct contact of two metal surfaces and their adhesion. When the two tooth surface relative movement, tooth surface soft torn grooves appear along the sliding direction (Figure 3 - 44), this phenomenon is called glue. In low speed heavy load transmission, it is possible to form scuffing due to the difficult formation of lubricant film between the gear teeth.Increasing the hardness and finish of the tooth surface can improve the scuffing resistance. Low speed transmission uses a more viscous lubricant; high speed transmission uses anti friction additive lubricant; it is also effective against scuffing.
