Drum gear coupling failure reasons: drum gear coupling carrying capacity and life depends on the intensity of the contact, and the radius of curvature of the tooth and the tooth meshing contact angle is a direct impact on the strength of the tooth meshing contact angle and radius of curvature of the intensity relationship - contact stress F- gear to withstand the circumferential force E- elastic modulus - the radius of curvature of the tooth surface - displacement radius - engagement angle - the height of the inner and outer radius of the tooth surface meshing teeth meshing angle of curvature and direct effects of exposure to stress, meshing angle small radius of curvature large radius of curvature is small contact stress. Abroad drum gear coupling engagement angle has 20 °, 21.5 °, 28 °, 30 °. We selected 20 ° meshing angle, favorable reduce contact stress. ① inner ring gear tooth wear serious .② generate a large amount of axial displacement, not even occur meshing teeth broken .④ .③ counterpart coupling bolts broken coupling faults lifting accessories:. ① severe tooth wear . ② the ring gear to produce a large amount of axial displacement, or even can not be engaged. ③ broken teeth phenomenon. ④ counterpart coupling bolts break. The main reason causing the above description is insufficient lifting accessories drum gear coupling oil or lack of oil. Two shafts levelness and concentricity error is too large, more than coupling, can compensate for the range, making the pinion meshing with the internal teeth inaccurate, resulting in partial contact, and again in the additional torque.