The crankshaft gear fracture failure analysis of the causes

The crankshaft gear fracture failure reason analysis - 2020 01 - 17 hsiao-yun chang into loyal to YanFeng ( Shaanxi diesel engine heavy industry co. , LTD. Technology research institute) My company's production of a certain type of Marine diesel engine crankshaft gear design requirements material mark of 12 crni3agb/T3077 - 1999. The depth of carburizing layer 0. 9 to 1. 3毫米( 1 process thick of carburized layer. 1 ~ 1. 5毫米) Hardness, carburized layer 58-61 HRC. The components of the machining process is: the raw materials into the factory inspection & rarr; Blanking & rarr; Forging of gear blank & rarr; Gear blank processing & rarr; Hob & rarr; Tooth geometry precision inspection & rarr; Carburizing & rarr; Go to the carbon layer & rarr; Quenching and tempering & rarr; Tooth shape finishing + grinding tooth & rarr; Clean up the tooth, rust and packaging. Retain only the teeth surface carbon layer, so the gear tooth surface hardness is high, the heart of the comprehensive mechanics performance is good. The gear USES about 100 h, produce the gear tooth broken accident, broken tooth fracture and not broken tooth, macro is shown in figure 1 shows, for inspection and found some broken gear ( Not break) Gear tooth surface exist crack as shown in figure 2. According to the fracture of the gear tooth, we made the following analysis. Figure 1 is broken tooth fracture and not broken tooth, macro figure 2 has not broken tooth tooth surface penetrant inspection, visible filters according to the location and distribution of 1. Material analysis of raw materials of 12 crni3a, specific see table chemical composition. 12 crni3a chemical composition ( The mass fraction) （ %） 2. The test process and results of fracture morphology analysis: the gear tooth are three connected from the tooth surface crack near the pitch, tooth root and tooth width direction to another gear tooth surface extension, final fracture, crack morphology as shown in figure 3, figure 4. Figure 3 without corrosion crack morphology in figure 4 after corrosion crack morphology with hardness method to detect the depth of carburizing layer ( See figure 5) And the curve of the induration layer ( See figure 6) 。 It is clear that there are crack hardening layer depth: 0 tooth face side. 73 mm, side 0. 75毫米; 0 no crack tooth face side. 78 mm, side 0. 81mm。 Hardness test: is cracked tooth surface hardness of 56. 3HRC、56. 7HRC； No crack tip hardness of 56. 5HRC、56. 2HRC。 Hardness and deep layer does not meet the design requirements. Figure 5 layer deep detection figure 6 hardening curve note: A1 is a crack on both sides of the tooth surface hardness curve; A2 is no crack on both sides of tooth surface hardness curve. 3. Conclusion can be seen from figure of oil pollution, clean up after it is gray, the tooth is broken near a pitch circle, visible to the obvious fatigue trench line on fracture and fatigue curve, the gear meshing process, pitch circle part main periodic pressure stress and rolling ( Or sliding) Caused by shear stress effect, is the comparison of the stress concentrated area, the parts easy to produce fatigue crack source. In addition, caused by a lack of depth of carburizing layer, lead to parts surface hardness is low, under the effect of high cyclic stress, the fatigue crack along tooth width direction (after the formation of Carburizing layer) On tooth rapidly expand, and eventually form a shallow and long fatigue crack, causing the gear fracture failure. Source: the metal processing: hot working 2015, 7