As one of the most basic transmission parts in the mechanical industry, gear is used to adjust the speed and transmit power in mechanical equipment. It plays a key role in automobile, machine tool and crane. In the process of gear operation, contact transmission force will be formed on the tooth surface, the tooth surface will be subjected to huge alternating bending stress and contact stress, and the meshing tooth surfaces will be subjected to friction stress at the same time. In the case of uneven meshing, even impact force will be generated. Under the action of these forces, the gear will have tooth surface wear and tooth breakage.
Based on the stress and damage form of gears, the quality requirements of gear blanks are generally high in mechanical design. At present, the commonly used gear blank manufacturing processes generally include forging and. For small gear blank, forging process is often used because forging is easy to ensure quality, while for large gear with diameter more than 2m, due to the limitation of processing range of forging equipment and blank cost, Forging process is often not adopted, but casting process with relatively low cost is adopted. For cast gears, the advantages are that the shape and structure of the gear can be easily obtained, the machining allowance is small, and the blank manufacturing cost is low. The main factor restricting the casting is that the quality of steel casting gear is difficult to be guaranteed, and the yield is about 60%. Due to its special shape, the gear rim milling depth generally reaches half of the flange thickness. After machining, casting defects are easy to appear at the tooth root, that is, the center of the flange, which seriously affects the service life of the gear.
ZHY gear undertakes the manufacturing task of 120t converter tilt reducer in a steel plant. The diameter of the large gear of its converter tilt secondary reducer is more than 3m. It is a large gear. It was originally designed to cast blank, and the material is zg40mn2. The flaw detection standard is required to meet the ultrasonic flaw detection test results specified in JB / t5000.14-1998 nondestructive testing of steel castings. It is qualified. The qualified rate of castings meeting such requirements is very low, and few domestic foundry manufacturers can undertake it. Based on this, after negotiation with the manufacturer, the casting blank is changed into casting forging composite structure without changing the gear quality.