The large gear of converter secondary reducer is the tilting of converter and the main bearing component in the process of tapping and feeding. Under the action of low speed, heavy load and impact load, pitting corrosion, wear and tooth breakage will occur on the gear surface. The most vulnerable part of the gear is the tooth part. Therefore, strengthening the strength of the tooth shape is the key point of gear blank transformation.
Fig. 1, Fig. 2 and Fig. 3 show the improved design of the suspension gear structure of the converter secondary reducer, that is, the gear is manufactured into two parts: the hub and the ring gear. The ring gear is formed by forging process. The ultrasonic flaw detection JB / t5000.15-1998 stipulates that the class II inspection is qualified. The hub part still adopts the casting process, because the hub part is not easy to fail, Therefore, the flaw detection requirements can be reduced to class III standard specified in JB / t5000.14-1998, so that the composite gear blank can not only meet the quality requirements, but also reduce the manufacturing cost.
(1) Material requirements: since the gear blank is changed into a split structure, it must be welded as a whole before gear hobbing, so the materials with good welding performance and mechanical properties meeting the gear use requirements should be selected. Considering these factors and combined with the original drawing design materials, it is recommended to select ZG35CrMo for the hub and forged 35CrMo for the ring gear.
(2) The hub is manufactured according to the casting process. The transition fillet R (17 ~ 25) mm is cast, and the draft angle is 1 ∶ 20. The casting is annealed and converted to machining. Roughen all parts of the hub, leave an allowance of about 5mm on one side, and then carry out quenching and tempering treatment. The quenching and tempering hardness shall be controlled at 250 ~ 280hbw. After quenching and tempering, it shall be machined after passing the flaw detection. After machining the parts combined with the gear ring and the welding groove, wait for the combination with the gear ring, and the welding groove shall be processed into a U-shaped groove with a size of 30mm × 8°。
(3) For the manufacturing of gear ring, the gear ring shall be forged and rolled. High quality and qualified steel ingot shall be selected for forging, and the forging ratio shall not be less than 3. Heat treatment shall be carried out after forging to reduce forging stress. Rough turning of gear blank, quenching and tempering of 250 ~ 280hbw, turning of the joint surface and groove with the hub, ultrasonic flaw detection as required, and transfer to the next process after passing the inspection.
(4) The ring gear is combined with the wheel hub. The wheel hub and ring gear after passing the inspection shall be assembled by the fitter, and the positioning pins shall be made in combination with the face position, with 8 pieces on both sides. The pins shall be positioned according to the marking. In order to ensure the strength of the tooth, the subsequent gear hobbing pins shall not be at the tooth root. After assembly, turn to the welding process, preheat before welding, and use flame heating (pay attention not to high energy efficiency flame centralized heating, so as to avoid the change of structure and composition caused by local overheating of materials and local stress concentration). The preheating temperature is 250 ~ 300 ℃, arc O2 mixed gas shielded welding is used, the welding wire is H08Mn2SiA, the welding current is 200A, and the welding voltage is 27 ~ 30V, Because the welding position is all position welding, in order to prevent deformation, it is necessary to weld repeatedly on both sides in turn. Two or more welders can be arranged to weld at the same time. After welding, it shall be wrapped and covered with asbestos cloth and cooled slowly. After cooling, the weld shall be cleaned and transferred to annealing process.
(5) Annealing. Since both the parent ring gear and the hub are subject to overheating treatment, the heat treatment here is only to remove the welding stress. The annealing temperature is set lower than the tempering temperature of the outer gear ring, which can be controlled at (520 ± 20) ℃. The holding time is 3H. After cooling to 350 ℃, it is discharged for air cooling.
(6) Machining: the gear blank compounded after welding is transferred to the machining process. According to the ordinary machining process, it is divided into semi-finished turning, finished turning of outer circle inner hole, gear making and keyway to complete the gear processing and manufacturing tasks.
Adopting the structure form and manufacturing process method of casting forging composite gear can make the large gear blank pass the inspection at one time, which can not only ensure the gear quality, but also reduce the production cost. It is a more reasonable structure form of gear blank.