How are large screw forgings forged?

2024-08-14 15:46:48

1. Process route

Electric furnace smelting (EF)+refining (LFV1)+VD - steel ingot red forging, isothermal annealing, rough machining, outer circle and inner hole ultrasonic testing, thread processing, normalizing+quenching and tempering treatment, mechanical property testing, ultrasonic testing.

2. Development process

2.1 Smelting

Reasonably mix the chemical composition, prepare high-quality low copper scrap steel, material heads, and pig iron, and strictly prohibit the use of soil iron. Maintain good furnace condition during electric furnace smelting. When the electric furnace is used for steelmaking, it is necessary to prevent the entry of oxidized slag into the refining package and remove oxygen after the furnace. The refining ladle should be in good condition, baked and dried, with sufficient argon stirring pressure, and the high-temperature smelting time should not be too long. After all components are specified, they should be subjected to low vacuum treatment at the vacuum station. Before placing the vacuum cover on the ingot mold system, draw air and absorb dust again to ensure that the ingot mold system is clean and dry. Adjust the pouring speed according to the steel mixing situation during pouring to prevent emptying and flow interruption. During pouring, the argon pressure should be sufficient to ensure good dispersion, and attention should be paid to observation and control of pouring height

2.2 Forging

Using two upsetting and two pulling methods, the forging is compacted and pressed through, and then stretched using the WHF method. Use pliers to forge two smaller diameter sections of the material, first forming the large end, and then turning around to form the small end. Strictly control the initial and final forging temperatures to effectively prevent the occurrence of surface cracks in forgings. Strictly control the dimensions of the forging process to ensure sufficient waste at the bottom and riser ends.

2.3 Heat treatment

Reasonably develop heat treatment processes, blunt all edges and corners of forgings after rough machining, and perform quenching and tempering treatment. After the mechanical properties are qualified, take a radial test rod for hardness gradient testing to ensure that the tooth surface hardness is qualified after precision machining.

3. Quality control in the production process

(1) When punching the core, all the surface sand is made of chromite resin sand, with a thickness of 40mm to 50mm. The grass rope placed between the thin teeth should not directly contact the polystyrene board, and a 16mm diameter round steel should be used to compact it. The force should not be too strong to prevent deformation of the polystyrene board. (2) Polish or shot peen the contact surface between the external cold iron and the live parts, remove oil and rust, and keep the surface clean. (3) The foam model in the mold cavity should be removed as far as possible, otherwise, not only the paint inside the mold cavity cannot be painted evenly, but also the metal liquid boiling phenomenon may occur in the mold cavity during pouring. The mold in the mold is affected by the high temperature molten metal. The foam first softens and melts, and then burns and vaporizes. The foam is prone to produce a large amount of gas to form pores. If the pouring speed inside the mold is slow or the permeability is good, and the gas pressure is low, it is conducive to the penetration or escape of decomposition products into the mold. But if the pouring speed is too fast and there is no time to exhaust the gas outside the mold cavity, it will be sucked into the steel water. Excessive gas pressure may cause boiling of the molten metal and result in the entrapment of partially vaporized residues into the molten metal or pressure onto the surface of the forging, causing defects. (4) Before painting, use a compressed air tube to remove surface debris. Brush the surface of the cavity with zircon powder coating 3-4 times to ensure even coating application. To ensure the surface of the mold cavity is dry and reduce surface moisture, hot air is blown into the mold cavity for 3-4 hours before pouring, with a heating temperature between 110-130 ℃.

(5) The pouring system and cavity must be kept clean, and a vacuum pump should be used to thoroughly sand the cavity and nozzle before pouring. (6) The molten steel requires refining (LH) to ensure uniform composition and stable temperature. The internal control of phosphorus and sulfur content should not exceed 0.015%. The metallurgical quality and residual element content should be strictly controlled, and the pouring temperature should be controlled between 1560 and 1570 ℃. After pouring, sprinkle insulation agent into the riser with a thickness greater than 200mm. (7) Remove the tension bars between the thin teeth after performance heat treatment. Stretching the thin teeth together to prevent deformation when subjected to overall force during contraction.

4. Conclusion

The forgings produced using optimized processes have solved various defect problems that occurred in the previous production process, reduced the cost of model production, and the surface quality and size of the castings meet the design requirements.