Vacuum heat treatment process of aircraft horizontal axis

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The horizontal axis is the abbreviation of the rotation axis of the horizontal stabilizer of the aircraft, and it is the key force component of the rear fuselage connecting the horizontal stabilizer. Since the installation point at one end of the shaft is close to the engine and has a certain temperature and gas effect, it is required that the material for making the horizontal large shaft should not only have high strength and rigidity, but also have good comprehensive mechanical properties such as stress corrosion resistance. . The large horizontal shaft has a complex structure, which is not only a thick-walled tube with one end closed, but also a cantilever beam with a circular section and inserted on the rear fuselage. The original design uses GC-4 medium-carbon low-alloy ultra-high-strength steel. Due to the high tendency of welding cracks in this material, it is necessary to use the whole bar to process not only the material utilization rate is low, but also the problem of poor processing technology of deep blind holes. very prominent. If the horizontal large shaft can be made of a welded structure, that is, one end is made of pipe material and the other end is made of bar material for rough machining, and then assembled and welded to form, which is not only economical and convenient, but also solves the design and manufacture of complex aviation stress components. problem. The rotating shaft of the horizontal stabilizer of the aircraft is designed according to the same strength, and the weight of a single piece can be reduced by more than 4kg. Therefore, this new process is of great significance for improving the performance of the energy-to-aircraft.

16Co14Ni10Cr2Mo steel is a new type of high-alloy ultra-high-strength aerospace structural steel successfully developed in recent years. This material has good weldability. After heat treatment, the fracture toughness is about one to several times that of general low-alloy ultra-high-strength steels at the same strength level. Due to these advantages, this material can be used for damage tolerance design and to manufacture high-performance, high-reliability long-life aircraft components, especially those with various stresses such as side holes, corners, grooves, and sudden changes in section. Or complex load-bearing parts in the strain concentration area, such as landing gear, horizontal beams, landing hooks, important joints, load-bearing frames and other key load-bearing components.

The main process flow of horizontal large shaft machining includes: blanking→rough turning→semi-finishing turning→finishing welding groove→boring inner hole→welding→welding flaw detection→annealing→turning outer circle and thread→milling fork opening→manufacturing combination Hole→vacuum heat treatment→finishing outer circle→grinding outer circle→reaming→acid etching inspection→surface strengthening and protection→general inspection.

A batch of 12 large horizontal shafts are all welded structures. The annealing process to eliminate the welding stress after welding of the large shaft is: electric furnace heating, the temperature is 680 ~ 700 ℃, the heat preservation is 6 ~ 8h, and the air cooling is performed.

The inner hole and other parts of the large shaft have been processed to the drawing size, and only the outer circle and matching size have a certain amount of grinding.

Because 16Co14Ni10Cr2Mo steel adopts double vacuum smelting process, its purity is high. The content of permanent elements (Si, Mn) and impurities (P, S, 0, N, H) in steel are very low; and there are strict controls. In order to give full play to the performance of the material, the pollution of harmful gases to the material should be minimized during processing (especially hot processing), so vacuum quenching is used.

The vacuum quenching of the large shaft is carried out in a large multifunctional vertical vacuum quenching furnace. Its process parameters are shown in the figure:

The cleaning and degreasing of the large shaft before and after vacuum quenching is carried out in a special cleaning tank with LCX-52 water-based cleaning agent with a concentration of 2% to 5%. furnace. In order to reduce the quenching deformation of the large shaft, a special quenching fixture is designed and manufactured to keep the large shaft vertically suspended on the vacuum furnace automatic hanger in a free state. Each furnace contains 3 pieces, weighing about 120kg.

When the vacuum working pressure of the heating chamber of the vacuum furnace is less than or equal to 6.7Pa, the large shaft is installed. On the premise of maintaining the working vacuum degree of 6.7~1.3×10-1Pa, preheating, heating and heat preservation are carried out according to the requirements of the process curve. The holding time is 150min (calculated according to the heating lag time + the “minimum holding time” specified by the size of the workpiece section). Before the end of the heat preservation of the large shaft, the oil tank should be evacuated to below 6.7Pa about 20min in advance, and heated and stirred to fully degas. Before the large shaft is quenched, the stirring should be stopped to reduce the pollution of oil vapor. After the large shaft is quenched into the oil: fill with general nitrogen; control the pressure within the range of 4×104～8×104Pa. After the large shaft is completely cold, put it into the atmosphere and take it out to clean the oil.

According to the specification, the large shaft should be ice-cold within 1h after quenching. The equipment is a self-made cold treatment tank with a working size of Ø350mm×1200mm, and the medium is solid CO2 soaked alcohol. When the large shaft self-cooling treatment temperature returns to room temperature, it should be installed in the furnace for tempering within 4 hours, and the tempering should be carried out in an air circulating electric furnace, and then blow it with a blower for cooling (hanging).

The new type of ultra-high-strength steel and the welded structure are used for the horizontal axis of the aircraft, which not only improves the machining conditions, ensures the uniform wall thickness of the axis, and improves the structural efficiency, but also reduces the weight of a single piece by more than 4kg. Improve flight performance.

16Co14Ni10Cr2Mo steel horizontal large shaft through vacuum heat treatment, its mechanical properties have fully reached the technical indicators, the surface is bright, basically no deformation. Compared with the original process of using GC-4 steel to heat in a methanol cracking atmosphere furnace and isothermal quenching in a nitrate bath, the hydrogen removal process of long-term low-temperature tempering (190℃±5℃×16h) can be omitted, and part of grinding can be saved. , correction, sand blowing, grinding man-hours, the technical and economic benefits are very significant.

Equipment selection: The VOGQ series vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment process of tooling and molds. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.