Where X represents the lateral direction of the compressor casing and Y represents the longitudinal direction of the compressor casing. The forming of the outer casing needs to be completed after more than ten steps, such as coiling, welding, punching, flanging, painting, etc. Therefore, the quality of the outer casing product is required to be reflected in the appearance of the air-conditioning compressor. High precision requirements, high surface quality requirements, close to the surface quality of cold-rolled sheets, and air-conditioning compressors are fully enclosed compressors with high working pressure, so the housing is also required to have high withstand voltage At present, the air-conditioner compressor for the new refrigerant R410A requires a pressure resistance of about 20 MPa. However, in the actual manufacturing process of the air-conditioning compressor casing, when the hot-rolled pickling plate is stamped, uneven cracking sometimes occurs after stamping and stamping. , affect the normal use of the manufacturer. Therefore, when selecting a suitable air-conditioning compressor casing for hot-rolled pickling, it is necessary to evaluate and investigate its various properties.
1 hot rolled pickling board performance
The forming properties of the steel sheet are mainly affected by the chemical composition and metallographic structure. In order to improve the forming properties of the steel sheet, it is necessary to obtain ultra-low carbon (C), phosphorus (P), and sulfur (S) molten steel, and then add an appropriate amount of alloying element titanium (Ti) or niobium (Nb) to carry out strict and Difficult smelting, rolling and other process control, so that C, nitrogen (N) and other non-metallic elements and metal elements are fully combined and precipitated to fix residual C and N in the steel, making the steel a gap-free atomic state and a large number of favorable Textured crystal structure, which has excellent deep drawability, high plastic strain ratio, high elongation, high hardening index, and low yield ratio.
1.1 chemical composition
Chemical composition is one of the important indicators for the purchase of shell materials by air-conditioner compressor manufacturers. The chemical composition of hot-rolled pickling plates is closely related to their forming properties, so the units must pay close attention.
1.2 Metallographic organization
The microstructure characteristics of the hot-rolled pickled deep-drawn steel sheet are ferrite equiaxed grains and a very small amount of cementite. This pure ferrite structure and its grain size determine the elongation and yield strength of the steel. Larger grain sizes correspond to smaller yield strengths and corresponding formability is better.
The low amount of cementite is also one of the main reasons for the high elongation of hot-rolled pickled deep-drawn steel sheets. As a brittle phase, cementite is not conducive to the increase of elongation, especially in the form of a network on the grain boundary, dividing the matrix, destroying the continuity of the structure, weakening the bonding force of the grain boundary, and reducing the elongation and formability of the steel. Due to the low C content in the hot-rolled pickled steel sheet and the partial fixation of Ti, the amount of cementite formed is extremely limited and is not obvious in the metallographic structure. This can be seen in the metallographic structure of the surface of the SPHE sample in Figure 2. Out.
In addition, Ti mentioned above, on the one hand, fixed C, N interstitial atoms, can reduce the solid solution strengthening effect of interstitial atoms, and is beneficial to increase the elongation and deep drawability of the steel sheet; on the other hand, the second phase of carbonitride is formed. Particles play an important role in controlling grain size, changing at various stages of steel sheet heating, rolling and coiling, and preventing grain growth, thereby lowering the elongation of the steel sheet and increasing the yield strength, which is detrimental to the forming properties. The second phase particles have a dual effect on the elongation, yield strength and formability of the hot-rolled pickled deep-drawn steel sheet. Therefore, the number of second phase particles should be moderate, and the amount of Ti added in the steel should be appropriate. The second phase particles can be Observation by backscattering scanning under a scanning electron microscope, and confirmation of specific components by an energy spectrometer.
In summary, hot-rolled pickled deep-drawn steel sheets require a low C content in the chemical composition and Ti microalloying, as well as a very small amount of cementite structure. The surface of the SPHE sample and the metallographic structure of the transverse and longitudinal sections. The metallographic examination showed that the grain size was about 8 grades, the inclusions were between 0.5 and 1.5 grades, and the free cementite grade was also normal.
With reference to the relevant standards, for hot-rolled pickled steel sheets, the grain size requirement is not less than 6 grades, and the inclusions of all the samples are in the range of 0.5-1.5, allowing the presence of free cementite structure. According to the GB/T13299 first rating chart rating, the deepest level of the level range is 0, 1, 2, 3, in a point-like, short-chain distribution.
1.3 mechanical properties
The materials used for stamping should not only meet the requirements of product design, but also meet the processing requirements of stamping process and stamping (such as cutting, welding, painting, etc.). The various stamping processes involved in the production process of the air-conditioner compressor casing have different requirements for the deformation of the hot-rolled pickled steel sheet, such as punching, bending, drawing, and extrusion, and the specific requirements for the performance of the sheet are also different. . The stamping properties of hot-rolled pickled steel sheets are mainly characterized by their mechanical properties. However, the current mechanical properties mainly have the following problems: usually only yield strength, tensile strength, elongation at break, etc. are specified, but other indicators are not specified. , such as yield ratio, elastic modulus, hardening index n, plastic strain ratio (plate thickness directivity coefficient) r, plate plane directionality r; test of sample properties without considering material anisotropy, should be from the same part 0#, 45#, 90# direction test to understand the difference in material performance.
In practical applications, such as the deep drawing process, the sheet is subjected to deformation mainly by compression, and the yield strength of the sheet is small, the tangential force of the deformation zone is small, the wrinkle tendency of the sheet is small, and the limit is increased. The degree of deformation is favorable. When stamping, the higher the tensile strength of the sheet, the higher the stress that the sheet can withstand, and the less likely it is to break, that is, the formability is good. Therefore, for hot-rolled sheet, in addition to requiring sufficient strength, it is mainly desirable to be easy to form and not easy to fail, that is, a low yield ratio.
The large value of n can not only improve the local strain capacity of the steel sheet, that is, increase the ultimate strain of the instability, but also tend to homogenize the strain distribution and improve the overall forming limit of sheet metal forming. The larger the r value is, the steel plate is easily deformed in the direction along the plane of the plate, and is not easily deformed in the thickness direction, and the stamping cracking phenomenon is not easily generated. The larger the value of |r|, the more serious the anisotropy in the plane of the plate. As a result, the edges of the stampings are not aligned, forming lugs, which affects the quality of the stampings and reduces the utilization of the sheets. The smaller the |r| value, the better the forming properties of the deep-drawn steel sheet. Therefore, the coil used for stamping has a low yield ratio, a high n value, an r value, and a low |r| value.
In addition, while confirming the material performance parameters, it is also considered its process performance, usually there are 2 tests:
(1) Cold bending test. The GB/T710 standard stipulates that steel plates and wide steel strips rolled with 08~35 steel shall be subjected to 180# transverse cold bending test under the delivery condition. The diameter of the bending core shall comply with the provisions of Table 2, and there shall be no cracks at the bends, cracks and Layering
(2) Cupping test. Rolling steel plates and steel strips with a thickness of not more than 2 mm are tested in the cupping test under delivery conditions.
Although GB/T710 does not mention SPHE hot-rolled pickled steel sheets, this standard is mainly for high-quality carbon structural steel hot-rolled steel sheets and strips. Therefore, the author believes that this standard is also applicable to SPHE materials that are currently used in large quantities. At the same time, the mechanical properties of the material can be of great help to the choice of processing equipment capabilities.
1.4 Texture
The texture is an orientation distribution structure in which the polycrystal orientation distribution state deviates significantly from the random distribution, which causes anisotropy of the mechanical properties of the steel sheet, thereby affecting the formability of the steel sheet. The hot-rolled steel sheet will have a strong texture under certain process conditions, which not only affects the texture formation of the subsequent cold-rolled steel sheet, but also directly affects the performance of the hot-rolled steel sheet.
After rolling, the original grain structure of the hot-rolled pickled steel sheet is elongated or flat. Through heat treatment, under the action of temperature, the inside of the deformed grains changes, and new fine grains are generated and continuously grown to form new equiaxed crystals, as shown by the lateral and longitudinal structures in FIG. The surface grains are coarser than the inner crystal grains, mainly due to the uneven distribution of the temperature field on the surface and the inside, the surface temperature is high, and the recrystallized grain growth rate is fast, as shown in Fig. 2. In fact, due to the existence of the temperature field, the growth rates of the lateral and longitudinal tissues are also different, resulting in microscopic differences in the size of their grains in different directions. In addition, as a polycrystalline material, the condition of one-way stress In the following, due to the difference in the orientation of the grains, the slip has a sequence and the deformation has a size, which causes the macroscopic material to exhibit a certain deformation texture, that is, at least one crystal orientation between the crystal grains is parallel or close to each other during deformation. Parallel, there is a preferred orientation, that is, there are differences in mechanical properties in different directions, resulting in a certain anisotropy.
1.5 Stress Analysis
After the hot-rolled pickled steel sheet is processed, it is made into the outer casing of the compressor. Since this process is always subjected to external force and different parts are subjected to different stamping processes, residual stress distribution exists in different parts of the shell after forming. The existence of residual stress has an impact on the subsequent use of the air conditioner compressor. This is because the air conditioner compressor is a totally enclosed refrigeration compressor. When the air conditioner compressor is working, its housing is at a certain high pressure state, and different. The pressure on the part is also different, and sometimes the leak of the refrigerator occurs in a weak part of the casing.
The stress analysis work can be carried out as follows: on the basis of obtaining the performance parameters of the hot-rolled pickled steel, the simulation simulation CAE analysis is performed to obtain the residual stress distribution and strain distribution of the air-conditioning compressor casing; the above data is analyzed and the compressor is analyzed. Sampling on the outer casing for the determination of residual stress. The stress distribution under the fixed working pressure condition of the shell of a certain type of air conditioner compressor, the stress concentration in the area between the two air inlets, especially at the flange of the casing, the highest stress. The air inlet is contracted in the vertical rolling direction and stretched in the rolling direction, as shown in Fig. 5, but the most severely deformed area during operation of the compressor is the bottom of the outer casing.
Combined with the results of long-term test statistics, the regional stress between the two inlets is the most concentrated, and the probability of failure under the condition of high force is high. Therefore, the macro stress test is carried out, and A is the shell material forming. The front surface stress state, B is the normal stress distribution between the two air inlets of the air conditioner compressor, and C is the stress state of the sample broken between the two air inlets of the partial compressor. The positive value represents the tensile stress and the negative value represents the compressive stress.
The hot-rolled pickling plate material usually exhibits tensile stress in the X direction and compressive stress in the Y direction. After the air conditioner compressor casing is fabricated, the stress in the X direction is slightly lowered due to processing, and the main change is in the Y direction. The compressive stress is significantly reduced. From the force analysis point of view, in the Y direction, the shell material is mainly subjected to tensile stress, so if there is a certain compressive stress, it is helpful to improve the pressure resistance of the shell. From the stress test results of some failed air conditioner compressor casings, that is, the area C in Fig. 6, it can be seen that the stress of these f samples in the XY direction has become a tensile stress.
1.6 damping analysis
Air-conditioning compressors are the main source of air-conditioning mechanical noise. The vibration (noise) of an object is mainly affected by the following factors: stiffness related to potential energy (small structure stiffness of the housing), kinetic energy-related quality (mass-increasing equipment is bulky), and Damping associated with energy consumption (increasing the internal friction of the material). Therefore, when the structure cannot be changed, that is, when the component design has been determined, and in the case of broadband random excitation, pulse excitation, etc., only the component or system damping method can be used to test the stress between the air inlets of the air conditioner compressor casing. Control vibration or noise. However, the trend of modern industry is to use the components of the overall processing technology as much as possible, select high-strength materials and achieve high-speed operation, and air-conditioning compressors are no exception. The result is bound to reduce the coupling damping of the system and the internal resistance of the components. To this end, it is necessary to develop a new type of housing material that has both high strength and high internal resistance, which helps to resolve the above contradiction. That is, under the premise of a given vibration structural factor, the internal resistance of the constituent materials is increased, so as to increase the energy consumption of the solid structure transmission path and change the vibration response characteristics of the acoustic radiation surface by increasing the internal damping of the vibration source system. Ways to achieve vibration or noise reduction purposes.
At present, the sound source, sound pressure level measurement and modal analysis are mainly used to identify the vibration of the air conditioner compressor, the main source of noise identification and comparative analysis, but the material damping performance index applied here has not been proposed so far.
By taking into account factors such as materials, test methods, test instruments, samples and test parameters, and by making standard samples and conducting extensive comparative tests, a uniform standard for testing the damping properties of metal materials will be developed to contribute to the air-conditioning compressor housing materials. Choice and application.
2 Conclusion
In summary, the application of hot-rolled pickling deep-drawn steel sheets on air-conditioning compressors can be guaranteed by the following requirements:
(1) The chemical composition of ultra-low C and Ti microalloying is beneficial to the ferrite matrix and the formation of metallurgical structure with a small amount of cementite;
(2) It is ensured that good mechanical properties are obtained by chemical composition and metallographic structure, which is favorable for cold formability of hot-rolled pickled steel sheets;
(3) obtaining the ideal microscopic texture of the coil by controlling the rolling and heat treatment processes, and improving the cold formability of the hot-rolled pickled steel sheet;
(4) By analyzing the residual stress and strain distribution, it is beneficial to the design and optimization of the air conditioner compressor housing structure;
(5) Through the discussion of the damping properties of the shell material, it is helpful to select the material of the air conditioner compressor housing and optimize the shell structure to reduce the noise of the compressor.
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