Anti-deformation casting process for gray iron castings

Abstract

The anti-deformation casting technology comprises the following steps that S1, a mold is pretreated, specifically, a, a thick-wall area and a thin-wall area are recognized according to a casting three-dimensional model, and a high-heat-conduction material insert is embedded into the mold corresponding to the thick-wall area; a low-heat-conduction material insert is embedded into the mold corresponding to the thin-wall area; b, a casting mold is preheated to 180-250 DEG C, and an anti-burnt-on sand coating is evenly sprayed on the inner surface of the mold; s2, low-pressure mold filling pouring is conducted, specifically, molten metal liquid is injected into a mold in a low-pressure mold filling mode; s3, solidification and vibration aging treatment, wherein the thick-wall area of the casting is solidified to 50%-70%; and S4, demolding treatment is conducted, specifically, the casting is demolded, and the casting is transferred into an argon protection heat preservation furnace after demolding. Through the synergistic effect of differential cooling control, stepped pressurization solidification and directional vibration aging, micro plastic deformation can occur in the casting, residual stress is homogenized, the dimensional stability of the gray iron casting is further improved, and deformation of the gray iron casting is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of metal casting, in particular to an anti-deformation casting process for gray iron castings. Background Art

[0002] Gray iron castings, as important engineering materials, are widely used in the machinery manufacturing field due to their excellent casting properties, shock absorption, and wear resistance. During the casting process, due to the complex structure and large variations in wall thickness, the thick-walled areas of the gray iron castings cool slowly while the thin-walled areas cool quickly. This differential cooling rate leads to uneven shrinkage, resulting in residual stresses and, in turn, deformations such as warping and twisting.

[0003] Currently, existing technologies often mitigate this problem by adding reinforcing ribs or uniformizing wall thickness. However, these methods fail to meet the heat conduction requirements of different regions. Inefficient cooling in thick-walled areas can lead to shrinkage defects, while excessive cooling in thin-walled areas can cause stress concentration. Therefore, a new deformation-resistant casting process for gray iron castings has been developed to address these shortcomings. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a deformation-proof casting process for gray iron castings.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A deformation-proof casting process for gray iron castings comprises the following steps:

[0007] S1. Mould pretreatment:

[0008] a. Identify thick-walled and thin-walled areas based on the three-dimensional model of the casting. Inserts of high-thermal-conductivity materials are embedded in the mold corresponding to the thick-walled areas, and a high-speed cooling circuit is configured. Inserts of low-thermal-conductivity materials are embedded in the mold corresponding to the thin-walled areas, and a low-speed cooling circuit is configured.

[0009] b. Preheat the casting mold to 180-250℃ and evenly spray the anti-sand coating on the inner surface of the mold;

[0010] S2. Low-pressure filling and pouring: The molten metal liquid is poured into the mold by low-pressure filling. After the pouring is completed, the temperature of the thick-walled area and the thin-walled area is detected in real time;

[0011] S3, solidification and vibration aging treatment: the thick wall area of ​​the casting solidifies to 50% to 70%, and local pressure is applied by the air pressure device until it is completely solidified, and vibration is performed after cooling;

[0012] S4. Demolding treatment: demold the casting, transfer it to an argon-protected insulation furnace, and slowly cool it to room temperature at a rate of 50-80°C / h for a holding time of ≥2h.

[0013] Wherein, in step S1, a transition cooling zone is set at the junction of the thick-walled area and the thin-walled area, and a medium thermal conductivity material is used for transition cooling, and the medium thermal conductivity material is an aluminum alloy.

[0014] In step S1, the anti-sand coating is composed of 60% to 75% by mass of zirconium oxide, 15% to 25% by mass of silica sol, and 5% to 15% by mass of nano-silicon carbide. The coating thickness is controlled at 0.15 to 0.25 mm. After spraying, the coating is dried and cured at 300 to 350°C.

[0015] Among them, in step S2, after the low-pressure filling is completed, the shrinkage pressure is applied in stages: the first stage is maintained at a pressure of 1.0-1.5 MPa for 10-30 seconds, and the second stage is maintained at a pressure of 2.0-3.0 MPa for 20-50 seconds.

[0016] In step S2, the cooling water flow rates of the thick-walled area and the thin-walled area are adjusted so that the cooling rate of the thick-walled area is 20% to 50% faster than that of the thin-walled area, and the temperature difference between the two areas is ≤60°C.

[0017] Wherein, in step S2, the cooling rate of the thick-walled region is 5-10°C / min, and the cooling rate of the thin-walled region is 15-25°C / min.

[0018] In step S3, after the casting is completely solidified and cooled to 80 to 120° C. below the solidus, the casting is continuously vibrated for 15 to 25 minutes.

[0019] Wherein, in step S3, the vibration frequency is 20-50 Hz, and the amplitude is 0.5-2.0 mm.

[0020] Wherein, the high thermal conductivity material insert is copper alloy, and the low thermal conductivity material insert is ceramic.

[0021] The casting mold is configured with thick-walled and thin-walled areas. The thick-walled area, due to its larger volume, has a slower cooling rate, which can easily lead to local overheating and uneven solidification. By embedding high-thermal-conductivity materials (such as copper alloys), the heat dissipation efficiency of the thick-walled area can be significantly improved, accelerating the cooling process. The thin-walled area, due to its smaller volume and faster cooling rate, is prone to internal stress and cracks due to excessive cooling. By embedding low-thermal-conductivity materials (such as ceramics), the heat dissipation rate in the thin-walled area can be slowed, avoiding local overcooling. This mold design ensures uniform cooling of the casting during solidification by specifically optimizing the cooling rates of the thick and thin-walled areas, thereby reducing thermal stress and deformation in gray iron castings.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] By embedding high thermal conductivity material inserts in the thick-walled area and configuring a high-speed cooling circuit, the cooling rate of the thick-walled area is accelerated; by embedding low thermal conductivity material inserts in the thin-walled area and adopting a low-speed cooling circuit, the cooling rate of the thin-walled area is slowed down. This differentiated cooling control can effectively reduce the temperature difference between the thick-walled area and the thin-walled area, making the cooling rate more uniform, thereby reducing the uneven shrinkage caused by the difference in cooling rate; through the synergistic effect of differentiated cooling control, stepped pressurized solidification and directional vibration aging, micro-plastic deformation can occur inside the casting, homogenizing residual stress, further improving the dimensional stability of gray iron castings and reducing deformation of gray iron castings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to specific examples. It should be understood that the following examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0026] Example 1:

[0027] (1) Mold design: Based on the three-dimensional model of the casting, thick-walled and thin-walled areas are identified. Copper alloy inserts are embedded in the mold corresponding to the thick-walled area, and a high-speed cooling circuit is configured. Ceramic inserts are embedded in the mold corresponding to the thin-walled area, and a low-speed cooling circuit is configured.

[0028] (2) Mold pretreatment: preheat the mold to 200°C, spray an anti-sand coating composed of 60% zirconium oxide, 20% silica sol and 20% nano-silicon carbide, with a coating thickness of 0.2 mm, and dry and cure at 325°C;

[0029] (3) Low-pressure filling and pouring: the molten metal is injected into the mold at a filling pressure of 0.3 MPa and the filling time is 10 s;

[0030] (4) Dynamic cooling control: After pouring is completed, the temperature of the thick-walled area and the thin-walled area is detected in real time, and the cooling water flow is adjusted. The cooling rate of the thick-walled area is 8°C / min, and the cooling rate of the thin-walled area is 20°C / min;

[0031] (5) Step-by-step pressurized solidification: solidify to 60% in the thick wall area, apply a local pressure of 1.2 MPa through the air pressure device, and continue until complete solidification;

[0032] (6) Vibration aging treatment: When the casting is cooled to 100°C below the solidus, vibrate at a frequency of 30 Hz and an amplitude of 1.0 mm for 20 min;

[0033] (7) Demolding: The casting is demolded and transferred to an argon-protected insulation furnace, where it is cooled to room temperature at a rate of 60°C / h for 2 h.

[0034] Example 2:

[0035] (1) Mold design: Based on the three-dimensional model of the casting, the thick-walled area and thin-walled area are identified. Copper alloy inserts are embedded in the mold corresponding to the thick-walled area, and a high-speed cooling circuit is configured; ceramic inserts are embedded in the mold corresponding to the thin-walled area, and a low-speed cooling circuit is configured; a transition cooling zone is set at the junction of the thick-walled area and the thin-walled area, and aluminum alloy inserts are embedded in the mold corresponding to the transition cooling zone, and a transition cooling circuit is configured;

[0036] (2) Mold pretreatment: The mold was preheated to 200°C, and an anti-sand coating composed of 60% zirconium oxide, 20% silica sol, and 20% nano-silicon carbide was sprayed on the mold to a thickness of 0.2 mm. The mold was then dried and cured at 325°C (same as in Example 1);

[0037] (3) Low-pressure filling and pouring: the molten metal is injected into the mold at a filling pressure of 0.4 MPa and the filling time is 15 s;

[0038] (4) Dynamic cooling control: After pouring is completed, the temperature of the thick-walled area and the thin-walled area is detected in real time, and the cooling water flow is adjusted. The cooling rate of the thick-walled area is 10°C / min, and the cooling rate of the thin-walled area is 25°C / min;

[0039] (5) Step-by-step pressurized solidification: solidify to 65% in the thick wall area, apply a local pressure of 1.5 MPa through the air pressure device, and continue until complete solidification;

[0040] (6) Vibration aging treatment: When the casting is cooled to 100°C below the solidus, vibrate at a frequency of 30 Hz and an amplitude of 1.0 mm for 20 min (same as in Example 1);

[0041] (7) Demolding: The casting was demolded and transferred to an argon-protected heat-insulating furnace, where it was cooled to room temperature at a rate of 60°C / h for 2 h (same as in Example 1).

[0042] Example 3:

[0043] (1) Mold design: Based on the three-dimensional model of the casting, thick-walled areas and thin-walled areas are identified. Copper alloy inserts are embedded in the mold corresponding to the thick-walled areas, and independent cooling circuits are configured. Ceramic inserts are embedded in the mold corresponding to the thin-walled areas, and a low-speed cooling circuit is configured (same as in Example 1).

[0044] (2) Mold pretreatment: The mold was preheated to 200°C, and an anti-sand coating composed of 60% zirconium oxide, 20% silica sol, and 20% nano-silicon carbide was sprayed on the mold to a thickness of 0.2 mm. The mold was then dried and cured at 325°C (same as in Example 1);

[0045] (3) Low-pressure filling and pouring: the molten metal is injected into the mold at a filling pressure of 0.2 MPa and the filling time is 5 s;

[0046] (4) Dynamic cooling control: After pouring is completed, the temperature of the thick-walled area and the thin-walled area is detected in real time, and the cooling water flow is adjusted. The cooling rate of the thick-walled area is 5°C / min, and the cooling rate of the thin-walled area is 15°C / min;

[0047] (5) Step-by-step pressurized solidification: solidify to 55% in the thick wall area, apply a local pressure of 0.8 MPa through the air pressure device, and continue until complete solidification;

[0048] (6) Vibration aging treatment: When the casting is cooled to 100°C below the solidus, vibrate at a frequency of 30 Hz and an amplitude of 1.0 mm for 20 min (same as in Example 1);

[0049] (7) Demolding: The casting was demolded and transferred to an argon-protected heat-insulating furnace, where it was cooled to room temperature at a rate of 60°C / h for 2 h (same as in Example 1).

[0050] Comparative Example 1:

[0051] The casting process of this comparison is basically the same as that of Example 1, except that high thermal conductivity and low thermal conductivity material inserts are not used, the cooling circuit is unified, and the anti-sand coating is not sprayed.

[0052] Comparative Example 2:

[0053] The casting process of this comparison is basically the same as that of Example 1, except that no solidification and vibration aging treatment is performed.

[0054] Comparative Example 3:

[0055] The casting process of this comparative example does not use inserts made of high thermal conductivity and low thermal conductivity materials, does not unify the cooling circuit, and does not perform solidification and vibration aging treatment.

[0056] The present invention measured the dimensional deviation, surface roughness, surface warpage, residual stress, shrinkage rate, hardness uniformity, deformation and production efficiency of the gray iron castings obtained in Examples 1 to 3 and Comparative Examples 1 to 3. The measurement results are shown in Table 1.

[0057] Table 1 Measurement results of various indicators of gray iron castings

[0058] index Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Dimensional deviation (mm) ±0.2 ±0.15 ±0.25 ±0.8 ±0.6 ±1.0 Surface roughness (μm) 1.2 1.0 1.5 3.5 2.8 4.2 Surface warpage (%) 0.08 0.05 0.10 0.70 0.25 0.85 Residual stress (MPa) 4.2 3.5 4.3 5.7 4.5 4.9 Shrinkage rate (%) 0.5 0.3 0.7 3.2 2.5 4.5 Hardness uniformity (HV) ±5 ±4 ±6 ±15 ±12 ±20 Deformation (mm) 0.3 0.2 0.4 1.5 1.2 2.0 Production efficiency (pieces / h) 12 10 15 8 9 7

[0059] According to Table 1, the dimensional accuracy of Examples 1 to 3 of the present invention is significantly better than that of Comparative Examples 1 to 3, which indicates that the process control of Examples 1 to 3 is more stringent, reducing the processing error.

[0060] The surface roughness and surface warpage of Examples 1 to 3 of the present invention are lower than those of Comparative Examples 1 to 3, indicating that the casting processes of Examples 1 to 3 help reduce defects and stress concentration points on the surface of the gray iron castings. In addition, the gray iron castings of Examples 1 to 3 have high surface flatness, which reduces the internal stress caused by local warping, thereby reducing the risk of deformation of the gray iron castings during subsequent processing or use.

[0061] Compared with Comparative Examples 1 to 3, Examples 1 to 3 of the present invention have lower residual stresses, with Example 2 having the lowest residual stress. This may be due to the provision of a transition cooling zone at the junction of the thick-walled and thin-walled regions, and the embedding of medium-thermal-conductivity material inserts in the corresponding mold, which makes the cooling process more uniform and stable, effectively reducing the thermal stress concentration caused by excessive differences in cooling rates. The residual stresses of Examples 1 and 3 are also at relatively low levels and relatively close, indicating that embedding high-thermal-conductivity and low-thermal-conductivity material inserts in the thick-walled and thin-walled regions, respectively, during the casting process of gray iron castings has a positive effect on controlling residual stress, thereby reducing deformation of the gray iron castings caused by stress release during subsequent processing or use.

[0062] In addition, the shrinkage porosity of Examples 1 to 3 of the present invention is low, especially Example 2, which indicates that the gray iron casting has fewer internal defects, making the material more uniform and strong, thereby reducing deformation caused by local defects; in terms of hardness uniformity, Examples 1 to 3 of the present invention are better than Comparative Examples 1 to 3, indicating that the casting process of Examples 1 to 3 helps to reduce local stress concentration, thereby reducing the risk of deformation.

[0063] Compared with comparative examples 1 to 3, the deformation amounts of inventive examples 1 to 3 are smaller, indicating that the gray castings have higher stability during processing or use, thereby reducing deformation in subsequent processing.

[0064] In terms of production efficiency, the production efficiency of Examples 1 to 3 is higher than that of Comparative Examples 1 to 3, which shows that the casting processes of Examples 1 to 3 of the present invention take into account both the efficiency and quality of gray iron castings.

[0065] In summary, the casting process adopted in Examples 1 to 3 is superior to that of Comparative Examples 1 to 3 in terms of multiple indicators such as dimensional deviation, surface roughness, surface warpage, residual stress, shrinkage rate, hardness uniformity, deformation and production efficiency. In particular, the deformation and surface warpage of Examples 1 to 3 are significantly reduced, which fully demonstrates that the process adopted in Examples 1 to 3 can effectively prevent the deformation of gray iron castings, while improving the production efficiency and overall quality of gray iron castings.

[0066] It should be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a..." does not preclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of protection of the present invention.

Claims

1. A deformation-proof casting process for gray iron castings, characterized in that: The following steps are involved: S1. Mould pretreatment: a. Identify thick-walled and thin-walled areas based on the three-dimensional model of the casting. Inserts of high-thermal-conductivity materials are embedded in the mold corresponding to the thick-walled areas, and a high-speed cooling circuit is configured. Inserts of low-thermal-conductivity materials are embedded in the mold corresponding to the thin-walled areas, and a low-speed cooling circuit is configured. b. Preheat the casting mold to 180-250℃ and evenly spray the anti-sand coating on the inner surface of the mold; S2. Low-pressure filling and pouring: The molten metal liquid is poured into the mold by low-pressure filling. After the pouring is completed, the temperature of the thick-walled area and the thin-walled area is detected in real time; S3. Solidification and vibration aging treatment: When the thick wall area of ​​the casting solidifies to 50% to 70%, apply local pressure through the air pressure device until it is completely solidified, and then vibrate after cooling; S4. Demolding treatment: demold the casting, transfer it to an argon-protected insulation furnace, and slowly cool it to room temperature at a rate of 50-80°C / h for a holding time of ≥2h.

2. A deformation-proof casting process for gray castings according to claim 1, characterized in that: In step S1 , a transition cooling zone is set at the junction of the thick-walled zone and the thin-walled zone, and a medium thermal conductivity material is used for transition cooling, wherein the medium thermal conductivity material is an aluminum alloy.

3. A deformation-proof casting process for gray castings according to claim 1, characterized in that: In step S1, the anti-sand coating is composed of 60% to 75% zirconium oxide, 15% to 25% silica sol and 5% to 15% nano-silicon carbide by mass fraction, and the coating thickness is controlled at 0.15 to 0.25 mm. After spraying, it is dried and cured at 300 to 350°C.

4. The anti-deformation casting process for gray iron castings according to claim 1, characterized in that: In step S2, after low-pressure filling is completed, the shrinkage pressure is applied in stages: in the first stage, the pressure is maintained at 1.0-1.5 MPa for 10-30 seconds, and in the second stage, the pressure is maintained at 2.0-3.0 MPa for 20-50 seconds.

5. The deformation-proof casting process of a gray iron casting according to claim 1, characterized in that: In step S2, the cooling water flow rates of the thick-walled area and the thin-walled area are adjusted so that the cooling rate of the thick-walled area is 20% to 50% faster than that of the thin-walled area, and the temperature difference between the two areas is ≤60°C.

6. A deformation-proof casting process for gray iron castings according to claim 5, characterized in that: The cooling rate of the thick-walled area is 5-10°C / min, and the cooling rate of the thin-walled area is 15-25°C / min.

7. A deformation-proof casting process for gray iron castings according to claim 1, characterized in that: In step S3, after the casting is completely solidified and cooled to 80 to 120°C below the solidus, the casting is continuously vibrated for 15 to 25 minutes.

8. A deformation-proof casting process for gray iron castings according to claim 7, characterized in that: The vibration frequency is 20~50Hz, and the amplitude is 0.5~2.0mm.

9. The deformation-proof casting process of a gray iron casting according to claim 1, characterized in that: The high thermal conductivity material insert is copper alloy, and the low thermal conductivity material insert is ceramic.

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