Preparation method of graphite-metal composite chilling block

Abstract

The invention provides a preparation method of a graphite-metal composite chilling block, the novel graphite-metal composite chilling block is composed of a metal matrix and an embedded porous graphite skeleton, and the graphite skeleton is completely wrapped by the metal matrix. The preparation method comprises the following steps: firstly, preparing mixed powder, rapidly preparing a porous graphite skeleton prototype model by utilizing a selective laser sintering molding technology, and then carrying out densification, carbonization and graphitization treatment on the porous graphite skeleton prototype model to obtain a high-thermal-conductivity and high-strength porous graphite skeleton preform; and finally, compounding the porous graphite skeleton prefabricated body with cast iron or cast steel in a sand mold casting manner. The preparation method of the novel graphite / metal composite chilling block has the advantages of being rapid, environmentally friendly, efficient, low in cost and the like, the good chilling effect is achieved, the heat storage capacity and the mechanical property are good, the space structure, the solid feature size and the volume fraction of the porous graphite framework can be changed, the comprehensive performance of the composite chilling block can be regulated and controlled, and the application prospect is wide. And wide application prospects are achieved in the casting field.

Description

Technical Field

[0001] The invention relates to the technical field of composite material forming, and in particular to a method for preparing a graphite-metal composite chiller. Background Art

[0002] In the foundry industry, chillers are a type of chiller placed inside or on the surface of a mold to accelerate local cooling of castings, adjust the solidification temperature field of castings, and prevent defects such as loose castings, shrinkage cavities, and abnormal metallographic structures. At present, chillers can be divided into two categories according to their materials: graphite chillers and cast iron chillers.

[0003] Graphite chillers are mostly made of high-strength, high-density and high-thermal conductivity artificial graphite blanks as raw materials through mechanical cutting. The obtained graphite chiller has a smooth surface, which is conducive to the uniform heat extraction of the casting. The graphite chiller has large thermal conductivity and specific heat capacity, and strong heat storage and chilling capabilities, but poor mechanical properties (weak tensile and compressive resistance), high crack sensitivity, and is very easy to break during use. In addition, artificial graphite blanks have high costs, long production cycles, low mechanical cutting efficiency, serious dust pollution, and require special recovery equipment. When the casting structure is irregular, the matching conformal graphite chiller is difficult to process and the cost is higher.

[0004] Ordinary chillers are usually made of grey cast iron and are obtained by sand casting. The advantages of cast iron chillers are good mechanical properties and easy processing into complex shapes, but the thermal conductivity of cast iron chillers is only 48Wm• -1 k -1 The specific heat capacity is low and the chilling effect is not significant. After repeated use, the surface of the cast iron chiller is oxidized and pinhole defects appear, and the chilling ability is greatly reduced. In addition, the thermal expansion coefficient of the cast iron chiller is large, which affects the accuracy of the casting and the size of the casting is too large.

[0005] The chiller material should have good thermal conductivity, high melting point and large heat capacity. The large heat capacity is related to the density and specific heat capacity of the material, while the chilling ability is mainly related to the heat transfer rate. Metal chillers have large heat capacity and good casting performance, while graphite has strong chilling ability, good thermal stability and small thermal expansion coefficient. If the two are combined in an appropriate manner, it is possible to obtain a composite chiller with excellent comprehensive performance. The invention patent (CN209918861U) provides a composite process method for graphite blocks and metal chillers (including cast iron, cast steel, and cast aluminum). The basic process is as follows: high-density and high-strength graphite blocks or recycled waste graphite electrodes are used as raw materials, mechanically cut into the desired shape, and used as the core. Sand casting is used to compound it with high-temperature molten metal to obtain a graphite / metal composite chiller in which the graphite core is completely wrapped by the molten metal (see Figure 3 ). This composite chiller has a simple structure and good integrity. It has the high strength of metal chiller and the low density and high thermal conductivity of graphite chiller. Summary of the Invention

[0006] The object of the present invention is to provide a preparation method of a graphite-metal composite chill, overcoming the deficiencies of graphite chills and cast iron chills, and obtaining a new type of composite chill with strong heat storage capacity, good chilling effect, excellent mechanical properties, and small thermal expansion coefficient. Its comprehensive performance can be adjusted according to actual production, providing process technical support for obtaining high-quality castings. At the same time, this production method is fast, efficient, and low-cost.

[0007] To achieve the above technical features, the object of the present invention is realized as follows: A preparation method of a graphite-metal composite chill includes the following steps: Step 1: Mix natural flake graphite powder, thermosetting phenolic resin powder, and high-purity titanium powder in a certain proportion to form a graphite / phenolic resin mixed powder. Step 2: Use selective laser sintering forming technology to quickly print a porous graphite skeleton prototype, complete secondary curing, and obtain a porous graphite skeleton green body. Step 3: Carbonize the porous graphite skeleton green body under the protection of high-purity nitrogen or argon. Step 4: Vacuum pressure impregnate the phenolic resin solution into the porous graphite skeleton green body after carbonization treatment. Step 5: Repeat the processes of Step 2 and Step 3 for 2 - 4 times to obtain a high-density porous graphite skeleton preform. Step 6: Perform high-temperature graphitization treatment on the high-density porous graphite skeleton preform obtained in Step 5 to obtain a high-thermal conductivity and high-strength porous graphite skeleton preform. Step 7: Preheat the porous graphite skeleton preform obtained in Step 6 to 200 - 300 °C, then place it in a sand mold and pour high-temperature molten metal to obtain a new type of graphite / metal composite chill.

[0008] Preferably, the composition of the graphite / phenolic resin mixed powder in Step 1 is as follows: The mass fraction of natural flake graphite powder is 50 - 68%, 100 - 500 mesh, and the carbon content is not less than 99%. The mass fraction of thermosetting phenolic resin powder is 25 - 43%, 200 - 900 mesh. The mass fraction of high-purity titanium powder is 5 - 7%, 150 - 300 mesh, and the titanium content is not less than 99.5%.

[0009] Preferably, in the preparation process of the graphite / phenolic resin mixed powder in Step 1, the natural flake graphite powder, thermosetting phenolic resin powder, and high-purity titanium powder are added to a dry ball mill and mixed for 4 - 6 hours to obtain the graphite / phenolic resin mixed powder.

[0010] Preferably, the process parameter combination for selective laser sintering in step 2 is as follows: layer thickness 0.1 - 0.3 mm, scanning pitch 0.1 - 0.2 mm, scanning speed 500 - 1000 mm / s, and laser power 5 - 10 w.

[0011] Preferably, the process parameters for the secondary curing in step 2 are as follows: the first stage is at 80°C - 90°C with a holding time of 10 - 15 min; the second stage is at 120°C - 130°C with a holding time of 20 - 30 min; the third stage is at 160°C - 180°C with a holding time of 10 - 15 min.

[0012] Preferably, the green body of the porous graphite skeleton in step 2 includes a porous woodpile structure, a porous honeycomb-like structure, or a porous diamond-like structure, the maximum physical feature size does not exceed 5 mm, and the volume ratio of the porous graphite skeleton in the composite chill is not less than 60%; The metal matrix is cast iron or cast steel.

[0013] Preferably, the carbonization treatment process in step 3 is as follows: first evacuate to below 100 Pa, heat from room temperature to 300°C at a rate of 120°C / h - 360°C / h, and introduce argon or nitrogen with a purity of 99%; then heat to 600°C at a rate of 30°C / h - 240°C / h; finally heat to 800°C at a rate of 120°C / h - 360°C / h, hold for 0.5 - 2 h, and cool to room temperature in the furnace.

[0014] Preferably, the vacuum pressure impregnation process in step 4 is as follows: first evacuate to below 200 Pa, then impregnate the impregnating agent into the internal pores of the porous graphite green body under a pressure of 0.1 - 0.5 MPa, and then dry and cure at a curing temperature of 160 - 180°C for 0.5 - 1 h.

[0015] Preferably, phenolic resin solutions with mass concentrations of 40 wt%, 35 wt%, 25 wt%, and 15 wt% are sequentially selected as the impregnating agent.

[0016] Preferably, the process parameters for the high-temperature graphitization in step 6 are as follows: first evacuate to below 10 Pa, heat from room temperature to 300°C at a rate of 120°C / h - 360°C / h, introduce nitrogen or argon with a purity of 99%, then heat to 600°C at a rate of 180°C / h - 240°C / h, and finally heat to 2400 - 2600°C at a rate of 240°C / h - 480°C / h, hold for 1 - 2 h; finally cool to room temperature in the furnace, take out, and obtain a high-thermal-conductivity and high-strength porous graphite skeleton preform.

[0017] The present invention has the following beneficial effects: 1. The present invention constructs a three-dimensional interpenetrating network structure of graphite and metal (cast iron / cast steel) to solve the problem that it is difficult to coordinate the thermal conductivity and mechanical properties of traditional chill blocks due to the single material. The selective laser sintering (SLS) technology is used to prepare a high-thermal-conductivity and high-strength porous graphite skeleton preform, and the sand casting process is combined to achieve the gapless composite of the molten metal and the graphite skeleton. The low thermal expansion characteristic of the graphite phase (<6×10 -6 °C -1 ) is used to inhibit the expansion of the metal phase, significantly improving the thermal conductivity (76 - 85 W•m -1 •K -1 ), heat storage capacity (specific heat capacity 510 - 760 J•kg -1 •°C -1 ) and mechanical properties (flexural strength 170 - 210 MPa, compressive strength 110 - 147 MPa) of the composite chill block. By regulating the volume ratio of the graphite skeleton (60% - 80%), spatial configuration (woodpile / honeycomb / diamond structure) and solid feature size, the flexible adaptation of the comprehensive performance of the chill block is realized, which has the advantages of rapid prototyping, strong interface stability and long service life, and is suitable for the chilling requirements of complex castings in the casting field.

[0018] 2. The present invention overcomes the deficiencies of graphite chill blocks and cast iron chill blocks, and obtains a new type of composite chill block with strong heat storage capacity, good chilling effect, excellent mechanical properties and small thermal expansion coefficient. Its comprehensive performance can be regulated according to the actual production, providing process technology guarantee for obtaining high-quality castings. At the same time, the production method is fast, efficient and low-cost.

[0019] 3. The novel graphite / metal composite chill block of the present invention belongs to a typical three-dimensional interpenetrating network structure composite material. The existence of the three-dimensional interpenetrating network structure helps to give full play to the excellent characteristics of the graphite phase and the metal phase respectively. The graphite phase exhibits characteristics such as high thermal conductivity, high specific heat capacity and low expansion, ensuring the chilling effect of the novel composite chill block, and can also maintain the volume stability during the rapid temperature change of rapid cooling and heating, restricting the thermal expansion of the metal phase; while the metal phase, as the reinforcing phase, can improve the strength of the novel composite chill block, prevent the oxidation of graphite, extend the use times of the composite chill block and broaden its application range. In short, combining the graphite and metal in the form of an interpenetrating network structure can not only increase the total heat storage of the composite chill block, but also form a temperature gradient in the composite structure due to the inconsistent thermal conductivities of the graphite phase and the metal phase, accelerating the heat transfer rate and further improving the chilling ability of the chill block. At the same time, according to the production requirements, the spatial structure, solid feature size and volume fraction of the porous graphite skeleton can be changed to regulate the comprehensive performance of the composite chill block. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the drawings and embodiments.

[0021] Figure 1 (a) (b) (c) Schematic diagrams of several typical porous graphite skeletons of the present invention.

[0022] 1(a) Woodpile porous graphite skeleton, 1(b) Honeycomb-like porous graphite skeleton, 1(c) Diamond-like porous graphite skeleton.

[0023] Figure 2 (a) (b) (c) are schematic diagrams of the unit body of the porous graphite skeleton of the present invention (1 cast iron, 2 graphite block).

[0024] 2(a) Unit body of woodpile porous graphite skeleton, 2(b) Unit body of honeycomb-like porous graphite skeleton, 2(c) Unit body of diamond-like porous graphite skeleton.

[0025] Figure 3 (a) (b) are the finished product diagrams provided in CN209918861U.

[0026] Figure 4 Process flow for preparing the graphite / metal composite chill of the present invention.

[0027] Figure 5 Schematic diagram of the process of combining the porous graphite skeleton and metal of the present invention (1 molten metal, 2 sand mold, 3 diamond-like porous graphite skeleton). Detailed implementation manners

[0028] The following further describes the implementation manners of the present invention with reference to the accompanying drawings.

[0029] Example 1: The object of the present invention is to provide a new type of graphite / metal composite chill and its rapid preparation method, overcome the deficiencies of graphite chills and cast iron chills, obtain a new type of composite chill with strong heat storage capacity, good chilling effect, excellent mechanical properties, and small thermal expansion coefficient, whose comprehensive performance can be adjusted according to actual production, provide process technical guarantee for obtaining high-quality castings, and at the same time, the production method is fast, efficient, and low-cost. From Q = CmΔT (where Q is the heat storage capacity of the material, C is the specific heat capacity of the material, m is the mass of the material, and ΔT is the temperature difference), it can be obtained that the heat capacity is related to the density and specific heat capacity of the material. The density of the graphite chill is about 1 / 4 of that of the ordinary chill (see Table 1), but its specific heat capacity is about 2 - 3 times that of the ordinary chill. When the volume is the same, the heat capacity of the graphite chill is only about 1 / 2 of that of the ordinary chill, while the density and specific heat capacity of the new type of graphite / metal composite chill are between the two. Therefore, it has strong heat storage capacity. From the formula V = -λΔT / ρCT (where V is the heat conduction speed, λ is the thermal conductivity, ΔT is the temperature difference, ρ is the material density, C is the specific heat capacity, and T is the casting temperature). The higher the thermal conductivity, the greater the temperature gradient, the faster the heat transfer speed, and the stronger the chilling ability. The new type of graphite / metal composite chill has a good chilling effect.

[0030] The novel graphite / metal composite chill belongs to a typical three-dimensional interpenetrating network structure composite material. The existence of the three-dimensional interpenetrating network structure helps to give full play to the excellent characteristics of the graphite phase and the metal phase respectively. The graphite phase exhibits characteristics such as high thermal conductivity, high specific heat capacity, and low expansion, ensuring the chilling effect of the novel composite chill, and can also maintain volume stability during rapid temperature changes of rapid cooling and heating, restricting the thermal expansion of the metal phase; while the metal phase, as the reinforcing phase, can improve the strength of the novel composite chill, prevent graphite oxidation, extend the service life of the composite chill, and broaden its application range. In short, combining graphite and metal in the form of an interpenetrating network structure can not only increase the total heat storage capacity of the composite chill, but also form a temperature gradient in the composite structure due to the inconsistent thermal conductivities of the graphite phase and the metal phase, accelerating the heat transfer rate and further enhancing the chilling ability of the chill. At the same time, according to production requirements, the comprehensive performance of the composite chill can be regulated by changing the spatial structure, physical characteristics size, and volume fraction of the porous graphite skeleton.

[0031] Idea of the present invention: The core idea of the present invention is to give full play to the synergistic effect of the two-phase materials by constructing a three-dimensional interpenetrating network structure of graphite and metal (cast iron / cast steel): the graphite phase serves as a continuous heat conduction network to provide a rapid heat transfer path, and its low coefficient of thermal expansion (<6×10 -6 °C -1 ) can inhibit the thermal expansion of the metal phase and ensure the dimensional stability of the composite material; the metal phase, as the mechanical support network, enhances the flexural strength (170 - 210 MPa) and compressive strength (110 - 147 MPa), and reduces the oxidation risk by wrapping the graphite skeleton, extending the service life. To achieve this structure, the invention proposes a rapid preparation technology that combines additive manufacturing and casting processes. First, a porous graphite skeleton prototype is formed by selective laser sintering (SLS). The pore characteristics are regulated by parameters such as layer thickness and scanning spacing. Through processes such as phenolic resin impregnation, carbonization, and high-temperature graphitization, the skeleton is densified, and finally a three-dimensional porous preform with high thermal conductivity and high strength is formed. Subsequently, the preform is combined with high-temperature molten metal (such as HT200 cast iron) through sand casting. By preheating (200 - 300 °C), the interfacial thermal stress is reduced, promoting the penetration of the molten metal into the graphite pores to form a gapless interpenetrating structure. This process breaks through the interfacial separation problem caused by the difference in thermal expansion coefficients of traditional composite chills. At the same time, by regulating the volume ratio of the graphite skeleton (60% - 80%), spatial configuration (woodpile, honeycomb, diamond structure), and physical characteristics size, the thermal conductivity, specific heat capacity, and mechanical properties can be flexibly adapted.

[0032] See Figure 4 , the present invention provides a rapid preparation method for the novel graphite / metal composite chill, which includes the following steps.

[0033] (1)Complete the design of the porous graphite skeleton. Preferably, it is a porous woodpile structure, a porous honeycomb-like structure, a porous diamond-like structure, etc. The maximum physical feature size does not exceed 5 mm, and the volume ratio of the porous graphite skeleton in the composite chill is not less than 60%.

[0034] (2)Prepare a mixed powder of natural flake graphite powder and thermosetting phenolic resin. The basic composition of the mixed powder is as follows: the mass fraction of natural flake graphite powder is 50 - 68% (100 - 500 mesh, carbon content not less than 99%); the mass fraction of thermosetting phenolic resin powder is 25 - 43% (200 - 900 mesh); the mass fraction of high-purity titanium powder is 5 - 7% (150 - 300 mesh, titanium content not less than 99.5%). Add them to a dry ball mill in batches and stir for 4 - 6 hours to obtain the graphite / phenolic resin mixed powder.

[0035] (3)Use selective laser sintering to rapidly print a prototype of the porous graphite skeleton. The combination of selective laser sintering process parameters is as follows: layer thickness 0.1 - 0.3 mm, scanning spacing 0.1 - 0.2 mm, scanning speed 500 - 1000 mm / s, laser power 5 - 10 w.

[0036] (4)Perform secondary curing on the porous graphite skeleton prototype. The secondary curing process parameters are: the first stage is 80℃ - 90℃, and the holding time is 10 - 15 min; the second stage is 120℃ - 130℃, and the holding time is 20 - 30 min; the third stage is 160℃ - 180℃, and the holding time is 10 - 15 min to obtain a green body of the porous graphite skeleton.

[0037] (5)Carry out carbonization treatment on the green body of the porous graphite skeleton under the protection of high-purity nitrogen or argon. The carbonization process is as follows: first evacuate to below 100 Pa, heat from room temperature to 300℃ at a rate of 120℃ / h - 360℃ / h, and introduce argon or nitrogen with a purity of 99%; then heat to 600℃ at a rate of 30℃ / h - 240℃ / h; finally heat to 800℃ at a rate of 120℃ / h - 360℃ / h, hold for 0.5 - 2 h, and cool to room temperature with the furnace to obtain a preform of the porous graphite skeleton.

[0038] (6)Perform ultrasonic cleaning on the preform of the porous graphite skeleton for 15 - 30 min to remove floating powder, and then dry it in a drying oven.

[0039] (7) Vacuum pressure impregnation with phenolic resin solution. Select phenolic resin solutions with gradually decreasing mass concentration as the impregnating agent in sequence. The preferred combination is as follows: 40 wt%, 35 wt%, 25 wt%, 15 wt%. The process of vacuum pressure impregnation is as follows: First, evacuate to a vacuum degree below 200 Pa, and then impregnate the impregnating agent into the internal pores of the porous graphite skeleton green body under the pressure of 0.1 - 0.5 MPa to densify it. Subsequently, dry and cure it. The curing temperature is 160 - 180 °C, and the time is 0.5 - 1 h.

[0040] (8) Repeat the processes of (5) and (6) 2 - 4 times to obtain a high - density and high - strength porous graphite skeleton preform; (9) Conduct high - temperature graphitization treatment on the porous graphite skeleton preform. The process and parameters of high - temperature graphitization are as follows: First, evacuate to a vacuum degree below 10 Pa. Heat from room temperature to 300 °C at a rate of 120 °C / h - 360 °C / h, and introduce nitrogen or argon with a purity of 99%. Then, heat up to 600 °C at a rate of 180 °C / h - 240 °C / h. Finally, heat up to 2400 - 2600 °C at a rate of 240 °C / h - 480 °C / h and hold for 1 - 2 h; Finally, cool down to room temperature in the furnace, take out, and obtain a high - thermal - conductivity and high - strength porous graphite skeleton preform.

[0041] (10) Preheat the porous graphite skeleton to 200 - 300 °C, then fix it in a sand mold, and pour high - temperature molten metal (preferably cast iron, cast steel) to finally obtain a new type of graphite / metal composite chill (see Figure 5 )

[0042] (11) By changing the physical characteristic dimensions, volume, and spatial structure of the porous graphite skeleton, etc., the purpose of actively regulating the comprehensive performance of the composite chill is achieved.

[0043] Example 2: (1) Design a porous graphite skeleton: Design a wood - pile porous graphite skeleton with a graphite volume ratio of 80% (see Figure 2 a)), the characteristic dimensions of its unit body are 5 mm × 5 mm × 42 mm, and the corresponding dimensions of the metal matrix skeleton are 1.5 mm × 5 mm × 42 mm.

[0044] (2) Preparation of natural flake graphite powder / thermosetting phenolic resin mixed powder: Weigh natural flake graphite powder, thermosetting phenolic resin powder, and high - purity titanium powder according to the mass ratio of 63 wt%: 30 wt%: 7 wt%. Among them, the carbon content of the natural flake graphite powder is not less than 99%, the particle size is 100 mesh, the particle size of the thermosetting phenolic resin powder is 500 mesh, and the titanium content of the high - purity titanium powder is not less than 99.5%, and the particle size is 100 mesh. Add them to a ball mill and mechanically mix for 3.5 h to obtain the mixed powder.

[0045] (3)Selective laser sintering to form a porous graphite skeleton prototype: Use selective laser sintering to rapidly manufacture a porous graphite skeleton prototype. The process parameter combination is as follows: laser power 18W, layer thickness 0.1 - 0.3mm, scanning spacing 0.1 - 0.2mm, scanning speed 500 - 1000mm / s, laser power 5 - 10w.

[0046] (4)Secondary curing: Put the porous graphite skeleton prototype into a hot air drying oven for secondary curing. The curing process is as follows: keep warm at 90°C for 15min; keep warm at 120°C for 15min; keep warm at 180°C for 15min to obtain a porous graphite skeleton green body.

[0047] (5)Carbonization treatment of the porous graphite skeleton: Put the porous graphite skeleton green body into a carbonization furnace, evacuate to 80Pa, heat up to 300°C at a rate of 120°C / h, and introduce 99% high-purity nitrogen for protection; then heat up to 600°C at a rate of 60°C / h; finally heat up to 800°C at a rate of 240°C / h, keep warm for 1h, cool down to room temperature with the furnace, take out to obtain a porous graphite skeleton preform.

[0048] (6)Densification of the porous graphite skeleton: After ultrasonic cleaning the porous graphite skeleton preform for 15min, remove the floating powder, dry it in a drying oven, and then impregnate it with a phenolic resin solution under vacuum pressure. The process is as follows: first evacuate to 160Pa, and then impregnate the phenolic resin solution with a mass concentration of 25wt% into the internal pores of the porous graphite preform under a pressure of 0.5MPa. After drying, complete the secondary curing.

[0049] (7)Secondary carbonization of the porous graphite skeleton: Put the porous graphite skeleton into a carbonization furnace, evacuate to 75Pa, heat up to 800°C at a rate of 240°C / h and keep warm for 0.5h, cool down to room temperature with the furnace, take out to obtain a porous graphite skeleton preform.

[0050] (8)Secondary densification: Perform secondary ultrasonic cleaning, select a phenolic resin solution with a mass concentration of 15wt% and impregnate it with phenolic resin solution again under vacuum pressure, then dry at 60°C for 1h, and then heat up to 180°C and cure for 1h to obtain a high-density porous graphite skeleton preform.

[0051] (9)Graphitization of the porous graphite skeleton: Put the preform of the porous graphite skeleton into a graphitization furnace, evacuate to a vacuum degree of 6 Pa, introduce nitrogen with a purity of 99%, then heat it to 600 °C at a rate of 180 °C / h and then to 2600 °C at a rate of 480 °C / h, and keep it at this temperature for 1 h; finally, cool it in the furnace to room temperature, take it out, and obtain the preform of the high thermal conductivity and high strength porous graphite skeleton.

[0052] (10)Composite the porous graphite skeleton preform with metal: Ultrasonically clean the porous graphite skeleton preform, dry it at 100 °C, continue to preheat it to 300 °C, take it out, fix it in a sand mold, pour the liquid HT200 into the sand mold to composite with the porous graphite skeleton preform, wait for it to solidify and cool, then take it out to obtain the porous graphite skeleton / HT200 composite chill.

[0053] The comprehensive performance test results are as follows: The density of the graphite / HT200 composite chill is 2.78 g•cm -3 , the thermal conductivity is 85.13 W•m -1 •k -1 , the specific heat capacity is 760 J•kg -1 •°C -1 , the melting point is 1535 °C, the thermal expansion coefficient <7×10 -6 •°C -1 , the flexural strength is 170 Mpa, and the compressive strength is 110 Mpa. The comprehensive performance of the prepared novel graphite / HT200 composite chill is superior to that of the graphite chill and the metal chill, and there are no obvious defects, and it is also easier to control the performance, showing broad industrial application prospects in the casting field.

[0054] Example 3: (1)Design a porous graphite skeleton: Design a graphite skeleton with a porous honeycomb-like structure according to the graphite volume ratio of 70%. The unit cell structure size is a regular hexagon with a side length of 6.5 mm, the inner hole is a regular hexagon with a side length of 2 mm, and the overall length is 50 mm (see Figure 2 b), and the diameter of the holes on the side of the solid is 4 mm.

[0055] (2)Preparation of natural flake graphite powder / thermosetting phenolic resin mixed powder: Weigh natural flake graphite powder: thermosetting phenolic resin powder: high-purity titanium powder according to the mass ratio of 60 wt%: 34 wt%: 6 wt%. Among them, the carbon content of the natural flake graphite powder is not less than 99%, and the particle size is 200 mesh; the particle size of the phenolic resin powder is 500 mesh; the titanium content of the high-purity titanium powder is not less than 99.5%, and the particle size is 200 mesh. Add the mixed powder into a ball mill and mechanically mix it for 3.5 h to obtain the mixed powder.

[0056] (3)Selective laser sintering to form a porous graphite skeleton prototype: Rapidly fabricate a porous graphite skeleton prototype using selective laser sintering. The process parameter combinations are as follows: laser power 18W, layer thickness 0.1 - 0.3mm, scanning spacing 0.1 - 0.2mm, scanning speed 500 - 1000mm / s, laser power 5 - 10w.

[0057] (4) Secondary curing: Put it into a hot air drying oven for secondary curing. The curing process is: keep warm at 90°C for 15min; keep warm at 120°C for 15min; keep warm at 180°C for 15min to obtain a porous graphite skeleton green body.

[0058] (5) Carbonization treatment of the porous graphite skeleton: Put the graphite skeleton green body into a carbonization furnace, evacuate to 80Pa, heat up to 300°C at a rate of 120°C / h, and introduce high-purity nitrogen with a purity greater than 99% for protection; then heat up to 600°C at a rate of 60°C / h; finally heat up to 800°C at a rate of 240°C / h and keep warm for 1h, cool down to room temperature with the furnace, take out to obtain a porous graphite skeleton preform.

[0059] (6) Densification of the porous graphite skeleton: After ultrasonic cleaning the porous graphite skeleton preform for 15min, remove the floating powder. Dry it in a drying oven, and then impregnate it with a phenolic resin solution under vacuum pressure. The process is as follows: first evacuate to a vacuum degree of 100Pa, and then impregnate the 35% phenolic resin solution into the internal pores of the three-dimensional porous graphite preform under a pressure of 0.5MPa. After drying, complete the secondary curing.

[0060] (7) Secondary carbonization of the porous graphite skeleton: Put the porous graphite skeleton into a carbonization furnace, evacuate to 75Pa, heat up to 800°C at a rate of 240°C / h and keep warm for 0.5h, cool down to room temperature with the furnace, take out to obtain a porous graphite skeleton preform.

[0061] (8) Secondary densification: Perform secondary ultrasonic cleaning, select a phenolic resin solution with a mass concentration of 15wt% and impregnate it with phenolic resin solution again under vacuum pressure. Then dry it at 60°C for 1h, and then heat up to 180°C and cure for 1h to obtain a high-density porous graphite skeleton preform.

[0062] (9) Graphitization of the porous graphite skeleton: Put the porous graphite skeleton preform into a graphitization furnace, evacuate to a vacuum degree of 6Pa, introduce nitrogen with a purity of 99%, then heat up to 600°C at a rate of 180°C / h, and finally heat up to 2600°C at a rate of 480°C / h and keep warm for 1h; finally cool down to room temperature with the furnace, take out to obtain a high thermal conductivity and high strength porous graphite skeleton preform.

[0063] (10)Composite of porous graphite skeleton preform and metal: The porous graphite skeleton preform is ultrasonically cleaned and then dried at 100 °C. It is further preheated to 300 °C, taken out and fixed in a sand mold. The liquid HT200 is poured into the sand mold to be composite with the porous graphite skeleton preform. After solidification and cooling, it is taken out to obtain a graphite / HT200 composite chill.

[0064] The comprehensive performance test results are as follows: The density of the graphite / HT200 composite chill is 3.37 g•cm -3 , and the thermal conductivity is 81.07 W•m -1 •k -1 , the specific heat capacity is 570 J•kg -1 •°C -1 , the melting point is 1535 °C, the thermal expansion coefficient <7×10-6•°C -1 , the flexural strength is 190 Mpa, and the compressive strength is 130 Mpa. The thermal conductivity, heat storage capacity, strength, etc. of the prepared novel graphite / HT200 composite chill are not the most excellent, but its comprehensive performance is better than that of graphite chills and metal chills, and there are no obvious defects. It is also easier to control the performance, and it has broad industrial application prospects in the casting field.

[0065] Example 4: (1)Design of porous graphite skeleton: Design a graphite skeleton with a spatial shape of a porous diamond-like structure according to the graphite volume ratio of 60%. The unit cell structure size is 1.5 mm × 4.5 mm × 5.2 mm (see Figure 2 c), and the reserved thickness of the metal outer layer is 5 mm.

[0066] (2)Preparation of natural flake graphite powder / thermosetting phenolic resin mixed powder: Weigh natural flake graphite powder: thermosetting phenolic resin powder: high-purity titanium powder according to the mass ratio of 57 wt%: 38 wt%: 5 wt%. The carbon content of the natural flake graphite powder is not less than 99%, and the particle size is 320 mesh; the particle size of the thermosetting phenolic resin powder is 500 mesh; the titanium content of the high-purity titanium powder is not less than 99.5%, and the particle size is 300 mesh. Add the mixed powder into a ball mill and mechanically mix for 3.5 h.

[0067] (3)Selective laser sintering to form a porous graphite skeleton prototype: Use selective laser sintering to rapidly manufacture a porous graphite skeleton prototype. The process parameter combination is as follows: laser power 18 W, layer thickness 0.1 - 0.3 mm, scanning spacing 0.1 - 0.2 mm, scanning speed 500 - 1000 mm / s, laser power 5 - 10 w.

[0068] (4)Secondary curing: Put it into a hot air drying oven for secondary curing. The curing process is as follows: keep the temperature at 90 °C for 15 min; keep the temperature at 120 °C for 15 min; keep the temperature at 180 °C for 15 min to obtain a green body of the porous graphite skeleton.

[0069] (5)Carbonization treatment of the porous graphite skeleton: Put the green body of the graphite skeleton into a carbonization furnace, evacuate to 80 Pa, heat up to 300 °C at a rate of 120 °C / h, and introduce high-purity nitrogen with a purity greater than 99% for protection; then heat up to 600 °C at a rate of 60 °C / h; finally heat up to 800 °C at a rate of 240 °C / h and keep it for 1 h, cool down to room temperature with the furnace, take it out to obtain a preform of the porous graphite skeleton.

[0070] (6)Densification of the porous graphite skeleton: Ultrasonically clean the preform of the porous graphite skeleton for 15 min to remove floating powder, dry it in a drying oven, and then impregnate it with a phenolic resin solution under vacuum pressure. The process is as follows: first evacuate to below 160 Pa, and then impregnate the phenolic resin solution with a concentration of 35% into the internal pores of the three-dimensional porous graphite preform under a pressure of 0.5 MPa. After drying, complete the secondary curing.

[0071] (7)Secondary carbonization of the porous graphite skeleton: Put the graphite skeleton green body into a carbonization furnace, evacuate to below 75 Pa, heat up to 800 °C at a rate of 240 °C / h and keep it for 0.5 h, cool down to room temperature with the furnace, take it out to obtain a preform of the high-density porous graphite skeleton.

[0072] (8)Secondary densification: Perform secondary ultrasonic cleaning, select a phenolic resin solution with a mass concentration of 15 wt% and impregnate it with phenolic resin solution again under vacuum pressure. Then dry it at 60 °C for 1 h, and then heat up to 180 °C and cure it for 1 h to obtain a preform of the high-density porous graphite skeleton.

[0073] (9)Graphitization of the porous graphite skeleton: Put the preform of the porous graphite skeleton into a graphitization furnace, evacuate to 6 Pa, introduce nitrogen with a purity of 99%, then heat up to 600 °C at a rate of 180 °C / h, and finally heat up to 2600 °C at a rate of 480 °C / h and keep it for 1 h; finally cool down to room temperature with the furnace, take it out to obtain a preform of the high-strength and high-thermal-conductivity porous graphite graphite skeleton.

[0074] (10)Composite of the porous graphite skeleton preform with metal: Put the porous graphite graphite skeleton preform into a cleaning agent for ultrasonic cleaning, and then dry it at 150 °C for 1 h. Place the cleaned and dried porous graphite graphite skeleton preform into a sand mold. Preheat to 300 °C and keep warm for 15 min. Finally, pour the HT200 metal liquid into the sand mold to be compounded with the porous graphite graphite skeleton preform. After solidification and cooling, take it out.

[0075] The comprehensive performance test results are as follows: The density of the graphite / HT200 composite chill is 5.56 g•cm -3 , and the thermal conductivity is 76.92 W•m -1 •k -1 , the specific heat capacity is 510 J•kg -1 •°C -1 , the melting point is 1535 °C, and the thermal expansion coefficient is <7×10 -6 •°C -1 , the flexural strength is 210 Mpa, and the compressive strength is 147 Mpa. The thermal conductivity, heat storage capacity, strength, etc. of the newly prepared graphite / HT200 composite chill are not the most excellent, but its comprehensive performance is better than that of graphite chills and metal chills, and there are no obvious defects. It is also easier to control the performance, and it has broad industrial application prospects in the casting field.

Claims

1. A method for preparing a graphite-metal composite chiller, characterized in that: The following steps are involved: Step 1, fully mixing natural flake graphite powder, thermosetting phenolic resin powder and high-purity titanium powder in a certain ratio to form a graphite / phenolic resin mixed powder; Step 2, using selective laser sintering technology to quickly print a porous graphite skeleton prototype, complete secondary curing, and obtain a porous graphite skeleton blank; Step 3, carbonizing the porous graphite skeleton blank under the protection of high-purity nitrogen or argon; Step 4, vacuum pressure impregnating the porous graphite skeleton blank after carbonization with a phenolic resin solution; Step 5, repeating steps 2 and 3 for 2-4 times to obtain a high-density porous graphite skeleton preform; Step 6, performing high-temperature graphitization treatment on the high-density porous graphite skeleton preform obtained in step 5 to obtain a high-thermal-conductivity and high-strength porous graphite skeleton preform; Step 7, preheating the porous graphite skeleton preform obtained in step 6 to 200-300° C., then placing it in a sand mold, pouring high-temperature molten metal, and obtaining a new type of graphite / metal composite chiller.

2. The method for preparing a graphite-metal composite chiller according to claim 1, characterized in that: The graphite / phenolic resin mixed powder in step 1 is composed of: The mass fraction of natural flake graphite powder is 50~68%, 100~500 mesh, and the carbon content is not less than 99%; Thermosetting phenolic resin powder has a mass fraction of 25-43% and a mesh size of 200-900; The mass fraction of high-purity titanium powder is 5~7%, 150~300 mesh, and the titanium content is not less than 99.5%.

3. The method for preparing a graphite-metal composite chiller according to claim 1, characterized in that: In the preparation process of the graphite / phenolic resin mixed powder in step 1, natural flake graphite powder, thermosetting phenolic resin powder and high-purity titanium powder are added into a dry ball mill and mixed for 4-6 hours to obtain the graphite / phenolic resin mixed powder.

4. The method for preparing a graphite-metal composite chiller according to claim 1, characterized in that: The process parameter combination of the selective laser sintering in step 2 is as follows: layer thickness 0.1-0.3 mm, scanning spacing 0.1-0.2 mm, scanning speed 500-1000 mm / s, laser power 5-10 W.

5. The method for preparing a graphite-metal composite chiller according to claim 1, characterized in that: The secondary curing process parameters in step 2 are: 80°C~90°C in the first stage, and the insulation time is 10~15min; 120°C~130°C in the second stage, and the insulation time is 20~30min; and 160°C~180°C in the third stage, and the insulation time is 10~15min.

6. The method for preparing a graphite-metal composite chiller according to claim 1, characterized in that: The porous graphite skeleton blank in step 2 comprises a porous wood pile structure, a porous honeycomb structure or a porous diamond-like structure, the maximum entity feature size does not exceed 5 mm, and the volume proportion of the porous graphite skeleton in the composite chill is not less than 60%; The metal substrate is cast iron or cast steel.

7. The method for preparing a graphite-metal composite chiller according to claim 1, characterized in that: The carbonization treatment process in step 3 is as follows: first evacuate to below 100 Pa, heat from room temperature to 300°C at 120°C / h~360°C / h, and introduce argon or nitrogen with a purity of 99%; then heat to 600°C at 30°C / h~240°C / h; finally heat to 800°C at 120°C / h~360°C / h, keep warm for 0.5~2h, and cool to room temperature with the furnace.

8. The method for preparing a graphite-metal composite chiller according to claim 1, characterized in that: The vacuum pressure impregnation process in step 4 is as follows: firstly, the vacuum degree is evacuated to below 200 Pa, and then the impregnating agent is impregnated into the internal pores of the porous graphite blank under the pressure of 0.1-0.5 MPa, and then dried and solidified at a curing temperature of 160-180° C. for 0.5-1 h.

9. The method for preparing a graphite-metal composite chiller according to claim 8, characterized in that: The phenolic resin solutions with mass concentrations of 40 wt %, 35 wt %, 25 wt % and 15 wt % are selected as the impregnating agents in sequence.

10. The method for preparing a graphite-metal composite chiller according to claim 1, characterized in that: The high-temperature graphitization process parameters in step 6 are as follows: first, evacuate the vacuum degree to below 10Pa, heat from room temperature to 300°C at 120°C / h~360°C / h, introduce nitrogen or argon with a purity of 99%, then heat to 600°C at 180°C / h~240°C / h, and finally heat to 2400~2600°C at 240°C / h~480°C / h, and keep warm for 1~2h; finally, cool to room temperature with the furnace, take out, and obtain a high thermal conductivity and high strength porous graphite skeleton preform.

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