Composite thermal insulation sand mold and preparation method thereof

Abstract

A composite thermal insulation sand mold is disclosed which comprises three layers, a first layer being a high-temperature contact layer, a second layer being a heat conduction layer, and a third lay

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of sand molds for fused-cast refractories, and in particular relates to a composite thermal insulation sand mold used in annealing of a fused-cast refractory and a preparation method thereof. BACKGROUND

[0002] The preparation of chromium-zirconium-corundum-based fused-cast refractories requires melting raw materials from solid to liquid using a high-temperature electric arc, and then casting an obtained high-temperature melt at a casting temperature generally not less than 2,000°C into a sand mold to allow molding. Due to a high annealing temperature, the casting needs to undergo a thermal insulation annealing process, which requires a thermal insulation box and a thermal insulation medium, but the sand mold generally does not have a thermal insulation function. When the casting temperature exceeds l,800°C, a surface of the sand mold requires thermal insulation in order to reduce a high temperature gradient caused by rapid heat dissipation of the casting. The thermal insulation of the sand mold is generally conducted by stacking lightweight thermal insulation bricks around the sand mold, and the thermal insulation bricks are reinforced on an outer surface of the sand mold by surrounding with steel wires. Since stacked thermal insulation bricks could not be well combined with the sand mold, a high temperature generated by the casting generally melts the steel wires, causing the thermal insulation bricks to loosen, thereby weakening a thermal insulation effect of the sand mold. Chinese utility model patent entitled “thermal insulation sand mold for production of wall bricks in fused zirconium corundum pool” (CN 213231986 U) discloses a thermal insulation sand mold, where a thermal insulation fiberboard is mainly adopted to insulate the sand mold. Although this utility model could achieve the thermal insulation of the sand mold, its production and assembly process is relatively complicated and could not be applied to thermal insulation annealing of large-size castings. In addition, a thermal insulation material used in the utility model is an aluminum oxide fiberboard (generally having a service temperature less than l,350°C), while a casting temperature of fused corundum material and fused chromium corundum material is generally at l,700°C to 2,200°C. This casting temperature could quickly cause the thermal insulation fiberboard to fail, thereby losing thermal insulation ability. Therefore, the above utility model patent could not effectively improve thermal insulation performance of the sand mold, and its production process is relatively complicated and difficult to promote and use. SUMMARY

[0003] An object of the present disclosure is to provide a method for preparing an integrated composite thermal insulation sand mold, thereby solving the problem of insufficient thermal insulation capacity of a sand mold. In the present disclosure, the composite thermal insulation sand mold includes three layers, a first layer being a high-temperature contact layer, a second layer being a heat conduction layer, and a third layer being a thermal insulation layer. Raw materials of the high-temperature contact layer include: 10 wt% to 20 wt% of a chromium oxide micro-powder, 5 wt% to 60 wt% of an aluminum oxide micro-powder, 3 wt% to 10 wt% of a magnesium oxide powder, 5 wt% to 20 wt% of a silica micro-powder, 10 wt% to 25 wt% of an aluminum dihydrogen phosphate solution as a main binder, and 9 wt% to 19 wt% of an aluminum sol as an auxiliary binder. Raw materials of the heat conduction layer include: 3 wt% to 5 wt% of the chromium oxide micro-powder, 50 wt% to 70 wt% of the aluminum oxide micro-powder, 3 wt% to 10 wt% of the magnesium oxide powder, 10 wt% to 15 wt% of the silica micro-powder, 0.5 wt% to 4.5 wt% of a copper oxide powder, and 10 wt% to 25 wt% of an aluminum dihydrogen phosphate solution as a main binder. Raw materials of the thermal insulation layer include: 2 wt% to 3 wt% of a chromium oxide aggregate, 12 wt% to 70 wt% of the aluminum oxide micro-powder, 15 wt% to 25 wt% of the silica micro-powder, 3 wt% to 20 wt% of a hollow aluminum oxide ball, 10 wt% to 35 wt% of an SQM300HB phenolic resin, and 1 wt% to 10 wt% of a GS resin curing agent. The chromium oxide micro-powder has a particle size of 1 mm to 2 mm, the aluminum oxide micropowder has a particle size of 1 mm to 3 mm, the copper oxide powder has a particle size of 0.5 mm to 1 mm, and the aluminum sol is the auxiliary binder and has a solute percentage of 30%. The raw materials requirements for the thermal insulation layer are as follows: the chromium oxide aggregate has a particle radius of 1 mm to 2 mm, and the hollow aluminum oxide ball has a diameter of 1 mm to 3 mm.

[0004] In the present disclosure, a preparation process of a mixture for the high-temperature contact layer includes: mixing a chromium oxide micro-powder, the aluminum oxide micropowder, the magnesium oxide powder, and the silica micro-powder in a mixer by stirring at a rotational speed of 80 rad / min for 3 min to 5 min, then adding the auxiliary binder and the aluminum dihydrogen phosphate solution into the mixer, and mixing rapidly by stirring at a rotational speed of 25 rad / min for 10 min to 15 min; and pouring a resulting mixed material into a wooden mold frame, and ramming quickly with an electric rammer at a ramming speed of 100 times / min to 400 times / min for 5 min to 10 min.

[0005] In the present disclosure, a preparation process of a mixture for the heat conduction layer includes: mixing the chromium oxide micro-powder, the aluminum oxide micro-powder, the copper oxide powder, the magnesium oxide powder, and the silica micro-powder in a mixer by stirring at a rotational speed of 80 rad / min for 3 min to 5 min, adding the aluminum dihydrogen phosphate solution into the mixer, and mixing rapidly at a rotational speed of 25 rad / min and then stirring rapidly at a rotational speed of 70 rad / min for 3 min to 5 min; and pouring the mixture into a wooden mold frame above the high-temperature contact layer, and ramming quickly with an electric rammer at a ramming speed of 100 times / min to 500 times / min for 3 min to 5 min.

[0006] In the present disclosure, a preparation process of a mixture for the thermal insulation layer includes: mixing the chromium oxide aggregate, the aluminum oxide micro-powder, the silica micro-powder, and the hollow aluminum oxide ball in a mixer by stirring at a rotational speed of 25 rad / min for 2 min to 20 min, and adding the SQM300HB phenolic resin and the GS resin curing agent into the mixer, and mixing for another 2 min to 6 min; and pouring a resulting mixed material into a wooden mold frame above the heat conduction layer, and ramming quickly with an electric rammer at a ramming speed of 50 times / min to 100 times / min for 1 min to 2 min.

[0007] In the present disclosure, the high-temperature contact layer has a thickness of 15 mm to 35 mm, the heat conduction layer has a thickness of 25 mm to 40 mm, and the thermal insulation layer has a thickness of 50 mm to 150 mm. In some embodiments, when a longest side of a casting has a length of less than 500 mm, the high-temperature contact layer has a thickness of 15 mm to 20 mm, the heat conduction layer has a thickness of 25 mm to 30 mm, and the thermal insulation layer has a thickness of 50 mm to 105 mm; when the longest side of the casting has a length of greater than or equal to 500 mm and less than 800 mm, the high-temperature contact layer has a thickness of 20 mm to 30 mm, the heat conduction layer has a thickness of 25 mm to 30 mm, and the thermal insulation layer has a thickness of 80 mm to 110 mm; when the longest side of the casting has a length greater than or equal to 800 mm, the high-temperature contact layer has a thickness of 20 mm to 35 mm, the heat conduction layer has a thickness of 20 mm to 40 mm, and the thermal insulation layer has a thickness of 100 mm to 150 mm.

[0008] In the present disclosure, the above composite sand mold template is placed in a drying chamber and dried at a temperature of 150°C to 550°C for 1 h to 4 h. According to the above process, the prepared composite sand mold template is assembled into a sand mold according to a drawing. A working layer has a cold compressive strength of 4.5 MPa to 10 MPa, a high-temperature flexural strength greater than or equal to 0.85 MPa at l,200°C; an average thermal conductivity of the high-temperature contact layer at 350°C is 20 W / (m- K) to 50 W / (m- K), and an average thermal conductivity of the thermal insulation layer at 350°C is 3.5 W / (m-K) to 15 W / (m-K).

[0009] The present disclosure has the following characteristics:

[0010] (1) Preparing a sand mold template with raw materials consistent with molten casting materials could effectively avoid the contamination of a high-temperature melt by other substances and reduce the erosion or reaction of foreign impurities on a casting surface. In addition, chromium oxide added to a mixture for the high-temperature contact layer could further improve the high-temperature tolerance of the sand mold template to the high-temperature melt, thereby preventing a melt from melting through a mold due to an excessively high temperature of a casting melt.

[0011] (2) Since a low-melting material is in a high-temperature environment for a long time, a large amount of glass phase seeps out during the material thermal insulation, causing sticking on a contact surface between a casting and the sand mold template, thus making it difficult to demold a blank and affecting the surface quality of the casting. A current sand mold design does not have an ability to quickly conduct heat away. However, in the present disclosure, a copper oxide powder is added to a mixture for the heat conduction layer, such that a thermal conductivity of the mixture for the heat conduction layer is significantly improved compared to that of the mixture for the high-temperature contact layer. It is detected that the heat conduction layer at l,350°C has an average thermal conductivity of 30 W / (m-K) to 100 W / (m-K), and the heat conduction layer at 350°C has an average thermal conductivity of 280 W / (m-K) to 415 W / (m-K). Thermal imaging analysis shows that after the mixture for the heat conduction layer is added, a high-temperature area has a significant backward shift, and heat energy could be quickly transferred to a thermal insulation layer through the mixture for the high-temperature contact layer.

[0012] (3) In the present disclosure, the combination of the high-temperature contact layer and the thermal insulation layer improves the integrity of the sand mold. After the heat is transferred to the thermal insulation layer, a speed of heat transfer to an outside could be slowed down. Moreover, the high-temperature contact layer and the thermal insulation layer are made of the same raw material type, such that there is no interlayer cracking caused by different thermal expansion coefficients. At present, thermal insulation bricks are used for brick wrapping design. Since a size of the thermal insulation bricks is fixed and a thickness of the thermal insulation layer on the sand mold could not be changed, the casting could not quickly or slowly transfer heat in places where thermal insulation is not needed or needs to be strengthened, resulting in excessive thermal gradients in some areas of the casting and leading to thermal cracking. In the present disclosure, since the thermal insulation layer is cured with resin, the thickness of the thermal insulation layer could be adjusted according to a speed of temperature loss at a thermal insulation part of the casting to reduce the thermal cracking of the casting. The present disclosure increases a yield of the castings by 40%.

[0013] After adopting the present disclosure, an outer surface temperature of the sand mold is measured after casting for 1 h, and is 360°C lower than that of an ordinary sand mold. The casting is a chromium-zirconium-corundum-based fused-cast casting without shrinkage cavities, and a heat loss rate of the sand mold is reduced by 15% at a casting temperature of 2,100°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 shows a process flow chart for preparing the composite thermal insulation sand mold according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] Example 1

[0016] A casting mold with a casting size of 300*350*1000 was prepared, with a longest side of a casting greater than 800 mm. Then, a total thickness of a sand mold was set to 160 mm, of which a high-temperature contact layer had a thickness of 30 mm, a heat conduction layer had a thickness of 30 mm, and a thermal insulation layer had a thickness of 100 mm. Raw materials of the high-temperature contact layer consisted of: 15 wt% of a chromium oxide micro-powder, 52 wt% of an aluminum oxide micro-powder, 3 wt% of a magnesium oxide powder, 10 wt% of a silica micropowder, 20 wt% of an aluminum dihydrogen phosphate solution as a main binder, and 9 wt% to 19 wt% of an aluminum sol as an auxiliary binder. Raw materials of the heat conduction layer consisted of: 5 wt% of the chromium oxide micro-powder, 60 wt% of the aluminum oxide micropowder, 5 wt% of the magnesium oxide powder, 10 wt% of the silica micro-powder, 0.5 wt% of a copper oxide powder, and 20 wt% of the aluminum dihydrogen phosphate solution as a main binder. Raw materials of the thermal insulation layer consisted of: 2 wt% of a chromium oxide aggregate, 60 wt% of the aluminum oxide micro-powder, 20 wt% of the silica micro-powder, 18 wt% of an SQM300HB phenolic resin, 20 wt% of a hollow aluminum oxide ball, and 5 wt% of a GS resin curing agent.

[0017] A chromium oxide micro-powder, the aluminum oxide micro-powder, the magnesium oxide powder, and the silica micro-powder were mixed in a mixer by stirring at 80 rad / min, and then the auxiliary binder and the aluminum dihydrogen phosphate solution were added thereto, and mixed rapidly by stirring at 25 rad / min for 15 min to obtain a mixture for the high-temperature contact layer. The mixture for the high-temperature contact layer was poured into a bottom layer of a mold, and flattened and rammed to a thickness of 30 mm, and then quickly rammed with an electric rammer at 150 times / min for 5 min. A mixture for the heat conduction layer was prepared as follows: the chromium oxide, the aluminum oxide micro-powder, the magnesium oxide powder, the silica micro-powder, the copper oxide powder, and the aluminum dihydrogen phosphate solution were quickly stirred in a mixer at 70 rad / min for 5 min to obtain the mixture for the heat conduction layer. The mixture for the heat conduction layer was poured onto an upper surface of the high-temperature contact layer, and the heat conduction layer was flattened and rammed to a thickness of 30 mm, and then quickly rammed with an electric rammer at 100 times / min for 3 min. A mixture for the thermal insulation layer was prepared as follows: the chromium oxide aggregate, the aluminum oxide micro-powder, the silica micro-powder, and the hollow aluminum oxide ball were weighed according to the proportion and mixed in a mixer by stirring at 25 rad / min for 10 min, and the SQM300HB phenolic resin and the GS resin curing agent were added thereto, and mixed for another 5 min to obtain the mixture for the thermal insulation layer. The mixture for the thermal insulation layer was poured onto an upper surface of the heat conduction layer, and rammed quickly with an electric rammer at 50 times / min for 1 min to obtain a composite sand mold template. The composite sand mold template was dried in a drying chamber at 550°C for 6 h. According to the above process, the prepared composite sand mold template was assembled according to a drawing to obtain the sand mold.

[0018] Example 2

[0019] A casting mold with a casting size of 300*350*1000 was prepared with a longest side of a casting greater than 800 mm. Then, a total thickness of a sand mold was set to 160 mm, of which a high-temperature contact layer had a thickness of 20 mm, a heat conduction layer had a thickness of 30 mm, and a thermal insulation layer had a thickness of 110 mm. Raw materials of the high-temperature contact layer consisted of: 15 wt% of a chromium oxide micro-powder, 52 wt% of an aluminum oxide micro-powder, 3 wt% of a magnesium oxide powder, 10 wt% of a silica micropowder, 20 wt% of an aluminum dihydrogen phosphate solution as a main binder, and 9 wt% to 19 wt% of an aluminum sol as an auxiliary binder. Raw materials of the heat conduction layer consisted of: 5 wt% of the chromium oxide micro-powder, 60 wt% of the aluminum oxide micropowder, 5 wt% of the magnesium oxide powder, 10 wt% of the silica micro-powder, 0.5 wt% of a copper oxide powder, and 20 wt% of the aluminum dihydrogen phosphate solution as a main binder. Raw materials of the thermal insulation layer consisted of: 2 wt% of a chromium oxide aggregate, 60 wt% of the aluminum oxide micro-powder, 20 wt% of the silica micro-powder, 18 wt% of an SQM300HB phenolic resin, 20 wt% of a hollow aluminum oxide ball, and 5 wt% of a GS resin curing agent.

[0020] A chromium oxide micro-powder, the aluminum oxide micro-powder, the magnesium oxide powder, and the silica micro-powder were mixed in a mixer by stirring at 80 rad / min, and then the auxiliary binder and the aluminum dihydrogen phosphate solution were added thereto, and mixed rapidly by stirring at 25 rad / min for 15 min to obtain a mixture for the high-temperature contact layer. The mixture for the high-temperature contact layer was poured into a bottom layer of a mold, and flattened and rammed to a thickness of 30 mm, and then quickly rammed with an electric rammer at 150 times / min for 5 min. A mixture for the heat conduction layer was prepared as follows: the chromium oxide, the aluminum oxide micro-powder, the magnesium oxide powder, the silica micro-powder, the copper oxide powder, and the aluminum dihydrogen phosphate solution were quickly stirred in a mixer at 70 rad / min for 5 min to obtain the mixture for the heat conduction layer. The mixture for the heat conduction layer was poured onto an upper surface of the high-temperature contact layer, and the heat conduction layer was flattened and rammed to a thickness of 30 mm, and then quickly rammed with an electric rammer at 100 times / min for 3 min. A mixture for the thermal insulation layer was prepared as follows: the chromium oxide aggregate, the aluminum oxide micro-powder, the silica micro-powder, and the hollow aluminum oxide ball were weighed according to the proportion and mixed in a mixer by stirring at 25 rad / min for 10 min, and the SQM300HB phenolic resin and the GS resin curing agent were added thereto, and mixed for another 5 min to obtain the mixture for the thermal insulation layer. The mixture for the thermal insulation layer was poured onto an upper surface of the heat conduction layer, and rammed quickly with an electric rammer at 50 times / min for 1 min to obtain a composite sand mold template. The composite sand mold template was dried in a drying chamber at 550°C for 6 h. According to the above process, the prepared composite sand mold template was assembled according to a drawing to obtain the sand mold.

[0021] Example 3

[0022] A casting mold with a casting size of 300*350*1000 was prepared with a longest side of a casting greater than 800 mm. Then, a total thickness of a sand mold was set to 160 mm, of which a high-temperature contact layer had a thickness of 20 mm, a heat conduction layer had a thickness of 20 mm, and a thermal insulation layer had a thickness of 120 mm. Raw materials of the high-temperature contact layer consisted of: 15 wt% of a chromium oxide micro-powder, 52 wt% of an aluminum oxide micro-powder, 3 wt% of a magnesium oxide powder, 10 wt% of a silica micropowder, 20 wt% of an aluminum dihydrogen phosphate solution as a main binder, and 9 wt% to 19 wt% of an aluminum sol as an auxiliary binder. Raw materials of the heat conduction layer consisted of: 5 wt% of the chromium oxide micro-powder, 60 wt% of the aluminum oxide micropowder, 5 wt% of the magnesium oxide powder, 10 wt% of the silica micro-powder, 0.5 wt% of a copper oxide powder, and 20 wt% of the aluminum dihydrogen phosphate solution as a main binder. Raw materials of the thermal insulation layer consisted of: 2 wt% of a chromium oxide aggregate, 60 wt% of the aluminum oxide micro-powder, 20 wt% of the silica micro-powder, 18 wt% of an SQM300HB phenolic resin, 20 wt% of a hollow aluminum oxide ball, and 5 wt% of a GS resin curing agent.

[0023] A chromium oxide micro-powder, the aluminum oxide micro-powder, the magnesium oxide powder, and the silica micro-powder were mixed in a mixer by stirring at 80 rad / min, and then the auxiliary binder and the aluminum dihydrogen phosphate solution were added thereto, and mixed rapidly by stirring at 25 rad / min for 15 min to obtain a mixture for the high-temperature contact layer. The mixture for the high-temperature contact layer was poured into a bottom layer of a mold, and flattened and rammed to a thickness of 30 mm, and then quickly rammed with an electric rammer at 150 times / min for 5 min. A mixture for the heat conduction layer was prepared as follows: the chromium oxide, the aluminum oxide micro-powder, the magnesium oxide powder, the silica micro-powder, the copper oxide powder, and the aluminum dihydrogen phosphate solution were quickly stirred in a mixer at 70 rad / min for 5 min to obtain the mixture for the heat conduction layer. The mixture for the heat conduction layer was poured onto an upper surface of the high-temperature contact layer, and the heat conduction layer was flattened and rammed to a thickness of 30 mm, and then quickly rammed with an electric rammer at 100 times / min for 3 min. A mixture for the thermal insulation layer was prepared as follows: the chromium oxide aggregate, the aluminum oxide micro-powder, the silica micro-powder, and the hollow aluminum oxide ball were weighed according to the proportion and mixed in a mixer by stirring at 25 rad / min for 10 min, and the SQM300HB phenolic resin and the GS resin curing agent were added thereto, and mixed for another 5 min to obtain the mixture for the thermal insulation layer. The mixture for the thermal insulation layer was poured onto an upper surface of the heat conduction layer, and rammed quickly with an electric rammer at 50 times / min for 1 min to obtain a composite sand mold template. The composite sand mold template was dried in a drying chamber at 550°C for 6 h. According to the above process, the prepared composite sand mold template was assembled according to a drawing to obtain the sand mold.

[0024] Example 4

[0025] A casting mold with a casting size of 300*350*1000 was prepared with a longest side of a casting greater than 800 mm. Then, a total thickness of a sand mold was set to 160 mm, of which a high-temperature contact layer had a thickness of 30 mm, a heat conduction layer had a thickness of 20 mm, and a thermal insulation layer had a thickness of 110 mm. Raw materials of the high-temperature contact layer consisted of: 15 wt% of a chromium oxide micro-powder, 52 wt% of an aluminum oxide micro-powder, 3 wt% of a magnesium oxide powder, 10 wt% of a silica micropowder, 20 wt% of an aluminum dihydrogen phosphate solution as a main binder, and 9 wt% to 19 wt% of an aluminum sol as an auxiliary binder. Raw materials of the heat conduction layer consisted of: 5 wt% of the chromium oxide micro-powder, 60 wt% of the aluminum oxide micropowder, 5 wt% of the magnesium oxide powder, 10 wt% of the silica micro-powder, 0.5 wt% of a copper oxide powder, and 20 wt% of the aluminum dihydrogen phosphate solution as a main binder. Raw materials of the thermal insulation layer consisted of: 2 wt% of a chromium oxide aggregate, 60 wt% of the aluminum oxide micro-powder, 20 wt% of the silica micro-powder, 18 wt% of an SQM300HB phenolic resin, 20 wt% of a hollow aluminum oxide ball, and 5 wt% of a GS resin curing agent.

[0026] A chromium oxide micro-powder, the aluminum oxide micro-powder, the magnesium oxide powder, and the silica micro-powder were mixed in a mixer by stirring at 80 rad / min, and then the auxiliary binder and the aluminum dihydrogen phosphate solution were added thereto, and mixed rapidly by stirring at 25 rad / min for 15 min to obtain a mixture for the high-temperature contact layer. The mixture for the high-temperature contact layer was poured into a bottom layer of a mold, and flattened and rammed to a thickness of 30 mm, and then quickly rammed with an electric rammer at 150 times / min for 5 min. A mixture for the heat conduction layer was prepared as follows: the chromium oxide, the aluminum oxide micro-powder, the magnesium oxide powder, the silica micro-powder, the copper oxide powder, and the aluminum dihydrogen phosphate solution were quickly stirred in a mixer at 70 rad / min for 5 min to obtain the mixture for the heat conduction layer. The mixture for the heat conduction layer was poured onto an upper surface of the high-temperature contact layer, and the heat conduction layer was flattened and rammed to a thickness of 30 mm, and then quickly rammed with an electric rammer at 100 times / min for 3 min. A mixture for the thermal insulation layer was prepared as follows: the chromium oxide aggregate, the aluminum oxide micro-powder, the silica micro-powder, and the hollow aluminum oxide ball were weighed according to the proportion and mixed in a mixer by stirring at 25 rad / min for 10 min, and the SQM300HB phenolic resin and the GS resin curing agent were added thereto, and mixed for another 5 min to obtain the mixture for the thermal insulation layer. The mixture for the thermal insulation layer was poured onto an upper surface of the heat conduction layer, and rammed quickly with an electric rammer at 50 times / min for 1 min to obtain a composite sand mold template. The composite sand mold template was dried in a drying chamber at 550°C for 6 h. According to the above process, the prepared composite sand mold template was assembled according to a drawing to obtain the sand mold.

[0027] Example 5

[0028] A casting mold with a casting size of 300*350*1000 was prepared. A total thickness of a sand mold was set to 160 mm, of which a high-temperature contact layer had a thickness of 50 mm, a heat conduction layer had a thickness of 40 mm, and a thermal insulation layer had a thickness of 70 mm. Raw materials of the high-temperature contact layer consisted of: 15 wt% of a chromium oxide micro-powder, 52 wt% of an aluminum oxide micro-powder, 3 wt% of a magnesium oxide powder, 10 wt% of a silica micro-powder, 20 wt% of an aluminum dihydrogen phosphate solution as a main binder, and 9 wt% to 19 wt% of an aluminum sol as an auxiliary binder. Raw materials of the heat conduction layer consisted of: 5 wt% of the chromium oxide micro-powder, 60 wt% of the aluminum oxide micro-powder, 5 wt% of the magnesium oxide powder, 10 wt% of the silica micro-powder, 0.5 wt% of a copper oxide powder, and 20 wt% of the aluminum dihydrogen phosphate solution as a main binder. Raw materials of the thermal insulation layer consisted of: 2 wt% of a chromium oxide aggregate, 60 wt% of the aluminum oxide micro-powder, 20 wt% of the silica micro-powder, 18 wt% of an SQM300HB phenolic resin, 20 wt% of a hollow aluminum oxide ball, and 5 wt% of a GS resin curing agent.

[0029] A chromium oxide micro-powder, the aluminum oxide micro-powder, the magnesium oxide powder, and the silica micro-powder were mixed in a mixer by stirring at 80 rad / min, and then the auxiliary binder and the aluminum dihydrogen phosphate solution were added thereto, and mixed rapidly by stirring at 25 rad / min for 15 min to obtain a mixture for the high-temperature contact layer. The mixture for the high-temperature contact layer was poured into a bottom layer of a mold, and flattened and rammed to a thickness of 30 mm, and then quickly rammed with an electric rammer at 150 times / min for 5 min. A mixture for the heat conduction layer was prepared as follows: the chromium oxide, the aluminum oxide micro-powder, the magnesium oxide powder, the silica micro-powder, the copper oxide powder, and the aluminum dihydrogen phosphate solution were quickly stirred in a mixer at 70 rad / min for 5 min to obtain the mixture for the heat conduction layer. The mixture for the heat conduction layer was poured onto an upper surface of the high-temperature contact layer, and the heat conduction layer was flattened and rammed to a thickness of 30 mm, and then quickly rammed with an electric rammer at 100 times / min for 3 min. A mixture for the thermal insulation layer was prepared as follows: the chromium oxide aggregate, the aluminum oxide micro-powder, the silica micro-powder, and the hollow aluminum oxide ball were weighed according to the proportion and mixed in a mixer by stirring at 25 rad / min for 10 min, and the SQM300HB phenolic resin and the GS resin curing agent were added thereto, and mixed for another 5 min to obtain the mixture for the thermal insulation layer. The mixture for the thermal insulation layer was poured onto an upper surface of the heat conduction layer, and rammed quickly with an electric rammer at 50 times / min for 1 min to obtain a composite sand mold template. The composite sand mold template was dried in a drying chamber at 550°C for 6 h. According to the above process, the prepared composite sand mold template was assembled according to a drawing to obtain the sand mold.

[0030] Comparative Example

[0031] A casting mold with a casting size of 300*350*1000 was prepared, a sand mold had a thickness of 30 mm, and an addition ratio of sodium silicate to aluminum oxide was 1 : 3. A aluminum oxide micro-powder and a sodium silicate solution were quickly mixed to obtain a mixture. The mixture was poured into a wooden mold, CO2 was blown onto a surface of a mold surface and stood for 10 min, and the mixture was dried in a drying room at 110°C for 100 min to obtain a molded template. The molded template was assembled according to a drawing to finally obtain the sand mold. A mold was placed in an insulation box, and an outer wall of the mold was surrounded by aluminum oxide lightweight thermal insulation bricks (no adhesive was used in the surrounding) with a thickness of 130 mm. After the surrounding with thermal insulation layer, iron wires were used to surround an outer side of the thermal insulation bricks.

[0032] The mold templates prepared in examples were assembled into rectangular molds with an inner wall size of 300*350*1000, while an aluminum oxide sand mold combined with the sodium silicate was used as a comparative example sample. The above examples and comparative samples were placed in a sandbox, and hollow aluminum oxide balls were used for thermal insulation outside the sandbox. The chromium-zirconium-corundum-based fused-cast melt was cast in each group of molds at 2,080°C. An outer surface of the sand mold was measured with a thermocouple, and the thermocouple was placed on an outer surface of the thermal insulation bricks in the comparative example, so as to measure a temperature of a center point of the outer surface after casting for 24 h, 48 h, 72 h, and 96 h, as shown in the following table.

[0033] Table 1 Sample SN Template center area Temperature (°C) 24 h 48 h 72 h 96 h Example 1 1660 1489 1300 704 Example 2 1645 1455 1204 998 Example 3 1570 1420 1185 1007 Example 4 1693 1550 1340 646 Example 5 1892 1789 1630 390 Comparative Example 1790 1725 1509 449

[0034] As shown in the table, an outer surface temperature of each group of samples in Examples 1 to 4 was measured to be lower than l,700°C after 24 h of thermal insulation, while an outer surface temperature of Example 5 and the comparative example sample was close to l,800°C. Since the thermal insulation layer showed desirable thermal insulation ability, the temperature in Example 5 was quickly exported through the heat conduction layer. Since a thermal insulation thickness was not set as required, the temperature of Example 5 was quickly exported at 24 h, 48 h, and 72 h. After 96 h of measurement, it was found that the outer surface temperature of Example 5 was the lowest, which was due to rapid export of internal heat through the heat conduction layer. In contrast, in Examples 1 to 4, since a thermal insulation thickness was set within a required range, heat was slowly dissipated through the thermal insulation layer, such that the outer wall temperature of the above examples was controlled at l,400°C to l,550°C at 24 h, and a temperature of a wall of Example 3 was still greater than l,000°C after 96 h. In contrast, although the comparative example sample adopted the thermal insulation bricks as the thermal insulation layer, the thermal insulation bricks could not be in well contact with the outer wall of the mold, resulting in more gaps between a cold surface of the outer wall of the sand mold and a hot contact surface of the thermal insulation bricks. A heat conduction method includes not only contact conduction but also air convection heat transfer, causing the heat to be lost too quickly in the later stage. When a composite sand mold was used, since the thermal insulation layer and the high-temperature contact layer were designed as an integrated part, the heat could only be transferred through thermal contact, reducing the subsequent heat dissipation rate. The results were different when different CuO powder contents were used in the examples. An increase in a dosage could increase an overall thermal conductivity of a material, and the internal heat was quickly introduced from the contact surface to the cold surface. This could effectively reduce a temperature difference between a surface and an interior of the casting, and reduce thermal cracking of the casting during annealing. The composite sand mold reduced thermal crack defects of a product by 34% compared with traditional molds, and thus improved a product qualification rate.

Claims

25AMENDMENTS TO THE CLAIMS1. A composite thermal insulation sand mold, comprising three layers, a first layer being a high-temperature contact layer, a second layer being a heat conduction layer, and a third layer being a thermal insulation layer,wherein the high-temperature contact layer has a thickness of 15 mm to 35 mm, the heat conduction layer has a thickness of 25 mm to 40 mm, and the thermal insulation layer has a thickness of 50 mm to 150 mm; andwherein the high-temperature contact layer is located at a bottom of the composite thermal insulation sand mold, the heat conduction layer is located on an upper surface of the high-temperature contact layer, and the thermal insulation layer is located on an upper surface of the heat conduction layer.

2. The composite thermal insulation sand mold of claim 1, wherein when a longest side of a casting has a length less than 500 mm, the high-temperature contact layer has a thickness of 15 mm to 20 mm, the heat conduction layer has a thickness of 25 mm to 30 mm, and the thermal insulation layer has a thickness of 50 mm to 105 mm.

3. The composite thermal insulation sand mold of claim 1, wherein when a longest side of a casting has a length greater than or equal to 500 mm and less than 800 mm, the high-temperature contact layer has a thickness of 20 mm to 30 mm, the heat conduction layer has a thickness of 25 mm to 30 mm, and the thermal insulation layer has a thickness of 80 mm to 110 mm.

4. The composite thermal insulation sand mold of claim 1, wherein when a longest side of a casting has a length greater than or equal to 800 mm, the high-temperature contact layer has a thickness of 20 mm to 35 mm, the heat conduction layer has a thickness of 20 mm to 40 mm, and the thermal insulation layer has a thickness of 100 mm to 150 mm.22 12 255. The composite thermal insulation sand mold of claim 1, wherein raw materials of the high-temperature contact layer comprise: 10 wt% to 20 wt% of a chromium oxide micro-powder, 5 wt% to 60 wt% of an aluminum oxide micro-powder, 3 wt% to 10 wt% of a magnesium oxide powder, 5 wt% to 20 wt% of a silica micro-powder, 10 wt% to 25 wt% of an aluminum dihydrogen phosphate solution as a main binder, and 9 wt% to 19 wt% of an aluminum sol as an auxiliary binder.

6. The composite thermal insulation sand mold of claim 1, wherein raw materials of the heat conduction layer comprise: 3 wt% to 5 wt% of a chromium oxide micropowder, 50 wt% to 70 wt% of an aluminum oxide micro-powder, 3 wt% to 10 wt% of a magnesium oxide powder, 10 wt% to 15 wt% of a silica micro-powder, 0.5 wt% to 4.5 wt% of a copper oxide powder, and 10 wt% to 25 wt% of an aluminum dihydrogen phosphate solution as a main binder.

7. The composite thermal insulation sand mold of claim 1, wherein raw materials of the thermal insulation layer comprise: 2 wt% to 3 wt% of a chromium oxide aggregate, 12 wt% to 70 wt% of an aluminum oxide micro-powder, 15 wt% to 25 wt% of a silica micro-powder, 3 wt% to 20 wt% of a hollow aluminum oxide ball, 10 wt% to 35 wt% of an SQM300HB phenolic resin, and 1 wt% to 10 wt% of a GS resin curing agent.

8. The composite thermal insulation sand mold of claim 5, wherein a preparation process of a mixture for the high-temperature contact layer comprises: mixing the chromium oxide micro-powder, the aluminum oxide micro-powder, the magnesium oxide powder, and the silica micro-powder in a mixer by stirring at a rotational speed of 80 rad / min for 3 min to 5 min, then adding the auxiliary binder and the aluminum dihydrogen phosphate solution into the mixer, and mixing rapidly by stirring at a rotational speed of 25 rad / min for 10 min to 15 min; and pouring a resulting mixed material into a wooden mold frame, and ramming quickly with an electric rammer at aramming speed of 100 times / min to 400 times / min for 5 min to 10 min.22 12 259. The composite thermal insulation sand mold of claim 6, wherein a preparation process of a mixture for the heat conduction layer comprises: mixing the chromium oxide micro-powder, the aluminum oxide micro-powder, the copper oxide powder, the magnesium oxide powder, and the silica micro-powder in a mixer by stirring at a rotational speed of 80 rad / min for 3 min to 5 min, adding the aluminum dihydrogen phosphate solution into the mixer, and mixing rapidly at a rotational speed of 25 rad / min and then stirring rapidly at a rotational speed of 70 rad / min for 3 min to 5 min; and pouring the mixture into a wooden mold frame above the high-temperature contact layer, and ramming quickly with an electric rammer at a ramming speed of 100 times / min to 500 times / min for 3 min to 5 min.

10. The composite thermal insulation sand mold of claim 7, wherein a preparation process of a mixture for the thermal insulation layer comprises: mixing the chromium oxide aggregate, the aluminum oxide micro-powder, the silica micro-powder, and the hollow aluminum oxide ball in a mixer by stirring at a rotational speed of 25 rad / min for 2 min to 20 min, and adding the SQM300HB phenolic resin and the GS resin curing agent into the mixer, and mixing for another 2 min to 6 min; and pouring a resulting mixed material into a wooden mold frame above the heat conduction layer, and ramming quickly with an electric rammer at a ramming speed of 50 times / min to 100 times / min for 1 min to 2 min.

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