Preparation method of ceramic riser tube for aluminum alloy

Abstract

The invention relates to a preparation method of a ceramic riser tube for aluminum alloy, which comprises the following steps: (1) using a base material ceramic tube, heating to 120-150 DEG C, immersing into a coating 1 (controlling the coating temperature at 50-70 DEG C), keeping for 15-30 seconds, taking out, draining and drying; (2) sintering in a vacuum furnace at 1450 + / -50 DEG C for 15-30 minutes, and then cooling to room temperature; (3) heating to 50-70 DEG C, immersing into a coating 2, keeping for 15-30 seconds, taking out, draining and drying; (4) sintering in a vacuum furnace at 1200 + / -50 DEG C for 1-2 hours, and then cooling to room temperature; (5) heating to 50-70 DEG C, immersing into a coating 3, keeping for 30 seconds, taking out, and draining; (6) preserving heat at 500 DEG C for 2 hours, sintering in a normal-pressure nitrogen furnace at 1350 + / -100 DEG C for 3 hours, and cooling to room temperature; the prepared riser tube has the effects of being long in service life and low in cost.

Description

Technical Field

[0001] The present invention relates to the technical field of riser pipe processing, and particularly relates to a preparation method of a ceramic riser pipe for aluminum alloy. Background Art

[0002] The riser pipe is one of the key components in low-pressure casting. During filling, under the action of air pressure, the molten metal enters the mold through the riser pipe. When the pressure is released, the unfrozen molten metal also flows back into the crucible through the riser pipe. Taking the low-pressure casting of aluminum alloy as an example, the aluminum liquid (temperature 700 - 800 °C) is pressed into the mold cavity from the riser pipe every 5 - 15 minutes. Therefore, the riser pipe must have a low coefficient of thermal expansion, good thermal shock resistance, and at the same time, it should not wet or react with the aluminum liquid.

[0003] In terms of materials, riser pipes are mainly divided into metal riser pipes and ceramic riser pipes. Among them, the metal riser pipe is mainly made of cast iron, which is extremely easy to pollute the aluminum liquid and has a short service life. The main materials of ceramic riser pipes are: 1. Aluminum titanate riser pipes, but this material is easy to decompose, resulting in poor stability of the riser pipe and affecting its service life; 2. Silicon nitride riser pipes, which have a long service life, good thermal shock resistance, and a low thermal expansion value, but the cost is extremely high. Summary of the Invention

[0004] The present invention aims to provide a preparation method of a ceramic riser pipe for aluminum alloy, which has the effects of long service life and low cost.

[0005] The above technical object of the present invention is achieved through the following technical solutions: A preparation method of a ceramic riser pipe for aluminum alloy, comprising the following steps:

[0006] (1) Use a base ceramic pipe, the open pore porosity of the base ceramic pipe is 10 - 30%, the material is corundum, and Al2O3 ≥ 99%. Heat it to 120 - 150 °C, immerse it in Coating 1 (control the coating temperature at 50 - 70 °C), keep it for 15 - 30 s and then take it out, drain it and dry it;

[0007] (2) Place the base ceramic pipe processed in step (1) in a vacuum furnace at 1450 ± 50 °C and sinter it for 15 - 30 min, and then cool it to room temperature;

[0008] (3) Heat the base ceramic pipe processed in step (2) to 50 - 70 °C, immerse it in Coating 2, keep it for 15 - 30 s and then take it out, drain it and dry it;

[0009] (4) Place the base ceramic pipe processed in step (3) in a vacuum furnace at 1200 ± 50 °C and sinter it for 1 - 2 h, and then cool it to room temperature;

[0010] (5) Heat the substrate ceramic tube processed in step (4) to 50 - 70 °C, immerse it in Coating 3, keep it for 30 s and then take it out and drain.

[0011] (6) Keep the substrate ceramic tube processed in step (5) at 500 °C for 2 h, then place it in an atmospheric pressure nitrogen furnace at 1350 ± 100 °C and sinter for 3 h, and then keep it cooled to room temperature.

[0012] As a further setting of the present invention, in step (1), the Coating 1 includes 60 - 70% silicon oxynitride, 15 - 20% silicon nitride, and 15 - 20% first sintering agent.

[0013] As a further setting of the present invention, in step (3), the Coating 2 includes 40 - 50% silicon oxynitride, 50 - 60% silicon nitride, and 5 - 10% first sintering agent.

[0014] As a further setting of the present invention, in step (5), the Coating 3 includes 90 - 95% silicon nitride, 2 - 5% metallic silicon powder, and 3% second sintering agent.

[0015] As a further setting of the present invention, the first sintering agent is silica powder, in which the purity of SiO2 is 90 - 95%, and the particle size D97 is about 1.2 μm.

[0016] As a further setting of the present invention, the second sintering agent is industrial silicon powder, with a purity of 99%, and the passing rate of 270 mesh is ≥ 85%.

[0017] As a further setting of the present invention, the Coating 1, the Coating 2, and the Coating 3 further include 0.1 - 0.5% suspending agent, 0.1 - 0.3% dispersing agent, 1 - 3% binder, 0.5 - 1% leveling agent, 1% preservative, and 1% defoaming agent.

[0018] As a further setting of the present invention, the suspending agent is ammonium polyacrylate.

[0019] As a further setting of the present invention, the dispersing agent is sodium hexametaphosphate and NNO.

[0020] As a further setting of the present invention, the binder is one or more of lithium - modified water glass, silica sol, and PVA solution.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. The present invention innovatively designs a composite lifting pipe. By using the liquid-phase impregnation method, it is impregnated and coated multiple times and sintered under different conditions to obtain a ceramic lifting pipe with a gradient concentration, transitioning from a corundum layer on the inner layer to a silicon nitride layer on the outer layer; giving full play to the characteristics of nitride materials with good erosion resistance and thermal shock resistance and the advantage of low cost of corundum ceramic pipes. Therefore, the expansion coefficients between various materials of the lifting pipe obtained by this method are appropriate, with good thermal shock resistance, good aluminum melt wettability resistance, long service life and low cost.

[0023] 2. The present invention uses a corundum pipe with an apparent porosity of 10 - 30%, replacing the original silicon nitride pipe, which greatly reduces the production cost. At the same time, using a corundum pipe with a certain porosity can, to a certain extent, solve the problem of thermal expansion mismatch between corundum and silicon nitride.

[0024] 3. The present invention adds a large amount of amorphous silica powder to Coating 1. The amorphous silica powder can form a small amount of liquid phase at high temperature. Coupled with the capillary action between particles, it promotes the filling of substances between particles towards the pores. The amorphous silica powder can block the pores of the corundum pipe to form a closed layer, resulting in a decrease in porosity and an increase in density. Therefore, the lifting pipe in the present invention gradually changes from an alumina layer, a silicon oxynitride and silicon nitride layer to a silicon nitride layer. The coating after three sinterings is denser, greatly improving the erosion resistance, thermal shock resistance, etc. of the lifting pipe. Specific Embodiments

[0025] The technical solutions in the embodiments will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0026] Embodiment 1

[0027] 1. Preparation of materials:

[0028] (1) Matrix ceramic pipe: A corundum pipe with a porosity of 10 - 15%, AL2O3 ≥ 99%;

[0029] (2) Coating 1: 70 parts of silicon oxynitride, 15 parts of silicon nitride, 15 parts of the first sintering agent silica powder, 0.2 parts of the suspending agent ammonium polyacrylate, 0.1 parts of the dispersing agent sodium hexametaphosphate, 1 part of the binder silica sol, 2 parts of lithium-modified sodium silicate, 1 part of the leveling agent, 1 part of the preservative, 1 part of the defoaming agent;

[0030] (3) Coating 2: 40 parts of silicon oxynitride, 50 parts of silicon nitride, 10 parts of the first sintering agent silica powder, 0.1 parts of the suspending agent ammonium polyacrylate, 0.2 parts of the dispersing agent sodium hexametaphosphate, 2 parts of the binder silica sol, 1 part of the leveling agent, 1 part of the preservative, 1 part of the defoaming agent;

[0031] (4) Coating 3: 95 parts of silicon nitride, 2 parts of metallic silicon powder, 2 parts of silicon oxynitride, 1 part of industrial silicon powder as the second sintering agent, 0.2 part of ammonium polyacrylate as the suspending agent, 0.3 part of NNO as the dispersing agent, 1 part of PVA as the binder, 1 part of leveling agent, 1 part of preservative, 1 part of defoamer;

[0032] (5) The leveling agent, preservative and defoamer used are all common commercially available materials. Among them, the leveling agent is acrylic acid, the preservative is zinc borate, and the defoamer is silicone defoamer.

[0033] (6) Silicon nitride: Commercially available ordinary silicon nitride, with a purity of ≥90% and a passing rate of ≥85% for 270 mesh;

[0034] Silicon oxynitride: The product obtained by calcining the above-mentioned silicon nitride at 600 - 700 °C for 3 h.

[0035] 2. Operation steps:

[0036] (1) Use the substrate ceramic tube, heat it to 120 °C, immerse it in Coating 1 (control the coating temperature at 50 °C), keep it for 15 s and then take it out, drain it and dry it;

[0037] (2) Place the substrate ceramic tube processed in step (1) in a vacuum furnace at 1500 °C and sinter for 30 min, and then cool it to room temperature;

[0038] (3) Heat the substrate ceramic tube processed in step (2) to 50 °C, immerse it in Coating 2, keep it for 15 s and then take it out, drain it and dry it;

[0039] (4) Place the substrate ceramic tube processed in step (3) in a vacuum furnace at 1200 °C and sinter for 2 h, and then cool it to room temperature;

[0040] (5) Heat the substrate ceramic tube processed in step (4) to 50 °C, immerse it in Coating 3, keep it for 30 s and then take it out, drain it;

[0041] (6) Keep the substrate ceramic tube processed in step (5) at 500 °C for 2 h, then place it in an atmospheric pressure nitrogen furnace at 1300 °C and sinter for 3 h, and then keep it cooled to room temperature.

[0042] Example 2

[0043] 1. Preparation of materials:

[0044] (1) Matrix ceramic tube: Corundum tube with a porosity of 25 - 30%, AL2O3 ≥ 99%;

[0045] (2) Coating 1: 60 parts of silicon oxynitride, 15 parts of silicon nitride, 25 parts of silica powder as the first sintering agent, 0.1 part of ammonium polyacrylate as the suspending agent, 0.1 part of sodium hexametaphosphate as the dispersing agent, 1 part of silica sol as the binder, 2 parts of lithium-modified water glass, 1 part of leveling agent, 1 part of preservative, 1 part of defoaming agent;

[0046] (3) Coating 2: 35 parts of silicon oxynitride, 60 parts of silicon nitride, 5 parts of silica powder as the first sintering agent, 0.1 part of ammonium polyacrylate as the suspending agent, 0.15 part of sodium hexametaphosphate as the dispersing agent, 3 parts of silica sol as the binder, 1 part of leveling agent, 1 part of preservative, 1 part of defoaming agent;

[0047] (4) Coating 3: 90 parts of silicon nitride, 4 parts of metallic silicon powder, 2 parts of industrial silicon powder as the second sintering agent, 4 parts of silicon oxynitride, 0.2 part of ammonium polyacrylate as the suspending agent, 0.3 part of sodium hexametaphosphate as the dispersing agent, 1 part of PVA as the binder, 1 part of leveling agent, 1 part of preservative, 1 part of defoaming agent;

[0048] (5) The leveling agent, preservative and defoaming agent used are all common commercially available materials. Among them, the leveling agent is acrylic acid, the preservative is zinc borate, and the defoaming agent is silicone defoaming agent.

[0049] (6) Silicon nitride: Commercially available ordinary silicon nitride, with a purity of ≥90% and a passing rate of ≥85% for 270 mesh;

[0050] Silicon oxynitride: The product obtained by calcining the above-mentioned silicon nitride at 600 - 700 °C for 3 h.

[0051] 2. Operating steps:

[0052] (1) Use a substrate ceramic tube, heat it to 150 °C, immerse it in Coating 1 (control the coating temperature at 70 °C), keep it for 30 s and then take it out, drain it and dry it;

[0053] (2) Place the substrate ceramic tube processed in step (1) in a vacuum furnace at 1450 °C and sinter for 15 min, then cool it to room temperature;

[0054] (3) Heat the substrate ceramic tube processed in step (2) to 70 °C, immerse it in Coating 2, keep it for 30 s and then take it out, drain it and dry it;

[0055] (4) Place the substrate ceramic tube processed in step (3) in a vacuum furnace at 1250 °C and sinter for 2 h, then cool it to room temperature;

[0056] (5) Heat the substrate ceramic tube processed in step (4) to 70 °C, immerse it in Coating 3, keep it for 30 s and then take it out, drain it;

[0057] (6) The substrate ceramic tube processed in step (5) is kept at 500 °C for 2 h, then placed in an atmospheric pressure nitrogen furnace at 1300 °C for sintering for 3 h, and then cooled to room temperature.

[0058] Experimental results

[0059] Table 1

[0060]

[0061] As can be seen from Table 1, compared with the commercially available silicon nitride lifting tube and commercially available aluminum titanate lifting tube, the composite lifting tube prepared from corundum ceramic tube as the raw material in this application has no significant difference in density and refractoriness; and compared with the commercially available silicon nitride lifting tube, the apparent porosity and thermal shock resistance at 900 °C of the composite lifting tube obtained in this application are not much different, and at the same time it is significantly better than the commercially available aluminum titanate lifting tube; it shows that the composite lifting tube prepared by the method of this application has a significant improvement in thermal stability compared with the commercially available aluminum titanate lifting tube; compared with the commercially available silicon nitride lifting tube, it has the advantages of long service life, good thermal shock resistance and low thermal expansion value of the silicon nitride lifting tube. At the same time, since corundum ceramic tube is used as the raw material in this application, the production cost can be greatly reduced.

Claims

1. A preparation method of a ceramic-type liquid-riser pipe for aluminum alloy, characterized in that, It includes the following steps: (1) Use a substrate ceramic tube. The open pore porosity of the substrate ceramic tube is 10 - 30%, the material is corundum, and Al2O3 ≥ 99%. Heat it to 120 - 150 °C, immerse it in Coating 1 (control the coating temperature at 50 - 70 °C), keep it for 15 - 30 s and then take it out, drain it and dry it; (2) Place the substrate ceramic tube processed in step (1) in a vacuum furnace at 1450 ± 50 °C and sinter it for 15 - 30 min, and then cool it to room temperature; (3) Heat the substrate ceramic tube processed in step (2) to 50 - 70 °C, immerse it in Coating 2, keep it for 15 - 30 s and then take it out, drain it and dry it; (4) Place the substrate ceramic tube processed in step (3) in a vacuum furnace at 1200 ± 50 °C and sinter it for 1 - 2 h, and then cool it to room temperature; (5) Heat the substrate ceramic tube processed in step (4) to 50 - 70 °C, immerse it in Coating 3, keep it for 30 s and then take it out, drain it; (6) Keep the substrate ceramic tube processed in step (5) at 500 °C for 2 h, then place it in an atmospheric pressure nitrogen furnace at 1350 ± 100 °C and sinter it for 3 h, and then keep it cooled to room temperature.

2. The preparation method of a ceramic type liquid riser pipe for aluminum alloy according to claim 1, characterized in that: In step (1), the Coating 1 includes 60 - 70% silicon oxynitride, 15 - 20% silicon nitride, and 15 - 20% first sintering agent.

3. The preparation method of a ceramic type liquid riser pipe for aluminum alloy according to claim 2, characterized in that: In step (3), the Coating 2 includes 40 - 50% silicon oxynitride, 50 - 60% silicon nitride, and 5 - 10% first sintering agent.

4. The preparation method of a ceramic-type liquid-riser pipe for aluminum alloy according to claim 3, characterized in that: In step (5), the Coating 3 includes 90 - 95% silicon nitride, 2 - 5% metallic silicon powder, and 3% second sintering agent.

5. The preparation method of a ceramic-type liquid-riser pipe for aluminum alloy according to claim 3, characterized in that: The first sintering agent is silica powder, in which the purity of SiO2 is 90 - 95%, and the particle size D97 is about 1.2 μm.

6. The preparation method of a ceramic-type liquid-lifting pipe for aluminum alloy according to claim 4, characterized in that: The second sintering agent is industrial silicon powder, with a purity of 99% and a passing rate of ≥ 85% for 270 mesh.

7. The preparation method of a ceramic type liquid riser pipe for aluminum alloy according to claim 4, characterized in that: The Coating 1, the Coating 2, and the Coating 3 also include 0.1 - 0.5% suspending agent, 0.1 - 0.3% dispersing agent, 1 - 3% binder, 0.5 - 1% leveling agent, 1% preservative, and 1% defoaming agent.

8. The preparation method of a ceramic riser pipe for aluminum alloy according to claim 7, characterized in that: The suspending agent is ammonium polyacrylate.

9. The preparation method of a ceramic type liquid riser pipe for aluminum alloy according to claim 7, characterized in that: The dispersing agent is sodium hexametaphosphate and NNO.

10. The preparation method of a ceramic type liquid riser pipe for aluminum alloy according to claim 7, characterized in that: The binder is one or more of lithium-modified sodium silicate, silica sol, and PVA solution.

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