A method for preparing building formwork using magnesium alloy industrial waste

Abstract

The invention discloses a method for preparing a low-cost magnesium alloy building template using magnesium alloy industrial waste, which belongs to the technical field of magnesium alloy waste recycling, and the steps are as follows: (1) waste recovery and pretreatment: industrial magnesium alloy waste is recovered and cleaned, and then dried for standby; (2) waste initial compaction: the cleaned waste is compacted at room temperature to obtain a cylindrical waste cake; (3) waste further compaction: the temperature is gradually increased between 200 and 550°C, and the waste cake is compacted for multiple times; (4) remelting and purification treatment: the compacted waste is placed in a smelting furnace for smelting and purification treatment to obtain a magnesium alloy solution; (5) die casting: the magnesium alloy solution is injected into a mold for die casting, and the die casting is subjected to subsequent treatment. The method of the invention has simple process, easy operation, low and controllable production cost, and the prepared magnesium alloy building template has low impurity content and good mechanical properties, and has good engineering application prospects in the construction industry.

Description

Technical Field

[0001] The invention relates to a method for preparing a building template by utilizing magnesium alloy industrial waste chips, wherein the main raw material is industrial magnesium alloy processing waste chips, and the method belongs to the technical field of magnesium alloy waste recycling. Technical Background

[0002] Building formwork is the main tool in the pouring construction process, which can play an important role in supporting and protecting the unformed concrete. In actual projects, building formwork consumption is huge, and formwork technology directly affects the quality and cost of construction projects.

[0003] Although traditional building formworks such as wood boards, bamboo boards, and plastic boards have low costs, they have problems such as poor performance, few recycling times, and environmental pollution. With the development of the construction industry, the trend of metal formwork replacing traditional wood boards, bamboo boards, and plastic boards has become increasingly obvious. Steel formworks and aluminum alloy formworks are currently the most common metal formworks. However, although steel formworks have good mechanical properties, they are heavy, not conducive to construction, and the labor intensity of construction workers is high, and there are safety hazards. Although aluminum alloy formworks have low density, good mechanical properties, and can be reused many times, they usually need to be coated on the surface during use to avoid corrosion by alkaline cement. After being reused 4-5 times, they need to be sprayed with coating, which is very inconvenient and increases costs.

[0004] Compared with aluminum alloy formwork, magnesium alloy formwork has a series of advantages such as lower density, good damping and shock absorption performance, casting performance, excellent processing performance, good alkali resistance, etc. It has greater advantages in reducing the intensity of construction personnel, reducing temporary storage yards and construction time, saving civil engineering general contracting costs, increasing the frequency of use, and green environmental protection. However, due to the high cost of raw materials and industrial production, the cost of magnesium alloy building formwork is still higher than that of aluminum alloy. This greatly limits the application of magnesium alloy in building formwork. With the further improvement of the requirements for lightweight metal formwork in construction, the construction market has increasingly strong calls for magnesium alloy formwork. How to reduce the cost of magnesium alloy formwork has become the main problem at present.

[0005] Industrial magnesium alloys generate a large amount of waste during the production, preparation and processing, including risers in the casting process, machining excess, and powder and chips in the cutting and milling process. The waste ratio can be as high as 30%. Among them, machining excess and cutting block residues are easy to reuse through remelting and other methods. However, for magnesium alloy powder and chips, since they are prone to combustion or even explosion during heating, they are difficult to recycle. Therefore, they are usually directly discarded in pollution-free landfills and other methods. The actual utilization rate is very low, resulting in a lot of waste. If magnesium alloy waste can be recycled and used for the preparation of building formwork, it will not only meet the development requirements of the green circular economy, but also is expected to greatly reduce the production cost of building formwork. How to optimize the recovery and reuse path of magnesium alloy industrial waste is an important technical problem.

[0006] Regarding the recycling of magnesium alloy waste, there is little disclosure in the prior art. Patent "CN109576521A" discloses a solid-state recycling method using rare earth magnesium alloy waste. This method, based on powder billet making, promotes metallurgical bonding and grain refinement between powders through equal channel and forward extrusion technology. However, in view of the limitations of equal channel extrusion, this method is costly and has low preparation efficiency, and is not suitable for the production of larger-sized products. In addition, the solid-state recycling method cannot effectively remove the oxide inclusions in the powder, which has an adverse effect on the alloy properties.

[0007] The Chinese invention patent application "CN114934184A" proposes a method for recycling and vacuum regeneration of magnesium-lithium alloy waste, which uses a vacuum melting method and multiple remelting to process magnesium-lithium alloy waste, and casts magnesium-lithium alloy ingots to achieve regeneration casting of magnesium-lithium alloy for further preparation and processing. However, the vacuum melting and multiple remelting processes in this method will inevitably increase the recycling cost.

[0008] It can be seen that high cost is still the main problem in the current recycling and reuse of magnesium alloy industrial waste. How to effectively improve the utilization rate of magnesium alloy raw materials and reduce the recycling and reuse cost of magnesium alloy waste has become a technical problem that needs to be urgently solved in this technical field. Summary of the invention

[0009] The purpose of the present invention is to provide a method for preparing low-cost magnesium alloy building formwork using magnesium alloy industrial waste, which has simple process, easy operation, short production cycle, high efficiency, low and controllable production cost, and the prepared magnesium alloy building formwork has low impurity content and good mechanical properties, and has good engineering application prospects in the construction industry.

[0010] The above object of the present invention is achieved through the following technical solutions:

[0011] A method for preparing low-cost magnesium alloy building formwork using magnesium alloy industrial scraps, the steps are as follows:

[0012] (1) Waste recovery and pretreatment: industrial magnesium alloy waste is recovered and cleaned, dried and set aside;

[0013] (2) Preliminary compaction of waste: The cleaned waste is compacted at room temperature to obtain a cylindrical waste cake;

[0014] (3) Further compaction of the waste: the temperature is gradually increased between 150 and 550 °C, and the waste cake is compacted multiple times;

[0015] (4) Remelting and purification: The compacted waste cake is placed in a smelting furnace for smelting and purification to obtain a magnesium alloy solution;

[0016] (5) Die casting: The magnesium alloy solution is injected into the mold for die casting, and the die casting is subsequently processed.

[0017] Preferably, in step (1), the magnesium alloy includes but is not limited to AZ series, ZM series, and VW series alloys.

[0018] Preferably, in step (1), the magnesium alloy waste chips are mainly powder chips generated during cutting and turning and milling.

[0019] Preferably, in step (1), the magnesium alloy waste chips are first cleaned with clean water to remove surface soluble salts, and then cleaned with industrial alcohol to remove surface oil and water stains.

[0020] Preferably, in step (2), the mold used for compaction is cylindrical, with a diameter of 100 mm to 300 mm and a height of 40 to 200 mm, and the density of the cylindrical waste obtained after preliminary compaction is not less than 1.25 g / cm 3 .

[0021] Preferably, in step (3), the cylindrical waste cake to be compacted is preheated at 150°C to be fully dried, and then compacted. The compaction process is 2 to 5 times, and the compaction temperature is set according to the composition of the magnesium chips and gradually increases in the range of 150 to 550°C. After this step, the density of the waste block is not less than 1.65g / cm 3 The aforementioned step-by-step heating and compaction method is used to greatly reduce the air between the cylindrical waste materials, improve the density of the waste materials, and prevent the burning of magnesium powder chips; and promote the rupture of the oxide layer on the surface of the powder chips, and connect them in the form of metallurgical bonding, further ensuring the safety of the subsequent smelting process.

[0022] Preferably, the specific steps of step (4) include:

[0023] 1) placing the cylindrical waste obtained in step (3) into a cast iron crucible and smelting at 750° C. to 800° C., covering the surface with a refining agent during the smelting process, and adding a protective gas, wherein the protective gas is specifically a mixture of Ar2 and SF6 in a ratio of 10:1 to 20:1;

[0024] 2) After the complete dissolution, lower the temperature to below 750°C, let it stand for 5-10 minutes, introduce argon gas for refining, keep the hydrogen content of the melt below 0.1mL / 100g, stir several times during the process, and use a preheated skimmer to remove the scum on the surface;

[0025] 3) Subsequently, the solution is filtered through a 15-30 mesh stainless steel filter and a 10-20 ppi magnesium oxide foam ceramic filter to obtain a magnesium alloy solution, which is kept at 670-700° C. and protected by a mixed gas of SF6 and CO2.

[0026] Preferably, the specific steps of step (5) include:

[0027] 1) Spray a release agent (such as M 2040) on the surface of the magnesium alloy template die-casting mold and preheat it to 200-300°C in advance;

[0028] 2) The magnesium alloy solution is subjected to pressure injection, and the process parameters are: injection pressure of 30-100 MPa, fast injection speed of 30-60 m / s, injection stroke of 15-22 cm, which can be selected and adjusted according to actual conditions; after injection casting, the pressure is maintained for 1-5 seconds; the die casting is ejected from the mold to obtain a casting, and the demoulding angle is 2-5°;

[0029] 3) The magnesium alloy die casting is trimmed and surface polished to obtain a magnesium alloy building template.

[0030] (6) Conduct non-destructive testing on the final material, including radiographic testing and ultrasonic testing.

[0031] Beneficial effects:

[0032] Compared with the prior art, the advantages of the present invention are as follows: before remelting the magnesium alloy powder, a step-by-step heating and compacting method is adopted to significantly improve the density and even promote the metallurgical bonding between the powders, thereby greatly reducing the gas content in the solution during the smelting process; during the smelting process, on the basis of refining with a refining agent, refining with argon gas and multiple stirring, a composite filtration treatment is performed through a 15-30 mesh stainless steel filter screen and a 10-20ppi magnesium oxide foam ceramic filter sheet, thereby effectively removing impurities in the solution, improving the mechanical properties of the magnesium alloy building formwork, and reducing the number of remelting and refining times, thereby reducing the cost; a short-process method for directly using the remelting liquid of magnesium alloy waste chips for magnesium alloy formwork die-casting is provided, the process is simple, easy to operate, the production cost is low and controllable, the prepared magnesium alloy building formwork has low impurity content and good mechanical properties, and has good engineering application prospects in the construction industry.

[0033] The present invention is further described below by means of specific embodiments, but this does not limit the protection scope of the present invention. DETAILED DESCRIPTION

[0034] Unless otherwise specified, the raw materials, additives or equipment used in the embodiments of the present invention are all commercially available products, and their models are conventional models in the art; the testing methods used are all conventional methods in the art.

[0035] Example 1

[0036] A method for preparing low-cost magnesium alloy building formwork using magnesium alloy industrial scraps, the steps are as follows:

[0037] (1) Waste recovery and pretreatment: The powder chips of AZ80M industrial magnesium alloy during cutting and turning and milling are recovered and cleaned: the magnesium alloy waste chips are first cleaned with clean water to remove the soluble salt on the surface, and then cleaned with industrial alcohol to remove the surface oil and water stains, and then dried for use;

[0038] (2) Preliminary compaction of waste: The cleaned waste is compacted at room temperature. The compaction mold is cylindrical with a diameter of 200 mm and a height of 120 mm. After preliminary compaction, the density of the waste cake obtained is not less than 1.25 g / cm 3 ;

[0039] (3) Further compaction of the waste: The cylindrical waste cake to be compacted is preheated at 150°C to fully dry it, and then compacted three times at 150°C, 250°C and 400°C respectively. The density of the waste block after this step is not less than 1.65g / cm 3 ;

[0040] (4) Remelting and purification: The compacted scraps are placed in a smelting furnace for smelting and purification to obtain a magnesium alloy solution; the details are as follows:

[0041] 1) placing the cylindrical waste obtained in step (3) into a cast iron crucible and smelting at 775° C., covering the surface with a refining agent during the smelting process, and adding a protective gas, wherein the protective gas is specifically a mixture of Ar2 and SF6 in a ratio of 15:1;

[0042] 2) After the complete dissolution, the temperature is lowered to below 750°C, and the mixture is allowed to stand for 7 minutes. Argon gas is introduced for refining to keep the hydrogen content of the melt below 0.1 mL / 100 g. During the process, the mixture is stirred several times, and the scum on the surface is removed with a preheated slag spoon.

[0043] 3) Subsequently, the solution was filtered through a 25-mesh stainless steel filter and a 15ppi magnesium oxide foam ceramic filter to obtain a magnesium alloy solution, which was kept at 685°C while being protected by a mixed gas of SF6 and CO2;

[0044] (5) Die casting: inject magnesium alloy solution into the mold for die casting, and then take subsequent treatment of the die casting;

[0045] The specific steps include:

[0046] 1) Spray the release agent M-2040 on the surface of the magnesium alloy template die-casting mold and preheat it to 250°C in advance;

[0047] 2) The magnesium alloy solution is subjected to pressure injection, and the process parameters are: injection pressure of 65MPa, fast injection speed of 45m / s, and injection stroke of 18cm; after injection casting, the pressure is maintained for 3s; the die casting is ejected from the mold to obtain a casting, and the demoulding angle is 3.5°;

[0048] 3) trimming and surface grinding the magnesium alloy die casting to obtain a magnesium alloy building template;

[0049] (6) Perform non-destructive testing on the final material, including radiographic and ultrasonic testing methods.

[0050] The composition and performance test results of the magnesium alloy template prepared in Example 1 are shown in Table 1 and Table 2 respectively.

[0051] Example 2

[0052] A method for preparing low-cost magnesium alloy building formwork using magnesium alloy industrial scraps, the steps are as follows:

[0053] (1) Waste recovery and pretreatment: The powder and shavings mixture of AZ91D and ZM21M industrial magnesium alloys during cutting and turning and milling are recovered and cleaned: the magnesium alloy waste shavings are first cleaned with clean water to remove the soluble salt on the surface, and then cleaned with industrial alcohol to remove the oil and water stains on the surface, and then dried for use;

[0054] (2) Preliminary compaction of waste: The cleaned waste is compacted at room temperature. The compaction mold is cylindrical with a diameter of 100 mm and a height of 40 mm. After preliminary compaction, the density of the waste cake obtained is not less than 1.25 g / cm 3 ;

[0055] (3) Further compaction of the waste: The cylindrical waste cake to be compacted is preheated at 150°C to fully dry, and then compacted four times at 150°C, 250°C, 350°C and 400°C respectively. The density of the waste block after this step is not less than 1.65g / cm 3 ;

[0056] (4) Remelting and purification: The compacted scraps are placed in a smelting furnace for smelting and purification to obtain a magnesium alloy solution; the details are as follows:

[0057] 1) placing the cylindrical waste obtained in step (3) into a cast iron crucible and smelting at 750° C., covering the surface with a refining agent during the smelting process, and adding a protective gas, wherein the protective gas is a mixture of Ar2 and SF6 in a ratio of 10:1;

[0058] 2) After the complete dissolution, the temperature is lowered to below 750°C, and the mixture is allowed to stand for 5 minutes. Argon gas is introduced for refining to keep the hydrogen content of the melt below 0.1 mL / 100 g. During the process, the mixture is stirred several times, and the scum on the surface is removed with a preheated slag spoon.

[0059] 3) Subsequently, the solution was filtered through a 15-mesh stainless steel filter and a 10ppi magnesium oxide foam ceramic filter to obtain a magnesium alloy solution, which was kept at 670°C while being protected by a mixed gas of SF6 and CO2;

[0060] (5) Die casting: inject magnesium alloy solution into the mold for die casting, and then take subsequent treatment of the die casting;

[0061] The specific steps include:

[0062] 1) Spray the release agent TH-200 on the surface of the magnesium alloy template die-casting mold and preheat it to 200°C in advance;

[0063] 2) The magnesium alloy solution is subjected to pressure injection, and the process parameters are: injection pressure of 30 MPa, fast injection speed of 30 m / s, and injection stroke of 15 cm; after injection casting, the pressure is maintained for 1 second; the die casting is ejected from the mold to obtain a casting, and the demoulding angle is 2°;

[0064] 3) trimming and surface grinding the magnesium alloy die casting to obtain a magnesium alloy building template;

[0065] (6) Perform non-destructive testing on the final material, including radiographic and ultrasonic testing methods.

[0066] The composition analysis and performance test results of the magnesium alloy template prepared in Example 2 are shown in Table 1 and Table 2, respectively.

[0067] Example 3

[0068] A method for preparing low-cost magnesium alloy building formwork using magnesium alloy industrial scraps, the steps are as follows:

[0069] (1) Waste recovery and pretreatment: The powder chips of VW84 industrial magnesium alloy during cutting and turning and milling are recovered and cleaned: the magnesium alloy waste chips are first cleaned with clean water to remove the soluble salt on the surface, and then cleaned with industrial alcohol to remove the surface oil and water stains, and then dried for use;

[0070] (2) Preliminary compaction of waste: The cleaned waste is compacted at room temperature. The compaction mold is cylindrical with a diameter of 300 mm and a height of 200 mm. After preliminary compaction, the density of the waste cake obtained is not less than 1.25 g / cm 3 ;

[0071] (3) Further compaction of the waste: The cylindrical waste cake to be compacted is preheated at 150°C to fully dry it. The compaction process is 5 times, and the compaction temperatures are 200°C, 300°C, 420°C and 530°C respectively. The density of the waste block after this step is not less than 1.65g / cm 3 ;

[0072] (4) Remelting and purification: The compacted scraps are placed in a smelting furnace for smelting and purification to obtain a magnesium alloy solution; the details are as follows:

[0073] 1) placing the cylindrical waste obtained in step (3) into a cast iron crucible and smelting at 800° C., adding a protective gas during the smelting process, wherein the protective gas is specifically a mixture of Ar2 and SF6 in a ratio of 20:1;

[0074] 2) After the complete dissolution, the temperature is lowered to below 750°C, and the mixture is allowed to stand for 10 minutes. Argon gas is introduced for refining to keep the hydrogen content of the melt below 0.1 mL / 100 g. During the process, the mixture is stirred several times, and the scum on the surface is removed with a preheated slag spoon.

[0075] 3) Subsequently, the solution was filtered through a 30-mesh stainless steel filter and a 20ppi magnesium oxide foam ceramic filter to obtain a magnesium alloy solution, which was kept at 700°C and protected by a mixed gas of SF6 and CO2;

[0076] (5) Die casting: inject magnesium alloy solution into the mold for die casting, and then take subsequent treatment of the die casting;

[0077] The specific steps include:

[0078] 1) Spray the release agent M-2040 on the surface of the magnesium alloy template die-casting mold and preheat it to 300°C in advance;

[0079] 2) The magnesium alloy solution is subjected to pressure injection, and the process parameters are: injection pressure of 100 MPa, fast injection speed of 60 m / s, and injection stroke of 22 cm; after injection casting, the pressure is maintained for 5 seconds; the die casting is ejected from the mold to obtain a casting, and the demolding angle is 5°;

[0080] 3) trimming and surface grinding the magnesium alloy die casting to obtain a magnesium alloy building template;

[0081] (6) Perform non-destructive testing on the final material, including radiographic and ultrasonic testing methods.

[0082] The composition and performance test results of the magnesium alloy template prepared in Example 3 are shown in Table 1 and Table 2 respectively.

[0083] Table 1 Magnesium alloy template composition (mass fraction / w%)

[0084] Mg Al Zn Mn RE G Y Zr Si Fe Cu Ni other Example 1 margin 7.8 0.3 0.18 0.3Ce 0.05 0.004 0.04 0.001 0.23 Example 2 margin 6.8 1.0 0.41 0.03 0.004 0.02 0.001 0.18 Example 3 margin 1.2 0.8 7.7 3.3 0.3 0.03 0.008 0.02 0.001 0.10

[0085] Table 2 Mechanical properties of magnesium alloy template at room temperature

[0086] <![CDATA[σ s (Yield Strength / MPa)]]> <![CDATA[σ b (Yield Strength / MPa)]]> δ(elongation / %) Example 1 148 223 7.3％ Example 2 157 237 6.0％ Example 3 178 268 8.5％

[0087] The process of the invention is simple and easy to operate, and the production cost is low and controllable. The prepared magnesium alloy die-casting template has low impurity content and good mechanical properties, and has good engineering application prospects in the construction industry.

[0088] The method of directly producing magnesium alloy building formwork using magnesium alloy waste chips of the present invention can not only realize the effective recycling of magnesium alloy waste chips, and has the advantages of simple scheme, high recycling efficiency, low cost, etc., but also utilizes a short process method to prepare the magnesium alloy building formwork, with a short production cycle and high efficiency, and has extremely broad application prospects in actual industrial production processes.

[0089] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing low-cost magnesium alloy building formwork using magnesium alloy industrial waste, characterized in that: The steps include: (1) Waste recovery and pretreatment: industrial magnesium alloy waste is recovered and cleaned, dried and set aside; (2) Preliminary compaction of waste: the cleaned waste is compacted at room temperature to obtain a cylindrical waste cake; (3) Further compaction of the waste: the temperature is gradually increased between 150 and 550 °C, and the waste cake is compacted multiple times; (4) Remelting and purification: The compacted scraps are placed in a smelting furnace for smelting and purification to obtain a magnesium alloy solution; (5) Die casting: injecting a magnesium alloy solution into a mold for die casting, and performing subsequent treatment on the die casting; in step (1), the magnesium alloy includes an AZ series, ZM series or VW series alloy; The specific steps of step (3) include: preheating the cylindrical waste to be compacted at 150°C to fully dry it, and the compaction process is 2 to 5 times. The compaction temperature of each pass is set according to the composition of the magnesium chips and gradually increases in the range of 150 to 550°C. After this step, the density of the waste block is not less than 1.65g / cm 3 .

2. The method for preparing low-cost magnesium alloy building formwork using magnesium alloy industrial waste according to claim 1, characterized in that: In step (1), the magnesium alloy waste chips are mainly powder chips generated during cutting and turning and milling.

3. The method for preparing low-cost magnesium alloy building formwork using magnesium alloy industrial waste according to claim 1, characterized in that: In step (1), the magnesium alloy waste chips are first cleaned with clean water to remove surface soluble salts, and then cleaned with industrial alcohol to remove surface oil and water stains.

4. The method for preparing low-cost magnesium alloy building formwork using magnesium alloy industrial waste according to claim 1, characterized in that: In step (2), the mold used for compaction is cylindrical, with a diameter of 100 mm to 300 mm and a height of 40 to 200 mm. After preliminary compaction, the density of the cylindrical waste obtained is not less than 1.25 g / cm 3 .

5. The method for preparing low-cost magnesium alloy building formwork using magnesium alloy industrial waste according to claim 1, characterized in that: The specific steps of step (4) include: 1) placing the cylindrical waste obtained in step (3) into a cast iron crucible and smelting at 750°C to 800°C, adding a protective gas during the smelting process, wherein the protective gas is specifically a mixture of Ar and SF6 in a ratio of 10:1 to 20:1; 2) After the complete dissolution, lower the temperature to below 750°C, let it stand for 5-10 minutes, introduce argon gas for refining, keep the hydrogen content of the melt below 0.1mL / 100g, stir several times during the process, and use a preheated slag spoon to scrape off the surface slag; 3) Subsequently, the solution is filtered through a 15-30 mesh stainless steel filter and a 10-20 ppi magnesium oxide foam ceramic filter to obtain a magnesium alloy solution, which is then kept at 670-700°C while being protected by a mixed gas of SF6 and CO2.

6. The method for preparing low-cost magnesium alloy building formwork using magnesium alloy industrial waste according to claim 1, characterized in that: The specific steps of step (5) include: 1) Spray the release agent on the surface of the magnesium alloy template die-casting mold and preheat it to 200-300℃ in advance; 2) The magnesium alloy solution is subjected to pressure injection, and the process parameters are: injection pressure of 30-100 MPa, fast injection speed of 30-60 m / s, injection stroke of 15-22 cm, which can be selected and adjusted according to actual conditions; after injection casting, the pressure is maintained for 1-5 seconds; the die casting is ejected from the mold to obtain a casting, and the demoulding angle is 2-5°; 3) The magnesium alloy die casting is trimmed and surface polished to obtain a magnesium alloy building template; 4) Perform non-destructive testing on the final material.