Magnesium oxysulfate board and high-temperature dual-mold hot press molding process thereof

Abstract

The invention discloses a magnesium oxysulfate board and a high-temperature dual-mold hot press molding process thereof, and belongs to the technical field of magnesium oxysulfate boards. Comprising 140-180 parts of light calcined magnesia, 30-45 parts of magnesium sulfate heptahydrate, 10-20 parts of calcium sulfate, 3-8 parts of tourmaline powder, 2-6 parts of sepiolite fibers, 1-4 parts of hydroxyapatite powder, 0.5-1.2 parts of a polycarboxylate superplasticizer, 0.3-0.8 part of a retarder calcium lignosulphonate, 0.2-0.5 part of a silane coupling agent, 2-4 layers of basalt fiber gridding cloth and 15-25 parts of a plant-based composite foaming agent. The forming and curing links are efficiently integrated through the high-temperature dual-mold hot press forming process. The stainless steel double-mold structure does not need a large-scale stacking space, so that the requirements on the area of a curing room, templates and the number of curing vehicles are reduced, the initial investment and long-term operation cost of related equipment are remarkably reduced, and the key bottleneck restricting the improvement of the productivity of the traditional process is broken through.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnesium oxysulfate plate, and particularly relates to a magnesium oxysulfate plate and a high-temperature double-mold hot-press forming process thereof. BACKGROUND

[0002] Traditional magnesium oxysulfate plate production usually adopts ABS / PVC material as a mold plate, and after the mixed and uniform magnesium oxysulfate slurry is laid on the surface of the mold plate, the slurry is transported to a curing vehicle through a production line for layering and stacking, and then is sent into a curing room for curing. After the curing is completed, the plate can be demolded.

[0003] When large-scale production is carried out, the process has a great demand for the area of the curing room, the number of mold plates and curing vehicles, and the investment and operation cost of related equipment is high, which becomes an important factor restricting the capacity improvement. After the slurry is laid, the environment on both sides of the plate during the curing stage is obviously different. One side is exposed to the air, and the other side is isolated from the outside world by being attached to the mold plate, which makes the strength and moisture content of both sides of the plate uneven, and the plate is prone to warping. At the same time, the distribution of the slurry is affected during the transportation and jolting process of the production line, resulting in inconsistent density of the plate from top to bottom, which leads to the deformation problem of the plate after curing.

[0004] Since ABS / PVC material is used to make the mold plate, the high-temperature resistance of such mold plate is limited, and it usually cannot withstand high temperature. During the curing process of magnesium oxysulfate material, a heat release reaction occurs, and even in the set curing environment, the internal temperature of the material may exceed the tolerance limit of the mold plate. The greater the thickness of the plate, the more heat accumulates inside, and the higher the temperature. Excessive temperature will directly cause the deformation of the mold plate, interrupting the production process.

[0005] In addition, the surface strength of the ABS / PVC mold plate is insufficient, and it is easy to produce friction scratches during cleaning and handling, which makes it difficult to achieve smoothness on the surface of the plate, and brings obstacles to subsequent surface deep processing. If the mold plate is deformed or the surface is severely worn and scratched, it is difficult to repair the original plate, and it often has to be processed back to the furnace, resulting in high cost loss. Such mold plate usually needs to be replaced or repaired regularly, significantly increasing the production investment.

[0006] Therefore, the present application designs a magnesium oxysulfate plate and a high-temperature double-mold hot-press forming process to solve the above problems. SUMMARY

[0007] In view of the above-mentioned shortcomings of the prior art, the present application provides a high-temperature double-mold hot-press forming process for a magnesium oxysulfate plate, which comprises the following steps:

[0008] S1: By weight, weigh 140-180 parts of lightly calcined magnesium oxide, 30-45 parts of magnesium sulfate heptahydrate, 10-20 parts of calcium sulfate, 3-8 parts of tourmaline powder, 2-6 parts of sepiolite fiber, 1-4 parts of hydroxyapatite powder, 0.5-1.2 parts of polycarboxylate superplasticizer, 0.3-0.8 parts of lignosulfonate retarder, 0.2-0.5 parts of silane coupling agent, 2-4 layers of basalt fiber mesh, and 15-25 parts of plant-based composite foaming agent obtained by compounding tea saponin and saponins in a molar ratio of 1:1;

[0009] S2: The basalt fiber mesh is completely immersed in an ethanol solution containing silane coupling agent, then removed and dried to obtain a pretreated basalt fiber mesh; sepiolite fiber is added to deionized water and stirred to obtain a sepiolite fiber suspension.

[0010] S3: Add magnesium sulfate heptahydrate to deionized water and stir to obtain a magnesium sulfate solution;

[0011] S4: Add lightly calcined magnesium oxide, calcium sulfate, and hydroxyapatite powder to a mixer and dry mix. Then add tourmaline powder and dry mix. Inject magnesium sulfate solution into the mixer and spray deionized water while mixing to obtain a base slurry. Add polycarboxylate superplasticizer and retarder calcium lignosulfonate to the base slurry and stir. Inject pre-mixed sepiolite fiber suspension and plant-based composite foaming agent mixture into the base slurry and stir to obtain a modified slurry.

[0012] S5: Adopting a symmetrical stainless steel double mold structure, preheat the two molds to 60-80℃ respectively, open the built-in vacuum exhaust channel of the mold, inject the modified slurry into the lower mold, lay 2-4 layers of pretreated basalt fiber mesh cloth, close the upper and lower molds, apply a pre-compression pressure of 1-3MPa, and hold the pressure for 5-10 minutes.

[0013] S6: It adopts a three-stage gradient heating and pressing mode. In the first stage, the temperature of the dual-mode is raised to 100-120℃, and the pressure is raised to 5-8MPa. Heating and pressing are carried out simultaneously.

[0014] The second stage involves holding the pressure at 120-150℃ and 8-12MPa for 30-60 minutes.

[0015] The third stage involves cooling the temperature to 60-70℃, applying a pressure of 5-7MPa, and maintaining the temperature for 20-30 minutes to cure the material. The material is then removed at room temperature and pressure.

[0016] S7: Send the boards from S6 into a constant temperature and humidity curing room for 7-14 days. After curing, trim the edges of the boards to obtain magnesium oxysulfate boards.

[0017] Furthermore, S2 specifically involves: immersing the basalt fiber mesh completely in an ethanol solution containing 2-3 wt% silane coupling agent for 5-8 minutes, removing it and drying it at 25-30℃ to obtain a pretreated basalt fiber mesh; adding sepiolite fiber to 20-30 parts of deionized water and stirring at 200-300 r / min for 5-10 minutes to obtain a sepiolite fiber suspension.

[0018] Furthermore, S3 specifically involves adding magnesium sulfate heptahydrate to 60-70 parts of deionized water, stirring at 25-40℃ and 300-500 r / min for 10-20 minutes to obtain a magnesium sulfate solution, and letting it stand for 5-10 minutes to remove surface foam before use.

[0019] Furthermore, S4 specifically involves: adding lightly calcined magnesium oxide, calcium sulfate, and hydroxyapatite powder into a mixer and dry-mixing at 500-600 r / min for 2-3 min; then adding tourmaline powder and increasing the speed to 800-1000 r / min while dry-mixing for 3-4 min; heating the magnesium sulfate solution to 40-45℃ at 2-3℃ / min and injecting it into the mixer at a rate of 10-15 mL / min; simultaneously spraying 10-20 parts of deionized water through a spraying device and stirring for 6-8 min to obtain the base slurry.

[0020] Add polycarboxylate superplasticizer and lignosulfonate calcium retarder to the base slurry, reduce the stirring speed to 600-700 r / min and stir for 3-5 min. Inject the pre-mixed sepiolite fiber suspension and plant-based composite foaming agent mixture into the base slurry, increase the stirring speed to 1200-1600 r / min and stir for 3-5 min to obtain the modified slurry. Let it stand for 6-10 min for later use.

[0021] Furthermore, the S5 specifically employs a symmetrical stainless steel double-mold structure. The inner surface of the mold is coated with a high-temperature resistant polytetrafluoroethylene coating with a thickness of 5-10μm. The two molds are preheated to 60-80℃, and the built-in vacuum exhaust channel of the mold is opened simultaneously. The vacuum degree is -0.08MPa to -0.06MPa, and the preheating time is 15-20min. The modified slurry is injected into the lower mold at a rate of 0.5-1.0L / s. When the modified slurry is poured to 1 / 3-1 / 2 of the mold depth, the first layer of pretreated basalt fiber mesh is laid. The slurry is poured to near the top of the mold, and the second layer of basalt fiber mesh is laid. When the plate thickness is >20mm, the number of layers is increased to 3-4. The upper and lower molds are closed, the vacuum channel of the mold is kept open, a pre-pressure of 1-3MPa is applied, and the pressure is held for 5-10min.

[0022] Furthermore, S6 specifically adopts a three-stage gradient heating and pressing mode. In the first stage, the temperature of the dual-mode is raised to 100-120℃ at a rate of 5-8℃ / min, while the pressure is increased to 5-8MPa. Heating and pressurization are carried out simultaneously.

[0023] The second stage involves raising the temperature to 120-150℃ and the pressure to 8-12MPa at a rate of 1-2℃ / min, and holding the pressure for 30-60min.

[0024] In the third stage, the temperature of the dual mold is reduced to 60-70℃ at a rate of 3-5℃ / min, the pressure is maintained at 5-7MPa, and the mold is kept warm and cured for 20-30 minutes. Then, the pressure is released to normal pressure at 0.5-1MPa / min, and the mold is allowed to cool naturally to room temperature before the board is removed.

[0025] Furthermore, S7 specifically involves: sending the boards from S6 into a constant temperature and humidity curing room, with curing conditions of 20-25℃ and 60-75% relative humidity, for 7-14 days. During the curing period, the surface of the boards is sprayed with water to keep them moist every 24 hours. After the curing is completed, the edges of the boards are trimmed to obtain magnesium oxysulfate boards.

[0026] A magnesium oxysulfate sheet produced by the high-temperature dual-mold hot pressing process described above.

[0027] Compared with the prior art, the beneficial effects of this invention are as follows:

[0028] 1. This invention efficiently integrates the molding and curing processes through a high-temperature dual-mold hot-pressing process. The stainless steel dual-mold structure eliminates the need for large-scale stacking space, reducing the requirements for curing chamber area, templates, and the number of curing carts. This significantly lowers the initial investment and long-term operating costs of related equipment, overcoming a key bottleneck that restricts the capacity improvement of traditional processes. Furthermore, the integrated dual-mold production process avoids the uneven slurry distribution problem in traditional assembly line transportation, allowing for simultaneous improvement in production efficiency and capacity stability, making it more suitable for large-scale industrial production needs.

[0029] 2. This invention utilizes a symmetrical dual-mold structure with a built-in vacuum exhaust channel to ensure the modified slurry maintains a uniform pressure and temperature environment throughout the molding process, eliminating differences in curing conditions between the two sides and preventing uneven moisture distribution. The basalt fiber mesh, pretreated with a silane coupling agent, exhibits stronger adhesion to the modified slurry, allowing for flexible adjustment of the number of layers based on the board thickness to form a uniform reinforcing skeleton, effectively suppressing warping and deformation caused by uneven internal stress. Furthermore, the gradient heating and hot-pressing mode achieves precise and simultaneous control of temperature and pressure, ensuring a thorough and uniform slurry hydration reaction, further guaranteeing the consistency and stability of the overall board structure and resolving the pain points of board deformation and uneven performance under traditional processes.

[0030] 3. The stainless steel double mold used in this invention has excellent high temperature resistance, can withstand the internal temperature rise during the curing process of magnesium oxysulfate, avoids mold deformation, and can reduce the adhesion between the slurry and the mold, ensuring that the surface of the plate is flat and smooth after demolding. At the same time, the high surface strength of stainless steel makes it less prone to scratches during cleaning and handling, extends the service life of the mold, reduces the frequency of mold replacement and repair, and reduces production losses. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] Example 1: This example discloses a high-temperature dual-mold hot pressing process for magnesium oxide sulfur sheet, including the following steps:

[0033] S1: By weight, weigh 140 parts lightly calcined magnesium oxide (Shandong Ocean Star Chemical Technology Co., Ltd.), 30 parts magnesium sulfate heptahydrate, 10 parts calcium sulfate, 3 parts tourmaline powder (Lingshou County Quanfeng Mineral Products Processing Plant, 600 mesh), 2 parts sepiolite fiber, 1-4 parts hydroxyapatite powder (50μm), 0.5 parts polycarboxylate superplasticizer (Jinan Quanchi New Materials Co., Ltd.), 0.3 parts retarder calcium lignosulfonate, 0.2 parts silane coupling agent (KH570), 2 layers of basalt fiber mesh (Shandong Qiantong Engineering Materials Co., Ltd., mesh size 25.4mm), and 15 parts plant-based composite foaming agent (a 1:1 molar ratio of tea saponin and saponins, solid content 15%).

[0034] S2: The basalt fiber mesh was completely immersed in an ethanol solution containing 2wt% silane coupling agent for 5 minutes, and then dried at 25°C to obtain a pretreated basalt fiber mesh; sepiolite fiber was added to 20 parts of deionized water and stirred at 200 r / min for 5 minutes to obtain a sepiolite fiber suspension.

[0035] S3: Add magnesium sulfate heptahydrate to 60 parts of deionized water, stir for 10 min at 25℃ and 300 r / min to obtain magnesium sulfate solution, let stand for 5 min to remove surface foam for later use.

[0036] S4: Add lightly calcined magnesium oxide, calcium sulfate, and hydroxyapatite powder to a mixer and dry mix at 500 r / min for 2 min. Then add tourmaline powder, increase the speed to 800 r / min and dry mix for 3 min. Heat the magnesium sulfate solution to 40℃ at 2℃ / min and inject it into the mixer at a rate of 10 mL / min. At the same time, spray 10 parts of deionized water through a spraying device and stir for 6 min to obtain the base slurry.

[0037] Add polycarboxylate superplasticizer and lignosulfonate calcium retarder to the base slurry, reduce the speed to 600 r / min and stir for 3-5 min. Inject the pre-mixed sepiolite fiber suspension and plant-based composite foaming agent mixture into the base slurry, increase the speed to 1200 r / min and stir for 3 min to obtain the modified slurry. Let it stand for 6 min for later use.

[0038] S5: Adopts a symmetrical stainless steel double-mold structure. The inner surface of the mold is sprayed with a high-temperature resistant polytetrafluoroethylene coating with a thickness of 5-6μm. The two molds are preheated to 60℃ respectively, and the built-in vacuum exhaust channel of the mold is opened at the same time. The vacuum degree is -0.08MPa and the preheating time is 15min. The modified slurry is injected into the lower mold at a rate of 0.5L / s. When the modified slurry is poured to 1 / 3 of the mold depth, the first layer of pretreated basalt fiber mesh is laid. The slurry is poured to near the top of the mold, and the second layer of basalt fiber mesh is laid. The upper and lower molds are closed, the vacuum channel of the mold is kept open, and a pre-compression pressure of 1MPa is applied and held for 5min.

[0039] S6: It adopts a three-stage gradient heating and pressing mode. In the first stage, the temperature of the dual-mode is raised to 100℃ at a rate of 5℃ / min, while the pressure is gradually increased to 5MPa at a rate of 1MPa / min. Heating and pressurization are carried out simultaneously.

[0040] The second stage involves raising the temperature to 120°C at a rate of 1°C / min and maintaining the pressure at 8 MPa for 30 minutes.

[0041] In the third stage, the temperature of the dual mold is reduced to 60℃ at a rate of 3℃ / min, the pressure is maintained at 5MPa, and the mold is kept warm and cured for 20 minutes. Then, the pressure is released to normal pressure at 0.5MPa / min, and the mold is allowed to cool naturally to room temperature before the board is removed.

[0042] S7: The boards from S6 are placed in a constant temperature and humidity curing room. The curing conditions are 20℃ and 60% relative humidity for 7 days. During the curing period, the surface of the boards is sprayed with water every 24 hours to keep it moist and ensure that the hydration reaction is complete. After curing, the edges of the boards are trimmed. The trimming dimensional error is controlled within ±0.5mm to finally obtain magnesium oxysulfate boards.

[0043] Example 2: This example discloses a high-temperature dual-mold hot pressing process for magnesium oxide sulfur sheet, including the following steps:

[0044] S1: By weight, weigh 180 parts lightly calcined magnesium oxide, 45 parts magnesium sulfate heptahydrate, 20 parts calcium sulfate, 8 parts tourmaline powder, 6 parts sepiolite fiber, 4 parts hydroxyapatite powder (50μm), 1.2 parts polycarboxylate superplasticizer, 0.8 parts calcium lignosulfonate retarder, 0.5 parts silane coupling agent (KH550), 4 layers of basalt fiber mesh, and 25 parts plant-based composite foaming agent (a 1:1 molar ratio of tea saponin and saponins, with a solid content of 25%).

[0045] S2: The basalt fiber mesh was completely immersed in an ethanol solution containing 3wt% silane coupling agent for 8 minutes, and then dried at 30℃ to obtain the pretreated basalt fiber mesh; the sepiolite fiber was added to 30 parts of deionized water and stirred at 300r / min for 10 minutes to obtain the sepiolite fiber suspension.

[0046] S3: Add magnesium sulfate heptahydrate to 70 parts of deionized water, stir at 40℃ and 500r / min for 20min to obtain magnesium sulfate solution, let stand for 10min to remove surface foam for later use.

[0047] S4: Add lightly calcined magnesium oxide, calcium sulfate, and hydroxyapatite powder to a mixer and dry mix at 600 r / min for 3 min. Then add tourmaline powder, increase the speed to 1000 r / min and dry mix for 4 min. Heat the magnesium sulfate solution to 45℃ at 3℃ / min and inject it into the mixer at a rate of 15 mL / min. At the same time, spray 20 parts of deionized water through a spraying device and stir for 8 min to obtain the base slurry.

[0048] Add polycarboxylate superplasticizer and lignosulfonate calcium retarder to the base slurry, reduce the speed to 700 r / min and stir for 5 min. Inject the pre-mixed sepiolite fiber suspension and plant-based composite foaming agent mixture into the base slurry, increase the speed to 1600 r / min and stir for 5 min to obtain the modified slurry. Let it stand for 10 min for later use.

[0049] S5: Adopts a symmetrical stainless steel double-mold structure. The inner surface of the mold is sprayed with a high-temperature resistant polytetrafluoroethylene coating with a thickness of 8-10μm. The two molds are preheated to 80℃ respectively, and the built-in vacuum exhaust channel of the mold is opened at the same time. The vacuum degree is -0.06MPa and the preheating time is 20min. The modified slurry is injected into the lower mold at a rate of 1.0L / s. When the modified slurry is poured to 1 / 2 of the mold depth, the first layer of pretreated basalt fiber mesh is laid. Continue to pour the slurry to near the top of the mold and lay the second layer of basalt fiber mesh. When the plate thickness is >20mm, the number of layers is increased to 4. Close the upper and lower molds, keep the mold vacuum channel open, apply a pre-compression pressure of 3MPa, and hold the pressure for 10min.

[0050] S6: It adopts a three-stage gradient heating and pressing mode. In the first stage, the temperature of the dual-mode is raised to 120℃ at a rate of 8℃ / min, while the pressure is gradually increased to 8MPa at a rate of 1MPa / min. Heating and pressurization are carried out simultaneously.

[0051] The second stage involves raising the temperature to 150°C at a rate of 2°C / min and maintaining the pressure at 12MPa for 60 minutes.

[0052] In the third stage, the temperature of the dual mold is reduced to 70℃ at a rate of 5℃ / min, the pressure is maintained at 7MPa, the heat is maintained and cured for 30 minutes, the pressure is released to normal pressure at 1MPa / min, the temperature is naturally cooled to room temperature, and the board is taken out.

[0053] S7: The boards from S6 are placed in a constant temperature and humidity curing room. The curing conditions are 25℃ and 75% relative humidity for 14 days. During the curing period, the surface of the boards is sprayed with water every 24 hours to keep it moist and ensure that the hydration reaction is complete. After curing, the edges of the boards are trimmed, and the dimensional error is controlled within ±0.5mm. Finally, the magnesium oxysulfate board is obtained.

[0054] Example 3: This example discloses a high-temperature dual-mold hot pressing process for magnesium oxysulfide sheets, including the following steps:

[0055] S1: By weight, weigh 153 parts lightly calcined magnesium oxide, 36 parts magnesium sulfate heptahydrate, 16 parts calcium sulfate, 6.5 parts tourmaline powder, 4.3 parts sepiolite fiber, 3.6 parts hydroxyapatite powder (50μm), 0.9 parts polycarboxylate superplasticizer, 0.7 parts calcium lignosulfonate retarder, 0.4 parts silane coupling agent (KH560), 3 layers of basalt fiber mesh, and 21 parts plant-based composite foaming agent (a 1:1 molar ratio of tea saponin and saponins, with a solid content of 18%).

[0056] S2: The basalt fiber mesh was completely immersed in an ethanol solution containing 2-3 wt% silane coupling agent for 6 min, and then dried at 27℃ to obtain the pretreated basalt fiber mesh; the sepiolite fiber was added to 27 parts of deionized water and stirred at 270 r / min for 8 min to obtain the sepiolite fiber suspension.

[0057] S3: Add magnesium sulfate heptahydrate to 66 parts of deionized water, stir at 32℃ and 420r / min for 17min to obtain magnesium sulfate solution, let stand for 8min to remove surface foam for later use.

[0058] S4: Add lightly calcined magnesium oxide, calcium sulfate, and hydroxyapatite powder to a mixer and dry mix at 550 r / min for 3 min. Then add tourmaline powder, increase the speed to 940 r / min and dry mix for 3 min. Heat the magnesium sulfate solution to 44℃ at 2℃ / min and inject it into the mixer at a rate of 12 mL / min. At the same time, spray 15 parts of deionized water through a spraying device and stir for 7 min to obtain the base slurry.

[0059] Add polycarboxylate superplasticizer and lignosulfonate calcium retarder to the base slurry, reduce the speed to 660 r / min and stir for 4 min. Inject the pre-mixed sepiolite fiber suspension and plant-based composite foaming agent mixture into the base slurry, increase the speed to 1450 r / min and stir for 4 min to obtain the modified slurry. Let it stand for 8 min for later use.

[0060] S5: Adopts a symmetrical stainless steel double-mold structure. The inner surface of the mold is sprayed with a high-temperature resistant polytetrafluoroethylene coating with a thickness of 5-8μm. The two molds are preheated to 72℃ respectively, and the built-in vacuum exhaust channel of the mold is opened at the same time. The vacuum degree is -0.08MPa and the preheating time is 17min. The modified slurry is injected into the lower mold at a rate of 0.8L / s. When the modified slurry is poured to 1 / 3 of the mold depth, the first layer of pretreated basalt fiber mesh is laid. Continue to pour the slurry to near the top of the mold and lay the second layer of basalt fiber mesh. When the plate thickness is >20mm, the number of layers is increased to 3. Close the upper and lower molds, keep the mold vacuum channel open, apply a pre-compression pressure of 2MPa, and hold the pressure for 8min.

[0061] S6: It adopts a three-stage gradient heating and pressing mode. In the first stage, the temperature of the dual-mode is raised to 112℃ at a rate of 6℃ / min, while the pressure is gradually increased to 5MPa at a rate of 1MPa / min. Heating and pressurization are carried out simultaneously.

[0062] The second stage involves raising the temperature to 136°C and the pressure to 11 MPa at a rate of 2°C / min, and holding the pressure for 52 minutes.

[0063] In the third stage, the temperature of the dual mold is reduced to 68℃ at a rate of 4℃ / min, the pressure is maintained at 6MPa, and the curing is carried out for 28 minutes. Then, the pressure is released to normal pressure at 0.8MPa / min, and the material is allowed to cool naturally to room temperature before being removed.

[0064] S7: The boards from S6 are placed in a constant temperature and humidity curing room. The curing conditions are 22℃ and 70% relative humidity for 10 days. During the curing period, the surface of the boards is sprayed with water every 24 hours to keep it moist and ensure that the hydration reaction is complete. After curing, the edges of the boards are trimmed. The trimming dimensional error is controlled within ±0.5mm to finally obtain magnesium oxysulfate boards.

[0065] Comparative Example 1: The difference between this comparative example and Example 3 is that in S1, the plant-based composite foaming agent contains only tea saponin and does not contain saponins.

[0066] Comparative Example 2: The difference between this comparative example and Example 3 is that tourmaline powder was not added in S4.

[0067] Comparative Example 3: The difference between this comparative example and Example 3 is that in S6, the three-stage gradient heating is replaced by a single-stage heating, that is, directly heating to 136°C and pressure of 11MPa, holding the pressure for 90min, and then depressurizing to atmospheric pressure at 0.8MPa / min and taking out the plate.

[0068] Comparative Example: The difference between this comparative example and Example 3 is that, in S5, ABS / PVC material from the traditional process is used as a template, and the modified slurry is spread evenly on the template surface; in S6, the board is removed after curing at 40°C for 15 hours.

[0069] Experimental Example 1: The compressive strength (MPa) and flexural strength (MPa) of the magnesium oxysulfate sheet prepared by the present invention were tested according to GB / T 30100-2013.

[0070] Experimental Example 2: The surface hardness (H) of the magnesium oxysulfate sheet prepared by this invention was tested according to GB / T 6739-2022 "Determination of Hardness of Paint and Varnish by Pencil Method".

[0071] The results are shown in the table below:

[0072]

[0073] As shown in the table above, the plant-based foaming agent composed of tea saponin and saponins, combined with modified ingredients such as tourmaline powder, makes the internal structure of the board more uniform and dense, and its compressive and flexural strength far exceeds that of the control example of traditional process. The performance of the control example 1 with only tea saponin or the control example 2 without tourmaline powder both showed a slight decline, which confirms the synergistic effect of the compound formula.

[0074] The embodiment using the gradient heating and pressurization mode can avoid stress concentration caused by temperature difference inside the slurry, reduce structural defects, and allow the hydration reaction to be more complete. Therefore, compared with the comparative example 3 which uses a one-stage heating mode, it has better strength and surface hardness.

[0075] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-temperature dual-mold hot pressing process for magnesium oxide sulfur sheet, characterized in that, Includes the following steps: S1: By weight, weigh 140-180 parts of lightly calcined magnesium oxide, 30-45 parts of magnesium sulfate heptahydrate, 10-20 parts of calcium sulfate, 3-8 parts of tourmaline powder, 2-6 parts of sepiolite fiber, 1-4 parts of hydroxyapatite powder, 0.5-1.2 parts of polycarboxylate superplasticizer, 0.3-0.8 parts of lignosulfonate retarder, 0.2-0.5 parts of silane coupling agent, 2-4 layers of basalt fiber mesh, and 15-25 parts of plant-based composite foaming agent obtained by compounding tea saponin and saponins in a molar ratio of 1:1; S2: The basalt fiber mesh is completely immersed in an ethanol solution containing silane coupling agent, then removed and dried to obtain a pretreated basalt fiber mesh; sepiolite fiber is added to deionized water and stirred to obtain a sepiolite fiber suspension. S3: Add magnesium sulfate heptahydrate to deionized water and stir to obtain a magnesium sulfate solution; S4: Add lightly calcined magnesium oxide, calcium sulfate, and hydroxyapatite powder to a mixer and dry mix. Then add tourmaline powder and dry mix. Inject magnesium sulfate solution into the mixer and spray deionized water while mixing to obtain a base slurry. Add polycarboxylate superplasticizer and retarder calcium lignosulfonate to the base slurry and stir. Inject pre-mixed sepiolite fiber suspension and plant-based composite foaming agent mixture into the base slurry and stir to obtain a modified slurry. S5: Adopting a symmetrical stainless steel double mold structure, preheat the two molds to 60-80℃ respectively, open the built-in vacuum exhaust channel of the mold, inject the modified slurry into the lower mold, lay 2-4 layers of pretreated basalt fiber mesh cloth, close the upper and lower molds, apply a pre-compression pressure of 1-3MPa, and hold the pressure for 5-10 minutes. S6: It adopts a three-stage gradient heating and pressing mode. In the first stage, the temperature of the dual-mode is raised to 100-120℃, and the pressure is raised to 5-8MPa. Heating and pressing are carried out simultaneously. The second stage involves holding the pressure at 120-150℃ and 8-12MPa for 30-60 minutes. The third stage involves cooling the temperature to 60-70℃, applying a pressure of 5-7MPa, and maintaining the temperature for 20-30 minutes to cure the material. The material is then removed at room temperature and pressure. S7: Send the boards from S6 into a constant temperature and humidity curing room for 7-14 days. After curing, trim the edges of the boards to obtain magnesium oxysulfate boards.

2. The high-temperature dual-mold hot pressing process for the magnesium oxide sulfur sheet according to claim 1, characterized in that, S2 specifically involves: immersing the basalt fiber mesh completely in an ethanol solution containing 2-3 wt% silane coupling agent for 5-8 minutes, removing it and drying it at 25-30℃ to obtain a pretreated basalt fiber mesh; adding sepiolite fiber to 20-30 parts of deionized water and stirring at 200-300 r / min for 5-10 minutes to obtain a sepiolite fiber suspension.

3. The high-temperature double-mold hot pressing process for the magnesium oxide sulfur sheet according to claim 1, characterized in that, S3 is specifically as follows: Add magnesium sulfate heptahydrate to 60-70 parts of deionized water, stir at 25-40℃ and 300-500r / min for 10-20min to obtain magnesium sulfate solution, let stand for 5-10min to remove surface foam for later use.

4. The high-temperature dual-mold hot pressing process for the magnesium oxide sulfur sheet according to claim 1, characterized in that, S4 specifically involves: adding lightly calcined magnesium oxide, calcium sulfate, and hydroxyapatite powder into a mixer and dry-mixing at 500-600 r / min for 2-3 min; then adding tourmaline powder and increasing the speed to 800-1000 r / min while dry-mixing for 3-4 min; heating the magnesium sulfate solution to 40-45℃ at 2-3℃ / min and injecting it into the mixer at a rate of 10-15 mL / min; simultaneously spraying 10-20 parts of deionized water through a spraying device and stirring for 6-8 min to obtain the base slurry. Add polycarboxylate superplasticizer and lignosulfonate calcium retarder to the base slurry, reduce the stirring speed to 600-700 r / min and stir for 3-5 min. Inject the pre-mixed sepiolite fiber suspension and plant-based composite foaming agent mixture into the base slurry, increase the stirring speed to 1200-1600 r / min and stir for 3-5 min to obtain the modified slurry. Let it stand for 6-10 min for later use.

5. The high-temperature dual-mold hot pressing process for magnesium oxide sulfur sheet according to claim 1, characterized in that, S5 specifically employs a symmetrical stainless steel double-mold structure. The inner surface of the mold is coated with a high-temperature resistant polytetrafluoroethylene coating with a thickness of 5-10μm. The two molds are preheated to 60-80℃, and the built-in vacuum exhaust channel of the mold is opened simultaneously. The vacuum degree is -0.08MPa to -0.06MPa, and the preheating time is 15-20min. The modified slurry is injected into the lower mold at a rate of 0.5-1.0L / s. When the modified slurry is poured to 1 / 3-1 / 2 of the mold depth, the first layer of pretreated basalt fiber mesh is laid. The slurry is poured to near the top of the mold, and the second layer of basalt fiber mesh is laid. When the plate thickness is >20mm, the number of layers is increased to 3-4. The upper and lower molds are closed, the vacuum channel of the mold is kept open, a pre-pressure of 1-3MPa is applied, and the pressure is held for 5-10min.

6. The high-temperature double-mold hot pressing process for magnesium oxide sulfur sheet according to claim 1, characterized in that, Specifically, S6 adopts a three-stage gradient heating and pressing mode. In the first stage, the temperature of the dual-mode is raised to 100-120℃ at a rate of 5-8℃ / min, while the pressure is raised to 5-8MPa. Heating and pressurization are carried out simultaneously. The second stage involves raising the temperature to 120-150℃ and the pressure to 8-12MPa at a rate of 1-2℃ / min, and holding the pressure for 30-60min. In the third stage, the temperature of the dual mold is reduced to 60-70℃ at a rate of 3-5℃ / min, the pressure is maintained at 5-7MPa, and the mold is kept warm and cured for 20-30 minutes. Then, the pressure is released to normal pressure at 0.5-1MPa / min, and the mold is allowed to cool naturally to room temperature before the board is removed.

7. The high-temperature double-mold hot pressing process for magnesium oxide sulfur sheet according to claim 1, characterized in that, S7 specifically involves: sending the boards from S6 into a constant temperature and humidity curing room, with curing conditions of 20-25℃ and 60-75% relative humidity, for 7-14 days. During the curing period, the surface of the boards is sprayed with water to keep them moist every 24 hours. After curing, the edges of the boards are trimmed to obtain magnesium oxysulfate boards.

8. A magnesium oxysulfate sheet produced by the high-temperature dual-mold hot pressing process according to any one of claims 1-7.

Images