Fireproof vacuum glass and production process thereof

Abstract

The invention relates to the field of glass production, and discloses fireproof vacuum glass and a production process thereof.The fireproof vacuum glass comprises an upper-layer glass plate and a lower-layer glass plate which are provided with supports at intervals, and glass solder is arranged on the peripheries of the opposite sides of the upper-layer glass plate and the lower-layer glass plate; the upper-layer glass plate and the lower-layer glass plate are sealed to form vacuum glass with a vacuum chamber, both the upper-layer glass plate and the lower-layer glass plate are made of tempered high borosilicate glass with the thermal expansion coefficient of (4.0-+ / -0.1) * 10 <-6 > K <-1 >, and the thermal expansion coefficient of the glass solder is similar to that of the tempered high borosilicate glass. The fireproof vacuum glass is prepared by using the tempered high borosilicate glass with high temperature resistance as a vacuum glass substrate, and the vacuum glass with the technical effects of heat insulation, fire prevention, lightness, thinness, safety and the like is obtained by combining the characteristics of heat insulation, sound insulation and thin thickness of the vacuum glass and the characteristics of high temperature resistance of the tempered high borosilicate glass; the whole structure is light and thin, the stability is high, the production cost is low, and the technical blank of vacuum glass with a fireproof function in the prior art is filled.

Description

Technical Field

[0001] The invention relates to the technical field of glass production, and in particular to fireproof vacuum glass and a production process thereof. Background Art

[0002] Fireproof glass, as a fireproof vacuum glass and its production process, is an important safety glass and plays a key role in the construction industry. Existing fireproof glass mainly includes four types: fireproof laminated glass, thin-coated fireproof glass, fireproof wired glass and single-piece fireproof glass. Fireproof laminated glass forms a fireproof and heat-insulating layer by compounding multiple pieces of glass with an expanding flame-retardant adhesive or pouring fireproof liquid between the glass. Thin-coated fireproof glass sprays fireproof transparent liquid on the surface to form a dense protective layer when it encounters fire. Fireproof wired glass uses metal wire or mesh to increase the stability of the glass after it breaks and prevent flames from penetrating. Single-piece fireproof glass undergoes physical and chemical treatment to improve its resistance to thermal stress. The above-mentioned composite fireproof glass has problems such as large thickness, low transmittance, high cost and short life. At the same time, the above-mentioned glass is obviously lacking in heat insulation and sound insulation.

[0003] Due to its unique structure, vacuum glass has a cavity between the upper and lower layers of glass, which are sealed on all sides by solder. The vacuum degree inside the cavity is at a set value, the gas is thin, almost in a vacuum state, and the thickness is relatively small. Therefore, vacuum glass has significant advantages in terms of thermal insulation and sound insulation, which can make up for the shortcomings of the above-mentioned fire-resistant glass.

[0004] However, due to the constraints of material selection and production process, there are few related records about vacuum glass with fireproof function in the prior art. In view of this, developing a fireproof vacuum glass and its production process is a technical problem that needs to be solved urgently. Summary of the invention

[0005] The purpose of the present invention is to provide a fireproof vacuum glass and its production process in response to the above problems, so as to achieve the technical effects of heat insulation, fire prevention, lightness, safety, etc. through the tempered high borosilicate glass and vacuum glass structure, thereby overcoming the technical problems in the current production process of vacuum glass with fireproof function.

[0006] The technical solution adopted by the present invention is: A fireproof vacuum glass, comprising an upper glass plate and a lower glass plate, wherein a support is arranged between the upper glass plate and the lower glass plate, glass solder is arranged around the sides opposite to the upper glass plate and the lower glass plate, and the upper glass plate and the lower glass plate are sealed to form a vacuum glass with a vacuum chamber, wherein the thermal expansion coefficient of the upper glass plate and the lower glass plate is (4.0~±0.1)*10 -6 K -1The tempered high borosilicate glass, and the thermal expansion coefficient of the glass solder is close to that of the tempered high borosilicate glass.

[0007] Preferably, an air extraction port for vacuum pumping operation of the vacuum chamber is formed on the upper glass plate. The air extraction port is composed of a through hole penetrating the upper glass plate and a counterbore coaxial with the through hole, and its vertical cross-section is T-shaped.

[0008] Preferably, the support is made of metal material, its height is 0.2 - 0.3 mm, the height of the vacuum chamber is 0.15 - 0.25 mm, and the distance between adjacent supports is preferably 45 - 65 mm.

[0009] A production process of a fireproof vacuum glass, characterized in that: the production process includes the following steps: S1. Prepare glass substrates. Select two pieces of high borosilicate glass. One of them is used as the upper glass plate and first undergoes a drilling operation to form the air extraction port of the upper glass plate. Subsequently, the two glass substrates are tempered to obtain the tempered upper glass plate and the lower glass plate. S2. Coat the glass solder. Uniformly coat the glass solder around the lower glass plate. S3. Place the supports. Place the supports on the lower glass plate according to the preset positions. S4. Assemble and seal the edges. Overlap the upper glass plate on the lower glass plate, and after clamping the two glasses with a fixture, send them into a high-temperature furnace to melt the glass solder and perform high-temperature edge sealing to obtain a semi-finished fireproof vacuum glass. S5. Vacuum pumping. Perform vacuum pumping operation on the vacuum chamber through a vacuum pumping device. S6. Seal the air extraction port. After the vacuum pumping operation reaches the preset vacuum degree, perform a high-temperature sealing operation on the air extraction port. Use a filling material and glass solder to block the air extraction port, and then heat the glass solder through a heating device to make the glass solder flat and formed inside the air extraction port to complete the vacuum glass sealing operation and obtain the finished fireproof vacuum glass.

[0010] Preferably, in the step S4, the high-temperature furnace starts heating from room temperature, the heating rate is 3 - 5 °C / min, heats up to 410 - 470 °C, keeps warm for 3 - 15 min, and then cools to room temperature to solidify the glass solder.

[0011] Preferably, in the step S5, it further includes a step of preheating and exhausting the fireproof vacuum glass before the vacuum pumping operation, so that the air, water molecules, and carbon oxides in the vacuum chamber are heated and exhausted to improve the subsequent vacuum pumping efficiency. The preheating temperature is 180 - 240 °C.

[0012] Preferably, the step S6 further includes a step of performing secondary protection on the air extraction port. After the sealing operation is completed, a sealing sheet is pasted on the air extraction port to achieve double protection of the sealing portion and form a flat seal.

[0013] A method for preparing solder for fireproof vacuum glass, characterized in that it comprises the following steps: Step 1, raw material preparation, weigh the following raw materials in weight proportion: ZnO 0-10.0, P2O5 15.0-32.0, B2O3 1.5-30.0, Al2O3 0-15.0, SnO 0-75.0, Li2O 0-15.0, Na2O 0-10.0, K2O 0-10.0, MgO 0-10.0, CaO 0-10.0, SrO 0-8.5, BaO 0-15.0, WO3 0-8.0, Sb2O3 0-12.0, Fe2O3 0-5.0, PbO 25.0-45.0 and Bi2O3 0-18.0, and fully mix the above raw materials to obtain a mixed material; Step 2: drying: drying the mixed material; Step 3, crushing and grinding, crushing and grinding the dried mixed material to obtain a powdered mixed material; Step 4: melting, melting the powdered mixed material at high temperature to fully melt the powdered mixed material; Step 5: Cooling and solidifying: placing the fully melted mixed material in a room temperature environment, cooling and solidifying it naturally to form a bulk glass solder; Step six, grinding, breaking up the cooled and solidified bulk glass solder and grinding it thoroughly to obtain a finished glass solder product.

[0014] Preferably, in step 2, the drying temperature is 110-130° C., and the drying time is 2-4 hours.

[0015] Preferably, in step 4, the melting temperature is 950-1050° C., and the melting time is 2-4 hours.

[0016] The beneficial effects of the present invention are as follows: The present invention utilizes the high temperature resistance of tempered borosilicate glass as the substrate of vacuum glass to prepare fireproof vacuum glass, combining the characteristics of heat insulation, sound insulation, thin thickness of vacuum glass and high temperature resistance of tempered borosilicate glass, and obtaining a vacuum glass with technical effects such as heat insulation, fire prevention, lightness, and safety. Its overall structure is light and thin, with high stability and low production cost, overcoming the problems of poor heat resistance of ordinary soda-lime glass, difficulty in withstanding high flame temperatures, easy deformation and cracking, as well as the problems of large thickness, low transmittance, high cost, and short lifespan of traditional fireproof glass, filling the technical gap of vacuum glass with fireproof function in the prior art. At the same time, due to the relatively high transmittance of borosilicate glass itself, the transmittance of the fireproof vacuum glass provided by the present invention can reach 85%, with excellent visual effects. At the same time, the glass solder prepared by the method for preparing glass solder provided by the present invention has a thermal expansion coefficient (20 - 300 °C) of (4.25 - 8.0) * 10 -6 K -1 , which is close to the thermal expansion coefficient of tempered borosilicate glass. The sealing temperature is 410 - 470 °C, which can be better applied to the sealing of fireproof vacuum glass. Its chemical stability can reach level 1, which can meet the sealing requirements of fireproof vacuum glass with tempered borosilicate glass as the substrate, effectively improving the problem of easy sealing failure when traditional glass solder is applied to fireproof vacuum glass. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0018] Figure 1 It is a schematic structural diagram of the fireproof vacuum glass of the present invention.

[0019] Figure 2 For Figure 1 top view structural schematic diagram.

[0020] In the figure: 1 - upper glass plate; 2 - lower glass plate; 3 - support; 4 - glass solder; 5 - vacuum chamber; 6 - air extraction port; 61 - through hole; 62 - counterbore; 7 - sealing piece. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0022] The present invention is used to solve the technical problems existing in the current production of fireproof vacuum glass. For example, in terms of substrate selection, ordinary soda-lime glass can hardly withstand the high temperature of fire, is prone to deformation and cracking, and the safety performance cannot be guaranteed. While using high-borosilicate fireproof glass as the substrate, there are still problems such as difficult sealing and easy sealing failure.

[0023] As Figure 1-2 shown, the present invention provides a fireproof vacuum glass, which includes an upper glass plate 1 and a lower glass plate 2. A support 3 is arranged at intervals between the upper glass plate 1 and the lower glass plate 2. Glass solder 4 is arranged around the opposite sides of the upper glass plate 1 and the lower glass plate 2 to seal and connect the upper glass plate 1 and the lower glass plate 2 to form a vacuum glass with a vacuum chamber 5. Both the upper glass plate 1 and the lower glass plate 2 are made of tempered high-borosilicate glass with a thermal expansion coefficient of (4.0~±0.1)*10 -6 K -1 and have fireproof performance. The thermal expansion coefficient of the glass solder 4 is close to that of the tempered high-borosilicate glass, so as to improve the problem that the traditional glass solder 4 is prone to sealing failure.

[0024] In this embodiment, the fireproof vacuum glass is prepared by using the high-temperature resistance of tempered high-borosilicate glass as the substrate of the vacuum glass, combining the heat insulation, sound insulation, thin thickness of the vacuum glass and the high-temperature resistance of the tempered high-borosilicate glass, and obtaining a vacuum glass with technical effects such as heat insulation, fire prevention, lightness, and safety. Its overall structure is light and thin, has high stability, and low production cost, overcoming the problems of poor heat resistance of ordinary soda-lime glass, difficulty in withstanding high flame temperature, easy deformation and cracking, and the problems of large thickness, low transmittance, high cost, and short life of traditional fireproof glass. It fills the technical gap of fireproof vacuum glass in the prior art. At the same time, due to the relatively high transmittance of the high-borosilicate glass itself, the transmittance of the fireproof vacuum glass provided by the present invention can reach 85%, and the visual effect is excellent.

[0025] As a preferred embodiment, as Figure 1 shown, an air extraction port 6 for vacuuming the vacuum chamber 5 is opened on the upper glass plate 1. The air extraction port 6 is composed of a through hole 61 penetrating the upper glass plate 1 and a counterbore 62 coaxial with the through hole 61, and its vertical cross-section is T-shaped, which is beneficial to the sealing operation of the air extraction port 6 and improves the sealing strength.

[0026] Preferably, the support 3 is made of metal, and its height is preferably 0.2 - 0.3 mm. The height of the vacuum chamber 5 is preferably 0.15 - 0.25 mm. The height of the vacuum chamber 5 is slightly lower than that of the support 3, so that the support 3 can firmly press between the upper glass plate 1 and the lower glass plate 2, avoiding the displacement of the support 3 and ensuring the support strength. The distance between adjacent supports 3 is preferably 45 - 65 mm. While ensuring the support strength, the number of supports 3 per unit area is reduced, the visibility of the supports 3 is reduced, and the aesthetics is improved. Preferably, the coating width of the glass solder 4 is 5 - 10 mm.

[0027] The production process of the fireproof vacuum glass includes the following steps: S1. Prepare glass substrates. Select two pieces of borosilicate glass. One of them, as the upper glass plate 1, is first perforated to form the air extraction port 6 of the upper glass plate 1. Subsequently, the two glass substrates are tempered to obtain the tempered upper glass plate 1 and the lower glass plate 2. S2. Coat the glass solder 4. Uniformly coat the glass solder 4 around the lower glass plate 2. S3. Place the supports 3. Place the supports 3 on the lower glass plate 2 at the preset positions. S4. Laminating and edge sealing. Place the upper glass plate 1 overlapping on the lower glass plate 2, and clamp the two pieces of glass with a fixture and then send them into a high-temperature furnace to melt the glass solder 4 for high-temperature edge sealing to obtain a semi-finished fireproof vacuum glass. Preferably, start heating from room temperature, with a heating rate of 3 - 5 °C / min, heat up to 410 - 470 °C, keep warm for 3 - 15 min and then cool to room temperature to solidify the glass solder 4.

[0028] S5. Evacuate the air. Perform an evacuation operation on the vacuum chamber 5 through an evacuation device.

[0029] S6. Seal the air extraction port 6. After the evacuation operation reaches the preset vacuum degree, perform a high-temperature sealing operation on the air extraction port 6. Use a filling material and the glass solder 4 to block the air extraction port 6, and then heat the glass solder 4 through a heating device to make the glass solder 4 flat and formed inside the air extraction port 6 to complete the vacuum glass sealing operation and obtain the finished fireproof vacuum glass.

[0030] Preferably, in the step S5, it further includes a step of preheating and exhausting the fireproof vacuum glass before the evacuation operation, so that the air, water molecules and carbon oxides in the vacuum chamber 5 are heated and exhausted, improving the subsequent evacuation efficiency. The preheating temperature is preferably 180 - 240 °C.

[0031] Preferably, the step S6 further includes a step of performing secondary protection on the air extraction port 6. After the sealing operation is completed, a sealing sheet 7 is pasted on the air extraction port 6 to achieve double protection of the sealing portion and form a flat seal.

[0032] In order to improve the sealing reliability, the present invention also provides a glass solder 4 suitable for use in fireproof vacuum glass. The preparation method of the glass solder 4 comprises the following steps: Step 1, raw material preparation, weigh the following raw materials in weight proportion: ZnO 0-10.0, P2O5 15.0-32.0, B2O3 1.5-30.0, Al2O3 0-15.0, SnO 0-75.0, Li2O 0-15.0, Na2O 0-10.0, K2O 0-10.0, MgO 0-10.0, CaO 0-10.0, SrO 0-8.5, BaO 0-15.0, WO3 0-8.0, Sb2O3 0-12.0, Fe2O3 0-5.0, PbO 25.0-45.0 and Bi2O3 0-18.0, and fully mix the above raw materials to obtain a mixed material; Step 2: drying: drying the mixed material, preferably at a temperature of 110-130°C and a drying time of 2-4 hours; Step 3, crushing and grinding, crushing and grinding the dried mixed material to obtain a powdered mixed material; Step 4: Melting: Melting the powdery mixed material at high temperature, preferably at a melting temperature of 950-1050° C. for 2-4 hours, to fully melt the powdery mixed material.

[0033] Step 5: Cooling and solidifying: placing the fully melted mixture in a room temperature environment, cooling and solidifying naturally to form a bulk glass solder 4.

[0034] Step six: grinding: breaking the cooled and solidified bulk glass solder 4 and grinding it thoroughly to obtain a finished glass solder 4.

[0035] The thermal expansion coefficient (20-300°C) of the glass solder 4 provided by the present invention is (4.25~8.0)*10 -6 K -1 , which is similar to the thermal expansion coefficient of tempered borosilicate glass, can meet the sealing requirements of fire-proof vacuum glass with tempered borosilicate glass as the substrate, and effectively improves the problem of sealing failure that is prone to occur when traditional glass solder 4 is used in fire-proof vacuum glass.

[0036] The following are specific examples of different raw material component contents: First Embodiment, the raw materials in parts by weight taken in Step 1 are: ZnO 1.0 - 3.0, P2O5 15.0 - 19.0, B2O3 1.5 - 10.0, Al2O3 1.0 - 5.0, SnO 10.0 - 35.0, Li2O 0.5 - 5.0, Na2O 0.5 - 5.0, K2O 0.5 - 5.0, MgO 0.5 - 5.0, CaO 0.5 - 5.0, SrO 0.5 - 2.5, BaO 0.5 - 4.0, WO3 0.5 - 2.0, Sb2O3 0.5 - 3.0, Fe2O3 0.5 - 1.0, PbO 25.0 - 28.0, and Bi2O3 0.5 - 4.0.

[0037] Second Embodiment, the raw materials in parts by weight taken in Step 1 are: ZnO 8.0 - 10.0, P2O5 15.0 - 28.0, B2O3 20.0 - 30.0, Al2O3 4.0 - 14.0, SnO 5.0 - 25.0, Li2O 0.5 - 5.0, Na2O 0.5 - 5.0, K2O 0.5 - 5.0, MgO 0.5 - 5.0, CaO 0.5 - 5.0, SrO 2.0 - 4.0, BaO 0.5 - 4.0, WO3 0.5 - 3.0, Sb2O3 3.0 - 8.0, Fe2O3 1.0 - 5.0, PbO 30.0 - 45.0, and Bi2O3 4.0 - 8.0.

[0038] Table 1 First Embodiment Second Embodiment <![CDATA[Coefficient of expansion (*10 -6 K -1 )]]> 6.2-7.3 4.35-4.8 Sealing Temperature (°C) 454-466 408-419 Chemical Stability Level 1 Level 1 Table 1 describes the performance parameters of the glass solder 4 prepared by the first and second embodiments with different raw material components and the same preparation method. Among them, the coefficient of thermal expansion is measured according to "Test Method for Average Coefficient of Linear Thermal Expansion of Electronic Glass (SJT11036 - 1996 (GB9622.2 - 1988))"; the sealing temperature is measured according to "Test Method for Softening Point of Electronic Glass (SJ / T11038 - 1996)"; and the chemical stability is measured according to "Test Method for Chemical Stability of Electronic Glass Against Water (SJ / T 11035 - 1996)".

[0039] It can be seen that by adjusting the content of raw material components within a certain range, the present invention can obtain glass solders 4 with different sealing temperatures and coefficients of thermal expansion. The coefficient of thermal expansion (20 - 300 °C) is (4.25 - 8.0) * 10 -6 K -1; The sealing temperature is 410 - 470 °C, and its chemical stability can reach Grade 1, indicating good chemical stability. Among them, the glass solder 4 prepared in the second embodiment has a lower sealing temperature compared to the first embodiment, and its coefficient of thermal expansion is closer to that of tempered high borosilicate glass, making it more suitable for the sealing of fireproof vacuum glass.

[0040] The specific embodiments of the present invention disclosed above are only examples, but the present invention is not limited thereto. For those of ordinary skill in the art, any modifications made without departing from the principles of the present invention shall be considered as falling within the scope of protection of the present invention.

Claims

1. A fireproof vacuum glass, characterized in that: The invention comprises an upper glass plate (1) and a lower glass plate (2), wherein a support (3) is arranged between the upper glass plate (1) and the lower glass plate (2), and glass solder (4) is arranged around the sides opposite to the upper glass plate (1) and the lower glass plate (2), and the upper glass plate (1) and the lower glass plate (2) are sealed to form a vacuum glass having a vacuum chamber (5), wherein the upper glass plate (1) and the lower glass plate (2) are both selected to have a thermal expansion coefficient of (4.0~±0.1)*10 -6 K -1 The glass solder (4) has a thermal expansion coefficient similar to that of the tempered high borosilicate glass.

2. The fireproof vacuum glass according to claim 1, characterized in that: The upper glass plate (1) is provided with an exhaust port (6) for evacuating the vacuum chamber (5); the exhaust port (6) is composed of a through hole (61) penetrating the upper glass plate (1) and a countersunk hole (62) coaxial with the through hole (61); and its vertical cross section is T-shaped.

3. The fireproof vacuum glass according to claim 1, characterized in that: The support (3) is made of metal and has a height of 0.2-0.3 mm. The height of the vacuum chamber (5) is 0.15-0.25 mm. The spacing between adjacent supports (3) is preferably 45-65 mm.

4. The production process of a fireproof vacuum glass according to claim 1, characterized in that: The production process comprises the following steps: S1, preparing glass substrates, selecting two pieces of high borosilicate glass, one of which is used as an upper glass plate (1) and firstly punching a hole to form an air evacuation port (6) of the upper glass plate (1), and then tempering the two glass substrates to obtain a tempered upper glass plate (1) and a lower glass plate (2); S2, applying glass solder (4), and evenly applying the glass solder (4) around the lower glass plate (2); S3, placing the support (3), placing the support (3) on the lower glass plate (2) at a preset position; S4, assembling and edge sealing, placing the upper glass plate (1) on top of the lower glass plate (2), clamping the two glass plates with a clamp and then sending them into a high-temperature furnace to melt the glass solder (4), and performing high-temperature edge sealing to obtain a fire-resistant vacuum glass semi-finished product; S5, evacuating the vacuum chamber (5) by using a vacuuming device; S6, sealing the exhaust port (6). After the vacuum operation reaches a preset vacuum degree, the exhaust port (6) is sealed at high temperature, and the exhaust port (6) is sealed with a filling material and a glass solder (4). The glass solder (4) is then heated by a heating device so that the glass solder (4) is flattened and formed in the exhaust port (6). The vacuum glass sealing operation is completed, and a fireproof vacuum glass product is obtained.

5. The production process according to claim 4, characterized in that: In step S4, the high temperature furnace is heated from room temperature at a heating rate of 3-5°C / min to 410-470°C, kept at this temperature for 3-15 minutes, and then cooled to room temperature to solidify the glass solder (4).

6. The production process according to claim 4, characterized in that: The step S5 also includes a step of preheating and exhausting the fireproof vacuum glass before the vacuuming operation, so that the air, water molecules and carbon oxides in the vacuum chamber (5) are discharged by heat, thereby improving the subsequent vacuuming efficiency, and the preheating temperature is 180-240°C.

7. The production process according to claim 4, characterized in that: The step S6 also includes a step of performing secondary protection on the air extraction port (6). After the sealing operation is completed, a sealing sheet (7) is pasted on the air extraction port (6) to achieve double protection of the sealing portion and form a flat seal.

8. The method for preparing solder for fireproof vacuum glass according to claim 1, characterized in that: The steps include: Step 1, raw material preparation, weigh the following raw materials in weight proportion: ZnO 0-10.0, P2O5 15.0-32.0, B2O3 1.5-30.0, Al2O3 0-15.0, SnO 0-75.0, Li2O 0-15.0, Na2O 0-10.0, K2O 0-10.0, MgO 0-10.0, CaO 0-10.0, SrO 0-8.5, BaO 0-15.0, WO3 0-8.0, Sb2O3 0-12.0, Fe2O3 0-5.0, PbO 25.0-45.0 and Bi2O3 0-18.0, and fully mix the above raw materials to obtain a mixed material; Step 2: drying: drying the mixed material; Step 3, crushing and grinding, crushing and grinding the dried mixed material to obtain a powdered mixed material; Step 4: melting, melting the powdered mixed material at high temperature to fully melt the powdered mixed material; Step 5: Cooling and solidifying: placing the fully melted mixed material in a room temperature environment, cooling and solidifying it naturally, to form a bulk glass solder (4); Step six: grinding, breaking the cooled and solidified bulk glass solder (4) into pieces and grinding them thoroughly to obtain a finished glass solder (4).

9. The method for preparing solder according to claim 8, characterized in that: In the step 2, the drying temperature is 110-130° C. and the drying time is 2-4 hours.

10. The method for preparing solder according to claim 8, characterized in that: In the step 4, the melting temperature is 950-1050° C. and the melting time is 2-4 hours.

Images