Zero-expansion glass-ceramic, casting method and device

Abstract

This application provides a zero-expansion microcrystalline glass, a casting method, and an apparatus. The apparatus includes: a melting furnace, comprising a first furnace body and a gas pressure control device, a water cooling device, and a glass melt outlet disposed therein; a casting auxiliary furnace, comprising a second furnace body and a glass melt inlet, a mold chamber, an in-furnace zone temperature control device, a furnace bottom zone cooling device, a lifting mechanism, a flow monitoring device, and a control device disposed therein; the in-furnace zone temperature control device is used to control the temperature of at least two zones of the upper part of the casting glass in a gradient heating from the inside to the outside; the furnace bottom zone cooling device is used to cool at least two zones of the bottom part of the casting glass in a gradient heating from the inside to the outside; and a flow channel for connecting the melting furnace and the casting auxiliary furnace. The method provided in this application significantly improves the intrinsic quality, surface smoothness, and uniformity of the glass through precise bidirectional temperature field control at the upper and lower parts, gas pressure-assisted casting, coordinated control of flow rate and liquid level, and multi-stage bubble removal technology.

Description

Technical Field

[0001] This application belongs to the field of special glass preparation technology, specifically relating to a casting method, apparatus and application of large-size zero-expansion microcrystalline glass, which is particularly suitable for the large-size preform forming process of zero-expansion microcrystalline glass. It can be widely used in high-end equipment manufacturing fields with extremely high requirements for thermal expansion coefficient, internal defects and dimensional accuracy, such as precision optical instruments, semiconductor lithography equipment, aerospace structural parts, and astronomical telescope lenses. Background Technology

[0002] Zero-expansion glass-ceramics are special functional materials that achieve a near-zero coefficient of thermal expansion by uniformly precipitating specific functional micro- and nano-crystalline phases within a glass matrix through controlled crystallization technology. They combine the transparency of glass with the high strength and near-zero thermal expansion of ceramics, maintaining high dimensional stability even under extreme temperature variations. This makes them an indispensable core material in high-end precision manufacturing. With the rapid development of semiconductor lithography, large-aperture astronomical optics, aerospace, and other fields, the dimensional requirements for zero-expansion glass-ceramics are constantly increasing, necessitating the fabrication of large-size monolithic blanks with side lengths exceeding 1500 mm. However, the casting process for large-size blanks is the core bottleneck restricting their industrialization. The performance of these materials is highly dependent on the precise control of the molding process, and casting is the key process for fabricating large-size, highly uniform zero-expansion glass-ceramic products. Its technological level directly determines the dimensional accuracy, internal quality, and performance consistency of the finished product.

[0003] The core logic of the casting process is to cool molten glass (typically at temperatures as high as 1550-1680℃) appropriately and then inject it into a precast mold through a specific casting device. Cooling and solidification occur within the mold, ultimately forming a preform with the desired shape and properties. However, the unique composition (typically Al2O3 and SiO2 content ≥80wt%) and thermodynamic properties of zero-expansion glass-ceramics impose stringent requirements on the stability of the casting process: Firstly, the viscosity of the molten glass is sensitive to temperature changes, requiring good fluidity at high temperatures to ensure complete filling while avoiding component segregation during casting; secondly, due to the high temperature and high viscosity of zero-expansion glass-ceramics, traditional gravity-flow casting methods have poor fluidity, easily leading to problems such as uneven casting and inconsistent flow rates. Furthermore, uncontrollable microbubbles remaining in the molten glass are difficult to remove effectively, ultimately forming bubble defects within the glass preform, severely affecting its optical performance and structural strength. While existing technologies employ mechanical stirring or static clarification for defoaming, their effectiveness is limited for high-flow-rate, high-viscosity molten glass, and they cannot eliminate micro-bubbles generated during casting. Traditional casting devices often use a single flow channel structure, where molten glass flows directly into the mold after exiting the furnace, lacking a precise control mechanism for flow rate and velocity. Since the fluidity of high-temperature molten glass is significantly affected by temperature, a single flow channel structure easily leads to fluctuations in the flow rate during casting, resulting in uneven filling within the mold and problems such as localized material shortages or overfilling. Thirdly, achieving zero expansion characteristics depends on a precise crystallization process, and crystallization behavior is directly related to the temperature field distribution and cooling rate after casting. Uneven temperature fields easily lead to internal stress concentration and inconsistent crystalline phases, ultimately causing product cracking and deviations in the coefficient of thermal expansion from the design value. After large-size molten glass is poured, the top surface area is large, and the heat loss rate at the edges is much faster than that in the center. This results in an uneven temperature field at the top, with a high temperature at the center and a low temperature at the edges. This can easily cause problems such as warping of the top surface of the glass blank, stress concentration, and uneven crystallization. In subsequent heat treatment, cracking and deformation are very likely to occur, making it impossible to guarantee the overall flatness of large-size glass. Existing casting furnaces only use single or double temperature zone control, which cannot specifically compensate for edge heat loss and have insufficient temperature field control precision. Fourth, the interaction between high-temperature molten glass and the mold needs to be strictly controlled. It is necessary to avoid the high-temperature molten glass reacting with the mold to avoid contamination or bubble defects, and to ensure the smoothness of the demolding process to prevent product damage caused by stress release during demolding. After the molten glass is poured into the bottom mold, the temperature at the contact point between the high-temperature molten glass and the mold is too high, and the gas dissolved inside the molten glass is easy to precipitate and form bubbles. Moreover, the bubbles will continue to rise under the action of high-temperature buoyancy, penetrating the glass blank to form through-bubble defects. If the mold temperature is simply reduced, although the generation of bubbles can be reduced, it will cause the fluidity of the molten glass to drop sharply, making it impossible to spread evenly in the mold, resulting in local accumulation and uneven thickness, making it difficult to achieve uniform molding of large-size glass.Existing technologies cannot simultaneously suppress bottom bubbles and achieve smooth glass molten material, and temperature difference control lacks precision. Fifth, the structural design of the casting device must balance stable glass molten material delivery, filling efficiency, and forming accuracy. In traditional casting processes, the glass molten flow rate and mold descent speed cannot be precisely matched. As the casting process continues, the glass molten material level rises, and the height difference between the pouring nozzle and the surface changes continuously. During the descent, the glass molten material is prone to vibration, splashing, and flow marks, which can trap air into the glass molten material, forming numerous irregular bubbles. The greater the height difference fluctuation, the more severe the bubble defects. This problem is particularly prominent for large-size glass casting, which involves long casting times and large flow rate fluctuations. Existing casting devices only focus on top or bottom temperature field control, failing to achieve bidirectional coordinated control of the top and bottom cooling zones. This results in an uneven temperature gradient across the entire glass preform, leading to uneven internal stress distribution, poor consistency in zero-expansion performance, and insufficient yield of large-size preforms.

[0004] Therefore, there is an urgent need to develop a method and apparatus that can comprehensively solve the casting defects of large-size zero-expansion microcrystalline glass. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a casting method, apparatus, and application for large-size zero-expansion microcrystalline glass. By employing air-pressure assisted casting, microbubble removal via platinum filter, top three-layer incremental temperature control, bottom three-layer gradient cooling control, and precise matching of casting flow rate and mold descent speed, the invention comprehensively solves problems such as bubble defects, uneven temperature field, and poor forming during the casting process of large-size zero-expansion microcrystalline glass. This results in the production of large-size, ultra-low-defect, and highly uniform zero-expansion microcrystalline glass preforms, improving product yield and performance stability, and meeting the application needs of high-end fields.

[0006] To achieve the above objectives, the present invention adopts the following technical solution.

[0007] In a first aspect, a casting apparatus for large-size zero-expansion microcrystalline glass is provided, comprising: A melting furnace, including a first furnace body and a gas pressure control device, a water cooling device and a glass melt outlet disposed therein; The casting auxiliary furnace includes a second furnace body and a glass melt inlet, a mold chamber, an in-furnace zone temperature control device, a furnace bottom zone cooling device, a lifting mechanism, a flow monitoring device, and a control device disposed within the furnace body; the mold chamber is mounted on the lifting mechanism; the in-furnace zone temperature control device is used to control the temperature of at least two zones of the upper part of the casting glass that are gradually heated from the inside to the outside; the furnace bottom zone cooling device is used to cool at least two zones of the bottom part of the casting glass that are gradually heated from the inside to the outside; the control device is used to control the lifting mechanism to move up and down based on the glass melt flow rate; The flow channel is used to connect the smelting furnace and the casting auxiliary furnace.

[0008] In one possible implementation, the device further includes a wire mesh and a filter screen; the wire mesh is disposed on a furnace bottom zoned cooling device; and the filter screen is disposed at the glass melt outlet.

[0009] In one possible implementation, the furnace zone temperature control device includes two or more independent zone heating and temperature control units; the temperature of the central temperature zone is 1250℃~1300℃, and the temperature increases outward from the central temperature zone, with a temperature gradient of 50-100℃.

[0010] Furthermore, the furnace bottom zone cooling device includes two or more independent zone cooling units; each zone cooling unit includes a cooling channel with built-in cooling medium, and zone gradient cooling is achieved by controlling the flow rate of the cooling medium; the zone cooling unit corresponds to the temperature zone of the zone heating and temperature control unit, and the temperature difference between the corresponding temperature zones is 300-650℃.

[0011] In one possible implementation, the control device is used to calculate the descent speed of the mold cavity based on the glass melt flow rate and the effective pouring area of ​​the mold cavity, and control the lifting mechanism to raise and lower, so as to ensure that the distance between the glass melt inlet end face and the glass melt surface in the mold cavity is relatively constant.

[0012] Secondly, a method for casting large-size zero-expansion microcrystalline glass is provided, comprising the following steps: The high-temperature, high-viscosity glass melt is defoamed to obtain the first glass melt; The first molten glass is pressurized with a protective gas to obtain thrust, and then filtered under the action of thrust to obtain the second molten glass. The second molten glass is injected into the mold cavity to form the casting glass; the temperature of the upper part of the casting glass is controlled in sections, and the temperature of the bottom part of the casting glass is cooled in sections. The descent speed of the mold cavity is controlled based on the pouring flow rate of the second molten glass. After heat treatment and annealing, the finished product is obtained.

[0013] In one possible implementation, the upper temperature of the cast glass is controlled in zones, including: The upper part of the casting glass is divided into at least two temperature-controlled zones from the inside out; The temperature control zones are set with a temperature range that increases gradually from the inside out; wherein, the temperature of the central temperature control zone is 1250℃~1300℃, and the temperature gradient is 50-100℃.

[0014] In one possible implementation, the bottom of the cast glass is cooled in sections, including: The bottom of the casting glass is divided into cooling zones from the inside out, the same number as the number of temperature zones in the zoned temperature control. The cooling zones are subjected to gradient cooling by setting cooling media with different flow rates, so that the temperature difference between the corresponding zone temperature control zone and the cooling zone is 300~650℃.

[0015] In one possible implementation, controlling the descent speed of the mold cavity based on the pouring flow rate of the second molten glass includes: Obtain the glass melt flow rate Q and the effective pouring area S of the mold; Calculate the mold descent speed V, V = Q / S; The descent speed of the mold cavity is controlled based on the mold descent speed V.

[0016] Thirdly, a large-size zero-expansion microcrystalline glass is provided, which is prepared using the method described in the first aspect.

[0017] Compared with the prior art, this application has the following beneficial effects: 1. Comprehensive elimination of bubble defects: Through four technologies, including air pressure-assisted glass melt flow promotion, platinum filter online defoaming, constant height difference to avoid air entrapment, and bottom gradient cooling to inhibit bubble growth, multi-stage removal of bubble defects is achieved. The resulting large-size zero-expansion microcrystalline glass has no bubbles larger than 30μm in diameter inside, and the bubble defect rate is reduced to below 0.1%, which is far superior to traditional processes.

[0018] 2. Significantly improved temperature field control precision: The three-layer increasing temperature zone at the top and the three-layer gradient cooling zone at the bottom work together to control the overall temperature difference of the large-size glass blank within ±5℃, and the temperature difference between the top and bottom is precisely controlled between 300℃ and 650℃, completely solving the problems of low temperature field at the edge and many bubbles at the bottom. The surface of the glass blank is flat and the internal stress is uniform.

[0019] 3. Excellent stability in large-size molding: The glass melt flow rate and mold descent speed are precisely matched, and the pouring process is stable and without fluctuations. It can successfully prepare integral zero-expansion microcrystalline glass preforms with a side length of ≥1500mm, without problems such as local accumulation, uneven thickness, cracking and deformation. The yield of large-size preforms has been increased from less than 30% in the traditional way to more than 90%.

[0020] 4. Significantly improved glass properties: The thermal expansion coefficient of the prepared zero-expansion microcrystalline glass is ≤ ±0.05×10⁻⁶. -7 / ℃ (0℃~50℃), flexural strength ≥220 MPa, stress birefringence ≤3 nm / cm, all performance indicators meet the stringent requirements of high-end fields, and the zero expansion performance is consistent.

[0021] 5. Strong process adaptability and industrialization: The casting method and device of the present invention have a high degree of automation, the process parameters can be precisely controlled, it is suitable for casting zero-expansion microcrystalline glass with different components, the device has a reasonable structure, is easy to maintain, and the waste heat recovery system reduces energy consumption, thus possessing the conditions for large-scale industrial production.

[0022] 6. Wide range of applications: The large-size zero-defect microcrystalline glass prepared can meet the core needs of high-end fields such as semiconductor lithography, large-aperture optics, and aerospace, breaking the foreign technology monopoly and filling the technological gap in high-quality casting of large-size zero-expansion microcrystalline glass in China. Attached Figure Description

[0023] Figure 1 A schematic diagram of the overall structure of the large-size zero-expansion microcrystalline glass casting device provided in the embodiments of this application; Figure 1 In the middle: 100-melting furnace, 101-air inlet pipe, 102-air outlet pipe, 103-water cooling device, 104-top cover, 105-crucible, 106-molten glass, 107-molten glass outlet, 108-filter screen, 109-molten glass gate; Figure 2 This is a top view of the temperature zone distribution at the top of the casting auxiliary furnace provided in an embodiment of this application; Figure 2 In the middle: 200-casting auxiliary furnace, 201-glass melt inlet, 202-mold chamber, 203-furnace internal zone temperature control device, 204-furnace bottom zone cooling device, 205-lifting mechanism, 206-cast glass, 207-wire mesh; Figure 3 This is a schematic flowchart illustrating the casting method for large-size zero-expansion microcrystalline glass provided in an embodiment of this application. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0026] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this technology based on the specific circumstances.

[0027] In the description of this application, spatial relation terms such as "below," "under," "below," "below," "above," "over," etc., are used herein to describe the relationship between one element or feature shown in the figures and other elements or features. It should be understood that, in addition to the orientation shown in the figures, spatial relation terms also include different orientations of the device in use and operation. For example, if the device in the figures is flipped, an element or feature described as "below" or "under" or "below" of other elements or features will be oriented "above" other elements or features. Therefore, the exemplary terms "below" and "under" can include both upper and lower orientations. Furthermore, the device may also include other orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptive terms used herein are interpreted accordingly.

[0028] In the description of this application, the term "for example" is used to mean "used as an example, illustration, or description." Any embodiment described as "for example" in this application is not necessarily to be construed as being more preferred or advantageous than other embodiments. The following description is provided to enable any person skilled in the art to make and use this application. Details are set forth in the following description for purposes of explanation. It should be understood that those skilled in the art will recognize that this application can be made without using these specific details. In other instances, well-known structures and processes will not be described in detail to avoid unnecessarily obscuring the description of this application. Therefore, this application is not intended to be limited to the embodiments shown, but is consistent with the broadest scope of the principles and features disclosed in this application.

[0029] Currently, the manufacturing of existing large-size zero-expansion microcrystalline glass faces technical problems such as uneven internal stress distribution, poor consistency of zero-expansion performance, and insufficient yield of large-size preforms.

[0030] In view of this, this application provides a zero-expansion microcrystalline glass, a casting method, and an apparatus.

[0031] See Figure 1 , 2 The present application provides a casting apparatus for large-size zero-expansion microcrystalline glass, comprising: The melting furnace 100 includes a first furnace body and a gas pressure control device, a water cooling device 103 and a glass melt outlet 107 disposed therein; The casting auxiliary furnace 200 includes a second furnace body and a glass melt inlet 201, a mold chamber 202, an in-furnace zone temperature control device 203, a furnace bottom zone cooling device 204, a lifting mechanism 205, a flow monitoring device, and a control device disposed within the furnace body. The mold chamber 202 is mounted on the lifting mechanism 205. The in-furnace zone temperature control device 203 is used to control the temperature of at least two zones of the upper part of the casting glass 206, which are gradually heated from the inside to the outside. The furnace bottom zone cooling device 204 is used to cool at least two zones of the bottom part of the casting glass 206, which are gradually heated from the inside to the outside. The control device is used to control the lifting mechanism to move up and down based on the glass melt flow rate. The flow channel is used to connect the smelting furnace and the casting auxiliary furnace.

[0032] In one possible implementation, the first furnace body includes a top cover 104 and a main body. The top cover 104 is equipped with a water-cooling device 103, which is a pipeline with a valve. The gas pressure control device includes an inlet pipe 101 and an outlet pipe 102, which are inserted from the top cover into the main body of the first furnace body. The gas pressure control device is used to introduce protective gas to prevent air from mixing in, while simultaneously generating a pressure thrust on the molten glass.

[0033] In one possible implementation, the molten glass outlet 107 is located at the bottom of the first furnace body, and a removable filter screen 108 is provided in the molten glass outlet 107.

[0034] Furthermore, the filter screen 108 is made of platinum-rhodium alloy with a rhodium content of 10%~15%, a pore size of 0.1~1mm, and a porosity of 40%~60%.

[0035] Furthermore, the glass liquid outlet 107 is also equipped with a glass liquid valve 109.

[0036] Specifically, the platinum filter is fixed inside the pouring channel by a high-temperature resistant clamp. The clamp is made of ceramic material to avoid reaction with the molten glass. The platinum filter fits seamlessly with the inner wall of the pouring channel to prevent the molten glass from flowing around the filter from the side.

[0037] In one possible implementation, the furnace zone temperature control device 203 includes two or more independent zone heating and temperature control units; the temperature of the central temperature zone is 1250℃~1300℃, and the temperature increases outward from the central temperature zone, with a temperature gradient of 50-100℃.

[0038] Furthermore, the partitioned heating temperature control unit includes a heating module and a temperature sensor.

[0039] Specifically, the heating module is used to provide a heat source, including electric heating, combustion heat, etc.

[0040] Specifically, the furnace zone temperature control device 203 includes three independent zone heating temperature control units.

[0041] For example, all three heating modules use silicon molybdenum rod heating elements, which are evenly distributed in a ring. The heating power of the outer ring heating module is greater than that of the middle ring, and the middle ring is greater than that of the inner ring. The power ratio is inner ring: middle ring: outer ring = 1:1.2:1.5, so as to achieve temperature incremental control.

[0042] It is understandable that the circular distribution is just one example, and other distribution forms are also possible.

[0043] In one possible implementation, the furnace bottom zone cooling device 204 includes two or more independent zone cooling units; each zone cooling unit includes a cooling channel with built-in cooling medium, and zone gradient cooling is achieved by controlling the flow rate of the cooling medium; the zone cooling unit corresponds to the temperature zone of the zone heating and temperature control unit, and the temperature difference between the corresponding temperature zones is 300-650℃.

[0044] Furthermore, the temperature difference between the corresponding temperature zones is 500-650℃.

[0045] It is understood that the furnace bottom zone cooling device includes two or more independent zone cooling units; the zone cooling units cool by air cooling or liquid cooling; and the heat is removed by cooling media with different flow rates to achieve gradient cooling, making the temperature zone at the bottom of the cast glass uniform and consistent, while ensuring that the temperature difference between the top and bottom of the cast glass is 300~650℃. The corresponding temperature zone refers to the physical spatial correspondence between the temperature zones of the zone cooling unit and the zone heating and temperature control unit. For example, the furnace zone temperature control device has three zone heating and temperature control units, each corresponding to one of the three temperature zones (high, medium, and low); the furnace bottom zone cooling device also has three zone cooling units, each corresponding to one of the three temperature zones (high, medium, and low); the temperature zones within the same area of ​​the furnace are corresponding temperature zones, i.e., high-high, medium-medium, and low-low.

[0046] Furthermore, the partitioned cooling unit includes a cooling module and a temperature sensor.

[0047] Specifically, the cooling module is used to cool the bottom of the molten glass, including air cooling and liquid cooling.

[0048] Specifically, the cooling module includes a chamber and a refrigerant, which circulates within the chamber to achieve cooling.

[0049] For example, the furnace bottom zoned cooling device includes three independent zoned cooling units. A cooling medium storage tank is connected to each of the three cooling chambers via pipelines. Each chamber is independently equipped with a flow regulating valve and a temperature sensor. By controlling the flow rate of the refrigerant, gradient cooling control is achieved. The three cooling chambers are independent of each other and not interconnected, each with its own medium inlet and outlet for circulating cooling.

[0050] Understandably, the furnace bottom zoned cooling device is made of materials with good thermal conductivity, such as metal, to improve thermal conductivity.

[0051] In one possible implementation, the device further includes a wire mesh 207.

[0052] Furthermore, the wire mesh 207 is multi-layered to ensure that the bottom of the cast glass 206 can fully contact the air, while also fully absorbing the thermal expansion generated by the furnace bottom cooling device during the heating process, without affecting the cast glass 206. It also facilitates the separation of glass products from the mold, preventing adhesion and ensuring product molding quality.

[0053] For example, the wire mesh 207 is made of 4mm steel wire, 8-12mm thick. 2 The mesh is stacked in four layers to ensure that the thickness of the stacked wire mesh 207 is at least 10mm. This number of layers ensures sufficient porosity on the bottom contact surface (too many layers will reduce porosity) while also saving costs.

[0054] In one possible implementation, the control device is used to calculate the descent speed of the mold cavity 202 based on the glass melt flow rate and the effective pouring area of ​​the mold cavity 202, and control the lifting mechanism 205 to lift and lower, so as to ensure that the distance between the glass melt inlet end face and the glass melt surface in the mold cavity is relatively constant.

[0055] Specifically, the control device includes a servo controller and a PLC.

[0056] In one possible implementation, the mold cavity is made of cast iron or platinum, which is resistant to high temperatures and has good thermal shock resistance. The side length of the mold pouring cavity is ≥1500mm to prevent glass melt from adhering.

[0057] In one possible implementation, the flow sensor is a Coriolis high-temperature flow sensor with a temperature tolerance of ≥1500℃ and a measurement accuracy of ±0.5%; the lifting mechanism is driven by a servo motor and coupled with a ball screw transmission, with a positioning accuracy of ±0.1mm, achieving a uniform and stable descent.

[0058] In one possible implementation, the casting device for the large-size zero-expansion microcrystalline glass is also equipped with a waste gas recovery system connected to the top of the casting auxiliary furnace to recover high-temperature waste gas and utilize waste heat, thereby reducing energy consumption; at the same time, a safety pressure relief valve is provided to automatically release pressure when the gas pressure in the storage chamber exceeds 0.25MPa, ensuring production safety.

[0059] The casting method for large-size zero-expansion microcrystalline glass is described below.

[0060] See Figure 3 The casting method for large-size zero-expansion microcrystalline glass provided in this application embodiment includes: S301. Defoaming treatment is performed on the high-temperature, high-viscosity glass melt to obtain the first glass melt.

[0061] In one possible implementation, the method for obtaining the high-temperature, high-viscosity glass melt includes: feeding a zero-expansion microcrystalline glass batch into a melting furnace, melting it at 1550℃~1680℃ and holding it at that temperature for 20~50h to obtain a high-temperature, high-viscosity glass melt with a viscosity of 102~103 Pa·s.

[0062] In one possible implementation, S201 includes: The high-temperature, high-viscosity molten glass is allowed to stand and remain at a constant temperature to clarify, and then defoaming is achieved through negative pressure.

[0063] Specifically, the high-temperature, high-viscosity glass melt is left to stand and clarify for 10 to 50 hours. After clarification, the top cover of the melting furnace is covered, and then the gas pressure control device is turned on to perform vacuum treatment. The pressure in the melting chamber is controlled at 0.02 to 0.05 MPa, and then the negative pressure is maintained for 30 to 120 minutes to initially remove large air bubbles.

[0064] S302. The first glass melt is pressurized by a protective gas to obtain thrust, and then filtered under the action of the thrust to obtain the second glass melt.

[0065] In one possible implementation, the protective gas comprises nitrogen or argon, and the gas pressure is 0.15 to 0.25 MPa.

[0066] Specifically, an inert protective gas (nitrogen or argon) is introduced into the melting chamber, and the pressure inside the chamber is adjusted to 0.15~0.25 MPa to form a pressure-assisted thrust, which propels the high-viscosity molten glass to flow into the pouring guide channel. When the molten glass flows through the platinum filter, the high-temperature stability of platinum and the sieving effect of the filter trap and break the uncontrollable micro bubbles remaining in the molten glass, achieving secondary defoaming. At the same time, it ensures that the molten glass flows out evenly and avoids excessively fast local flow rates.

[0067] S303. The second molten glass is injected into the mold cavity to form the casting glass; the temperature of the upper part of the casting glass is controlled by zones, and the temperature of the bottom part of the casting glass is cooled by zones.

[0068] In one possible approach, zoned temperature control of the upper part of the cast glass includes: S303a, Divide the upper part of the casting glass into at least two temperature-controlled zones from the inside out; S303b, The two temperature control zones are set with a temperature range from the inside to the outside according to the gradient temperature increase; wherein, the temperature of the central temperature zone is 1250℃~1300℃, and the temperature gradient is 50-100℃.

[0069] Specifically, the furnace-level temperature control device of the casting auxiliary furnace is activated, dividing the upper temperature zone into three independent temperature control areas: an inner ring temperature zone, a middle ring temperature zone, and an outer ring temperature zone. The three temperature zones are distributed in concentric circles. The inner ring temperature zone corresponds to the central area of ​​the glass blank, the middle ring temperature zone corresponds to the middle area of ​​the glass blank, and the outer ring temperature zone corresponds to the edge area of ​​the glass blank. Combining the high-temperature heat dissipation characteristics of molten glass, the temperature of the three temperature zones is set in an increasing pattern. Specifically, the temperature of the inner ring temperature zone is controlled at 1250℃~1300℃, the temperature of the middle ring temperature zone is controlled at 1300℃~1350℃, and the temperature of the outer ring temperature zone is controlled at 1350℃~1400℃. The high temperature of the outer ring compensates for the defect of rapid heat loss at the edge, so that the overall temperature difference of the top plane of the large-size glass is controlled within ±5℃, ensuring that the top surface is flat and free of stress concentration.

[0070] In one possible approach, zoned cooling of the bottom of the cast glass includes: S303c: Divide the bottom of the casting glass from the inside out into cooling zones, the same number as the number of temperature zones in the zoned temperature control. S303d, The cooling zones are set with temperature ranges according to a gradient cooling from the inside to the outside; wherein, heat is conducted through cooling media with different flow rates to achieve gradient cooling, and the temperature difference between the corresponding zone control zone and the cooling zone is ensured to be 300~650℃.

[0071] For example, the furnace bottom partition cooling device is preheated to 550℃~700℃. The bottom of the mold is also divided into three independent cooling zones: an inner cooling zone, a middle cooling zone, and an outer cooling zone, which correspond one-to-one with the three temperature zones at the top. Cooling compressed gas or high-temperature resistant silicone oil is used as the cooling medium to implement gradient cooling in the three cooling zones. The flow rate of the cooling medium is distributed in a pattern of high in the inner ring and low in the outer ring. The specific parameters are as follows: the cooling medium flow rate in the inner cooling zone is 15~20L / min, and the temperature is controlled at 550℃~600℃; the cooling medium flow rate in the middle cooling zone is 10~15L / min, and the temperature is controlled at 600℃~650℃; the cooling medium flow rate in the outer cooling zone is 5~10L / min, and the temperature is controlled at 650℃~700℃. Through the three-layer gradient cooling at the bottom, middle and outer, the temperature difference between the bottom and top of the glass blank is controlled at 300℃~650℃. This avoids the formation and floating of bubbles caused by high temperature at the bottom, and ensures that the molten glass is evenly spread in the mold without local accumulation or uneven thickness.

[0072] Preferably, the cooling compressed gas is high-purity nitrogen gas that has been dried and has a dew point of ≤-40℃ or compressed air; the kinematic viscosity of the high-temperature resistant silicone oil is 100~200mm² / s, the temperature range is -50℃~300℃, and continuous cooling is achieved through the circulation pipeline with a temperature control accuracy of ±2℃.

[0073] S304, The descent speed of the mold cavity is controlled based on the pouring flow rate of the second molten glass.

[0074] In one possible implementation, S204 includes: S304a, Obtain the glass melt flow rate Q and the effective pouring area S of the mold; S304b, Calculate the mold descent speed V, V=Q / S; S304c: The descent speed of the mold cavity is controlled based on the mold descent speed V to maintain a relative distance of 10~15mm between the lower end face of the glass melt inlet and the glass melt surface, thus completing the pouring process.

[0075] In one possible implementation, the flow rate fluctuation of S204 is controlled within ±2%, and the speed fluctuation is controlled within ±1%, eliminating the vibration of the falling glass liquid and the entrainment of air, and avoiding the generation of new bubbles.

[0076] S305, heat preservation annealing and post-treatment are used to obtain the finished product.

[0077] In one possible implementation, the glass preform, along with the mold, is fed into an annealing furnace and subjected to stepped annealing according to the zero-expansion microcrystalline glass annealing process. First, the temperature is lowered to 550°C at a rate of 3~5°C / h and held for 4 hours. Then, the temperature is lowered to 100°C at a rate of ≤3°C / h and cooled to room temperature in the furnace to obtain a large-size zero-expansion microcrystalline glass preform, which can then be crystallized and polished.

[0078] This application addresses the core pain points of casting large-size zero-expansion microcrystalline glass by achieving high-quality molding through the synergistic effect of multiple technologies, specifically including: 1. Dual defoaming with air pressure assistance and platinum filter: High-viscosity molten glass cannot flow stably under gravity. Inert gas pressure assistance provides uniform thrust, solving the problem of poor flowability. The platinum filter is resistant to high temperature and has strong chemical stability. Its pore size is precisely controllable, which can effectively trap tiny bubbles with a diameter greater than 50μm in the molten glass. At the same time, it can break some bubbles with weak bonding, realizing online defoaming during the pouring process and avoiding bubble residue.

[0079] 2. Three progressively increasing temperature zones in the upper part for heat replenishment and temperature uniformity: The top edge of the large-size glass dissipates heat quickly. It adopts three progressively increasing temperature zones: the outer ring is high-temperature to specifically replenish the edge heat, the middle ring provides transition, and the inner ring is heat-insulating, so that the temperature field of the entire upper plane is highly uniform, eliminating stress, warping and deformation caused by uneven temperature field, and ensuring the flatness of the glass surface.

[0080] 3. Three-gradient cooling at the bottom balances bubble suppression and flattening: If the temperature at the bottom of the glass is too high, dissolved gases are prone to precipitate and rise to form bubbles; if the temperature is too low, the molten glass cannot be flattened. By regulating the heat conduction rate of the cooling medium through internal, internal, and external flow rate gradients, a temperature gradient with a lower inner temperature and a higher outer temperature is formed at the bottom. This gradient works in synergy with the temperature zone at the top, suppressing the generation and rising of bubbles at the bottom while ensuring that the molten glass spreads evenly within the mold. This maintains a highly uniform temperature field at the bottom plane, thereby achieving large-size uniform molding.

[0081] 4. Higher upper temperatures reduce glass viscosity, which is beneficial for the injection and filling effect and the improvement of forming streaks. Therefore, higher upper temperatures are more conducive to glass casting. The bottom requires a lower temperature, mainly because high temperatures in the bottom mold can easily cause air bubbles to overflow into the glass, forming irreparable bubble defects. Therefore, to improve the casting quality of the glass, a certain temperature field needs to be formed between the upper and lower parts.

[0082] 5. Closed-loop matching of flow rate and speed to eliminate height difference fluctuations: The flow rate sensor collects the outflow data of the molten glass in real time, and the control system quickly calculates and adjusts the mold descent speed to keep the pouring gate and the surface of the molten glass at a constant small height difference. The molten glass flows smoothly without vibration or splashing, and completely eliminates the formation of new air bubbles caused by air entrapment.

[0083] 6. Overall temperature field coordinated regulation reduces internal stress: The upper increasing temperature zone and the bottom gradient cooling zone form a uniform temperature field. The temperature gradient from the surface to the interior of the glass preform is gentle, and the internal stress is greatly reduced, avoiding cracking problems during annealing and crystallization, and improving the yield of large-size preforms.

[0084] In this embodiment, the size range of the large-size zero-expansion microcrystalline glass covers square and round blanks with a side length of 500mm to 2500mm. The mold size and process parameters can be adjusted according to actual needs. The pore size of the platinum filter can be adjusted according to the viscosity of the glass melt. A large-pore filter is selected for high-viscosity glass melt, and a small-pore filter is selected for low-viscosity glass melt, so as to ensure both defoaming effect and flow efficiency.

[0085] The temperature increment of the top three temperature zones can be adjusted according to the size of the glass blank. The larger the size, the greater the temperature difference between the outer and inner rings should be to ensure sufficient temperature field compensation at the edge. The choice of cooling medium at the bottom can be determined according to the production conditions. Cooling compressed gas is suitable for rapid cooling, while high-temperature resistant silicone oil is suitable for precise temperature control. Both methods can achieve the ideal gradient cooling effect.

[0086] The casting device provided in this application embodiment can realize automated continuous production. It is equipped with a PLC control system, and all process parameters can be preset, stored and retrieved. It is easy to operate, has high production efficiency, and the casting time of a single furnace is shortened to 30-60 minutes. Compared with the traditional process, the production efficiency is increased by more than 50% and the energy consumption is reduced by more than 20%.

[0087] The following detailed embodiments illustrate this point.

[0088] Example 1 (1) Casting method A method for casting large-size zero-expansion microcrystalline glass includes the following steps: S1: Preparation and Pretreatment of High-Viscosity Molten Glass A Li2O-Al2O3-SiO2 system zero-expansion microcrystalline glass batch was selected. The mass fractions of each component in the batch were as follows: quartz sand 45.22%, aluminum hydroxide 30.82%, lithium carbonate 7.98%, aluminum phosphate 8.95%, titanium dioxide 1.92%, zirconium dioxide 1.78%, magnesium oxide 0.95%, zinc oxide 1.12%, sodium nitrate 0.11%, potassium nitrate 0.37%, clarifying agent 0.68%, and other components 0.1%. After uniformly mixing the batch, it was put into a melting furnace and melted at 1660℃ for 100 hours. Then, it was clarified and held at the same temperature for 50 hours. Subsequently, the gas pressure control system and cooling system were turned on to vacuum the melting chamber, and the pressure was controlled at 0.03MPa to initially remove large and small air bubbles in the glass melt. S2: Air pressure assisted casting and platinum filter defoaming The molten glass is cooled to 1580℃ to obtain a high-temperature molten glass with a viscosity of 1.5×10³Pa·s. High-purity nitrogen gas with a purity of 99.999% is introduced into the melting chamber, and the gas pressure inside the chamber is adjusted to 0.18 MPa to push the molten glass to flow into the casting channel. A platinum-rhodium alloy filter screen (90% platinum and 10% rhodium) with a pore size of 100μm and a porosity of 50% is installed in the casting channel. The molten glass undergoes secondary defoaming when it flows through the filter screen. S3: Top three-layer incremental temperature control The top temperature zone of the casting auxiliary furnace is divided into three layers: inner, middle and outer, with a width ratio of 2:3:2. The inner ring temperature zone is 1280℃, the middle ring temperature zone is 1330℃, and the outer ring temperature zone is 1380℃. The temperature control accuracy is ±1℃, and the overall temperature difference of the top plane is ±4℃. S4: Three-layer gradient cooling control for the bottom mold The bottom graphite mold is preheated to 680℃. The bottom three-layer cooling zone is cooled with high-purity nitrogen. The airflow rate of the inner cooling zone is 18L / min and the temperature is 580℃; the airflow rate of the middle cooling zone is 12L / min and the temperature is 630℃; the airflow rate of the outer cooling zone is 7L / min and the temperature is 680℃. The temperature difference between the top and the bottom is 620℃. S5: Precise matching of pouring flow rate and mold descent speed The flow rate of the molten glass was monitored by a Coriolis high-temperature flow sensor. The flow rate was set to 25 L / min, the effective pouring area of ​​the mold was 1.8 m², the mold descent speed was calculated to be 13.89 mm / min, the flow rate fluctuation was controlled within ±1.5%, the speed fluctuation was ±0.8%, and the distance between the pouring gate and the liquid surface was kept at 12 mm. S6: Heat preservation annealing After casting, the glass preform along with the mold is sent into an annealing furnace, cooled to 550°C at 5°C / h, held for 4 hours, and then cooled to 100°C at 3°C / h. The preform is then cooled to room temperature in the furnace to obtain a square zero-expansion microcrystalline glass preform with a side length of 1800mm.

[0089] (2) Casting device The casting apparatus described in this application has a smelting furnace volume of 500L, a casting auxiliary furnace storage chamber volume of 300L, a platinum filter screen size of 300mm×150mm, a top temperature zone heating module power of 15kW for the inner ring, 18kW for the middle ring, and 22.5kW for the outer ring, a bottom mold size of 1800mm×1800mm×200mm, and a mold lifting mechanism using a servo motor with a rated thrust of 50kN. Embodiments 2 and 3 below are the same.

[0090] (3) Performance testing The prepared glass preform was tested and found to be pale yellow or light brown, with no bubbles larger than 20 μm inside, and a bubble defect rate of less than 0.05%; the surface was smooth; and the coefficient of thermal expansion was -0.02 × 10⁻⁶. -7 / ℃ (0℃~50℃); Bending strength 228MPa; Stress birefringence <3nm / cm; Yield 95%.

[0091] Example 2 (1) Casting method A method for casting large-size zero-expansion microcrystalline glass includes the following steps: S1: Preparation and Pretreatment of High-Viscosity Molten Glass A low-silicon, zero-expansion microcrystalline glass batch was selected and melted at 1650℃ for 110 hours to obtain a high-temperature glass melt. This melt was then clarified and held at the same temperature for 40 hours. Subsequently, the gas pressure control system and cooling system were activated to vacuum the melting chamber at a pressure of 0.03 MPa, initially removing large and small air bubbles from the glass melt. The glass melt was then cooled to 1580℃ to obtain a high-temperature glass melt with a viscosity of 1.2 × 10³ Pa·s. S2: Air pressure assisted casting and platinum filter defoaming High-purity argon gas was introduced, and the gas pressure in the storage chamber was adjusted to 0.2 MPa. The platinum filter screen had a pore size of 60 μm and a porosity of 55%. The rhodium content in the platinum-rhodium alloy was 12%. S3: Top three-layer incremental temperature control The inner ring temperature is 1260℃, the middle ring temperature is 1310℃, the outer ring temperature is 1360℃, and the overall temperature difference of the top plane is ±3℃. S4: Three-layer gradient cooling control for the bottom mold The bottom silicon carbide mold is preheated to 660℃ and cooled by circulating high-temperature silicone oil. The silicone oil flow rate in the inner cooling zone is 20L / min and the temperature is 560℃; the flow rate in the middle cooling zone is 14L / min and the temperature is 610℃; the flow rate in the outer cooling zone is 8L / min and the temperature is 660℃. The temperature difference between the top and bottom is 640℃. S5: Precise matching of pouring flow rate and mold descent speed The glass melt flow rate is 22L / min, the effective mold area is 1.5㎡, the calculated descent speed is 14.67mm / min, and the distance between the pouring gate and the liquid surface is maintained at 10mm. S6: Heat preservation annealing The annealing process is the same as in Example 1, resulting in a circular zero-expansion microcrystalline glass preform with a side length of 1600 mm.

[0092] (2) Performance testing The prepared glass preform had no obvious internal bubbles, with a bubble defect rate of 0.03%; surface flatness of 0.012 mm / m; and a coefficient of thermal expansion of +0.02 × 10⁻⁶.-7 / ℃ (0℃~50℃); flexural strength 225MPa; yield rate 92%.

[0093] Example 3 (1) Casting method A method for casting large-size zero-expansion microcrystalline glass includes the following steps: S1: Preparation and Pretreatment of High-Viscosity Molten Glass A high-silicon, zero-expansion microcrystalline glass batch was selected and melted at 1680℃ for 120 hours to obtain a high-temperature glass melt. This melt was then clarified and held at the same temperature for 50 hours. Subsequently, the gas pressure control system and cooling system were activated to vacuum the melting chamber at a pressure of 0.025 MPa, initially removing large and small air bubbles from the glass melt. The glass melt was then cooled to 1590℃ to obtain a high-temperature glass melt with a viscosity of 1.8 × 10³ Pa·s. S2: Air pressure assisted casting and platinum filter defoaming High-purity nitrogen gas was introduced, and the gas pressure in the storage chamber was adjusted to 0.25 MPa. The platinum filter screen had a pore size of 100 μm and a porosity of 45%. S3: Top three-layer incremental temperature control The inner ring temperature is 1300℃, the middle ring temperature is 1350℃, the outer ring temperature is 1400℃, and the overall temperature difference of the top plane is ±5℃. S4: Three-layer gradient cooling control for the bottom mold The bottom cast iron mold is preheated to 700℃ and cooled with high-purity nitrogen. The airflow rate in the inner ring is 15L / min and the temperature is 600℃; the flow rate in the middle ring is 10L / min and the temperature is 650℃; the flow rate in the outer ring is 5L / min and the temperature is 700℃. The temperature difference between the top and bottom is 600℃. S5: Precise matching of pouring flow rate and mold descent speed The glass melt flow rate is 30 L / min, and the effective mold area is 2.0 m². 2 Calculate the descent speed as 15 mm / min, and maintain a distance of 15 mm between the pouring nozzle and the liquid surface; S6: Heat preservation annealing The annealing process is the same as in Example 1, resulting in a square zero-expansion microcrystalline glass preform with a side length of 2000 mm.

[0094] (2) Performance testing The prepared glass preform had a bubble defect rate of 0.08%, a surface flatness of 0.018 mm / m, and a coefficient of thermal expansion of -0.03 × 10⁻⁶. -7 / ℃ (-40℃~800℃); flexural strength 188MPa; yield rate 90%.

[0095] Comparative Example 1 Using the traditional gravity self-flow casting process, without air pressure assistance or platinum filter, the top single temperature zone is 1300℃, the bottom mold is kept at a constant temperature of 650℃, the flow rate and mold speed are not adjusted, and the other parameters are the same as in Example 1. The prepared glass preform has a bubble defect rate of 12%, a surface flatness of 0.15mm / m, obvious warping, and a yield of 28%.

[0096] Comparative Example 2 The device is the same as in Example 1, except that it only uses air pressure assistance and a platinum filter, and does not perform top three-layer temperature zone and bottom gradient cooling control. The other parameters are the same as in Example 1. The prepared glass blank has a low edge temperature field, more bottom bubbles, a bubble defect rate of 5%, and a yield of 45%.

[0097] Comparative Example 3 The device is the same as in Example 1, except that it only controls the temperature zone and does not match the pouring flow rate and mold speed. The other parameters are the same as in Example 1. The falling vibration of the molten glass introduces a large number of air bubbles, resulting in a bubble defect rate of 8% and a yield of 35%.

[0098] Based on the test data from the embodiments, it can be seen that the large-size zero-expansion microcrystalline glass prepared in this application has a bubble defect rate as low as 0.03%, extremely high surface flatness, extremely low coefficient of thermal expansion, high bending strength, and a yield of over 90%. Compared with the comparative example, many parameters have been significantly improved.

[0099] In summary, the large-size zero-expansion microcrystalline glass casting method and apparatus of this application embodiment can realize continuous industrial production. The prepared large-size zero-defect zero-expansion microcrystalline glass has stable performance, meets the material standards of high-end fields, has passed pilot-scale verification, and can be directly applied to the manufacturing of semiconductor lithography equipment, large-aperture astronomical telescopes, aerospace vehicles and other products, and has significant economic and social value.

[0100] Large-sized zero-expansion microcrystalline glass preforms prepared using the above-mentioned casting method or casting device, after crystallization heat treatment and precision polishing, are applied in the following fields: 1. Conductor lithography field: Fabrication of lithography machine lens support structures and lithography substrates to ensure dimensional accuracy under extreme temperatures and improve lithography resolution; 2. Precision optics: Fabrication of large-aperture astronomical telescope lenses, laser interferometer bases, and high-precision optical mirrors to achieve distortion-free optical imaging; 3. Aerospace field: Manufacturing spacecraft optical windows, satellite attitude control components, and precision structural components for aerospace engines to adapt to the extreme temperature environment of space; 4. High-end instrument field: manufacture precision measuring instrument bases and spectrometer core components to eliminate measurement errors caused by temperature changes. The above description is only a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any modifications, equivalent substitutions and improvements made by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A casting apparatus for large-size zero-expansion microcrystalline glass, characterized in that, include: A melting furnace, including a first furnace body and a gas pressure control device, a water cooling device and a glass melt outlet disposed therein; The casting auxiliary furnace includes a second furnace body and a glass melt inlet, a mold chamber, an in-furnace zone temperature control device, a furnace bottom zone cooling device, a lifting mechanism, a flow monitoring device, and a control device disposed within the furnace body; the mold chamber is mounted on the lifting mechanism; the in-furnace zone temperature control device is used to control the temperature of at least two zones of the upper part of the casting glass that are gradually heated from the inside to the outside; the furnace bottom zone cooling device is used to cool at least two zones of the bottom part of the casting glass that are gradually heated from the inside to the outside; the control device is used to control the lifting mechanism to move up and down based on the glass melt flow rate; The flow channel is used to connect the smelting furnace and the casting auxiliary furnace.

2. The apparatus according to claim 1, characterized in that, The device also includes a wire mesh and a filter screen; the wire mesh is installed on the furnace bottom zone cooling device; the filter screen is installed at the glass melt outlet.

3. The apparatus according to claim 1, characterized in that, The furnace zone temperature control device includes two or more independent zone heating and temperature control units; the temperature of the central temperature zone is 1250℃~1300℃, and the temperature increases from the central temperature zone outwards, with a temperature gradient of 50-100℃.

4. The apparatus according to claim 3, characterized in that, The furnace bottom zone cooling device includes two or more independent zone cooling units; each zone cooling unit includes a cooling channel with built-in cooling medium, and zone gradient cooling is achieved by controlling the flow rate of the cooling medium; the zone cooling unit corresponds to the zone heating temperature control unit, and the temperature difference between the corresponding temperature zones is 300-650℃.

5. The apparatus according to claim 1, characterized in that, The control device is used to calculate the descent speed of the mold cavity based on the glass melt flow rate and the effective pouring area of ​​the mold cavity, and control the lifting mechanism to raise and lower, so as to ensure that the distance between the glass melt inlet end face and the glass melt surface in the mold cavity is relatively constant.

6. A method for casting large-size zero-expansion microcrystalline glass, characterized in that, Includes the following steps: The high-temperature, high-viscosity glass melt is defoamed to obtain the first glass melt; The first molten glass is pressurized with a protective gas to obtain thrust, and then filtered under the action of thrust to obtain the second molten glass. The second molten glass is injected into the mold cavity to form the casting glass; the temperature of the upper part of the casting glass is controlled in sections, and the temperature of the bottom part of the casting glass is cooled in sections. The descent speed of the mold cavity is controlled based on the pouring flow rate of the second molten glass. After heat treatment and annealing, the finished product is obtained.

7. The method according to claim 6, characterized in that, The upper temperature of the molten glass is controlled in zones, including: The upper part of the casting glass is divided into at least two temperature-controlled zones from the inside out; The temperature control zones are set with a temperature range that increases gradually from the inside out; wherein, the temperature of the central temperature control zone is 1250℃~1300℃, and the temperature gradient is 50-100℃.

8. The method according to claim 6, characterized in that, The bottom of the cast glass is cooled in sections, including: The bottom of the casting glass is divided into cooling zones from the inside out, the same number as the number of temperature zones in the zoned temperature control. The cooling zones are cooled by using cooling media with different flow rates to conduct heat and achieve gradient cooling, so that the temperature difference between the corresponding temperature control zone and the cooling zone is 300~650℃.

9. The method according to claim 6, characterized in that, The method of controlling the descent speed of the mold cavity based on the pouring flow rate of the second molten glass includes: Obtain the glass melt flow rate Q and the effective pouring area S of the mold; Calculate the mold descent speed V, V = Q / S; The descent speed of the mold cavity is controlled based on the mold descent speed V.

10. A large-size zero-expansion microcrystalline glass, characterized in that, Prepared using the method described in any one of claims 6-9.

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