Method for inhibiting structural stress in glass casting molding

Abstract

The invention provides a method for inhibiting structural stress in glass casting molding, and belongs to the technical field of glass manufacturing, the method comprises the following steps: transferring molten glass from a smelting furnace to a casting container, and controlling the viscosity of the molten glass to be kept within a preset range; the molten glass with the viscosity kept within the preset range is controlled to flow into a mold from the casting container, and in the process, the casting linear speed of the molten glass with the viscosity kept within the preset range is controlled to meet the corresponding relational expression; meanwhile, the temperatures of an inlet area and an outlet area of the mold are controlled to meet corresponding relational expressions respectively; and after the molten glass is filled in a mold and molded to form a casting, sequentially carrying out relaxation heat treatment and two-stage annealing on the casting to obtain the casting cooled to room temperature, thereby completing structural stress suppression in glass casting molding. According to the invention, the problem that the structural residual stress which is difficult to eliminate exists in the glass part in the existing glass casting molding process can be solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of glass manufacturing, and particularly relates to a method for inhibiting structural stress in glass casting forming. BACKGROUND

[0002] In the manufacture of special glass, the combination of an elevator muffle furnace and a platinum crucible for melting and manual casting is a common process. However, when producing large-sized or thick glass parts (for example, 5 kg glass liquid castings), this process often faces a thorny problem: after annealing, there are significant residual stresses in the interior of the glass part, especially in the middle region along the initial flow direction of the glass liquid, which are difficult to completely eliminate through conventional prolonged annealing time (such as up to 10 days) or multiple annealing operations. Such stresses are usually manifested as obvious birefringent stripes or cause the product to crack during subsequent processing or use.

[0003] Analysis shows that this stress is mainly caused by two aspects: one is flow-induced structural stress, that is, during manual casting, the speed, flow rate and flow pattern of the glass liquid flowing into the mold are difficult to accurately control, and a high shear rate or turbulent tendency will cause the glass molecular chain or network structure to be oriented and arranged in the flow direction (molecular orientation stress), and when the glass cools and solidifies, this orientation is "frozen" down, forming a structural stress source, which is most obvious in the area with the highest flow rate in the center of the runner; the other is non-uniform thermal shrinkage stress, that is, the temperature of the mold is usually uniform or the gradient is unreasonable.

[0004] The existing technology mainly attempts to eliminate the stress by prolonging the annealing time or optimizing the annealing curve or secondary annealing, but the cost is often high and the effect is not good, especially for the above-mentioned structural stress. Therefore, there is an urgent need for a process method that can effectively inhibit the generation of such structural stress from the source of casting and early heat treatment. SUMMARY

[0005] The purpose of the present application is to provide a method for inhibiting structural stress in glass casting forming, so as to solve the problem of residual structural stress in the interior of the glass part in the existing glass casting forming process.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: In a first aspect, a method for inhibiting structural stress in glass casting forming, comprising the following steps: transferring the glass liquid from a melting furnace to a casting container, and controlling the viscosity of the glass liquid to remain within a preset range; controlling the glass liquid with viscosity remaining within the preset range to flow into a mold from the casting container, and in the process, controlling the pouring line speed of the glass liquid with viscosity remaining within the preset range to satisfy a corresponding relationship formula; at the same time, controlling the temperatures of the inlet region and the outlet region of the mold to satisfy corresponding relationship formulas, respectively; After the glass liquid fills the mold to form a casting, the casting is sequentially subjected to a relaxation heat treatment and a two-stage annealing, and then the casting is cooled to room temperature, thereby completing the structural stress inhibition in the glass casting process.

[0007] In some embodiments, the step of subjecting the casting to the relaxation heat treatment specifically comprises: The casting is heated to a preset relaxation holding temperature interval at a heating rate of less than or equal to 5℃ / min, and is held in the preset relaxation holding temperature interval for 20min~40min.

[0008] In some embodiments, the preset relaxation holding temperature interval is (T g +20℃)~(T g +40℃), wherein T g is the measured glass transition temperature of the glass corresponding to the glass liquid.

[0009] In some embodiments, the step of subjecting the casting to the two-stage annealing specifically comprises: The casting is cooled from the preset relaxation holding temperature interval to (T g -30℃)~(T g -20℃) at a cooling rate of 1℃ / min~2℃ / min; The casting is cooled from (T g -30℃)~(T g -20℃) to room temperature at a cooling rate of 0.3℃ / min~0.5℃ / min.

[0010] In some embodiments, the viscosity of the glass liquid is maintained in a preset range of 105~107Pa·s. ~ .

[0011] In some embodiments, the pouring line speed of the glass liquid in the process in which the viscosity is maintained in the preset range satisfies the corresponding relationship formula:

[0012] wherein, is the pouring line speed, in mm / s, is the instantaneous height of the glass liquid surface from the pouring gate to the mold, in mm, is a speed coefficient.

[0013] In some embodiments, the speed coefficient has a value in the range of 0.15 ~0.25 .

[0014] In some embodiments, the temperature of the mold inlet zone satisfies a corresponding relationship formula: (T c - 50℃) ~ (T c - 30℃), wherein T c is the glass liquid temperature corresponding to the viscosity of the glass liquid.

[0015] In some embodiments, the temperature of the mold outlet zone satisfies a corresponding relationship formula: (T c - 100℃) ~ (T c - 80℃), wherein T c is the glass liquid temperature corresponding to the viscosity of the glass liquid.

[0016] In some embodiments, the instantaneous value of the casting line speed of the glass liquid fluctuates within ±10% of the calculated value of the casting line speed of the corresponding relationship formula.

[0017] Compared with the prior art, the present application has the following beneficial effects: The present application provides a method for inhibiting structural stress in glass casting forming, which comprises the following steps: transferring the glass liquid from a furnace to a casting container and controlling the viscosity of the glass liquid to remain within a preset range; controlling the glass liquid with the viscosity remaining within the preset range to flow from the casting container into a mold, wherein the casting line speed of the glass liquid with the viscosity remaining within the preset range satisfies a corresponding relationship formula; at the same time, controlling the temperature of the inlet zone and the outlet zone of the mold to satisfy corresponding relationship formulas respectively; and after the mold is filled with the glass liquid to form a casting, sequentially performing relaxation heat treatment and two-stage annealing on the casting, and obtaining the casting cooled to room temperature. The method can effectively solve the problem of structural stress of the glass liquid in the middle region along the flow direction by controlling the flow orientation and early relaxation release from the source and combining with gradient solidification. The method is based on glass rheology and relaxation theory, and is suitable for casting forming of optical glass and special glass with various components.

[0018] Further, the casting is heated to a preset relaxation holding temperature interval at a heating rate of less than or equal to 5℃ / min, and is held in the preset relaxation holding temperature interval for 20min~40min; the casting is cooled from the preset relaxation holding temperature interval to (T g - 30℃) ~ (T g - 20℃) at a cooling rate of 1℃ / min ~ 2℃ / min; and the casting is cooled from (T g - 30℃) ~ (T g - 20℃) to room temperature at a cooling rate of 0.3℃ / min ~ 0.5℃ / min. Most of the difficult-to-eliminate structural stress can be effectively treated in the relaxation stage after casting through relaxation heat treatment and two-stage annealing, the subsequent standard annealing efficiency is improved, and the total annealing time is shortened from several days to within 24 hours.

[0019] Furthermore, the viscosity of the molten glass is maintained within a preset range. ~ The velocity coefficient has a range of 0.15. ~0.25 The temperature in the mold exit zone satisfies the following relationship: (T c -100℃)~(T c -80℃), where T c The temperature of the molten glass corresponds to the viscosity of the molten glass. The process parameters of the entire method are quantifiable and controllable, reducing fluctuations caused by manual operation and stabilizing the product qualification rate. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating a method for suppressing structural stress during glass casting, as provided in an embodiment of the present invention. Detailed Implementation

[0021] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and 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.

[0022] like Figure 1 As shown, this embodiment provides a method for suppressing structural stress during glass casting, including the following steps: S1, the molten glass is transferred from the furnace to a casting vessel, and the viscosity of the molten glass is controlled. Keep within the preset range; Specifically, controlling the temperature of the molten glass to adjust its viscosity Meets the preset range ~ The viscosity of the molten glass is controlled at ~ The "optimal rheological window" is based on the theory of glass rheology. Within this viscosity range, the molten glass has sufficient fluidity to avoid premature solidification, and its viscoelasticity is sufficient to suppress turbulence and facilitate the formation of laminar flow.

[0023] S2, the molten glass with its viscosity controlled within a preset range flows from the casting container into the mold, and the pouring linear velocity of the molten glass with its viscosity controlled within the preset range satisfies the corresponding relationship during the process; at the same time, the temperatures of the inlet and outlet areas of the mold are controlled to satisfy the corresponding relationship respectively. Specifically, the linear velocity of molten glass flowing from the casting vessel into the mold should satisfy the following relationship:

[0024] wherein, is the casting line speed, in mm / s, is the instantaneous height of the glass melt from the casting gate to the glass melt surface in the mold, in mm, is the speed coefficient, the speed coefficient is in the range of 0.15 ~0.25 . The instantaneous value of the casting line speed of the glass melt fluctuates within ±10% of the calculated value of the casting line speed according to the above relationship.

[0025] The above formula is derived based on the consideration of fluid mechanics and minimum shear rate; the speed coefficient value range ensures that the casting Reynolds number (Re) is low enough to maintain a laminar flow state, significantly reducing the molecular orientation caused by high shear. Controlling the flow stability further reduces disturbances.

[0026] Specifically, the mold has a temperature gradient along the main flow direction of the glass melt, the temperature at the inlet zone of the mold is set to T m1 , and the temperature at the outlet zone of the mold is set to T m2 , wherein the temperature T m1 at the inlet zone of the mold satisfies the corresponding relationship: (T c -50℃)~(T c -30℃), and the temperature T m2 at the outlet zone of the mold satisfies the corresponding relationship: (T c -100℃)~(T c -80℃), wherein T c is the temperature of the glass melt corresponding to the viscosity of the glass melt in S1. The mold temperature in this embodiment is no longer uniform, but is set to a decreasing gradient (T m1 >T m2 ) along the main flow direction of the glass melt (from the inlet to the outlet). The higher temperature (T c -50℃)~(T c -30℃) at the inlet zone allows the newly flowing glass melt to maintain a relatively flowing state, reducing the interfacial shear with the slightly cooled glass. The lower temperature (T c -100℃)~(T c -80℃) at the outlet zone promotes the glass in this region to pass through the maximum shrinkage temperature range (T g nearby) more quickly. This design aims to coordinate the solidification shrinkage process of the glass in the axial direction (flow direction), reducing the tensile and compressive stresses caused by uneven axial shrinkage.

[0027] S3, after the glass melt fills the mold to form a casting, the casting is sequentially subjected to relaxation heat treatment; Specifically, the cast is heated to a preset relaxation holding temperature interval of (T g + 20℃)~(T g + 40℃) at a heating rate of less than or equal to 5℃ / min, and is held for 20min~40min in the preset relaxation holding temperature interval, wherein T g is the measured glass transition temperature of the glass corresponding to the glass liquid. The post-casting relaxation treatment in this embodiment specifically refers to immediately heating the glass to T g 20~40℃ (at this time, the glass is in a viscoelastic state, and the molecular motion ability is significantly enhanced) and holding for a period of time: holding at a temperature above T g for a period of time, which provides sufficient energy and time for the "frozen" molecular chains or network units in the glass to rearrange and relax, and is particularly helpful for releasing the conformational stress generated by flow orientation during casting, and the effect is much better than long-time holding at a lower temperature (such as standard annealing temperature).

[0028] S4, after the relaxation heat treatment, the cast is subjected to two-stage annealing to obtain a cast cooled to room temperature, and the structural stress inhibition in the glass casting forming is completed.

[0029] Specifically, the first stage annealing: the cast is cooled from the preset relaxation holding temperature interval to (T g - 30℃)~(T g - 20℃) at a cooling rate of 1℃ / min ~2℃ / min; The second stage annealing: the cast is cooled from (T g - 30℃)~(T g - 20℃) to room temperature at a cooling rate of 0.3℃ / min~0.5℃ / min.

[0030] In this embodiment, the two-stage annealing is optimized. After the relaxation treatment effectively releases most of the structural stress, a more efficient two-stage annealing is used to further eliminate the residual thermal stress. The first stage is a relatively fast cooling through the region above T g , and the second stage is a slow cooling below T g to room temperature (in this region, the risk of stress freezing is high), which shortens the total annealing time while ensuring quality.

[0031] The method for inhibiting structural stress in glass casting forming provided in the above embodiment is applied to the following scene: Take the case of manually clamping a platinum crucible for casting after melting 10kg of glass liquid of a certain brand of glass (measured T g =520℃) in an up-and-down muffle furnace: 1. Casting preparation and viscosity control: Pour the molten glass into a preheated platinum casting vessel. Control the temperature of the glass at a point corresponding to a viscosity of = 1050°C) using a dip-type high temperature viscometer or according to a known viscosity-temperature curve (η-T curve) of the glass. Maintain this temperature until casting. c

[0032] 2. Casting flow rate control: Start casting. Control the angle of the platinum vessel or the opening of the casting port so that the linear velocity of the glass flow satisfies mm / s. The operator can estimate and adjust the flow rate by observing the flow pattern and timing the amount of casting. For example, when = 100 mm, the target ≈ 2.0 mm / s. The fluctuation of the flow rate is less than ±10%.

[0033] 3. Gradient mold temperature control: The mold can be selected from different materials according to the specific type of glass, production rhythm, and budget, etc. The materials of the mold include but are not limited to heat-resistant steel, silicon carbide, ductile iron, etc. Before casting, the temperature of the inlet end of the mold (close to the nozzle) is heated and maintained at T m1 = T c - 40°C = 1010°C. The temperature of the outlet end of the mold (far from the nozzle) is heated and maintained at T m2 = T c - 90°C = 960°C. The temperature of the middle region of the mold is naturally transitioned or can be set to an intermediate temperature zone. The mold needs to be uniformly preheated and well insulated.

[0034] 4. Post-casting relaxation treatment: After the glass fills the mold, immediately move the entire mold together with the casting into a programmable temperature-controlled annealing furnace (or use a covering heating device). Heat the entire casting to T g + 30°C = 550°C at a rate of 4°C / min, and maintain at 550°C for 30 minutes. This process needs to ensure that the uniformity of the overall temperature of the casting is good (±5°C).

[0035] 5. Two-stage annealing: After the relaxation and holding process is completed: First stage: cool the casting from 550°C to (T g - 30°C)~(T g - 20°C) = 490°C~500°C at a rate of 1.5°C / min.

[0036] Second stage: slowly cool the casting from 490°C to room temperature (about 25°C) at a rate of 0.4°C / min. ​​

[0037] 6. Stress detection: after the annealing is completely finished, the internal stress of the glass piece is detected by using a polarizing stress meter, compared with a traditional process (uniform mold casting + at least 3 days of annealing), the number of stripes in the central region of the glass piece using the process of the application is significantly reduced, and the overall stress distribution is uniform, and the total annealing time is about 20 hours.

[0038] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method of suppressing a structural stress in a glass cast molding, characterized by, The method comprises the following steps: transferring the glass liquid from a melting furnace to a casting container and controlling the viscosity of the glass liquid to be within a preset range; controlling the glass liquid with the viscosity within the preset range to flow into a mold from the casting container, and controlling the casting line speed of the glass liquid with the viscosity within the preset range to satisfy a corresponding relationship formula; meanwhile, controlling the temperatures of the inlet area and the outlet area of the mold to satisfy corresponding relationship formulas, respectively; after the glass liquid fills the mold to form a casting, sequentially performing relaxation heat treatment and two-stage annealing on the casting, obtaining the casting cooled to room temperature, and completing the structural stress inhibition in the glass casting forming.

2. The method of suppressing structural stress in glass cast forming according to claim 1, wherein The step of performing relaxation heat treatment on the casting specifically comprises: heating the casting to a preset relaxation holding temperature interval at a heating rate less than or equal to 5 ℃ / min, and holding the temperature in the preset relaxation holding temperature interval for 20 min to 40 min.

3. The method of claim 2, wherein the glass is a glass-cast formed glass. The preset relaxation holding temperature range is (T g + 20℃)~(T g + 40℃), wherein T g is the measured glass transition temperature of the glass corresponding to the glass liquid.

4. The method of claim 3, wherein the glass is a glass-ceramic. The step of performing two-stage annealing on the casting specifically comprises: cooling the cast from the preset relaxation holding temperature range to (T g -30°C) ~ (T g -20°C); The cast is cooled from (T g -30°C) to room temperature at a cooling rate of 0.3°C / min to 0.5°C / min. g -20°C).

5. The method of claim 1, wherein the glass is a glass-cast formed glass. The viscosity of the glass liquid is maintained in a preset range ​​ 6. The method of claim 1, wherein the glass is a glass-cast formed glass. the corresponding relationship formula that the casting line speed of the glass liquid with the viscosity within the preset range satisfies in the process is: wherein, is the casting line speed in mm / s, is the instantaneous height of the glass level in the mould from the nozzle in mm, is the speed coefficient.

7. The method of claim 6, wherein the glass is a glass-cast formed glass. The speed coefficient ranges from 0.15 to 0.25 .​ 8. The method of claim 1, wherein the glass is a glass-cast formed glass. the material of the mold is heat-resistant steel, silicon carbide or nodular cast iron; The temperature of the mold entrance zone satisfies a corresponding relationship formula: (T c - 30°C), wherein T c is the glass liquid temperature corresponding to the viscosity of the glass liquid. c is the glass liquid temperature corresponding to the viscosity of the glass liquid.

9. The method of claim 1, wherein the glass is a glass-cast formed glass. The temperature of the mold exit zone satisfies a corresponding relationship formula: (T c - 100°C) ~ (T c - 80°C), wherein T c is the glass liquid temperature corresponding to the viscosity of the glass liquid.

10. The method of claim 6, wherein the glass is a glass-cast formed glass. the instantaneous value of the casting line speed of the glass liquid fluctuates within ±10% of the calculated value of the casting line speed of the corresponding relationship formula.

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