Method for manufacturing a fused metal window having an optical material with a high flow temperature

Abstract

This is a method for manufacturing fused metal viewing windows by fusing the metal of the frame around the window, instead of the traditional method of fusing the window to the frame. Many of the best optically transparent materials (e.g., fused silica, sapphire, YAG, ALON, diamond, fused quartz, magnesium fluoride) have higher melting points than most metals, making it previously impossible to manufacture fused metal viewing windows using these materials. Fusing the frame to the window enables a variety of new combinations of metal and optical material while maintaining the strength of the viewing window that results from fusing the metal and optical material together.

Description

[[Technical Field]]

[0001] One or more embodiments of the present invention relate to the field of methods for manufacturing sight windows. More specifically, but not exclusively, one or more embodiments of the present invention enable a method for manufacturing a fused metal sight window having an optical material with a high flow temperature. [[Background Art]]

[0002] A sight window provides an observation window for an operator to observe processes occurring inside a container such as an industrial chemical container, or outside a system exposed to external pressure, temperature and chemicals such as a submersible or an oil well. Sight windows need to withstand the harsh conditions in the container or the external environment, including very high pressure, temperature and exposure to hazardous chemicals, without failure such as cracking. To achieve the required robustness, sight windows are often made from a glass disc fused to a metal frame. Fusing glass directly to the frame can eliminate points of failure such as gaskets or other types of seals. The elimination of the need for seals and gaskets extends the service life of the sight window by years, and in some cases, decades. In addition, fusing glass to the metal frame strengthens the glass, because the metal frame contracts around the disc during cooling, compressing the disc to increase its strength.

[0003] Existing fused glass windows are manufactured by melting glass into a metal frame. Because metal has a higher coefficient of thermal expansion than glass, the metal compresses the glass as the molten assembly cools. This conventional method works well when the glass-based transparent window material has a softening point low enough not to melt the metal or cause unwanted grain growth (reduction in metal strength) in the metal. In other words, for most applications, the softening point required for flow must be below 1000°C. This can be a limitation when high-temperature glass such as fused silica, aluminosilicate, or fused quartz glass is required, or crystalline materials whose crystalline structure is damaged when melted, such as sapphire, zinc selenide, or diamond, or sintered materials (such as ceramics) that do not melt unless the material is destroyed, such as alumina, zirconia, or nitride refractory materials. [Overview of the project] [Problems that the invention aims to solve]

[0004] At least due to the limitations mentioned above, a method for manufacturing a fused metal viewing window having an optical material with a high flow temperature is required. [Means for solving the problem]

[0005] One or more embodiments described herein relate to a method for manufacturing a fused metal window having a high-flow-temperature optical material. Embodiments of the present invention may involve melting the metal of the frame surrounding the window, which is the reverse of the conventional process for manufacturing fused windows in which glass is melted into a metal frame.

[0006] One or more embodiments of the present invention can enable a method for manufacturing a fused metal window having a high-flow-temperature optical material. This method may include the steps of preparing a window, preparing a frame, placing the window within the frame, heating the window and frame until the frame melts and fuses with the window, and cooling the window and frame to form a fused metal window. The window may contain an optical material that can be heated to a threshold temperature below which the optical material does not flow and is not damaged. The window may have an outer window edge. The frame may contain a metal with a melting point below the threshold temperature. The frame may have an inner frame edge and an outer frame edge. The outer window edge may be fitted inside the inner frame edge. The heating step may involve heating the window and frame to a temperature above the melting point and below the threshold temperature. Heating may continue until the inner frame edge melts and flows onto the outer window edge, and the metal of the inner frame edge fuses with the outer edge of the optical material of the window.

[0007] In one or more embodiments of the present invention, the frame may have a ring shape. In one or more embodiments, the frame may have a geometric shape other than a ring shape. In one or more embodiments, the outer edge of the window may have a circular shape, and the inner edge of the frame may have a circular shape.

[0008] In one or more embodiments, the optical material of the window may be a crystalline optical material. In one or more embodiments, the optical material may include one or more of fused silica, aluminosilicate, borosilicate glass, YAG, ALON, sapphire, zinc selenide, zinc sulfide, quartz crystal, fused silica, diamond, and magnesium fluoride.

[0009] In one or more embodiments, the optical material may include sapphire, and the metal may include at least one of stainless steel, Inconel®, Hastelloy®, nickel-based alloys, copper, brass, gold, titanium, platinum, and rhodium.

[0010] In one or more embodiments, the process of manufacturing a fused metal viewing window includes preparing an outer housing, placing a frame within the outer housing, placing a window within the frame, and heating all components until the inner frame edge melts and flows into the outer window edge and fuses with the window, and the outer frame edge melts and flows into the inner edge of the outer housing and fuses with the outer housing. The window, frame, and outer housing are cooled to form a fused metal viewing window. The outer housing may contain a second metal having a second melting point higher than the melting point of the frame metal. The outer frame edge may be fitted inside the inner edge of the outer housing. In one or more embodiments, the optical material of the window may contain zinc selenide, the second metal of the outer housing may contain stainless steel, and the frame metal may contain a transition metal. In one or more embodiments, the inner frame edge may melt and flow onto the outer window edge without the use of capillary action, and the outer frame edge may melt and flow onto the inner housing edge without the use of capillary action. In one or more embodiments, the process of joining the window, frame, and outer housing to form a fused metal viewing window does not require the use of brazing or soldering.

[0011] The above and other aspects, features and advantages of the present invention will become more apparent from the following more specific description, presented in conjunction with the following drawings: [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 shows a typical fused glass window in which a transparent window is fused to a metal frame. [Figure 2] Figure 2 shows a typical manufacturing process used in the prior art to produce fused glass viewing windows, in which the glass is heated and flowed into a metal frame for housing it. [Figure 3] Figures 3(a) and 3(b) show alternative methods used in the prior art when the window cannot be fused to the frame. View windows fabricated using these methods are not as robust as fused view windows. [Figure 4]Figure 4 shows a flowchart of an exemplary embodiment of the present invention, in which a fused window is fabricated by melting the metal frame around the window. This is the reverse process of the process currently used in the prior art. [Figure 5] Figure 5 shows each step in the flowchart of Figure 4. [Figure 6] Figure 6 shows each step of the flowchart in Figure 4 for viewing windows with geometric shapes other than circular. [Figure 7] Figure 7 shows a modified version of the flowchart in Figure 4, which may be used when the material of the viewing window housing has a melting point high enough to damage the window material. [Figure 8] Figure 8 shows each step in the flowchart of Figure 7. [Modes for carrying out the invention]

[0013] A method for manufacturing a fused metal viewing window having a high-flow-temperature optical material is described below. The following illustrative description includes many specific details to provide a more complete understanding of embodiments of the invention. However, it will be apparent to those skilled in the art that the invention can be implemented without incorporating all of the specific details described herein. In some cases, certain functions, quantities, or measurements well known to those skilled in the art are not described in detail so as not to obscure the invention. Readers should note that while illustrative descriptions of the invention are provided herein, the entire scope of the claims and all equivalents defines the scope of the invention.

[0014] Figure 1 shows an exemplary fused glass viewing window 100 having a transparent window 102 within a metal frame 101. The viewing window may also have features such as threads 103 for mounting to equipment, bolt holes on a flange, or other fasteners. The viewing window can be of any shape and size. In this exemplary viewing window 100, the material of the window 102 is fused to the metal of the frame 101 at the boundary 105 between the glass (or other optical material) and the metal of the frame 101. By fusing the glass and metal, a robust viewing window is created that can withstand high pressure 104 (or high pressure 106) that presses outward against the window.

[0015] Figure 2 shows a typical manufacturing method used in the art to produce a fused glass window. A window 201 is obtained from a transparent material such as glass, and typically a metal frame 202 is obtained. In existing methods known in the art, the window material melts so that it flows into the metal frame, so the melting point 211 of the optical material of the window must be lower than the melting point 212 of the metal in the frame 202. This constraint significantly limits the materials that can be used for fused glass windows in existing manufacturing methods. Many excellent optical transparent materials have melting points higher than most metals. Optical materials such as fused silica, aluminosilicate, borosilicate glass, sapphire, YAG, ALON, diamond, fused quartz, and magnesium fluoride are examples of window materials that cannot currently be fused to a metal frame due to their high melting points. There are only a few types of glass that can be melted into a metal ring using conventional methods. Soda-lime glass and borosilicate glass, for example, are unsuitable for optical use. There are very few optical glasses that can be melted into common low-melting-point metals such as aluminum, brass, copper, or gold. Crystalline optical materials cannot be melted and are therefore excluded from conventional methods for creating fused glass viewing windows. Some of the most important optical materials are crystalline, including YAG, sapphire, zinc selenide, zinc sulfide, quartz crystal, and diamond.

[0016] Figure 2 shows subsequent steps 205, 206, and 208 in a conventional manufacturing process for a fused viewing window, with side and top views of the components during manufacturing. In step 205, the window 201a is placed inside the metal frame 202a with a small gap between them. In its initial state, the window 201a is, for example, a disc-shaped glass blank. Next, in step 206, the assembly (window and frame) is heated to a temperature above the melting point 211 of the window material and below the melting point 212 of the metal frame material. This causes the window blank to enter state 201b and flow into the metal frame. The frame also expands slightly due to the heating, entering state 202b. In step 208, the assembly is cooled, and finally the window 201c is held fused to the side wall of the metal frame 202c. During cooling, the frame has a higher coefficient of thermal expansion than the optical window and therefore contracts, exerting a compressive force 210 on the periphery of the window 201c, thereby strengthening the window.

[0017] As mentioned above, the method shown in Figure 2 cannot be used for many desirable types of optical materials because the melting points of these materials are too high. In applications where these materials are essential, other methods are currently used to manufacture viewing windows, as shown in Figures 3(a) and 3(b). In these other methods, the metal of the frame does not fuse with the window material, resulting in lower quality viewing windows. In these other methods, the metal frame is not heated, so it does not shrink around the glass during the cooling process, and does not compress and strengthen the glass inward. In the method shown in Figure 3(a) (side cross-sectional view), the window material 201 is sandwiched between two gaskets or O-rings 301a and 301b, and these two gaskets or O-rings 301a and 301b are then sandwiched between two metal pieces 202 and 302 with a fastener such as 303. This method can be used in low-pressure (low-strength requirements) applications, including ultra-high temperature environments where fiber gaskets are the only sealing method. The strength of the window is determined solely by the material properties of the window material, as the window material is not compressed. This method is not suitable for high-pressure applications. In the method shown in Figure 3(b), the window material 201 is bonded to the metal frame 202 by adhesive 310. The adhesive is selected based on the environmental requirements of the window. Similar to the gasket / O-ring method in Figure 3(a), this method cannot increase the strength of the window material by generating high compressive forces. The strength of the window is determined solely by the material properties of the window material, as the window material is not subjected to compression. Therefore, this method is also not suitable for high-pressure applications. Both of these methods are susceptible to chemical and thermal degradation, but fusion-bonded windows do not have a seal that can be damaged.

[0018] To address the limitations of the prior art methods shown in Figures 2, 3(a) and 3(b), one or more embodiments of the present invention enable a method for manufacturing fused metal windowings in which the metal surrounding the window is melted, rather than melting the window into a metal frame. In one or more embodiments of the present invention, a transparent (e.g., glass or crystal) pack is prepared in the same manner as the conventional fused glass methods described above, but without melting. Instead, the pack is placed within a metal frame (the form of the metal may be solid, semi-sintered, pressed powder, etc.), and the metal is heated to a temperature high enough to flow around the glass, and then cooled. As the assembly cools, the metal solidifies and compresses the window material, which has a low coefficient of thermal expansion. Ultimately, this approach yields the same high-strength windowings achieved with low-melting-point glass in a metal ring.

[0019] Figure 4 shows a flowchart of the manufacturing steps of an exemplary embodiment of the present invention. One or more embodiments of the present invention may use additional steps or a subset of the steps shown in Figure 4. The steps may be reordered or modified as appropriate for each application. In step 401, a window 421 is prepared having an optical material that is typically transparent and may have other desired properties such as strength, chemical resistance, or stability. The flow temperature of the optical material is above a threshold temperature 411, and when the window 421 is heated to a temperature below this threshold temperature 411, the optical material does not flow and is not otherwise damaged. In step 402, a frame 422 is prepared having a metallic material having a melting point 412 below a threshold temperature 411. When the frame 422 is heated to a temperature above this melting point 412, the metal melts and flows around the window.

[0020] Since the dimension of the outer edge of the window is smaller than the dimension of the inner edge of the frame, in step 405, the window can be placed inside the frame. In step 406, the window and the frame are heated to a temperature 416 that is not lower than the melting point 412 of the metal and not higher than the threshold temperature 411. At this temperature 416, the metal in the frame melts and flows around the window, while the optical material of the window does not flow and is not damaged. In step 407, this temperature (or any temperature between 412 and 411) is maintained for a sufficient time to allow the inner edge of the frame to flow around the outer edge of the window and for the metal of the frame to fuse to the window. Then, in step 408, the assembly is cooled. This causes the metal to shrink around the window and compress the window, resulting in the formation of a fused-metal sight window 430. Additional steps for post-treating the sight window 430 may be performed, for example, surface and gloss polishing to make all surfaces optically transparent, coplanar and parallel, and chemical surface treatments such as chemical conversion treatment, plating, anodizing, and metal machining.

[0021] In the process shown in Figure 4, the window 421 can be made of any material that flows or is damaged at a temperature higher than the melting point of the metal frame 422. Exemplary combinations of window and frame materials include, for example, a combination of a sapphire window and a 316 stainless steel metal ring, and a combination of a window made of fused quartz, sapphire or fused silica with an aluminum frame. As another combination, for example, a titanium housing (melting point 1668°C) can be arranged around a sapphire window (melting point 2030°C). This combination can only be used in an oxygen-free environment. In other environments, as an exemplary combination, for example, a platinum / rhodium alloy frame can be used around a sapphire window. This frame is not oxidized even when it withstands extreme temperatures in oxygen. As another exemplary combination, for example, one or more frames selected from stainless steel, Inconel, Hastelloy, nickel-based alloys, copper, brass, or gold can be arranged around a sapphire window.

[0022] Examples of window materials include, but are not limited to, one or more of fused silica, YAG, ALON, aluminosilicate, borosilicate glass, sapphire, zinc selenide, zinc sulfide, quartz crystal, fused quartz, diamond, and magnesium fluoride. Crystalline optical materials can be used for the window. Since these materials cannot be melted, they cannot be used in conventional manufacturing methods as shown in FIG. 2, but they can be easily used in the method of the present invention as shown in FIG. 4. Examples of frame materials include, but are not limited to, one or more of Inconel, Hastelloy, aluminum, brass, copper, gold, tin, Babbitt alloy, indium, beryllium, steel, titanium, platinum, rhodium, or any of hundreds of pure metals or alloy metals having a relatively low melting point.

[0023] FIG. 5 shows the steps of FIG. 4 together with schematic side cross-sectional views and plan views of the components as the manufacturing process progresses. In this example, the window and the frame are circular. In step 405, an initial window 421a is arranged inside a ring-shaped initial frame 422a. The frame 422a and the window 421a are arranged inside a sealing structure 430 that accommodates the frame 422a when melted in step 406. Step 406 shows the window 421b and the frame 422b after heating. The material of the frame 422b flows from the inner edge of the frame to the outer edge of the window. Since the temperature does not exceed the threshold temperature, the state of the window 421b does not substantially change. The outer edge of the molten frame 422b is accommodated in the sealing structure 430. After the cooling step 408, the frame 422c shrinks around the window 421c and applies a compressive force 410 to strengthen the window. Thereafter, the fused metal sight glass including the frame 422c and the window 421c is taken out from the sealing structure 430.

[0024] Figure 6 shows the same steps 405, 406, and 408 in plan view only, for a hexagonal window and a hexagonal frame. In one or more embodiments, the window and frame may be any desired shape, including, but not limited to, circular, elliptical, oblong, and polygonal shapes having any number of sides. Similar to Figure 5, the inner edge of the heated metal frame 622b flows to the outer edge of the heated window 621b in step 406, and after cooling, the frame 622c is compressed around the window 621c. In this example, the sealing structure 630 surrounding the frame and window is also hexagonal.

[0025] Depending on the application, it may be desirable to combine window material and frame material even if heating the window material to the melting point of the metal frame would damage it. An example of this is the sealing of a zinc selenide window into a stainless steel 316 metal housing. Zinc selenide is a crystalline material that breaks above 350°C, while the stainless steel 316 housing melts above 1375°C. A solution to this situation is to extend the flowchart in Figure 4 and construct a three-part assembly consisting of a window, a low-melting-point inner frame positioned around the window, and a high-melting-point metal outer frame surrounding the inner frame. The inner frame melts and fuses between the window and the outer housing. For example, the inner frame can be made of a transition metal such as indium or a low-temperature indium alloy, or a gold / tin alloy. Figure 7 shows a flowchart of an exemplary embodiment of this process. The window 421 and frame 422 are obtained as shown in Figure 4. In this embodiment, the "frame" is the inner frame sandwiched between the window and the outer housing 723. The outer housing contains a second metal having a melting point of 713, which is higher than the melting point of the frame material, 412. In step 405a, the window is placed inside the (inner) frame, and the frame and window are placed inside the outer housing. In step 406a, the assembly is heated to a temperature of 416a, which is above the melting point of the (inner) frame, 412, but lower than the melting points of the window and outer frame. In step 407a, the high temperature is maintained until the inner edge of the frame flows into and fuses with the outer edge of the window, and the outer edge of the frame flows into and fuses with the inner edge of the outer housing. In step 408a, the entire assembly is cooled, forming a complete fused metal viewing window 430a.

[0026] Figure 8 shows the steps of the process in Figure 7, along with schematic side and top views of the components. In step 405a, the (inner) frame 422a is sandwiched between the window 421a and the outer housing 723a. In step 406a, the heated inner frame 422b flows in and comes into contact with the inner edge of the heated outer housing 723b and the outer edge of the heated window 421b. In step 408a, the components are cooled, and a final viewing window is obtained in which the inner frame 422c is fused to the window 421c and the outer housing 723c.

[0027] In the process shown in Figures 7 and 8, the inner frame is melted to join the window to the outer housing. Unlike brazing, this process does not rely on capillary action for the metal to flow into the joint space between the parts being joined. Instead, the entire inner and outer edges of the inner frame are melted and flow to contact the window and outer housing, respectively. Because the inner frame melts and flows both inward and outward, it can fill large gaps between the window and the outer housing. In contrast, brazing can only be used to join parts that are in close contact.

[0028] The process shown in Figures 7 and 8 differs from the typical soldering process. This is because soldering uses filler alloys that melt at relatively low temperatures (usually below 450°C). Also, soldering results in relatively weak joints and is not suitable for viewing windows. (Silver brazing is an exception, but like brazing, it relies on capillary action and cannot be used to fill large gaps.) In contrast, the process in Figures 7 and 8 melts the inner metal frame at a higher temperature and allows it to flow until it fills the entire gap between the window and the outer housing, forming a strong joint.

[0029] Although the inventions disclosed herein are described by their specific embodiments and applications, numerous modifications and variations can be made by those skilled in the art without departing from the scope of the invention as defined in the claims. [Explanation of Symbols]

[0030] 100 Viewpoints 101 Metal Frame 102 Transparent window 103 screw threads 104 High Voltage 105 Boundary 106 High Voltage 201 Window Materials 201a Window 201b Status 201c window 202 Metal Frame 202a Metal frame 202b status 202c Metal Frame 205 steps 206 steps 208 steps 210 Compression force 211 Melting point 212 Melting point 301a, 301b O-rings 310 Adhesive 316 Stainless Steel 401 Steps 402 steps 405 steps 405a Step 406 steps 406a Step 407 steps 407a Step 408 steps 408a Step 410 Compression force 411 Threshold temperature 412 Melting point 416 Temperature 416a Temperature 421 windows 421a (Initial) Window 421b Window (Condition) 421c window 422 frames 422a Frame 422b frame 422c frame 430, 630 Sealing structure 430 Viewpoint 430a Fused metal viewing window 621b Window 621c window 622b frame 622c Metal Frame 713 Melting point 723 Outer housing 723a Outer housing 723b Outer housing 723c Outer Housing

Claims

1. A method for manufacturing a fused metal viewing window having an optical material with a high flow temperature, A step of preparing a window, wherein the window includes an optical material and can be heated to a threshold temperature below which the optical material does not flow or get damaged, and the window is provided with an outer window edge; A step of preparing a frame, wherein the frame comprises a metal having a melting point below the threshold temperature, the frame comprises an inner frame edge and an outer frame edge, and the outer window edge is fitted inside the inner frame edge; A step of placing the window within the frame; A step of heating the window and the frame to a temperature above the melting point and below the threshold temperature, and continuing the heating until the inner frame edge melts and flows onto the outer window edge, and the metal of the frame at the inner frame edge fuses with the optical material of the window at the outer window edge; and A step of cooling the window and the frame to form a fused metal viewing window; A method that includes this.

2. The method for manufacturing a fused metal viewing window having a high-flow temperature optical material according to claim 1, wherein the frame is ring-shaped.

3. A method for manufacturing a fused metal viewing window having a high-flow temperature optical material, according to claim 1, wherein the frame has a geometric shape other than a ring shape.

4. A method for manufacturing a fused metal viewing window having a high-flow-temperature optical material according to claim 1, wherein the optical material includes a crystalline optical material.

5. A method for manufacturing a fused metal viewing window having a high-flow temperature optical material according to claim 1, wherein the optical material comprises at least one of fused silica, aluminosilicate, borosilicate glass, YAG, ALON, sapphire, zinc selenide, zinc sulfide, quartz crystal, fused silica, diamond, and magnesium fluoride.

6. The optical material includes sapphire, A method for manufacturing a fused metal viewing window having a high-flow temperature optical material according to claim 1, wherein the metal comprises at least one of stainless steel, Inconel®, Hastelloy®, nickel-based alloy, copper, brass, gold, titanium, platinum, and rhodium.

7. A step of preparing an outer housing, wherein the outer housing comprises a second metal having a second melting point higher than the first melting point, the outer housing comprises an inner housing edge, and the outer frame edge fits inside the inner housing edge; A step of placing the frame inside the outer housing and the window inside the frame; The window, the frame, and the outer housing are heated to a temperature above the melting point, below the threshold temperature, and below the second melting point. The inner frame edge melts and flows onto the outer window edge, causing the metal of the frame to fuse with the optical material of the window, and The heating process continues until the outer frame edge melts and flows onto the inner housing edge, causing the frame metal to fuse with the second metal of the outer housing; A method for manufacturing a fused metal viewing window having a high-flow temperature optical material according to claim 1, further comprising the steps of: cooling the window, the frame, and the outer housing to form a fused metal viewing window;

8. The optical material includes zinc selenide, The second metal includes stainless steel, and A method for manufacturing a fused metal viewing window having a high-flow temperature optical material according to claim 7, wherein the metal includes a transition metal.

9. The inner frame edge melts and flows onto the outer window edge without using capillary action. A method for manufacturing a fused metal viewing window having a high-flow-temperature optical material according to claim 7, wherein the outer frame edge melts and flows onto the inner housing edge without using capillary action.

10. A method for manufacturing a fused metal viewing window having a high-flow-temperature optical material according to claim 7, wherein joining the window, the frame, and the outer housing to form a fused metal viewing window does not involve brazing or soldering.

11. A method for manufacturing a fused metal viewing window having an optical material with a high flow temperature, A step of preparing a window, wherein the window includes an optical material and can be heated to a threshold temperature below which the optical material does not flow or get damaged. The optical material includes at least one of fused silica, aluminosilicate, borosilicate glass, YAG, ALON, sapphire, zinc selenide, zinc sulfide, quartz crystal, fused silica, diamond, and magnesium fluoride. The aforementioned window is equipped with an outer window frame. The aforementioned outer window frame is circular in shape. A step of preparing a frame, wherein the frame comprises a metal having a melting point below the threshold temperature, and the metal comprises at least one of stainless steel, Inconel, Hastelloy, nickel-based alloy, copper, brass, gold, titanium, platinum, and rhodium. The frame comprises an inner frame edge and an outer frame edge, the outer window edge fits inside the inner frame edge, and the inner frame edge is circular in shape. A step of placing the window within the frame; A step of heating the window and the frame to a temperature above the melting point and below the threshold temperature, and continuing the heating until the inner frame edge melts and flows onto the outer window edge, and the metal of the frame at the inner frame edge fuses with the optical material of the window at the outer window edge; and A step of cooling the window and the frame to form a fused metal viewing window; A method that includes this.

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