Method for manufacturing fused metal viewing windows with high flow temperature optical materials

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 viewing windows. More particularly, but not exclusively, one or more embodiments of the present invention enable methods for manufacturing fused metal viewing windows having high flow temperature optical materials. [Background technology]

[0002] Sight windows provide an operator with a viewing window to observe processes occurring inside a vessel, such as an industrial chemical vessel, or outside a system exposed to external pressures, temperatures, and chemicals, such as a submersible or oil well. Sight windows must be able to withstand the harsh environments inside the vessel or the external environment, including extremely high pressures, temperatures, and exposure to hazardous chemicals, without cracking or other failure. To achieve the required robustness, sight windows are often made from a glass disk fused to a metal frame. Fusing the glass directly to the frame eliminates failure points such as gaskets and other types of seals. Eliminating the need for seals and gaskets extends the life of the sight window by years, or even decades. Fusing the glass to the frame also strengthens the glass, as the metal frame contracts around the disk upon cooling, compressing it and increasing its strength.

[0003] Existing fused-glass viewing windows are manufactured by fusing glass to a metal frame. Because metals have a higher coefficient of thermal expansion than glass, the metal compresses the glass when the fused assembly cools. This traditional method works well when the glass-based transparent window material has a softening point low enough not to melt the metal or induce unwanted grain growth (which reduces its strength). For most applications, the softening point required for flow must be below 1000°C. This can be a limitation when using high-temperature glasses such as fused silica, aluminosilicates, and fused quartz glass; crystalline materials such as sapphire, zinc selenide, and diamond, whose crystalline structure is damaged upon melting; or sintered materials (e.g., ceramics) that cannot be melted without destroying the material, such as alumina, zirconia, and nitride refractory materials. Summary of the Invention [Problem to be solved by the invention]

[0004] Due to at least the limitations noted above, there is a need for a method of manufacturing fused metal viewing windows having high flow temperature optical materials. [Means for solving the problem]

[0005] One or more embodiments described herein relate to a method for manufacturing a fused metal viewing window having a high flow temperature optical material. Embodiments of the invention may fuse the metal of the frame around the window, which is the opposite of the traditional fused viewing window manufacturing process of fusing glass to a metal frame.

[0006] One or more embodiments of the present invention may enable a method for manufacturing a fused metal viewing window having an optical material with a high flow temperature. The method may include providing a window, providing a frame, placing the window within the frame, heating the window and frame until the frame melts and fuses to the window, and cooling the window and frame to form a fused metal viewing window. The window may include an optical material that can be heated to a temperature below a threshold temperature at which the optical material does not flow or become damaged. The window may have an outer window edge. The frame may include a metal having 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 fit inside the inner frame edge. The heating step may heat the window and frame to a temperature above the melting point but below the threshold temperature. Heating may continue until the inner frame edge melts and flows onto the outer window edge, fusing the metal of the inner frame edge to 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, which 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 can include sapphire, and the metal can include at least one of stainless steel, Inconel®, Hastelloy®, a nickel-based alloy, copper, brass, gold, titanium, platinum, and rhodium.

[0010] In one or more embodiments, a process for manufacturing a fused metal viewing window includes providing 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 onto the outer window edge and fuses with the window, and the outer frame edge melts and flows onto the inner edge of the outer housing and fuses with the outer housing. The window, frame, and outer housing are cooled to form the fused metal viewing window. The outer housing may include a second metal having a second melting point higher than the melting point of the metal of the frame. The outer frame edge may fit inside the inner edge of the outer housing. In one or more embodiments, the optical material of the window may include zinc selenide, the second metal of the outer housing may include stainless steel, and the metal of the frame may include a transition metal. In one or more embodiments, the inner frame edge may melt and flow onto the outer window edge without capillary action, and the outer frame edge may melt and flow onto the inner housing edge without capillary action. In one or more embodiments, the process of joining the window, frame, and outer housing to form the fused metal viewing window may not involve brazing or soldering.

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

[0012] [Figure 1] FIG. 1 shows a typical fused glass viewing window, in which a transparent window is fused to a metal frame. [Figure 2] FIG. 2 illustrates a typical manufacturing process used in the prior art to produce fused glass viewing windows, in which the glass is heated and flows into a containing metal frame. [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. Windows made using these methods are not as robust as fused windows. [Figure 4]4 shows a flow chart of an exemplary embodiment of the present invention for creating a fused viewing window by melting the metal frame around the window, a process that is the reverse of that currently used in the prior art. [Figure 5] FIG. 5 shows the steps in the flowchart of FIG. [Figure 6] FIG. 6 illustrates the steps of the flowchart of FIG. 4 for a viewing window having a geometric shape other than circular. [Figure 7] FIG. 7 shows a variation of the flowchart of FIG. 4 that may be used when the material of the viewing window housing has a melting point high enough to damage the window material. [Figure 8] FIG. 8 shows the steps in the flowchart of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] A method for manufacturing a fused metal viewing window having a high flow temperature optical material is described. In the following exemplary description, numerous specific details are set forth to provide a more thorough understanding of embodiments of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without incorporating all of the specific details set forth herein. In some instances, specific features, quantities, or measurements known to those skilled in the art have not been described in detail so as not to obscure the invention. The reader should note that although an exemplary description of the present invention is set forth herein, it is the claims, along with the full scope of any equivalents, that define the scope of the present invention.

[0014] FIG. 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, bolt holes on a flange, or other fasteners for attachment to equipment. The viewing window may be 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 interface 105 between the glass (or other optical material) and the metal of the frame 101. Fusing the glass to the metal creates a strong viewing window that can withstand high pressures 104 that are forced outward on the window (or high pressures 106 that are forced inward).

[0015] Figure 2 illustrates a typical manufacturing method used in the art for producing fused-glass viewing windows. A window 201 is obtained from a transparent material such as glass, and a frame 202, typically made of metal, is obtained. In existing methods known in the art, the window material melts so that it flows into the metal frame, requiring the melting point 211 of the window's optical material to be lower than the melting point 212 of the metal in the frame 202. This constraint severely limits the materials that can be used for fused-glass viewing windows using existing manufacturing methods. Many excellent optically 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 metal frames due to their high melting points. Only a few types of glass can be fused to a metal ring using conventional methods. Some, such as soda-lime glass and borosilicate glass, are unsuitable for optical applications. Few optical glasses can be fused to common low-melting-point metals such as aluminum, brass, copper, or gold. Crystalline optical materials cannot be melted, eliminating them as options for making fused glass viewing windows using conventional methods. Some of the most important optical materials are crystalline, including YAG, sapphire, zinc selenide, zinc sulfide, quartz crystal, and diamond.

[0016] FIG. 2 illustrates subsequent steps 205, 206, and 208 in a conventional manufacturing process for a fused viewing window, with side cross-sectional and top views of the components during the manufacturing of the viewing window. In step 205, window 201a is placed inside metal frame 202a, with a small gap between them. Initially, window 201a may be, for example, a disk-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 but below the melting point 212 of the metal frame material. This causes the window blank to assume state 201b and flow into the metal frame. The frame also expands slightly upon heating, assuming state 202b. In step 208, the assembly is cooled, ultimately leaving window 201c fused to the sidewall of metal frame 202c. During cooling, the frame, having a higher coefficient of thermal expansion than the optical window, contracts, exerting a compressive force 210 on the periphery of window 201c, strengthening the window.

[0017] As noted above, the method shown in FIG. 2 cannot be used for many desirable types of optical materials because the melting points of these materials are too high. For applications where these materials are essential, other methods are currently used to manufacture viewing windows, as shown in FIGS. 3(a) and 3(b). These other methods produce inferior viewing windows because the metal frame does not fuse to the window material. In these other methods, the metal frame is not heated, so it does not shrink around the glass during the cooling process, compressing the glass inward and strengthening it. In the method shown in FIG. 3(a) (side cross-sectional view), the window material 201 is sandwiched between two gaskets or O-rings 301a and 301b, which are in turn sandwiched between two metal pieces 202 and 302b with fasteners such as fasteners 303. This method can be used for low-pressure (low strength requirements) applications involving extremely 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, since it is not compressed. This method is not suitable for high-pressure applications. In the method shown in FIG. 3(b), the window material 201 is bonded to the metal frame 202 with an adhesive 310. The adhesive is selected based on the environmental requirements of the viewing window. Like the gasket / O-ring method of FIG. 3(a), this method does not 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, since it 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 the fused viewing window does not have a seal to damage.

[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 a fused metal viewing window by fusing the metal around the window rather than fusing the window to a metal frame. In one or more embodiments of the present invention, a transparent (e.g., glass or crystalline) puck is created in the same manner as the traditional fused glass method described above, but is not melted. Instead, the puck is placed within a metal frame (the metal may be in a solid, pre-sintered, pressed powder, or other form), heated to a high enough temperature 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 results in a viewing window with the same high strength as achieved with a low-melting-point glass within a metal ring.

[0019] FIG. 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 FIG. 4. The steps may be reordered or modified as appropriate for each application. In step 401, a window 421 is provided having an optical material, which 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; if the window 421 is heated to a temperature below this threshold temperature 411, the optical material will not flow or otherwise be damaged. In step 402, a frame 422 is provided having a metallic material with a melting point 412 below the 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] The outer edge of the window has dimensions smaller than the inner edge of the frame, so that the window can be placed inside the frame in step 405. In step 406, the window and frame are heated to a temperature 416 above the melting point 412 of the metal but below a 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 remains intact and undamaged. In step 407, this temperature (or any temperature between 412 and 411) is maintained long enough for 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. The assembly is then cooled in step 408, causing the metal to contract around the window, compressing it and resulting in the formation of a fused metal viewing window 430. Additional steps can be performed to post-process the viewing window 430, such as surface polishing and polishing to make all surfaces optically clear, flush, and parallel, chemical surface treatments such as conversion coating, plating, anodizing, and metal machining.

[0021] In the process shown in FIG. 4, the window 421 can be made of any material that will flow or break at temperatures above the melting point of the metal frame 422. Exemplary combinations of window and frame materials include a sapphire window with a stainless steel 316 metal ring, or a fused quartz, sapphire, or fused silica window with an aluminum frame. Another combination, for example, a titanium housing (melting point 1668°C) around a sapphire window (melting point 2030°C). This combination is only usable in oxygen-free environments. In other environments, an exemplary combination, for example, a platinum / rhodium alloy frame around a sapphire window, which can withstand extreme temperatures in oxygen without oxidizing. Another exemplary combination, for example, a sapphire window with one or more frames of stainless steel, Inconel, Hastelloy, nickel-based alloy, copper, brass, or gold around a sapphire window.

[0022] Window materials can include, but are not limited to, one or more of the following: fused silica, YAG, ALON, aluminosilicate, borosilicate glass, sapphire, zinc selenide, zinc sulfide, quartz crystal, fused silica, diamond, and magnesium fluoride. Crystalline optical materials can be used for the window. These materials cannot be melted and therefore cannot be used with conventional manufacturing methods such as those shown in Figure 2, but can be easily used with the method of the present invention shown in Figure 4. Frame materials can include, but are not limited to, Inconel, Hastelloy, aluminum, brass, copper, gold, tin, Babbitt, indium, beryllium, steel, titanium, platinum, rhodium, or any one or more of hundreds of pure or alloyed metals with relatively low melting points.

[0023] FIG. 5 illustrates the steps of FIG. 4 with schematic side cross-sectional and top views of the components as they progress through the manufacturing process. In this example, the window and frame are circular. In step 405, an initial window 421a is placed inside a ring-shaped initial frame 422a. The frame 422a and window 421a are placed inside a sealing structure 430 that will contain the frame 422a when fused in step 406. Step 406 shows the window 421b and frame 422b after heating. Material from the frame 422b flows from the inner edge of the frame to the outer edge of the window. Because the temperature does not exceed the threshold temperature, the state of the window 421b remains substantially unchanged. The outer edge of the fused frame 422b is contained within the sealing structure 430. After cooling step 408, the frame 422c contracts around the window 421c, exerting a compressive force 410 to strengthen the window. The fused metal viewing window, including frame 422c and window 421c, is then removed from sealing structure 430.

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

[0025] In some applications, it may be desirable to combine a window material with a frame material, even if heating the window material to the melting point of the metal frame would damage it. An example of this is sealing a zinc selenide window to a 316 stainless steel metal housing. While zinc selenide is a crystalline material that breaks down above 350°C, the 316 stainless steel housing melts above 1375°C. A solution to this situation extends the flowchart in Figure 4 to construct a three-part assembly consisting of a window, a low-melting-point inner frame surrounding the window, and a high-melting-point metal outer frame surrounding the inner frame. The inner frame melts and fuses the window to 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. A window 421 and frame 422 are obtained as shown in Figure 4. The "frame" in this embodiment refers to the inner frame sandwiched between the window and the outer housing 723. The outer housing comprises a second metal having a melting point 713 higher than the melting point 412 of the frame material. In step 405a, the window is placed into the (inner) frame, and the frame and window are placed into the outer housing. In step 406a, the assembly is heated to a temperature 416a above the melting point 412 of the (inner) frame, but below the melting points of the window and outer frame. In step 407a, the elevated temperature is maintained until the inner edge of the frame flows and fuses to the outer edge of the window, and the outer edge of the frame flows and fuses to the inner edge of the outer housing. In step 408a, the entire assembly is cooled, forming a fully fused metal viewing window 430a.

[0026] Figure 8 illustrates the steps of the process of Figure 7, with schematic cross-sectional side views 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 contacts 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, resulting in the final viewing window, where the inner frame 422c is fused to the window 421c and the outer housing 723c.

[0027] The process shown in Figures 7 and 8 melts the inner frame to join the window to the outer housing. Unlike brazing, this process does not rely on capillary action to allow the metal to flow into the joint space between the joining parts. Instead, the entire inner and outer edges of the inner frame are melted and flow into contact with 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 outer housing. In contrast, brazing can only be used to join tightly fitting parts.

[0028] The process shown in Figures 7 and 8 differs from typical soldering processes because soldering uses a filler alloy that melts at a relatively low temperature (typically less than 450°C). Soldering also creates a relatively weak joint, making it unsuitable 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 shown in Figures 7 and 8 melts the metal inner frame at a higher temperature and allows it to flow until it fills the entire gap between the window and outer housing, creating a strong joint.

[0029] While the invention disclosed herein has been described in terms of specific embodiments and applications thereof, numerous modifications and variations could be made by those skilled in the art without departing from the scope of the invention as set forth in the claims. [Explanation of symbols]

[0030] 100 Viewing window 101 Metal Frame 102 Transparent Window 103 thread 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 Step 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 Window 421a (early) window 421b Window (condition) 421c Window 422 frames 422a frame 422b frame 422c frame 430, 630 Sealing structure 430 Viewing window 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. 1. A method of manufacturing a fused metal viewing window having a high flow temperature optical material, comprising: providing a window, the window including an optical material and heatable to a temperature below a threshold temperature at which the optical material will not flow or be damaged, the window having an outer window edge; providing a frame, the frame comprising a metal having a melting point below the threshold temperature, the frame having an inner frame edge and an outer frame edge, the outer window edge fitting within the inner frame edge; placing the window within the frame; heating the window and the frame to a temperature above the melting point and below the threshold temperature, and continuing heating until the inner frame edge melts and flows onto the outer window edge, fusing the metal of the frame at the inner frame edge with the optical material of the window at the outer window edge; and cooling the window and the frame to form a fused metal viewing window; A method comprising:

2. 2. The method for manufacturing a fused metal viewing window with a high flow temperature optical material as recited in claim 1, wherein the frame is ring-shaped.

3. 10. The method of claim 1, wherein the frame is a geometric shape other than a ring.

4. The method for manufacturing a fused metal viewing window with a high flow temperature optical material according to claim 1 , wherein the optical material comprises a crystalline optical material.

5. 2. The method for manufacturing a fused metal viewing window with 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; 2. The method of claim 1, wherein the metal comprises at least one of stainless steel, Inconel, Hastelloy, nickel-based alloys, copper, brass, gold, titanium, platinum, and rhodium.

7. providing an outer housing, the outer housing including a second metal having a second melting point higher than the melting point, the outer housing including an inner housing rim, the outer frame rim fitting inside the inner housing rim; placing the frame within the outer housing and placing the window within the frame; heating the window, the frame, and the outer housing to a temperature equal to or greater than the melting point, equal to or less than the threshold temperature, and less than the second melting point; the inner frame edge melts and flows onto the outer window edge, fusing the metal of the frame with the optical material of the window; and continuing heating until the outer frame edge melts and flows onto the inner housing edge, fusing the metal of the frame with the second metal of the outer housing; 10. The method of claim 1 further comprising the step of: cooling said window, said frame, and said outer housing to form a fused metal viewing window.

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

9. the inner frame edge melts and flows onto the outer window edge without capillary action; 8. The method for manufacturing a fused metal viewing window with a high flow temperature optical material as set forth in claim 7, wherein the outer frame edge melts and flows onto the inner housing edge without the use of capillary action.

10. 8. The method of claim 7, wherein joining the window, the frame, and the outer housing to form a fused metal viewing window does not include brazing or soldering.

11. 1. A method of manufacturing a fused metal viewing window having a high flow temperature optical material, comprising: providing a window, the window including an optical material and capable of being heated to a temperature below a threshold temperature at which the optical material will not flow or be 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 window having an outer window edge; the outer window edge is circular; providing a frame, the frame comprising a metal having a melting point below the threshold temperature, the metal comprising at least one of stainless steel, Inconel, Hastelloy, a nickel-based alloy, copper, brass, gold, titanium, platinum, and rhodium; The frame includes 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; placing the window within the frame; heating the window and the frame to a temperature above the melting point and below the threshold temperature, and continuing heating until the inner frame edge melts and flows onto the outer window edge, fusing the metal of the frame at the inner frame edge with the optical material of the window at the outer window edge; and cooling the window and the frame to form a fused metal viewing window; A method comprising:

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