Strengthening the furnace brazing cycle

Abstract

A method for reducing cycle time of a brazing process is provided, the method including: placing together first and second pairs of brazing components, each of the first and second pairs having a brazing material interposed therebetween, stacking the first and second pairs of brazing components to form a stack, interposing pyrolytic graphite (PG) between the first and second pairs of brazing components in the stack, and heating the first and second pairs of brazing components to a brazing temperature to braze together the first and second pairs of brazing components.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Patent Application No. 17 / 992,322, filed November 22, 2022, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] Exemplary embodiments of the present disclosure relate generally to vacuum brazing and, in one embodiment, to vacuum brazing cycle strengthening using pyrolytic graphite (PG).

[0003] PG is a general term that includes pyrolytic graphite (TPG), annealed pyrolytic graphite (APG), and highly oriented pyrolytic graphite (HOPG). 2 Other materials exist that have high thermal diffusivities, exceeding 1 / s or more. These include, but are not limited to, carbon fiber, pyrolytic carbon, diamond, and carbon-containing materials such as nitrides and carbides.

[0004] Brazing is a metal joining process in which two or more metals are joined together using a filler metal with a lower melting point than the adjacent metals, causing the filler metal to melt and flow into the joint. Brazing differs from welding in that it does not involve melting the workpieces. Brazing differs from soldering in that it uses higher temperatures (liquidus temperatures above 450°C or 840°F). During the brazing process, the filler metal flows into the gap between adjacent parts by capillary action. The filler metal is heated slightly above its melting (liquidus) temperature while protected by a suitable atmosphere, usually a vacuum. The filler metal then wets and reacts with the base metal and is cooled to join the workpieces together.

[0005] Many technologies utilize a significant number of brazed parts. For example, some technologies may require hundreds of chassis, each with multiple individual braze points. Cold plate technologies, in particular, often have multiple parts brazed together to form the cold plate. Summary of the Invention

[0006] According to one aspect of the present disclosure, there is provided a method for reducing cycle time of a brazing process, the method including: placing together first and second pairs of brazing components, each of the first and second pairs having a brazing material interposed therebetween; stacking the first and second pairs of brazing components to form a stack; interposing pyrolytic graphite (PG) between the first and second pairs of brazing components in the stack; and heating the first and second pairs of brazing components to a brazing temperature to braze together the first and second pairs of brazing components.

[0007] According to additional or alternative embodiments, PG increases the effective thermal diffusivity of the laminate, correspondingly decreasing the cycle time required to braze together each brazed part of the first and second pairs of brazed parts.

[0008] According to additional or alternative embodiments, the PG increases the effective thermal diffusivity of the laminate by a factor of about 3.0 or more.

[0009] According to additional or alternative embodiments, the PG has a thermal diffusivity of about 500 mm2 / s or greater.

[0010] According to additional or alternative embodiments, the brazing temperature is between about 1050 and 1200°F.

[0011] According to additional or alternative embodiments, the method further includes interposing a first stop-off layer and a second stop-off layer between the PG and each of the first and second pairs of brazed parts, respectively.

[0012] According to additional or alternative embodiments, the method further comprises encasing the PG in a metal housing.

[0013] According to additional or alternative embodiments, the method further includes providing a layer of PG on at least one of the top and bottom of the stack.

[0014] According to additional or alternative embodiments, the method further includes at least one or more of: bending the PG around an outer edge of at least one of the first pair and the second pair of brazed parts; and attaching an additional PG piece to the PG for abutting the outer edge of at least one of the first pair and the second pair of brazed parts.

[0015] According to one aspect of the present disclosure, there is provided a method for reducing cycle time of a brazing process, the method including: placing together a plurality of pairs of brazing components, each of the plurality of pairs having a brazing material interposed therebetween, stacking the plurality of pairs of brazing components to form a stack, interposing pyrolytic graphite (PG) between adjacent ones of the plurality of pairs of brazing components, and heating the plurality of pairs of brazing components to a brazing temperature to braze together the respective brazing components of the plurality of pairs of brazing components.

[0016] According to additional or alternative embodiments, PG increases the effective thermal diffusivity of the laminate, correspondingly decreasing the cycle time required to braze together each brazed part of multiple pairs of brazed parts.

[0017] According to additional or alternative embodiments, the PG increases the effective thermal diffusivity of the laminate by a factor of about 3.0 or more.

[0018] According to additional or alternative embodiments, the PG has a thermal diffusivity of about 500 mm2 / s or greater.

[0019] According to additional or alternative embodiments, the brazing temperature is between about 1050 and 1200°F.

[0020] According to additional or alternative embodiments, the method further includes interposing a stop-off layer between the PG and each of the corresponding ones of the plurality of pairs of brazed parts, respectively.

[0021] According to additional or alternative embodiments, the method further comprises encasing the PG in a metal housing.

[0022] According to additional or alternative embodiments, the method further includes providing a layer of PG on at least one of the top and bottom of the stack.

[0023] According to additional or alternative embodiments, the method further includes at least one or more of: bending the PG around an outer edge of at least one of the plurality of pairs of brazed parts; and attaching an additional PG piece to the PG for abutting the outer edge of at least one of the first pair and the second pair of brazed parts.

[0024] According to one aspect of the present disclosure, a method for reducing cycle time of a brazing process includes forming first and second stacks, each stack comprising a plurality of pairs of brazed components, positioning the first and second stacks adjacent to one another, interposing pyrolytic graphite (PG) between at least one adjacent pair of brazed components in the first stack, providing a layer of PG on at least one of the top and bottom of the first and second stacks, bending an end of the PG to extend between the first and second stacks along one or more of the pairs of brazed components in the first and second stacks, and heating the pairs of brazed components of the first and second stacks to a brazing temperature to braze them together to the respective brazed components of the first and second stacks.

[0025] According to additional or alternative embodiments, the PG has a thermal diffusivity of greater than or equal to about 500 mm / s and increases the effective thermal diffusivity of at least the first laminate by a factor of greater than or equal to about 3.0, and correspondingly reduces the cycle time required to braze together the brazed components of each of the first and second laminates.

[0026] These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. The following description should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numbered alike. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a flow diagram illustrating a method for reducing cycle time of a brazing process, according to an embodiment. [Figure 2] 1 is a schematic diagram of a stack of brazed parts with alternating layers of pyrolytic graphite (PG), according to an embodiment. [Figure 3] 3 is an enlarged view of the portion of FIG. 2 enclosed by dashed line 3, according to an embodiment. [Figure 4]3 is a schematic diagram of a stack of brazed parts in a brazing furnace with alternating layers of PG from FIG. 2, according to an embodiment. [Figure 5] 1 is an enlarged schematic view of a brazed part with alternating layers of PG with edges having increased surface area, according to an embodiment. [Figure 6] 1 is an enlarged schematic view of a brazed part with alternating layers of PG with attachment portions with increased surface area, according to an embodiment. [Figure 7] FIG. 10 is a flow diagram illustrating a method for reducing the cycle time of a brazing process according to a further embodiment. [Figure 8] 1A-1C are schematic diagrams of stacks of brazed parts with alternating layers of PG to illustrate a method for reducing the cycle time of a brazing process, according to an embodiment.

[0028] These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. DETAILED DESCRIPTION OF THE INVENTION

[0029] In technical fields involving the brazing of multiple components, it has recently become apparent that brazing cycle times can be problematic. For example, when components are brazed to form cold plates, the brazing cycle time can be very long. In these and other cases, each component may be provided as a metal layer brazed to an adjacent metal layer. Each pair of adjacent layers is stacked together with alternating layers of material having a thermal conductivity equal to or less than that of the base material (e.g., steel) and placed in a brazing furnace. Operating the brazing furnace to raise the temperature of the stack to the brazing temperature often takes a long time. This is due to the relatively low thermal diffusivity of the stack material, which causes the center of the stack to heat only slowly. For large stacks, the brazing cycle time can be up to 12 hours or more. Therefore, a method is needed to reduce the brazing cycle time for large stacks of components.

[0030] Thus, as described below, a method is provided for reducing the cycle time of a brazing process for a large stack of parts, the method comprising replacing alternating layers of material in the large stack of parts with graphite sheets made from pyrolytic graphite (PG), which has a relatively high thermal diffusivity and therefore transfers heat to the center of the large stack more quickly than would be possible using other methods.

[0031] 1 and 2-5, a method 100 for reducing the cycle time of a brazing process is provided.

[0032] The method 100 initially includes placing a first pair of brazed components 110 and a second pair of brazed components 120 together (block 101), stacking the first pair of brazed components 110 and the second pair of brazed components 120 to form a stack 130 (block 102), and interposing a PG 140 between the first pair of brazed components 110 and the second pair of brazed components 120 in the stack 130 (block 103). Additional PGs 145 may be provided or layered on one or both of the top and bottom of the stack 130 (block 1035). For clarity and simplicity, the stack 130 in FIGS. 2 and 4 only shows the first pair of brazed components 110 and the second pair of brazed components 120, but it will be understood that additional pairs of brazed components and layers may be included in the stack 130. The first pair of brazing parts 110 may include a filler or brazing material 111 interposed between brazing parts 112. The brazing parts 112 may be provided as generally flat, planar blocks or layers of metallic material. The second pair of brazing parts 120 may similarly include a filler or brazing material 121 interposed between brazing parts 122. The brazing parts 122 may be provided as generally flat, planar blocks or layers of metallic material.

[0033] The method 100 may further include placing the stack 130 including the PG 140 in a brazing furnace 401 (see FIG. 4 ) and heating the first pair of brazing parts 110 and the second pair of brazing parts 120 to a brazing temperature of approximately 1050-1200° F. (Block 104). This effectively brazes the brazing parts 112 of the first pair of brazing parts 110 together and brazes the brazing parts 122 of the second pair of brazing parts 120 together. While this process would require a significant amount of time to fully heat the center of the stack 130, the presence of the PG 140 and additional PG 145 in the stack 130 increases the effective thermal diffusivity of the stack 130 and correspondingly reduces the cycle time required to braze together the brazing parts 112, 122 of each of the first pair of brazing parts 110 and the second pair of brazing parts 120. According to embodiments, the PG 140 and the additional PG 145 can increase the effective thermal diffusivity of the stack 130 by several times (i.e., by about 3.0 times or more) and correspondingly reduce the cycle time required to braze together the brazing parts 112, 122 of each of the first pair of brazing parts 11 and the second pair of brazing parts 120 by several times (i.e., by about 3.0 times or more). According to further embodiments, the PG 140 and the additional PG 145 can have a relatively high thermal diffusivity of about 500 mm / s or more.

[0034] The reduction in cycle timing is determined at least in part by the structure of the PG 140. The PG 140 (and additional PG 145) includes multiple sheets 141 of PG material or other similar material. The relatively high thermal diffusivity of the PG 140 is due in part to the structure of the multiple sheets 141, generally indicated by the plane P of the PG 140. Thus, when heat is applied to the stack 130 including the PG 140 in the brazing furnace 401, the heat is transferred along the plane P of the PG 140 at a relatively faster rate than any other portion of the stack 130. This transferred heat is then conducted from the PG 140 into at least the central portion 131 of the stack 130 and outwardly therefrom.

[0035] The method 100 of FIG. 1 may further include covering the PG 140 (and additional PG 145) with a metal housing 300 (block 105) and interposing a first stop-off layer 301 and a second stop-off layer 302 between the PG 140 and each of the first pair of brazed parts 110 and the second pair of brazed parts 120 (block 106). As seen in FIG. 3 , the metal housing 300 may be formed from aluminum or another similar metal material or alloy and aligned with at least the top and bottom surfaces of the PG 140. In some cases, the metal housing 300 may completely cover the entire PG 140. In some or all cases, the metal housing 300 may be provided as a solid sheet with few or no openings, or as a frame with one or more relatively large openings. The first stop-off layer 301 and the second stop-off layer 302 may be formed from a metal oxide powder such as aluminum oxide, titanium oxide, yttrium oxide, magnesium oxide, or another similar material, and prevent PG 140 (where no metal housing 300 is provided or in openings in the metal housing 300 provided as a frame) or the metal housing 300 from sticking to either the first pair of brazed parts 110 or the second pair of brazed parts 120 during or after heating / brazing.

[0036] According to an embodiment, the heating may be performed in a brazing furnace 401, as shown in FIG.

[0037] The method 100 of FIG. 1 may also include at least one or more of: bending the end 142 of the PG 140 around at least one outer edge of the brazing components 112, 122 of at least one of the first pair of brazing components 110 and the second pair of brazing components 120 (block 108); and attaching an additional PG piece to the end 142 of the PG 140 to abut against at least one outer edge of the brazing components 112, 122 of at least one of the first pair of brazing components 110 and the second pair of brazing components 120 (block 109). As shown in FIG. 5, bending can be performed if there is excess length of PG 140. As long as the bend 501 is smooth and free of kinks or folds, the multiple sheets 141 of PG 140 will remain intact and capable of transferring heat longitudinally. Therefore, heat applied from the side is transferred toward the bend 501 along the plane P of the PG 140, as shown in FIG. 5. At the bend 501, heat is transferred along and around the bend 501 and then vertically along the length of the end 142, whose plane P is oriented vertically. The heat transferred to the end 142 can then be conducted into a proximal portion of at least one of the brazing parts 112, 122 of the first pair of brazing parts 110 and the second pair of brazing parts 120. As shown in FIG. 6, attaching the additional PG piece effectively lengthens the PG 140. Thus, heat applied from the side, as shown in FIG. 6, is transferred along the plane P of the PG 140 toward the additional PG piece 601. At the additional PG piece 601, heat is transferred vertically along the length of the additional PG piece 601 and the vertically oriented additional PG piece 601. The heat transferred to the additional PG piece 601 can then be conducted into a proximal portion of at least one brazing part 112, 122 of at least one of the first pair of brazing parts 110 and the second pair of brazing parts 120. The bending and attachment of the additional PG piece can be performed similarly for the additional PG 145.

[0038] 7, a method 700 for reducing the cycle time of a brazing process is provided. Method 700 is generally similar to method 100 and need not be described in detail. Method 700 includes placing together a plurality of pairs of brazed components, each having a brazing material interposed between the brazed components (block 701), stacking the pairs of brazed components to form a stack (block 702), interposing a PG between adjacent ones of the pairs of brazed components (block 703), providing additional PG 145 as layers on one or both of the top and bottom of the stack 130 (block 703), and heating the pairs of brazed components to a brazing temperature (block 704). The method 700 may further include covering the PG with a metal housing (Block 705) and interposing a first stop-off layer and a second stop-off layer between the PG and each corresponding one of the plurality of pairs of brazed components (Block 706). Additionally, the method 700 may further include bending an end of the PG around an outer edge of at least one brazed component (Block 708).

[0039] 8 , a method 800 for reducing cycle time of a brazing process is provided. Referring to FIG. 8 , the method includes forming a first laminate 810 and a second laminate 820, each of which includes a plurality of pairs 811, 821 of brazed parts. The method further includes positioning the first laminate 810 and the second laminate 820 adjacent to one another, interposing a PG 830 between at least one adjacent pair of the plurality of pairs 811 of brazed parts in the first laminate 810, and bending at least one end 831 of the PG 830 to extend between the first laminate 810 and the second laminate 820, along one or more of the plurality of pairs 811, 821 of brazed parts in the first laminate 810 and the second laminate 820. The end 831 of the PG 830 is elongated and may actually extend along a substantial height of the first laminate 810 and the second laminate 820, and in some cases may extend between at least one adjacent pair of the plurality of pairs 821 of brazed parts in the second laminate 820. An additional PG layer 832 may also be provided as a layer on at least one of the top and bottom of at least one of the first laminate 810 and the second laminate 820. The method further includes heating the plurality of pairs 811, 821 of brazed parts of the first laminate 810 and the second laminate 820 to a brazing temperature to braze the respective brazed parts 811, 821 of the first laminate 810 and the second laminate 820 together. As noted above, PG830 has a thermal diffusivity of about 500 mm / s or greater and increases the effective thermal diffusivity of at least the first laminate 810 (and in the illustrated case, the second laminate 820) by several times (i.e., about 3.0 times or greater), and correspondingly reduces the cycle time required to braze together the brazed components of each of the first laminate 810 and the second laminate 820.

[0040] 8, when heat is applied to the first stack 810 and the second stack 820, the heat is transferred along the plane of the PG 830, along the plane of the portion of PG 830 that is between the first stack 810 and the second stack 820, at a relatively faster rate than to any other portion of the first stack 810 and the second stack 820. This transferred heat is then conducted outward from the (vertical) portion of PG 830 that is between the first stack 810 and the second stack 820 (where the plane of PG 830 is vertically oriented) to the proximal side of the first stack 810 and the second stack 820.

[0041] It is therefore apparent that multiple stacks of brazed components can be brazed simultaneously in a brazing furnace and with reduced cycle times.

[0042] An advantage of the features described herein is the provision of a method for reducing the cycle time of the brazing process for large stacks of parts, including, for example, replacing alternating layers of material in a large stack of parts with graphite sheets made of PG, which has a relatively high thermal diffusivity and therefore transfers heat to the center of the large stack more quickly than would be possible using other methods.

[0043] The term "about" is intended to include the degree of error associated with measurement of a particular quantity with the equipment available at the time of filing.

[0044] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. It will be further understood that the terms "comprises" and / or "comprising / including," when used herein, specify the presence of stated features, components, steps, operations, elements, and / or ingredients, but do not exclude the presence or addition of one or more other features, components, steps, operations, elements, ingredients, and / or groups thereof.

[0045] While the present disclosure has been described with reference to one or more exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from essential scope thereof. Therefore, it is not intended that the disclosure be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the disclosure, but rather that the disclosure will include all embodiments falling within the scope of the appended claims.

Claims

1. 1. A method for reducing cycle time of a brazing process, comprising: disposing together first and second pairs of brazing components, each of the first and second pairs of brazing components having a brazing material interposed therebetween; stacking the first pair of the brazed components to form a first stack; stacking the second pair of brazed components to form a second stack; interposing a plurality of sheets of pyrolytic graphite (PG) between the first laminate and the second laminate; heating the first and second pairs of brazing components to a brazing temperature to braze together the brazing components of each of the first and second pairs of brazing components; A method comprising:

2. 2. The method of claim 1, wherein the PG increases the effective thermal diffusivity of the stack and correspondingly reduces the cycle time required to braze together the brazed parts of each of the first and second pairs of brazed parts.

3. The method of claim 2 , wherein the PG increases the effective thermal diffusivity of the laminate by a factor of about 3.0 or more.

4. The PG is about 500 mm ２ 10. The method of claim 1, wherein the material has a thermal diffusivity of 1 / s or greater.

5. The method of claim 1, wherein the brazing temperature is about 1050-1200°F.

6. 10. The method of claim 1, further comprising interposing a first stop-off layer and a second stop-off layer between the PG and each of the first and second pairs of brazed components, respectively.

7. The method of claim 1 , further comprising encasing the PG in a metal housing.

8. The method of claim 1 further comprising providing a layer of PG on at least one of the top and bottom of the stack.

9. bending the PG around an outer edge of at least one of the first pair and the second pair of the brazed parts; and attaching an additional PG piece to the PG for abutting the outer edge of the at least one of the first and second pairs of the brazed parts.

10. 1. A method for reducing cycle time of a brazing process, comprising: disposing together each of a plurality of pairs of brazed components, each of the plurality of pairs of brazed components having a brazing material interposed therebetween; stacking the pairs of brazed components to form a plurality of stacks; interposing a plurality of sheets of pyrolytic graphite (PG) between adjacent ones of the plurality of laminates; heating the plurality of pairs of brazing components to a brazing temperature to braze together the brazing components of each of the plurality of pairs of brazing components; A method comprising:

11. 11. The method of claim 10, wherein the PG increases the effective thermal diffusivity of the laminate and correspondingly reduces the cycle time required to braze together the brazed parts of each of the plurality of pairs of brazed parts.

12. 12. The method of claim 11, wherein the PG increases the effective thermal diffusivity of the laminate by a factor of about 3.0 or more.

13. The PG is about 500 mm ２ 11. The method of claim 10, wherein the material has a thermal diffusivity of 1 / s or greater.

14. The method of claim 10, wherein the brazing temperature is between about 1050 and 1200°F.

15. The method of claim 10 , further comprising interposing a stop-off layer between the PG and each of the corresponding ones of the plurality of pairs of the brazed components.

16. The method of claim 10 further comprising encasing the PG in a metal housing.

17. The method of claim 10 further comprising providing a layer of PG on at least one of the top and bottom of the stack.

18. Bending the PG around an outer edge of at least one of the pairs of brazed parts; attaching an additional PG piece to the PG for abutting the outer edge of the at least one of the first pair and the second pair of brazed parts; The method of claim 10, further comprising at least one or more of:

19. 1. A method for reducing cycle time of a brazing process, comprising: forming a first stack and a second stack, each stack comprising a plurality of pairs of brazed components; disposing the first stack and the second stack adjacent to one another; interposing pyrolytic graphite (PG) between at least one adjacent one of the plurality of pairs of the brazed components in the first stack; providing a layer of PG on at least one of the top and bottom of the first and second stacks; bending an end of a PG to extend between the first and second stacks along one or more of the pairs of brazed components in the first and second stacks; heating the pairs of the brazing components of the first and second stacks to a brazing temperature to braze together the brazing components of each of the first and second stacks; A method comprising:

20. The PG is about 500 mm ２ 20. The method of claim 19, wherein the brazing component has a thermal diffusivity of at least about 3.0 times greater than or equal to 1 / s and increases the effective thermal diffusivity of at least the first laminate by a factor of about 3.0 or greater, and correspondingly reduces the cycle time required to braze together the brazed components of each of the first and second laminates.

Images