GB2151965A

GB2151965A - Brazed joint and method of making

Info

Publication number: GB2151965A
Application number: GB08418411A
Authority: GB
Inventors: Edward Bernard Gempler
Original assignee: United Aircraft Products Inc
Current assignee: United Aircraft Products Inc
Priority date: 1983-12-23
Filing date: 1984-07-19
Publication date: 1985-07-31
Also published as: JPS60141366A; DE3428590A1; GB8418411D0

Abstract

In a brazed joint in which a tube or other rod-like member 10 has an end received in a recess 12, the recess wall and the received tube end have complementary tapered configurations and, as a part of the joining process, the tube is thrust to a seat in the recess so that attainment of a temperature sufficient to melt the braze material occurs while there is a pressured contact between mating tube and wall surfaces. <IMAGE>

Description

SPECIFICATION Brazed joint and method of making Background of the invention 1. Field of the Invention: This invention relates to the art of joining metal parts by brazing, that is, through the use of a filler or braze alloy the melting point of which is slightly below melting temperatures of the parent metals.

In particular the invention is concerned with the brazing of tubular or rod-like members into a body recess when materials involved or quality of braze requirements pose special difficulties.

2. Description of the Prior Art: Although not so limited, the invention has special reference to the brazing technique known as vacuum furnace brazing. In that method, parts to be joined together are bought to an assembled relation. A filler metal or braze alloy is positioned between mating part surfaces or is positioned so that upon melting it will flow by gravity or capillary influence between the mating part surfaces. With the parts maintained in an assembled relation, they are put in a furnace, the air in the furnace is evacuated, and the temperature therein raised to the melting point of the braze alloy but below the melting point of the parts being joined. Upon the assembly being allowed to cool, it will be found that the braze alloy has distributed itself within the joint between the parts, and in solidifying, has united the parts one with another.

Intimacy of contact between the mating surfaces of parts to be joined, at the moment the braze temperature is reached, is important to successful brazing. It is usually attempted to insure this by a locking-up of parts in a fixture, prior to brazing.

However, this practice will not of itself resolve the problem of obtaining pressured contact between a rod or tube end and the side wall of a hole or recess in which it is received. These parts are sized to allow for the presence of interposing filler (braze) material, which may typically be foil wrapped around a tube prior to inserting it into a hole. There being no practicable way in which either an expanding pressure can be applied to the tube end or a contracting pressure applied to the hole wall, in a holding fixture, the presence of voids has been regarded as an unavoidable part of the accomplished joint.

The problem, particularly found in furnace brazing but occuring also in dip brazing, obviates brazing as a jointing technique for some applications.

For example, the joining of unlike metals requires a uniformly sound braze, as do assemblies which must function under conditions of mechanical stress or under conditions of positive containment of fluid pressure.

The inventor and others substantially involved in the preparation of this application have no knowledge of prior art more pertinent than as indicated above.

Summary of the invention A brazed joint and method of making according to the invention provides for putting of slight, complementary tapers on both the hole wall and the tube or rod end portion to be installed therein. Further, a positive pressure is applied to seat the tube or rod end to the hole wall and this pressure is maintained while the temperature of the assembly is raised to the melting temperature of the provided braze alloy. In this manner, intimacy of contact between mating surfaces is achieved and conditions satisfied for the making of a uniformly sound joint. A relatively small taper, as on the order of 2 , is regarded as desirable since it makes possible a long bearing or contact area between mating surfaces. Tapers up to at least 10 , however, will produce satisfactory results.The technique has been successfully used in assembling a non-aluminum tube or rod to an aluminum body and it is expected that it would serve equally well in other applications involving like or unlike metals.

An object of the invention is to provide a brazed joint and method of making substantially as in the foregoing.

Other objects and structural details of illustrative embodiments of the invention will appear from the following description when read in connection with the accompanying drawings, wherein: Figure 1 is a view in perspective of a sub-assembly brazed in accordance with concepts of the invention; Figure 2 is a view of parts of the sub-assembly in an assembly process; Figure 3 is a view in cross-section of an assembled sub-assembly, prior to brazing, but with an end thrust being applied to the parts; Figure 4 is a fragmentary view of the joint of Figure 3, shown as it appears after brazing; and Figure 5 is a view like Figure 1, showing an alternate manner of bringing braze material to the joint.

Referring to the drawings, the metal fabrication arts provide a number of instances in which the invention can be used to advantage. For illustrative purposes, and for simplicity of disclosure, the brazing technique is here shown as uniting a rod-like member 10 and a body 11, the latter having a recess into which one end of the tube is inserted.

The body recess is in the illustrated instance a through hole 12 and member 10 an open ended tube. One end of the tube 10, that end received in hole 12, is externally reduced to form a tapered surface 13. Hole 12 is drilled and reamed, or otherwise formed, to present a tapered wall surface 14 complementary to surface 13.

The hole 12 is sized to allow tube 10 to enter therein while wrapped with braze material in the form of a foil 15. With the tube end so wrapped, as shown in Figure 2, and inserted in hole 12, as shown in Figure 3, an end thrust can be applied to the parts pressuring the tube to a seat in hole 2.

While this will ordinarily be done in an appropriately constructed fixture, it is here shown as resulting from application of a weight 16 to the outer end of the tube 10 while reactant pressure is sup plied by a support 17. The assembly comprising pressures parts 10 and 11 now subjected to the brazing operation in a furnace, by a dip process, or otherwise. Thus the temperature of the assembly or specifically of the joint to be brazed is raised to the melting temperature of the braze foil, maintained at such temperature for a selected interval, and then reduced. As braze foil 15 melts, the continuing thrust applied by weight 16 forces part surfaces 13 and 14 into intimate contact. All conditions promoting or necessary for an excellent brazed joint are accordingly present and, upon cooling of the parts, a long, sound braze will be seen to have been affected (see Figure 5).

In the drawing, the degree of taper of the surfaces 13 and 14 has been exaggerated for illustrative purposes. A taper on the order of 2 to 10 will perform satisfactorily. However, a taper which most closely approaches a straight line is desirable as giving maximum contact area between the mating surfaces. Also, and again for illustrative purposes, the existance of filler metal between the surfaces 13 and 14 has been exaggerated in Figure 3. The filler or braze material is advantageously put in place as a wrapping of foil 15. It can, however, be supplied in other forms. As shown in Figure 5, for example, a tube 18 is received in a recess or hole in a body 19. On the upper surface of the body, in a relatively closely surrounding relation to the tube, is an annulus 21 of brazing material. At the critical or brazing temperature, the material of annulus 21 melts and under gravity and capillary influences flows into the body recess, distributing itself around the inserted tube end. The resulting joint will have the appearance and quality substantially as indicated in Figure 4.

As has been indicated, hole 12 could instead be a recess terminating within the body and tube 10 could be a solid rod-like member. As a preparatory step to brazing, foil 15 could be inserted to line hole 12, rather than being wrapped on tube 10 as shown.

Claims

1. An assembly united by brazing, including a metal body having a recess opening to at least one side thereof and a rod-like metal member having an end received in said recess, said rod-like member end and the body wall defining said recess being sized to accomodate the presence therebetween of a filler or braze material, said recess wall and the received end of said rod-like member having complementary taper formations allowing a braze operation to be carried out in the presence of applied and reactant pressures between surfaces in contact through the braze material.

2. An assembly according to claim 1, said braze material being in a form for interposing between complementary taper formations as a part of an operation inserting said member end into said recess.

3. An assembly according to claim 2, said braze material having the form of a foil wrapped around said received end of said rod-like member prior to its being inserted into said recess.

4. An assembly according to claim 1, said braze material having a ring-like shape and being placed on said body around a respective recess to melt at a braze temperature and flow into said recess around the received end of said rod-like member.

5. An assembly according to claim 1. the complementary taper formations on said recess wall and on the received end of said rod-like member being in the range of 2 to 10 degrees.

6. An assembly according to claim 1, said recess being a through aperture in said body, said rod-like member being a tube.

7. A method of making an assembly as in claim 1, wherein said assembly with provided braze material is heated to a temperature rising to a value at which the braze material melts. and as the temperature rises to and reaches said temperature generating said applied and reactant pressures.

8. A method according to claim 7, said generated pressures being applied as an end thrust to said rod-like member against the resistance of a supported body, seating the received end of said rod-like member to taper on said recess wall.

9. A method according to claim 7, wherein said braze material is provided by wrapping a braze foil around the tapered end of said rod-like member prior to its being inserted into said recess.

10. A method according to claim 7, wherein said braze material is provided in a form and at a location to slow into said recess upon the attainment of brazing temperatures.

11. An assembly united by brazing substantially as hereinbefore described with reference to Figure 1, 4 or 5 of the accompanying drawing.

12. A method of manufacturing an assembly united by brazing substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings.