Brazed hydraulic fittings with interference fit and method of making same

The present invention is a brazed fitting suitable for use as a hydraulic coupling for pressurized fluids. In the first embodiment, the male component has a tapered surface which mates and creates an interface with a similarly tapered surface of a female component. A brazing material is heated to diffuse and alloy within the interface, forming a connection between the surface portions which is stronger than the metal being connected. A groove on the male component retains the brazing material within the surface portions so that after the components are joined in an interference fit, the assembly is heated and the brazing material melts within the interface and connects together the mating surface by diffusing and alloying. The counterbore of the female component does not require a base, and the resulting structure has improved fluid flow characteristics. In the second embodiment, the male component is generally cylindrical and the female component has a bore with a first aligning portion having a greater diameter than the male components, a second mating portion with approximately the same diameter, and a third guiding portion having a tapered surface connecting the first and second portions. The male portion is first positioned and aligned in the first portion before being pressed and creating an interference fit in the second portion before brazing. In the third embodiment, a tube is used as the male component which is pressed into the bore as in the second embodiment, but with the second portion of the bore having a shoulder portion for abutting the end of the tube.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to hydraulic or pneumatic fittings. 
More specifically, the field of the invention is that of brazed fittings 
for forming hydraulic couplings. 
2. Description of the Related Art 
Hydraulic fittings are conventionally of brazed construction, particularly 
those fittings having a specially shaped design. Conventional brazed 
fittings are manufactured by a press fit methodology, whereby the 
typically steel components are bored or counterbored to a precise 
diameter. There is usually a lead-in taper of 45.degree. at the outer end 
of the conduit which has counterbore aiding in locating the mating port. 
The conduit end includes a spigot which enters the counterbore with an 
interference fit of between 0.0005 inches and 0.005 inches, requiring that 
each part be made to a maximum tolerance of .+-.0.001125 inches. A brazing 
material, for example a pure copper or copper compound formed in a ring, 
is located between the bottom of the spigot and the base of the 
counterbore. During the heating, the brazing material melts and is drawn 
up the interference fit by capillary attraction. The brazing material 
diffuses and alloys with the metal of the components so that the interface 
between the spigot and the counterbore is stronger than material of the 
components. Ideally, the resulting integral fitting produces a high degree 
of integrity and reliably performs its intended function, while minimizing 
production costs. 
An alternative to brazed fittings involves the use of multiple fittings 
which are required in order to connect different sized tubes, ports, etc.. 
However, the formation of the multiple connections requires additional 
material, as well as additional manufacturing time, which is duplicative 
and wasteful. Further, each connection provides another possible leak path 
for the pressurized medium within the fitting. Therefore, brazed fittings 
are preferable because they are generally less expensive to manufacture, 
less expensive to install, and have fewer potential leak paths. 
However, on the rare occasions when a brazen fitting fails, the failure is 
typically catastrophic. For example, the intruding component of the brazed 
fitting may break loose from its mating part, usually while containing 
fluids under high pressure, resulting in a rapid deterioration of the 
hydraulic system. This is usually the result of the brazed fitting being 
poorly formed, typically due to insufficient "wetting" of the mating 
surfaces which are brazed together. The insufficient "wetting" may be due 
to misalignment or imprecise manufacture of the components which are press 
fit together. Additionally, poorly formed brazed fittings may leak in 
service, and also may contribute to improper alignment with other 
components in a system. 
One particular problem with such fittings involves the intruding part being 
subject to misalignment during assembly. For example, the lead-in of the 
intruding conduit end may not be evenly aligned with the corresponding 
lead-in chamfer of the port which allows the conduit end to cant over 
prior to the application of assembly force. When assembly force is 
applied, the conduit end is driven down the chamfer and areas of 
alternating high and low interference fit are created. These areas of low 
integrity interference fit are areas of potential porosity and of weakness 
under pressurized loads. 
Also, a common side effect of conventional brazing is the formation of a 
sharp-edged skin at the visible joint line between the assembled conduit 
end and the port. This is caused by the port gouging some material from 
the surface of the conduit end as it is press fit during assembly, and the 
gouged material is an unsightly blemish. Further, the seal between the 
brazed surfaces may become porous and have substantially reduced strength 
similar to misaligned components. 
Another potential problem with conventional brazing techniques, although 
much rarer than the aforementioned problems, is that penetration of the 
brazing material into the interface between the mating surfaces may be 
insufficient to form a reliable brazed connection. The brazing connection 
depends on the mating surfaces being closely positioned, and on the 
brazing material being in contact with the mating surfaces when in the 
liquid state. If the mating surfaces are not properly formed, or the 
brazing material is not in contact with both of the mating surfaces, the 
liquid brazing material tends to flow away from the mating surfaces--being 
drawn by its own surface tension into a rounded mass of liquid away from 
the interface of the mating surfaces. After the rounded mass cools, it 
forms a solid mass which does not aid in bonding together the mating 
surfaces, and which also may go undetected until failure of the coupling. 
What is needed is an improved method of brazing together components of 
hydraulic fittings. 
A further need exists for a brazing method which aligns the components more 
precisely. 
Another need exists for a brazing method which avoids gouging the 
components during manufacture. 
Also needed is a brazing method which ensures penetration of the brazing 
material into the interface of mating surfaces. 
SUMMARY OF THE INVENTION 
The present invention involves a method of brazing together components of 
hydraulic fittings which has greater reliability and accuracy than the 
aforementioned prior art methods. The female component is formed with an 
aligning portion which facilitates the alignment of the components. The 
female component also includes a guiding portion having a tapered surface 
which eases insertion of the male component and deters gouging of the 
components during the manufacture. Also, the female component has a mating 
portion which forms an interference fit with the male component to 
maximize penetration of brazing material into the interface between the 
components. This structure thereby facilitates the connection of the male 
and female components by first facilitating the alignment of the 
components, then facilitating the creation of an interference fit while 
minimizing gouging so that when the joined components are heated, the 
brazing material diffuses evenly through the interference fit and secures 
the mating surfaces. 
One advantage of the present invention is that the fitting components may 
be manufactured more easily. The relatively slight taper of the guiding 
surface allows for greater manufacturing tolerances, for example about 
.+-.0.003 inches, which lowers the difficulty and expense of manufacturing 
the components of the fitting. Further, the slight tapers are 
self-aligning in a relatively tight interference fit and do not tend to 
gouge when pressed together so that the components may be readily and 
reliably assembled. Misalignment of the components is also minimized by 
the aligning portion which constrains the male component from lateral 
movement prior to assembly. 
Another advantage is obtained by locating the brazing material in a groove 
in the spigot of the male component. This locates the brazing material at 
the site of the brazing and the interference fit between the mating 
surfaces ensures that the liquid brazing material penetrates and secures 
the interface. This causes the brazing material to diffuse within the 
metal and form a region of alloy which is stronger than the pure metal 
itself. Both peel testing and shock loading testing on fittings made 
according to the present invention have shown that the pure metal breaks 
before the alloy portion at the brazing site. 
The internal flow characteristics are improved for a hydraulic coupling 
formed according to the invention. The port may be machined without a base 
so that the fluid flow is not disturbed by turbulence normally caused by 
the base of the port. The base is no longer required because the brazing 
material is located in the groove on the spigot. Further, the internal 
bore of the spigot may include an internal taper to provide a more laminar 
flow through the path defined by the receiving taper of the port and the 
spigot of the conduit end. 
Other advantages are also derived from the present invention. For example, 
unsightly material from one component gouging another is minimized or 
eliminated. The assembly of the components is much more accurate, making 
the fittings easier to be used in manufacturing plants. Also, the 
resulting hydraulic couplings may withstand far greater pressures than 
those with the prior art brazed fittings, with porosity at the interface 
being virtually eliminated. In addition, the present invention provides a 
reliable fitting using a tube as one of the components. 
A cylindrical embodiment of the invention particularly addresses the 
problem of misalignment of the fitting components in the brazing process. 
Tapered components may be subject to differential expansion during the 
heating cycle of the brazing process causing partial separation. This 
potential problem may be countered by strict adherence to machining 
specifications in an ideal processing environment, but maintaining such 
adherence to specifications and an ideal processing environment may not be 
economically feasible. However, mating cylindrical surfaces are much less 
prone to such separation caused by differential expansion, and this 
cylindrical embodiment of the invention helps to avoid such potential weak 
points in the interface between fitting components. 
This cylindrical embodiment of the invention is important in securing a 
tube as one of the components of the hydraulic fitting. When a tube is 
pressed into a conventional braze counterbore, the outer surface of the 
tube tends to scrape off and peel back at the corner between the chamfer 
and the sides of the counterbore ("skinning"). The gouged surface of the 
tube contacts the internal diameter of the bore only where the "skinning" 
is minimal, and gaps are formed in the areas of scraping and peeling which 
work against the formation of a strong brazed connection. Also, the 
standard lead-in chamfer is oriented at a 45.degree. angle which does not 
provide any means for properly aligning the tube. This cylindrical 
embodiment of the invention has a specially configured counterbore, with a 
first guiding portion having a diameter greater than the tube, a second 
tapered portion which provides a transition to a third interference 
portion which has an inner diameter designed to create an interference fit 
with the outer diameter of the tube. The first guiding portion also 
provides stress relief to the tube by spreading the stress of the assembly 
over a greater length, and by the soft braze material which supports the 
tube in the bore. 
The present invention, in one form, is a process for brazing together a 
male and a female component of a fitting for forming a hydraulic coupling, 
wherein the male component is generally cylindrical. First, a bore is 
formed in the female component, with the bore having three distinct 
portions. The first generally cylindrical aligning portion of the bore has 
a diameter greater than the diameter of the male component. The second 
generally cylindrical mating portion of the bore has a diameter 
approximately equal to the diameter of the male component. The third 
guiding portion of the bore has a tapered surface connecting the first and 
second portions of the bore. In the next step, the male component is 
located within the first portion of the bore and thereby aligns the male 
component within the bore. Then, the male component is pressed into the 
second portion of the bore to create an interference fit between the male 
and female components. A brazing material is located adjacent the 
interference fit. Lastly, the male and female components are heated to 
melt brazing material whereby liquid brazing material penetrates the 
interference fit. 
The present invention, in another form, is a brazed fitting formed by the 
above process wherein the brazing material is diffused and alloyed between 
the surfaces of the interference fit. 
One object of the present invention is to provide an improved method of 
brazing together components of hydraulic fittings. 
A further object is to provide a brazing method which aligns the components 
more precisely. 
Another object is to provide a brazing method which avoids gouging the 
components during manufacture. 
Also an object is to provide a brazing method which ensures penetration of 
the brazing material into the interface of mating surfaces. 
An additional object is to provide a structure which maintains the 
alignment of the fitting components.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiments disclosed below are not intended to be exhaustive 
or limit the invention to the precise forms disclosed in the following 
detailed description. Rather, the embodiments are chosen and described so 
that others skilled in the art may utilize their teachings. 
The present invention involves a fitting formed by brazing which is adapted 
to serve as a hydraulic coupling for a pressurized fluid. FIG. 1 shows two 
components of the first embodiment, namely port body 4 and conduit end 6, 
which are brazed together to form brazed fitting 8 shown in FIG. 3. Port 
body 4 includes internal fluid passageway 10 in fluid communication with 
port opening or counterbore 12 defined by port surface portion 14. Conduit 
end or spud 6 includes spigot 16 which has a surface portion which is 
shaped to match the contour of port surface portion 14, with spigot 16 
extending from shoulder 18. Bore 20 extends through the axial center of 
conduit end 6, with bore 20 including optional radially outwardly 
extending tapered surface 22 within spigot 16. As shown in FIG. 3, port 
surface portion 14 and spigot 16 abut to form interface 24 between their 
outer surfaces. 
In accordance with one aspect of the present invention, port surface 
portion 14 and spigot 16 are tapered. Interface 24 has a relatively high 
unit loading up which a brazing material flows by capillary attraction 
during the brazing process. The tapered fit of port surface portion 14 and 
spigot 16 help to align interface 24, and shoulder 18 further facilitates 
the alignment of conduit end 6 in port body 4. The taper angle, relative 
to the central axis of conduit end 6, is slight, for example equal to or 
less than about 10.degree., and preferably about 5.degree.. This allows 
port surface portion 14 and spigot 16 to be produced within greater 
tolerances than conventional surfaces prepared for brazing. 
In accordance with another aspect of the invention, conduit end 6 includes 
groove 26 which is used to retain brazing material 28 before the insertion 
of spigot 16 into port surface portion 14 (FIG. 2). While conventional 
brazing involves depositing the brazing material at one end of the 
interface of surfaces to be brazed together, groove 26 advantageously 
locates brazing material 28 within the interface 24. This location 
prevents any pooling away of any melted brazing material from interface 
24, because groove 26 remains in communication with interface 24. Groove 
26 is preferably located in spigot 16 at the end proximate to port surface 
portion 14, although a groove for retaining brazing material may be 
located in either the port surface portion or the spigot. 
Fitting 8 is manufactured from two components to be connected together. The 
two components, for example port body 4 and conduit end 6, have their 
mating surfaces formed with a slight taper. The manufacture continues by 
depositing brazing material within a groove of one of the components, for 
example groove 26 of spigot 16. Next with this example, spigot 16 is 
positioned to intrude into port opening 12 and pressed to form an assembly 
by interference fit with port surface portion 14. The assembled components 
are heated to a brazing temperature so that the brazing material is drawn 
into interface 24 by capillary attraction. In the brazing process, the 
melted brazing material diffuses into the interstices between port surface 
portion 14 and spigot 16, associates with the metal material of the 
components, and forms alloys with that metal material which have greater 
strength than the original metal material. 
The enlarged view of interface 24 in FIG. 4 shows that alloyed regions 30 
are created after the brazing material melts and bonds with the material 
of port 4 and conduit end 6. Although not desired, the imperfections of 
the mating tapered surfaces also create small pockets 32 of brazing 
material between the material of port 4 and conduit end 6. Although 
ideally all of interface 24 would consist of alloyed regions 30, 
practicalities of manufacturing result in some of the braze interface 24 
being pure brazing material. However, the tapered structure formed with 
taper angle 34 greatly facilitates the formation of alloyed regions 30. 
Used as a hydraulic coupling, fitting 8 provides improved fluid flow 
characteristics due to the continuous taper of counterbore 12 to fluid 
passageway 10. Compared to prior art brazed hydraulic couplings which 
include a base portion forming a surface perpendicular to flow coming 
through bore 20, port surface portion 14 has a surface which tapers only 
slightly from being parallel to the flow through bore 20 and which 
continuously and uninterruptedly extends to passageway 10. Also, surface 
22 of bore 20 may taper outwardly and further promote more uniform fluid 
flow by providing a gradual expansion of the cross-sectional fluid flow 
area. The slight taper of the surfaces exposed to fluid flow, along with 
the absence of any significant stop or drag in the port-conduit 
connection, minimizes the turbulence created at bend 36 of the hydraulic 
coupling provided by fitting 8. 
In the preferred form of the first embodiment, port body 4 and conduit end 
6 are formed conventionally from steel. Brazing material 28 may be any 
suitable metal or alloy, for example copper. The copper may be in the form 
of a wire inserted into groove 26 as depicted in FIG. 2, or alternatively 
a copper paste or other brazing material may be deposited within groove 
26. The depth of groove 24 is in the range of about 0.3 mm to 1.0 mm, and 
preferably about 0.75 mm. 
FIG. 5 shows the two components of the second embodiment, namely port body 
38 and conduit 40, which are brazed together to form brazed fitting 42 
shown in FIG. 8. Port body 38 includes counter bore 44 which has three 
separately defined portions, which together comprise the braze port into 
which mating component 40 is assembled. FIG. 6 shows an intermediate step 
in forming brazed fitting 42, wherein spigot 45 of conduit 40 is partially 
inserted into bore 44 of port body 38. As shown in more detail in FIG. 7, 
bore 44 includes aligning portion 46 which has an inner diameter slightly 
greater than the outer diameter of spigot 45. Bore 44 also includes a 
mating portion 48 which has an inner diameter approximately equal to or 
slightly smaller than the outer diameter of spigot 45 so that mating 
portion 48 interferes with the outer diameter of spigot 45. Guiding 
portion 50 of bore 44 has a tapered surface joining the inner diameters of 
aligning and mating portions 46 and 48 which serves to facilitate the 
insertion of spigot 45 into port body 38 to form an interference fit 
between mating portion 48 and spigot 45 without gouging either component. 
The taper angle at which the guiding portion 50 of bore 44 is disposed 
relative to the axis of bore 44 is less than the conventional 45.degree. 
lead-in chamfer. More particularly, the angle of tapered guiding portion 
50 ranges from approximately 35.degree. to approximately 5.degree. 
relative to the bore axis. In the preferred embodiment, tapered guiding 
portion 50 is disposed at approximately 15.degree. relative to the bore 
axis. 
Similar to the first embodiment, spigot 45 may include groove 52 which 
receives brazing material 54, and may also include tapered portion 56 of 
conduit bore 58. However, in the second embodiment, spigot 45 has a 
generally cylindrical outer surface. In particular, lead-in portion 60 has 
an outer cylindrical surface which is slightly smaller than the inner 
cylindrical surface of mating portion 48 of bore 44. Further, mating 
surface 62 of spigot 45 has an outer cylindrical diameter which is 
slightly greater than the inner diameter of bore 44 so that mating 
surfaces 62 and 48 form an interference fit. 
Spigot 45 is inserted into port body 38 in a two step process. First, the 
components are aligned by inserting spigot 45 into aligning portion 46 
until mating surface 62 of spigot 45 abuts guiding portion 50. During this 
first step, no force is needed because lead-in portion 60 has a smaller 
outer diameter than the inner diameter of mating surface 48 of bore 44. 
The second step of the process involves press fitting the two components 
to form the interference fit. In this second step, the pressing of spigot 
45 causes mating surface 62 to travel down guiding portion 50. The taper 
of guiding portion 50 aids uniform movement of mating surface 62 into 
mating portion 48 of bore 44. Aligning portion 44 tends to keep the axis 
of spigot 45 generally coincident with the axis of bore 44. The pressing 
force continues until stop portion 64 of conduit 40 abuts the top surface 
of port body 38. At this point the components are connected by an 
interference fit. Conduit 40 and port body 38 are heated to a temperature 
in which the brazing material melts and fills the interstices between 
mating portion 48 and mating surface 62 to form alloyed regions such as 
described above. 
In the second embodiment, the length of aligning portion 46, the length of 
mating portion 62, and the size of port body 38 may be varied according to 
different specific applications. Generally, adding to the length of mating 
portion 62 requires a greater size for port body 38 which requires more 
materials and adds to the expense of the resulting fitting. Increasing the 
length of aligning portion 46 increases its effectiveness in maintaining 
the alignment of spigot 45 within bore 44. However simply increasing the 
length of aligning portion 46 correspondingly decreases the length of the 
interference fit between mating portion 48 and mating surface 62. 
The third embodiment is shown in assembled form in FIG. 9. Brazed fitting 
66 includes port body 68 and tube 70. Port body 68 defines bore 72 which 
has aligning, guiding, and mating portions similar to bore 44 of the 
second embodiment. In addition, bore 72 has shoulder 74 which provides an 
abutting surface for the end of tube 70, and which preferably has a 
through bore with a diameter approximately equal to the inner diameter of 
tube 70 to facilitate fluid flow through brazed fitting 66. Located near 
the end of tube 70, optional groove 76 may provide a location for brazing 
material. The aligning and guiding portions of bore 72 facilitate the use 
of tube 70 as the spigot or male member of the fitting. Similar to the 
second embodiment, the outer diameter of tube 70 is slightly greater than 
the inner diameter of the mating portion of bore 72 so that an 
interference fit is created between tube 70 and bore 72. 
The aligning portion of the bore helps to align the male fitting or tube 
and relieve stress applied to the male fitting or tube subsequent to 
forming the brazed connection. The degree of alignment and the amount of 
stress relief provided by that outer portion increases according to its 
length. However, the greater the length of the outer portion of the female 
component, a corresponding amount of material must be used to provide that 
greater length thus increasing the cost of the female component. 
Therefore, the length of the outer portion of the bore depends on the 
considerations relating to ease of manufacture, durability of the 
resulting fitting, and cost of the component material. 
The disclosed embodiments show the brazing material as a paste which is 
applied to the components of the fitting. Alternatively, the brazing 
material may be formed as a ring or other suitable shape and assembled 
together with the other fitting components prior to the melting step of 
the manufacturing process. As another alternative, the brazing material 
may be made in wire form, e.g., copper wire, which is wrapped about the 
connection of the fitting components so that the wire may melt and diffuse 
into the interstices between the mating surfaces. In the second and third 
embodiments, the aligning portion of the bore may provide an alternate 
location for the application of the brazing material, so that a groove 
does not need to be formed in the male member or tube. 
While this invention has been described as having a preferred design, the 
present invention may be further modified within the spirit and scope of 
this disclosure. This application is therefore intended to cover any 
variations, uses, or adaptations of the invention using its general 
principles. Further, this application is intended to cover such departures 
from the present disclosure as come within known or customary practice in 
the art to which this invention pertains.