Means for providing very small bend radii in the tube-like structures

The method disclosed allows the bending of tubular structures with much smaller radius bends than is normally acceptable for the diameter of the tubing section that is being bent. The method is very useful for making various fittings which perform bent routing functions in piping systems. The method also allows more controllable stretching of the tube metal, because stretching is done prior to bending of the angle.

BACKGROUND AND SUMMARY OF THE INVENTION 
Making various angle fittings or bending tubes has been a practice for many 
years. In some applications, long sweeping bends are used where the lowest 
possible pressure drop in the bend is desired. In other applications the 
space available, or the necessity to lie close to a right angle corner 
prompts the manufacturers to reduce the bend radius of the tube. 
The use of castings, and the like, has become commonplace. This is because 
the stretching required to bend most tubing or piping around the outside 
of the bend, or the compression that is required of the pipe wall material 
in the inside radius of the bend limits the radius of the bend to some 
multiple of the tube diameter. In many important cases a large savings in 
cost would be possible if it were possible to approximate the small bend 
radius of a casting or machined port fitting with a tubular fitting. 
An example of this situation is the use of large numbers of what are called 
"Banjo" fittings. A "Banjo" fitting has a body which looks a little like a 
Banjo, in that a stem, to which tubing is attached, extends from a 
circular end with a hole in the flat circular face of the circular end. 
This emulates the fret and string arm of a banjo extending from a circular 
sound box. Banjo fittings also require a bolt, through its center, through 
a hole in the circular end, to attach the "Banjo" fitting to the port. The 
fluid passage way is provided by drilling out the arm, and drilling out 
the center of the bolt. A hole is cross-drilled through the shank of the 
bolt to allow the fluid to enter the drilled out portion of the centerline 
of the bolt. Sealing, usually accomplished by a washer shaped gasket, is 
required between the banjo body and the port and the bolt head. The high 
cost of a "Banjo" connector is justified by the extensive work and 
material required to manufacture one. The use of "Banjo connections" has 
been worldwide for so many years and is eloquent testimony to the benefits 
which are gained by being able to make very small radius bends which are 
afforded by a "Banjo" connection. 
A "straight-out" connection, and a bend in the pipe or tubing being 
connected is much less expensive, and much more reliable. If it were not 
for the routing advantage of a "Banjo" type connection, it is doubtful 
that any "Banjos" would be used at all. 
The means disclosed herein provide a method of achieving the "Banjo" 
routing advantage, without having to also pay the high cost of a Banjo 
connection. 
It is the object of this invention to provide a tube-like structure which 
achieves a very small bend radius. 
Another object is to provide a complete family of fittings. 
Heretofore difficult to obtain advantageous benefits may be more easily and 
inexpensively gained. 
A more clear understanding of the means herein disclosed may be had by 
referring to the figures and discussion of the figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a tubular portion 10 is prepared for bending by the 
method herein disclosed. A portion 30-O (outside radius) and 30-I (inside 
bend radius) is shown with numbers 16 through 44 assigned to various walls 
and radii of the bulged section of the tube between tube segments 12 and 
14 as will be explained herein. 
The walls 18, 22, 26, 34, 38 and 42 are shown substantially flat and planar 
so as to make radii 16, 20, 24, 28, 32, 36, 40 and 44 more plainly 
visible. It is noted that it is not necessary that walls 18, 22, 26, 34, 
38, and 42 be flat and planar, only that radii 16, 20, 24, 28, 32, 36, and 
40 be well enough defined to cause the bending accommodations shown in 
FIG. 2 to take place as shown in FIG. 2. 
Forming this bulged bead-like structure will be accompanied by thinning of 
the wall 46, due to stretching of the material in the bulged area. It is 
also noted that there will be "work hardening" of this bent and thinned 
material if the material is metal. There is, therefore, a benefit to 
annealing this material before the bending in FIG. 2. If the material is 
thermoplastic then the deformed material should be heated after the 
bending of FIG. 2 to "set" the plastic in the bent configuration. 
Referring to FIG. 2, the surfaces (walls and radii) of the bulged portion 
are described using the numbers of FIG. 1. These numbers are not shown on 
FIG. 2 in order that the maximum clarity of the description of the 
movements of these surfaces be gained. 
FIG. 2 shows tube portions 12 and 14 after bending in the amount of angle 
"A" and the accommodations in the bulged area that have accommodated this 
angle of bend. The inner radius area of the portion 30-I folds together by 
bending to a more acute angle radii 16, 20, 24, and 28. Some bending of 
wall portions 18, 22, and 26 will also occur. The outer radius of the bend 
30-0 shows radii 32, 36, 40, and 44 getting larger as walls 34, 38, and 42 
come to their new orientation. In between these extremes intermediate 
bending of the bulged portion occurs. 
When this bending to angle "A" takes place a metal material will again work 
harden, helping to "set" the bend. 
Note that the minimum dimensions of the lengths of wall segments 18-34, 
20-38, and 26-42 depend on the angle "A" to which the tubes 12 and 14 are 
bent. In production it is convenient to assume that the maximum angle "A" 
will be around 110 degrees and made a bulged area that will accommodate 
that and all smaller angles. One might logically ask why would 110 degrees 
rather than 90 degrees be chosen? This is because in certain 
configurations of FIG. 3, one can put a slight bend into the tube leading 
to one of the terminal ends of device 100 in order that the tube will lay 
near the surface to which the other end of device 110 is attached. The 
"Banjo" replacement application is one of these configurations. 
Referring to FIG. 3, a device 100 is shown that is terminated by ends 1 and 
2. The small radius "R" is also shown. 
Terminations 1 and 2 may be tubes, swivel nuts, or any ends that facilitate 
the piping system and connection of that piping system. Radius "R" will 
depend on materials, diameters, wall thicknesses, the bulged area, or any 
other factor. Use of the means herein disclosed only permits a smaller 
radius "R" than other methods, given similar conditions. The method, 
however, offers the extremely attractive economic prospect of being able 
to replace many cast and machined fittings with less expensive fittings 
that offer very beneficial functional capabilities that were in many cases 
not economically possible with the older technology. 
FIG. 4 shows one of the above replacements, where one end of the fitting of 
FIG. 3 has been finished as a replacement for a "Banjo" connector. One 
immediate benefit is that even after end 1 of device 110 has been threaded 
into the port, the end 2 is 360 degree swivelable, about the axis of the 
port, and the nut is sealed to the tubing portion. In the case of a 
"Banjo" connector, when the bolt is tightened, the "Banjo" shaped portion 
is no longer swivelable. If the exit direction of the "Banjo" arm is not 
exactly in the direction required of the exiting piping, this pipe must be 
bent (if that is possible) or the "Banjo" must be loosened and 
repositioned. 
Combining the "Banjo" treatment of 1 in FIG. 3 with some sort of swiveling 
quick connector for the 2 arm of device 110 now allows swiveling about two 
axis. If this quick connector further allows some "wobbling" (of the 
incoming tube about the quick connector axis), then it is not necessary to 
have any strain on the incoming piping that results from trying to connect 
an incoming pipe that is not perfectly formed for a perfect fit. 
Since many, many factors can cause a non-perfectly formed pipe or tube, a 
perfectly fitting pipe is an unusual and rare commodity. The normal 
variations (even when both ends of the pipe do not move relative to each 
other during operation) is to use a length of flexible hose or tubing to 
accommodate non-perfect variations that are inevitably encountered. 
Obviously if it is not necessary to use this flexible section, the pipe 
costs much less, and lasts much longer. 
There are many benefits that may be gained by employing the means herein 
disclosed. Because fittings that allow for lower cost and the ability to 
achieve very small bend radii are not currently available, and because 
fittings that are available are difficult to have accommodate some of the 
superior connecting capabilities that are becoming available, individuals, 
whose business it is to route and attach the multitude of pipes and tubes 
that are necessary to the functioning of many everyday devices, are 
rethinking old strategies that they were forced to use in the past when 
these very accommodating solutions were not available. 
The means disclosed may also be used near the end of a thin wall pipe or 
tube where it is possible to pre-stretch this type of form. The form is 
not a simple bead in dimension, and a bead is much harder to subsequently 
bend. Also a simple bead on a pipe does not allow the large angle bend 
with no stretching of the pipe wall material during the bending operation. 
When this form is annealed after the preform stretching, the pipe may be 
bent to fit at assembly. For this reason, the combination of preforming 
and annealing is an important benefit that can be obtained with the means 
herein disclosed. In this latter case, ends 1 and 2 of 100 in FIG. 3 are 
continuing pieces of the pipe or tube. 
From the foregoing, it is clear that there are many functional and economic 
benefits which may be derived from the relatively simple expedient of 
forming a relatively large bulge on a tubular pipe or conduit. For a given 
bend, a forming mandrel may be positioned far enough into the bulged area 
to round slightly the outer radius of the bend (30-O, in FIG. 2), a slight 
stretching of that material may be cosmetically beneficial. It is noted 
that since the entire bend area has been pre-expanded prior to bending, 
there is no constriction of flow area compared to the flow area of the 
tube portions (see 12 and 14 of FIG. 2) as a result of the bend. 
While the above description constitutes the preferred embodiment of the 
invention, it will be appreciated that the invention is susceptible to 
modification, variation, and change without departing from the proper 
scope or fair meaning of the accompanying claims.