FIELD OF INVENTION
The present invention relates to a method of holding 90° bend elbows having
88.9 mm Outer Diameter (OD) in a holding device and turning and edge preparation in
a turning center.
BACKGROUND OF THE INVENTION
It is known that a piping system in utility boilers is used to transport steam,
water, air and mixture of steam and water to various systems associated with the
boiler.
The piping system assist in mass transfer of steam, water etc. the elbows are
available at different angles, 22.5°, 37.5°, 44.4°, 45°, 66.5°, 89.4°, 90°. The elbows of
suitable thickness, specification, Outer Diameter etc are arrived and procured from
vendors. 99% elbows procured by BHEL are 90° elbows which has been converted to
required angles. In the manufacturing of steam generators, 90° elbows are mostly used
because of the nature of the layout. These elbows are known for maneuvering the pipe
line to prevent fouling. The elbows of different size are machined for edge preparation
which involves machining OD as well as Internal Diameter (ID) & matching the dl value
of the mating pipe. The concerned 90° elbow has a OD of 88.9 mm and 15.24mm
thickness. Machining of elbow involves horizontal boring for horizontal edge
preparation. Machining in horizontal boring is a time consuming process and it involves

form tool which deteriorates the surface finish which in-turn leads to failure in welding
joints.
To execute machining of elbows by incorporating single point cutting tool (i.e)
Throw away inserts is not possible as because the contour of elbow is not suitable for
holding in a lathe or turning centre. So this demands a suitable arrangement for holding
elbows in lathe or turning centre. Using the above said arrangement elbows of size 88.9
mm OD can be held in a turning centre which can involve single point cutting tool.
Thus, there is a need to propose a holding device to facilitate edge preparation of 88.9
OD, 90° elbows in turning centre which can in-turn increase productivity and utilize the
capacity effectively. Normally while welding high thickness pipes, the end of the pipes
will be machined angularly in the shape of 'v' or 'j' so that more amount of weldment
will be filled in the pipe to pipe butt welding. The machining to the required shape
depends on the kind of materials to be joined and the thickness of the pipes to be
joined. This operation is known as edge preparation.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a method of holding 90°
bend elbows having 88.9 mm OD in a holding device and turning and edge preparation
in a turning center which is capable of holding the said elbow and turning the same for
stock removal and edge preparation using single point cutting tool.

Another object of the invention is to propose a method of holding 90° bend
elbows having 88.9 mm OD in a holding device and turning and edge preparation in a
turning center which is able to enhance productivity and improved quality of the work.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1: Shows the side view of holding device and the elbows.
Fig. 2: Shows the front view or elevation of the holding device and the elbow.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The holding arrangement (3) as shown in Fig. 1 and Fig. 2 to hold the 90° elbow
of 88.9 mm OD consists of a fabricated box type shell where the arms a, b, c, d, e, f, g,
h are welded to form the box type holding arrangement. The job is held in place by the
help of screws 1A1, 1A2, 1B1, 1B2, 1B3 and 1C1, 1C2 and 1C3 so that there is no
movement of the job during machining and the holding is rigid enough to sustain the
pressure of machining with a single point cutting tool. Before the holding, the shell (3)
on both sides i.e. left and right, profile of elbow is drawn and three points along the
neutral axis are marked for drilling and tapping. The tapping of these holes matches
with the thread of six alien screws (1B1, 1B2, 1B3 and 1C1, 1C2 and 1C3) three on
each side each side of the holding device (3) disposed for clamping the elbow (2).
Upward and downward movement is arrested by single alien screw (1A1,1A2) each

from the top and bottom of the shell. Portion of the job to be machined is made to
protrude out of the box like structure which facilitates machining with ease. Before
machining, the elbow is marked for excess stock that has to be removed in machining.
The required edge preparation style is obtained by using the arrangement which helps
in achieving the surface finish, quality, dimensional accuracy etc.
According to the present invention, the pre marked elbow is made to seat inside
the holding arrangement (3) and the job is held tightly by the alien screws on both right
and left hand side of the arrangement. Then the top and bottom movement is arrested
by tightening the alien screw on the top and bottom of the arrangement. The job is
rigid as all the degrees of freedom for elbow is arrested. The 90° bend elbow (2) with
88.9 mm OD is now ready for machining. Machining process involves stock removal as
well as edge preparation. Stock removing limit is marked manually on the elbow, in
accordance with the radius of elbow and arm length of the elbow. The edge preparation
operation starts after stock removal. In order to make to different drawings for different
size of the components, a tabulation is be made with style names. Style P is one such
edge preparation.
In the holding arrangement the setting of 90° bend does not require any setting
in terms of its positioning in the box.

WE CLAIM
1. A method of holding 90° bend elbows having 88.9 mm OD (2) in a holding device
(3) for machining and edge preparation in a turning center, comprising;
developing a fabricated box like shell or holding arrangement (3) to hold 90°
bend elbows having 88.9 mm outer dia (2);
drawing a profile of the elbow (2) on the left and right sides of the shell (3) to
mark three points on each side of the shell to drill and tap along a neutral axis of the
elbow (2) to accommodate six (1B1, 1B2, 1B3, 1C1, 1C2 and 1C3) alien screws to
clamp the elbow (2);
drilling and tapping at top and bottom of the shell to accommodate two alien
screws (1A1,1A2) to sit on the job to arrest the upward and downward motion;
marking the elbow (2) for excess stock to be removed during machining;
wherein the elbow is held in the box making the portion to be machined
protruding out of the shell to facilitate machining when all the alien screws are allowed
to sit tight on the elbow during turning when edge preparation of the said elbow is
carried out.
2. The method as claimed in claim 1, wherein stock removing limit is marked
manually on the elbow in accordance with the radius of elbow and arm length of elbow.