FIELD OF THE INVENTION
The present invention relates to a method of edge preparation in high thickness
metal tube for fabricated elbows. More particularly, the invention relates to a
method of edge preparation of high thickness (carbon and low alloy steels) pipes
for fabrication of elbows disposed in high pressure steam generators.
BACKGROUND OF THE INVENTION
During manufacturing of elbows for high pressure steam generators the elbows
edges are to be machined with bends for better weld deposition during welding.
The shape of the edge preparation will vary according to the pipe diameter,
thickness of the pipe, and the material.
Normally the edge preparation can be carried out in the horizontal boring
machine with a maximum of 2.5mm depth of cut. The outside diameter of the
pipe is varying from 219 mm to 558 mm. The material is low alloy steel with a
grade of SA335 P12, P22 and P91. The edge preparation is to be carried out on
both ends and it takes about 16 hours to complete the job. In contrast thereto,
the advanced CNC machines, where the depth of cut is up to 16 mm at least four
elbows can be finished in 8 hours. The known profile cutting machines allow
such edge preparations when the job is fixed horizontally. However, the known
profile cutting machines such as SAFOP does not allow edge preparation for
bend pipes like elbows. Hence, there is a need for a device and a method for
holding a work piece on known profile cutting machines to achieve faster and
better quality of edge preparation on elbows for high pressure steam generators.

OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a methods of profile
machining in high thickness pipe materials to make elbow joints which eliminates
the draw backs in the prior art methods and increases productivity.
Another object of the invention is to propose a method of profile machining in
thickness pipe materials to fabricate elbows, which allows easy-holding of the
elbow on a CNC machine so that accurate profiles can be accurately generated.
SUMMARY OF THE INVENTION
Accordingly, there is provided a method of profile machining in high thickness
pipe material to fabricate elbow used in high pressure steam generated, the
method comprising the steps of : placing an elbow horizontally or vertically in
between a top 'V' block (10) and a bottom 'V' block (11); clamping an elbow
using a top clamp box nut unit (04) and at least one 45 deg angular box nut unit
(06); adjusting the elbow to accurate position by simultaneous movement of a
top clamp screw rod (03) and at least one 45 deg angular supported screw rod
(05); and determining a positioning distance according to the outside diameter of
the elbow to be machined which varies from 219 mm to 558 mm.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows an isometric view of a holding device of the invention.
Figure 2 shows an elevation of the device of figure 1, with elbow in position.

Figure 3 shows a side view of the holding device to show how the elbow is held
in position and ready for machining.
DETAILD DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
According to the present invention, the machine operation is carried out in two
stages. In the first stage, one side of the elbow is machined in edge prepared to
the required profile depending upon the style required for welding/joining the
elbow with another pipe/elbow by welding process. In the second stage, the
same operation is repeated with another side of the elbow to complete the
machining operation.
Figure 1 shows the internal parts of the device without elbow and base screw. A
suitable opening was made in the base pipe (01) so that a top clamp screw rod
(03) can be positioned vertically in said base pipe (01). The outside diameter of
the base pipe (01) is 960 mm which is more than the maximum out side
diameter of 558 mm of the elbow and an opening is made at the top for easy
positioning.
The minimum outside diameter of the elbow is 219 mm. In the base pipe (01),
two rectangular openings are made diametrically opposite to each other, and
being exactly perpendicular to the top opening already made. These rectangular
openings are used to fix a front 'V' block base (11) so that the one end of the
elbow (02) can be placed on the bottom side. Angular stiffeners are provided
(not shown) on the side of the top opening of the base pipe (01) to provide
enough strength/stiffness while machining.

Figure 2 shows the side view wherein the elbow (02) is fixed on the holding
device, by rotating the top clamp screw rods (03) and at least one 45 deg
angular supported screw rod (05) which are assembled in a top clamp box nut
unit (04) and at least one 45 deg angular box nut unit (06) respectively. The
simultaneous rotation of the screw rods (03,05), the elbow is placed in such way
that one axis is perpendicular to the base frame and the other axis parallel to the
base frame (01) for accurate machining. A top clamp unit (08) is used to make
the to and fro motion to position the elbow in the horizontal direction. Figure 3
shows the elbow (02) in a position between a top (10) and the base (11) of the
'V' blocks and arresting the degrees of freedom in the upward and downward
direction.
Because of this inventive step of this method of fixing the job in position, it is
easy to complete the edge preparation accurately on both sides without much
difficulty in both horizontal and vertical direction. There by the machining time is
reduced to 56 Hrs comparing to the existing method.

WE CLAIM :
1. A method of profile machining in high thickness pipe material to fabricate
elbow used in high pressure steam generated, the method comprising the
steps of:
placing an elbow horizontally or vertically in between a top 'V' block
(10) and a bottom 'V' block (11);
clamping an elbow using a top clamp box nut unit (04) and at least
one 45 deg angular box nut unit (06);
adjusting the elbow to accurate position by simultaneous movement of
a top clamp screw rod (03) and at least one 45 deg angular supported
screw rod (05); and
determining a positioning distance according to the outside diameter of
the elbow to be machined which varies from 219 mm to 558 mm.
2. The method as claimed in claim 1, wherein the vertical distance varies
according to the outside diameter of the elbow from a base frame (7).
3. The method as claimed in claim 1, wherein the machining time is reduced to
25%.

ABSTRACT

The invention relates to a method of profile machining of high thickness pipe
material to fabricate elbows used in high pressure steam generators, the method
comprising the steps of placing the elbow between top and bottom 'V' blocks and
positioning with top clamp screw and 45 deg angular bottom clamp screw. The
movement on the horizontal direction was arrested with top clamp box nut unit.
The vertical direction movement was arrested with 45 deg Angular box nut unit.
The edge preparation is carried out on one end of the elbow in the above
position and the operation is repeated to machine on the other side of the elbow
to complete the operation. The profile thus made is ready for welding. The
positioning distance is determined according to the outside diameter of the
elbow to be machined which is varying from 219mm to 558 mm.