FIELD OF THE INVENTION
The present invention relates to a device for holding larger diameter jobs for
drilling. More particularly the invention relates to a method of drilling of
hemispherical work pieces having large diameter and high thickness by placing
the work piece in a holding device.
BACKGROUND OF THE INVENTION
It is known that a start of system in super critical boilers is used to protect
heaters of the boilers from carry-over water by separating the carry-over water
from steam and recirculating it through evaporator surfaces during start up, low
load operation and shut down of the boiler. The water flow in the evaporator is
more than evaporation rate of the evaporator, to prevent the evaporation from
overheating. The recirculation mixing sphere is used as intersection points of the
piping and it consists of a vertical inlet for hot water at the top. The cold water
from feed water line enters radially through a nozzle connection on the side of
the sphere. The mixing sphere is made up of two halves of semi sphere and one
semi sphere needs to be drilled with two holes for radial entry at an angle of

90 deg between the two holes. The outside diameter of the semi sphere is about
812mm having thickness of about 80 mm and the weight of the semi sphere is
around 4030 kgf. A good distribution of the feed water flow prevents the thermal
shock and results in long life of the pressure components of the hemisphere. So
it is essential to drill the holes accurately in the semi sphere with available
machine tools.
To execute drilling of the holes at an angle of 45deg to vertical axis is not
possible and conventional method of fixing the large size job having high
thickness of 80mm and hemisphere shape needs specifically developed holding
device to drill holes to insert pipes and welding the pipes in the drilled holes,
wherein the two hemispheres are connected together to form a reservoir which
is used in supercritical boilers having no drum for steam water separation. Thus,
there is a need to propose a holding device to make holes in the hemispherical
objects in particular making inclined holes in conventional vertical
stroke/horizontal boring machines and to handle such heavy weight work pieces.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method of drilling of
hemispherical work pieces having large diameter and high thickness by placing
the work piece in a holding device. Another object of the invention is to propose

a method of drilling of hemispherical work pieces having large diameter and high
thickness by placing the work piece in a holding device, in which at least two
inclined holes can be drilled vertically and horizontally.
Another further object of the invention is to propose a method of drilling of
hemispherical work pieces having large diameter and high thickness by placing
the work piece in a holding device, in which at least two holes can be drilled in
the inclined axis with high accuracy.
A still further object of the invention is to propose a method of drilling of
hemispherical work pieces having large diameter and high thickness by placing
the work piece in a holding device, in which an innovative holding device is used
to hold the work piece on vertical/horizontal boring machines.
SUMMARY OF THE INVENTION
Accordingly, there is provided a method of drilling of hemispherical work pieces
having large diameter and high thickness by placing the work piece in a holding
device. Thus, the inventive method when implemented on the innovative holding
device allows drilling of holes at an angle of 45 deg / or other angles required for
connecting the stubs to the vertical axis.

The method includes:
In order to drill the holes in the available vertical and horizontal boring machines
the job should be placed at an angle same as the required inclined angle.
For example: If the hole is required to be drilled on the job at an angle of 45° on
the vertical axis, the job to be positioned at an angle of 45 deg in the developed
device. A first hole drilling can be carried out in the vertical boring machine and a
second hole can be drilled in the horizontal boring machine without rotation of
either the work piece or the cutting tool of the boring machine. The two required
holes at required angle are automatically drilled without measurement by
predetermined dimensioning accurately using the novel holding device from
multipurpose positioning.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig (1) shows the holding device with the work piece in position for drilling.
Fig (2) shows the job which is to be drilled.
Fig (3) shows the finished work piece with drilled holes taken out from the
device.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
According to the present invention, the drilling operation is carried out in two
stages. In the first stage, a first hole is drilled in the horizontal boring machine.
In the second stage, a second hole is drilled in the vertical boring machine. Fig.
(1) shows a pre drilled work piece (11) positioned on the developed device. This
device for making inclined profile comprises two plates (01 and 02) fixed
perpendicular to each other by welding and a plurality of stiffness (03.04 and
05) are provided at spaced apart locations to position the holding device
unremovably in the machine bed while drilling. The 'L' shape plates (01 and 02)
are connected by a third plate (06) in such way to facilitate placing a triangular
plate assembly (12) on the inner side of the third plate (06) which is required to
conform to an inclination angle precisely between the third and second plate (06
and 02) on the top side of the device and between third plate and the first plate
(06 and 01) on the bottom side of the device to carry out the drilling operation
without further measurement. A circular plate (7) with a step to fix the work
piece (11) having no straight portion for holding. The work piece (11) is
clamped accurately by placing a holding plate (10) and tightened with fasteners
(08 and 09).

Now, the invented device with the work piece is ready for clamping to the
machine bed either to the horizontal boring machine or vertical boring machine
to make horizontal and vertical holes so that the inclined holes thus arrived
automatically in the conventional machines.

WE CLAIM :
1. A method of drilling holes in a hemispherical work piece having high
thickness, comprising :
- placing the work piece in an inclined position on an inclined circular plate
(07);
- clamping the work piece with fasteners (08, 09) so that the displacement
of the work piece in any of the three planes (XYZ) is arrested;
- positioning the work piece to the required angle by a plurality of triangle
fabricated frames (12) which is placed in between a third plate and a
second plate (06, 02) on the vertical direction between the third plate and
a first plate (06, 01) in the horizontal direction; and
- drilling a first hole in the vertical boring machine and drilling a second
hole in a horizontal boring machine without further measurement of the
first hole-dimension.

2. The method as claimed in claim 1, wherein the inclined holes at 45 deg to
each other are drilled automatically without rotation of the job on rotation
of the cutting tool.
3. The method as claimed in claim 1, wherein holes at any inclined angle
can be carried out by changing the triangular frame (12).

ABSTRACT

The invention relates to a method of drilling holes in a hemispherical work piece
having high thickness, comprising placing the work piece in an inclined position
on an inclined circular plate (07) ; clamping the work piece with fasteners (08,
09) so that the displacement of the work piece in any of the three planes (XYZ)
is arrested; positioning the work piece to the required angle by a plurality of
triangle fabricated frames (12) which is placed in between a third plate and a
second plate (06, 02) on the vertical direction between the third plate and a first
plate (06, 01) in the horizontal direction; and drilling a first hole in the vertical
boring machine and drilling a second hole in a horizontal boring machine
without further measurement of the first hole-dimension.