FIELD OF THE INVENTION
The invention generally relates to rotary table in an oil rig and particularly to a
rotary base of the rotary table, the rotary base housing a driving system with
bearings and seals. More particularly, the invention relates to an Improved
process for manufacturing rotary housing of Oil Rig.
BACKGROUND OF THE INVENTION
An oil rig is a drilling machine that creates boreholes into the ground. Major parts
of an oil rig are the crown block, traveling block, swivel, Kelly, rotary table. The
crown block is fixed to the top of the derrick. The traveling block moves vertically
up and down. When the winch turns, it raises the traveling block up towards the
crown block. The swivel hangs from the hook in the traveling block. The Kelly,
the long square pipe, is fixed to the swivel at one end. The lower end of the Kelly
is attached to the drill pipe. It goes through the turn table which fits snugly into
the Rotary table. The square shape of the Kelly slides exactly into the square
hole of the turn table. When the engines are on, the rotary table rotates along
with the turntable. The turn table turns the Kelly and the Kelly turns the drill
pipe. When the drill pipe rotates, the drill bit rotates and cuts the rock as and
when the operator gives a feed at the controls.
A rotary table is a mechanical device on a drilling rig that provides bi-directional
rotational force to the drill string to facilitate the process of drilling a bore hole or
pulling up the drill string in case of a stuck-up pipe. Rotary table consists of a
bevel gear pinion unit supported on thrust bearings and guide bearings used to
drive the drill stem and the corresponding drill bit connected to it. The transfer of
motion and torque is in the right angle direction.

The rotary housing consists of a base in the form of rectangular shape, a Bowl
and a bush.
In the prior art, the housing for the Bevel gear and pinion unit is one single piece
steel casting unit having a varied cross sectional thickness between 19 mm and
about 85 mm at different load bearing points at the interior surfaces of the
housing.
The process for manufacturing prior art rotary housings of oil rig have the
following drawbacks :-
1) The variation in thickness renders the process of manufacture very
difficult and expensive.
2) Owing to the complexity of the casting, the rejection rate is quite high and
rework on the defective castings if feasible, leads to cost escalations.
OBJECT OF THE INVENTION
It is therefore an object of the invention to propose an Improved process for
manufacturing rotary housing of Oil Rig.
Another object of the invention is to propose an Improved process for
manufacturing rotary housing of Oil Rig, which reduces rejection of the casting
used in the rotary housing.

A further object of the invention is to propose an Improved process for
manufacturing rotary housing of Oil Rig, which reduces cost of manufacturing of
the rotary housing.
SIMMARY OF THE INVENTION
According to the invention, a combination of castings for the higher section
modules materials, and wherein plate members for the lower cross section
materials are used in the manufacturing process of the rotary housing. The
integration between the plates and the castings is ensured by welding with
compatible materials. This results in a robust structure with improved
performance capability.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows an assembly of the rotary housing consisting of a fabricated
rotary base and the castings as per the invention.
Figure 2 shows the fabricated plates assembly of figure 1.
Figure 3 shows a Bowl and Bush Castings of figure 1.
DETAILED DESCRIPTION OF THE INVENTION
The process involves the following steps :
The components for example, the bowl and the bush with required profiles are
casted so that the load transfer points do not cause stress concentration at the
time of manufacture and also at the time of operation.

The plate materials (figure 2) are machined to match with the required profiles
of the castings such that the bonding between the plate surface and the profile
of the castings matches to ensure a smooth load transfer.
The plate materials are matched with the profile of the castings conical/spherical
surfaces all round so that imperfections due to casting process if any are
accommodated without compromising on the quality of the welding joints being
processed.
The welding process is devised in such a manner that there is more than 75% to
85% fusion between the cast member and the plate materials.
After matching the contact joints between the plates and the conical surface of
the Bowl casting and also between the plate surfaces and the spherical surface
of the bush, the outer structure of the rotary base (housing) is assembled and
the overall shape is obtained by tack welding of all the plates (figure 2). This
provides a superstructure which is checked thoroughly for dimensional
compatibility before proceeding ahead with the next step.
The superstructure is then processed for sequential welding so as to
minimize/avoid distortion at the time of welding.
The superstructure is then inspected for integrity after the manufacturing
process.
The cast units - Bowl and the Bush are then placed onto the superstructure and
another evaluation check is made to verify that all surfaces are in contact.
Rectifications is required is carried out at this stage.

The cast Bowl, the bush and the fabricated plates are initially tack welded at
various locations so that distortions if any during the final welding are avoided to
a maximum extent (figure 1).
Final welding of the cast Bowl, cast Bush and the plates are carried out in a pre-
determined sequential welding process so that distortions are bare minimum.
The Rotary base is then inspected again thoroughly and then sent for stress
relieving and further operations.

WE CLAIM :
1. An Improved process for manufacturing rotary housing of Oil Rig, the
rotary housing of oil rig essentially consisting of a shaped rotary base, a
bowl, and a bush(-,), replacing In lieu of the housing constituting a single
piece steel casting having a varied cross sectional thickness at different
load bearing points at the interior surface/areas, the improvement is
characterized in that the rotary housing is manufactured as combination
of castings for higher section modules materials and plate members for
lower cross section materials, the process comprising the steps of :-
- casting the bowl and the bush to their required profiles such that the load
transfer locations remain free from stress concentration;
- fabricating the rotary base with plate materials including machining the
base to generate profiles all around corresponding to the profiles of the
bowl and bush;
- constructing an outer surface of the rotary base by matching the contact
joints between the conical surface of bowl and the plate surface including
the spherical surface of bush and the plate surface;
- developing a superstructure by assembling the outer structures of the
rotary base, and processing the super structure by a series of sequential
welding to minimize welding distortion;
- placing and tack welding the cast bowl and bush inside the superstructure
to verify contact of all the surfaces and conducting rectification if
necessary; and
- carrying out the final welding of the cast bowl, cast bush and the plates in
a pre-determined sequential welding process to ensure elimination and/or
minimization the distoration.

2. The process as claimed in claim 1, wherein the selected welding process
ensures more than 75-80% fusion between the cast members and the
plate members.
3. The process as claimed in claim 1, comprising stress-relieving of the rotary
base after the final welding.

ABSTRACT

The invention relates to an Improved process for manufacturing rotary housing
of Oil Rig which uses a combination of castings for the higher section modules
materials, and wherein plate members for the lower cross section materials are
used in the manufacturing process of the rotary housing. The integration
between the plates and the castings is ensured by welding with compatible
materials. This results in a robust structure with improved performance
capability.