FIELD OF THE INVENTION
The present invention generally relates to manufacturing of Seamless Steel Tubes. In particular, the invention relates to a method of manufacturing of pusher used in Seamless Steel tube production plants by Cross Piercing Elongation Process. More particularly, the invention relates to a method of manufacturing a single piece weld-less pusher rod out of two pieces.
BACKGROUND OF THE INVENTION
Pusher rod is one of the critical tooling components in Hot Mill for pushing operation. Hot Mill production output is measured in terms of number of pushes performed by a pusher rod to push the Push Bench Mandrel along with the hot billet to form a shell. During this activity, the pusher rod is subjected to a severe impact load. In each cycle of operation, the pusher rod exerting about 120 Tons of force to push the mandrel along with the hot bottle through series of die cages. As the pusher rod is travelling to and fro for every pushes, surface on the outside of the pusher wears out which lead to damage of the front end cone. In normal cases, 2 or 3 Nos. pusher rod per year are sufficient to run a mill i.e. one will be under use in mill, another one will be kept as a spare and the third one will be under reconditioning.
The criticality of a pusher rod is
a) It's slenderness in size i.e., dia 116 x Length 20350 mm
b) Manufacturing a single solid bar of such longer length, and
c) Heat treatment of 20.5 meter bar to withstand impact force.
During the normal operation of pushing, the following conditions may occur.
a) Temperature difference of the hot billet and the mandrel,
b) Set-up arrangement of the stands change on push bench ring bed.
c) Stand Roll pass diameter varies.
d) Speed variation on rolls take place,
e) Insufficient water cooling & Roll bearing lubrication may occur,

f) Over load on the pusher rod due to fluctuation is noticed,
g) Non alignment of the stand on the ring bed is very common, and h) Axis mismatch between mandrel bar and pusher rod takes place.
Any or all the above condition lead to bending of pusher rod to the extent of irreparable condition, causing a forced shut down of the plant. The lead time is about 8 months to procure new pusher rod. Pusher rod is used in the production of seamless steel tube to push the mandrel with shell at 1200 deg C through a series of die gauges.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a method of manufacturing a single piece weld-less pusher rod out of two pieces.
Another object of the present invention is to propose a method of manufacturing a single piece weld-less pusher rod out of two pieces, in which the two pieces forming the pusher rod are having threaded ends.
A further object of the invention is to propose a method of manufacturing a single piece weld-less pusher rod out of two pieces, which produces a push rod capable of withstanding 120 tons impact load.
A still further object of the invention is to propose a method of manufacturing a single piece weld-less pusher rod out of two pieces, which provides a push rod with perfect axial alignment between the two joined pieces.
SUMMARY OF THE INVENTION
Push Bench mandrel bars are taken up as raw material for preparation of pusher rod which meets the properties ofan original pusher rod. Available size of the mandrel bars are normally 116mm diameter and 16,350mm length are selected. To make 20350mm length pusher rod, a first mandrel bar of length 16000mm and a second mandrel bar of 4350mm are gas cut providing around 100mm machining allowance. The straightness and surface finish are ensured.

On the first mandrel bar, a cone of 90 degree and M1 (M64x4) internal thread machined on a lathe machine with suitable steady rests as shown in FlG-02. On the second mandrel bar, one each connecting male thread of M2 (M64x4) and M3 for adopter assembly are machined as shown in FIG-03.
The threads are inspected using precise thread plug and ring gauges respectively. A plurality of locating and locking relief grooves are machined for proper tightness and inspected. Both the machined rods (2,3) are positioned on at least a plurality of support levelled stands. The first mandrel bar is fixed using suitable clamps. The second mandrel bar is gradually tightened using chain jack ensuring smooth insertion of threads, co-axial alignment and perfect matching of OD at the joint/Thus the new pusher rod was manufactured and assembly is shown in FIG-04.Trials made using this newly invented pusher rod and the process is established. Put in regular operation and working as that of original pusher rod.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
FIG-01 shows the original pusher rod being used for the production at Hot Mill
FIG-02 Shows the machined mandrel bar of length 16000mm-the first piece.
FIG-03 Shows the machined mandrel bar of length 4350mm-the second piece.
FIG-04 Shows the new pusher rod of length 20350mm by connecting the threads of the two machined mandrel bars.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION
1. On the first mandrel bar (2) of length 16000mm and dia. 116mm, a cone of 90 degree and M1 (M64x4) internal thread is machined on a lathe machine with suitable steady rest as shown inFIG-02.

2. On the second mandrel bar (3) of length 4500mm and dia.116mm, one each connecting male thread of M2 (M64x4) and M3 for adopter assembly are machined as shown in FIG-03.
3. The threads were inspected using precise plug and ring gauges respectively.
4. The locating and locking relief groove are machined for perfect tightening.
5. Both the machined items (2,3) are positioned on a leveled plot form.
6. The first bar (2) is fixed on the supports with suitable clamps.
7. The second bar (3) is gradually tightened using a chain jack ensuring smooth insertion maintaining the co-axial alignment.
8. Perfect matching of OD and straightness within accuracy of 2mm for the length of 20350mm is also ensured.
FIG -01 shows the original pusher rod being used in regular production having front end with cone for pushing the mandrel and back end with thread of M64x4 for adopter assembly.
FIG-04 shows the invented pusher rod prepared by joining 2 pieces with threaded joint similar to the original one.

WE CLAIM
1. A method of manufacturing a single piece weld-less pusher rod out of two pieces, the method comprising the steps of:-
- loading the first piece (2) of mandrel on a lathe machine and machining the first followed by end, drilling and boring the front end including machining a 90° cone;
- reversing the first piece and machining the second end followed by boring for internal thread machining (Ml);
- loading the second piece of mandrel (3) on the machining a first end followed by drilling and boring;
- carrying-out external thread machining followed by checking with a thread ring gauge;
- reversing the second piece for machining followed by drilling and boring; Carrying-out internal thread machining (M3); and
- joining the machined external thread (M2) of the second piece (3) and the machined internal thread (M1) of the first piece (2).