FIELD OF THE INVENTION
The present invention generally relates to the field of entry pusher in Cross
piercing and elongation(CPE) process during manufacturing of seamless steel
tubes. More particularly, it relates to the reduction of pusher speed using PLC
during piercing operations.
BACKGROUND OF THE INVENTION
Background description includes information that may be helpful in
understanding the present subject matter.
Seamless steel tubes are manufactured by the Cross Piercing and Elongation
(hereafter CPE) push bench mill process. In this process, a round billet
previously heated in a furnace is pierced by a barrel type rolls of the piercing
mill to form holes which are thick but short in length. Then a mandrel bar is
placed inside the hole of pillet for crimping of side walls and pushed along
length along with the mandrel for decreasing diameter of the cross-section.
This is repeated through a series of three rolls successively for reducing wall
thickness of the hollow pillet and elongating through the length. The hollow
shell is further subjected to size reduction in the stretch reducing mill according
to the tube dimensions. Piercing process is started by pushing the billet into the
main rolls by means of entry pusher which is also in the same pass line as that
of main rolls. Linear speed of entry pusher is very high so that billet is pushed
quickly into the main rolls without loss in billet temperature. Entry pusher head
assembly is prone for shearing in the piercing process frequently. The function
of entry pusher is to push the billet from inlet trough to CPE main rolls.

OBJECT OF THE INVENTION
It is therefore, primary object of the invention to propose a system for identifying
the underlying causes for the shearing of entry pusher head.
Yet another object of the invention is to nullify the continual rotational force
imparted by varying the entry pusher linear speed.
Still another object of the invention is to improve service life of the entry pusher
by preventing it from damages.
SUMMARY OF THE INVENTION
The present invention is therefore intended to solve one or more of the above
problems by providing a method for reducing linear speed of entry pusher.
According to the method entry pusher linear speed is reduced than the CPE
rolling speed so that no continual rotational force is transmitted to the entry
pusher, thereby improving its service life.
The method is disclosed as preventing continuous rotational force of the entry
pusher wherein entry pusher pushing the billet into the CPE main rolls, so that
said CPE main rolls moving forward at a higher speed than said entry pusher
thereby reducing the in-contact duration between the entry pusher and the billet
during the CPE rolling process. Linear speed of the entry pusher < CPE rolling
speed, for reduction of in-contact duration between the entry pusher and the
billet during the Cross piercing and Elongation rolling process.
The CPE process having a pair of main rolls (3) opposed to each other and
having a specified pass line (5) for inner regulation of the CPE main rolls.
The method also discloses a plug (6) provided along the pass line as an inner
surface regulating tool and, a disc rolls (4) opposed to each other as shell
guiding tools. With this method wherein CPE rolling starting during 2500-3430
mm stroke of hydraulic cylinder, the entry pusher speed reduced to about 20%.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The illustrated embodiments of the subject matter will be best understood by
reference to the drawings, wherein like parts are designated by like numerals
throughout. The following description is intended only by way of example, and
simply illustrates certain selected embodiments of apparatus that are
consistent with the subject matter as claimed herein.
Figure 1 illustrates the existing method of entry pusher operation at start of
CPE rolling.
Figure 2 illustrates the proposed method of entry pusher operation at start of
CPE rolling.
Figure 3(b) illustrates the graph for modified linear speed of the Entry Pusher
Vs stroke.
DETAIL DESCRIPTION OF THE INVENTION
The embodiments as described below are exemplary means to describe the
present invention and may subject to various modifications in alternate form
falling within the scope of the invention. The drawings as illustrated are for
explaining details of the present disclosure in pertinent way and could be easily
understood by person ordinarily skilled in the art.
Referring to one of the embodiments, figure 1 illustrates the existing method of
pushing a billet into CPE main rolls (3) wherein entry pusher (1) speed is > than
the linear speed of billet (2) at the start of rolling process. At such speed billet
(2) remains in contact with the entry pusher. After rolling is started rotational
force is imparted to the entry pusher (1) till the time of its retraction, and life of
the entry pusher (1) is significantly reduced as it cannot absorb rotational force.
As a result, the entry pusher start retracting once the CPE main roll (3) drive
motor current reaches to about 85amps. Time when retraction starts may vary
depending upon the type of material.

Referring to another embodiment, figure 2 illustrates proposed method for
preventing retraction. The continuous rotational force which is imparted to the
entry pusher (1) by the billet (2) during rotation should be avoided for
preventing retraction. In order to prevent the continual rotational force entry
pusher (1) linear speed is < than the CPE rolling linear speed, so that once the
CPE main rolls (3) catches the billet (2) it moves forward at a higher speed than
the entry pusher thereby significantly reducing the duration of contact between
entry pusher (1) and billet (2) during CPE rolling.
Figure 3 illustrates graph between linear speed Vs stroke. The existing method
of pushing billet into CPE main rolls (3) is shown in FIG 3a wherein entry pusher
(1) speed is more than the linear speed of billet (2) at the start of rolling process
and due to which billet (2) remain in contact with the entry pusher. Retraction
of entry pusher starts once the CPE main roll (3) drive motor current reaches
85amps and the time duration may vary based on material.
Once rolling is started rotational force is imparted to the entry pusher (1) till the
time of its retraction and life of entry pusher (1) is significantly reduced as it
cannot absorb rotational force.
The existing program before modification is as follows:
Creep Speed enabling logic (1900 mm)
L "ENTRY_PUSHER_REF_POS_VAL" MD1320
L 1.900000e+003
+R
T "EP_STOP_POS_VAL_FWD" MD1324
NOP 0
Creep Speed Reference to Proportional Valve (30 %)
A "TEMP_EP_FWD_START" M73.0 -- ENTRY PUSHER AUTOMATIC FWD
START CMD
AN "TEMP_EP_BWD_START" M73.3 -- ENTRY PUSHER AUTOMATIC
BACKWARD CMD
= L 24.0
A L 24.0
AN "TEMP_EP_CREEP_SPD_FWD" M73.1

JNB _009
L 1.000000e+002
T "INLET_SIDE_DB".EP_REF_SP_IN DB6.DBD0
_009: NOP 0
A L 24.0
A "TEMP_EP_CREEP_SPD_FWD" M73.1
JNB _00a
L 3.000000e+001
T "INLET_SIDE_DB".EP_REF_SP_IN DB6.DBD0
_00a: NOP 0
Referring to figure 3(b), the entry pusher speed has been reduced to 20% as
shown in the graph. So in the proposed method, continual rotational force
imparted to entry pusher (1) by billet (2) during rotation to be prevented. In
order to prevent the continual rotational force entry pusher (1) linear speed is
reduced lesser than the CPE rolling linear speed so once the CPE main rolls
(3) catches the billet (2) it moves forward at a higher speed than the entry
pusher thereby significantly reducing the duration of contact between entry
pusher (1) and billet (2) during CPE rolling. It is shown in Fig 2.
Entry pusher linear speed vs stroke is shown in Fig 3. Entry pusher starts at
30% speed for 200mm stroke, then it moves at full speed during 200-1600mm
stroke and then speed reduces to 30% till end of stroke which is referred as
creep speed. It is during 2500-3430 mm stroke CPE rolling starts so entry
pusher creep speed is reduced from 30% to 20%. Also at the same time full
speed stroke is increased from 1600mm to 2200mm so that there is no
increase in CPE process cycle time by reducing the entry pusher creep speed.
Automation of entry pusher operation is carried out through S7400 PLC. Speed
reduction is done by modifying the programs of entry pusher proportional valve
in S7400 PLC.
The Modified Program is as below:

Creep Speed enabling logic (2500 mm)
L "ENTRY_PUSHER_REF_POS_VAL" MD1320
L 2.500000e+003
+R
T "EP_STOP_POS_VAL_FWD" MD1324
NOP 0
Creep Speed Reference to Proportional Valve (20 %)
A "TEMP_EP_FWD_START" M73.0 -- ENTRY PUSHER AUTOMATIC FWD
START CMD
AN "TEMP_EP_BWD_START" M73.3 -- ENTRY PUSHER AUTOMATIC
BACKWARD CMD
= L 24.0
A L 24.0
AN "TEMP_EP_CREEP_SPD_FWD" M73.1
JNB _009
L 1.000000e+002
T "INLET_SIDE_DB".EP_REF_SP_IN DB6.DBD0
_009: NOP 0
A L 24.0
A "TEMP_EP_CREEP_SPD_FWD" M73.1
JNB _00a
L 2.000000e+001
T "INLET_SIDE_DB".EP_REF_SP_IN DB6.DBD0
_00a: NOP 0

WE CLAIM:
1. A method for reduction of pusher speed in piercing operation for increased
life of entry pusher, the method comprising steps of:
- preventing continuous rotational force of an entry pusher (1) characterised
in that the entry pusher pushing a billet (2) into a Cross Piercing and
Elongation (CPE) main rolls (3), so that
said CPE main rolls moving forward at a higher speed than said entry pusher
thereby reducing the duration of in-contact between the entry pusher and
the billet during the CPE rolling.
2. The method as claimed in claim 1, wherein linear speed of the entry pusher
(1) < CPE rolling speed, for reduction of in-contact duration between the
entry pusher (1) and the billet during the Cross piercing and Elongation
rolling process.
3. The method as claimed in claim1, wherein said CPE process having a pair
of main rolls (3) opposed to each other and having a specified pass line (5)
for inner regulation of the CPE main rolls (3).
4. The method as claimed in claim 3, wherein a plug (6) provided along the
pass line as an inner surface regulating tool and, a disc rolls (4) opposed to
each other as shell guiding tools.

5. The method as claimed in claim 1, wherein CPE rolling starting during 2500-
3430 mm stroke of hydraulic cylinder so that the entry pusher speed reduced
to about 20%.