Work Roll change in a Hot Rolling Mill ( especially in a steel industry)

Friday, December 13, 2013

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PRESENTED BY:
1. SWARUP RANJAN LENKA (AE)
2. SRICHANDAN SUBUDHI (GET)
CSP-E&A, BPSL
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WHAT IS ROLL CHANGE ???

The extraction of old roll set from the mill stand
and insertion of new roll set into the mill stand is
referred as RC.

WHEN RC IS DONE ???

RC is done depending upon the following factor:
1. Roll wear scale
2. No. of slab that it has rolled
3. Steel grades
4. Cobble
Continue..


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WHAT’LL BE THE CONSEQUENCES IF RC IS NOT
DONE ???
Formation of wear scale on the strip surface which
will degrade its surface quality.

HOW RC IS DONE ???
 Roll Change can be done in auto mode as well as
in manual mode.
 In auto mode Roll change follows a sequential
chart called Sequence Flow Chart (SFC).
 The complete RC can be categorized by 3 steps:
1. Prepare SFC
2. SFC 1
3. SFC 2
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PRECONDITIONS
1.
2.
3.
4.
5.

Hydraulic OK
Local Enable
WR Cycle home Pos.
Tilting Floor Lower
Auto Mode select

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SIDE SHIFTING

TILTING FLOOR UP

WR CHANGING CYLINDER TO E7
POS.
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1. Side shifting
The mill floor covering all mill stands can be
shifted parallel to the direction of rolling which
can
be used to replace the old roll sets in front of
mill stands
by new sets.

It has 2 function:
I. Side shift towards coiler (Home position)
II. Side shift towards furnace

During the WR changing sequence the side
shifting hydraulic cylinder must approach 4 (four)
positions which is detected by 4 proximity switches.
Pos. E1: Piston rod is fully stroked out
Pos. E2: switch over to slow forward
Pos. E3: switch over to slow backwards
Pos. E4: piston rod fully stroked in


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2. Tilting floor up


Each WR retracting cylinder is secured on the
underneath tilting floor plate. The tilting floor plates are
raised by means of hydraulic cylinders for a roll
chang
so that the WR retracting cylinders are then
located at mi
floor level.

There are 2 proximity switches in a tilting floor plate
for detection of end positions i.e. raise or lower pos.

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3. WR changing cylinder to e7
pos.


At the time of a WR change the roll sets are run out
and back in to the mill stands using the changing
cylinders. The connection to the WR set is made by
a locking hook which is located at the end of the
piston rod.

During the WR changing sequence the WR changing
hydraulic cylinder has 8 positions. The single
positions of the hydraulic cylinder are defined in
the
following:
Pos. E1: piston rod in fully stroked in position
(home position)
Pos. E2: stop position for WR side shifting/ switch
over to slow reverse for moving piston rod
in fully stroked in position (home
position)
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Continue..



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Pos. E3: piston rod 20 mm forward in contrast to
E2 (automatic release of the hook)
Pos. E4: switch over to slow reverse: WR-set run out
of the mill stand
Pos. E5: switch over to slow forward: WR-set run back
in the mill stand
Pos. E6: lower position for top WR in mill stand
Pos. E7: raise position for the top WR in mill stand /
waiting position
Pos. E8: piston rod in fully stroked out position bottom WR in mill stand
The respective positions detection and the adjustment
of the traveling speed of the hydraulic cylinder is
controlled by means of a volumetric flow transducer and 1
proximity switch for detection of home position.


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E8 (6420mm)
E7 (6100mm)
E6 (6060mm)

E3 (480mm)
E2 (460mm)

E1 (0mm)

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PRECONDITION
1.
2.
3.
4.
5.
6.
7.
8.
9.

Hydraulic OK
WR Change Selection
Local Enable
WRP at E7
Tilting Floor Raised
Side Shift at coiler pos.
Strip tail left
Auto Mode
WR Cooling ON

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COLLAPSE HGC CYL.
SHIFT CVC TO ZERO POS.
DRIVE SPINDLE SPOTTING
WR COOLING OFF
WR BAL. TO EMERGENCY
BAL.


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1. Collapse HGC cylinder


HGC is used to maintain the Roll gap between

WRs.


HGC having common rod side pressure of 80 bar
(constant) on both sides OS and DS.

At roll change, this const. pressure is reduced by
means of a proportional valve to collapse the
HGC cylinder.

By collapsing the cylinder, we get free space for
lifting and lowering of top WR in order to stool it
above the bottom WR.

1 proximity switch in each cylinder( DS and OS)
is used to detect the collapsing condition.

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2. Shift CVC to zero pos.
The axial shifting of the WRs against each other
produces the effect of a Continuously Variable
Crown (CVC).

Before roll change the CVC should come to centre
position(i.e. Top and Bottom WRs are positioned
symmetrically to the centre lines of the mill housing
and symmetrically to each other),
B’coz of proper stooling of top WR
above the bottom WR.

4 position transducers are used in CVC for
measuring the shifting positions of WRs.


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3. Drive Spindle spotting





For proper locking of WR chocks with spindles,
spindle spotting is done.
1 proximity switch is equipped in each pinion gear
stand.
This switch indicates the RC position approximately.

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4. WR cooling OFF
Basic reason of roll cooling is to keep the
temperature inside the rolls nearly const. during
rolling.

WR cooling is connected to 1.5 bar (DC3) system.

1 electro-pneumatic controlled valve and 1 flow
transducer are installed for WR cooling system to
adjust the water quantity for WR cooling.

WR cooling off is done as there is no need of cooling
during WR change.


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5. WR Bal. to Emergency Bal.




WR balancing is used for lifting and lowering of the
top WR.
To avoid the disturbance of WR Bending System
during RC, a const. emergency balancing pressure of
120 bar is provided to the piston side of the WR
Balancing cylinder.

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PRESENTED BY:
1. SWARUP RANJAN LENKA (AE)
2. SRICHANDAN SUBUDHI (GET)
CSP-E&A, BPSL


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Work roll latches
•
In the closed position, the latches are connecting the Work
roll chocks with the CVC-shifting cylinder. In roll change the latches
must be opened so that the work rolls (WR) can be removed from the
mill stand. The top and bottom latches are driven by two (2)
hydraulic cylinders. The entry- and exit side latches are driven
simultaneously.
•
The open and close positions of the work roll carrier latch are
controlled by limit switches.

Lifting rails

•
For the roll change the bottom work rolls must be lifted in the roll
change position (mill floor level) by means of the lifting rails.
•
The top end position of the bottom work is controlled by a limit
switch.
•
The force created by the lifting rails for LIFTING function must
exceed the force correlating to the weight of both work rolls and the
overbalancing force of the top work roll. Because both rolls are combined by
the balancing cylinder. Therefore the overbalancing must be reduced to a
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minimum by switching the balancing pressure to 52 bar. Friday, December 13, 2013

Spindle carrier
•

The spindle carriers are used to keep the drive spindles in
their position at the time of a work roll change when the rolls have
been moved out of the mill stand, so that the new rolls can be moved
into the spindle heads. The spindle carriers remain open during
rolling.
•
Th e open and close positions of the spindle carriers are
controlled by limit switches.

Looper
•
Between all the stands of the finishing mill a looper is installed for the
purpose of ensuring that there is a particular strip tension between any two
stands.
•
The reason is to prevent the necking of the strip as a result of
excessive tension. Too strong tension will finally lead to a strip break. This can
occur when the mass flow through the following stand is higher then the flow
through the previous stand as a result of a too high speed in the following
stand. When the mass flow through the following stand is smaller a loop is
built up. A steadily increasing loop leads to the formation of folds. If a fold is
formed, the strip may enter the next stand with triple strip thickness. The result
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Side guide retracting device
•
Entry and exit guides have been allocated to each mill stand
whose side provide a lateral guidance of the strip.
•
The entry (F2 – F5) and delivery guides (F1 – F5) are pulled
back by hydraulic cylinders during a roll change so that the work rolls
can be run out. The device is only moved in the "Roll change" mode.
After completion of the roll change the entry and delivery guides are
run forward again (to the rolls). The guides can be operated manually
from the local operator station of the roll change stand F1 – F5.

Wipers
•
Wipers operated by pneumatic cylinders are arranged on the
housing. The purpose of the wipers is to deflect the cooling water from
the work rolls. The wipers are only swivelled in the "Roll change"
mode. They move out after the guides are moved out and in before the
guides are in the mill.

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Thrust blocks
•
The thrust blocks are used to increase the variety of
different work roll (WR) and back-up roll (BUR) diameters to be
used in one mill stand. It also reduces the change of shim plates.
Furthermore large roll gap ranges can be covered even with a small
gap setting cylinder stroke.
•
Thrust blocks consist of solid metal plates with a thickness
of 45 mm or 90 mm. They are shifted (if they are required) between
the top of the mill housing and the gap setting cylinders.
•
Four (4) stages are possible:
Stage 0: Back-up roll change position
Stage 1: Rolling position, roll change position,
thickness 0 mm
Stage 2: Rolling position, thickness 45 mm
Stage 3: Rolling position, thickness 90 mm
•
In order to be able to pull out the blocks the top WR and
the top BUR must be lowered by approximately 15-20 mm before.

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PRECONDITIONS


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PRECONDITIONS


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
In case of failures during an individual movement
when the sequence will not continue, the operator can
bypass the interlocking conditions by using the key switch
»UNLOCK«.

After manually executing that movement, operator
can lock this to start the sequence in auto mode from the
next step.


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Work Roll change in a Hot Rolling Mill ( especially in a steel industry)

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