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

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PRESENTED BY:PRESENTED BY:

1. SWARUP RANJAN LENKA (AE)2. SRICHANDAN SUBUDHI (GET)

CSP-E&A, BPSL

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WHEN RC IS DONE ???RC is done depending upon the following factor:

1. Roll wear scale2. No. of slab that it has rolled3. Steel grades 4. Cobble

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.

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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.

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 SFC2. SFC 13. SFC 2

HOW RC IS DONE ???

PRECONDITIONS

1. Hydraulic OK2. Local Enable3. WR Cycle home Pos.4. Tilting Floor Lower5. Auto Mode select

SIDE SHIFTING

TILTING FLOOR UP

WR CHANGING CYLINDER TO E7 POS.

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 outPos. E2: switch over to slow forwardPos. E3: switch over to slow backwardsPos. E4: piston rod fully stroked in

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 change, so that the WR retracting cylinders are then located at mill floor level.

There are 2 proximity switches in a tilting floor plate for detection of end positions i.e. raise or lower pos.

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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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.

E2 (460mm)

E3 (480mm)

E6 (6060mm)

E7 (6100mm)

E8 (6420mm)

E1 (0mm)

PRECONDITION

1. Hydraulic OK2. WR Change Selection3. Local Enable4. WRP at E75. Tilting Floor Raised6. Side Shift at coiler

pos.7. Strip tail left8. Auto Mode9. WR Cooling ON

COLLAPSE HGC CYL.

SHIFT CVC TO ZERO POS.

DRIVE SPINDLE SPOTTING

WR COOLING OFF

WR BAL. TO EMERGENCY BAL.

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.

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.

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.

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.

PRESENTED BY:PRESENTED BY:

1. SWARUP RANJAN LENKA (AE)2. SRICHANDAN SUBUDHI (GET)

CSP-E&A, BPSL

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 minimum by switching the balancing pressure to 52 bar.

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 may be a breakage of a roll or of a spindle.

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.

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 positionStage 1: Rolling position, roll change position,

thickness 0 mmStage 2: Rolling position, thickness 45 mmStage 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.

PRECONDITIONS

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.

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

wr set

wr cycle home

position home position

piston rod

lower position

auto mode roll change

cylinder ds

detection of home position

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