PT. Krakatau Steel (KS) is state-owned steel industry located in Cilegon, approximately 100km west Jakarta . KS is the largest steel industry in indonesia, with integrated plants producing various steel product such as billet, slab, wire rod, and sheet/coil. The total capacity of KS is around 2.500.000 ton per annual. KS industrial compolex comprises seven different plant/mill direct reduction plant, two slab steel plants, billet steel plant, hot strip mill, wire rod mill, and cold rolling mill. In production tonnage, KS represent around 50% country capacity. Largest portion of KS production is of steel sheet/coils, both of hot/cold rolled coils. KS produce HRC ( Hot Rolled Coil ) around 1.9 million ton, and around 40% of which are further rolled at the Cold Rolling Mill		PT. KRAKATAU STEEL
		MELTING PROCESS		ROLLING PROCESS
		DR  DIRECT REDUCTION		HSM   HOT STRIP MILL
		SSP  SLAB STEEL PLANT		CRM  COLD ROLLING MIL
		BSP  BILLET STEEL PLANT		WRM  WIRE ROD MILL

REDUCTION

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The total reduction for the realization of steels coil is imposed by the metallurgical road, it must be imperatively respected
The reduction at the last stand is imposed by the aimed strip roughness, which must be between 0.6 and 1.1 micron for steel of quality
( Target value = 0.85 ).
For the first four stands, it is common to use reductions which balance the power of stands, in order to maximize the productivity . However this rule may not applicable for reason of :

• Flatness defect

• Torque availbility on certain stands

These two parameters must have priority in the case they are close to their limit.

 

 

 

WORK ROLLS

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* Mini hardness : 86 shore C

 

The work roll crowns must be adjusted to obtain an interstand and exit flatness of the slight long edge type " The adjustment values depend on the equipment.

it may be necessary to have specific work roll crowns to roll steel products, in particular for the last stand . All depends on the ranges of effectiveness of the positive and negative bending and of the other flatness actuator , if any.

 

It is preferable that the stand 1 work roll are crome plated 

 

• That their surface appearance does not present any defect which can affect the quality of the coils to be rolled.

• That the roll crowns correspond to that which was programmed.

• That the roughness of the rolls correspond to that which was programmed.

In the even of defect , refuse the roll.

EMULSION

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The main dimensioning parameter are :

• The minimum flow which must be at least equal in litre/minute to the installed power in kw.
• The pressure level of the spray feeding lines which must range between 2 and 6 bars.

The main parameters to be monitored are :

•  The oil concentration which has to be controlled at least once per shift, it must be stable within +/- 20% , by comparison to target value. That the nominal given below are indicates, they may have to adapted accoring to the obtained cleanliness result :

1. For stands 1 and 2, concentration higer han 1.8% ( Ranging between 1.8% - and 3% )
2. For stands 3 and 4, concentration lower than 1.8% ( Ranging between 1.5% and 1.8% )
3. For stan 5, concentration lower than 1% ( ideal 0.7%)

• The sponification number gas to be controlled at least once by shift. its nominal values is often ranging between 130 and 150 ( to be adapted according to the obtain ed cleanliness result ) . It must be maintained within +/- 10%, by comparison to its target values.

• The temperature measured near the stand , upstream of the lubrication system spray valves, must be monitored by a temperature control loop within a tolerance of =/-2 C , compared to the aimed temperature . This target values depends on the lubrication . Its often close to 50C.

• The iron content inside the emulsion of the last stand must have a values lower than  60 mg/l , for that it is recomended to filtr totality
  of the emulsion flow of the last stand throught a magnetic filter.

• There should not be particles of more than 250 micron in the emulsion at the level of the lubrication feeding lines, it is those recommended to install 250 micron filters upstream of them.

• The PH has to be supervised once by shift, it should not record signicicant variations  

POSITIVE AND NEGATIVE BENDING

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The positive and negative bending must be adjusted to control the interstand and exit flatness of the tandem mill. the variation range must
be enough to carry out this objective.

 

 

 

 

If the problem persist it is necessary to repair , after having detected the gage  which is giving a bad measurement of the coil diameter on
the coiler. The longitudinal thickness must be recorded for ecah strip, over all it lenght. The thickness tolarance is given by customer, if not,
a tolerance of +/-4% must be taken into account.

• The thickness is out of the tolerance in the strip body , except at the end (100 m at both ends)
• Or if the head plus tail out gage lenght exceeds 50m.

Other constraint related to the thickness :

• There should not be weld inside coils.
• Every coil must have experienced an audible chattering must be blocked.
• Every coils having experienced a line stop must be divide ( if the lenght of one of the two parts is still sufficient ) or be blocked ( if not )

 

 

The total flatnes must be such as it is not seen at the tandem mill exit, it must those be lower than 20 UI ( Flatness become latent under a minimal tension of 4 kg/mm2
The differential flatness must be lower than 10 UI, in case one of the flatness criteria exceeds its allowed value over a strip lenght more than 100m ( except 10 m at head and tail ends ), the coil must be blocked.
If the bad flatness is persistent, it is necessry to change the work roll of the last stand. If the change of the work roll did not solve anything , the back-up roll should be changed.
The aimed flatness in the interstands must also be with slight long edge, to avoid edge crack.