STEEL MANUFACTURING

Cold Rolling Mill

INTRODUCTION:- COLD ROLLING MILL

The cold rolli ng mill is used to pass hot-rolled coils produced from the hot rolling mill between two rotating rolls and produce products of the desired thickness.

The cold rolling process provides a more refined surface, improved mechanical properties and excellent thickness product precision.

Cold rolling mills are largely divided into the TCM (Tandem Cold Rolling Mill) and the RCM (Reversing Cold Rolling Mill). In the TCM, material passes 5 or 6 rolling mills continuously to obtain the desired thickness, while in the RCM, material passes a single rolling mill multiple times.

DIFFERENCE BETWEEN HOT AND COLD ROLLING MACHINE

1.HOT ROLLING MACHINE:-

Hot rolling is a mill process which involves rolling the steel at a high temperature (typically at a temperature over 1700° F), which is above the steel’s recrystallization temperature. Hot rolled steel is typically cheaper than cold rolled steel due to the fact that it is often manufactured without any delays in the process, and therefore the reheating of the steel is not required (as it is with cold rolled). When the steel cools off it will shrink slightly thus giving less control on the size and shape of the finished product when compared to cold rolled.

● COLD ROLLING MACHINE:-

1. Cold rolled steel is essentially hot rolled steel that has had further processing.

2. The steel is processed further in cold reduction mills, where the material is cooled (at room temperature) followed by annealing and/or tempers rolling.

3. This process will produce steel with closer dimensional tolerances and a wider range of surface finishes.

COLD ROLLING MILLFLOW CHART:-

ROLL BENDING 26 zones(stressometer) divided into 4

groups(S1,S2,S3,S4)S(Roll bend degree) = (24*(2*(S1+S4)-S2-S3))/10*L.L= Number of stress meter in contact with the strip.S(delta) = (S(required profile)-S(current profile))*kThen analog signal is send in order to provide the

correct roll bending.Roll bending produces a cylindrical shaped product

from plate or steel metal.

ADDITIONAL BENDING

ANTI BENDING

Adjusting with the help of roll bending we can use tension measurement/value in all 26 zones

ROLL GAP INTRODUCTION:-

Tension in the strip is adjust using roll gap adjustment.

Press down screws are used to optimize tension.On the side where the tension is more to decrease it

we use press down screws.Threshold Tension is 20N/mm^2.

STRIP PROFILE

ROLL GAP PARAMETERS:-

ROLL GAP(WRAPPING)26 zones(stressometer) divided into 4 groups.S(Roll gap degree) = (4*(S1+S2-S3-S4))/L.L= Number of stress meter in contact with the strip.S(delta) = S(required profile)-S(current profile)We can remove the defects with the help of

comparaters.

CONTINUE..If there is signal that mill is ready to available or working and speed

more than 3.9m/sec roll gap adjust start to work with 10sec delay time.The time of pulse is 4.5 sec.

If rolling pressure is more than 40N/mm*mm or less than -40N/mm*mm than pulse with 500 millisecond with 20m/sec turn-on delay is created.

If rolling pressure is more than 16N/mm*mm or less than -16N/mm*mm there is impulse time 250milli sec with 500 milli sec turn-on delay time.The time of pulse is 2.75sec.

Profile Regulation & Temperature ControlDetailed Analysis

In this Section we remove local errors in flatness.(for eg. bubbles in metal sheet)

Removes Phenomenon bend from the steel sheet.

Principle Of Working

Zone Cooling Working Theory

Step 1: Stressometer evaluates the input signals.

Step 2: Commands are delivered for Cooling.

Step 3: Coolant materials are thereafter supplied to Sprayers.

Specifications About Zone Cooling Working Theory :

Sprayers here assure the optimal flatness of the sheet.

Powering on sprayers depends on the specific profile.

Received values on every zone come to filters with reaction time equals 4.5 seconds.(these filters are used to control the flow of coolants from the sprayers)

There are 2 types of Cooling processes for steel sheets:

1.Basic Cooling

2.Selective Cooling

Basic Cooling Process :Basic coolants are supplied in all zones except of 1st & last zone.

If speed goes below 4 m/s , basic cooling goes impulsive. ( switching on & off again and again ).

Intensity of sprayers decreases more when speed goes below 1 m/s.

(IMPULSIVE: At this speed we open the sprayer for 6 sec and then stops again for 6 seconds, this cycle goes on.)

SELECTIVE COOLING PROCESS :

This process is followed only in special zones(Special zones are those having -5 to -15 N/mm^2 tension)

These Deviations are different from values in separate zones but depend on specific profile.(Eg: 23 zone at 14 profile must have tension 10 N/mm^2)

In this cooling sprayers deliver cooling materials untill the tension becomes 5 N/mm^2 in this zone.

SELECTIVE COOLING PROCESS :Quantity of sprayers vary from 5 to 15 in this zone but the recommended quantity is from 7 to 10 and in this recommended quantity, selective cooling assures maximum cooling effect.

Zones in which cooling liquid is supplied, is defined dynamic starting zone.

SELECTIVE COOLING PROCESS :We burn the metal then by increasing the pressure and then basic cooling make it flat.

Zone displacement depends on changing value of tension in zone but it can’t be more than -5 N/mm^2 and less than -40 N/mm^2.

SELECTIVE COOLING PROCESS :Working Principle For Selective Cooling :

Profile Regulation of Cooling Stands :

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