Paper Title (use style: paper title)

Understanding Emulsion System of Tandem Cold Mill

1Aditya Narayan

1P.G Student

1Dept.of Mechanical Engineering,

1Muzaffarpur Institute of Technology, Muzaffarpur (Bihar),India

1aditya.narayan3012@gmail.com

Abstract— Tandem cold mill is a very important section of any metal forming process where sheet of metal is rolled to get the desired thickness of the sheet. It wears contact between sheet and roller which produce very large heat due to friction. So to reduce this good emulsion management system is needed to provide smooth movement of sheet through roller and reduce heat dissipation .Presently emulsion tanks are used to provide emulsion to various stand of the mill. But the effective discharge if waste emulsion and its filtration still have scope of improvement.

IndexTerms—1. CRM; Cold Rolling Mill, 2. TCM; Tandem Cold Mill 3. Emulsion

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I. Introduction

Cold Rolling is plastic deformation of the metal by passing between rolls to grant it the will shape with the appliance of compressive forces. Rolling would be able to produce components having constant cross section throughout it length. Figure1 illustrates an example of a 5- stand 6-high cold rolling tandem mill[1]. As seen during this figure 1, endless cold rolling wheel mill consists of 5 main parts: coils gap half, fastening machine that welds the end of the opened coil to the new coil to form the cold rolling line continuous, loop automotive that stores strip in rolling line sort of a condenser in electrical circuits, stands of cold rolling that scale back strip thickness, and strip cutting machine and coil collector that collects the rolled strips. Since coils open in an exceedingly rate quicker than strip rolling speed, additional strip is keep by loop automotive in line until the beginning of the new coil is welded to the tip of the opened coil. At this moment, the speed of coil opening reaches zero. The strip needed for rolling line is provided by loop automotive.

Fig.1 Outline of 5-stand 6-high tandem mill process

The strip is engaged in several stands simultaneously, enabling high tension force to be applied with increasing compressive forces at each stand. It operates at a very high speed and lot of heat generated due to friction[2]. This heat can change the electrical, magnetic and structural properties of the metal [3]. It can also lead to the breaking of the sheet and distortion in the sheet granule. So to eliminate the consequence of the heat generated during rolling process[4], heat need to be eliminated efficiently. for this an efficient Emulsion system is required for a tandem mill.

II. Necessity of Emulsion Management

Emulsion could be a mixture of two or additional liquids that are unremarkably immiscible. Emulsion is a component of a more general category of two-phase system of matter referred to as colloids. In an emulsion one liquid (the dispersed phase) is spread within the different (the continuous phase).

Emulsion plays a very important role in the proper functioning of TCM.

Role of emulsion in tandem cold mill:

· Emulsion is used as a coolant and lubricant for the passage of the strip through the TCM.

· It Improve the capacity of the TCM in terms of thickness reduction.

· It Increase the surface quality of the rolled strips.

· Emulsion reduces the friction between the strip and the rolling stand.

· A good quality of Emulsion can be used no of times which reduce the cost of manufacturing.

· which reduce the cost of manufacturing.

The type of emulsion we use her in TCM is a mix of oil and water, constituting 0-4% of oil in water. This emulsion contains demineralised water, so most of all of its minerals and salt ions are removed such as calcium, magnesium, sodium, chloride, sulphate, nitrate and bicarbonate [5].

So after use if the waste product is disposed can lead to serious health problem for both human and for the rest of ecosystem. Oil is a costly commodity so using fresh oil for emulsion can increase the cost of production. also there are numerous bad effects of emulsion when disposed. Emulsion also contains hazardous chemicals and small solid particle which disturb the ecology of the nature. Due to harmful effect, a proper emulsion management is needed to reduce environmental concerns and its effect on human system. But at the same time emulsion is also necessary for tandem mill. So an effective system is needed for discharge of emulsion to the tandem mill. There is very risk of blockage and damaging of the machines thus a proper clean management is required.

III. Emulsion Management of TCM

There are three emulsion tank used for the tandem mill in CRM. Tank A and tank C provide the supply of emulsion to stand 1 to stand 4 of the tandem mill, while a separate tank B is provided for the stand 5. The separate tank is required to meet the higher requirement of emulsion in stand 5. The three emulsion tank. tank A, B & C are internally divided into three parts, namely clean, intermediate and dirty.

Fig.2. Internal Section of Emulsion Tank

As the name suggest clean oil is stored in the clean part while the dirty oil from the stands is feed back to the dirty compartment. Through oil is used here for cooling as well as cleaning the metal surface it is used numbers of times. Now the oil from the mill is move to dirty compartment. Where after settlement of solid particles the liquid part flows to the intermediate compartment.

Here the boundary between dirty and intermediate compartment is separated by short wall. The three emulsion tank containing emulsion which is feed to the recirculating system pipe and then through nozzle it is discharged at the point between the rolls.

There are a total of eight positive displacement pump connected from the three different emulsion tank. And all the pump is connected to a single input line pipe coming from the tanks. out of eight pumps first four are used for mill stand one to four respectively. while the pump five and six are kept at standby .in case of failure of any of the first four pump. The pump seven and eight are only used for fifth stand out of two, only one is used at a time while the next is kept at stand by Fig.3.

fig.3. Arrangement of eight positive displacement pump connected from the three different emulsion tank

The main feed pipe is blocked into two part between the pump 6 & 7 by a valve. So that the emulsion from tank B and A or C, do not get mixed. An emulsion to be used in operation it should be in a specific temperature range, here in case of tandem cold mill it temperature must be between 52-60⁰C. So when oil is taken from the tank by the suction pump it is first passed through heat exchanger. A heat exchanger is an emulsion tubetype, where emulsion is passed through the tube which lies in a steam chamber.

After the emulsion raise to the specific desired temperature it is send to the various pipes through which it is sprayed to the various points between the roll.

Fig.4. point of application of emulsion coming from various pipes

It must be taken into consideration that not excess of emulsion is placed as excess emulsion can led to slipping of the metal sheet. The flow of emulsion is controlled by valve with the help of Nitrogen(N2). Nitrogen is an inert gas and easily available, also it is non-corrosive with metal. So nitrogen is used to operate valves of nozzle.

IV. Need of Separate Emulsion Tank for Stand 5

There is three emulsion tank in CRM, two tank A & C are used for stand 1 to 4, while the tank B is used for stand 5. There is a need of separate emulsion tank for stand 5 because, the speed of rolling in stand five is very high, which generate lots of heat. The Excess heat can deteriorate the quality of the steel.

We can see that:

Rolling speed α flow of emulsion α temperature α valve opening

and since while rolling volume of sheet remains constant.

So.

Area × length = const.

Width × thickness × length = const. (area= thickness ×width)

The width of the roll is remains constant while rolling.

So. Thickness × length = const.

On Differentiating, we get:

Thickness × velocity = const.

So, for all five stand.

t1v1 = t2v2 = t3v3 = t4v4 =t5v5. (t=thickness, v= velocity)

Here we see. t1 > t2 > t3 > t4 > t5 Hence v1 < v2 < v3 < v4 < v5.

V5 is maximum, So speed of rolls in stand 5 will be maximum, i.e. heat generated is also maximum.

V. Emulsion Section

Emulsion section consist of three parts. One which contains emulsion in fresh form. Second which is the tank preparation(tank section). And third is the filtration unit where dirty emulsion from the mill is filtered to use it again. The pre filtration unit is basis for providing makeup emulsion to the tank, as in CRM we use same emulsion again and again.

(Emulsion Section)

(Mill preparation (tank section)) (Filtration unit) (Pre filtration)

Pre-filtration

An emulsion passes through various places in between working machine part. Where it get Exposed to a very high temperature, corrosive elements, and sparks. So Emulsion must be treated before applying. So Emulsion is first treated with various chemical substance.

Pre filtration is very important requirement as it improve strip and support mill cleaning also it reduce the consumption. It maximize the production, prevent rusting. This led to reduction of cost.

Mill Preparation( Tank Section)

The distribution of Emulsion in various stands comes under mill preparation which has already explained in point III & IV.

Filtration unit

Dirty emulsion from the mill contains lots of impurities including iron-particle and dirt which, Need to be removed before reusing to feed in tank.

The filtration is done in two step.

1. Flatbed filter:- A flat-bed filter consists of number of filter membranes with pore sizes ranging from 30 microns to 180 microns. These membranes are laid out on an incline plane. The muck is scoop from the tank with the help of long shallow plates which are mounted on a chain conveyer. This conveyer continuously draws out the muck and dumps it on the top of the filtering membranes. The relative clean emulsion passes through the pores, and goes back to the tank while the large size impurities cannot pass through the tiny pores and are collected in a tank. It Arrangement is provided for tank-A only.

2. Magnetic Separator:- There are particles in the size of microns which may remain suspended in the emulsion and cannot be separated with the help of bed-type filter. Out of these particles, iron constitutes the majority of the portions and its presence has proved to be detrimental to the rolled coils. If its percentage in the emulsion reaches above 42-46%. A high concentration lead to high dark patches on the rolled coils and results in quality issues. As a result, the separation of such particles is necessary to keep their percentage in the emulsion to a minimum or at least below the detrimental levels. Hence, the use of a magnetic separator comes into the picture. This system isprovided for Tank-B and tank-C separately.

This unit has a number of long cylinder magnetic tubes which are mounted on a chain conveyer. This conveyer moves slowly through the tanks. The magnetic particles get attracted towards these rods and thus adhere to its surface. A reciprocating scraper arm is provided at the top of the assembly where it scraps of the muck present of the surface of the tubes onto a screw conveyer which discharge it to the drum of respective tanks.

VI. Muck

After the filtration process, the filtered emulsion is feed again to the tank where it gets used again. But the lighter substance which floats at the surface is known as muck. A number of flat belt oil skimmers are used to pull out this muck from the tank. These are fixed and mounted vertically in one location and have a skimming capacity of about 60 liters per hour. It consists of polymer belt wrapped around two pulleys. One of the pulley is driven by an electric motor while the other serves as an ideal. The muck adheres to the polymer belt and get lifted from the surface to the wipe-off blades/ scraper while the liquid emulsion drips back into the tank. The muck is scrapped off this section, and then passed onto a long flow pipe with a gentle slope

.

Fig.5. The pump used to pump muck into the filtration tanks

VII. Conclusion

This system is operational and various units of this system is implemented after lot of research. The effective use of Emulsion includes various stage from storage to discharge. Emulsion is first stored in large emulsion tank then pass through a heat exchanger. Total Eight positive displacement pump, pumps the emulsion (fig.3) to various nozzle and spray emulsion at required point(fig.4). the flow of emulsion at various section is controlled by nitrogen(N2) operated valves. Whole emulsion management in CRM is divided into three section i.e. pre-filtration, Mill Preparation and filtration unit. At the end we left with Muck. Though this system is used in CRM for tandem mills but still discharge of Muck in sustainable way is still a challenge.

Author and Affiliations

1Aditya Narayan

1P.G Student

1Dept. of Mechanical Engineering

1Muzaffarpur Institute of Technology, Muzaffarpur (Bihar), India

1aditya.narayan3012@gmail.com

VIII. Acknowledgment

I take this opportunity to place an record my deep sense of gratitude and heartfelt thanks to Steel Authority of India limited, Bokaro (Jharkhand) for its guidance and constant supervision as well as for providing necessary information regarding the seminar and also for their support in completing this journal.

I must convey my deepest affection to My Family, friend Mohit Kumar & Abhinav Anil for guiding me during this paper and correcting my mistakes. Thanks to all!

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