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CHAPTER 3

EXPERIMENT DETAILS AND MEASUREMENTS

3.1 INTRODUCTION

The experimental investigation was carried out on the work rolls

used in the sendzimir mill and these mills are known for their ability to roll

extremely hard materials to very thin gauges. The pyramid configuration of

the back-up rolls transmits the roll separating force along the length of the

work rolls, through the intermediate rolls, to the backup assemblies and

finally to the rigid mono block housing. Rolls are tools used in rolling mills to

reduce the cross section of metal stock and take all kinds of stresses; loads

from normal and abnormal rolling and changing with roll wear during a

rolling operation.

Both the work rolls of the mills are driven by contact friction. By

rotating the bearing shafts the positions of the backing bearings, with respect

to housing can be changed to control the gap between the work rolls. This is

the basic control movement of the sendzimir mill that permits rapid parallel

and extremely accurate positioning of its work rolls. Table 3.1 and Figure 3.1

shows the characteristics details of the sendzimir mills.

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Table 3.1 Characteristics of sendzimir mill rolls

Diameter (mm)Type of Rolls No. of

rolls Maximum MinimumLength(mm)

Work rolls 2 69 56 1530

First Intermediate 4 104 94 1424

Second Intermediate(Drive) 4 175 169 1380

Second intermediate 2 175 169 1344

Backup rolls each providedwith roller bearing 8 300 298

Figure 3.1 Schematic diagram of Sendzimir rolling mill

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3.2 MACHINE

Experimental investigations have been carried out with varying

depth of cut, feed, speeds and number of passes for rough work rolls and for

the finish work rolls varying the dressing parameters also been included to

obtain fine finish in a roll grinder. For the attainment of good surface finish

with high hardness, a SHIBAURA roll grinding machine as shown in

Figure 3.2 with silicon carbide grinding wheel for finish work rolls and self

sharpening wheel for rough work rolls is employed. The roll grinder selected

is a semi-automatic machine and commonly used in steel rolling industries. In

this study, the parameters are varied according to an orthogonal array’s used

in different experimental conditions based on Design of Experiments. The

specification of grinding machine is given in the Table 3.2. Both rough and

finish rolls regularly redressed to rebuild the desired shape and to eliminate

the worm, fire cracked and fatigued surface.

Figure 3.1 Toshiba/Shibaura Sendzimer Roll Grinder

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Table 3.2 Specification of Work Roll Grinding Machine

TOSHIBA/SHIBAURA SENDZIMER ROLL GRINDER

CAPACITY:

Max. crown and concavity on diameter: 0.02"

Swing over Bed Maximum: 8.46" (215mm)

Max. Overall Roll Length: 57" w/Long Center, 60" w/Short

Max. Length Between Centers: 78.8"

Max. Roll Weight: 440 lbs.

HEADSTOCK:

Speed of work (continuous): 60-300 rpm

Roll speeds, DC Variable: 60-300 rpm

TABLE:

Traverse speed (continuous): 2" - 200" min

WHEELHEAD:

Wheel speed (continuous): 300 - 1,800 rpm

Wheel size (diameter x width x hole): 14" x 1.5" x 5"

Spindle Speeds, DC Variable: 300-2000 rpm

Spindle Horsepower: 5

BACKREST:

Supportable journal diameter: 1.58" - 3.93"

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3.3 WORK ROLL MATERIAL

The rough and finish work rolls are made of High carbon high

chromium D2 forged and hardened steel. These work rolls are produced from

electroslag refined steel and is forged on a 3000 tonne or 1000 tonne open die

forge. The forgings are immediately annealed to remove internal stresses

incurred during the forging processes. The forged work rolls then hardened up

to HRC 60.

3.3.1 Estimation of Chemical Composition

Chemical composition of the work roll materials is analyzed with

optical emission spectrometer (Figure 3.3). Sample preparation is extremely

important when analyzing samples in a spectro-lab. The work roll materials

are generally ground using a band or disc grinder. A 60 grit paper is

recommended. The spectrometer works on the principle of optical emission,

and its specifications are given in Table 3.3.The chemical composition of

work roll material is presented in the Table 3.4.Thermo-Mechanical

properties is presented in the Table 3.5.

Table 3.3 Specification of Optical Emission Spectrometer

Model : Spectrolab

Power details

Voltage -220 V AC , Frequency - 50 Hz, Power- 1.2 KVA

Argon supply - Quality 4.8 Argon- 300 liters/hr

Environmental condition

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Table 3.4 Chemical composition of the work roll material

Table 3.5 Thermo-Mechanical Properties of the work roll

Figure 3.3 Spectrolab - Optical Emission Spectrometer

Carbon - 1.4 % - 1.6% Cobalt - Max. 1%

Chromium - 11% - 13% Manganese - Max. 0.6%

Molybdenum - 0.7% - 1.2% Phosphorus - Max. 0.03%

Sulfur - Max 0.03% Silicon - Max. 0.6%

Vanadium - Max 1.1%

Thermal Expansion : 10.4 x 10-6 at 20-100oC

Density : 7700 kg/m3 at 25°C

Poissions ratio : 0.27-0.30 at 25°C

Elastic Modulus : 190-210 Gpa at 25°C

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3.4 SELECTION OF GRINDING WHEEL

Two problems, wheel glazing and wheel loading occur in grinding

process due to wrong selection of grinding wheel or improper cutting

conditions. Wheel glazing refers to the conditions when the grains are worn

down to the level of bond and held for too long for grinding the material. The

problem can be remedied either by changing the wheel or by changing the

cutting conditions. Wheel loading occurs when work piece chips are

embedded in the cutting face of the wheel, which reduces the effective depth

of penetration of the wheel abrasive into the work surface and thereby

reducing the rate of cutting. Wheel loading is aggravated by the presence of

small voids on the face of the grinding wheel. This can be cured by increasing

the wheel speed or using different wheel even.

Thus, the selection of grinding wheel for correct, continuous

efficient cutting demands the correct selection of the type of abrasive, the size

of grains, and the type of bonding agents and its strength and the size of

voids. Further, the behaviour of the grinding wheel is influenced by the work

piece materials, cutting speed, depth of cut, feed rate and the dressing

parameters.

Abrasives like Aluminium oxide and Silicon carbide have high

hardness in comparison to hardened steel and thus can be used for metal

removal by plastic deformation. The cutting tool materials have to be harder

for material removal by plastic deformation and also to maintain its shape and

for less wear. Work rolls used in this investigations having a hardness of HRC

60, length of work rolls are about 1630mm and diameter varies from 56mm to

68mm.To grind these work rolls, the grinding wheels must possess high

hardness, self- sharpening characteristics to avoid thermal damages on work

rolls and imparts uniform abrasive actions throughout the length of the work

rolls. For these reasons, in this experimental investigation, a self-sharpening

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black silicon carbide grinding wheel was selected and used to grind the rough

work rolls. Green silicon carbide grinding wheel with fine grain sizes was

used to grind the finish work rolls, which require higher surface finish as

compare with rough work rolls. The specifications of the grinding wheels

used in this work are reported in the Table 3.6.

3.5 MEASUREMENT OF SURFACE ROUGHNESS

The surface roughness of the grounded work rolls is measured using

Taylor Hobson’s surtronic 25 with a diamond stylus tip of radius 5 m. It

measures Ra value at a touch of button and shows the results on a LCD

window. Figure 3.4 shows the method of measurement using this instrument

provided with roll and bore fixture. Table 3.7 shows the specification of the

instrument.

Table 3.6 Specification of the Grinding Wheels

Specification of SiC grinding wheel(Black)

Wheel diameter – 610mm

Wheel width – 76mm

Internal Diameter – 305mm

Abrasive – Silicon Carbide

Wheel grade – C60E7B14

Specification of SiC grinding wheel(Green)

Wheel diameter – 610mm

Wheel width – 76mm

Internal Diameter – 305mm

Abrasive – Silicon Carbide

Wheel grade – GC120H8BF09

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Figure 3.4 Taylor Hobson Surface roughness measuring instrument

Table 3.7 Specification of the surface roughness measuring Instrument

Model : Surtronic 25

Power - 9V Battery or Main

Traverse speed - When measuring – 0.5mm/sec, When returning – 1mm/sec

Cut-off values ( c) - 0.25, 0.8 and 2.5mm

Pickup Type - Inductive Parameters - Ra, Rt, Rz, Rq and Rmax

Gauge Range - 300 m Resolution - 0.01 m

Gauge Force - 150 – 300mg

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3.6 MEASUREMENT OF POWER AT GRINDING WHEEL

SPINDLE

A Digital Clamp Power Meter (DCPM) is used to take the

measurements of grinding power requirement. During grinding operation, the

power meter is attached to the electric cables of the grinding wheel spindle

motor. Figure 3.5 shows the Digital power clamp meter and its specification is

reported in the Table 3.8.

Figure 3.5 Digital Clamp Power Meter

Table 3.8 Specification of the Digital Clamp power Meter

Model : DPM 035

DC Current Ranges : 35A,350A,1000A,

AC Current Ranges : 35A,350A,1000A,

Active Power Ranges : 3.5kW,35kW,350kW,

Apparent Power Ranges : 3.5k,35k,350kVar,±(2%+5dgts)

AC Voltage (45-400Hz) Ranges : 350V,600V,

DC Voltage Ranges : 350V,600V,

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3.7 MEASUREMENT OF HARDNESS OF WORK ROLL

MATERIAL

The measurement of surface hardness of the work roll material is

done with the use of Rockwell hardness tester. It works on the principle that

the depth of penetration varies with the hardness of material. The higher the

hardness, the smaller will be the depth of penetration and vice-versa. In this

test the depth of penetration is not measured, instead of the hardness value can

be read directly on a dial attached to the tester. A 120 degree diamond cone

also known as Brale indenter with a major load of 60kg is used in the

measurement. For this combination of indenter and load, ‘C’ scale readings

are taken.

3.8 Experiment Details

Table 3.9 shows the details of machinery used, grinding wheel,

parameters considered, work material, measuring instruments, coolant and

dressing tool used for experimentation with rough and finish work rolls.

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Table 3.9 Details of Machinery and accessories used for experimentation

For Rough work rolls For Finish work rolls

Machine

SHIBAURA semi-

automatic roll-grinding

machine

SHIBAURA semi-automatic

roll-grinding machine

Grinding wheel

Self-sharpening Black

silicomentn carbide

grinding wheel with the

grit size of 60 microns

Green silicon carbide

grinding wheel with the grit

size of 120 microns

Controllable

Machining

Parameters

chosen

Traverse speed, wheel

speed, work speed, in-

feed and Number of idle

passes.

Traverse speed, wheel

speed, work speed, in-feed,

Dress depth and Dress lead.

Work Material

D2 forged steel with

hardness of HRc 60

D2 forged steel with

hardness of HRc 60

Measuring

instrument used

For Surface roughness:

Taylor-Hobson’s

surtronic 25 instrument

with the cut off length of

0.25mm.

For Surface roughness:

Taylor-Hobson’s surtronic

25 instrument with the cut

off length of 0.80mm.

For Power: Digital Clamp

Meter

Coolant usedWater with 3% synthetic

oil

Water with 3% synthetic oil

Dressing tool -

Single point Diamond tool

dresser with 0.2mm nose

radius, nose angle of 60-700

and drag angle of 10-150