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The present invention relates to "A process of rolling smaller diameter bars from square billets in a mute Pass Wire Rod Mill"
Abstract:
This invention is a process to produce 5.0mm bars m a 25 pass Wire Rod Mill from 130mm * 130mm square billet that are continuously cast. The pass design for developing the strategy takes into acount input process parameters such as groove parameters, roll speeds, initial billet temperature. The outputs are strain, strain rate, reduction, roll load, torque, temperature power, and shape of deformed work piece at each pass.
The invention uses Finite difference technique to calculate evolving temperature distribution within the wire rod at reach pass. The surface profile of outgoing workpiece at each pass is formulated using weighing function and linear interpolation of the radius of curvature of an incoming workpiece and that of roll groove to the roll axis direction.
Finite Difference Technique
The finite difference technique is a numerical method that calculates the value of a variable based on its neighbourhood. This concept is explained in Figure 1. The value of a variable R is to be calculated. The variable is physically located in a hypothetical two dimensional space designated by(i,j). The neighbours are designated as R(i-1,j),R(i+1,J),R(i,j-l)and R(I,J+1).

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The invention is based on the following figure where
Figure 1 is the two dimensional finite difference diagram and
Figure 2a is the present method and
Figure 2b is the simplified method possible with the present invention and
Figure 3a is the sequence of passes and their shapes for the first six passes and
Figure 3c is the sequence of passes and their shapes for passes 13 and 14and
Figure 3d is the sequence of passes and their shapes for passes 15 to 25 and
Figure 4 is the applicant of equivalent rectangle approximation into oval-round pass to
calculate the effective height for workpiece, roll diameter and
Figure 5a is the geometrical designation of roll groove and radius of surface profile
(Rs) of a workpiece I oval-found pass rolling and
Figure 5b is the geometrical designation of roll groove and radius of surface profile RE
of a workpiece in round-oval pass rolling and
Figure 6 is the samples showing the evolving cross section shapes after (a) 7thpass (b)
15th pass (c) 25th pass for a square billet rolled to a smaller diameter bar and
Figure 7 is the evolution of center, surface and sub surface temperature profile for
smaller diameter bar rolling and
Figure 8 is the difference in roll load a stands 20th to 25th for a higher and smaller bar
rolling.
Experimental verification of the bar shape is done by collecting samples at specified
passes from the running mill.

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Field of INVENTION:
This invention is a new process developthent to roll smaller diatheter bars in a multi-pass Wire Rod Mill.
Need of invention:
Wire rod and bars are used for producing automobile parts. These bars are of small diatheters that are conventionally produced by secondary drawing processes of a larger diatheter bar. Due to the need to reduce processing costs, custothers want to simplify the secondary processing steps. Figure 2a is the present thethod where Step I and IV ace the surface treatthents and Step II and V are the Drawing operation and StepIII is the Annealing and StepVI is the Heat Treatthent. These steps convert a rod of Xh into a final product.
The present invention claims a process a smaller diatheter bar that can simplify the secondary process steps.
With a smaller diatheter rod (Xs) produced using the proposed invention, Steps I,II,III and V are omitted.
Additional, the proposed invention eliminates stands required for drawing operation, reduces, power consumption, cost and time.

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With this as the background, the invention develops a process for rolling smaller diameter bars in the Wire Rod Mill.
According to the present invention a process ofproducing smaller diameter bars of 5 mm or less from square billets below 130 mm using a multi pass wire rod mill in 25 distinct steps comprising the steps of admitting the work piece into the inputs of the different passes wherein the inputs to each pass that are measured and adjusted are the groove parameters and roll speeds, and the outputs from each pass that are measured and adjusted are the loads, torques, temperatures, distribution within the bar at each pass is measured and adjusted using a "Finite Difference Technique" and the shape of the bar is measured and adjusted by using a weighing function the radius of curvature of the incoming bar to that of the groove along the roll axis direction.
Introduction:
The figure 3a, 3b 3c and 3d show the sequence of passes and their shapes of the multipass wire and rod mill. The first seven passes are the roughing passes with an average of 28% reduction.
The next six passes are the intermediate passes with an average or 23% reduction The next two passes are the pro-finishing passes with an average of 18% reduction The last 10 stands consists the No Twist Mill with 18% with inter-stand cooling.

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Prior Art:
Presently small diameter bars of 5.5 mm and above are produced in multi-pass wire rod mills. This invention claims a process to produce smaller diameter bars of 5.0 mm and below using the multi-pass wire rod mill
Summary of Invention:
a) Measurement and Adjustment of parameters to obtain deformed bar shapes in
different passes in a multi-pass 25 pass wire rod mill.
b) Measurement and Adjustment of temperatures, rolling loads and roll torques in
different passes in a multi-pass 25 pass wire rod mill.
c) A process for rolling smaller diameter bars of 5.0 mm and below in a multi-pass
wire rod mill.
Detailed Description of Innovation:
Measurement and Adjustment of parameters to obtain deformed bar shape
The deformed bas shape is the surface profile of the bar as it progresses pass by pass in the multi pass mill. The deformed bar shape is based on the maximum possible spread during deformation, a linear interpolation of the radius of curvature of an incoming bar to that of roll groove along the roll axis direction. The spread is the amount of billet material that moves in a direction perpendicular to the rolling direction when the material moves through a pass.

7 The shape change that occurs during an oval to round pass is shown in the figure 4.
Here Ah is the area fraction that falls outside the groove geometry whik As is the area fraction beyond the rectangular region within the groove. As is the material that moves perpendicularly to the rolling direction and is called the spread.
The rectangular region of above Figure 4 is based on the equivalent rectangular transformation method that transforms the curved cross section into a rectilinear one such that the net cross sectional area remains same. The shape is measured by two parameters Ho and Hi.

The maximum spread of an outgoing workpiece is a function of the area fraction between incoming workpiece and geometry of groove, the mean roll radius and maximum size of an incoming workpiece. The maximum spread is

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The shape change that occurs during a oval to round pass is in Figure 5a. The radius of surface profile (Rs) is measured by linear interpolation of radius of curvature of an incoming workpiece (R|) and that of the roll groove (Rg) to the roll axis and is given by

When the incommg oval workpiece is deformed inside the round groove, it can potentially reach a spread equivalent to the face width of round groove Wf(i.e. 2Rg). Hence it is reasonable to assume the surface profile of the deformed workpiece to be a circle of radius Rf As in Figure5(a) cennter pointofthe newly generated surface is

Figure 5b shows one of the possible surface profiles for a round workpiece entering into an oval pass. Here, the radius of surface profile of workpiece (Rs) is measured linear interpolation of radius of curvature of an incommg workpiece (Ro) and that of

9 the roll groove (R1) to the roll axis and is given by

When incoming round workpiece is deformed inside the oval groove, it can potentially reach a spread equivalent to the face width of the oval groove Wf. Hence, it is appropriate to assume the final surface profile of the deformed workpiece to be a circle of radius Rf given by

The center point of the newly generated surface Dx is calculated using equation 3o.
Measurement and adjustment of temperature:
The evolving work-piece temperature during rolling depends on various factors such as rolling speed, initial billet temperature, plastic deformation behaviour of the work-piece determining the cross sectional shape of the work-piece at each pass, distribution of cooling at each stand and equalization zone between stands. To take care of the combined action of these parameters, a finite differnce method is used

10 wherein the following assumptions apply.
1) Uniform initial billet temperature.
2) Heat transfer along longitudinal direction is neglected due to high roling speed
3) Uniform heat generation across the cross section of the deforming bar due to
plastic deformation in the roll gap.
4) Oxide layer formation between the deforming bar and roll is not considered.
The one-dimensional transient heat conduction in Cartcsian coordinate system is

The following boundary conditions apply
• Within the deformation zone, the two boundary areas are The contact area with roll:

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The area at which the billet has no contact with work rolls

• In the inter-stand section, heat is lost due to heat convection and radiation to the surrounding atmosphere, so the boundary condition is

Thermo-physical properties of deforming bar have been assumed to be temperature dependent. Table 3 shows the values of k and Cp as a function of rolling temerature.
Measurement and adjustment of rolling loadS and roll torque
The roll force(F) at any pass is

The projected contact area (Ad) is

In bar rolling, deformation of bar in the lateral direction is constrained due to groove shape. As a result, the deformation inside the roll groove is assumed to be a semi-plain strain type such that s1 not zero. Average contact stress in bar rolling is

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The Roll torque (M) is calculated by multiplying roll load (F) with the effective projected contact length and lever arm coefficient (a).

Where
For round-oval pass, the lever arm coefficient is

For oval-round pass, the lever arm coefficient is

The motor power (P) is calculated from the torque and the rolling speed (n).
Validation with Plant Data:
Samples of rolled wires were collected from Pass Nos. 7,15 end 25 that are the crop shear ends. These ends were polished using sand paper and optically photographed for measurements using a micro-meter scale. Figure 6 shows a typical sample for the three passes.
The invention shows the evolving temperature both within the pass and its exit from the pass. This temperature measurement using pyrometers is also indicated by the filled

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circle in Figure 7. Figure 7 shows the evolving temperature at the surface, sub surface and center of the 5.0 mm bar.
In the past process set up, shape factor (ratio of groove width to height ratio) of 2.0 to 2.2 is used. As groove geometry plays a major role, the invention increased shape factor to between 2.8 to 3.0 for last 5 stands. By this modification, the roll load is increasing by 22KN, but that is within permissible range. Figure 8 shows the difference in roll load at stands 20th to 25th for a smaller and higher diameter bar rolling with a diametrical difference of 0.5 mm.
Industrial Applicability:
In traditional processing, high carbon wire rod is usually required to be annealed because or hardness of material resulting from drawing processing. On the contrary, production of smaller diameter wire eliminates need of drawing, annealing and surface treatment in secondary processing. Presently only 5.5 mm wire rods and above are drawn into smaller diameter wires in 7-8 stands by drawing operation. On the contrary, production of smaller diameter rod results in eliminating one of the stands for further drawing, require less reduction in drawing operation, thereby reducing power consumption and time.

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Nomenclature
Wi Maximum width of incoming workpiece
Hi Maximum height of incoming cross section
Hg Height of roll groove
G Roll gap
Hp Pass height

Wf Face width of the oval groove
a Relief angle of round groove
WMAX Maximum spread of exit cross section
Hi Equivalent height of an incoming workpiece
Ho Equivalent height of an outgoing workpiece
Bc Equivalent width of an incoming workpiece
Y Spread correction coefficient
Ao Area of incoming round/oval workpiece
As,Ah Area fraction between incoming workpiece and geometry or
Roll groove as shown in figure 3a, 3b, 4a and 4b
Rmean Mean roll radius
Rmax Maximum roll radius
Rs Predicted radius of curvature of outgoing cross section
Rs Radius of round groove
Ra Radius of incoming round workpicce
Rf Radius of final surface profile of workpiece after rolling
Wt Weighing function
Dx Center point of radius of surface profile of workpiece on X-
axis
#AHp Amount of decrement or increment of pass height

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N Number ofpoint wise roll radii
#e1 Principal plastic strain along X-axis
#e 2 Principal plastic strain along Y- axis
#e3 Principal plastic strain along Z-axis
tp Roll bite time
#e Mean effective plastic strain.
#e Mean effectivc strain rate
L Effective projected contact length
R Effective roll radius
n Roll rpm
g Volumetric rate of heat generation due to plastic deformation
k Thermal conductivity
Cp Specific heat
hihtc Interface heat transfer coefficient
ha convection heat transfer coefficient
Ta Ambient temperature
Tr Roll temperature
T Temperature of the deformed workpiece
p Density of the material.
F Roll force
#sC Average contact stress
Ad Projected contact area
Lmax Maximum distance of the projected contact area
Cx x coordinate of cross point of surface profile of deformed work-
piece with roll groove
m Dimensionless parameter -1/3
Km Average deformation resistance of the material

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µ Coulomb friction coefficient=0.35
hm Mean height of the workpiece=0.5*(Hi+Hp)
M Roll torque
P Motor power

17 WE CLAIM:
1) A prooess of producing smaller diameter bars of less than 5 mm less from
square billets below 130 mm using a multi pass wire rod mill in 25 distinct
steps composing the steps of admitting the work-piece into the inputs of the
different passes wherein the inputs to each pass that are measured and adjusted
are the groove parameters and roll speeds and the outputs from each pass that
are measured and adjusted are the loads, torques, temperatures, power and
shape and wherein the evolving temperature distribution within the bar at each
pass is measured and adjusted using a "Finite Difference Technique" and the shape of the bar is measured and adjusted by using a weighing function relating
the radius of curvature of the incoming bar to that of the groove along the roll axis direction.
2) A prooess as claimed in Claim 1, wherein the width of the evolving bar is
measured in terms of maximum spread of the evolving bar in round to oval,
oval to round or box passes and the height of the evolving bar is measured in
terms of the groove depth.
3) A process as claithed in Claim 1, whereon the necessary roll speed required the
roll force supplied by a motor and the roll force required depends on the
maximum distance of the projected contact area and the contact point of the
deformed workpiece and the roll torque is obtained by multiplying roll load
with the lever arm length.
3)
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4) A process as claimed in Claim 3, wherein the power sapplied by the motor
depends on the roll torque and the roll speed.
5) A process of producing smaller diameter bars of 5 mm or less from square
billets below 130 mm using a multi pass wire rod mill in 25 distinct steps as
described and illustrated.
6) Smaller diameter bars produced by the process as claimed in any of the claims 1
to 4.

This invention is a process to produce 5.0mm bars in a 25 pass wire rod mill from 130mm * 130mm square billet that are continuously cast. The pass design for developing the strategy takes into account input process parameters such as groove parameters, roll speeds, initial billet temperature. The outputs are strain, strain rate, reduction, roll load, torque, temperature, power, and shape of deformed work piece at each pass. The invention uses finite difference technique to calculates evelving temperature distribution within the wire rod at reach pass. the surface profile of outgoing workpiece at ech pass is formulated using weighing function and linear interpolation of the radius of curvature of an incoming workpiece and that of roll groove to the roll axis direction.