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A PROCESS FOR IMPROVEMENT IN SURFACE FINISH, GAUGE
VARIATION AND YIELD OF PLATES IN PLATE MILL THROUGH
SCARFING.
FIELD OF THE INVENTION
The invention relates to an improved method for better surface finish, improved
gauge variant ion and better yield in Plate mills through scarfing. More
particularly, the present invention relates to improve the shape of the plates of
special quality steels (DMR249 Gr.A).
DESCRIPTION OF THE PRIOR ART
Plate Mill of Steel Plant deals with heating, rolling, finishing, stacking and
dispatching plates as per customer order. Earlier, plates were being scarfed non-
uniformly to remove surface defects. Normally, scarfing of edges is done more
frequently. This does not help in controlling the shape of the plates and also
results in yield loss.
Scarfing processes are carried out on steel for three distinct reasons. The first is
to remove flaws such as cracks in a piece of steel, e.g. a slab. This is carried out
by means of a hand-held flame torch, which is used to melt the metal entirely in
order to remove the flaw. The operator applies the torch and moves it according

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to the nature of the flaw being removed. Secondly, scarfing is used to remove a
complete surface layer of the steel, particularly with a view to removing any flaws
which may be present at the surface.
The third purpose for which scarfing is used is to inspect the quality of a steel
slab. When a slab is rolled into sheet, flaws which may not be visible on the
surface of the slab are revealed in the sheet. It is therefore desirable to estimate
the number of such subsurface flaws in the slab, before it is rolled. This may be
done, as described in more detail below, by scarfing an inspection track on the
slab.
Although the improved method according to the invention is applied for removal
of flaws, it is particularly designed and intended for improved quality of a steel
slab. The invention will be explained here in relation to this purpose.
A criterion for the quality of a slab of steel which is to be rolled is thus the number
and type of defects which lie 1 to 3 mm deep under the surface of the slab.
These defects, which are formed by inclusions of AI2 03 and Si02 and, in the
case of continuously cast slab, also by residual casting powder, come to the
surface during the further working of the slab due to oxidation of the sheet
surface during heating in a furnace and hot-rolling. The oxidized surface layer
falls off exposing the steel beneath. They determine the quality of the surface in

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the finished product. This surface quality is in many cases of great importance,
for instance in the case of car bodywork.
A known method for judging the quality of a slab of rolled steel consists of
scarfing an inspection channel on the slab surface using a hand-held blow-torch,
the channel having a depth equal to the thickness of the layer which will
subsequently be lost by oxidation. The number and type of defects in the
inspection channel can then be ascertained. By inspection channel (or track) we
mean here a channel obtained by scarfing over a width of e.g. about 10 cm for at
least a part of the length of the slab parallel to its longitudinal direction.
The invention depends on the realisation that, for a satisfactory solution of the
problem, the human factor must be removed. As mentioned above, scarfing
machines are known for overall or partial scarfing of steel, but these machines
are very expensive and are only usable profitably if there is a high throughput.
When scarfing a channel for inspecting the quality of a slab of steel for rolling,
one is concerned on the other hand with removing a very small part of the
surface of the sheet. It is only necessary for example to form an inspection
channel on a very small proportion of the products of a single charge of a
continuous casting machine in order to establish the quality of the whole charge.
Scarfing procedures of the conventional type are therefore not profitable for
forming tracks for the estimation of the quality of steel slabs, and for extensive
technical reasons these machines are not suitable for this purpose.

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SUMMARY OF THE INVENTION
Such as herein described an improved method of scarfing to improve the shape
of the plates is introduced in special quality steels comprising the steps of
scarfing of the edges of the slab followed by, scarfing the other portions of the
slab to a depth lower than the edge.
Therefore it is the primary object of the present invention is to provide a better
surface finish of special steel plate.
Another object of the present invention is to provide a higher yield of special steel
resulting in cost effectiveness
Yet another object of the present invention is to provide better shape control in
special steel plates.
As per another exemplary embodiment of the present invention the improved
method of scarfing provides a concave surface of the slab. This further gives a
surface finish as good as that achieved through plan view rolling.

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Another object of the present invention is to provide a minimal belly formation
which is otherwise a common phenomenon in a single stand reversing mill.
Therefore the need of implementing of new technology in the Mill stand for rolling
special steel plate is no more required on adopting the scarfing method as
disclosed herein and as set out in the subsequent claims..
The object of the present invention is to provide a scarfing apparatus, which can
be simple and cheap, for use in scarfing a regular inspection track, e.g. of
uniform depth, in such a way that the quality of a slab of steel can be estimated
in a reproducible manner.
Given the following detailed description, it should become apparent to the person
having ordinary skill in the art that the invention herein provides a novel
engineered method permitting exploitation of significantly augmented efficiencies
while mitigating problems of the prior art.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The preferred embodiment of the invention will be described below by way of
non-limitative example with reference to the accompanying drawings, in which:

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FIG. 1 is a perspective view of ordinary scarfed slab as prior art;
FIG. 2 is a perspective view of the PVR Scarfed Slab according to the present
invention.
DETAILED DESCRIPTION
Our invention is in the area of slab surface. This area earlier needed lot of
attention as this was the problem area so far as the surface quality and yield was
concerned. So the earlier practice of scarfing the slab surface resulted in poor
quality of plate surface. Therefore, the new practice of scarfing the edge first and
other portion of slab later to a depth lower than the edge gives us the shape
equal to that of a slab chosen in plan view rolling (PVR).
Earlier, when the special steel slabs were being rolled, these invariably resulted
in dimensional problems in the plates. Various problems like surface quality
(waviness), pit formation, gauge variation, camber formation and belly formation
cropped up during such rolling. As such, many special plates were rejected.
Good surface finish and better shape control are of the paramount importance in
case of special steel plates. Based on the above problem, lot of innovative ideas
were tried by the inventors to surmount this problem.

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Among the various innovations tried, one of the innovations, which was
successful, was the modified practice of scarfing the slab surface. This resulted
in good surface finish and shape control. Henceforth, all the required parameters
of special steel plates are being achieved with this new method of scarfing the
slab surface. Here, no extra investment was required and also there was no need
of implementing of any new technology in the Mill stand. This has also resulted in
higher yield leading to cost effectiveness.
This innovative idea basically deals with scarfing the edge of the slab first and
the rest of the surface of the slab is then scarfed to a greater depth so as to
achieve a concave surface as shown in figure 2. This helps in controlling belly
formation which is otherwise a normal phenomenon in a Single Stand Mill. This
gives us a surface finish equivalent to that available through plan view rolling
(PVR). Better surface finish, thus achieved, eliminates dimensional problems, pit
formation etc.
In modern Plate Mills, worldwide various automatic gadgets like Plan View
Rolling (PVR), Hydraulic Auto-gauge Control (HAGC), Control Variable Crown
(CVC) and Roll Bending are being increasingly used with the help of
computerized system to achieve excellent surface finish, accurate dimensional
control of the rolled plate. But in our case, we did not possess such modern
gadgets. Simultaneously, special steel plates for defence purposes do require
surface finish and dimensional accuracy of the highest order. The first 40 special

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steel slabs rolled for defence purposes were rejected on account of poor surface
finish, poor dimensional control.
The innovation of scarfing to improve the shape of the plates is introduced in
special quality steels (DMR249 Gr.A). In this process, scarfing of the edges is
done first. Then the other portion of the slab is scarfed to a depth lower than the
edge. Hence the slab takes the shape equal to that of a slab chosen in plan view
rolling. This new process of scarfing differs from the older process in the
following manner:
• Scarfing of edge done first
• Scarfing of other slab surface done later
• Better surface finish
• Higher yield
• Better shape control
The inventors, through various innovative trials, attempted to achieve the same
surface finish and dimensional control as available through the use of most
modern gadgets. The innovative idea, which ultimately, led to excellent surface
finish and dimensional control, is what we call as PVR Scarfing. This idea did not
incur any extra investment.

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RESULTS OF 1ST 40 DMR 249A SLABS ROLLED

Slab
SI. No. Waviness Belly
Formatio
n Surface
defects Camber Dimensiona
I accuracy Final
acceptanc
e
DMR-1 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-2 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-3 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-4 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-5 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-6 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-7 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-8 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-9 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-10 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-11 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-12 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-13 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-14 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-15 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-16 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-17 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-18 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-19 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-20 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-21 Pronounce High Not More Not up to the Rejected

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d accepted standard
DMR-22 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-23 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-24 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-25 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-26 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-27 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-28 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-29 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-30 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-31 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-32 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-33 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-34 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-35 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-36 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-37 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-38 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-39 Pronounce
d High Not
accepted More Not up to the
standard Rejected
DMR-40 Pronounce
d High Not
accepted More Not up to the
standard Rejected
Although the foregoing description of the present invention has been shown and
described with reference to particular embodiments and applications thereof, it

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has been presented for purposes of illustration and description and is not
intended to be exhaustive or to limit the invention to the particular embodiments
and applications disclosed. It will be apparent to those having ordinary skill in the
art that a number of changes, modifications, variations, or alterations to the
invention as described herein may be made, none of which depart from the spirit
or scope of the present invention. The particular embodiments and applications
were chosen and described to provide the best illustration of the principles of the
invention and its practical application to thereby enable one of ordinary skill in the
art to utilize the invention in various embodiments and with various modifications
as are suited to the particular use contemplated. All such changes, modifications,
variations, and alterations should therefore be seen as being within the scope of
the present invention as determined by the appended claims when interpreted in
accordance with the breadth to which they are fairly, legally, and equitably
entitled.

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We Claim:-
1. An improved method of scarfing to improve the shape of the plates is
introduced in special quality steels comprising the steps of:-
scarfing of the edges of the slab is done first; and then
scarfing the other portions of the slab to a depth lower than the edge.
2. An improved method of scarfing to improve the shape of the plates as
claimed in claim 1, wherein the surface of the slab is scarfed into a concave
surface which gives a surface finish as good as that achieved through plan view
rolling.
3. . An improved method of scarfing to improve the shape of the plates as
claimed in claim 1, wherein the steel is of grade DMR249 Gr.A or the like.

4. An improved method of scarfing to improve the shape of the plates is
introduced in special quality steels, substantially as described herein with
reference to the accompanying drawings.
Dated this 06th day of March, 2008
To,
The Controller of Patents,
The Patent Office, Kolkata.

The present invention relates to An improved method of scarfing to improve the
shape of the plates is introduced in special quality steels comprising the steps of
scarfing of the edges of the slab is done first, and then scarfing the other portions
of the slab to a depth lower than the edge