FIELD OF THE INVENTION
The present invention is directed to an on-line cooling system for arresting the
temperature rise of the hot saw blade comprising suitable nozzles adapted to spray water
jet at selective water pressure and flow rate. Importantly, high pressure efficient water jet
cooling device for online hot saw blade cooling system of the invention ensure improved
cutting performance and longer operating life of the circular hot saw before
regrinding/replacement, reducing the hot saw downtime and related costs. The hot saw
cooling system comprise two specially designed parallel cooling headers fitted with in built
array of nozzles adapted to impinge water jet from both sides of the circular saw, covering
full length of cutting stroke, such that the blade teeth temperature rise is low and thus the
teeth hardness and sharpness is retained for longer cutting operation without tip failure.
Advantageously also, the on-line cooling system for the circular hot saw according to the
present invention allow the water jets fall on blade teeth in backward down motion and
used water is suppressed down in tunnel and does not fall on stock being cut. The heat
transfer from hot cutting tips are effectively carried away by water jet at a controlled flow
rate in the range of 6-10 m/sec such that the life of Hot Saw blades increased from 4
hours (about 300 cuts) to more than 8 hrs (> 500 cuts), improving significantly the
productivity of hot saw plant and thus making such online cooling system capable of wide
industrial application with significant economic advantage in hot saw/shear plants for
cutting of hot rolled sections in still mills.
BACKGROUND ART
It is known in the steel plant operations and in particular in hot rolling plants producing
different hot rolled steel sectional bars like joist, beam, channel, angles, rails and other
asymmetrical / unsymmetrical sections, are on-line hot cut by circular saw machines for
achieving good quality of cut lengths with desired end finish. The hot saw machine has
circular saw blade with peripheral teeth, which rotates at high speed. The hot rolled
section bar is positioned in front of the machine and the circular blades cut the bar in
desired length in forward stroke at slow feed rate. After completion of cutting stroke, the
blade comes back to its original position.
In Rail and Structural Mill of the applicants' Bhilai Steel Plant, the hot rolled rails and other
sections are cut by sliding frame type circular hot saws at operating product temperature

in the range of 800-850°C. The circular blades are usually of 1800mm diameter with
peripheral tooth pitch of 19 mm are made from Cr-V-Mo steel plates of 8-10mm thickness
and the teeth are heat-treated to impart hardness in the range of 29 to 36 RC. The hot
saw blade is mounted on the machine shaft and rotates at 1800 rpm during cutting
operation. Hot rolled rail or structural sections move on roller table and cut to desired
length by hot saws. There are vertically inserted grill plates in the assembly fixed on roller
table in front of hot saw to facilitate blade movement in the gap during the cutting and
return stroke.
The hot saw machine is provided with two numbers of water spray pipes which are fitted
with blade cover. The water pressure in the cooling pipes is normally at less than
1.0kg/cm2. Thus the existing cooling arrangement for the hot saw blade teeth has been
found to be inadequate to control undesirable temperature rise of blade teeth that reduces
tooth tip life. In absence of adequate cooling with the existing set up, the hot saw blade
not only picks-up sufficient heat from hot stock during the cutting operation, but also
subjected to large amount of heat generated at cutting interface due to friction. As a
result, the temperature at teeth tips rise by about 140°C during the fractional contact time
of hot stock cutting and subsequently cools by about 90°C during rest part of each
rotation. This causes temperature build-up of 25-50°C in each rotation for the first 10-15
revolutions and thereafter, the temperature of teeth tips fluctuates between 275-425°C
cyclically. Due to increase in temperature in the said range, the blade teeth lose original
hardness and as a consequence wear out fast resultantly loosing sharpness also. Since the
temperature of teeth tips rises high during the cutting operation, the cutting edges of tips
gets blunt faster and the chips generated during cutting gets welded on teeth which
adversely affects the quality of cut. Thick burrs are inevitably generated at the cut ends by
cutting with blunt saw teeth and consequently tend to damage the on-line NDT sensors
down the stream of finishing line. Moreover, excessive cutting force with blunt saw teeth
causes bending of rail ends, therefore, hot-saw blades necessitate replacement after 4-5
hours resulting in mill stoppage for 20 minutes, thus adversely affecting the productivity of
hot saw plant.
There has therefore been a persistent need to develop a cooling system for online effective
cooling of the circular hot saw such that the disadvantages experienced in the existing
practice shall be eliminated. The device for hot saw cooling during cutting operation would

on one hand restrict the rise in temperature of blade tips within safe limit such that the
important properties of the cutting tool e.g. the hardness or sharpness is not lost at a
faster rate and the tool life is extended and on the other hand it arranges the water jet
cooling system by selective disposition of suitably designed nozzles to deliver desired flow
rate and at required pressure to enable desired heat transmission. The cooling device also
ensure detachment of burrs from saw tips avoiding being welded to it and thus ensuring
quality cut and end finish of sections and collecting and recycling coolant water carrying
finer burrs in a manner, so as to save damage of NDT sensors down the stream. The
invented device aims at arresting the temperature rise of the hot saw blade using efficient
cooling system fitted with suitable nozzles to work at optimized water pressure and flow
rate directed to enhance hot saw tool life and thus reducing the downtime and associated
costs with consequent improvement in plant productivity.
OBJECTS OF THE INVENTION
The basic object of the present invention is thus directed to a high pressure efficient
cooling device for online hot saw blade cooling during cutting operation whereby the blade
teeth temperature rise is controlled within safe limit, such that the teeth hardness and
sharpness is retained for longer period/higher number of cuts and thus enhancing the tool
life, improving cutting quality of rolled sections and increasing the productivity in the
rolling mill.
Another object of the online device for hot saw blade cooling during cutting operation of
the present invention is to prevent heat conduction from teeth tip to base and arrest rise
in its' temperature, thereby retaining hardness and sharpness of teeth tips for higher
number of cuts.
Yet another object of the present invention is directed to an efficient online cooling system
for hot saw blade cooling during cutting operation wherein the specially designed cooling
headers fitted with suitable nozzles are selectively disposed to impinge water jets covering
full length of cutting stroke on both sides of the circular hot saw.

A still further object of the present invention is directed to an efficient online cooling
system for hot saw blade cooling during cutting operation wherein high pressure jets
prevent chips from getting welded at teeth tips and gullet.
A still further object of the present invention is directed to an efficient online cooling
system for hot saw blade cooling during cutting operation wherein burrs generated in
cutting do not stick to cut end of bar/section, due to retention of sharpness of teeth
through control of rise in temperature during cutting and thus improving quality of cuts.
A still further object of the present invention is directed to an efficient online cooling
system for hot saw blade cooling during cutting operation wherein water is suppressed
down to tunnel and do not fall on hot bar being cut.
A still further object of the present invention is directed to an efficient online cooling
system for hot saw blade cooling during cutting operation wherein the chances of any
damage of NDT sensor probes by attached burrs down the finishing stream is eliminated.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to an online cooling system for
hot saw blade cooling during cutting operation with improved cooling efficiency, comprising
roller table supporting the movement of the hot rolled rail or structural sections ;
Vertically disposed pair of grill plates adapted to support the hot saw blade movement in
the gap therebetween during the cutting and return stroke;
two parallel headers with suitable nozzles in-built with respect to the said two opposite U-
shaped grill plates facing each other adapted to cool the circular hot saw blade from both
side by water jets immediately as the hot saw blade individual tooth leaves contact with
hot metal after cutting the same.
A further aspect of the present invention is thus directed to an online system for hot saw
blade cooling wherein, said cooling headers are fitted with array of nozzles covering the
teeth on the circular blade periphery adapted to operate at high water pressure and with

selective velocity of water jet impingement on said blade teeth for high rate of heat
extraction;
said selective high-pressure and velocity of water jets adapted to cool blade teeth after
each revolution of the circular hot saw and thereby limiting temperature rise to favour
retention of hardness and sharpness of tip/teeth for longer operation time/number of cuts
maintaining desired cut quality of stock;
A still further aspect of the present invention is thus directed to an online system for hot
saw blade during cutting operation with improved cooling efficiency, wherein said nozzles
adapted to impinge water jet on blade teeth at a supply pressure in the range of 3 to 4
kg/cm2 and a velocity in the range of 6-10 m/sec to achieve desired cooling effect of hot
saw blade to limit the temperature rise within ambient to 275 °C and preferably less than
100°C.
A still further aspect of the present invention is thus directed to an online system for hot
saw blade cooling during cutting operation with improved cooling efficiency, wherein said
nozzles impinge water jets on blade teeth covering full length of cutting stroke.
A still further aspect of the present invention is thus directed to an online system for hot
saw blade cooling during cutting operation with improved cooling efficiency, wherein said
nozzles are selectively disposed depending upon the heat generated during cutting such as
to increase the life of blades.
According to a further aspect of the present invention directed to an online system for hot
saw blade cooling during cutting operation with improved cooling efficiency, wherein the
nozzles and headers are fitted inside the grill plates for protection from any damage.
A still further aspect of the present invention is thus directed to an online system for hot
saw blade cooling during cutting operation with improved cooling efficiency, wherein high
pressure water jets through nozzles adapted to wash away the red hot chips generated
during cutting and do not allow them to get welded in the tooth gullet.
According to yet another aspect of the present invention is directed to an online system for
hot saw blade cooling during cutting operation with improved cooling efficiency, wherein

the water jets fall on blade teeth in backward down motion such that the water is
suppressed down in tunnel and does not fall on cutting stock.
The present invention and its objects and advantages are described in greater details with
reference to the accompanying non-limiting illustrative drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: is the schematic diagram of the hot saw machine showing the conventional
cooling system.
Figure 2: is the schematic diagram of the newly developed modified water jet cooling
system/device for the hot saw machine, according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING FIGURES
Reference is first invited to the accompanying Figure 1, that illustrates schematically the
conventional cooling system for existing circular hot saw machine.
The existing hot saw machines are generally fitted with circular blades of 1800mm
diameter with peripheral tooth pitch of 19 mm that are made from Cr-V-Mo steel plates of
8-10mm thickness and the teeth are heat-treated to impart hardness, preferably in the
range of 29 to 36 RC. The schematic arrangement of hot saw with existing cooling system
shows that the circular saw blade(l) is mounted on the machine shaft(2) and rotates at
1800rpm during cutting operation. In the hot rolling mills, the hot rolled rail or structural
sections moves on roller table(3) and are cut to desired length by hot saws. There are
vertically inserted grill plates(4) in the assembly fixed on roller table in front of hot saw to
facilitate blade movement in the gap(lO) during the cutting and return stroke. In the prior
art systems, the hot saw machine is provided with two numbers of water spray pipes(5)
which are fitted with blade cover(6). The water pressure in the cooling pipes is even less
than 1.0kg/cm2. As such the existing arrangement of cooling hot saw blade teeth is

inadequate to prevent temperature rise of blade teeth. In the conventional hot saw cooling
system, water falls on blade teeth after lapse of considerable time while it has rotated
about 1/3rd of revolution from contact of hot stock. As a result of which a part of heat
already gets conducted to blade. The blade picks-up sufficient heat from hot stock due to
inadequate cooling of blade, during the cutting operation. Additionally, large amount of
heat generated at cutting interface due to friction, results in temperature rise at teeth tips
by about 140°C during the fractional contact time of hot stock cutting and subsequently
cools by about 90°C during rest part of each rotation. This causes temperature build-up of
25-50°C in each rotation for the first 10-15 revolutions and thereafter, the temperature of
teeth tips fluctuates between 275-425°C cyclically.
The existing cooling system is suffering from limitations due to uncontrolled rise in
temperature, the blade teeth loose hardness and therefore wear out fast and also loose
sharpness of tips. As the temperature of teeth tips rise high during the cutting operation,
cutting edges get blunt at a faster rate and chips get welded on teeth which adversely
affects the quality of cut. Thick burrs are unavoidably generated at the cut ends as cutting
continued with blunt saw teeth and consequently tend to damage the on-line NDT sensors
down the stream of finishing line. Moreover, excessive cutting force with blunt saw teeth
causes bending of rail ends, and over loading the hot saw machine. The hot-saw blades
therefore, necessitate replacement after 4-5 hours, resulting in mill stoppage for 20
minutes, thus reducing productivity and increasing the operating costs.
Reference is now invited to the accompanying Figure 2, that illustrates schematically the
online cooling device for circular hot saw according to the present invention adapted to
control the rise in temperature of hot saw tips/teeth during cutting operation in order to
achieve longer tool (circular hot saw) life, prevent loss of hardness and sharpness of teeth,
improved quality of cut section and enhanced productivity of hot saw operation as well as
hot rolling plant.
The online hot saw cooling device/system according to the present invention is aimed at
arresting the temperature rise of the hot saw blade in the range of ambient to 275 °C and
preferably less than 100 °C, using efficient cooling system fitted with suitable nozzles to
work at optimized water pressure and flow rate. The basic objective of the invention is to
prevent heat conduction from teeth tip to base and arrest rise in the temperature and
thereby retaining hardness and sharpness of teeth tips for higher number of cuts.

It is well understood that the cooling efficiency of water jets depend on velocity of water
impingement on blade teeth and thus the parameters like water pressure and nozzle
configuration has been selectively adopted such that the velocity of water falling on blade
teeth is maintained in the optimum range of 6-lOm/sec, at a supply water line pressure of
3 to 4 kg/cm2. It is also known that heat conduction is dependant on time and
temperature, hence the cooling headers of newly developed on line hot saw cooling device
have been located nearest to the cutting zone so that the blade teeth are cooled
immediately as they leave contact with hot metal. Additionally, for protection from any
damage, the nozzles and headers are fitted inside the grill plates. The modified cooling
device thus facilitates water cooling to start immediately as the blade teeth leave the
contact zone, hence the cooling effect is very high and temperature rise of blade teeth is
prevented. This helps in retention of teeth hardness and sharpness for higher number of
cuts.
It is clearly apparent from the accompanying Figure 2, that in order to facilitate adequate
cooling of blade during cutting and enhance its life through retention of sharpness and
hardness of teeth, an efficient cooling system is developed using nozzles of suitable design
configuration. The system consists of two parallel headers (7) with suitable nozzles(8) in-
built with the two opposite U-shaped grill plates(9) facing each other to cool the blade
from both side wherein an array of nozzles selectively disposed covering most of the teeth
on blade periphery. The length and positioning of the headers and nozzle spacing is such
that the spray jets of water cover the entire length of cutting stoke. The vertical position
and orientation of the nozzles is specially designed to impinge the jets on individual blade
teeth immediately after it leaves contact with hot cutting stock. The selection of nozzles
and water pressure is based on heat transfer requirement and the impact velocity of water
jet selected to wash away the chips preventing them from sticking in the gullet. The
hardness measured at teeth varied between 29-36Rc after each cut/use of hot circular saw
blades and no change is observed in hardness pattern when cutting operation carried out
under original or modified cooling condition.
It is further observed that with the application of modified cooling system, the life of
blades increased from 4 hours (about 300 cuts) to more than 8 hrs (> 500 cuts) at Hot
Saw. The high-pressure water jets enabled better cooling of the blade teeth after each
revolution of the circular saw and prevented abnormal temperature rise. Moreover, high-
pressure water jets enabled chips to be washed away and thereby prevented accumulation

in the teeth gullets. Also since the water jets fall on blade teeth in backward down motion,
the water is suppressed down in tunnel and does not fall on cutting stock. Further, due to
the water jet impinging on blade teeth at high velocity and sharpness of teeth is retained
over longer period, burrs do not stick to cut end of bar and thus the chances of damage of
NDT sensor probes down the finishing stream is also eliminated.
Thus, with the introduction of the improved cooling system for hot saw operation as of the
present invention, blade life has been increased through lesser tooth wear, and
consequently lower blade consumption. Moreover, longer life of blades resulted in reduced
downtime on account of blade changing and effectively increased the productivity of the
mill.
It is thus possible by way of the present invention to develop a cooling system for online
cooling of hot saw blade during cutting operation of hot rolled steel sections such that the
temperature rise of the tips of circular hot saw is effectively controlled and the saw life is
increased by enhancing the number of cuts and lesser downtime by retaining the hardness
and sharpness of the teeth tips for longer periods of operation. The invention thus ensure
improved quality of cut sections, lower downtime of hot saw due to requirement of
repair/replacement of saw with reduction in teeth wear and thus resulting in improved
productivity in hot rolling and sawing plant at lesser cost of production, making the system
capable of wide industrial application in steel industry.

We Claim:
1. An online cooling system for hot saw blade cooling during cutting operation with
improved cooling efficiency, comprising
roller table supporting the movement of the hot rolled rail or structural sections ;
Vertically disposed pair of grill plates adapted to support the hot saw blade and
facilitate blade movement in the gap therebetween during the cutting and return
stroke;
two parallel headers with suitable nozzles in-built with respect to the said two
opposite U-shaped grill plates facing each other adapted to cool the circular hot saw
blade from both side by water jets immediately as the hot saw blade leaves
contact with hot metal after cutting the same.
2. An online cooling system for hot saw blade cooling as claimed in claim 1 wherein
said cooling headers are fitted with array of nozzles covering the teeth on the
circular blade periphery adapted to operate at high water pressure and with
selective velocity of water jet impingement on said blade teeth for high rate of heat
extraction;
said selective high-pressure and velocity of water jets adapted to cool blade teeth
after each revolution of the circular hot saw and thereby limiting temperature rise
to favour retention of hardness and sharpness of tip/teeth for longer operation
time/number of cuts maintaining desired cut quality of stock;
3. An online cooling system for hot saw blade cooling during cutting operation with
improved cooling efficiency as claimed in anyone of claims 1 or 2, wherein said
nozzles adapted to impinge water jet on blade teeth at a supply pressure in the
range of 3 to 4 kg/cm2 and a velocity in the range of 6-10 m/sec to achieve desired
cooling effect of hot saw blade to limit the temperature rise within ambient to 275
°C and preferably less than 100°C.

4. An online cooling system for hot saw blade cooling during cutting operation with
improved cooling efficiency as claimed in anyone of claims 1 to 3, wherein said
nozzles impinge water jets on blade teeth covering full length of cutting stroke.
5. An online cooling system for hot saw blade cooling during cutting operation with
improved cooling efficiency as claimed in any one of claims 1 to 4, wherein said
nozzles are selectively disposed depending upon the heat generated during cutting
such as to increase the life of blades.
6. An online cooling system for hot saw blade cooling during cutting operation with
improved cooling efficiency as claimed in any one of claims 1 to 5, wherein the
nozzles and headers are fitted inside the grill plates for protection from any
damage.
7. An online cooling system for hot saw blade cooling during cutting operation with
improved cooling efficiency as claimed in any one of claims 1 to 6, wherein high
pressure water jets through nozzles adapted to wash away the red hot chips
generated during cutting and do not allow them to get welded in the tooth gullet.
8. An online cooling system for hot saw blade cooling during cutting operation with
improved cooling efficiency as claimed in any one of claims 1 to 7, wherein the
water jets fall on blade teeth in backward down motion such that, the water is
suppressed down in tunnel and does not fall on cutting stock.
9. An online cooling system for hot saw blade cooling during cutting operation with
improved cooling efficiency, as herein described with reference to the
accompanying non limiting illustrative drawings.

An on-line cooling system adapted to arrest the temperature rise of the hot saw blade
comprising nozzles adapted to spray water jet at selective pressure and flow rate, through
two specially designed parallel cooling headers fitted with in- built nozzles that impinge
water jet from both sides of the circular saw teeth, immediately after the teeth comes out
of hot cutting stock. The water jets cover the entire cutting stroke such that the blade
teeth temperature rise is limited to ≤ 275°C, and thus retaining the hardness and sharpness of tip. The heat from hot cutting tips are carried away efficiently by water jets at a controlled flow rate in the range of 6-10 m/sec such that the life of Hot Saw blades increased to more than 8 hrs (> 500 cuts), from existing 4 hours/300 cuts, thus improving the productivity of hot saw plant, suitable for application in steel industry.