Note: Descriptions are shown in the official language in which they were submitted.
CA 02427097 2007-12-14
UNINTERRUPTED CONTINUOUS ROLLING OF BAR AND ROD PRODUCTS
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the production of bar and rod products in
continuous
rolling mills by hot rolling discrete billets through roughing, intermediate
and finishing mill
sections, and is concerned in particular with a method and apparatus for the
end-to-end welding
of separate product lengths at a selected location along the rolling line,
thereby making it
possible to continue rolling uninterruptedly throughout the remainder of the
mill.
2. Description of the Prior Art
In conventional bar and rod rolling mills currently in operation, the accepted
practice is to
begin the process with individual billets that are heated in a furnace and
then discharged for
separate rolling into product lengths having reduced cross sectional areas and
front and tail ends.
A number of drawbacks are associated with this practice. For example, the gap
time between
billets can account for as much as 10% lost production time.
Also, the front and tail ends of each product length are dimensionally and/or
metallurgically unacceptable and must therefore be trimmed and discarded,
resulting in
considerable scrap losses. The front ends are also prone to cobbling,
particularly at the higher
speeds reached in the finishing section of the mill.
In an effort at avoiding these problems, technology has been developed to weld
the billets
end-to-end before they are introduced in the mill. However, this too has
proven to be somewhat
problematical. Welding of the large billet cross sections requires massive
equipment and a
2
CA 02427097 2007-12-14
heavy consumption of electrical energy. Excessive electrical energy is
additionally required to
inductively reheat the billet segments that have been chilled by contact with
the heavy clamping
devices required to force the billet ends together.
A further drawback with billet welding stems from the fact that the fused
metal at the
welded joint is subsequently rolled into a substantial length of the finished
product. For
example, when billets having a typical cross sectional area of 22,500 mm2 are
welded and then
rolled into 5.5 mm rod, the fused metal of the welded joint will extend
through approximately 94
meters of the finished product. If the billets are metallurgically dissimilar,
this length may well
have to be scrapped, at a considerable loss to the mill operator.
The present invention applies welding technology to the rolling process in a
manner and
at a location along the rolling line that avoids or at least significantly
minimizes the problems
and disadvantages associated with current practices.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided a method of
rolling discrete
product lengths having front and tail ends through successive roll stands
arranged on a mill pass
line, the method being operable alternatively in first and second modes, the
first mode
comprising: operating a first of the roll stands at a delivery speed that
exceeds the take up speed
of a successive second roll stand; directing first and second product lengths
as they exit from the
first roll stand away from the mill pass line along an entry path leading to a
welding station
positioned laterally with respect to the mill pass line, and from the welding
station along a
delivery path leading back to the same mill pass line for continued rolling in
the second roll
3
CA 02427097 2007-12-14
stand; temporarily accumulating a first portion of the first product length
along the delivery path
while rolling of the first product length is taking place in the second roll
stand; retaining the tail
end of the first product length at the welding station during a time interval
in which the
accumulated first portion continues to be rolled in the second roll stand;
retaining the front end of
the second product length at the welding station during the time interval,
while temporarily
accumulating a second portion of the second product length along the entry
path; welding the
retained front and tail ends together during the time interval to form welded
ends; and releasing
the welded ends; and the second mode comprising bypassing the entry path and
directing the first
and second product lengths along the mill pass line from the first roll stand
directly to the second
roll stand.
According to another aspect of the invention, there is provided an apparatus
for rolling
discrete product lengths having front and tail ends through successive roll
stands arranged on a
mill pass line, the apparatus comprising: first and second roll stands
arranged in succession along
a mill pass line, the first roll stand being operable at a delivery speed that
exceeds the take up
speed of the second roll stand; guide means operable in one mode to direct
first and second
product lengths exiting successively from the first roll stand directly to the
second roll stand, and
operable alternatively in another mode to direct first and second product
lengths successively
exiting from the first roll stand away from the mill pass line along an entry
path leading to a
welding station positioned laterally with respect to the mill pass line, and
from the welding
station along a delivery path leading back to the same mill pass line and to
the roll stand; a first
storage means for temporarily accumulating a first portion of the first
product length along the
delivery path while rolling of the first product length takes place in the
second roll stand;
retaining means for retaining the tail end of the first product length and the
front end of the
3a
CA 02427097 2007-12-14
second product length at the welding station during a time interval in which
the accumulated first
portion of the first product length continues to be rolled in the second roll
stand; second storage
means for temporarily accumulating a second portion of the second product
length along the
entry path during the time interval; and welding means at the welding station
for welding the
retained front and tail ends together, whereupon release of the thus welded
front and tail ends
will permit continued and uninterrupted rolling of the first and second
product lengths in the
second roll stand.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a plan view of one embodiment of an apparatus in accordance with
the present
invention;
3b
CA 02427097 2003-04-30
D-1196
Figures 2A - 2J are diagrammatic views showing successive stages in the
operation of
the apparatus depicted in Figure 1;
Figure 3 is a plan view of an alternative embodiment of an apparatus in
accordance
with the present invention; and
Figure 4 is an enlarged cross section taken along line 4-4 of Figure 3 and
schematically
depicting the stacked storage capacity of the accumulator.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
With reference initially to Figure 1, first and second vertical and horizontal
roll stands
10 and 12 are shown positioned along a mill pass line "P". Roll stand 10 may,
for example
comprise the last roll stand of the mill's roughing section, and stand 12 may
comprise the first
roll stand of the mill's intermediate section. The delivery speed of roll
stand 10 will exceed
the take-up speed of roll stand 12. Thus, in an exemplary operation, with a
mill rolling a 2000
kg billet at a rate of 150 metric tons per hour, roll stand 10 would produce a
bar having a cross
sectional area of 57.4 mm at a delivery speed of 2052.5 mm/sec, The take up
speed of roll
stand 12 would be 1642 mm/sec.
Switches 11 are arranged to direct successive product lengths exiting from
roll stand 10
away from the mill pass line P and along an entry path 14 leading to a welding
station 16, and
from the welding station along a delivery path 15 back to the mill pass line
for continued
rolling in the roll stand 12 and all subsequent roll stands (not shown).
Alternatively, the
4
CA 02427097 2003-04-30
D-1196
switches 11 may be operated to bypass the entry path 14 and to thereby allow
discrete product
lengths to continue along the pass line P.
A first storage means in the form of a repeater 18 is located along the
delivery path 15,
and a second storage means, also in the form of a repeater 20 is located along
the entry path
14. The repeaters 18, 20 may be of conventional design well known to those
skilled in the art.
The welding station 16 includes a welder 22 configured to weld abutting
trailing and
leading ends of product lengths. The welded joints are deburred by a deburring
device 24
before continuing along delivery path 15. The welded joints and adjacent
product segments
may, if necessary, be reheated in advance of roll stand 12 by an induction
heater 26. Driven
pinch rolls 28, 30, 32 and 34 are strategically positioned to control the
forward movement of
the product lengths being processed.
The operation of the apparatus will now be described with reference to Figures
2A-2J.
Figure 2A
A first product length A is being rolled through roll stand 10 at a rate of
150 tons per
hour and a speed of 2052.5 mm/sec. The product length A has passed along entry
path 14,
through the welding station 16 and along delivery path 15, and its front end
AFE has arrived at
pinch roll unit 34 where it has been temporarily stopped. A first portion of
the first product
length has begun to accumulate in the form of a loop AL in repeater 18.
Figure 2B
5
CA 02427097 2003-04-30
D-1196
The loop AL in repeater 18 has increased considerably, and the front end AFE
of the first
product length has now passed through pinch roll unit 34 into roll stand 12.
The rolling rate of
roll stand 12 is 120 tons per hour, with a take in speed of 1642 mm/sec.
Figure 2C
The loop AL in repeater 18 has reached its maximum. The tail end ATE of the
first
product length is just clearing roll stand 10, and the front end Bra of the
second product length
B is approaching roll stand 10.
Figure 2D
The tail end ATEof the first product length A is now moving into the entry
path 14 as
the front end BFE of the second product length B enters roll stand 10.
Figure 2E
The tail end ATE of the first product length A and the front end BFE of the
second
product length B have arrived at the welding station 16 where they are held
stationary in an
abutting relationship by pinch roll units 32, 30. Welding of the front and
tail ends begins.
Figure 2F
While welding of the front and tail ends takes place, the loop AL of the first
product
length in repeater 18 is gradually depleted, and the second product length B
accumulates in a
loop BL form in repeater 20.
Figure 2G
6
CA 02427097 2003-04-30
D-1196
The welded front and tail ends have progressed from the welding station 16 to
roll stand
12, and the loop BL previously accumulated in repeater 20 is now being
transferred by the
pinch roll units 30, 32 to repeater 18.
Figure 2H
As transfer of the product loop BL from repeater 20 to repeater 18 continues,
the tail
end BTa of the second product length arrives at roll stand 10.
Figure 21
As described previously with reference to Figure 2D, the tail end BTE of the
second
product length is now moving into the entry path 14 as the front end CrE of a
third product
length C enters roll stand 10.
Figure 2J
Welding of the tail end BTE of the second product length to the front end CFE
of the
third product length has commenced, as described previously with respect to
Figure 2E.
The pinch roll units 28, 30, 32 and 34 are individually driven and thus may be
selectively controlled to accelerate, decelerate and stop the successive
product lengths in order
to effect the above described movements. Although welding is preferably
accomplished with
the front and tail ends arrested at station 14, alternatively, the pinch roll
units 30, 32 could be
operated to simply slow the front and tail ends, with the welder 22 being
movable at the same
speed to effect welding on the fly.
7
CA 02427097 2003-04-30
D-1196
Once a lead product is fed to roll stand 12, uninterrupted rolling continues
thereafter in
that stand and any subsequent stands throughout the remainder of the mill.
Welding of front and tail ends with reduced cross sectional areas at station
16 can be
achieved quickly, with minimum consumption of energy, and with smaller, less
expensive
welding equipment.
Figures 3 and 4 illustrate an alternative embodiment of the invention, where
components identical to those of the Figure 1 embodiment have been identified
by the same
reference numerals. Here, the repeater 20 of the first embodiment has been
replaced by a
multilevel accumulator 40.
It will be seen from Figure 4 that the accumulator comprises vertically
stacked pairs of
guide rollers 42 arranged around a circular footprint 44. The guide rollers
define a helical
delivery path 46 configured and dimensioned to provide a product storage
capacity comparable
to that of the repeater 20 of the Figure 1 embodiment.
In light of the forgoing it will now be understood by those skilled in the art
that the
present invention operates to divert successive product lengths exiting from
roll stand 10 away
from the pass line P and along entry paths 14 (or 46) to the welding station
16, and from the
welding station along a delivery path 15 back to the pass line for continued
rolling in roll stand
12. Repeater 18 operates in conjunction with pinch roll units 32 and 34 on the
delivery side of
the welding station to temporarily store a first accumulation of one product
length and to arrest
or slow the trailing end of that product length at the welding station.
Repeater 20 (or accumulator 44) operates in conjunction with pinch roll units
28 and 30
on the entry side of the welding station to arrest or slow the leading end of
the next product
8
CA 02427097 2003-04-30
D-1196
length at the welding station, and to temporarily store a second accumulation
of that product
length.
The first and second product accumulations allow sufficient time for welding
the
arrested or slowed tail and front ends at the welding station. Thus, a
continuous product is fed
to roll stand 12 from the discrete product lengths being received from roll
stand 10.
The present invention is most advantageously employed to join product lengths
having
reduced cross sectional areas ranging from about 700-4400 mm2. Here, the fused
metal of the
welded joints will extend through relatively small lengths on the order of 3-
18 meters. Thus,
even when billet lengths having dissimilar metallurgy are being welded, scrap
losses will be
mini.mized in comparison to those experienced when welding billets prior to
rolling.
We claim:
9
