Note: Descriptions are shown in the official language in which they were submitted.
1079064
This invention relates to the continuous production
of metal strip or sheet material (hereinaiter reierred
to simply as strip) and relates especially to transporting
green strip produced by the roll compaction oi metal or
ore powder from a compaction mill to a sinter iurnace.
In Canadian Patent No 1013180
there is described and claimed a method and apparatus
for the continuous produ~tion of metal strip in which
compacted powder in the iorm oi green strip is ied to
a sinter ~urnace and is supported by a gaseous cushion
as it is transported through the iurnace, the strip
transport being controlled to perm~t the strip to
shrink linearly as it passes through the iurn~ce.
In order to minimise the tensile stress imposed on
the green strip and thereby to permlt the strip to shrink
linearly as it passes through the iurnace, it is necessary
to ensure that as the strip enters the iurnace it is
isolated, so iar as is practicable, ~rom tensile
stresses present in the strip upstream o~ the iurnace,
and that lt is transported to the iurnace in a
substantlally stress ~ree condition.
I It is also necessary to provide within the strip
¦ length a loop in which a sui~icient length o~ strip can
be stored to provide a means o~ accommodating any
l 25 temporary mismatch between the speeds at which the strip
¦ is supplled to and withdrawn irom the iurnace. Such a
I mismatch would occur, ~or example, during changes i~ line speed.
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1~)79064
According to the present invention in one aspect,
there is provided apparatus for transporting strip
materials comprises a floatation table formed with a
strip support s~r~ace having in the intended direction
o~ travel of strip over the table surface a downwardly
inclined entry section and an exit section inclined at
an angle to the horizontal less than that of the entry
section but greater than the angle of friction of the
strip which is to travel over the strip support sur~ace,
means being provided in the vicinity of the transition
between the entry and exit sections o~ the support
surface for senslng the proximity of or changes ln the
proximity of strip passing over the table to said support
surface. By 'angle o~ iriction' is meant the angle oi'
- inclination at which the strip ~ust slides down the
support surface under its own weight.
According to the present invention in a further
aspect,apparatus ~or transporting metal strip to and
through a sinter furnace comprises means for guiding the
strip downwardly on to the support suri'ace oi' a
. 20 iloatation table ~ormed, in the intended direction of
strip over the table, with downwardly inclined entry
anA exit sections oi dii'~ering ~lope, the exit section
being inclined at an angle to the horizontal less than
I that o$ the entry section, but greater than the angle
¦25 of friction of strip travelling over its support surface, : -
meaDs ~or seDsing the proximlty o~ tho strlp to the
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support suriace as the strip passes between the entry
section and the exit section o~ the table, means ior
propelling the strip through the sinter iurnace and
means ior controlling the strip propelling means in
r~ dependence upon the sensed proximity to maintain the
tensile stress imposed in the strip entering the furnace
minimal.
According to the present invention in a still
further aspect, there is provided a method oi transporting
strip to a ~urnace through which it is propelled by a
pair oi pinch rolls positioned downstream of the iurnace,
the method comprising the steps oi transporting the
strip to the iurnace over the support surface oi a
, downwardly inclined iloatation table formed with an
;, ~5 entry section and an exit section inclined at an angle
the horizontal less than that oi the entry section but
greater than the angle oi iriction of strip travelling
over its suriace, sensing the proximity oi the strip
to the support suriace oi the iloatation table as it
~ passes irom the table entry section to the table exit
section and controlling the rate at which strip
approaches the entry section oi the iloatation table in
¦ dependence upon the sensed proximity to minimise the
.1 tensile stiess imposed in the strip as it enters the
. 25 i'urnace.
. In one embodiment o~ the invention ior transporting
green strip produced by roll compacting metal powder
. continuously to a sinter iurnacej the entry section
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1079064
o~ the support suriace of the iloatation table is
inclined at an angle oi between 50 and 80 to the
horizontal and the exit section is inclined at an ang~e
o~ between 2 and 15 to the horlzontal. In a
pre~erred embodiment the entry section is inclined at
an angle of between 60 and 70 and the exit section
~rom betweeen 5 and 10 to the horizontal.
The proximity oi the strip to the support sur~ace ~ -
o~ the table may be sensed by means o$ one or more
pressure sensors located in or on the suriace oi the
table at the transition between the entry and exit
sections oi the table. Alternatively, the proximity
or changes in proximity may be sensed by one or more
position transducers located ad~acent the table at
the transition between lts entry and exit sections.
i As the strip is transported through the iurnace
` it may be supported on a gas cushion. The gas
cushion within the iurnace may consist oi any gas or
mixtures oi gases whose physical and chemical properties
are compatible with the support system and the strip
mate~ial being processed. For example, the gas çushion
may consist o~ argon or nitrogen or mixtures oi argon
j and nitrogen, oi' nitrogen and hydrogen, or argon,
nitrogen and hydrogen, or oi argon/nitrogen and
methane. Prei'erably, the gas mixture employed comprises
approximately 80% o~ dense support gas ti.e. argon and/
' or nttrogen).
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1079~64
In a preferred embodiment, green strip produced
by roll compacting metal powder is transported to a
sinter ~urnace in a manner in accordance with one o~ the
aspects oi the invention re~erred to above. The green
strip is propelled through the ~urnace by means o~ a
pair o~ pinch rolls located downstream o~ the furnace
and is supported by means oi a gas cushion during its
passage through the ~urnace. In this pre~erred
embodiment, the strip is subjected to substantially
]o zero tension during sintering. By 'substantially zero
tension' is meant tensile stress applied to the strip
whllst in the ~urnace o~ a value which does not exceed
a value which permits the sintering strip to shrink
linearly. The tensile stresses applied to ~erritic
and austenitic stainless steel green strip should be
less than 50 and 70 kN/m2 respectively. For both
materials the tensile stresses applied may suitably be
less than 15 kN/m2 and pre~erably less than 10 kN/m2.
Negative tensile stresses (that is to say compressible
stresses) may be applied t~ the strip during sinterlng
but only in so ~ar as the application o~ such stresses
does not cause the green strlp to buckle as it passes
through the iurnace.
The lnvention will now be described by way o~
example with reiterence to the accompanying diagrammatic
drawings in which :
Figure 1 is a s~de elevational view partly in
section o~ apparatus i?or producing metal strip in
accordance with the lnvention,
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~079064
Figure 2 is a section taken through the iurnace
illustrated in Figure l, and
Figure 3 illustrates an alternative arrangement
for carrying out the invention.
The apparatus illustrated in Figures l and 2
includes a hopper l which contains metal powder "P".
The powder may be manufactured i'rom a rerrous material
ior example, ferritic or austenitic stainless steels,
a non-ferrous material such as aluminium, a metal
bearing ore or a metallic oxide. Immediately below
the hopper 1 a pair oi compacting rolls 2-2 are arranged
so that the powder which leaves the hopper 1 is drawn .
into the nip between the rolls 2-2. As illustrated the
rolls 2-2 are constrained to rotate in opposite directions.
lS and the whole assembly oi rolls 2-2 and hopper l . . .
compri~es a compaction mill through which green strip
. "S" is produced.
Downstream oi the compaction mill are provided
in sequence a iirst guide roll 4, and edge trimming and
riveting assembly 5, pinch rolls 6, 7 ror respectively
transporting green strip to and irom the assembly 5,
a..second guide roll 8, a floatation table 9, a sinter
iurnace lO, a pair of take-oii pinch rolls 11 and a
coiler assembly 12.
The pinch rolls 7 eiiectively isolate the strip
downstream oi the guide roll 8 irom tensile stresses
imposed prior to the guide roll 8 and their speed is
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~079064
controlled to maintain a given catenary loop "L" in the
green strip between the compaction mill and the iirst
guide roll 4. The loop "L" accommodates variations in
output from the compaction mill. The rolls 4, 6, 7 and
8 are all driven irom a common drive and their speeds of
rotation are controlled through a speed controller 13.
The pinch rolls 6 are employed at start up to ieed
~reen strip initially into the edge trimming and riveting
assembly 5. The leading end of the strip is riveted to
the tail end oi the strip already present in the assembly
5 to overcome threading problems.
~ reen strip leaving the pinch rolls 7 is ied
around the circumierence oi the guide roll 8 and
- passes downwardly on to the suriace oi the iloatation
table 9.
The iloatation table 9 has a strip support
suriace iormed with an entry section 14 and an exit
section 15. As will be seen irom Figure 1, the exit
section 15 is inclined downwardly at an angle to the
horizontal which is less than the angle at which the entry
section 14 is incllned. The angle oi inclination oi the
entry section conventiently lies between 50 and 80 to
the horizontal and that oi the exit section between 2 and
20 to the horozontal. Preierably, these angles lie
;l 25 respectively between 50 and 60 and 5 and 10 to the
~ horizontal. In any event the an~le oi 1nc1lnation oi
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1079064
the exit section 14 ~s selected to be greater than the
angle o~ iriction oi the strip passing over the table.
The support sur~ace oi the table 9 is iormed with
a plurality oi round or slot like aperatures through
which gas under pressure ilows Upwardly towards the under
suriace of the strip to support the strip above the
table suriace. The gas supplied to the sections 14
and 15 may either be supplied irom a common source or ~-
~rom independent sources. The gas may, ior example,
~e air.
One or more spaced position transducers 16 are
positioned above the suriace oi the table at the
transition between the entry and exit sections 14, 15
respectively and are operable to sense changes in the
proximlty oi the strip to the table suriace. The
- transducers 16 provide a measure oi the tensile stress
existing within the strip as it passes over the table
and are connected to pass common signals to the speed
controller 13.
In an alternative unlllustrated embodiment, the
transducers 16 are connected to pass comm~nd signals
to a speed controller oi the take-oii' pinch rolls 11.
The sinter iurnace 10 has a reiractory lining 18
and is provided with an entry seal 19 and an exit
25 seal 20 located at each respective end oi the ~urnace. ~ -
'J, Alternatively the gas entry ports 21 may be spaced
along one or both sides oi the iurnace 10.
At least a part oi the gas contained in the iurnace
lO may be w1t~drawn through a conduit 22 ~nd return-d to
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1~79064
the entry ports 21 via a cooler 23, compressor 24 and
a gas treatment chamber 25 in which impurities such as
oxygen are removed. Additional gas ~rom a source 26
o~ the required composition is added to the recirculating
S gas prior to its return to the iurnace. Prior to re-
entry to the iurnace, the recirculating and additional
gas are heated to a predetermined temperature.
Electrical heatlng elements 27 are incorporated
inside the ~urnace 10 together with one or more
temperature controllers (not shown). A pair oi lips
2~ are mounted one on each vertical wall oi the iurnace
and extend lengthwise hori~ontally through the iurnace.
Each lip is inclined laterally towards the centre line
o~ the iurnace. In an alternative arrangement the lips
~8 are inclined downwardly at a small angle in a
lengthwise as well as lateral sense.
; On leaving the sinter furnace 10, the strip is
cooled, passes through the take-oii pinch rolls ll and
is coiled by a strip coiler 12.
In operation oi the apparatus illustrated, steel
powder "P" irom the hopper 1 is drawn into the nip
between the compaction rolls 2-2 and emerges as green
strip "S". The str~p is guided around the circumierence
o~ the guide roll 4 and transported through the assembly
5 by the pinch rolls 6, 7. Aiter leaving the assembly
5 the green strip is ied around the circum~erence oi
the guide roll 8 and passe~ downwardly onto the suriace
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1~7~64
of the iloatation table 9 by which it is guided into
the iurnace 10 through the entry seal 19. When in
the furnace, the strip is supported by means of gas
supplied under pressure through the gas inlet ports
S 21. Gas losses through the entry and exit ports are
compensated ior by addition oi gas from a source
- external to the iurnace.
As the strip passes irom the entry section 14 oi
the iloatation table 9 on to the exit section 15 a
shallow loop or catenary i5 iormed in the strip. The
coniiguration oi this loop or catenary provides a
control oi the tensile stress existing within the
green strip passing irom the guide roll 8 and the entry
vestible oi the iurnace and the coniiguration oi the
loop or catenary is determined by the rotation oi speed
oi the guide roll 8. In addition to providing a control
oi the tensile stress, the loop provides a suiiicient
stored strip length to accommodate any temporary
mismatch between the speeds at which strip is supplied
to and withdrawn irom the iurnace 10 as may occur
during changes in line speed.
The rate at which the strip is transported
through the iurnace 10 is determlned by the speed oi
rotation oi the pinch rolls 11 and the tensile stress '
exist~ng in the strip is caused in part by tension
in the strip upstream oi the iurnace and irictional
drag between the strip and furnace hearth at local
points oi contact along the length of the iurnace.
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1C~79~64
Back tension applied upstream of the pinch rolls 7 is
isolated from the strip by the pinch rolls 7. Tensile
stress within the strip at the entry to the ~urnace
are minimised by controlling the speed at which strip
approaches the entry section 14 of the ~loatation table
so as to maintain a given strip path between the guide
roll 8 and the ~urnace. This desired path is maintained
by sensing changes in the proximity of the strip to the
table surface by means of the transducers 16 and controlling
the rotational speed oi' the rolls 4, 6, 7 and 8 through
controller 13 in dependence on any sensed changes.
Thus, the strip being sintered within the ~urnace is
e~rectively isolated ~rom accelerations or decelerations
caused by operation o~ the control following command
signals received rrom the transducers 16. Tensile
s~resses imposed in the strip within the ~urnace ch~mber
are minimised by controlling the ~low o~ gas into the
strip support systems so as substantially to eliminate
~riction between the strip and the furnace hearth.
In the embodiment illustrated ln Figure 1 the
~loatation table comprises two straight sections 14, 15
joined together in any convenient manner. In the
embodiment illustrated in Figure 3 the ~loatation table
comprises a single curved surrace having a steeply
inclined entry section and a more shallow inclined
exit section, the transition between these two sect-ions
taking the i'orm o~ a curved sur~ace.
~079064
Also, as illustrated in Figure 1 the section 15
o~ the iloatation table terminates ~ust upstream oi
the entry seal 19. In an alternative arrangement
the exit section 15 oi the table may protrude through
the seal 19 and terminate ~ust inside the iurnace 10.
In an unillustrated embodiment the iloatation
table 9 may comprise more than two diiierently inclined
sections. For example, an additional sloping suriace
may be provided between the entry and exit sections of
the table illustrated in Figure 1 the angle of inclination
oi this intermediate section lying between those oi the
entry and exlt sectlons.
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