Note: Descriptions are shown in the official language in which they were submitted.
Field of the Invention
The present invention relates to a method of and an
apparatus for descaling hot strip steel. More particularly this
invention concerns a system for descaling hot strip s-teel as it
emerges from a hot-rolling string and before it is coiled up or
surface-treated for distribution and sale.
Background of the Invention
Stretch~bending, such as described in my United States
patent 3,924,428, is frequently used for descaling hot strip steel.
As the strip steel is bent back and forth over the stretch-bending
rollers the scale is mostly broken free. At such a stretch-bend-
ing station it is therefore possible to collect enormous amounts
of scale. The normal procedure is to follow up such a s-tretch-
bending descaling operation with a pickling. In this manner
relatively clean, scale-~ree strip steel is produced.
It has been suggested to eliminate the pickling- operation
by various procedures which eliminate the residual scale on the
strip steel and which remove the dust also. Any residual scale
or dust left on the steel will adhere to the downstream feed
bridle, normally two or more spaced rollers that are ariven-to
advance the strip along its transport path. If scale or dust is
left on the strip it will build up on this donwstream bridle,
requiring periodic cleaning while at the same time roughening
the roller surfaces so that they can slip on the steel stock.
The equipment for eliminating residual scale and dust is
often relatively complex. It normally requires a massive hood
and vacuum arrangement to surround the path downstream of the
stretch-bending descaler. E'orming such a closed chamber around
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the downstream equipment makes it difficult to monitor the opera-
tions. Such an arrangement also normally is provided even in
the old-fashioned pickling process, in order to prevent the pick-
ling solution from being excessively fouled with particles and
dust.
It has also been suggested to wash or rinse the dust and
loose scale off the strip steel by means of a water bath or
low-pressure spray. While such a procedure does lay the dust
and carry off most of the loose scaIe, it nonetheless is relative-
ly ineffective against the still attached scale. Furthermore,thus wetting the band makes driving it by means of the downstream
feed bridle relatively difficult as an aquaplaning effect takes
place allowing considerable slippage between the bridle rollers
and the strip steel.
Objects of the Invention
It is therefore an object of the present invention to
provide an improved descaling method and apparatus for hot strip
steel.
Another object is -to provide such a method which over-
comes the above-given disadvantages, producing in a relatively
simple manner a clean dust-and-scale-free steel strip.
- Summary of the Invention
These objects are attained according to the instant
invention in an arranyement wherein, after the hot steel strip
has been stretch-bent to free scale from it and this freed scale
has been collected, high-pressure water jets are played on the
strip downstream of the stretch-bending s-tation to separate the
remaining scale from the strip, this remaining scale being
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collected a-t the spray-descaling station. The strip is then
passed through the nip between a pair of pinch-drying rollers
which drive all of the surface water from the strip. Thence the
strip can pass through the downstream feed bridle.
The me-thod and apparatus according to the invention thus
ensure that the high-pressure wa-ter streams, working with water
pressures of at least 100 a-tmospheres, strip the remaining scale
from the strip. The use of such high-pressure streams directly
in the stretch-bending descaler has been found completely ineffec-
tive, since one of the purposes of such a stretch-bender is to
level the steel strip. According to this invention the spray de-
scaling takes place in a separate enclosure from the stretch
bending so that the strip remains perfectly planar.
As a result of the near perfect planarity of the strip
the pinch rollers that follow the spray descaler are able to drive
virtually all of the water from the strip. Residual heat in the
strip will ensure its complete drying before it enters the down-
stream bridle. Thus any aquaplaning effect is completely out of
the question. Further treatment of the thus leveled and descaled
strip is relatively easy. The strip can, for example, be fed to a
subsequent pickling and galvanizing step with ease since the
leveled and descaled strip is relatively easy to handIe.
According to further features of this invéntion the jets
that emit the descaling water streams are provided above and
below the strips and in sets spaced above and below the path the
strip follows. These jets can be mounted on beams extending
horizontally perpendicular to the displacement direction of the
strip and themselves set up so that they can oscillate and thereby
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movably play their water streams over the surfaces of the strips,
Provided between these sets of jets are support rollers on which
the strip rides, so that it remains perfectly positioned between
the jets. These support rollers further ensure that the planarity
of the still relatively hot strip is maintained. It is necessary
to maintain this planarity in order to ensure efficient operation
of the downstream pinch-drying rollers.
The pinch-drying rollers may according to the instant
invention be contained in a second downstream enclosure largely
lQ separate from the downstream enclosure surrounding the jets. This
downstream enclosure has intake and outle-t slots through which
the strip passes and is provided with elastic lips at these slots
to prevent leakage between the enclosures and to strip part of the
water off the strip.
According to this invention all of the enclosures have
inclined floors along which water sprays may be directed to drive
the freed scale to the lower floor end where a drain is provided.
The upstream enclosure can be constituted at least in
part as an exhaust hood and provided with an exhaust blower that
carries off air from the enclosure and airborne scale. A cyclone
or the like downstream of the blower can separate out these air-
borne particles for recovery. Such a procedure is preferred to
using a fine spray in the upstream enclosure to lay the dust.
The system according to the instant invention ensures a
good prelimlnary descaling of the strip before it enters the
downstream feed-roller bridle. Any loose particles left on the
strip after leaving the stretch bender are removed in the subse-
quent water descaler by the high-pressure water. Thus any build-
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up of scale on the downstream bridle rollers is impossible. ,Thestretch bender itself operates dry so that it will have a long
service life. A pickling operation following the apparatus
according to this inven-tion is not going to be subjected to any
substantial dust buildup, as the strip will enter such a pickling
operation relatively clean. Thus acid consumption is reduced.
As a result it is possible to operate with substantially higher
conveyor speed so as to increase the overall processing speed and
efficiency.
Description of the Drawing
FIG. 1 is a side partly sectional and schematic view of
the apparatus for carrying out the method of this invention; and
FIG, 2 is a similar view showing an alternative arrange-
ment according to this invention.
Specific Description
As seen in FIG. 1 a hot steel strip 5 straight from a
production facility is displaced in a transport direction D from
an upstream feed bridle 2 having bridle rollers 2a to a down-
stream feed bridle 3 having bridle rollers 3a. The rollers 2a,
like the rollers 3a, are driven positively by a motor 21 and are
spaced from each other by a distance substantially greater than
the thickness of the strip 5 so that they do not pinch this strip
Immediately downstream of the upstream feed bridle 2 is
a stretch-bender 1 having a plurality of stretch-bending roliers
la within an enclosureor chamber 4. This chamber 4 has a roof 16
formed as a hood connected to an exhaust blower 17 and an inclined
floor 18 terminating at i-ts lower end at a drain 19 provided with
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a gate valve 20. ~ater jets 7a are directed downwardly parallel
to the sloping floor 18 to wash scale freed from the strip 5 by
the rollers la down to the drain 19 whence it can pass out
through the valve 20 into a collec-ting cart 27. Thus in this
stretch-bender 1 much of the scale on the strip 5 will be removed
and either sucked out by the blower 17 as airborne particles or
collected in the wa-ter a-t the bottom of the enclosure 4. Further
details about stretch-bending and drive arrangements can be seen
in my earlier United States patents 3,777,532 and 3,924,428.
Immedi'ately downstream of the enclosure 4 as seen in
FIG. 1 is another enclosure 6 provided internally with two
longitudinally spaced pairs of idler-type support rollers 12
and four sets of descaling sprayers 7_ directed generally
opposite to the direction D at the strip 5. These jets 7_ are
supplied with water at at least 100 atmospheres. They are
mounted on water-feed beams ll which may be oscillated by means
of a motor 22 driving a wheel 23 having an eccentric 24 connected
via a link 25 to an arm 26 extending from each beam 11. Thus
as the motor 22 rotates the wheel 23 each beam 11 will be pivot-
ed about its axis which extends horizontally perpendicular to the
- direction D on the respective side of the strip 5. Two sets of
sprays 7_ are provided between the two pairs of support rollers
12 and a further pair of sets is provided immediately downstream
of these rollers 12.
The compartment 6 has a floor 14 at whose lower end is
provided a drain 15 and at whose upper end is provided a sprayer
7c that washes particles down the'floor'14 toward the drain 15.
In addition the compartment or chamber 6 is provided at its up-
stream and downstream ends with slots 28 through which the strip
5 passes and provided with elastic lips or skirts 13 that prevent
water from the jets 7_ from spraying out of the enclosure 6.
The support rollers 12 ensure that the leveled and
partially descaled strip 5 will remain perfectly planar and posi-
tioned between the jets 7_ whlch cool it substantially. These
jets 7_ will wash virtually all of the remaining scale as
particles from -the surfaces of the strip 5 so that these particles
can be collected in a water slurry at the drain 15.
FIG. 1 shows how two pairs of idler-type pinch rollers 8
are provided in the chambers 6 downstream of the furthest down-
stream jets 7b. These rollers 8 are perfectly cylindrical and
define nips that pinch the strip 5. Since the strip 5 is almost
perfectly descaled by the time it reaches the rollers 8 and is
nearly perfectly planar, these rollers 8 can drive virtually all
oE the liquid from the surfaces of the strip 5. Thus when the
strip 5 exits from the.downstream slot 28 it will be almost per-
fectly dry. The rollers 8 are themselves not driven, like the
rollers 12, but instead are rotated by engagement with the strip
5-
FIG. 2 shows how a partition 9 having a slot 29 in line
with the slots 28 can form a downstream compartment 10 containing
the drying rollers 8. This slot 29 is provided with elastic lips
13 like the slots 28 to prevent any spray from entering the
chamber 10 directly. A second drain 15' is provided in the floor
18 upstream of the partition 9 to allow it to drain.
On leaving the downstream slot 28 the belt is almost
perfectly dry and passes through -the bridle 3 to a subsequent
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operation, such as a pickling tank. The treatment accordiny to
the instant invention can operate relatively rapidly, as the
stretch-bending rollers la operate dry and the strip 5 issues
from the apparatus perfectly dry. Buildup of particles on the
downstream feed rollers 3a is impossible, since the strip 5 is
free of particles by the time it engages these rollers 3a.
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