BACKGROUND
1. Field of the Invention
[0001] This invention relates to the cleaning of metal strip or plate (hereinafter called
"strip"), particularly but not limited to stainless steel strip, whereby adherent
oxides are mechanically removed from the surface of the strip to provide a surface
finish at least equal to a pickled surface and superior to prior art mechanically
cleaned surface without the use of pickling acids.
2. Description of the Prior Art
[0002] Mechanical scale removal, e.g. by cleaning, e.g. by abrasive grinding the surface
of metal strip, is known to the art. Useful abrasive compositions and articles are
shown and described in U.S. Patent No. 5,273,558. Such prior art processes are effective
only on metal strip that is substantially uniformly dimensioned, completely flat and
well controlled during the grinding process. It is known, for example as shown and
described in U.S.Patent No. 2,759,301, to use staggered or intercalated upper and
lower leveler or flattener rolls to straighten or flatten strip before grinding. Such
devices, now known within the industry as "flatteners," require the strip to be flexed
over the flattening rolls and are useful only to remove coil set from the uncoiled
strip by bending the strip, by the flattening rolls, uniformly across the strip width.
Accordingly, such flatteners are not applicable to leveling high strength steels or
heavy gauge steel strip or plate which cannot be so flexed. Moreover, coiled metal
strip as produced in a rolling mill frequently exhibits, in addition to coil set,
non-uniform dimensions, out-of flatness and other processing irregularities, such
as waves, bubbles, herringbone patterns, and cross-bowing. Waves are produced by elongation
of the strip, in the width direction, more than another width direction. If the edges
of the strip are elongated more than the center, waves are produced; if the center
is elongated more than the edges of the strip, bubbles or center waves or side waves
are formed. If the strip goes into the rolling mill at an angle, a diagonal wave,
called a herringbone pattern, is produced. Cross-bowing of the strip results from
differential cooling of the strip or by too much crown in the strip. Such dimensional
irregularities are not amenable to correction by use of flattener apparatus such as
that of the latter patent. Consequently, the surface finish produced by such conventional
prior art processes are not acceptable for production of fully mechanically cleaned
strip of high surface finish, for example strip which is intended for certain post-processing
treatments of the cleaned strip surface.
SUMMARY OF THE INVENTION
[0003] The present invention provides a metal strip uncoiling device followed by a device,
such as a rolling mill, a tension leveler or a corrective (roller) leveler, capable
of flattening the strip, correcting any strip irregularities, such as waves, bubbles,
herringbone patterns and cross-bowing, in addition to coil set, and delivering an
acceptable shape to the following cleaning step which includes grinding, brushing
and polishing of the strip surface. The cleaning step is followed by a device to tension
the strip at a level of tension at least sufficient to provide effective material
handling and control during cleaning and thereby to aid in achieving or maintaining
a flat strip surface during leveling and cleaning.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004]
Fig. 1 is a schematic drawing in side elevation of a processing line in accordance
with the invention, showing the leveling, cleaning and tensioning devices;
Fig. 2 is a side elevational sketch of a prior art rolling mill of a type useful in
the leveling aspect of the invention;
Fig. 3 is a side elevational sketch of a prior art tension leveler of a type useful
in leveling strip in the invention, and
Fig. 4 is a side elevational sketch of a prior art corrective or roller leveler of
a type useful in leveling strip in the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0005] Fig. 1 shows an uncoiler 1, a strip leveller 2, a cleaner 3 and a tensioning device
4, as well an optional surface conditioning device 5 and material post-processing
apparatus 6, and a strip recoiler 7.
[0006] The essential steps of the invention, levelling and surface cleaning, comprise a
process and apparatus capable of removing oxides from metal strip efficiently and
in a form possessing an acceptable surface finish for post-processing without acid
pickling of the strip. For effective strip cleaning, as hereinafter described, all
of the above-mentioned strip irregularities must be removed so that the strip, ready
for cleaning, is substantially uniformly dimensioned and completely flat in order
to provide a mechanically cleaned surface of high quality, e.g. equal or superior
to pickled strip.
[0007] Removal of such dimensional irregularities may be achieved by one or another of several
types of prior art levelers, i.e. a rolling mill, a tension leveler or a corrective
or roller leveler.
[0008] Fig. 2 shows a prior art rolling mill denoted generally by the numeral 8 having a
pair of work rolls 9 and 11 and corresponding upper and lower backup rolls 12 and
13. Guide rolls 14, 16 and 17 aid in guiding a strip 18 through the work rolls of
the mill. Such a device reduces the thickness and increases the length of the strip
18 as it passes through the mill, thereby loosening and aiding in the removal of surface
oxides.
[0009] Fig. 3 shows a prior art tension leveler, denoted generally by the numeral 19 having
a plurality of stands, e.g. 21 and 22 each of which includes vertically movable upper
and lower clusters 23 and 24 of tensioning rolls. Passage of the strip 18 through
such a leveler device results in elongation of the strip, again loosening and aiding
in the removal of adherent surface oxides as well removing strip irregularities and
flattening the strip.
[0010] Fig. 4 shows a prior art corrective (roller) leveler generally denoted by the numeral
26 having a plurality of upper and lower leveler rolls 27 and 28, respectively, each
of which is backed up by a set of corresponding upper and lower backup rolls 29, 31.
By applying different pressures, through the backup rolls, to different pairs of opposed
upper and lower leveler rolls, the latter rolls, or either of them, may be bent resiliently
in a plurality of desired configurations as necessary to correct specific types of
irregularities of the strip as it passes through this type of leveler.
[0011] Any one of these three types of levelers, the mentioned irregularities, including
but not limited to coil set, can be removed from the strip to provide a substantially
completely level surface. Normally only one of these types of levelers will be used
in a particular facility. Selection of the type of leveler to be used depends upon
the particular facility and operator experience with one form of leveler or another.
In each case, deformation of the strip during leveling also aids in removing scale
from the strip surface.
[0012] The cleaning step of the invention comprises three aspects. First, the strip is ground,
e.g. with a suitable grinding disc. A suitable article for this purpose is a "DBX"
grinding wheel manufactured by Minnesota Mining and Manufacturing Co. and described
in the aforesaid U.S. Patent No.5,273,558. Such devices are in the form of articles,
such as discs, incorporating a bonded abrasive composition comprising abrasive particles
dispersed throughout and bonded to an elastomeric polyurea matrix formed from the
polymerization reaction product of a polyfunctional amine and an isocyanate. Secondly,
the strip is brushed, e.g. with a suitable brush, for example a 7A medium brush formed
of a porous resin matrix and a mineral filler, as produced by Minnesota Mining and
Manufacturing Co. A suitable wire brush also may be used. Thirdly, the strip is polished
with a suitable abrasive polishing wheel, such as "Scotch-Brite"--a trade-marked product
of Minnesota Mining and Manufacturing Co.
[0013] At least one of these cleaning steps is used and preferably all three are used, and
more than one unit of each type of cleaning may be used, depending on the extent and
type of initial oxide and the type of final surface which is desired.
[0014] Disposition of the tensioning device 4 following the cleaner enhances material handing
and control and hence a level strip.
[0015] Conventional pickling processes typically produce strip with a surface roughness
of about 60 microinches. The strip mechanically processed in accordance with the present
invention has a surface roughness of about 5 microinches in the direction of the grinding
lines, and up to about 30 microinches in a direction transverse to the grinding lines--at
least a 100% improvement over the prior art.
[0016] After cleaning by grinding, brushing and polishing, optionally there may be an acid
bath and rinse section 5 in the processing line to aid in removal of the ground surface
material and to condition the surface to a more preferred condition. Such acid bath
and rinse section may be replaced with a rolling device (not shown) to roll the material
in order to further enhance the surface of the strip. In many applications, the strip
material may only need to be oiled and recoiled after mechanical grinding, brushing
and polishing because all these elements rotate in a counterclockwise direction and
tend to throw debris back toward the entry of the strip into the cleaner.
[0017] A number of other post-processing steps may be utilized between grinding and recoiling,
such as, but not limited to, side trimming, shot-blasting, painting, galvanizing and
other coating operations. Moreover, some of such further processing steps could be
carried out between the leveling and cleaning steps. For example, the strip may be
side-trimmed and/or shot blasted after leveling but before cleaning. Further, it is
possible to pass the strip through an acid pickling bath before the strip is cleaned:
in this way the speed and quality of an existing pickle line may be increased.
[0018] Practice of the above-described invention provides a means for producing pickled
surface finishes with little or no pickling acid requirement, as well as producing
far superior surface finishes to those of conventional mechanical cleaning and grinding
processes.
1. A method of removing oxide scale from metal strip, comprising providing an elongated
section of wound strip, uncoiling the wound strip, directing the unwound strip into
a leveling device capable of removing substantially all strip dimensional irregularities
and leveling the strip, and mechanically cleaning the strip surface by a process selected
from the group consisting of the steps of grinding, brushing, polishing and combinations
thereof, to remove adherent surface oxides.
2. A method according to claim 1, comprising selecting the leveling device from the group
consisting of a rolling mill, a tension leveler and a corrective roller leveler capable
of correcting strip irregularities including coil set, waves, bubbles, herringbone
pattern and cross-bowing.
3. A method according to claim 2, comprising carrying out the grinding step with use
of an abrasive grinding wheel incorporating a bonded abrasive composition comprising
abrasive particles dispersed throughout and bonded to an elastomeric polyurea matrix
formed from the polymerization reaction product of a polyfunctional amine and an isocyanate.
4. A method according to claim 3, wherein the mechanical cleaning of the strip comprises
grinding, brushing and polishing.
5. A method according to claim 1, further comprising applying tension to the strip as
it is being leveled and mechanically cleaned.
6. A method according to claim 5, wherein the mechanical cleaning of the strip consists
of grinding, brushing and polishing.
7. A method according to claim 1, further comprising passing the cleaned strip through
an acid bath and rinse to remove ground surface material and to condition the strip
surface.
8. A method according to claim 1, further comprising passing the leveled strip through
an acid pickling bath and rinse, and then mechanically cleaning the leveled and pickled
strip, thereby further enhancing the speed of the pickling step and the surface quality
of the treated strip.
9. A method according to claim 5, further comprising passing the cleaned strip through
an acid pickling bath and rinse to remove ground surface material and to condition
the strip surface.
10. A method according to claim 1, further comprising post-processing the leveled and
cleaned strip, and recoiling the post-processed strip.
11. A method according to claim 5, further comprising post-processing the leveled and
cleaned strip, and recoiling the post-processed strip.
12. A method according to claim 9, further comprising post-processing the leveled, pickled
and cleaned strip.
13. An apparatus for cleaning metal strip by mechanically removing oxides from the strip
surface, comprising an uncoiler on which the strip may be wound, a strip leveling
device capable of removing substantially all strip dimensional irregularities, a cleaner
device for cleaning the surface of the strip to remove surface oxides therefrom and
capable of grinding, brushing and polishing the strip, and means for recoiling the
strip.
14. Apparatus according to claim 13, wherein the leveling device comprises a rolling mill
adapted to reduce the strip thickness, to elongate the strip and to reduce strip dimensional
irregularities, including coil set, waves, bubbles, herringbone pattern and cross-bowing
of the strip, and aiding in removing oxides from the strip surface.
15. Apparatus according to claim 13, wherein the leveling device comprises a tension leveler
for applying tension to the strip of a magnitude sufficient to elongate the strip
and capable of correcting dimensional irregularities in the strip, including coil
set, waves, bubbles, herringbone pattern, and cross-bowing, and to aid in removing
oxides from the strip surface.
16. Apparatus according to claim 13, wherein the leveling device comprises a corrective
roller leveler comprising at least one pair of leveling rolls having a length extending
substantially across a width of the strip, and a plurality of backup rolls spaced
apart along the length of the leveler rolls and adapted to be moved toward and away
from the leveler rolls whereby the leveler rolls may be bent resiliently into a configuration
adapted to correct dimensional irregularities in the strip, including coil set, waves,
bubbles, herringbone pattern, and cross-bowing.
17. Apparatus according to 14, wherein the cleaner device is selected from the group consisting
of a grinder, an oxide removing brush, a polisher and combinations thereof.
18. Apparatus according to claim 15, wherein the cleaner device is selected from the group
consisting of a grinder, an oxide removing brush, a polisher and combinations thereof.
19. Apparatus according to claim 16, wherein the cleaner device is selected from the group
consisting of grinder, an oxide removing brush, a polisher and combinations thereof.
20. Apparatus according to claim 17, wherein the grinder comprises an abrasive grinding
wheel incorporating a bonded abrasive composition comprising abrasive particles dispersed
throughout and bonded to an elastomeric polyurea matrix formed from the polymerization
reaction product of a polyfunctional amine and an isocyanate.
21. Apparatus according to claim 20, wherein the cleaner device comprises, in addition
to the grinder, an oxide removing brush and a polisher.
22. Apparatus according to claim 18, wherein the grinder comprises an abrasive grinding
wheel incorporating a bonded abrasive composition comprising abrasive particles dispersed
throughout and bonded to an elastomeric polyurea matrix formed from the polymerization
reaction product of a polyfunctional amine and an isocyanate.
23. Apparatus according to claim 22, wherein the cleaner device comprises, in addition
to the grinder, an oxide removing brush and a polisher.
24. Apparatus according to claim 19, wherein the grinder comprises an abrasive grinding
wheel incorporating a bonded abrasive composition comprising abrasive particles dispersed
throughout and bonded to an elastomeric polyurea matrix formed from the polymerization
reaction product of a polyfunctional amine and an isocyanate.
25. Apparatus according to claim 24, wherein the cleaner device comprises, in addition
to the grinder, an oxide removing brush and a polisher.
26. An apparatus according to claim 13, further comprising a tensioning device disposed
after the cleaner device.
27. An apparatus according to claim 25, further comprising a tensioning device disposed
after the polisher for applying tension to the strip during grinding, brushing and
polishing.
28. An apparatus according to claim 13, further comprising an acid bath and rinse apparatus
disposed after the cleaner device to remove ground surface material and condition
the strip.
29. An apparatus according to claim 13, further comprising a post-treatment device following
the cleaner device for further treatment of the strip.
30. An apparatus according to claim 29, wherein the post-treatment device is selected
from the group consisting of a device to side trim, shot-blast, paint, galvanize,
and otherwise to coat the cleaned strip.
31. A metal strip made by the method of claim 1 having a maximum surface roughness in
a direction of grinding lines of about 5 microinches and a maximum surface roughness
in a direction across grinding lines of about 30 microinches.
32. A metal strip made by the method of claim 2 having a maximum surface roughness in
a direction of grinding lines of about 5 microinches and a maximum surface roughness
in a direction transverse to the direction of grinding lines of about 30 microinches.
33. A metal strip made by the method of claim 3 wherein the cleaned strip has a maximum
surface roughness in a direction of grinding lines of about 5 microinches and a maximum
surface roughness in a direction transverse to the direction of grinding lines of
about 30 microinches.
34. A metal strip made by the method of claim 3, wherein the mechanical cleaning step
comprises, in addition to grinding, oxide-removing brushing, and polishing.
35. A metal strip made by the method of claim 34 wherein the cleaned strip has a maximum
surface roughness in a direction of grinding lines of about 5 microinches and a maximum
surface roughness in a direction transverse to the direction of grinding lines of
about 30 microinches.