U.S. patent application number 10/510432 was filed with the patent office on 2005-07-28 for surface treatment facility of metal plate, method for producing metal plate and system for producing metal plate.
Invention is credited to Kimura, Yukio, Sodani, Yasuhiro, Ueno, Masayasu.
Application Number | 20050160780 10/510432 |
Document ID | / |
Family ID | 29243357 |
Filed Date | 2005-07-28 |
United States Patent
Application |
20050160780 |
Kind Code |
A1 |
Kimura, Yukio ; et
al. |
July 28, 2005 |
Surface treatment facility of metal plate, method for producing
metal plate and system for producing metal plate
Abstract
A surface treatment apparatus for metallic sheet has at least
one centrifugal blasting machine to blast solid particles having 30
to 300 .mu.m of mean particle diameter against the continuously
traveling metallic sheet. The blasting machine is structured by a
centrifugal rotor having a rotation axis. The line of intersection
between the plane vertical to the rotation axis and the plane of
the metallic sheet is positioned in parallel to or at 45.degree. or
smaller angle to the travel direction of the metallic sheet.
Inventors: |
Kimura, Yukio; (Fukuyama,
JP) ; Ueno, Masayasu; (Fukuyama, JP) ; Sodani,
Yasuhiro; (Fukuyama, JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN & CHICK, PC
220 5TH AVE. FL 18
NEW YORK
NY
10001-7708
US
|
Family ID: |
29243357 |
Appl. No.: |
10/510432 |
Filed: |
October 6, 2004 |
PCT Filed: |
March 14, 2003 |
PCT NO: |
PCT/JP03/03048 |
Current U.S.
Class: |
72/53 |
Current CPC
Class: |
B24C 9/006 20130101;
Y02P 70/10 20151101; B24C 3/14 20130101; C21D 7/06 20130101; Y02P
70/179 20151101 |
Class at
Publication: |
072/053 |
International
Class: |
B21J 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 16, 2002 |
JP |
2002-113502 |
Claims
What is claimed is:
1. An apparatus for surface treatment of metallic sheet comprising:
at least one centrifugal blasting machine for blasting solid
particles having a mean particle diameter of 30 to 300 .mu.m
against a metallic sheet which continuously travels, said at least
one centrifugal blasting machine having a centrifugal rotor having
a rotation axis, and being positioned so as the line of
intersection between the plane vertical to the rotation axis and
the plane of the metallic sheet to become parallel to or 45.degree.
or less angle to the direction of travel of the metallic sheet.
2. The apparatus according to claim 1, wherein said at least one
blasting machine has a centrifugal rotor having a rotation axis,
and is positioned so as the line of intersection between the plane
vertical to the rotation axis and the plane of the metallic sheet
to become an angle in a range from 5.degree. to 45.degree. to the
direction of travel of the metallic sheet.
3. The apparatus according to claim 1, wherein said at least one
blasting machine has a centrifugal rotor having a rotation axis,
and is positioned so as the line of intersection between the plane
vertical to the rotation axis and the plane of the metallic sheet
to become parallel to the direction of travel of the metallic
sheet.
4. The apparatus according to claim 1, wherein said at least one
blasting machine comprises a blasting machine positioned so as the
line of intersection between the plane vertical to the rotation
axis and the plane of the metallic sheet to become parallel to the
direction of travel of the metallic sheet, and a blasting machine
positioned so as the line of intersection between the plane
vertical to the rotation axis and the plane of the metallic sheet
to become an angle in a range from 5.degree. to 45.degree. to the
direction of travel of the metallic sheet.
5. The apparatus according to claim 1, wherein said at least one
blasting machine comprises a plurality of centrifugal blasting
machines arranged in the width direction of the metallic sheet, and
at least two centrifugal blasting machines among the plurality of
centrifugal blasting machines are positioned so as the line of
intersection between the plane vertical to the rotation axis of the
centrifugal rotor and the plane of the metallic sheet to become
parallel each other.
6. The apparatus according to claim 1, wherein at least one
blasting machine comprises a plurality of centrifugal blasting
machines arranged in the width direction of the metallic sheet, and
at least two centrifugal blasting machines among the plurality of
centrifugal blasting machines are driven by the common driving
shaft at the respective centrifugal rotors thereof.
7. A method for producing metallic sheet comprising the step of
applying surface treatment to a continuously traveling metallic
sheet by blasting solid particles having a mean particle diameter
of 30 to 300 .mu.m against the metallic sheet using the surface
treatment apparatus for metallic sheet according to claim 1.
8. An apparatus for producing metallic sheet comprising: a hot-dip
coating line having a coating bath; the hot-dip coating line
including a cooling device or an alloying furnace after the coating
bath; and the apparatus according to claim 1 being located at
downstream side of the cooling device or the alloying furnace.
9. An apparatus for producing metallic sheet comprising: a
continuous annealing line having an annealing furnace; and the
apparatus according to claim 1 being located at downstream side of
the annealing furnace.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an apparatus for surface
treatment on producing a metallic sheet such as galvanized steel
sheet having excellent press formability and image sharpness after
coating by creating a surface roughness configured by dense
microscopic irregularities on the surface thereof by blasting fine
solid particles against the surface of the metallic sheet, and
relates to a method for producing metallic sheet as an application
of the apparatus, and specifically relates to an apparatus for
surface treatment being able to efficiently create a surface
roughness even under a high line speed, further to an apparatus for
surface treatment being able to provide a compact design therefor,
a method for producing metallic sheet using the apparatus, a
hot-dip coating line of metallic sheet using the apparatus, and a
continuous annealing line of metallic sheet using the
apparatus.
DESCRIPTION OF THE PRIOR ARTS
[0002] Thin steel sheets such as those of galvanized steel sheets
and cold-rolled steel sheets used for press-forming are requested
to have an adequately adjusted surface roughness. This is because
the necessity of increase in oil-retaining property between the die
and the steel sheet during press-forming, thus to prevent troubles
of die-galling, break of steel sheet, or the like by creating a
specific surface roughness on the steel sheet. For example,
increased sliding resistance between the steel sheet and the die
likely induces break of steel sheet on the punching face thereof or
near the bead sections thereof.
[0003] A general practice of adjusting the surface roughness of
steel sheet is to create a specific microscopic irregularity on the
surface of mill roll to transfer the irregular pattern onto the
surface of steel sheet in the temper rolling stage. The method to
transfer the surface roughness of the roll in temper rolling stage,
however, raises problems of failing in creating fine irregularity
and of varying the surface roughness on the steel sheet resulted
from the change of the roughness on roll with time caused by wear
of roll or the like.
[0004] As a different means from the means using temper rolling
according to the prior art, the inventors of the present invention
derived a method for adjusting the surface roughness of galvanized
steel sheet and the like by blasting fine solid particles directly
onto the surface thereof. According to the derived method,
collisions of spherical solid particles against the surface of
steel sheet form large number of microscopic concavities to create
microscopic irregularities in what is called the "dimple shape".
That kind of surface morphology gives superior effect of increasing
the oil-retaining property between the steel sheet and the die
particularly during press-forming stage, which significantly
improves the press-formability. Furthermore, smaller size of solid
particles being blasted creates denser irregularities of small
pitch pattern on the surface of steel sheet, thus the image
sharpness after coating is improved, and the prepared steel sheet
is suitable for external plates of automobiles and the like.
[0005] Typical methods for blasting solid particles are centrifugal
blasting machine and air blasting machine. The air blasting machine
accelerates compressed air at an ejection nozzle, and accelerates
the solid particles utilizing the drag of the compressed air. In
particular, the air blasting machine is suitable for blasting fine
solid particles having small mass thereof, and has a feature of
extremely increasing the speed of solid particles. On the other
hand, the centrifugal blasting machine blasts solid particles using
the centrifugal force of rotating vane. Since the centrifugal
blasting machine is able to blast large quantity of solid particles
compared with the air blasting machine, the centrifugal blasting
machine is more suitable blasting means to treat steel sheet with
large width traveling at a high speed in the producing line for
iron and steel sheets such as galvanized steel sheet and
cold-rolled steel sheet.
[0006] A method for treating steel sheets using that type of
centrifugal blasting machine is disclosed in Japanese Patent
Laid-Open No. 63-166953, as a blast treatment method aiming to
prevent crack generation on hot-dip galvanized steel sheet during
forming work. The disclosed method is to treat a steel sheet using
a centrifugal blasting machine under a condition that metallic
powder having 80 to 180 .mu.m of particle size is blasted at 30 m/s
or higher particle speed. The disclosure, however, does not give
the location of the centrifugal blasting machine to treat the wide
width steel sheet which travels at a high speed.
[0007] On the other hand, the blast treatment using centrifugal
blasting machine is widely used to conduct descaling treatment for
hot-strip of stainless steel. According to the method, to blast the
particles over a wide range on the steel sheet, centrifugal
blasting machines are arranged so as the line of intersection
between the plane vertical to the rotation axis of the centrifugal
rotor and the plane of the steel sheet to become an angle
near-vertical to the direction of travel of the steel sheet.
[0008] The distance between the center of rotation of the rotor of
centrifugal blasting machine and the metallic strip, (hereinafter
referred to as the "blast distance"), is generally set to about 1
to 1.5 meter. For a metallic strip having about 1500 mm in width,
generally about two to four units of centrifugal blasting machines
are arranged for each face thereof. In that case, if the particle
size is small, the blasted particles are decelerated in air, and
the kinetic energy thereof is decreased at the moment of colliding
thereof against the metallic strip. Therefore, particles having
about 0.5 to 2 mm are applied because particles smaller than those
sizes fail to obtain desired descaling effect.
[0009] FIG. 8 shows a typical arrangement of centrifugal blasting
machines mainly aiming at descaling according to the prior art.
FIG. 8 is a embodiment of arranging two units of centrifugal
blasting machines on one side of the steel sheet 1. Centrifugal
rotor sections 31 and 33 are driven to rotate by motors 32 and 34,
respectively. At this moment, the solid particles are blasted from
the centrifugal rotor sections 31 and 33 against the steel sheet 1.
Generally the centrifugal rotor sections 31 and 33 have a specific
inclination to the surface of the steel sheet 1, (hereinafter
referred to as the "blast angle").
[0010] Since once-blasted solid particles collide against the steel
sheet while generating a certain spread thereof along the
rotational direction of the centrifugal rotor sections 31 and 33,
the zone to which the solid particles collide against the surface
of steel sheet, (hereinafter referred to as the "blast range"), has
a spread along the rotational direction of the rotor sections.
[0011] In this case, a general practice for arranging the
centrifugal blasting machines according to the prior art is that
the centrifugal blasting machines are arranged so as the direction
having a spread of blast range, (hereinafter referred to as the
"longer side direction of blast range"), to become vertical or to
have a small angle to the direction of travel of the steel sheet.
This is because the arrangement matching the long side direction of
the blast range with the sheet width direction enlarges the range
of treatment by a single centrifugal blasting machine. When more
than one centrifugal blasting machine are arranged along the width
of the steel sheet, generally the blasting machines are located in
row in the direction of travel of the steel sheet at a certain
distance therebetween, which is shown in FIG. 8.
[0012] For creating a surface roughness on the steel sheet by
blasting fine solid particles in an iron and steel making line, it
is necessary to apply plurality of centrifugal blasting machines to
blast large quantity of solid particles to treat wide width steel
sheet. In that case, generally the number or the quantity of solid
particles colliding against the unit area of the surface of steel
sheet, (hereinafter referred to as the "blast density"), is
adjusted to a constant level to control the morphology of
microscopic irregularity created on the surface of steel sheet to a
specified embodiment. Since, in this case, the increased line speed
decreases the time that the steel sheet passes through the blast
range, the quantity of solid particles blasted has to be changed
proportional to the line speed. As a result, the line which treats
steel sheets traveling at a high speed needs to apply centrifugal
blasting machine which has a capacity of blasting large quantity of
solid particles.
[0013] Increased quantity of solid particles blasted to a specific
blast range, however, raises a problem of likely inducing
interference between solid particles. That is, increase in the
quantity of solid particles blasted in a unit time from a single
centrifugal blasting machine decreases the distance between
particles in a space between the blasting position and the
colliding position on the surface of steel sheet, which increases
the total weight of solid particles existing per unit volume during
blasting, (hereinafter referred to as the "particle density of
solid particles"). In this state, as shown in FIG. 7 as a schematic
drawing, the solid particles traveling from the centrifugal
blasting machine toward the surface of the steel sheet,
(hereinafter referred to as the "blasted particles") become easily
collide with the solid particles which collided against the surface
of steel sheet to create dents thereon, then scattered therefrom,
(hereinafter referred to as the "repelled particles").
[0014] When the blasted particles collide with other blasted
particles or repelled particles, before colliding against the
surface of steel sheet, the kinetic energy of the blasted particles
is lost, or the blasted particles are scattered to fail in
colliding against the specified blast range. As a result, the
number of solid particles colliding against the surface of steel
sheet reduces, or the speed of collision speed of the solid
particles decreases to fail in forming sufficient number of dents
on the surface of steel sheet, which fails to create desired
surface roughness.
[0015] The phenomenon expresses that, even when the quantity of
blasting solid particles is increased proportionally to the
increase of line speed to maintain the blast density on the surface
of the steel sheet, the reduction in the surface roughness created
on the surface of the steel sheet decreases the efficiency to
create the surface roughness under the condition of increase in
line speed or increase in blast quantity. Consequently, to prevent
the degradation in the surface roughness of steel sheet under the
condition of increase in the line speed, larger quantity of solid
particles is requested to blast, which results in further decrease
in the efficiency of creating surface roughness.
[0016] The problems described above, however, do not appear so
significantly in the case of shot-blasting aiming at descaling of
hot-rolled steel sheet, which uses coarse particles having 500
.mu.m or larger size. This is because the solid particles blasted
from a centrifugal blasting machine have large mass and large
kinetic energy so that they gain sufficient collision speed to
conduct descaling even if they collide with each other in air
before colliding against the surface of the steel sheet. Therefore,
the above-described problems are specific ones to attain the object
of the present invention to create uniform and dense surface
roughness on the surface of the steel sheet by blasting solid
particles having 300 .mu.m or smaller size.
SUMMARY OF THE INVENTION
[0017] It is an object of the present invention to provide an
apparatus for surface treatment which is able to efficiently create
a surface roughness on a steel sheet even when the steel sheet
travels at a high speed, further to an apparatus for surface
treatment which is able to provide compact design therefor, and a
method for producing metallic sheet using the apparatus.
[0018] To attain the object, the present invention provides an
apparatus for surface treatment of metallic sheet having: a
centrifugal blasting machine for blasting solid particles having a
mean particle diameter of 30 to 300 .mu.m against the metallic
sheet which continuously travels, which centrifugal blasting
machine is positioned so as the line of intersection between the
plane vertical to the rotation axis of the centrifugal rotor
thereof and the plane of the metallic sheet to become parallel to
or 45.degree. or smaller angle to the direction of travel of the
metallic sheet.
[0019] The metallic sheet according to the present invention is
mainly a cold-rolled steel sheet and a surface-treated steel sheet.
The cold-rolled steel sheet includes, other than ordinary steel
sheet, high carbon steel sheet, magnetic steel sheet, and special
grade steel sheet such as invar sheet. The surface-treated steel
sheet includes various kinds of surface-treated steel sheets
subjected to surface treatment by hot-dip coating, electroplating,
or the like, and as of these, galvanized steel sheet is a main
article because the requirements often given are press-formability
and image sharpness after coating, which needs dense and uniform
surface roughness (microscopic irregularity morphology on the
surface) on the steel sheet. Accordingly, descaling treatment of
hot-rolled steel sheet aiming at grinding by blasted solid
particles is not the target of the present invention. As described
above, the above-described means and other means mainly deal with
steel sheet such as cold-rolled steel sheet and surface-treated
steel sheet. Nevertheless, the present invention is applicable to
other metallic sheets such as aluminum or aluminum alloy sheets,
and titanium or titanium alloy sheets, and the present invention
deals with all kinds of metallic sheets.
[0020] The blasting of solid particles having a mean particle
diameter of 30 to 300 .mu.m against the surface of steel sheet is
given to create dense irregularities at short pitch thereof on the
surface of steel sheet. That is, blasting solid particles against
the surface of steel sheet converts the kinetic energy of the solid
particles into the press-in work thereof into the surface of steel
sheet, thus creating dents (concavities) on the surface of steel
sheet. The size of dents decreases with the reduction in the size
of solid particles, and forms fine concavities.
[0021] That is, blasting large quantity of solid particles forms
large number of fine dents on the surface of steel sheet, and
creates microscopic irregularities having dense and very short
distance between dents. By creating what is called the "dimple"
morphology, or forming large number of concavities in a unit area,
on the surface, the oil-retaining capacity between the die and the
steel sheet during press-forming is improved to significantly
improve the press-formability.
[0022] If the mean particle diameter of the solid particles exceeds
300 .mu.m, a short-pitched microscopic irregularities cannot be
created, thus the effect to improve the press-formability cannot be
expected, and the long-pitched irregularities, or the waviness,
increase on the surface of steel sheet, which results in degraded
appearance and image sharpness after coating. In this respect, for
creating surface roughness on the surface of cold-rolled steel
sheet or surface-treated steel sheet, the mean particle diameter of
solid particles is requested to adjust to 300 .mu.m or smaller, and
preferably adjust to 150 .mu.m or smaller.
[0023] The means for blasting solid particles adopts the
above-described centrifugal blasting machine because of the
superiority of centrifugal blasting machine in increasing the blast
quantity to continuously treat a steel sheet with wide width under
a high traveling speed. In this case, if the size of solid
particles is smaller than 30 .mu.m, the blasted solid particles are
likely decelerated in air, and the collision speed thereof against
the surface of steel sheet decreases to fail in forming sufficient
size of dents on the surface of steel sheet, in some cases.
Consequently, the mean particle diameter of the solid particles is
specified to 30 .mu.m or more, and preferably 50 .mu.m or more.
[0024] According to the means described above, the centrifugal
blasting machine is positioned so as the line of intersection
between the plane vertical to the rotation axis of the centrifugal
rotor and the plane of the metallic sheet to become parallel to or
angles of 45.degree. or smaller to the direction of travel of the
metallic sheet. The centrifugal blasting machine supplies solid
particles to the central section of the centrifugal rotor, and
accelerates the solid particles applying centrifugal force thereto
using a rotating impeller and plurality of vanes, thus blasts the
solid particles against the object. At this moment, the solid
particles are blasted within a plane vertical to the rotation axis
of the rotating section of rotor, and are spread in fan shape over
the surface of steel sheet to collide thereto, (the blasted range
having a spread is hereinafter referred to as the "long side of
blast range", and the vertical direction thereto is referred to as
the "short side of blast range").
[0025] On the other hand, the positioning of a centrifugal blasting
machine according to the prior art is to position thereof so as the
long side of blast range to become vertical to or angles of
70.degree. or larger to the direction of travel of the steel sheet.
According to the arrangement of centrifugal blasting machines given
in FIG. 8, a specified quantity of solid particles is blasted while
the steel sheet 1 passes through the short side of a blast range,
given in the figure, so that the particle density in air becomes
very high, which likely induces interference between particles.
That is, according to the prior art, large number of solid
particles are blasted in a narrow range (within the distance of
short side of blast range), thus degrading the efficiency to create
surface roughness.
[0026] To the contrary, the means according to the present
invention secures long blast range in the direction of travel of
the steel sheet so that, even the same quantity of solid particles
is blasted, the particle density in air is reduced. That is, when
the solid particles are blasted to wider area, the distance between
the particles in air becomes large, which suppresses the
interference between particles in air even when the quantity of
blasted solid particles is increased.
[0027] FIG. 4 is a schematic drawing expressing the above-described
state. FIG. 4 illustrates the behavior of blasted particles or
repelled particles viewed from vertical position to the traveling
direction of the steel sheet. FIG. 4(a) is the means according to
the present invention, and FIG. 4(b) is that of the prior art,
comparing the behavior of solid particles for the same blast
density to the surface of steel sheet. As shown in the figure, the
means according to the present invention reduces the particle
density in air compared with that of the prior art, and the
interference between particles in air becomes less.
[0028] According to the surface treatment apparatus for metallic
sheet described above, a plurality of the centrifugal blasting
machines is arranged in the width direction of metallic sheet, and
at least two centrifugal blasting machines among them are
preferably arranged so as the line of intersection between the
plane vertical to the rotation axis of the centrifugal rotor and
the plane of the metallic sheet to become parallel each other.
[0029] For a steel sheet having wide width, only one centrifugal
blasting machine often fails to create surface roughness over the
whole surface area thereof. Accordingly, a plurality of centrifugal
blasting machines is required to arrange in the width direction of
steel sheet to create surface roughness. In this case, however, the
solid particles blasted from a centrifugal blasting machine may
hinder the creation of surface roughness by other centrifugal
blasting machine.
[0030] To this point, there is an arrangement of plurality of
centrifugal blasting machines to avoid the interference between
solid particles. That is, the centrifugal blasting machines are
arranged so as the spreading direction of solid particles blasted
from a centrifugal blasting machine to become parallel to the
spreading direction thereof blasted from other centrifugal blasting
machine, thus avoiding entering the solid particles spread from a
centrifugal blasting machine into the blast range of other
centrifugal blasting machine. The means according to the present
invention solves the above-described problems, on applying
plurality of centrifugal blasting machines, by arranging them so as
the long side of the blast range of the respective centrifugal
blasting machines to become parallel with each other.
[0031] Regarding the above-described surface-treatment apparatus
for metallic sheet, it is preferable that a plurality of the
centrifugal blasting machines is arranged in the width direction of
metallic sheet, and at least two centrifugal blasting machines
among the plurality of centrifugal blasting machines are driven by
the common driving shaft at the respective centrifugal rotors
thereof.
[0032] The surface-treatment apparatus for metallic sheet arranges
centrifugal blasting machines so as the line of intersection
between the plane vertical to the rotation axis of the centrifugal
rotor and the plane of the metallic sheet to become parallel to or
45.degree. or smaller angle to the direction of travel of the
metallic sheet. By selecting a blast range elongated in the
direction of travel of the steel sheet, the interference between
the blasted particle and other blasted particle or repelled
particle is reduced.
[0033] Since, however, the blast range of a single centrifugal
blasting machine is not varied, if the blast range is elongated in
the direction of travel of the steel sheet, the number of necessary
centrifugal blasting machines to cover the width of the steel sheet
increases. In this case, if a plurality of centrifugal blasting
machines is arranged in the width direction of steel sheet, the
total apparatus length increases to often fail to install the
apparatus in an existing continuous annealing line or hot-dip
coating line.
[0034] In particular, since the motor section to drive the
centrifugal rotor of the centrifugal blasting machine is required,
there may occur a restriction on arranging plurality of centrifugal
blasting machines. To this point, according to the means of the
present invention, a single rotary shaft drives plurality of
centrifugal rotors, thus allowing arranging the long side of blast
range in parallel with each other, and shortening the total
apparatus length.
[0035] The blast range of a centrifugal blasting machine is close
to rectangle, and assumes the presence of a long side and a short
side. Even with an air blasting machine, however, the nozzle shape
with ellipse or flat may form a blast range close to rectangle
giving a long side and a short side. Accordingly, with a blasting
apparatus other than centrifugal blasting apparatus, if the blast
range has a long side and a short side, similar effect with the one
described above is attained in view of reduction of interference
between solid particles and of avoidance of degraded efficiency in
creating surface roughness even under the blast of large quantity
of solid particles. Therefore, the present invention is independent
of the means for blasting solid particles, and is widely utilizable
if the blast range has a shape close to rectangle. Thus, an
apparatus which substitutes the centrifugal blasting machine with a
blasting machine having that feature is equivalent with the present
invention.
[0036] Furthermore, the present invention provides a method for
producing metallic sheet having the step of applying surface
treatment to a continuously traveling metallic sheet by blasting
solid particles having 30 to 300 .mu.m of mean particle diameter
against the metallic sheet using the above-described surface
treatment apparatus for metallic sheet.
[0037] In addition, the present invention provides a hot-dip
coating line for metallic sheet, having a hot-dip coating line and
the above-described apparatus for surface treatment of metallic
sheet located at downstream side of a cooling device or an alloying
furnace after a coating bath in the hot-dip coating line.
[0038] Further the present invention provides a continuous
annealing line for metallic sheet, having a continuous annealing
line and the above-described apparatus for surface treatment of
metallic sheet located at downstream side of an annealing furnace
in the annealing line.
[0039] The apparatus for surface treatment of metallic sheet
according to the present invention is positioned in a metallic
sheet producing line, and is applied to manufacture metallic sheet
having excellent surface characteristics. For example, the
apparatus for surface treatment is located at least one of upstream
side and downstream side of the temper rolling mill after the
hot-dip coating line or the continuous annealing line, thus
producing hot-dip galvanized steel sheet and cold-rolled steel
sheet having superior surface characteristics.
[0040] The hot-dip coated steel sheet described herein includes
hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel
sheet, hot-dip Al--Zn alloy coated steel sheet, and hot-dip Zn--Al
alloy coated steel sheet. The surface characteristics described
herein designate the characteristics of surface such as
press-formability and image sharpness after coating, which
characteristics give influence on the quality of steel sheet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] FIG. 1 is a schematic drawing of a surface treatment
apparatus for steel sheet according to a first embodiment for
carrying out the present invention.
[0042] FIG. 2 is a schematic drawing of a surface treatment
apparatus for steel sheet according to a second embodiment for
carrying out the present invention.
[0043] FIG. 3 shows the blast range in the embodiment given in FIG.
2 according to the present invention.
[0044] FIG. 4(a) shows the particle density of solid particles in
air according to the present invention.
[0045] FIG. 4(b) shows the particle density of solid particles in
air according to the prior art.
[0046] FIG. 5 is a schematic drawing of an example of centrifugal
blasting machine used in the embodiment according to the present
invention.
[0047] FIG. 6 shows an example of circulation system of solid
particles, including the centrifugal blasting machine used in the
embodiment according to the present invention.
[0048] FIG. 7 is a schematic drawing of interference state between
the repelled solid particles and the blasted solid particles on
steel sheet.
[0049] FIG. 8 is a schematic drawing of an example of arrangement
of centrifugal blasting machines according to the prior art, as a
comparative example.
[0050] FIG. 9 shows the relation between the blast quantity of
solid particles and the mean roughness on the surface of steel
sheet per a single blasting machine in an example according to the
present invention and in a comparative example, respectively.
[0051] FIG. 10 is a schematic drawing of the blast density
distribution of blasted particles given by a centrifugal blasting
machine.
[0052] FIG. 11 shows the mean roughness on the surface of steel
sheet in an example according to the present invention and in a
comparative example, respectively.
[0053] FIG. 12 shows the mean roughness distribution on the surface
of steel sheet in the width direction thereof in an example
according to the present invention.
[0054] FIG. 13 is a schematic drawing of spreading blasted
particles using a centrifugal blasting machine.
[0055] FIG. 14 is a schematic drawing of spreading blasted
particles on the steel sheet using plurality of centrifugal
blasting machines arranged in the width direction thereof according
to the prior art.
[0056] FIG. 15 illustrates the arrangement of plurality of
centrifugal blasting machines in the width direction of steel sheet
and in the direction of travel of the steel sheet according to the
prior art.
[0057] FIG. 16 illustrates the arrangement of plurality of
centrifugal blasting machines in the width direction of steel sheet
according to the arrangement of centrifugal blasting machines in an
example of the present invention.
[0058] FIG. 17 shows the blast range in the embodiment according to
the present invention, giving the blast ranges of the centrifugal
blasting machines arranged conforming to FIG. 1.
[0059] FIG. 18 shows the blast range in the embodiment according to
the present invention, giving the blast ranges of the centrifugal
blasting machines arranged conforming to FIG. 2.
[0060] FIG. 19 is a graph showing the mean roughness on the surface
of steel sheet in the width direction thereof in an example
according to the present invention.
[0061] FIG. 20 is a schematic drawing of a blast density
distribution in the width direction of steel sheet.
[0062] FIG. 21 is a schematic drawing of a blast density
distribution in the width direction of steel sheet.
[0063] FIG. 22 shows an example of arrangement of blasting machines
in a hot-dip coating line.
EMBODIMENT FOR CARRYING OUT THE INVENTION
[0064] FIG. 5 is a schematic drawing of an example of centrifugal
blasting machine used in an embodiment according to the present
invention. The centrifugal blasting machine is an apparatus to
accelerate solid particles utilizing centrifugal force generated by
an impeller 45 and a vane 46, which are driven by a motor 44, (the
impeller 45, the vane 46, and sections rotating therewith are named
the "centrifugal rotor"). The solid particles stored in a tanker or
the like are fed to the central section of the impeller 45 of the
centrifugal blasting machine via a particle feed pipe 43. Generally
the outer diameter of the vane section of the centrifugal rotor
type blasting machine is about 300 to 500 mm. When the distance
between the center of rotation of the rotor and the steel sheet 1,
(hereinafter referred to as the "blast distance"), is large, the
size of blasted solid particles is small, and the deceleration of
the blasted particles in air becomes large. Accordingly, the
embodiment for carrying out the present invention preferably has
700 mm or smaller blast distance, and more preferably the blast
distance is same magnitude with the diameter of the vane
section.
[0065] FIG. 6 shows the configuration of apparatus for blasting
solid particles using the centrifugal blasting machine of FIG. 5.
The centrifugal blasting machine given in FIG. 5 corresponds to the
centrifugal blasting machine 3 in FIG. 6. According to the
embodiment of the present invention, the section blasting solid
particles, in the centrifugal blasting machine 3, is located in the
blasting chamber 2, and forms a space surrounded by partition to
prevent scattering-out the blasted solid particles. Within the
blasting chamber 2, the blasted solid particles collide against the
surface of steel sheet to leave dimple-shape dents thereon, then
repel therefrom to spread in surrounding space. Many of the
repelled particles fall down to the lower section of the blasting
chamber 2 by gravity. In particular, most of the repelled particles
are removed from the steel sheet by the air flow generated by the
rotation of vane, and fall down into the lower section of the
blasting chamber. The fallen particles are collected by a particle
collecting device 8. The collected so lid particles are fed to a 6.
The solid particles which are pulverized in the classifier 6 are
removed from the circulation system, while other particles are
stored in a storage tank 5.
[0066] There is a continuous route from the storage tank 5 to the
centrifugal blasting machine 3 via the particle feed pipe, placing
a particle supply rate adjusting device 4 therebetween. The
particle supply rate adjusting device 4 may be a means to adjust
the gate opening depending on the operating conditions such as the
line speed, the target surface roughness of steel sheet, and the
required blast quantity of solid particles.
[0067] FIG. 6 shows the state that the solid particles are blasted
against the upper face of the steel sheet 1 using the centrifugal
blasting machine. The solid particles, however, may be blasted to
both the upper face and the lower face of the steel sheet 1. If the
width of steel sheet is large, a plurality of centrifugal blasting
machines is arranged in the width direction of steel sheet.
Furthermore, plurality of centrifugal blasting machines may be
arranged in the longitudinal direction of steel sheet. The
arrangement may respond also to the line speed, the available blast
quantity of solid particles for a single centrifugal blasting
machine, and other variables.
[0068] An example of the embodiment for carrying out the present
invention is the arrangement of centrifugal blasting machines given
in FIG. 1. That is, the centrifugal blasting machines 3 are
arranged so as the line of intersection between the plane vertical
to the rotation axis of the centrifugal rotor and the plane of the
steel sheet becomes an angle of 30.degree. to the direction of
travel of the steel sheet. In this case, at an arbitrary position
in the width direction of the steel sheet, the time for passing
through a blast range is secured for longer period than that of the
arrangement according to the prior art shown in FIG. 8. In other
words, if the blast density to the surface of steel sheet is the
same, the particle density of the blasted solid particles becomes
smaller than that of the prior art, and the degradation of
efficiency to create the surface roughness is prevented.
[0069] When the embodiment for carrying out the present invention
given in FIG. 1 is compared with the embodiment of the prior art
given in FIG. 8, the embodiment according to the present invention
raises an anxiety that the blast range in the width direction of
steel sheet covered by a single centrifugal blasting machine may
decrease compared with that of the prior art shown in FIG. 8, which
increases the number of centrifugal blasting machines necessary to
cover the whole width of steel sheet, thus increases the total
necessary power.
[0070] If, however, the embodiment according to the present
invention is compared with the embodiment of the prior art, it is
understood that, to attain the same blast density against the
surface of steel sheet, the quantity of blasting solid particles
per a single centrifugal blasting machine according to the prior
art is large, while the embodiment according to the present
invention needs less quantity of solid particles to be blasted from
a single centrifugal blasting machine. As a result, for treating a
steel sheet having the same width with the same blast density, the
total quantity of blasted solid particles is the same, and the
required motor power is, in principle, the same for both
embodiments. According to the embodiment of the present invention,
the efficiency to create surface roughness increases so that the
blast quantity of the solid particles is reduced from that of the
prior art, which allows totally decreasing the necessary power by
the embodiment according to the present invention.
[0071] FIG. 2 shows another example of the embodiment according to
the present invention. The machine has a mechanism of plurality of
centrifugal rotors connected with each other on the same shaft 22,
which shaft 22 is driven by a single motor 24. Each of the
centrifugal rotors 21a to 21e has an impeller and a vane. The
centrifugal rotor sections in normal centrifugal blasting machine
are arranged at certain spacing. The centrifugal rotor sections 21a
to 21e have the respective solid particle feed pipes 23a to 23e
therebetween. Thus the solid particles are fed to the respective
centrifugal rotor sections 21a to 21e to blast thereof against the
surface of steel sheet 1.
[0072] The centrifugal blasting machine having above-described
configuration does not need to locate drive motor to each of the
centrifugal rotor sections 21a to 21e. Furthermore, there is no
limitation in the positioning of centrifugal blasting machine,
which limitation occurs in the case of allotting drive motors for
individual centrifugal rotor sections 21a to 21e, thus the compact
design of total apparatus is attained.
[0073] FIG. 3 shows the blast ranges on the surface of steel sheet
using the above-described blasting machine. FIG. 3 is a schematic
drawing of the blast ranges in the case that two sets of
centrifugal blasting machines given in FIG. 2 are applied. Since
the centrifugal blasting machine shown in FIG. 2 has the solid
particle feed pipes 23a to 23e between the centrifugal rotor
sections 21a to 21e, respectively, there are appeared areas where
the solid particles are not blasted on the surface of steel sheet
at places corresponding to the respective solid particle feed
pipes. Consequently, by combining that type of centrifugal blasting
machines, the area where the surface roughness could not be created
at upstream can obtain the surface roughness by the downstream
centrifugal blasting machine, thus attaining a specified surface
roughness along the whole width of steel sheet.
[0074] Between the two units of centrifugal blasting machines, an
air purge nozzle may be placed, although the figure does not show,
to blow off the solid particles scattered on the steel sheet to
prevent the scattering of solid particles in adjacent blast ranges
to inhibit the creation of surface roughness.
EXAMPLE 1
[0075] Example 1 according to the present invention is the result
of creating a roughness on the surface of steel sheet using four
units of centrifugal blasting machines given in FIG. 1. Also there
is given the description of a comparative example which is the
result of creating a roughness on the surface of steel sheet using
two units of centrifugal blasting machines given in FIG. 8. For the
case of FIG. 1, the line of intersection between the plane vertical
to the rotation axis of the centrifugal rotor and the plane of the
steel sheet was set to have an angle of 30.degree. to the direction
of travel of the steel sheet. For the case of FIG. 8, on the other
hand, the line of intersection between the plane vertical to the
rotation axis of the centrifugal rotor and the plane of the steel
sheet was set to become vertical to the direction of travel of the
steel sheet.
[0076] Example 1 used a hot-dip galvanized steel sheet as the steel
sheet to create a surface roughness. The hot-dip galvanized steel
was prepared from a cold-rolled steel sheet having 0.8 mm in
thickness and 800 mm in width, applying a coating film made of
mainly .cedilla. phase thereon. After applying the hot-dip
galvanization, the material was adjusted to give 0.8% of elongation
by temper rolling using a bright roll for leveling the
irregularities on the coating film to reduce waving.
[0077] The solid particles used to create the surface roughness
were the solid particles of SUS 304, having 85 .mu.m of mean
particle diameter. The solid particles were in almost spherical
shape prepared by gas atomizing method. Since the solid particles
are able to form dimple-shape microscopic irregularities on the
surface of steel sheet, a steel sheet having excellent
press-formability is attained.
[0078] The applied centrifugal blasting machine was a normal
centrifugal blasting machine shown in FIG. 5, having a vane with
330 mm of outer diameter and 3900 rpm of maximum rotational speed.
The weight of solid particles which can be blasted by the
centrifugal blasting machine is 100 kg/min per unit thereof.
[0079] According to Example 1, the blast distance was set to 350 mm
and the rotational speed of the centrifugal rotor was set to 3900
rpm, while changing the line speed of steel sheet in a range from 5
to 50 mpm to create the surface roughness on the steel sheet. The
feed rate of solid particles to each centrifugal blasting machine
was adjusted to 5 kg/m.sup.2 of blast density on the surface of
steel sheet.
[0080] Specifically, for the case of 50 mpm of line speed, Example
1 of the present invention given in FIG. 1 adopted 50 kg/min of
blast quantity of solid particles for each centrifugal blasting
machine, and the comparative example given in FIG. 8 adopted 100
kg/min of blast quantity of solid particles for each centrifugal
blasting machine. That is, the total quantity of blast quantity per
unit time by the total centrifugal blasting machines was set to the
same between Example 1 and the comparative example. The blast
quantity of each centrifugal blasting machine was adjusted
proportional to the line speed, and the blast density was adjusted
to the same under both conditions.
[0081] From each steel sheet which was provided with surface
roughness by blasting solid particles thereto, small samples were
cut to collect. The surface morphology of the samples was
evaluated. The typical evaluation index was selected to the mean
roughness Ra of steel sheet.
[0082] Regarding the variations of mean roughness Ra on the surface
of steel sheet with line speed in Example 1, FIG. 9 shows the
comparison between Example 1 and the comparative example according
to the prior art. The figure gives the relation between the blast
quantity of solid particles and the line speed. The result of the
comparative example shows that the increased blast quantity of
solid particles degrades the mean roughness Ra on the surface of
steel sheet in spite of the same blast density against the steel
sheet. This is because the particle density of the blasted solid
particles in air increases with the increase in the blast quantity
of solid particles, and the solid particles interfere with each
other to increase the number of solid particles which fail in
colliding against the surface of steel sheet at a sufficient
speed.
[0083] On the other hand, according to Example 1, at a low line
speed, the mean roughness Ra is almost the same with that of the
comparative example. However, when the line speed is increased and
the blast quantity of solid particles is increased, the difference
between Example 1 and the comparative example becomes distinctive.
That is, Example 1 varies the mean roughness created on the surface
of steel sheet very little even at increased line speeds, and does
not degrade the efficiency of creating surface roughness.
[0084] The reason of the phenomenon is the following. At small line
speeds, the particle density is inherently low even in the prior
art so that the interference between solid particles raises no
significant problem. When, however, the line speed increases and
the blast quantity of solid particles increases, the prior art
raises significant interference between solid particles to degrade
the mean roughness Ra. To the contrary, Example 1 hardly induces
that kind of interference, thus the difference between the present
invention and the prior art becomes distinctive in treating steel
sheet at high travel speeds.
[0085] As described above, according to Example 1, the difference
from the comparative example of the prior art becomes large at 50
mpm or larger line speed, and a significant effect appears at 100
mpm or larger line speed.
EXAMPLE 2
[0086] Example 2 according to the present invention is the result
of creating a roughness on the surface of steel sheet using the
centrifugal blasting machine given in FIG. 2. In this case, the
line of intersection between the plane vertical to the rotation
axis of the centrifugal rotor and the plane of the steel sheet was
set to become parallel to the direction of travel of the steel
sheet. As a comparative example, the description is given also to
the result of creating a roughness on the surface of steel sheet
using two units of centrifugal blasting machines applied in Example
1, shown in FIG. 8.
[0087] Example 2 according to the present invention is the result
of creating a roughness on the surface of steel sheet using the
centrifugal blasting machine given in FIG. 2. In this case, the
line of intersection between the plane vertical to the rotation
axis of the centrifugal rotor and the plane of the steel sheet was
set to become parallel to the direction of travel of the steel
sheet. In Example 2, two rows of the blasting machines were applied
in a staggered arrangement to blast solid particles over the whole
width of steel sheet, and each row has five centrifugal rotors. A
comparative example adopted two units of centrifugal blasting
machines applied in Example 1, shown in FIG. 8. At each edge
section of long side in a blast range, the arrangement of blasting
machines is requested to overlap a part of the respective blast
ranges with each other because the centrifugal blasting machine
unavoidably generates a density distribution of the blasted
particles in the rotational direction of the centrifugal rotor, (or
along the long side of blast range), which is shown in FIG. 10.
That is, unless the sections of decreased particle density of the
blasted particles are overlapped with each other at each edge
section of the long side of blast range to increase the total blast
density, a uniform surface roughness in the width direction of
steel sheet cannot be attained.
[0088] Example 2 used a hot-dip galvanized steel sheet as the steel
sheet for creating surface roughness. The hot-dip galvanized steel
sheet was prepared from a cold-rolled steel sheet having 0.8 mm in
thickness and 800 mm in width, applying a coating film made of
mainly .cedilla. phase thereon. After applying the hot-dip
galvanization, the material was adjusted to give 0.8% of elongation
by temper rolling using a bright roll for leveling the
irregularities on the coating film to reduce waving.
[0089] The solid particles used to create the surface roughness
were the solid particles of SUS 304, having 85 .mu.m of mean
particle diameter. The solid particles were in almost spherical
shape prepared by gas atomizing method. Since the solid particles
are able to form dimple-shape microscopic irregularities on the
surface of steel sheet, a steel sheet having excellent
press-formability is attained.
[0090] The applied centrifugal blasting machine was a normal
centrifugal blasting machine shown in FIG. 5, having a vane with
330 mm of outer diameter and 3900 rpm of maximum rotational speed.
The weight of solid particles which can be blasted by the
centrifugal blasting machine is 100 kg/min per unit thereof.
[0091] According to Example 2, the blast distance was set to 350 mm
and the rotational speed of the centrifugal rotor was set to 3900
rpm, while changing the line speed of steel sheet in a range from
10 to 160 mpm to create the surface roughness on the steel sheet.
The feed rate of solid particles to each centrifugal blasting
machine was adjusted to 5 kg/m.sup.2 of blast density on the
surface of steel sheet.
[0092] Specifically, for the case of 50 mpm of line speed, Example
2 given in FIG. 2 applied 5 units.times.2 rows of blasting machines
to cover the blast range shown in FIG. 3, with 20 kg/min of blast
quantity of solid particles for each centrifugal blasting machine.
In a comparative example shown in FIG. 8, however, two units of
blasting machines were arranged with 100 kg/min of blast quantity
of solid particles per one unit. That is, the total quantity of
blast quantity per unit time by the total centrifugal blasting
machines was set to the same between Example 2 and the comparative
example. The blast quantity of each centrifugal blasting machine
was adjusted proportional to the line speed, and the blast density
was adjusted to the same under both conditions.
[0093] From each steel sheet which was provided with surface
roughness by blasting solid particles thereto, small samples were
cut to collect. The surface morphology of the samples was
evaluated. The typical evaluation index was selected to the mean
roughness Ra of steel sheet.
[0094] Regarding the variations of mean roughness Ra on the surface
of steel sheet with line speed in Example 2, FIG. 11 shows the
comparison between Example 2 and the comparative example according
to the prior art. The result of comparative example gave a degraded
mean roughness Ra on the surface of steel sheet in spite of the
same blast density against the steel sheet. To the contrary,
Example 2 kept the mean roughness Ra within a range from 1.0 to 1.5
.mu.m even at 150 mpm or higher line speed to maintain the desired
roughness. According to Example 2, since wide blast range is
secured in the longitudinal direction of the steel sheet even at
increased line speeds, the particles in air becomes less dense, and
interference therebetween occurs less, thus the desired surface
roughness is secured.
[0095] With the arrangement of blasting machines in Example 2, the
uniformity of surface roughness was evaluated at the boundary of
adjacent blast ranges. FIG. 12 shows the surface roughness
distribution on steel sheet in the width direction thereof under
blasting from only two adjacent centrifugal rotors. As shown in the
figure, almost uniform surface roughness is attained even at the
boundary of adjacent blast ranges.
[0096] Even with the arrangement of blasting machines according to
the comparative example referred in the description of Example 2,
the desired surface roughness can be created by reducing the blast
quantity per unit of centrifugal blasting machine and by arranging
a plurality of blasting machines in the longitudinal direction of
steel sheet. That type of arrangement of blasting machines,
however, increases the length of apparatus, and the increased total
length of apparatus raises a problem of increased investment. The
problem is described below.
[0097] The particles blasted by a centrifugal blasting machine
collide against the surface of steel sheet, as shown in FIG. 13, to
form dents thereon, then move in the direction of rotation of the
centrifugal rotor. When other centrifugal blasting machine is
positioned in the direction of rotation of the rotor (the direction
vertical to the rotation axis), solid particles enter the blast
range of the original blasting machine. As a result, the particles
blasted by the original centrifugal blasting machine are interfered
by the entering solid particles blasted by other blasting machine,
which results in reduction in the speed of the blasted particles to
fail in creating satisfactory surface roughness. Accordingly, for
the case of arrangement of plurality of centrifugal blasting
machines according to the comparative example, placing other
centrifugal blasting machine in the scattering direction of solid
particles blasted by the original centrifugal blasting machine, as
shown in FIG. 14, raises a problem of treatment.
[0098] Consequently, to attain a desired surface roughness with the
arrangement of blasting machines according to the comparative
example while reducing the blast quantity per unit blasting machine
to reduce the interference between particles, the arrangement
thereof shown in FIG. 15 is required. In that case, it is necessary
that at least seven units of centrifugal blasting machines are
arranged in the width direction of steel sheet, and that four sets
of these seven units or larger number of blasting machines are
combined. This arrangement requires at least 28 h of apparatus
length (2800 mm) in the traveling direction of steel sheet. To the
contrary, according to Example 2, the longitudinal apparatus length
is 2 W (800 m) or more, as shown in FIG. 16. Therefore, even when
the space for installing the apparatus has a limitation, as in the
case of installation of the apparatus in a hot-dip coating line or
a continuous annealing line, Example 2 can provide high efficiency
for creating surface roughness while keeping the total apparatus
length short.
EXAMPLE 3
[0099] Example 3 according to the present invention is the result
of creating a roughness on the surface of steel sheet using: the
centrifugal blasting machines arranged as given in FIG. 1, applied
in Example 1, (hereinafter referred to as the "arrangement A"); and
the centrifugal blasting machines arranged as given in FIG. 2,
applied in Example 2, (hereinafter referred to as the "arrangement
B").
[0100] According to the arrangement A, the line of intersection
between the plane vertical to the rotation axis of the centrifugal
rotor of the centrifugal blasting machine and the plane of the
metallic sheet is set to have an angle (=30.degree.) to the
direction of travel of the metallic sheet. The arrangement gives
the blast ranges shown in FIG. 17. For the arrangement B, the line
of intersection between the plane vertical to the rotation axis of
the centrifugal rotor of the centrifugal blasting machine and the
plane of the metallic sheet is set to become parallel (=0.degree.)
to the direction of travel of the metallic sheet. The arrangement
gives the blast ranges shown in FIG. 18.
[0101] Example 3 used a hot-dip galvanized steel as the steel sheet
for creating surface roughness. The hot-dip galvanized steel sheet
was prepared from a cold-rolled steel sheet having 0.8 mm in
thickness and 800 mm in width, applying a coating film made of
mainly .cedilla. phase thereon. After applying the hot-dip
galvanization, the material was adjusted to give 0.8% of elongation
by temper rolling using a bright roll for leveling the
irregularities on the coating film to reduce waving.
[0102] The solid particles used to create the surface roughness
were the solid particles of SUS 304, having 85 .mu.m of mean
particle diameter. The solid particles were in almost spherical
shape prepared by gas atomizing method. Since the solid particles
are able to form dimple-shape microscopic irregularities on the
surface of steel sheet, a steel sheet having excellent
press-formability is attained.
[0103] The applied centrifugal blasting machine was a normal
centrifugal blasting machine shown in FIG. 5, having a vane with
330 mm of outer diameter and 3900 rpm of maximum rotational speed.
The weight of solid particles which can be blasted by the
centrifugal blasting machine is 100 kg/min per unit thereof.
[0104] According to Example 3, the blast distance was set to 350
mm, the rotational speed of the centrifugal rotor was set to 3900
rpm, and the line speed of steel sheet was set to 50 mpm to create
the surface roughness on the steel sheet. The feed rate of solid
particles to each centrifugal blasting machine was adjusted to 5
kg/m.sup.2 of blast density on the surface of steel sheet.
[0105] From each steel sheet which was provided with surface
roughness by blasting solid particles thereto, small samples were
cut to collect. The surface morphology of the samples was
evaluated. The typical evaluation index was selected to the mean
roughness Ra of steel sheet.
[0106] Regarding the variations of mean roughness Ra on the surface
of steel sheet along the width thereof in Example 3, FIG. 19 shows
the comparison between the arrangement A and the arrangement B of
centrifugal blasting machines. For the arrangement A, (in FIG. 19),
the adjustment of overlapped blast regions for individual blasting
machines is favorably performed so that the distribution of mean
roughness Ra on the surface of steel sheet in the width direction
thereof is flat and good compared with the result of the
arrangement B (in FIG. 19).
[0107] The superiority of the arrangement A is described below
referring to the schematic drawings of FIG. 20 and FIG. 21. With
the arrangement A, since the angle of the blasting machine is
30.degree., the blast range per unit blasting machine in the width
direction of steel sheet widens, and a certain blast density
distribution widened in the width direction thereof is generated.
That type of blast density distribution, however, can be eliminated
by overlapping the adjacent blast ranges to each other, (FIG. 20).
That is, for the case of arrangement B, or =00, the boundary
between adjacent blast regions generates somewhat discontinuous
area, though the blast density distribution in the width direction
of steel sheet is small, (FIG. 15). To this point, by giving a
slight angle to the centrifugal blasting machine, as in the case of
the arrangement A, the overlap margin is secured to assure smooth
changes of surface roughness between adjacent blast ranges, thus
eliminates the above-described discontinuous areas.
[0108] Consequently, it is preferable that, considering the
uniformity of distribution of mean roughness on the steel sheet in
the width direction thereof, the centrifugal blasting machines are
arranged so as the line of intersection between the plane vertical
to the rotation axis of the centrifugal rotor and the plane of the
steel sheet to become some degree of angle to the direction of
travel of the steel sheet, and more preferably 5.degree. or more.
If the angle is smaller than 5.degree., the adjustment of overlap
of blast ranges of individual centrifugal blasting machine becomes
difficult, and the uniform roughness distribution in the width
direction of steel sheet becomes difficult to attain. On the other
hand, if the angle exceeds 45.degree., sufficient roughness becomes
difficult to create for the case of high line speeds, over 100 mpm.
Accordingly, the angle is preferably 45.degree. or smaller.
[0109] From the viewpoint of compact design of total apparatus, the
practical angle range is from 5.degree. to 30.degree..
EXAMPLE 4
[0110] FIG. 16 shows an arrangement of the surface treatment
apparatus according to the present invention on a hot-dip
galvanizing line, as Example 4 of the present invention.
[0111] Example 4 is the result of adjusting the surface roughness
using the apparatus shown in FIG. 1. The hot-dip galvanized steel
sheets were prepared from cold-rolled steel sheets having 0.5 to
1.8 mm in thickness and 750 to 1850 mm in width, respectively,
giving 0.8% of elongation by temper rolling. The elongation by
temper rolling was applied to adjust the material, and the temper
rolling was done by bright roll. Example 4 dealt with hot-dip
galvanized steel sheets with a coating film made of mainly
.cedilla. phase.
[0112] The line speed of the hot-dip galvanizing line was 100 mpm
at the maximum. The solid particles used to create the surface
roughness were the stainless steel fine particles having 85 .mu.m
of mean particle diameter. The applied blasting machine was a
mechanical blasting machine having 330 mm of impeller diameter. The
blast to the steel sheet was done at 3900 rpm of rotational speed.
The blast density of solid particles was 5 kg/m.sup.2 of steel
sheet, thus manufactured the galvanized steel sheets for
automobiles, having 1.2 .mu.m of mean roughness Ra and 0.2 .mu.m or
smaller dispersion of roughness in the width direction of steel
sheet.
[0113] As described above, the present invention provides an
apparatus for surface treatment being able to efficiently create a
surface roughness even in the treatment of metallic sheet traveling
at a high speed, further to an apparatus for surface treatment
being able to provide compact design therefor, a method for
producing metallic sheet using the apparatus, a hot-dip coating
line of metallic sheet using the apparatus, and a continuous
annealing line of metallic sheet using the apparatus.
* * * * *