Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OF THE INVENTION
Method of washing off magnetically separated
particles
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a method of washing
filters that continuously remove magnetic particles,
produced by metal processing or wear, that are present in
water and in the atmosphere, microorganisms accompanying
magnetism and magnetic particles entrained in fluids.
Description of the Prior Art
Magnetic separators employing permanent magnets
and electromagnetic or permanent magnetic filters employing
ferromagnetic fibers or beads are conventionally used to
remove magnetic particles and microorganisms accompanying
magnetism entrained in fluids (hereinafter the removal of
magnetic particles and the like adhering to electromagnetic
filters will also be referred to-as "washing").
However, magnetic separators have a poor
performance ard provide insufficient washing.
Electromagnetic filters, on the other hand, have superior
magnetic-particle-removal performance but it is necessary
to clean the filters effectively. In JP-A-54(1979)-86878,
for example, in which a ferroelectromagnet is used to set
the magnetic field to zero, a large apparatus is required
to free the filter from the magnetic field, involving a
large consum~tion of electricity and a major outlay in
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manufacturing costs that make the cost-performance thereof
unsatisfactory.
Washing ~ater, hydraulic fluid, cooling water,
process fluids and other such fluids used in product
manufacturing processes in the steel industry, automotive
pressed parts and processing industries, for example,
contain large quantities of magnetic particles entrained
therein. As well as reducing the surface cleanliness of
the products, this has a major effect on product quality,
producing blemishes and the like, and also because of these
magnetic particles, washing tanks and piping has become
very costly.
In fresh-water and waterworks treatment
facilities, too, the formation of rust, iron bacteria and
the like from tanks and pipes is unavoidable and is a cause
of scaled waste water and the like in the waterworks
system. ~arge purification tanks and separation equipment
are required to remove this at a huge cost.
Thus, for manufacturing industries, the efficient
removal of magnetic particles in such fluids is beneficial
in terms of product quality and equipment maintenance
costs, and for water treatment facilities it also helps to
reduce the equipment costs and to make the water supply
safer. However, because such magnetic particles are so
small, ordinary filters are quickly clogged, and the cost-
performance of conventional magnetic separation apparatuses
renders them unsuitable.
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In the example of the steel-making industry,
minute steel particles produced during the cold-rolling of
steel sheet adhere to the sheet. The sheet is therefore
subjected to a process to remove the particles, for
example, an electric cleaning process, before it is sent on
to be heat-treated, plated, and so forth.
Drum-type magnetic separators and cloth filters
are generally used to reduce the amount of steel dust in
the tanks of rolling oils and washing fluids. However,
drum-type magnetic separators have a very low removal
efficiency, because the magnetic particles are only held by
the magnetic force in the vicinity of the surface of the
drum. With cloth filters, too, the minute size of the
steel particles makes the removal efficiency lower, in
addition to which the filters quickly become clogged,
involving large outlays for cloth.
Conventional apparatuses include electromagnetic
filters that employ ferromagnetic small-gage wire.
Utilizing the principle of high-gradient magnetic
separation, a large magnetic gradient is generated around
the ferromagnetic small-gage wires to effect separation of
the magnetic particles with good efficiency~ However, with
current constructions it is difficult to clean the filters.
In the cleaning process huge electromagnetic coils are used
to control the magnetic field, so the cleaning involves the
use of a large apparatus, major fabrication expenditures
and the consumption of enormous amounts of electricity.
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27257-11
Therefore the ma~or problem is how to remove the magnetlc
particles adhering to the filters economically and efficiently.
There are apparatuses that combine the low cost of the
magnetic separator with the high efficiency of the electromagnetic
filter, but the washing efficiency of such apparatuses ls poor and
the hlgh efficiency cannot be maintalned over a long perlod.
SU~ARY OF THE INVENTION
The ob~ect of the present invention is to provide a
method of cleaning magnetic filters by efficiently removlng
magnetically separated particles adhering to the magnetic fllters.
Another ob~ect of the present invention is to provide a
method of washing a magnetic filter using centrifugal force, and
pulsed washing and an alternating magnetic fleld.
According to the present inventlon there is provided a
method of washing a magnetic fllter constltuted by ferromagnetlc
small-gauge wlres and having a longltudlnal axis and opposlte
ends, by removing from the magnetlc fllter magnetic particles
cllnging thereto, comprlslng: establishing a magnetic fleld
through the filter and which alternates ln polarity in a dlrection
around said longitudinal axis and whlch extends in a dlrection
parallel to said longltudlnal axis; rotating the magnetic filter
with respect to sald magnetic field about sald longltudinal axls;
and ~ettlng washlng fluld through the magnetic filter between the
respective opposite ends of the filter in a direction transverse
to sald longltudinal axls whlle rotatlng the magnetlc fllter.
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27257-11
BRIEF DESCRIPTION OF THE DRAWINGS
Figures l(a~ and l(b) are explanator~ draw:Lngs of the
cleanlng method according to the present inventlon;
Flgure 2~A) is an explanat:ory drawing of the interior of
the filter concerned; Flgure 2(B) ls an explanatory drawing
showing when the fllter is cleaned; Figure 2(C) is a graph of the
alternating magnetic field; Figure 2~D) shows a part of the view
shown in Flgure 2(A~; and Figure 2(E) shows a part of the view
shown ln Figure 2(B);
4a
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Figure 3(A) is an explanatory drawing showing the
interior of another example of a filter; Figure 3~B) is an
explanatory drawing showing an another example of when a
filter is cleaned; Figure 3(C~ is a graph of another
example of an alternating magnetic field; and Figures 3(D)
and 3(E) each shows part of the views shown in Figures 3(A)
and 3(B) respectively;
Figure 4 is an explanatory drawing of the washing
situation when washing fluid is supplied continuously (not
intermittently);
Figure 5 is an explanatory drawing of an example
of the apparatus used;
Figure 6 is an explanatory drawing of another
example of the apparatus used;
Figure 7 is an explanatory drawing of the
operation of another example of the invention;
Figure 8 is an explanatory drawing of another
example of an apparatus for the method of the invention;
Figures 9 and 10 are curves showing the effect of
implementing the method of the invention;
Figure 11 is an explanatory drawing showing a
magnetic-particle magnetic separation system;
Figures 12 and 13 are explanatory drawings
showing conventional filter washing methods.
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DETAILED DESCRIPTION OF THE INVENTION
The magnetic-separation system for removing
magnetic particles in a fluid will now be described briefly
with reference to Figure 11.
Rolling oil used in a cold-rolling system 1, for
example, contains magnetic particles produced during the
cold rolling. The rolling oil is sent via a passage A1 to
a magnetic filter 2 where the magnetic particles are
removed, after which the cleaned fluid is pumped into a
circulation tank 3 via passage A2, and after it has
accumulated therein it is again used in the cold-rolling
system 1.
In another system the rolling oil used in the
cold-rolling system 1 is collected in the tank 3 via a
passage A3, and is passed along passages A4 and A2, in the
course of which the fluid is cleaned by the magnetic filter
2.
Because in both of these fluid cleaning systems
the particle-removal capability of the magnetic filter 2
deteriorates over time, the filter has to be cleaned
periodically or in response to the deterioration in its
particle-removal capability.
To wash the filter, the washing medium (water,
steam, oil, etc.) is fed in via passage B1 and the magnetic
filter element is rotated at 300 to 3,000 rpm. The
magnetic particles expelled thereby pass through passage B2
and are collected in a discharge tank 5. By repeating this
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process, particles can be continuously removed from the
rolling oil with good efficiency.
The present invention comprises expediently
washing the filter by removing magnetic particles adhering
to the magnetic filter following the use of the filter to
remove the magnetic particles from the fluid. For this,
the method of the invention comprises disposing magnets
above and below the magnetic filter, and with these magnets
fixed in place, rotating the magnetic filter to thereby
effect the washing of the filter by the centrifugal force
and alternating magnetic field thereby generated.
Namely, as shown by Figure 12, a magnetic filter
2 in general use is provided with magnets 6 arranged
radially in the filter's plane of rotation and in the
thickness direction of the filter. When the said magnetic
filter 2 is rotated to utilize the centrifugal force thus
generated to remove magnetic particles from the filter, the
washing fluid applies a fluid drag on the particles that
is greater than the magnetic force of the particles. The
behavior of the washing fluid is shown in Figure 13.
Namely, when the magnetic filter 2 is rotated the washing
fluid describes a parabola, as shown by arrow a, as it
tries to flow in the opposite direction to the rotation,
but as it is obstructed by the magnets 6, in the latter
half of its flow, as shown by arrow b, it moves along the
magnets to form a stagnant area c, which is forms a non-
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cleaning area, and thus, magnetic particles in the filter
are unable to be removed completely.
During the washing, when there is no fluctuation
in the magnetic field in the filter, the centrifugal force
acting on the particles, and the action of only the washiny
fluid the drag of which has been increased by the
centrifugal force, can be cited as causes of low washing
efficiency.
In accordance with the present invention, as
shown in Figure 1, a multiplicity of magnets 6 are disposed
above and below the rotating surface of the magnetic filter
2. With the magnets arranged above and below in a mutually
attractive formation and in an alternating-pole formation
in the direction of filter rotation, the magnatic field
thus formed perpendicularly to the direction of filter
rotation and the multipllcity of magnetic fields in the
direction of filter rotation produce an alternating
magnetic field. Therefore, as shown in Figure l(b), by
having just the filter rotate in the alternating magnetic
field, the alternating magnetic field is applied to the
filter, enabling the magnetic particles to be removed with
good washing efficiency.
The washing effect according to this invention
is shown in Figure 2. When the ferromagnetic small-gage
wires constituti~g the filter have the same magnetic
characteristics as the magnetic particles to be removed,
during filtration, as shown by Figure 2(A) 2(D), the
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particles are adhering to the ferromagnetic wire, a
situation which is shown by state (a) in Figure 3(C). As
shown by Figure 2(B) and 2(E), at the start of the washing,
there is a chance to degauss the ferromagnetic wires
together with the magnetic particles, by an amount
proportional to the rate at which the generated alternating
magnetic field revolves. As a result, it becomes easy to
separate the particles from the wires, and cleaning of the
filter can be facilitated by the centrifugal force acting
on the particles and the increase in the fluid drag
produced by the centrifugal force. In this case, the
particles degauss at state (b) in Figure 2(C).
Fiyure 3 illustrates the effect of the invention
when the ferromagnetic small-gage wires and the magnetic
particles to be removed have different magnetic
characteristics. During filtration, as shown by Figure
3(A) and 3(D), the magnetic particles are adhering to the
ferromagnetic wires, a situation that is shown by state (a)
in Figure 3(C). As shown in Figures 3~B) and 3(E), at the
start of the cleaning, by as much as the amount of the
revolving of the alternating magnetic field generated there
is a chance to separate the particles from the wires when
the two repel each othér. As a result, cleaning of the
filter can be facilitated by the centrifugal force acting
on the particles and the increase in the fluid drag
produced by the centrifugal force. This situation is shown
by state (b) in Figure 3(C).
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As shown in Figure 4, when the washing fluid is
supplied to the filter in a continuous flow, the particles
are removed in channels. The subsequent inflow of washing
fluid flows into the channel offering the least resistance
to the flow, preventing any improvement in washing
efficiency. In the drawing, Do indicates a channel with
lower particle density and D1 the area with a higher
particle density; the arrow a shows the direction of the
flow of washing fluid.
When washing fluid is thus supplied
intermittently, rotating the filter when the fluid is not
jetting out even when channels have formed will close the
channels, so that the next spurt of fluid will provide an
effective washing action.
Figure 5 shows an example of an apparatus used in
the invention.
Fluid containing magnetic particles to be
filtered provided by a pump 8 enters the magnetic filter 2
and is passed through a magnetic field formed by permanent
magnets 6 disposed above and below the filter. In the
course of this, the large magnetic gradient generated by
the ferromagnetic small-gage wires that constitute the
filter cause the particles to be removed from the fluid to
the wires. The fluid thus cleaned is pumped back to the
original tank, via valve lO, by a pump 9.
When a motor ll is used to rotate the magnetic
filter at a high speed, the filter is washed by the
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centrifugal force of the rotation and the alternating
magnetic field acting on the particles produced in the
filter by the rotation, and a continuous or intermittent
jet of washing fluid from a nozzle 13. Thus, when the
ferromagnetic wires constituting the filter have the same
magnetic characteristics as the magnetic particles to be
removed, the degaussing effect provided by the alternating
magnetic field enhances the washing effect. When the wires
and particles have unlike magnetic characteristics, the
washing efficiency is enhanced by the magnetic pole
inversion effect provided by the alternating magnetic
field. Washing efficiency is further enhanced by the
intermittent jetting of the washing fluid, which prevents
the formation of flow channels in the filter.
Figure 6 shows anther example of the invention,
wherein one of the groups of upper and lower magnets is
fixed and the other group is rotatable.
~ ith reference to Figure 6, magnets are provided
above and below the magnetic filter 2. As the washing
fluid flows between the upper magnets 6a and the lower
magnets 6b, high-efficiency cleaning is possible because
there is nothing obstructing the flow-path.
As shown in Figure 6(C), in the upper magnets 6a
and the lower magnets 6b, are arranged so that the poles of
adjacent magnets are unlike. In addition, the magnets 6a
and 6b are arranged so that unlike poles face each other.
Provided between the magnets 6a and 6b is a filter 2
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constituted of ferromagnetic small-gage wires. By
producing a magnetic field in the wires, the magnetic
particles are caused to adhere thereto.
With such an arrangem~ent, when the lower magnets
are rotated, the unlike polarity of the opposed upper and
lower magnets will be changed to like polarity, with south
poles facing south poles and north poles facing north
poles.
With such a configuration, an alternating
magnetic field acting on ferromagnetic wires provided
between the upper and lower magnets produces a state of
apparent non-magnetism, enabling even higher-efficiency to
be effected.
Figure 7 shows the washing effect obtained with
the example shown in Figure 6. Namely, Figure 7(A) and
7(D) show the interior of the filter (when magnetic
particles are adhering thereto). Figure 7(B) and (E) show
the degaussing state of the ferromagnetic wires and the
magnetic particles that accompanies the rotation of the
filter and the upper magnet, during filter washing. That
is, as shown in Figure 7(C), state (a) is when the magnetic
parts are adhering, and during filter washing it becomes
state (b) by an amount proportional to the rate at which
the generated alternating magnetic field revolves, and the
external magnetic field is removed.
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In this state, the magnetization of the
ferromagnetic wires disappears and the magnetization of the
magnetic particles is reduced.
~ t this point, as mentioned above, high-
efficiency filter washing can be effected by the
centrifugal for~e generated by the filter rotation and the
pulsed supply of washing fluid.
Figure 8 shows an example of an apparatus for the
cleaning system of the invention.
Fluid containing the magnetic particles to be
filtered out is delivered by a pump 8 into the apparatus.
The fluid is passed through a magnetic field formed by
permanent magnets 6 disposed above and belowO In the
course of this, a large magnetic gradient generated by a
filter constituted of ferromagnetic small-gage wires causes
the particles to be captured by the wires. The fluid thus
cleaned is pumped back to its original tank, via valve 10,
by a pump 9.
The lower magnets 6b are provided on a filter
unit 12. In operation, the motor 11 is used to rotate the
magnetic filter unit 12 at a high speed to produce a jet of
washing fluid from a nozzle 13 for the washing.
Example l
After rolling oil used in the cold-rolling
process has been cleaned by passing it through a magnetic
filter to filter out magnetic particles contained in the
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fluid, the filter was washed using the method of this
invention.
Washing was conducted for 5 minutes at a constant
fluid flow-rate of 20 liters/minute. The results are shown
in Figure 9. In the figure, A and B show the results
gained with the method of this invention; A is the result
of the filter with respect to which both the upper and the
lower magnets are fixed, and B is the result of the filter
with respect to which the upper magnets are fixed and the
lower magnets are rotatable.
Washing efficiency is as follows:
Washing efficiency (%) = The amount of particles
discharged/the amount of particles removed.
The accompanying numeral 1 shows when the
ferromagnetic small-gage wires and the particles had
different magnetic characteristics, and numeral 2 shows
when the magnetic characteristics were the same.
At a filter speed of 2,000 rpm the filter washing
effect obtained with the method of the present invention is
good, being substantially unaffected by the magnetic
characteristics of the ferromagnetic small-gage wires.
Figure 10 shows the washing results obtained when
washing fluid was supplied intermittently (at 20
liters/minute during actual delivery) for a washing time
of 5 minutes. The results show the relationship between
filter speecl (rpm) and washing efficiency. The
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experimental conditions (A1, A2, B1, B2) are the same as in
Figure 9.
These results show that the filter washing effect
obtained with the method of the present invention is good.
Even when compared with the results obtained using a
continuous delivery of washing fluid (see Figure 9), filter
washing is substantially perfect from filter speeds as low
as 300 rpm.
Also, compared to when the ferromagnetic wires
constituting the filter have different magnetic
characteristics to the magnetic particles to be removed,
when the wires and particles have the same magnetic
characteristics quite a high washing efficiency can be
obtained at even lower speeds (i.e., below 300 rpm).
Therefore, by giving the ferromagnetic small-gage
wires that constitute the filter element magnetic
characteristics that are different from those of the
magnetic particles, and by also using an intermittent
delivery of washing fluid, a high washing efficiency can
be obtained at relatively low filter speeds and with a
small amount of washing fluid, from which it can be seen
that the method of the invention is advantageous in terms
of both cost and washing efficiency.
Example 2
Rolling oil used in the cold-rolling process was
cleaned using the method of the present invention.
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Washing was conducted for 5 minutes at a washing-
fluid flow-rate of 10 liter.s/minute and a washing filter
speed of 1,300 rpm, and the quantity of steel particles
that remained adhered to the magnetic filter was measured.
The results are shown in Table 1.
Table 1
Magnet location. Particles remalning
and rotation format on the magnetic filter
No. 1 Rotation of upper500 ppm(100 mg)
and lower magnets
_
Fixing upper magnets
No. 2 and rotating lower5 ppm(1 mg)
magnets
Rotation of upper
No. 3 magnets and fixing6 ppm(1 mg)
of lower magnets
..._
Partitioning the filter
and providing the magnets(1000 mg)
on the partition
As can be seen from No. 1 in Table 1, washing
efficiency was increased when washing was performed using
a rotating Eilter with an alternating magnetlc field
produced by fixed magnets provided above and below the
magnetic filter. Also, as shown by No. 2 and No. 3,
washing efficiency was further increased when performed by
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fixing one set of magnets and generating an attraction-
repellent magnetic field.
