Note: Descriptions are shown in the official language in which they were submitted.
47~
S P E C`I F I C A T I O N
TITLE
"ELECTRO~UGNETIC EXTENDED NIP PRESS"
FIELD OF THE INVENTION
.
This invention relates to the art of extended nip
presses for papermaking machinery and the like utili~in~ electro-
magnets with large area core faces coextensive with the extended
nip area on at least one side of the nip maintaining a concentrated
ma~netic field through an opposed conforming paramagnetic nip member
for efficiently creating or augmenting the nip load on the paper
web conveyed through the nip. Specifically this invention deals
with extended nip presses having electroma~nets on one or both sides
of the nip with cores defining extended area shoes attracting opposed
confor~ing magnetic nip members minimizing flux gaps between the
opposed members to increase the attraction force for creating or
augmenting the nip load on paper webs or the like conveyed through
the nip.
THE KNOWN PRIOR ART
Extended nip presses for papermaking machines are known
in the art, for example fro~ the disclosures of the Busker et al
United States Pa~ent 3,738,225, issued July 24, 1973, and the lus~us
United States Patent 3,783,097, issued January 1, 1374. In these
d~sclosures ~mperviou~ belts convey the web through an extended wide
' ~ 2 ~ 7'~3
nip created by hydraulically loaded shoes or pads. Roll presses
with electromagnets in one roll attracting ~n opposing roll to
create a nip load are also known, for example, from the disclosures
of the McClenathan United States Patent 3,456,582, issued July 22,
1969. In such magnetic presses only a line nip is provided and
wide gaps between the magnet and the opposed roll are formed due
to the thickness of the roll housing the electromagnet and the
converging and diverging air spaces at the entrance and exit to
the line nip. These gaps substantially reduce the effectiveness
of the electromagnet in creating the nip load.
It would, therefore, be an improvement in this art
to create nip pressures or loads in extended nip presses by
electromagnets having large area massive cores immediately ad-
jacent an opposed magnetic member to minimiæe gaps therebetween
for maintaining a strong wide magnetic field creating a desired
nip load.
SU~ARY OF T~IE INVENTION
According to this invention an extended pressure nip
for dewatering or calendering fibrous webs, such as paper, is
formed by magnetically attracting a wide shoe on one side of the
web and a wide conforming paramagnetic member on the opposite side
of the web which may take the form of a roll or a p,ressure shoe.
The magnet core is coextensive with the wide nip area, ~orms or
intimately supports the shoe and develops a concentrated magnetic
field across the entire nip area. The field flux only traverses a
minimum path to the opposed nip member. The web is conveyed through
the nip by an impermeable belt and may be covered on one or both
faces with an ab~orbent felt in dewatering press installations or
may directly engage a hard finishing roll in calendPring installa-
~ions. The nip forming component on one side of the web is shiftable
~ 3'~
under the influence of the magnetic flux created by the energized
electromagnet. Thus, in installations having an electromagnet
shoe and a roll,either the shoe or the rolL is shiftable and in
installations having electromagnets on both sides of the nip either
one or both of the magnets may be shiftable.
A feature sf the inventi~.is the minimization of the
gap through which the magnetic flux must pass to establish the nip
load. This is accomplished by forming the pressure shoe with the
electromagnet so that the flux does not have to pass through a
surrounding roll before reaching the paramagnetic nip forming
member on the oppositeside of the web. The shoe and opposed member
have coextensive wide large areas increasing and concentrating the
magnetic inductance to more effectively pull the two sides of the
wide area nip together.
Another feature of the invention is the provision
of individual electromagnetic cores along the length of the nip
to compensate for any irregularities in nip loads caused by deflec-
tion, uneven expansion and the like, of the components.
A still further feature of the invention is to pro-
vide individual coils for the electromagnetic cores which are
adapted to be individually energized to control loads along the
length of the nip.
It is then an ob;ect of this inventio~ to provide
extended nip presses for papermaking machines and the like where
the nip loads are created or augmented by wide area electromagnetic
shoes.
A further object of the invention is to provide de-
watering presses and calenders for papermaking machines with wide
extended magnetized nips establishing nip loads by magnetic
attraction.
p~
A further object of the invention Ls to provide
a press roll assembly with an electromagnet energized shoe form-
ing an extended nip with a cooperating magnetic roll and havin~ a
minimum gap between the electromagnet and the magnetic roll.
Another object of this invention is to provide an
extended nip press for papermaking machines where the wide area
nip is formed by opposed electromagnets enhancing magnetic coupling
of opposed rigid nip members.
A still further ob;ect of the inventi~n is to pro-
vide an electromagnet ex~ended nip press where the press loads are
created by concentrated flux lines between opposed confor~ing wide
area rigid nip members.
Other and further objects and features of this inven-
tion will be apparent to those skilled in this art from the follow-
ing detailed description of the annexed sheets of drawings, which
by way of preferred examples show several best mode embodiments of
the invention.
ON THE DRA~INGS:
FIG. 1 is a schematic side view of an extended nip
press of this invention having a shiftable elec~romagnet on one
æide of the nip and a fixed axis ferromagnetic roll on the opposite
side of the nip;
FIG~ 2 is a schematic side view of an extended nip
press of this invention having a fixed electromagnet on one side
of the nip and a shiftable axis ferromagnetic roll on the opposite
side of ~he nip;
--4--
FIG. 3 is a schematic side view of an extended nip
double felt press of this invention wi~h a vented nip;
FIG. 4 is a schematic ~ide view of an extended nip
press of this in~ention havin~ electroma~nets on both sides of the
nip;
FIG. 5 is a schematic side view of an extended nip
calender type press of this invention;
FIG. ~ is an isometric view of a ~hiftable electro-
magnet shoe assembly for presses of this inventlon;
FIG. 7 is an isometric view of another form of electro-
magnet core for presses of this invention;
FI~. 8 is a schematic longitudinal vie~ of an electro-
magnet shoe $or the presses of this invention having a plurality of
cores individually energized by coils and with expanded core heads
to accommodate the individual coil wrappings;
FIG. 9 is an end view along the line IX-IX of FIG. 8;
FIG. 10 is a cross-sectional view alon~ the line X-X
of FIG. 3;
FIG, 11 is a cross-sectional view along the line XI-XX
of FIG. 3;
FIG. 12 is a schematic side view of multiple extended
nip press of this invention;
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FIG. 13 is a schematic longitudinal cross section
view of a laminated press roll useful in the presses of this
invention to minimize heating;
FIG. 14 is a graph showing nip loading as a function
of electromagnet excitation and illustrating the increases in
ma~entic coupling with decreases in gaps between the electromagnet
core and the opposing magnetic member,
AS SHOWN ON T~IE DRAWINGS:
The extended nip press assembly 10 of FIG. 1 has an
electromagnet 11 on the bottom side of the wide or extended nip N, and
a ferromagnetic top roll 12 on the opposite side of this nip. An
impermeable belt 13 is trained in an open loop around rolls 14, one
of which can be driven as shown at M and another can be biased as
shown at B to tighten the belt. An external roll 15 guides the belt
in its path having a top run through the nip. A porous felt 16 is
trained around rolls 17 through the nip and receives the bottom
face of a web W as it passes through the nip. The ferromagnetic
roll 12 rotates about a fixed horizontal axis 18. The electro-
magnet 11 is slidably mounted in an open top fixed trou,~h-like hous-
ing 19 and the top face of the electromagnet is covered with an
arcuat~ non-magnetic thin sheet shoe 20, preferably formed from a
sheet of stainless steel. This shoe 20 slidably supports the
impermeable belt 13 and a shower pipe 21 ejects l~bricating fluid
between the shoe 20 and belt 13 at the entrance to the nip N.
As shown in FIG. 6, the electromagnet 11 is formed
from a plurality of iron or magnetic steel core blocks 22 in side-
by-side relation. The core blocks 22 are rectangular in shape
with a flat bottom 23, flat parallel sides 24 and a transversely
convex top 25. The blocks 25 have flat faces 26 adapted to
slidably mat~ in side-by-side relation as illustrated.
Each block 22 also has a pair of spaced side-by-side
open top slots 27 extended between the opposite faces 26 thereof.
These slots ~erminate above the bottom 23 of each block. An
electromagnetic coil 28 is wound through the slots 27 terminating
below the top 25 of each block and extending beyond the end blocks
as shown.
The slotted convex tops 25 of the blocks are covered
with the thin non-magnetic ~hoe 20 which is curved to seat snugly
on the tops of ~he blocks and which also has downturned lips 29
extendlng over and beyond the sides 24 of ~he blocks so that the
impermeable belt 13 will be smoothly guided into and out of the
nip N.
The open top trough-like housing 19 is fixedly anchored
and extends across the full length of the press assembly 10 inside
the loop of the belt 13. The electromagnet 11 slides vertically
in this housing and the sidewalls 24 of the magnet blocks 22 are
slidably guided by the sidewalls of the trough and sealed to the
trough by seals or packings such as 30.
A sealed chamber 31 is provided between the bottoms
23 of the blocks 22 and the bottom of the trough ànd this chamber
may receive hydraulic fluid under pressure fr~m a pressure
source 32 to force the electromagnet 11 and its cover ~0 upwardly
from the housing 19 to establish initial loading of the nip N.
Other means ~or raising the electromagnet 11, such às screw rods,
springs, or the liXe could be provided to hold the co~er 20 against
the impermeable belt 13 ~nd to establish the initial loading of the
nip.
The coil 28 is energized from a generator G or the
like power source through a resistor R controllin~ the amplitude
o the curren~ to crea~e inductor excitation of ~he electromagnet
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establishing a controlled flux,drawing the slidable electro-
magnet and its cover shoe 20 toward the magnetic roll 12,and
establishing the desired nip loading. Since the cover 20 is
supported on the core blocks 22 and since these blocks are relative-
ly slidable, irregularities in the nip contour due to sagging,
heat expansion and the like will be neutralized and the blocks will
maintain a uniform loading along the full length of the nip.
In the extended nip press lOa of FIG. 2, parts
corresponding with the parts described in the press 10 have been
marked with the same reference numerals. In the press lOa, however,
the ferromagnetic top roll 12, instead of being mounted on the fixed
axis 18 of the FIG. 1 embodiment, is mounted on an axis 18a supported
from a bearings carried by swing arms such as 40, pivoted about
a center 41 and actuated by hydraulic or pneumatic cylinders such
as 42. The roll 12 is thus raised and lowered relative to the nip
N.
The electromagnet lla, instead of being shiftable
in a support such as 19, is fixedly mounted on a support l9a.
As shown in FIG. 7, the electromagnet lla has a single
core block 43 with a central open top slot 44 receiving one leg of
an electromagnet coil 45. The coil 45 thus envelops only one side
of the block 43 and has one leg lying in ~he slot 44 while the other
leg is wrapped around an outer side face of the block. The top of
the coil is below the slotted convex top 46 of theiblock and the cover
20 is supported on this slotted top 46.
Initial loading of the nip N in the press lOa is
accomp~ished by actuating the cylinder such as 42 to pull the ends
of the arms 40 forcing the bearings for the axis 18a downward into
pressure nip relatlon with the cover 20. The desired nip pressure
is then established by energizing the coil 45 creating the magne~ic
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7C3
flux which pulls the ferromagnetic roll 12 to the core 43 and
establishes the nip loading. The web is conveyed through the
pressure nip on the impermeable belt 13 which slides over the shoe
20 and the felt 16 covers the bottom face of the web in the same
manner as in the press embodiment 10.
From these descriptions of the press embodiments 10
and lOa it will be understood that the nip loading can initially
be created by forcing the electromagnet core against the shoe 20
on one side of the nip or by forcing the roll 12 toward the shoe
on the opposite side of the nip and then energizing the electro-
magnets to create a dense concentrated magnetic field through the
entire nip area pulling the magnet and roll together to create
the desired augmented nip load.
In the press lOb of FIG. 3 parts corresponding to
parts illustrated and described in the embodiments 10 and lOa have
been marked with the same reference numerals. In the embodiment
lOb, however, a double-felted ~ress is provided with the web pass-
ing through the nip N between the bottom felt 16 and a top felt
50 which is wrapped around the bottom of the roll 12 and directed
by guide rolls 51 to meet the web W as it enters the nip N and
to leave this web as it exi~s from the nip.
To facilitate drainage of water squeezed from the
web W out of the extended nip N, the roll 12 is circumferential-
ly grooved as illustrated at 52 forming channels for the flow of
water out of the nip N as shown in FIG. 10.
The impermeable belt 13 may be longitudinally grooved
as illustrated at 53 in FIG. 11 to form channels draining the water
out of the nip.
It will be understood that either the roll 12 or
the belt 13, or both, may be grooved.
~Z ~
It will also be understood that the press lOb may
have the shiftable roll 12 and the fixed electromagnet lla of the
press lOa in place of the fixed roll 12 and the shiftable magnet 11
of the press 10.
The extended nip press lOc of FIG. 4 includes
components the same as those illustrated and described hereinabove
and the same reference numerals have been used to identify the
components. In the press lOc, the roll 12 is replaced with the
shiftable electromagnet 11 and the trough support housing 19. This
magnet slides in the housing 19 and acts through the shoe 20 to
form the top face of the extended nip N. A top impermeable belt 60
trained around guide rolls 61 and a drive roll 62 in an open loop
surrounding the housing 19 has a bottom run extending through the
nip under the top shoe 20.
A fixed lower electromagnet lla is surrounded by the
looped bottom impermeable belt 13 riding over the bottom shoe 20. The web
W is conveyed through the nip between the belts 13 and 60. Lubricant
can be fed between the belts and shoes 20 at the entrance to the
nip.
The top electromagnet 11 can slide by gravity in the
housing 19 to create an initial nip load. In addition, the initial
load can be increased by hydraulic fluid, springs, or mechanical
screws forcing the electromagnet 11 out of its housing 19 as
described in the FIG. 1 embodiment.
The fixed bottom electromagnet lla can be in the form
of the ~ingle core end coil 45 with the external leg as shown in
FIG. 7 or can be constructed as shown in FIG. 6.
The bottom belt 13 is eonvenien~ly driven by a driver
roll 63 with a superimposed nip loading roll ~4, the belt passing
through the nip between the rolls 63 and 64.
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A fibrous absorbent felt 65 is also provided between
the top belt and the web W.
When the coils of the electromagnets 11 and lla are en-
ergized the cores of these magnets are drawn orpulled together push~
the shoes 20 on opposite sides of the web to~ard each other and
loading the nip to establish the d~sired pressure. Since both
sides of the nip have electrom~gnets, ~he attraction force will be
substantially greater, probably double, the force ob~ained in
the embodimen~s 10, lOa and lOb where the electr~magnet is pro-
vided only on one side of the nip.
The press lOd of FIG. 5 illustrates a calender roll
embodimentfor surface finishing a dry web D.W. threaded through the
nip N between a calender roll 70 rotatable about a fixed axis 71
and a shiftable electromagnet 11 carried in a housing 19 is described
hereinabove. The electromagnet 11 is covered by the non-magnetic
shoe Z0 described hereinabove which in turn receives the impermeable
belt 13 conveying the web D.W. through the nip N. Controlled
energization of the electroma~net 11 creates the desired calender
nip loading for treating the dry web D.W.
As shown in FIGS. 8 and 9 an elPctromagnetic loading of
the shoe 20 for an extended nip press or a calender press as
described hereinabove can be created by a modified electromagnet
arrangement 80 composed of a plurality of electromagnet core blocks
81 each havin~ its own individual exciting coil 82. As shown, the
magnetic iron or steel core blocks have open top parallel slots 83
receiving the coil 82 with the ends of the coil pr~ecting from the
open end~ of the 810ts. To provide for coil clearance between the
ad;acent core blocks ~1, heads 83 are provided on the blocks extend-
ing beyond their front and bsck faces. This provides gaps or spaces
85 for the coils 82 without opening up wide gaps or spaces under
the cover 20.
7 ~
As diagrammatically illus~rated in FIGURE 8, the
ends of each of the coils 82 can be individually energized from a
power source 86 through controls 86a to vary the input to each coil
as desired. In this manner, the cores 81 spaced along the lenF,th
of the nip can exert selective loads on increments of the shoe 20
to compensate for variations in nip pressures caused by sagging
rolls, non-uniform expansions, etc. along the length of the nip.
It will be noted any gaps between the nip and the
magnetic cores are minimized since the cores only act through very
thin non-magnetic shoes 20 to establish the flux lines creating
the attraction with opposed ferromagnetic rolls or cores. Further
these flux lines only have very short paths between opposite sides
of the nip and are concentrated over the complete nip area without
passing through air gaps which are formed in all line presses at
the entrance and exit sides of the nip. In the extended nip presses
of this invention the extended nip area has a width controlled
by the width of the shoe and all of this area has a magnetic field
passing directly therethrough wlthout going through an air gap,
although a very small gap will be formed by the non-magnetic material
goi.ng through the nip.
The press lOe of FIGURE 12 provides a series of nips
N successively receiving the web. Components similar to those
shown in the presses 10, lOa, lOb and lOc of FIGS. 1-4 have been
marked with the same reference numerals. As shown,` the press lOe has
three nips N, each defined by a roll 12 and a shiftable electromagnet
ll in a trough housing l9 with a thin non-magnetic shoe 20 covering
the core blocks 22 and a pressured chamber 31 urging the magnet and
shoe toward the opposing roll to establish an initial nip load.
Each roll 12 has a separate press felt 90 wrapped therearound through
the nip N provided by ~he roll and opposed shoe 20. Each felt 90
as illustrated on the third roll 12 ~s looped around rolls 91, one
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~ 2~'~4"~
of which can be driven as shown at M. An external stretcher
roll 92 keeps the loop taut and an external guide roll 93 keeps
the felt on path around the roll 12, through the nip N and around
the rolls 91. A single impermeable looped belt 94 has a top run
through all three nips N, around a drive roll 95 beyond the last
nip N, around rolls ~6 back to the front nip N and over a guide
roll 97 along a bottom run thereof.
The magnets 11 can be energized to exert increasing
nip loads in t~e successive nips N.
The rolls 12 of the press lOe can be replaced with
electromagnets 11 as in the press lOc of FIG. 4.
A porous metal belt (not shown) can be used to
replace the felts in the presses 10, lOa, lOb, lOc and lOe to there-
by further reducing the non-magnetic gaps between the ~pposite
rolls of the nips. Further the shoes 20 in the presses and calender
stack arrangements can be eliminated to reduce the gaps, but
because they are very thin, serve to keep the lubricating fluid
away from the magnetic coils, and smooth out the nip surface,
they are a desirable addition.
As show~ in FIG. 13, a press roll 12a for the presses
of this invention can be provided to minimize eddy current heating
of the nip. The roll 12a has a cylindrical steel core 98 with end
heads 99 carrying axles 99a to rotatably support the roll. The core
receives a stack of thin laminates 100 therearound and squeezed to-
gether by the end heads 99. The stacked laminates 100 are washers
about .004 to .020 inches thick and about 2 ~o 3 inches wide. They
fit snugly on the core 98 and are composed of metal which does not
develop eddy currents in the m~gnetic field generated by the electro-
magnets. Such eddy eurrents are created in conventional paramagnetic
materials and heat the roll when it is driven through ~he magnetic
field. When heat i~ not desired, laminated rolls such as 12a are used.
- -13-
Useful materials for the laminates are oriented
silicon iron forming an oxide coating on the surfaces of the thin
washers 100, noncrystallines or amorphous ferrites and the like.
FIG. 14 illustrates the increases in attractive
magnetic forces made possible by diminishing the gap through which
~he magnetic field must pass. Thus, as illustrated in the graph
101, plotting inductor excitation in ~erms of amperage turns from
0 to 14000 as abscissa 102 and static attractive forces in terms of
pounds per linear inch as ordinates 103, the attractive force
g~eatly increases as the gaps decrease from 3/4" down to 1/8".
Extrapolating the 0.125" curve to 14000 amp. turns shows that the
electromagnets used in the extended press nip assemblies of this
invention are capable of producing a force of 50~ pounds per linear
inch and that about twice this value can be achieved with two
mutually attractive magnets as in the press assembly lOc of FIG. 4.
The stacked heights of the non-magnetic shoes, belts,
felts, and webs in the nips N Qf the presses of this invention,
only result in gaps of .05" to .36" between the magnetic cores
and the ferromagnPtic rolls or the opposed magnet core. As ex-
plained above, the impermeable belt can ride on the lubricated
core legs of the electromagnet eliminating the shoe 20. The shoe,
however, helps to keep the lubricant fluid from the coils. In such
assemblies the shoe would only have a thickness of not more than
about .125 inches, each belt would have a thickness; of .020 to .10
inches and, of course, the thickness of the webs would be negligible
in the order of .002 to .010 inches. The impermeable belts are
preferably composed of rubber or a plastic material such as poly-
urethane, but could be thin impermeable metal belts fur~her reducing
the non-magnetic gaps. The felts, as explained above, can be re-
placed by thin porous flexible metal belts into and through which
the expelled wa~er can flow and stlll further reduce the gaps.
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c~
The shoes 20 can be any non-magnetic material such as hard rubber,
plastics material, stainless steel or the like. The machine
direction width of the shoe can vary to suit conditions, but is
wide enough to develop a large area magnetic fleld. A reasonable
minimum width is about 4" with a maximum of about 18". The cross
machinP direction width of the shoes can vary from narrow up to the
full width of the machine. The full width shoe should be flexible
with cross machine direction to conform to irregularities in the
belts, felts, web and mating faces of the roll and magnet core. If
desired the shoes can be spaced up to 6" apart.
As explained above, as the metal rolls rotate through
the magnetic field, heat is generated which can be helpful in wet
presses. If heat is not wanted the rolls can be laminated as shown
in FI~,. 13 and as described above.
From the above description it should be understood
that this invention provides extended nip presses for treating
wet or dry fibrous webs wherein nip loading is created or augmented
by electromagnets having cores acting only through minimum gaps
creating the flux lines across the entire wide nip area which
pull opposite sides of the nips toward each other to establish
~he desir~d nip loading throughout the entire width and length of
the extended nip.
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