Note: Descriptions are shown in the official language in which they were submitted.
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CAPPING BOARD
WITH PULTRUDED FILLING BARS
BACKGROUND OF THE INVENTION
a) Field of the invention
The present invention relates to improvements made to the
invention disclosed and claimed in U.S. patent No. 4,213,842 issued on
July 22, 1980 and Canadian patent No. 1,102,737 issued on June 9, 1981,
. both in the name of the present inventor.
More particularly, the invention relates to an improved capping
board incorporating puitruded filling bars.
b) Brief descriation in the prior art
In the hydro-metallurgical industry, it is of common practice to
electrically refine some metal in electrolytic cells especially devised for
this
purpose. Usually, the metal to be refined, or the metal used to carry the
electric current, is in the form of plates of a given thickness which are
provided
at their upper end with two laterally extending projections. Such projections
facilitate gripping, handling and hanging of the plates on the lateral
sidewalls
of the cells. In use, the plates, which can each weight several hundred
pounds,
are immersed into the cells in parallel relationship and are used as anodes,
cathodes or both, depending on the affinity of the metal being refined.
In order to avoid damage to the masonry or concrete forming the
lateral side walls of the cells during the insertion and removal of the
heaving
electrodes, it is a common practice to place a protective member, called
"capping board", onto the top surface of each lateral sidewall of the cells.
Such capping boards serve not only as a support but also as an insulator for
the plates used as anodes or cathodes. Such capping boards also serve to
position the plates with respect to each other and some of them may also be
used as electric insulators between adjacent cells and/or the ground.
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U.S. patent No. 4,213,842 and its Canadian counterpart
No. 1,102,737 discloses and claims a capping board made of plastic material
reinforced with glass fibers, which capping board is resistant to compression,
abrasion, moisture, heat and corrosion and thus particularly useful to meet
the
industry requirements in terms of low costs, life span and reduced
maintenance. More particularly, these patents disclose and claim a capping
board molded from a plastic resin selected from the group consisting of
polytetrafluoroethylene and polyester, vinylester, epoxy and phenolic resins
resistant to corrosion by acids, to which are added from 10 to 20% by weight
of glass fibbrs, from 2 to 10% by weight of silica, from 2 to 10% by weight
of mica and from 2 to 10% by weight of feldspar.
According to a preferred embodiment of the invention disclosed
in these patents, the glass fibers are in the form of a pressed mat or a woven
cloth. This mat or cloth is impregnated with the selected resin in which mica
has been added, and then is folded or layered in a mold so as to form a
plurality of layers and give the desired shape to the capping board. During
the
folding operation, the cloth is reimpregnated with the selected resin and the
silica mixed with the resin, in order to ensure a perfect adhesion between the
layers.
According to another preferred embodiment of the invention
disclosed in these patents, one or more wooden bars can be embedded in the
capping board in order to reduce the quantities of resin and additives that
are
necessary for obtaining a thick capping board. Such use of wooden bars has
proved so far to be very interesting in terms of manufacturing cost reduction.
However, it has also proved to be a source of problems, especially because of
their shrinkage on the overall length of the board, their lack of structural
strength over the time, and their poor heat-conductive properties which
prevent heat dissipation and may be the source of unwanted burning.
SUMMARY OF THE INVENTION
it has recently be discovered that the above mentioned problems
encountered with the capping boards incorporating wooden bars, can easily be
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solved if use is made of filling bars obtained by pultrusion and covered with
a
surface layer of a resin bonding agent.
Thus, the present invention provides an improved capping board
for supporting electrodes immersed into an electrolytic cell.
This improved capping board is molded from a plastic resin
selected from the group consisting of polytetrafluoroethylene and acid
resistant
polyester, vinylester, epoxy and phenolic resins, to which are added from 3 to
30% by weight of glass fibers, from 2 to 10% by weight of silica sand, from
2 to 10% by weight of mica and from 2 to 40% by weight of silica rocks in
the form of' particles of a size preferably ranging from 1 /16" to 1 /8" .
Like all the existing capping boards, the improved capping board
also comprises at least one and preferably two or more filling bars embedded
in it.
In accordance with the invention, the capping board is improved
in that every bar embedded in it is a pultruded bar obtained by pultrusion of
glass fibers selected from the group consisting of glass fibers, cizal fibers
Kevlar~ fibers and carbon fibers, with a resin selected from the group
consisting of polyester, vinylester, epoxy and phenolic resins and their
mixtures, the pultruded bar being further coated with a surface layer of a
resin
bonding agent, like silane.
The bars that are so embedded act not only as a filled but also
as a reinforcing material for the capping board.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention and its advantages will be better understood upon
reading the following non-restrictive detailed description made with reference
to the accompanying drawings, wherein the single figure is a perspective view
of a cut portion of a capping board according to a preferred embodiment of the
invention.
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DETAILED DESCRIPTION OF THE INVENTION
Like all the existing capping boards, the improved capping board
1 according to the invention is intended to be used as a support for the
electrodes of electrolytic cells. More particularly, it is intended to be
positioned
on the top surface of the lateral sidewall of a cell vn which electrodes are
hanged, in order to protect said top surface from shocks occurring when
handling the electrodes and to avoid damage caused by the heavy weight of
the electrodes.
~~ The improved capping board 1 comprises a flat bottom surface
11 and preferably, as is shown, a plurality of laterally opening compartments
13 of different depths into which the lateral projections of the electrodes
may
be inserted and held.
The improved capping board is made of a plastic resin 3 selected
from the group consisting of polytetrafluoroethylene, acid resistant
polyester,
polyvinylester, epoxy and phenolic resins, and blends of such resins, tv which
' from 3 to 30% of glass fibers, from 2 to 10% of silica sand and from 2 to
40% of silica rocks 6 in the form of particles, have been added.
The plastic resin can be polytetrafluoroethylene. It can also be an
acid-resistant polyester resin, like those sold by the firm REICHHOLD
CHEMICbLS LTD. under the trademarks POLYLITE 31,02 alld 31,830, or by the
firm ALPHA OWENS CORNING under the tradenames V21-053 and E 650.
Any other high temperature and acid resistant epoxy resin, vinylester resin or
phenolic resin can also be used.
In practice, use is preferably made of an acid-resistant polyester
resin because this resin is less expensive in addition of being easy to handle
and providing good material stability:
The glass fibers that are used are preferably 1 to 2 inches long.
Alternatively, use can be made of a woven glass fibers civth in order to
facilitate formation and molding of the capping board, or of a chopped glass
fiber mat containing from 1 to 2 ounces of fiber per square foot. Preferably,
use can be made of a combination of a woven glass fiber cloth and a pressed
glass fiber mat in order to obtain a~good laminate quality.
..
As silica sand, use can be made of the one sold by the firm
INDUSTMIN LTD.
As mica, use can be made of the mica flakes sold under the
trademark SUZORITE.
The fabrication of the capping board according to the invention
can be carried out by any conventional casting method. Preferably, such
fabrication is carried out in a mold having the desired final shape of the
capping board.
In order to facilitate extraction of the capping board after
molding, a mold releasing agent such as for example, polyvinyl alcohol, can be
used. Such releasing agent can be introduced in the resin as an additive.
Alternatively, wax or an equivalent thereof can be previously spread onto the
surfaces of the mold.
Before casting the capping board, the mica is incorporated into
the resin and mixed with the same. Such is preferably carried out a few hours
before using the resin. This improves the homogeneity of the resulting capping
board by facilitating elimination of the air bubbles created by the
introduction
of the mica into the resin. Advantageously, a resin bonding agent can also be
added to the resin at this stage. This bonding agent is preferably a silane
like
the one sold by DOW CORNING under the tradename Z 6032 or those sold by
CHEMLOCK.
A catalyst is introduced into the resin and mixed with the same
just before it is used in order to accelerate hardening of the same. As
catalyst,
use can be made of any conventional catalyst compatible with the selected
resin, such, as for example, methyl ethyl ketone peroxide in an amount ranging
of from 0 to 1 % by weight relative to the total weight of the resin.
In use, the glass fibers are impregnated with the mixture of the
resin with the mica, while the other additives are added. if needed, a
dilution
agent or solvent can be introduced in the resin to dilute the same and reduce
its viscosity. Such facilitates the impregnation of the glass fibers and
improves
the homogeneity of the resulting capping board. Any conventional dilution
agent compatible with the selected resin can be used as the solvent. The
amount of solvent to be used depends on the viscosity desired for the resin.
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This amount preferably ranges from 0 to 1 % by weight relative to the total
weight of the resin.
In order to ensure complete impregnation of the glass fibers and
to remove any air bubbles that may be formed therein, the glass fibers can be
mechanically pressed or, when using a cloth, manually folded, rolled or
brushed.
After impregnation of the fibers, the capping board is shaped. To
do so, the impregnated glass fibers can be pressed, folded, rolled or brushed
in the mold until the desired final shape is obtained.
~ During this shaping, the silica sand, the particles of silica rocks
and the other additives are introduced into the resin by dusting, as the mold
is filled up or, when use is made of a cloth ~f glass fibers, at every folding
of
the cloth.
To ensure a perfect homogeneity of the additives in the resin, the
silica sand and rock particles may advantageously be impregnated within same
resin before being introduced between the layers of impregnated glass fibers.
In order to reduce the amount of resin, glass fibers and additives
needed to produce a desired shape of the capping board, one or more bars 7
are introduced as a reinforcement into the resin during the molding.
(n accordance vvith the invention, such bars consist of pultruded
bars obtained by pultrusion of fibers selected from the group consisting of
glass fibers, cizal fibers, resin fibers like Kevlar° fibers and carbon
fibers, with
a resin selected from the group consisting of polyester, vinylester, epoxy and
phenolic resins and their mixtures.
For obvious economical reasons, use is preferably made of
continuous glass fibers or cizal fibers.
Still preferably, use is made of glass fibers and of a high heat
distorsion isophthalic polyester, and the puitrusion is carried out with 15 to
40% by weight of a low curing polyester like the one sold by REICHHOLD
under the tradename 31-022 and 60 to 85% by weight of glass fibers under
a pressure of about 1200 Ibs at a temperature of 150 to 350°F.
Such conditions of pultrusion cause the selected polyester resin
to cure in a very fast manner.
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In accordance with a very important aspect of the invention, the
pultruded bars that are so-obtained are coated with a surface layer of a resin
bonding agent prior to being inserted into the capping board resin. Such a
coating is preferably made after sanding and washing of the external surfaces
of the bars in order to improve adherence. The resin bonding agent is
preferably the same as previously incorporated into the resin mixtures, namely
a silane like the one sold by DOW CORNING under the tradename Z 6032 or
those sold by CHEMLOCK.
in use, the pultruded bars are inserted into the capping board
during fabrication of the same in such a manner as to be completely embedded
in the resin and covered by a protective layer of from 0.06 to 1 inch in order
to avoid direct contact between the embedded bars, the electrodes made of
metal to be refined and the electrolyte used in the cell.
The number and the shape of the pultruded filling bars that mNst
be used is dependent on the thickness of the desired capping board.
Preferably, the dimensions of the bars will be about (0.1 or .75) x 1 x (30 to
216) inches. Such bars are preferably spaced apart and positioned in parallel,
staggered position within the capping board so as to extend over the full
length
of the capping board.
The general shape and size of the capping board 1 manufactured
in this manner can vary within a large range, depending on the consumer's
requirements. Generally, these capping boards 1 are cast in a single piece
having the length of the vertical sidewalis of the cells on which they Ne.
This
length usually ranges from 10 to 20 feet depending on the size of the
electrolytic cells.
The capping boards 1 are also preferably cast so as to have
substantially the same width as the sidewalis of the cells which width usually
ranges from 3 to 7 inches, typically from 3 to 6 inches.
The shape of the capping boards 1 only depends on the
consumer's requirements and the electrolytic refining method that is used.
Thus, there could be no compartment 13. Alternatively there could be more
CA 02171412 2005-08-29
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compartments 13 of different shape.
As aforesaid, the location of the pultruded bars embedded in the
capping board resin, depends on the shape of the capping board and on the
thickness thereof. The size and shape of the bars may also. vary according to
the final shape and thickness of the capping board. Thus, for a capping board
as shown in Fig. 1, the bars 7 are of the same dimensions and extends along
the length of the capping board. Under some circumstances, shorter bars
extending vertically in the partitions between the compartment 13 of
transversally within the same partitions could also be used.
' As can be understood, the width of the cappirig boards depends
on the thickness of the top surfaces of the sidewalis of the cells and their
height and structure are selected so that the boards may resist the combined
weight of the electrodes, which may amount to several tons.
The improved capping board according to the invention, like those
disclosed in the above mentioned prior art references, are resistant to the
chemical compounds used as electrolyte, such as sulphuric acid and
chlorine. They are also capable of resisting to peak temperatures up to
230°C
or sometimes up to 260°C which can occur in the case of a short circuit
during the electrolytic operation.
In addition, they also have numerous other advantages directly
associated to the use of pultruded filling bars in the place of wooden cores,
as
was done before.
Because of their pultruded structure and their coating with a
bonding agent, the puitruded bars form an integral part of the capping board
according to the invention. Indeed, they are added to the capping board resin
while the same is still in a liquid form, before curing.
The use of such rigid pultruded bars as compared to the use of
wooden cores, is a source of quality improvement, Indeed, they add rigidity to
the product, making it almost unbreakable. They also prevent overall length
curving and they eliminate shrinkage on the overall length of the capping
boards. Such is an important gain for the metal refining plants, as they are
using precise dimensions from center to center of their anodes and their
cathodes.
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The use of pultruded bars has numerous further advantages:
- they increase the life-span of the capping boards and thus
reduce the maintenance and replacement cost for the consumers;
- they improve the final qualities of the refined metal by
reducing the amount of impurities contained in the final product;
- they keep the electrodes in the right exact refining position
as shrinkage is eliminated;
' - as compared to the previous wooden cores, they are not
subject to microscopic crackings which allow the electrolyte acid solutions to
penetrate them, thereby making them non-insulating; and
- thanks to their structure and composition, they allow heat
transfer in the case of a short-circuit in the refining operation and prevent
burning of the capping boards.
Therefore, the use of pultruded bars obviously has a numerous
advantages, which make the capping boars trouble-free for about eight to
twelve years of operation.
