|Title of Invention||
"ALUMINUM CATHODE BASE PLATE WITH INSERT OF DIELECTRIC MATERIAL"
|Abstract||There is provided an aluminum cathode base plate which has an insert of dielectric material at an upper edge thereof, in the vicinity of the solution line of the electrolytic cell when the cathode is placed into such cell for the purpose of electrodeposition of zinc. The insert has a flat surface which is raised or projected above the surface of the aluminum base plate by a distance of 0.5 mm to 1.5 mm on both sides of the base plate. In this manner, when the stripping knife strikes the dielectric insert during stripping of the electrodeposited zinc sheets and then penetrates between the zinc sheets and the aluminum base plate, it will not hit and damage the perpendicular interface between the dielectric insert and the aluminum base plate. This will avoid rapid deterioration of the base plate and will significantly improve its life span.|
|Full Text||BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to an aluminum cathode base plate used in the electrodeposition of zinc sheets and subsequent stripping or peeling of the electrodeposited zinc sheets therefrom., In particular, the invention relates to a cathode base plate provided with an insert of dielectric or insulating material at an edge of the base plate in the vicinity of the solution line of the electrolytic cell. 2. Brief Description of the Prior Art
It is generally known in the art to provide aluminum cathode base plates with inserts of dielectric material so that the blades of the stripping knife would first strike the dielectric surface and then penetrate between the zinc sheets and the cathode base plate in order to strip the zinc sheets from the latter. This is disclosed, for example, in applicant's Canadian patent application No. 2,178,776 filed June 11, 1996 entitled "Method and Apparatus ror Automated Stripping of Zinc Sheets from Aluminum Cathode Base Plates".
Such prior art base plates use dielectric or insulating inserts which are essentially flush with the adjacent surface of the plate as disclosed, for example, in Canadian patent No. 1,169,025 issued June 12, 1984.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved aluminum cathode base plate wherein the surface of the insert of dielectric material is raised with reference to the adjacent surface of the plate.
Another object of the present invention is to provide an insert which has a predetermined shape and protrusion, particularly in the area where the knifes penetrate between the zinc sheets and the cathode.
Other objects and advantages of the present invention will become apparent from the following description of the invention.
In conventional aluminum cathode base plates, where the dielectric inserts are flush with the base plate, the base plate has a life span of less than 200 strips and thus remains in service approximately 12-13 months. Thus, such base plates must be replaced approximately once a year at a cost usually exceeding one million dollars, depending on the size of the zinc plant.
The failure of aluminum cathode base plates with flush dielectric inserts has been identified as being produced by a gradual opening of the interface between the insert and the adjacent aluminum surface; this is the interface which is perpendicular to the surface of the base plate. When the base plates with flush inserts are stripped by the stripping machine, the knife travels across the interface and, over a period of cycles, pushes back the aluminum and opens up the interface. Zinc is
electrodeposited in the interface after every strip and when it is subsequently stripped, it further damages the interface. Eventually the interface becomes so wide,that the stripping knives are prevented from peeling the zinc deposit. The cathode base plate must thus be removed from service prematurely because of its inability to be stripped by the automated stripper.
The applicant has surprisingly found that this deficiency can be readily obviated by raising the level of the dielectric insert slightly above the surface of the aluminum cathode, so that the knife will still penetrate between the cathode and the zinc sheet, but will not strike the perpendicular aluminum-dielectric interface when doing so. This protrusion of the flat surface of the dielectric insert is usually between 0.5 mm and 1.5 mm over the aluminum base plate surface and most preferably about 0.8 mm. Although, to simplify the installation of the dielectric insert, the entire insert surface may be so raised, it is sufficient to raise only the area where the knifes penetrate between the cathode base plate and the zinc sheets, while the remainder of the insert may be essentially flush with the cathode plate.
Although a dielectric insert of any suitable shape can be used in conjunction with the present invention, it has been found that an insert having the shape of a teardrop is especially advantageous. The area where it extends furthest into the base plate is made to
correspond with the spot where the knife penetrates between the plate and the zinc sheets to strip the latter and at least this area is made to project above the surface of the aluminum cathode as indicated above.
/ACCOMPANYING BRIEF DESCRIPTION OF THE/DRAWINGS
The invention will further be described with reference to the accompanying drawings in which:
Fig. 1 shows a plan view of an edge portion of an aluminum cathode base plate according to an embodiment of the present invention;
Fig. 2 shows a section view along line A-A of Fig. 1;
Fig. 3 shows a plan view of an edge portion of an aluminum cathode base plate according to another embodiment of the present invention;
Fig. 4 is a section view along line D-D of Fig. 3; and
Fig. 5 shows a stripping machine for automatically stripping zinc sheets from the base plates of the present invention.
DETAILED DESCRIPTION OF THE INVENTION In all figures, the same elements are identified by the same reference numbers.
Portion 10 of the aluminum cathode base plate illustrated in Fig. 1 and Fig. 3 is in the area also shown in Fig. 5 as portion 10 of the aluminum cathode base plate 12. According to one embodiment of the
invention the upper edge of the base plate 12 is provided with an elongated, generally parabolic insert 14 of a dielectric material having a shape of a tear-drop. , Although this is a preferred shape of the dielectric insert, any other suitable shape may also be used.
As shown in Fig. 2, the insert 14 is so mounted on plate 12, that it projects over the surface of plate 12 by a distance illustrated by arrows C-C which may, for example, be 0.8 mm. The dielectric material may, for instance be a polyester or a vinyl ester polymer, such as an epoxy-based vinyl ester with added elastomer, however, any suitable dielectric resin material that can be properly shaped and mounted would be satisfactory. Preferably the resin material is used with inert fillers, such as silicon based fillers. The projection C-C should be provided at least in the area B of Fig. 1 where the stripping knife shown by broken lines 30 strikes in order to strip the zinc sheet deposited by electrolysis on the aluminum cathode base plate 12. During the electrodeposition, both sides of the base plate 12 are coated with zinc except for the portion 14 covered with the dielectric material and the side strips 16 also made of appropriate dielectric material and clipped, as is known in the art, on each edge of the cathode plate to prevent deposition of zinc on the edges, which would render automatic peeling or stripping impossible.
Dielectric insert 14 is mounted onto plate 12 in any suitable manner. One method is to machine the desired
area of the base plate to a smaller thickness and then coat this area with the dielectric material by resin transfer molding or compression molding. So that the dielectric material will be well anchored, one or a plurality of holes 18 (see Fig. 2) may be provided in the thinned down area, thus permitting interconnection of the dielectric material from both sides. The exact manner in which the dielectric material is applied is, however, not important, for the purpose of the present invention, so long as it is well mounted and fastened and has a predetermined projection as illustrated by arrows C-C in Fig. 2 at least in area B shown in Fig. 1. Also, as shown in Fig. 2, the edge 20 of the raised portion may be chamfered for instance at an angle of 45°.
Figs. 3 and 4 show another way of providing plate 12 with the dielectric insert 14. Here, a cut-out is made in the upper edge of plate 12 along line 15 shown as a broken line. The thinned down section of plate 12 is then formed only of the strip 17 which runs between the cutout line 15 and the edge of the raised portion 20. This strip 17 is provided with a plurality of holes 18 which permit interconnection of the dielectric material which is thereby connected with the plate 12 only within the area of strip 17 while the rest of the insert 14 remains a solid dielectric insert. This is particularly well illustrated in Fig. 4 which represents a cross section along line D-D of Fig. 3 and where the projection C-C is the same as in Fig. 2 and the edge 20 of the raised
portion is also chamfered.
Referring to Fig. 5, it shows an automatic stripping machine such as described in applicant's Canadian patent application No. 2,178,776, in which a plurality of aluminum cathode base plates 12, with zinc sheets electrodeposited on each side thereof, are suspended in parallel by their supporting bars 24 within the framework 26 and are then automatically stripped one by one by a stripping assembly 28 with knives 30 which swing in a predetermined sequence about a pivot 32. During stripping, the cathodes 12 are maintained in a straight position with the help of an arm 34 which is lowered simultaneously with the stripping assembly 28. Once the zinc sheets are stripped, they fall into the U-shaped trough 36 having a conveyor at its bottom which carries the stripped sheets out of the stripping machine. Area 10 on the aluminum cathode base plate 12 shown in Fig. 5 represents the gist of the present invention. When using standard plates where dielectric insert 14 is flush with the surface of the cathode 12, and operating the stripping machine as outlined above, no more than 200 strips could be achieved before the cathodes 12 had to be replaced. On the other hand, when using the same machine on the cathodes of the present invention with a 0.8 mm protrusion of the dielectric insert 10 above the surface of the cathode 12, over 360 stripping cycles have been achieved in 25 months of stripping and the cathodes are still in operation. Accelerated erosion tests have shown
that with such design, the cathode 12 is able to endure about 500 stripping cycles before the surface of the dielectric insert wears down to become flush with the aluminum surface. Thus, the life of the cathodes of the present invention may be more than doubled compared to those having flush surfaces of cathode and dielectric insert. This is clearly a significant advance in the art.
WE CLAIM :
1 1. An aluminum cathode base plate having an insert of dielectric material at an upper edge thereof, in the vicinity of the solution line of the electrolytic cell when the base plate is placed in such cell, said insert having a flat surface raised above the surface of the base plate by a distance such that a stripping knife will penetrate between the base plate and zinc sheets eiectrodeposited thereon without hitting the perpendicular interface between the aluminum cathode base plate and the dielectric insert, said insert being so raised at least in the area where said stripping knife strikes the insert prior to penetrating between the base plate and the zinc sheets eiectrodeposited thereon.
2. An aluminum cathode base plate according to claim 1,
in which the distance by which the surface of the
dielectric insert projects over the surface of the base
plate on each side of said base plate is between about
0.5 mm and 1.5 mm.
3. An aluminum cathode base plate according to claim 2,
in which said distance is about 0.8 mm.
4. An aluminum cathode base plate according to claims
1, 2 or 3, in which the raised edge of the dielectric
insert is chamfered in the region where it meets the
aluminum base plate.
5. An aluminum cathode base plate according to claim 4,
in which said raised insert is chamfered at an angle of
6. An aluminum cathode base plate according to any one
of the preceding claims 1 to 5, in which the curvature of
the raised dielectric insert where it meets the aluminum
cathode has the shape of a tear-drop, and the stripping
knife is adjusted to strike said insert in the area where
it projects furthest into the base plate.
7. An aluminum cathode base plate according to any one
of claims l to 6, in which the insert is made of an
epoxy-based vinyl ester polymer.
8. An aluminium cathode plate, substantially as herein
described, particulary with reference to the accompanying
There is provided an aluminum cathode base plate which has an insert of dielectric material at an upper edge thereof, in the vicinity of the solution line of the electrolytic cell when the cathode is placed into such cell for the purpose of electrodeposition of zinc. The insert has a flat surface which is raised or projected above the surface of the aluminum base plate by a distance of 0.5 mm to 1.5 mm on both sides of the base plate. In this manner, when the stripping knife strikes the dielectric insert during stripping of the electrodeposited zinc sheets and then penetrates between the zinc sheets and the aluminum base plate, it will not hit and damage the perpendicular interface between the dielectric insert and the aluminum base plate. This will avoid rapid deterioration of the base plate and will significantly improve its life span.
|Indian Patent Application Number||2057/CAL/1998|
|PG Journal Number||08/2007|
|Date of Filing||23-Nov-1998|
|Name of Patentee||FALCONBRIDGE LIMITED|
|Applicant Address||SUITE 1200, 95 WELLINGTON STREET WEST, TORONTO, ONTARIO, CANADA M5J 2V4|
|PCT International Classification Number||C25 C 7/02|
|PCT International Application Number||N/A|
|PCT International Filing date|