WO1994005833A1

WO1994005833A1 - Method for fabricating and electroconducting plate, means for implementing such method and conducting plate thus obtained

Info

Publication number: WO1994005833A1
Application number: PCT/FR1993/000812
Authority: WO
Inventors: Pierre Berthe; Yves Duthoit; Martial Legardez
Original assignee: Batiss Plastiques, S.A.
Priority date: 1992-09-08
Filing date: 1993-08-16
Publication date: 1994-03-17
Also published as: DE69316582T2; ATE162558T1; JPH07500879A; EP0611402A1; FR2695411B1; DE69316582D1; FI101982B; FI942121A0; FI942121A; EP0611402B1; KR100199222B1; AU4963993A; JP2821816B2; FI101982B1; FR2695411A1; ES2114067T3

Abstract

The invention relates to a method for fabricating an electroconducting plate (1) provided with a protection device comprising at least one of the protection elements which are a batten and an insert, said method being characterized in that the fabrication and the fixing of both the batten and the insert are achieved in a single operation and regardless of the specificity of the insulating material used for the protection elements of each type; to this effect, a thermoplastic material specific to the corresponding protection element is injected in each half-shell (11, 12) while controlling for each injection point at least the injection speed, the pressure and the temperature of the injected material.

Description

METHOD FOR MANUFACTURING AN ELECTRICALLY CONDUCTIVE PLATE. The means relates to a method of manufacturing an electrically conductive plate, provided with a protection device, which plate finds particular application as a cathode for the refining of metals.

It also relates to the means for implementing this process and to the conductive plate thus obtained.

For the refining of metals, such as the production of zinc, it is known to use an electrolysis process.

To this end, in an electrolytic cell containing the material in the form of an ionic solution, at least one conductive plate is immersed which is polarized and on which plate is formed a deposit obtained by migration of certain ions on the plate.

Conventionally, a conductive plate has at its upper part means for suspending it in the electrolytic bath, means for allowing its manipulation and means for electrical connection to a current line.

After a determined electrolysis time, the plate is covered on both sides with a layer of electrolysed material.

The layers of material are recovered by detaching these layers.

To facilitate this detachment, the device for protecting the plate comprises at least one of the protective elements which are, on the one hand, a protective element, hereinafter called a strip made of an electrically insulating material, possibly split in several sections lining at least the side edges of the plate and which prevents the deposition of material on the edges and, therefore, the connection by a material bridge of the layers of material deposited on both sides and, on the other hand , at least one other protective element below called insert made of an insulating material, housed in the thickness of the plate, in a predetermined area of this plate which generally is located in the upper part of this plate and will be partially covered by the layer of material to allow priming peeling off said layer of material using a generally wedge-shaped tool.

Specifically, this second protective element called insert facilitates the insertion of the tool behind the layer of material and prevents the said tool from damaging or scratching the conductive plate which would then be unusable.

The main problems in making these conductive plates lie in the qualities of the connection between each protective element and the conductive plate.

This connection must, on the one hand, be watertight to prevent the formation of material deposits between the plate and the protective element and, on the other hand, be sufficiently resistant mechanically to guarantee good impact resistance in particular during the initiation of detachment.

These quality problems of the connection are common to the two types of protection elements, that is to say to the battens and to the insert, but at different levels because these two types of protection elements do not undergo the same constraints.

It will also be noted that, for the same reasons, it is preferable to use different materials for the manufacture of the insert and the battens. In the prior art, to ensure this connection, it is known to fix the battens using glue but, if the seal is relatively good, the mechanical resistance is excessively low.

According to another known method, the conductive plate is pierced with a plurality of holes and the battens are fixed with plastic rivets.

Unfortunately, if the connection is mechanically good, the seal is poor. We also know (US-A-4,207,147) a method of manufacturing a conductive plate which, for fixing each strip, comprises the following steps:

- along the edges of the plate which are to be filled, drilling of a plurality of holes opening onto the two faces of the plate,

- laying of a preformed U-shaped strip so as to cover the edge of the plate then,

- concomitantly, heating the batten and pressure on either side of the branches of the U of the batten so as, on the one hand, to soften the material constituting the batten and, on the other hand, to make it flow in the holes for , after cooling, thus form an anchorage ensuring the mechanical connection. If this type of process provides good results, it is expensive.

Conductive plates having anchors are also known from documents DE-A-3219300 and US-A-

4357225 but the embodiment does not take into account the specific characteristics of the insert or the strip because precisely the strip and the insert are in one piece

(US-A-4357225).

If the plate protection device includes both types of protection elements, independently of the batten fixing operations, the insert fixing operations must be carried out by a separate process.

Thus, conventionally, to produce a conductive plate provided with a protection device consisting of at least one protection element, whatever the type

a zone is determined for each protection element which, when the corresponding element is fixed on the plate, will be covered with said protection element, - in each of the zones thus determined, at least one orifice is pierced through the conductive plate and , then, each protective element is fixed to the conductive plate so that the two parts each adjoining one of the two faces of the plate are interconnected by bridges of material passing through the aforementioned holes and for this,

- For a conductive plate of determined dimensions and shape, two main half-molds are constituted, each comprising at least indirectly means for positioning the plate as well as at least in a predetermined location to correspond on the plate to the areas which will be covered by the protective element at least one molding half-shell and,

- the said protective element is molded onto the plate, which is why:. the two half-molds are moved aside, the conductive plate is positioned between the half-molds,

. we close the half-molds and. a thermoplastic material is injected,. we then remove the half-molds and,. we remove the plate.

One of the results which the invention aims to obtain is a method of manufacturing a conductive plate of the aforementioned type which overcomes in particular the problems mentioned above.

To this end, it relates to such a process notably characterized in that:

- a single operation is carried out, manufacturing and fixing both the battens and the insert, regardless of the specificity of the insulating material used for the protective elements of each type and, for this,

- A thermoplastic material specific to the corresponding protective element is injected into each half-shell by controlling for each injection point at least the injection speed, the pressure and the temperature of the injected material. The invention will be clearly understood on reading the description below made by way of nonlimiting example with reference to the appended drawing which schematically represents: FIG. 1: a front view of a conductive plate,

FIG. 2: a section along II-II of FIG. 1,

- Figure 3: a section on III-III of Figure 1,

- Figure 4: a simplified view of the means for implementing the method, - Figure 5: a view of a detail of the unfinished plate.

Referring to the drawing, we see that the conductive plate 1, used for refining a material such as zinc, has, conventionally, the shape of a rectangular parallelepiped and has in its upper part means 2 for its suspension in an electrolytic cell, its manipulation and its electrical connection in order to polarize it.

This conductive plate is provided with a protection device.

This protective device consists of at least one of the protective elements (4, 5) that are on the one hand, a protective element (4), hereinafter called a strip made of an electrically insulating material, possibly split in several sections lining at least the side edges of the plate and which prevents the deposition of material on the edges and, therefore, the connection by a material bridge of the layers of material deposited on both sides and, on the other hand , at least one other protective element (5) hereinafter called an insert consisting of an insulating material, housed in the thickness of the plate, in a predetermined area of this plate which generally is located in the upper part of this plate and will be partially covered by the layer of material to allow to initiate the detachment of said layer of material using a generally wedge-shaped tool. The insert is housed in the plate so that the visible faces 6 of this insert are coplanar with the two faces 7 of the plate.

Conventionally, for its realization: - a zone 8, 9, 10 is determined for each protection element which, when the corresponding protection element is fixed to the plate, will be covered with said protection element, which zones are called lateral 8 , 9 for the battens and upper 10 for the insert,

- in each of the zones thus determined, at least one hole is drilled through the conductive plate and,

- Each protective element 4, 5 is fixed on the conductive plate 1 so that the parts of the protective element adjoining the faces of the plate are interconnected by members 4a, 5a fitting into the aforementioned holes.

Preferably, the material constituting the batten is different from that used for the insert but, in all cases, the material used for the manufacture of the protective elements is electrically insulating and chemically resistant to the ionic solution.

For example, for the refining of zinc, the conductive plate is made of aluminum but its composition may be different, in particular in the case of any other type of metal production by electrolytic deposition. Conventionally:

- For a conductive plate of determined dimensions and shape, two main half-molds 11, 12 are constituted, each comprising at least indirectly means for positioning the plate as well as at least at a predetermined location to correspond on the plate to the zones which will be covered by the protective element at least one half-shell 13, 14 of molding and, - said protective element is molded on the plate, which is why:

. we discard the two half-molds 11, 12, . the conductive plate 1 is positioned between the half-molds,

. we close the half-molds and. a thermoplastic material is injected,. the thermoplastic material is at least partially cooled,

. we then remove the half-molds and,. we remove the plate.

The insert and / or the battens are therefore produced by the injection molding technique. According to the invention:

- A thermoplastic material specific to the corresponding protective element is injected into each half-shell by controlling for each injection point at least the injection speed, the pressure and the temperature of the injected material.

In the case of the insert, on each of the faces of the plate, over the entire section occupied by the insert and over a depth determined so as to preserve a sufficiently thick core to ensure sufficient resistance to the stresses of a wedge-shaped tool , a counterbore is made and the said core is pierced with a plurality of through holes 17a, 17b whose sizes and arrangement in space are determined so as to tend towards an equal distribution of the material over the entire surface of the insert and ensure perfect solidarity with the plate.

Advantageously, the closing pressure is adapted for each group of half-shells. The material intended for producing the insert is injected at low speed and under low pressure to avoid, on the one hand, the deformation of the core and, on the other hand, the appearance of grooming at the periphery. Also, the material intended for the insert is injected into the center of the corresponding half-shell and, in order to tend towards an equal distribution of the material over the entire surface of the insert, the holes drilled in the core are distributed according to a size going decreasing towards the outside.

For this distribution, preferably, a central hole 17a is produced in the core and around it, distributed over at least one circle, a series of peripheral holes 17b of smaller diameters than the central hole 17a.

Advantageously, the edges of the counterbore in which the insert is housed are chamfered.

The means for implementing the method include: - two half-molds 11, 12, each comprising means for positioning the plate and as many half-shells 13, 14 as there are protective elements 4, 5 to realize, means 19 for controlling the closing pressure of each group of half-shells.

In the case of plates provided with protection elements of two different types, the means further comprise at least two independent injection groups with their means for controlling the injection speed, pressure and temperature.

Advantageously, each injection nozzle of each injection group is connected to each injection point of the half-shells by a thermoregulated hot channel 21.

Advantageously, at least the half-shells for the overmolding of the battens have a lip 30 which extends slightly outside the volume which will be filled with the molding material, which lips under the effect of the closing pressure penetrate slightly. in the conductive plate and thus avoid, on the one hand, having to rectify the plate before molding and, on the other hand, the cloth of the material.

The conductive plate thus obtained is remarkable in that the protective elements are molded onto the plate which, in the covered areas, has holes for anchoring the material.

In the case of the insert, it is further characterized in that it is provided in a predetermined area with two counterbores 15 each accommodating a fraction of the insert and the depth of which preserves a core 16 whose thickness is sufficient to provide mechanical rigidity to the mechanical stresses usually exerted by a wedge-shaped tool. According to the invention, at the insert, the core is traversed by a central hole 17a and comprises a plurality of other holes 17b which, distributed over the entire section, are of decreasing size going towards the outside .

According to the invention, the edges of the counterbore housing the insert has a chamfer 24.

Advantageously, this chamfer increases the seal at the insert when the material is removed during cooling.

According to another characteristic of the invention, the orifices of the core are distributed at a predetermined angular pitch and, for example, are distributed in two concentric circles at an angular pitch of 45 °, the orifices of a circle being angularly offset about 22 ° 5 compared to those of the other circle. The area of material preserved from the core is greater than the sum of the areas of the cutouts.

In an exemplary embodiment, for a conductive aluminum plate seven millimeters thick:

- the depth of the counterbore is two millimeters, - the thickness of the core is three millimeters, the central hole is twenty millimeters in diameter,

- the first series of holes is eight millimeters in diameter and, - the second series of holes six millimeters in diameter. The thermoplastic used for the insert is preferably polypropylene loaded with 30% glass fiber.

The thermoplastic used for the battens is, for example, an unfilled polypropylene.

The process developed for equipping battens and protective inserts provides the following advantages:

- the use of a bi-injection machine allows the complete covering of a cathode to be carried out in a single operation, the use of a dimensioned hydraulic closing machine makes it possible to use the cathode as an insert and to ensure an adjustable and constant locking force in order to respond to variations in thickness and small surface irregularities of the cathode as well as to control any creep of the aluminum plate used as an insert,

- the mold design will allow the molding of the two battens as well as the protective insert, - the thermoplastic injection process makes it possible to apply the material very intimately on the aluminum plate in order to avoid infiltration of zinc during electrolysis which have the effect of tearing off the battens and the protective insert over time; moreover, the molding operation makes it possible to follow all the surface irregularities and to drown the hanging holes by making them integral with the batten,

- the injection process does not require precise machining in the bores determining the protective insert as well as for the perforated holes ensuring the good behavior of the battens,

- the injection process also makes it possible to choose different thermoplastics of low density, charged or uncharged, colored or non-colored, - the injection process gives a lifetime of the thermoplastic equipment close to that of the cathode with as benefits :

. process reliability, . economic cost of assembly,. extremely low maintenance cost,. productivity improvement,. recycling of cathodes in the event of incidents,. increase in the active surface of the cathodes by reduction in the width of the battens.

Claims

CLAIMS 1. Method for manufacturing an electrically conductive plate, provided with a protection device, which protection device consists of at least one of the protection elements (4, 5) which are on the one hand, an element protection, hereinafter called a strip made of an electrically insulating material, possibly split into several sections lining at least the lateral edges of the plate and which prevents the deposition of material on the edges and, therefore, the connection by a material bridge of the layers of material deposited on the two faces and, on the other hand, at least one protective element (5) hereinafter called an insert made of an insulating material, housed in the thickness of the plate, in a predetermined area of this plate which generally is located in the upper part of this plate and will be partially covered by the layer of material to allow initiation of the separation of said layer of material using a generally wedge-shaped tool, in which process:

- A zone (8, 9, 10) is determined for each protection element which, when the corresponding protection element is fixed on the plate, will be covered with said protection element, which zones are called lateral (8, 9) for the battens and upper (10) for the insert,

- Each protective element (4, 5) is fixed on the conductive plate (1) so that the parts of the protective element adjoining the faces of the plate are interconnected by members (4a, 5a) s' inserting into the aforementioned holes, and in which process: - for a conductive plate of determined dimensions and shape, two main half-molds (11, 12) are constituted, comprising at least indirectly each of the means for positioning the plate as well as at least in a predetermined location to correspond on the plate to the areas which will be covered by the protective element at least one half-shell (13, 14) of molding and, - said protective element is molded on the plate, which is why:

. we discard the two half-molds (11, 12),. the conductive plate (1) is positioned between the half-molds. we close the half-molds and

. a thermoplastic material is injected, the thermoplastic material is at least partially cooled,

. we then remove the half-molds and,. the plate is removed, this process being CHARACTERIZED in that:

2. Method according to claim 1 characterized in that one adapts the closing pressure for each group of half-shells.

3. Method according to claim 1 characterized in that, in the case of the insert, on each of the faces of the plate, over the entire section occupied by the insert and over a depth determined so as to preserve a sufficiently thick core to ensure sufficient resistance to the stresses of a wedge-shaped tool, a countersink is made and the said core is pierced with a plurality of through holes (17a, 17b) the sizes and arrangement of which in space are determined so as to strive for a equal distribution of the material over the entire surface of the insert and ensuring perfect solidarity with the plate.

4. Method according to claim 1 characterized in that the material intended for the production of the insert is injected at low speed and under low pressure to avoid, on the one hand, the deformation of the core and, on the other hand, the appearance of grooming on the periphery.

5. Method according to claim 4 characterized in that the material intended for the insert is injected into the center of the corresponding half-shell and, in order to tend towards an equal distribution of the material over the entire surface of the insert, the holes drilled in the core are distributed according to a decreasing size towards the outside.

6. Means for implementing the method according to claim 1 comprising a conductive plate (1) provided, on the one hand, on at least two of its edges (3) with a protective element (4) in the form of U said batten (4) whose branches (4b, 4c) cover said edges and, on the other hand, in a predetermined area of another protective element (5) said insert, in two parts, each housed in a fraction of the thickness of the plate so that the visible faces (6) of this insert (5) are coplanar with the two faces (7) of the plate, these means being characterized in that they further comprise:

- two half-molds (11, 12), each comprising means for positioning the plate and as many half-shells (13, 14) as there are protective elements (4, 5) to be produced,

- Means (19) for controlling the closing pressure of each group of half-shells.

7. Electrically conductive plate provided, on the one hand, on at least two of its edges (3) with a protective element (4) in the form of a U said batten (4) whose branches (4b, 4c) cover the said songs and, on the other hand, in a predetermined area of another element (5) of protection said insert, in two parts, each housed in a fraction of the thickness of the plate so that the visible faces (6) of this insert (5) are coplanar with the two faces (7) of the plate, characterized in that that it is obtained with the method according to claim 1.

8. Electrically conductive plate according to claim 7 characterized in that, in the case of the insert, it is provided in a predetermined area with two countersinks (15) each housing a fraction of the insert and the depth of which preserves a core 16, the thickness of which is sufficient to provide mechanical rigidity to the mechanical stresses usually exerted by a wedge-shaped tool.

9. Electrically conductive plate according to claim 8 characterized in that at the level of the insert, the core is traversed by a central hole (17a) and comprises a plurality of other holes (17b) which, distributed over all the section, are decreasing in size going outwards.