OA17446A - A cathode and method of manufacturing. - Google Patents

Abstract

An electrode for electrolytic processes, the electrode comprising a conducting bar and a plate attached to the conducting bar, wherein the conducting bar has a conducting member attached thereto to increase the conductivity of the conducting bar.

Description

This invention is concerned with an electrode for electrolytic processes. The invention is concerned particulariy, although not exclusively, with a cathode for an electrolysis process.

BACKGROUND OF THE .INVENTION

Cathodes for electrolytic processes consist of a conducting bar and a plate of stainless steel or titanium placed in an electrolytic solution hanging 10 from the conducting bar,

A problem with existing cathodes is that the conducting bar made of copper (which is a highly conductive métal) is welded to the stainless steel or titanium plate. The problem is that such a weld is difficult to produce and has bad résistance to acid mist which is produced, potentially resulting in the 15 weld being quickly corroded and the plate becoming detached.

A problem with replacîng the copper with a different métal is that there would be a significant voltage drop, this, multiplied by the number of eiectrodes in use and the high currents increases the operating costs substantially. One way around this is to coat a stainless steel conducting bar 20 in copper, however, the copper coating séparâtes from the stainless steel after a while due to the corrosion produced by the acid mist of the electrolytic operation, leading to a larger voltage drop.

Another prior art solution is to weld the stainless steel to the copper in a three part process where the first zone is formed of a copper-nickel alloy,

an intermediate zone of mostly a nickel alloy and a second zone of stainless steel-nickel. This results in a satisfactory solution but requires a spécial welding process using nickel électrodes.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the présent spécification is solely for the purpose of providing a context for the présent invention. It is not to be taken f

as an admission that any or ail of these matters form part of the prior art base or were common general knowledge in the field relevant to the présent invention as it existed before the priority date of each claim of this 10 application.

OBJECT OF THE INVENTION

It is an object of the invention to overcome or at least alleviate one or more of the above problème and/or provide the consumer with a useful or commercial choice.

Other preferred objects of the présent invention will become apparent from the following description.

SUMMARY OF THE INVENTION

In one form, although it need not be the only or indeed the broadest form, the invention résides in an electrode for electrolytic processes, the 20 electrode comprising:

a conducting bar; and a plate attached to the conducting bar, wherein the conducting bar has a conducting member attached thereto to increase the conductivity of the conducting bar.

Preferably, the electrode is a cathode. More preferably, the cathode can be used for electrolytic processes of copper production.

Preferably, the electrolytic processes are electrolytic processes of copper production. For example, copper electro refining or electro wlnning.

Preferably, the conducting bar is made of stainless steel. Altematively, the conducting bar may be made from another suitable métal or alloy, such as titanium. It will be appreciated that the conducting bar may also be referred to as a hanger bar. Preferably the conducting member is attached to the conducting bar by welding. The conducting bar preferably has an inside surface. Preferably the conducting bar is hollow. More preferably the conducting bar has a tubular shape that is made by roll forming.

Roll forming Is typically a continuous bending operation in which a long strip of sheet métal is passed through sets of rolls mounted on consecutive stands, each set performing only an incrémental part of the 15 bend, until the desired cross-section profile is obtained. Design of the rolls used in the roll forming operation typically starts with a flower formation, ~x which is the sequence of profile cross-sections, one profile for each stand of rolls.

Preferably the conducting member is made of copper or a copper alloy. Altematively, the conducting member may be made from another suitable métal or alloy having low resistivity. Typically the conducting member is welded to an inside surface of the conducting bar. Preferably the conducting member is welded to an inside surface of the conducting bar before the conducting bar is formed. For example, the conducting member is

welded to a sheet or plate which is then roll formed into a conducting bar.

Preferably the plate is made from stainless steel. Altematively, the plate may be made from another suitable métal or alloy, such as titanium.

Preferably the conducting bar is made from the same material as the plate. More preferably the conducting bar and plate are made of stainless steel. Typîcally the plate is welded to the conducting bar. Altematively, the plate may be integraliy formed with the conducting bar.

In one embodiment, the conducting bar may hâve a first and second portion substantially in axial alignment, a third portion axially offset from the first and second portion, a fourth portion disposed between the first and third portion and a fifth portion disposed between second and the third portion. Typîcally the plate is attached to the third portion, Preferably the axis of the third portion is below the level of the axis of the first and second portion. A benefit of this is that more of the plate can be in contact with an electrolyte solution. Preferably the conducting bar is roll formed into such a shape.

In another form, thè invention résides in a method of manufacturing an electrode, the method including the steps of:

attaching a conducting member to an inside surface of a conducting bar; and attaching a plate to the conducting bar.

Preferably the step of attaching the conducting member to an inside surface of the conducting bar involves welding the conducting member to the conducting bar.

Preferably the step of attaching the plate to the conducting bar

involves welding the plate to the conducting bar.

Preferably the method includes the step of forming the conducting bar into a hollow shape and/or a tubular shape. Preferably, the step of forming the conducting bar into a hollow shape and/or a tubular shape in volves roll 5 forming the conducting bar.

Preferably the method includes the step of forming the conducting bar such that a first and second portion are substantially in axial alignment, a third portion is axially offset from the first and second portion, a fourth portion is disposed between the first and third portion and a fifth portion is disposed 10 between second and the third portion. Preferably, the step of forming the conducting bar into such a configuration involves roll forming the conducting bar. More preferably the method includes the step of forming the conducting bar such that a first and second portion are substantially in axial alignment, a third inclined portion and fourth inclined portion are disposed between the 15 first and second portions, wherein the axes of the third inclined portion and fourth inclined portion are angled relative to the axes of the first and second portions. Preferably the third inclined portion and the fourth inclined portion form an obtuse angle. Altematively the third inclined portion and the fourth inclined portion form a right angle or an acute angle. Preferably the third 20 inclined portion is adjacent to the fourth inclined portion.

In a further form, the invention résides in an electrode for electrolytic processes, the electrode comprising:

a conducting bar; and a plate attached to the conducting bar,

wherein at least part of the conducting bar dips below an upper edge of the plate.

Preferably at least a top part of the conducting bar dips below an upper edge of the plate. Preferably, the conducting bar has a first and 5 second portion substantially in axial alignment, a third inclined portion and fourth inclined portion disposed between the first and second portions, wherein the axes of the third inclined portion and fourth inclined portion are angled relative to the axes of the first and second portions. Preferably the third inclined portion and the fourth inclined portion form an obtuse angle.

Altematively the third inclined portion and the fourth inclined portion form a right angle or an acute angle. Preferably the third inclined portion is adjacent to the fourth inclined portion. Preferably the third inclined portion and the fourth inclined portion are inclined inwardly relative to an upper edge of the plate.

Preferably the plate comprises at least one cut-out. Preferably the at least one cut-out is located between a plane defined by the upper edge of the plate and a plane defined by the lowest part of the conducting bar.

Preferably the conducting bar is a conducting bar as disclosed in this spécification. Altematively, the conducting bar may be made of copper 20 and/or a copper alloy.

In another form, the invention résides in a hollow conducting bar for an electrode having:

a conducting member attached to an inside surface of the conducting bar.

Preferably, the conducting baris made of staînless steel. Altematively, the conducting bar may be made from another suitable métal or alloy, such as titanium. Preferably the conducting member is attachèd to the conducting bar by welding.

Preferably the conducting member is made of copper or a copper alloy. Altematively, the conducting member may be made from another suitable métal or alloy having low resistivity. Preferably the conducting member is welded to an inside surface of the conducting bar before the conducting bar is formed. For example, the conducting member is welded to 10 a sheet or plate which is then roll formed into a conducting bar.

Preferably the conducting bar has a first and second portion substantially in axial alignment, a third portion axially offset from the first and second portion, a fourth portion disposed between the first and third portion and a fifth portion disposed between second and the third portion.

More preferably, the conducting bar has a first and second portion substantially in axial alignment, a third inclined portion and fourth inclined portion disposed between the first and second portions, wherein the axes of the third inclined portion and fourth inclined portion are angled relative to the axes of the first and second portions. Preferably the third Inclined portion and 20 the fourth inclined portion form an obtuse angle. Altematively the third inclined portion and the fourth inclined portion form a right angle or an acute angle. Preferably the third inclined portion is adjacent to the fourth inclined portion.

BRIEF DESCRIPTION OF THE DRAWINGS

To assist in understanding the invention and to enable a person skilled in the art to put the invention into practical effect, preferred embodiments of the invention will be described by way of example only with reference to the accompanying drawings, wherein:

FIG 1 shows a section of a prior art cathode;

FIG 2 shows perspective schematic view according to an embodiment of the invention;

FIG 3 shows a schematic cross sectional viewof a conducting bar and a conducting member according to an embodiment of the invention;

FIG 4 shows a schematic cross sectional view of the conducting bar and a conducting member of figure 3 welded together;

FIG 5 shows a schematic cross sectional view of the conducting bar of figure 4 formed into a hollow shape;

FIG 6 shows a schematic cross sectional view of the conducting bar of figure 5 welded;

FIG 7 shows a schematic cross sectional viewof the conducting bar of figure 6 and a plate;

FIG 8 shows a schematic cross sectional view of the conducting bar and the piate of figure 7 welded together;

FIG 9 shows a schematic cross sectional view of a conducting bar according to an embodiment of the invention; ·

FIG 10 shows a schematic view of an electrode according to an embodiment of the invention;

FIG 11 shows a schematic view of an electrode according to an embodiment of the invention;

Fig 12 shows a schematic view of an electrode according to an embodimentofthe invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 shows a prior art cathode 100 having a copper conducting bar 101 and a stainless steel plate 103, The stainless steel plate 103 is welded to the conducting bar 101 by welds 105. A problem with the stainless steel/copper welds 105 is that they are susceptible to corrosion and do not 10 provide welds of high structural strength.

With reference to figure 2, there is shown an electrode in the form of a cathode 10. The cathode 10 comprises a conducting bar 20 attached to a plate 30 by welds 32. A conducting member 26 is attached to the conducting

J bar 20 by welds 28.

The conducting bar 20 and the plate 30 are made of stainless steel and as such the welds 32 are stainless steel welds of high structural strength having résistance to corrosion. The conducting bar 20 is hollow, with an inside surface 22. The conducting bar 20 is welded by a weld 24 to provide a tube shaped conducting bar 20.

The conducting member 26 is made of copper and the welds 28 are not required to be as strong as the welds 32, as there is minimal structural load placed on welds 28.

The welds 28 are primarily for conductive purposes such that the conductivity of the stainless steel conducting bar 20 is increased by the

copper conducting member 26. A benefit of having the conductive member welded to an inside surface 22 of the conducting bar 20 is that the conductive member 26 and the weids 28 are less susceptible to corrosion. A benefit of welding the conductive member 26 to the conductive bar 20 is that the conductive member 26 is not required to provide structural strength to the conductive bar 20, as such, less copper material can be used, resulting in reduced costs.

With reference to Figures 3,4,5,6,7 and 8, there is shown a cathode during various stages of production. In figure 3, the conducting member

26 is placed on the inside surface 22 (i.e. this will become the inside surface) of conducting bar 20 (i.e. this plate or sheet material will become the conducting bar). In figure 4, the conducting member 26 is attached to the conducting bar 20 by weids 28. In figure 5, the conducting bar 20 is roll formed to provide a hollow shape. In figure 6, the conducting bar 20 is sealed along its length by weld 24. In figure 7, the plate 30 is positioned adjacent to the conducting bar 20. In figure 8, the plate 30 is attached to the conducting bar by weids 32.

i

With reference to figure 9, there is shown a cross sectional view of a conducting bar 20 according to an embodiment of the présent invention. The conducting bar 20 is made of stainless steel and has a conducting member made of copper attached to an inside surface 22 ofthe conducting bar 20 by weids 28. As can be seen from figure 9, the conducting member 26 has a ‘U’ shape cross section. A benefit of this is that the conducting member 26 can be made by bending or roll forming a sheet or plate material.

With reference to figure 10, there is shown a cathode 10 according to the présent invention with a “straight” shaped conducting bar 20 and a plate 30 which is placed in electrolyte solution 50.

With reference to figure 11, there is shown a cathode 10 according to the présent invention with conducting bar 20 having a first portion 70 and a second portion 72 substantially in axial alignment, a third portion 74 is axially offset from the first portion 70 and second portion 72, à fourth portion 76 is « disposed between the first portion 70 and third portion 74 and a fifth portion

-78 is disposed between second portion 72 and the third portion 74. A plate 10 30 is attached to the third portion 74 of the conducting bar 20. The plate 30 is placed in electrolyte solution 50.

As can be seen by comparing figures 10 and 11, the cathode 10 in figure 11 has more of the plate 30 in the electrolytic solution, this results in a lower voltage drop between the conducting bar 20 and the part of the plate k

30 which is in the electrolytic solution 50.

With reference to figure 12, there is shown a cathode 10 according to the présent invention with a conducting bar 20 having a first portion 80 and second portion 82 substantially in axial alignment, a third inclined portion 84 and a fourth inclined portion 86 are disposed between the first portion 80 and 20 the second portion 82. The third inclined portion 84 and the fourth inclined portion 86 are angled relative to the first portion 80 and the second portion 82. The plate 30 is attached to the conducting bar 20 and is placed in electrolyte solution 50. As can be seen from figure 12, part of the third inclined portion 84 and the fourth inclined portion 86 of conducting bar 20 dip

below an upper edge 90 of the plate 30. Cut-outs 60 are located adjacent to the conducting bar 20 and an upper edge 90 of the plate 30.

Throughout the spécification the aim has been to describe the invention without limiting the Invention to any one embodiment or spécifie 5 collection of features. Persons skilled in the relevant art may realize variations from the spécifie embodiments that will nonetheless fall within the scope of the invention. For example, indîvidual features from one embodiment may be combined with another embodiment.

It will be appreciated that various other changes and modifications may be made to the embodiment described without departing from the spirit and scope of the invention..

Throughout this spécification the Word comprise, or variations such as comprises or comprising, will be understood to imply the Inclusion of a stated element, integer or step, or group of éléments, integers or steps, but

Claims (7)

1. An electrode for electrolytic process, the electrode comprising:

a conducting bar; and a plate attached to the conducting bar;

5 wherein at least part of the conducting bar dips below an upper edge of the plate.

2. An electrode as claimed in claim 1, wherein at least a top part of the conducting bar dips below an upper edge of the plate.

3. An electrode for electrolytic processes, the electrode comprising:

a conducting bar, and a plate attached to the conducting bar;

wherein the conducting bar has a conducting member attached

15 thereto to increase the conductivity of the conducting bar.

4. An electrode as claimed in claim 3, wherein the plate is integrally formed with the conducting bar.

20 5. An electrode as claimed in claim 3 or claim 4, wherein at least part of the conducting bar dips belowan upperedge ofthe plate.

6.

conducting bar dips below an upper surface of the plate.

7. An electrode as claimed in claim 3 or ciaim 4, wherein the conducting bar has a first portion and a second portion substantially in axial alignment, a

5 third portion axially offset from the first portion and the second portion, a fourth portion disposed between the first portion and the third portion and a fifth portion disposed between the second portion and the third portion.

8. An electrode as claimed in claim 7, wherein the axis of the third

10 portion is below the level of the axes of the first portion and the second portion.

9. An electrode as claimed in claim 7 or claim 8, wherein the plate is attached to the third portion.

10. An electrode as claimed in any one of claims 3 to 9, wherein the conducting bar has a tubular shape and the conducting member is welded to an innersurfaceofthe conducting bar.

20 11. An electrode as claimed in any one of the preceding claims, wherein the electrode is a cathode used for electrolytic processes of copper production.

12. An electrode as claimed in any one of the preceding claims, wherein the conducting bar is made of stainless steel.

13. A hollow conducting bar for an electrode, the hollow conducting bar

5 having:

a first and second portion substantially in axial alignment; and a third inclined portion and a fourth inclined portion disposed between the first and second portions;

wherein the axes of the third inclined portion and fourth inclined

10 portion are angled relative to the axes of the first and second portions, and wherein a conducting member is attached to an inside surface of the conducting bar.

14. An electrode or a hollow conducting bar as claimed in any one of the

15 preceding claims, wherein the conducting bar is formed by roll forming.

15. A method of manufacturing an electrode, the method including the steps of:

attaching a conducting member to an inside surface of a conducting

20 bar; and attaching a plate to the conducting bar.

16. A method as claimed in claim 15, further including the step of forming the conducting bar such that a first and second portion of the conducting bar are substantially in axial alignment, a third portion of the conducting bar is axially offset from the first and second portion, a fourth portion of the conducting bar is disposed between the second and third portion.

17. A method as claimed in claim 15, further including the step of forming the conducting bar such that a first and second portion of the conducting bar are substantially in axial alignment, a third inclined portion and fourth inclined portion of the conducting bar are disposed between the first and second 10 portions, wherein the axes ofthe third inclined portion and the fourth inclined portion are angled relative to the axes of the first and second portions.

18. A method as claimed in claim 17, wherein the third inclined portion and the fourth inclined portion form an obtuse angle.

19. A method as claimed in claim 18, wherein the third inclined portion and the fourth inclined portion form a right angle or an acute angle.

20. A method as claimed in any one of claims 16, 17, 18 or 19 wherein

20 the step of attaching a conducting member to an inside surface of a conducting bar involves welding the conducting member to an inside surface of the conducting bar before the conducting bar is formed.

21 A method as claimed in any one of claims 16, 17, 18, 19 or 20, wherein the step of forming the conducting bar involves roll forming the conducting bar.

(Prior Art)

FIG. 1

FIG. 2

3/7

4/7

FIG. 8

5/7

FIG. 9

6/7

20 50 30 •

10 FIG. 10

7/7

FIG. 12

17446—

International application No,

PCT/AU2013/001109

INTERNATIONAL SEARCH REPORT ^CLASSIFICATION OF SUBJECT MATTER

C25C 7/02(2006.01} C25C 1/12(2006.01) C25C 5/00(2006.01)

According to International Patent Classification (TPC) or to both national classification and 1PC

B. FIELDS SEARCHED

Minimum documentation searclied (classification system followed by classification symbols)

Documentation searched other than minimum documentation to the estent tliat sucli documents are included in tlie fields searclied

Electronic data base consulted during tlie hitcmatioiial search (naine of data base and, where practicable, search ternis used)

EPODOC and WPI: IPC, CPC: C25C1/12, C25C7/LOW, C25C5/LOW; keywords: electrode, conducting, bar, weld (with their similar keywords);

Google Patent, Esp@cenet, Patent Lens: Cathode, lianger bar, weid (with similar words).

C. DOCUMENTS CONSIDERED TOBE RELEVANT

Category* Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No. Documents are listed in the continuation of Box C

Further documents are listed in tlie continuation of Box C

See patent family annex * Spécial categories of cited documents:

A document defining the general state of tlie ait which is not considered to be of particular telcvance

E cahier application or paient but published on or after the international filing date

L document which may tluow doubts on priority claim(s) or which is cited to establish tlie publication date of another citation or other spécial reasoii (as specified)

O document refenûig to au oral disclosure, use, exhibition or otlier means

P document published prior to the international filing date ________but later than the priority date claimed___________________ Date of tlie actual compietion of tlie international search

17 December 2013

Namc and mailing address of the ISA/AU

T Jater document published after tlie international filing date or priority date atld not iu conflict with tlie application but cited to understand the priiicipie ortheoiy underlyipg tlie invention ’X document of particular relcvance; llie claimed invention cannot be considered novel or cairnot be considered to involve an inventive step when llie document is laken aloae

Y document of particular reievance; tlie claimed invention cannot be considered to involve an inventive siep when tlie document is combined with one or more othei such documents, such combination being obvious to a peison skilled in tlie ait document meinber of the saine patent family

Date of mailing of tlie international search report

18 December 2013

Au thon se (I offîcer

AUSTRALIAN PATENT OFFICE

PO BOX 200, WODEN ACT 2606, AUSTRALIA

Email address: pct@ipaustralia.gov.au

Facsùnile No.: +61 26283 7999

Konika Khan

AUSTRALIAN PATENT OFFICE (ISO 9001 Quality Ceitified Service) Téléphoné No. 0262223659

Form PCTZISA/210 (fifth sheet) (July 2009)

INTERNATIONAL SEARCH REPORT * * J C (Continuation). DOCUMENTS CONSIDERED TO BE RELEVANT International application No. PCT/AU2013/001109 Cft^ory* Citation of document, with indication, where appropriate, of tire relevant passages Relevant to claim No. X US 2009/0050488 Al (Jickilîng et al.) 26 Februaiy 2009 see abstract, figures 1-13, paragraphe 0039- 0069 1-20 X US 4647358 A (Baitsch et al.) 03 March 1987 see abstract, figures 1-7, col I line 49- col 5 line 10 1-20 FormPCT/ISA/21û (fifth sheet) (July 2009)

International application No.

INTERNATIONAL SEARCH REPORT

PCT/AU2013/001109

Observations where certain daims were found unsearchable (Continuation of item 2 of first sheet)

This international search report lias not been established in respect of certain claims under Article 17(2)(a) for tlie following reasons:

· □ Claims Nos.:

because they relate to subject matter not required to be searched by this Authority, namely:

the subject matter listed in Rule 39 on which, under Article 17(2)(a)(i), an international search is not required to be carried out, including

2- □ Claims Nos.:

because they relate to parts of the international application that do not coniply with the prescribed requirements to such an extent that no meaningful international search can be canried out, specifically;

3· □ Claims Nos:

because they are dépendent claims and are not drafted in accordance with tlie second and third sentences of Rule 6.4(a)

Box No. III Observations where unity of invention is laclung (Continuation of item 3 of first sheet)

This International Searching Authority found multiple inventions in this international application, as follows:

See Supplémentai Box for Details

1- □

2. E

3 □

As ail required additional search fees were tiniely paid by tlie applicant, tliis international search report envers ail searcliable claims.

As ail searchable claims could be searched without effort juslifying additional fees, tliis Authority did not invite payaient of additional fees.

As only some of tlie required additional search fees were tiniely paid by tlie applicant, tliis international search report covers only those claims for which fees were paid, specifically claires Nos.:

No required additional search fees were timely paid by tlie applicant. Consequently, this international search report is restricted to tlie invention first mentioned in the claims; it is covered by claims Nos.:

Remark on Protest □ The additional search fees were accompanied by the applicant's protest and, where applicable, the payaient of a protest fee.

| | Tlie additional search fees were accompanied by the applicant's protest but tlie applicable protest fee was not paid within tlie tirne limit specified in the invitation.

□ No protest accompanied tlie payment of additional search fees.

FonnPCT/ISA/210 (third sheet) (July 2009)

47445

INTERNATIONAL SEARCH REPORT

International application No.

PCT/AU2013/001109 ilemental Box

Continuation of: Box ΠΙ

This International Application does not comply with the requirements of unity of invention because it does not relate to one invention or to a group of inventions so linked as to form a single general inventive concept.

This Authority has found that there are different inventions based on tire following features that sepaialc the claims into distinct groups:

• Claims 1-2 are directed to an electrode comprising a conducting bar and a plate wherein at least part of tlie conducting bar dips below an upper edge of tlie plate. Tire feature of tlie conducting bar dips below an upper edge of tlie plate is spécifie to tliis group of claims.

• Claims 3- 12,14-20 are directed to an electrode comprising a conducting bar, a plate and a conducting member. Tlie feature of conducting member is spécifie to this group of claims.

• Claims 13 is directed to a hollow conducting bar having a first and second portion substantially in axial alignment; and a third inclined portion and a fourth inclined portion disposed between tlie first and second portions; wherein tlie axes of the third inchned portion and fourth inclined portion are angied relative to tlie axes of the first and second portions, and wherein a conducting member is attached to an inside surface of the conducting bar. The feature of tliird inclined portion and fourth inchned portion of hollow conducting bar is spécifie to this group of claims.

PCT Rule 13.2, first sentence, states that unity of invention is only fulfilled when there is a technical relationship among tlie claimed inventions involving one or more of the same or corresponding spécial technical features. PCT Rule 13.2, second sentence, defines a spécial technical feature as a feature which makes a contribution over tlie prior art.

When there is no spécial technical feature conmion to ail the claimed inventions there is no unity of invention.

In the above groups of claims, the îdentified features may hâve tlie potential to make a contribution over tlie prior art but are not common to ail tlie claimed inventions and therefore cannot provide the required technical relationship. The only feature conmion to ail of the claimed inventions and which provides a technical relationship among them is electrode having conducting bar

However this feature does not make a contribution over the prior art because it is disclosed in:

DI US 2009/0050488 Al (Jicklhig et al.) 26 Febmary 2009

Therefore in the light of tliis document tliis common feature cannot be a spécial technical feature. Therefore there is no spécial technical feature common to ail the claimed inventions and the requirements for unity of invention are consequently not satisfîed a posteriori.