Method for producing a nickel strip

1. A method of making a nickel strip composed of a plurality of at least substantially solid cathode sheets, the method comprising the steps of:

hot-rolling the sheets individually before or after being joined to one another to form the strip, and

prior to the hot rolling, establishing that a starting material of the sheets has a minimum nickel content and a maximum trace element content as follows:

Element

NI

C

S

Mn

Mg

Al

Ti

Si

Unit

% by

ppm by

ppm by

ppm by

ppm by

ppm by

ppm by

ppm by

weight

weight

weight

weight

weight

weight

weight

weight

Value

≧99.94

<35

<5

<14

<11

<7

<25

<15.

2. The method according to claim 1 , wherein the minimum nickel content and the maximum trace element content is limited as follows:

Element

Ni

C

S

Mn

Mg

Al

Ti

Si

Unit

% by

ppm by

ppm by

ppm by

ppm by

ppm by

ppm by

ppm by

weight

weight

weight

weight

weight

weight

weight

weight

Preferably

≧99.98

≦20

≦2

≦5

<5

≦5

<10

≦10.

3. The method according to claim 1 , wherein during the hot rolling differences in thickness within individual cathode sheets are reduced by a minimum reduction rate of ≧20% and the differences in thickness between cathode sheets are removed by the hot rolling to a uniform thickness such that, as the result of the minimum reduction rate of all sheets to be joined or already joined, even the thinnest of the sheets is reduced in thickness by at least 20%.

4. The method according to claim 3 , wherein the hot-rolled, essentially solid sheets are joined by forging.

5. The method according to claim 1 , further comprising the step after the hot rolling of:

subdividing hot-rolled sheets or hot-rolled strip or end pieces or side strips that are not dimensionally accurate longitudinally, transversely, or in a pattern and used as a starting material for an ultrapure welding wire.

6. The method according to claim 1 , further comprising the step of:

aligning edges of the sheets to be joined after the hot rolling;

cutting the sheets to size after being aligned such that the aligned and cut-to-size strips abut one another with a technical zero gap to impart to the strip a linear axis; and

joining the edges are subsequently by welding.

7. The method according to claim 6 , wherein

the sheets are joined by TIG fusion welding using a pure nickel welding wire having the nickel content defined for the sheets in claim 1 ,

gases used in the TIG fusion welding are free of nitrogen and helium,

a weld-shielding gas being used that is 100% argon, and

a welding gas being used that is composed of argon and contains at least 5% hydrogen.

8. The method according to claim 7 , wherein prior to joining by fusion welding, the hydrogen content of the sheets, which is determinable by melt extraction, is reduced by heat treatment to ≦0.5 ppm by weight.

9. The method according to claim 6 , wherein the hot-rolled, essentially solid sheets are joined by resistance butt welding or by friction stir welding using an abrasion-resistance tool manufactured using PCBN.

10. The method according to claim 1 , wherein the essentially solid sheets are aligned and cut to size at the edges to be welded in such a way that they abut one another with a technical zero gap and are joined before hot-rolling by fusion welding, (flash-) butt welding, or friction stir welding, or forging.

11. The method according to claim 10 , wherein for the joining by fusion welding, a pure nickel wire that meets the analytical values defined in claim 1 for the sheets is used as a welding wire, and gases used are free of nitrogen and helium, weld-shielding gas being composed of 100% argon, and a welding gas also composed of argon and containing at least 5% hydrogen.

12. The method according to claim 1 , wherein an oxide layer that results from the hot rolling is converted by reduction annealing in hydrogen to pure nickel that firmly adheres to a base body.

13. The method according to claim 12 , further comprising the step of:

removing a sponge-like structure and surface roughness of an oxide layer that developed as a result of the annealing by cold rolling using reel tension, and

further reducing a thickness of the strip to final dimensions by cold rolling under reel tension such that emulsion or oil taken in by the sponge-like structure during rolling is removed by the subsequent annealing under hydrogen.

14. A method of making a nickel strip, the method comprising the steps of:

providing a plurality of solid cathode sheets that have a minimum nickel content of 99.94% by weight and a maximum trace element content, in ppm by weight, of <35 carbon, <5 sulphur, <14 manganese, <11 magnesium, <11 aluminum, <25 titanium, and <15 silicon;

hot-rolling the sheets individually in a single layer/ply; and

joining the sheets to form the strip.