Method for producing regular electronickel or S nickel rounds from electroplating baths giving highly stressed deposits

A permanent electrodeposition mandrel for use in making buttons or rounds of electrodeposited metal comprises a masked stainless steel plate having exposed islands of bare metal. Each of the islands has at least a recess in the bare metal surface at or near the perimeter of the island, the depth of the recess being about 0.12 mm to about 1.3 mm with the major dimension of the island being about 5 to about 50 times the depth of the recess and in the range of about 7 to about 50 mm. The mandrel is used in electrodeposition processes wherein thick deposits of high internal tensile stress metal are produced.

The present invention is concerned with permanent electrodeposition 
mandrels and more particularly with permanent electrodeposition mandrels 
useful for the production of thick buttons of metals which are highly 
stressed as deposited. 
PROBLEM 
Electrolytically formed rounds or buttons of the order of 25 millimeter 
(mm) in diameter and 6 mm thick of nickel are at present a conventional 
article of commerce used in the electroplating industry as anodes. 
Generally speaking, these materials are produced by electrodeposition on 
permanent mandrels and comprise metal which has a low internal stress as 
electrodeposited. If the metal deposited has a high internal stress as 
deposited there is a tendency for the button to exfoliate from the 
conventional permanent mandrel during electrodeposition or to drop-off as 
the mandrel is being removed from the electrodeposition bath. These 
tendencies cause significant operating difficulties in large-scale 
production of nickel rounds. 
The conventional masked permanent mandrel having islands of metal exposed 
to the electrodeposition bath is not really permanent. The mask of 
electrical resist on the mandrel deteriorates in the electrodeposition 
bath and must be removed and replaced on the average after about 10 or so 
production cycles. Treatments of the bare metal islands to enhance 
adhesion of highly stressed deposits which have been proposed heretofore 
are either not effective at all in solving the problem of button adhesion 
or operate only for up to 5 or so production cycles. Thus, the best of the 
proposals alternative to the present invention involves refinishing of 
cathode mandrels about twice as often as is required to re-establish the 
mask of electrical resist. 
PRIOR ART 
Applicant is aware of U.S. Pats. Nos. 3,577,330 and 3,668,087 and Canadian 
Pat. No. 955,195. Each of these prior art documents discloses subject 
matter relative to the production of electrolytic nickel rounds or 
buttons. The totality of these prior art disclosures and the pragmatics of 
carrying them into practice is the basis for the aforestated problem. 
In addition, applicant is aware of U.S. Pat. No. 2,530,842 which discloses 
electroforming of phonograph record stampers. The disclosure of this 
patent while having superficial similarity to the invention claimed herein 
has as its object a completely different purpose than the purpose of the 
present invention. 
OBJECTS OF THE INVENTION 
It is an object of the invention to provide a novel electrodeposition 
mandrel for the production of rounds or buttons of highly stressed 
electrodeposited metal. 
A further object of the present invention is to provide a novel process of 
electrodeposition employing the novel electrodeposition mandrel. 
Other objects and advantages of the invention will become apparent in light 
of the drawing and the following general description.

Referring now the drawing, the mandrel of the present invention comprises 
essentially flat metal plate 11 coated with adherent mask 12 defining 
isolated islands 13 of bare plate metal and hanging means 14 which serve 
to provide contact with direct current energizing means (not shown) and to 
support the mandrel in an electrodeposition bath. Flat metal plate 11 is 
made of a metal which resists the corrosive environment of the 
electrodeposition bath and which forms only an emphemeral bond with 
electrodeposited metal. For nickel electrowinning and electrorefining 
baths, metals such as stainless steel (especially the austenitic varieties 
thereof), titanium and aluminum can usually be used. In large scale 
commercial use flat plate 11 is normally about 1 meter square and about 3 
mm thick. Mask 12 can advantageously be an organic coating such as an 
epoxybased paint. Other organic-type coatings and ceramic coatings can 
also be used for this purpose provided that they are resistant to the 
effects of the electrolyte and they do not significantly conduct 
electricity at the voltages normally encountered in electrodeposition 
cells, e.g., less than 10 volts. Each of the islands 13 has a major 
lateral dimension of about 7 to about 50 mm. As depicted in FIG. 1 the 
islands are uniformly circular so that the major lateral dimension is the 
diameter. It will be appreciated, of course, that other shapes of islands, 
e.g., oval, square, rectangular, etc., can be used. As shown in FIG. 2, a 
groove or depression 15 is located in the surface of the base metal of 
plate 11 at the periphery of island 13. Groove 15 is continuous around the 
circumference of island 13. and must be so fashioned as to avoid undercuts 
which could mechanically lock electrodeposited metal to the mandrel 
surface. An alternate form of grooving or depressioning is depicted in 
FIG. 3 which comprises a series of concentric grooves or depressions 15 
across a major portion of the surface of island 13. The essential groove 
or depression is the one at the periphery of island 13. If a continuous or 
essentially continuous groove is not present at the periphery, the 
electrodeposit formed on island 13 will tend to peel at the edges. 
Interiorly of the peripheral continuous groove or depression other grooves 
or depressions can be present in any desired configuration. For example, a 
product identification number or trademark can be depressed in the central 
portion of island 13 provided of course that no undercuts are present in 
the grooves or depressions. 
The depth of peripheral groove or depression 15 is important. It must be in 
the range of about 0.12 to about 1.6 mm and the ratio of major lateral 
dimension of island 13 to the depth of groove 15 must be about 5 to about 
50. This dimension and relationship assures that electrodeposited metal 
having internal tensile stresses higher than about 200 megapascals (MPa) 
will adhere to the mandrel during electrodeposition to thicknesses up to 
about 10 mm and will adhere to mandrel at the completion of 
electrodeposition with a force not significantly exceeding about 50 
newtons (N) so that removal is facilitated. In designing a specific 
mandrel in accordance with the concepts expressed herein it is important 
that the depth of groove 15 not exceed one-half the thickness of plate 11 
because resist 12 and islands 13 are normally present on both sides of 
plate 11. It is also, advantageous that the width of the groove at the 
metal surface be approximately equal to the depth of the groove. 
PROCESS CONDITIONS 
The mandrel of the present invention is only useful in electrodeposition 
processes where the metal (including alloys) deposited has an internal 
stress in excess of about 140 MPa tensile and is deposited for times 
necessary to produce deposits about 2 to about 15 mm thick. Using nickel 
electrodeposition as an example, it is difficult to broadly state the 
exact electrodeposition conditions which will result in specific internal 
tensile stresses because internal tensile stresses are sensitive to 
electrolyte impurities which may be difficult to measure or identify. 
Consequently, unless prior experience is available, internal stress of 
deposits should be measured by any one of the known methods such as 
described by Robert Brugger at pages 69 and 70 of the text Nickel Plating, 
Robert Draper Ltd. 1970. 
As illustrative of the process of using the mandrel of the present 
invention a mandrel of stainless steel having groove patterns similar to 
those depicted in FIGS. 2 and 3 cut on separate circular islands bounded 
by an epoxy resist was employed as a cathode to produce nickel from an 
electrodeposition bath containing the following: 
Ni SO.sub.4 .6H.sub.2 O;135 gpl 
Ni Cl.sub.2 .6H.sub.2 O;160 gpl 
H.sub.3 bo.sub.4 ;18 gpl 
pH; 4.0 
Temperature; 60.degree. C. 
islands having groove pattern of FIG. 2 of the drawing were 9.52 mm in 
diameter with the groove depth being 1.58 mm. Islands having the groove 
pattern of FIG. 3 of the drawing were 31.7 mm in diameter with the groove 
depth again being 1.58 mm. 
Nickel was electrodeposited from the bath at a cathode current density of 
about 486 Amperes per square meter A/M.sup.2 measured on the basis of 
exposed bare metal area for two periods of 6 days each with removal of the 
buttons after each 6-day period. At the end of this time the buttons which 
had an internal stress of 402 MPa tensile were adherent to the mandrel 
with an average adhesion force of about 18 N. 18 
A similar test was made with groove patterns die punched into the surface 
of islands 15.9 mm in diameter on a stainless steel mandrel. The depth of 
the stamped impression ranged from 0.20 mm to 0.38 mm. Nickel rounds grown 
for 6 days on this mandrel from a synthetic electrorefinery electrolyte 
had internal stresses of 303 MPa tensile. The force to remove the rounds 
from the mandrel was 30 N. 
While the foregoing tests directly demonstrate the utility of the present 
invention with respect to nickel electrodeposition, the mandrel of the 
invention is also useful with any electrodepositable metal which deposits 
in a form which is highly stressed internally. Such metals include cobalt, 
iron, chromium, and alloy deposits of nickel-cobalt and nickel-iron. 
Although the present invention has been described in conjunction with 
preferred embodiments, it is to be understood that modifications and 
variations may be resorted to without departing from the spirit and scope 
of the invention, as those skilled in the art will readily understand. 
Such modifications and variations are considered to be within the purview 
and scope of the invention and appended claims.