Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
36~9
BRIEF SUMMARY OF THE INVENTION
This invention relates generally to the manufacture of
grounZ rods and like products. More particularly, the invention
relates to a method and apparatus for rapidly plating steel core
rods with a sufficient thickness of dense, non-porous copper to
protect the steel core from corrosion and to provide a durable
electrical connection between the ground and a clamp for connec-
tion to a structure or equipment to be grounded.
S
s It ~ long been known that a copper thickness of .007
10 inch bonded over a steel core provides a ground rod having a
useful life of at least 30 years in almost all soils normally
encountered. The principal publication on this subject is the
National Bureau of Standards Circular No. 579 entitled "Under-
ground Corrosion." In view of the saving in copper as compared
with solid copper rods, certain manufacturing processes for
producing copper bonded steel rods have been in commercial use
for many years. An early method was to cast copper around a steel
billet or wire which was then rolled to the desired finished
diameter to produce a copper clad rod.
In the practice of this method, great care must be
taken to prevent voids from being created between the copper and
the steel due to the lack of concentricity resulting from the
forming operation and the conse~uent lack of adherence. The
presence of such voids could ultimately result in accelerated
corrosion of the steel core and reduction in the useful life of
the ground rod.
According to another known method, copper is electro-
plated upon coils of steel wire. The coils of wire are continu-
ously axially rotated to dip ~he turns repetitively into and out
~0 of a cyanide copper solution. Thus the thickness of the copper
plating builds up as the result of repeated immersions in the
plating solution or bath. In the practice of this method, care
must b~ taken to avoid the introduction of undesirable products
of oxidation and contaminants such as plant dust that may be
layered into the plate each time a coil leaves the solution.
In use, such contaminants reduce adhesion between laminae and
provide localities for accelerated corrosion, producing voids
through which ground moisture may attacX the steel core. A
further drawback of this method is that the cyanide in the bath
is an undesirable pollutant and difficult to dispose of without
damaging the environment.
The plating industry has long known that in place
of a cyanide bath, an acid copper bath may be employed. In this
bath a sufficient concentration of sulfuric acid is provided
to maintain bath conductivity. Copper sulfate is present to
supply the necessary copper ions in solution. Chloride ions
must also be present, either by addltion of hydrochloric acid
or as the result of the chlorination o~ the municipal water
supply. Typically, other agents are added to the bath to enhance
~O the luster and leveling of the deposited copper. These
brighteners are commercially available as proprietary compounds.
The use of bright acid copper plating has hitherto
applied to a wide variety of work pieces as to shape, material
content and surface characteristics. Published material on the
process states that various parameters must be held within
maximum and minimum limits. For example, the prescribed
temperature range for the plating bath has been described as
between 70 and 80F., above which the literature states that
the finish dulls due to the breakdown of the brighteners which
also contaminates the bath.
3~9
1 Still further and economically i~portant limitations
in bright acid copper plating have been described in the
literature with respect to the permissible cathode current
densities as measured at the surface to be plated. Published
standards call for an upper limit of between 50 and 75 amperes
per square foot, with greater current densities being described
as producing a rough or powdery deposit of the copper, referred
to as "hurning".
For the reasons above noted, the current densities
commonly employed in bright acid copper plating processes have
been such as to require considerable time periods for plating
even modest thicknesses of copper upon the work pieces. For
example, plating .010 inch of copper on steel rods would require
177 minutes at 60 amperes per square foot, according to published
tables used in the industry. The duration of time required for
copper plating to achieve the requisite quality and thickness of
plating has very large economic implications. The industry
standards that have developed for copper bonded rods, which
result from the particular and uni~ue conditions under which
~0 they are used, are such that the employment of established
bright acid copper plating processes within the generally
accepted limits of operation would require an extremely long
period of immersion in the plating bath and the resulting costs
of manufacture would render the process uneconomical.
An important object of this invention is to provide
an improved method and apparatus for bright acid copper plating
that is economical. This would permit the attainment of the
inherent advantages that this plating method has over cyanide
plating. Such advantages include a copper plate with a finer
grain structure and a smoother, harder and more uniform surface,
3ti~9
1 better leveling or ability to fill in imperfections in the sur-
face of the steel core, substantially greater ductility of the
copper plating and the elimination of cyanide, --a hazardous
substance.
As noted above, the object of attaining an economical
process for the production of ground rods must he viewed in the
light of the established structural and performance standards for
such rods. The pertinent references are currently Underwriters'
Laboratories Specification 467 and American National Standards
Institute Specification 33.8(1972). These specifications call
for a steel core rod not less than one-half inch in diameter
and up to one inch diameter with a copper jacket having a minimum
thickness of 0.010 inch at any point. Adherence of the copper
jacket must be demonstrated by driving the plated rod between two
steel clamping plates or jaws of a vice set to shear off suffi-
cient metal to expose the bond between the jacket and rod which
shall exhibit no evidence of bond separation. Further, there
shall be no evidence of cracking of the jacket if at room
temperature a length of the rod is rigidly held in a clamp or
vice and the free end bent by applying a force normal to the rod
at a distance from the clamping device equal to 40 times the
rod diameter. The magnitude of the force and the direction of
application shall be such that the rod is permanently bent to a
30 degree angle.
The achiev~ment of an economical plating process
reqllires not only the satisfaction of the foregoing specifications,
but also the achievement of economies in the use of materials and
the disposal of waste products. An additional important object
of this invention is to minimize the build-up of copper sulfate
which was predicted to result from current densities and plating
I solution temperatures above the recommended limi LS . ~n this
respect, it has long been known that a degree of control over
the build-up of copper sulfate can be attained ~y using copper
Pl os,~7~ or4S
~ anodes containing small amounts of phosphorou3. To be effective,
,al oSp~ orus
this-~hosphorous must be more than sufficient to combine with
the oxygen in the copper anodes to form phosphate. However, such
control has been generally applied only to the established
cathode current density levels noted above.
A further object of this invention is to achieve the
desired economical operation without an unduly high rate of
consumption of brightener additives.
Having in view the foregoing and other objects herein-
after appearing, this invention employs bright acid copper
plating at bath temperatures above 110F. and at cathode current
densities substantially higher than the previously published
maximums, for example 120 amperes per square foot and up to 240
amperes per square foot, with consequent large reductions in
immersion times for adequate plating up to the foregoing standards.
By the careful control of all process conditions, the build-up of
coppar sulfate at these higher cathode current densities has
been reduced below the levels predicted from published informa-
tion. ~urther, the rate of consumption of brightener additives
has been reduced to 66% of predicted levels.
The plating apparatus herein described comprises
racks for supporting the steel core rods horizontally in
vertically arranged tiers. The rods remain continuously immersed
in the copper plating bath until the desired thickness of plating
has been deposited.
While the foregoing results are attributable to a
substantial number of factors entering into the process, certain
1~")3~9
1 f these factors appear to have major significance. First, a
nickel strike coating is electroplated on the steel core rods to
a closely controlled thickness adequate for sealing the surface
but not sufficiently thick to cause stress cracking, which would
result in inadequate adherence. Second, the rods are dipped in
an acified rinse bath after receiving the nicXel strike and
before reaching the acid copper bath to prevent passivation of
the nickel. Third, the permanent immersion of the rods in the
copper plating bath throughout the deposit of copper, with cathode
connections made to the rods only at their ends, appears to
produce a plating of substantial uniformity and density in the
bright acid copper bath. Fourth, the copper plating process
proceeds with a high level of air agitation around the anodes
and at the rod surfaces. Fifth, the temperature of the bath is
closely maintained within a predetermined temperature range by
continuous recirculation through a heat exchanger, this tempera-
ture being substantially above the previously published
recommended levels.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an elevation in section of the bright acid
copper plating tank, showing a rack loaded with rods immersed
therein.
Fig. 2 is a fragmentary plan view corresponding to
Fig. 1 showing a single rack carrier.
Fig. 3 is an elevation in section taken on line 3-3
in Fig. 1.
Fig. 4 is a~ end view of a rack carrier illustrating
the attachment of a vertical end rack member thereto.
Fig. 5 is a fragmentary elevation illustrating the
rack supports for a rod or work piece and the electrical end
1~36-~39
1 connections thereto.
Fig. 6 is a side elevation taken on line 6-6 of Fig. 5.
Fig. 7 is a side elevation taken on line 7-7 of Fig. 5.
Fig. 8 is a side elevation taken on line 8-8 of Fig. 5.
Fig. 9 is a schematic diagram representing, in plan
view, the sequential stations in the plating process according
to this invention.
DETAILED DESCRIPTIO~
The sequential steps of the plating process are next
described in outline. Following this, the structures of the
racks and rack carriers, the electrical connections thereto and
their orientation with respect to the anodes, the air agitating
means and the other components of the copper plating tank are
described. Finally, details and parameters of the several steps
in the platiny process are more fully described.
Fig. 9 shows 14 stations through which the rods pass
in a complete plating cycle. These stations are identified in
the drawing numbered in the sequence of progression, namely:
1 Load
2 Soak clean
3 Anodic electroclean
4 Rinse
Rinse
6 Muriatic acid
7 Rinse
8 Nickel 5 trike
9 Rinse
Acidified rinse
11 Acid copper
12 Rinse
13 Rinse
14 ~ot rinse
6s-~9
1 The core rod~ are preferably C1018 cold drawn steel
rods, although other cores having the desired mechanical strength
and substantially uniform surface condition may be used. Cold
drawing of the rods generally provides the requisite surface
condition for use in the present process. The rods are loaded
in vertical tiers in racks more fully described hereinafter
with reference to Figs 1 to 8.
After the rods are loaded in a rack at station 1, they
are transported by an automatically programmed hoist to a soak
clean station 2. This station and each of the successively
numbered stations up to a station 14 comprise separate lined or
coated steel tanks of sufficient length to receive the loaded
racks, and all tanks except tank 11 are intended to receive a
single rack at a time.
In an exemplary embodiment, the tank 11 is of sufficient
size to accommodate 5 racks at a time, thereby allowing for the
relatively greater immersion time in this tank. The hoist is
preferably program-controlled in a known manner to advance each
rack through the stations in sequence, and allowing each rack to
remain at each station for the correspondin~ time period herein-
after more fully detailed.
The rinse tanks are pro~ided with suitable inlet and
outlet connections leading to a supply of water (not shown) for
continuous circulation. In addition, water is conserved by
cascading as illustrated from certain rinse tanks such as the
tank 5 to a preceding rinse tank such as the tank 4, in a
conventional manner.
Air agitation is employed in a number of the tanks, and
is illustrated in Fig. ~ schematically by broken lines at the
left side of the diagram. A perforated pipe is mounted
longitudinally at the bottom of each such tank, and connected
externally to a source of oil free air. Preferab~y, these air
pipes are located directly beneath the rods when the racks are
in position.
Titanium steam pipes 16 are mounted in the tank 11,
and steam is circulated to bring the temperature of the plating
bath in the tank 11 to the predetermined operating temperature,
for example 120F. Once the plating current has been turned on,
the plating process produces heat that must be dissipated in
order to maintain the above temperature. This is accomplished
by continuous recirculation o~ the plating bath solution through
a graphi-te heat exchan~er coil 18 by means of a pump 20. A
filter 22 is provided to remove sedimen-t. The means ~or dissi-
pating heat rom the heat exchanger coil is entirel~ conventional,
.
and therefore the drawing is intended only as a schematic
representation. A water jacket represented at 24 is pre~erably
connected externall~ of the building to a cooling tower 26, all
. .
in accordance with conventional practice.
Vuring~the plating process the concentration of ~he
brighteners in the plating bath is constantly maintained by a
monitor 28 which monitors the ampere hours o~ operation and ~eeds
. .
in the make-up brightener and maintenance brightener at pre-
deterL~ined rates.
A valve 30 1s provided ~or~optional use to prov1de
.
make-up water for the tank ll, thereby compensating for~evaporation.
Figs. 1 to 3 show the tank 11 with a rack 32 immersed
therein. The rack is supported by~a rack carrier ~enerally
designated 34. The rack; carrier 34 is a rigid structure
includin~ two elongate~ steel carrier bars/of channel cross
sectio~ rlgldly connected~together in parallel spaced relationship
:
g ~ ;
:
: ~: :~ .
:
~,
:
: -
:. - . ~ .. . .
1~;}6`~9
by end brackets 37 and welded steel struts 38. An elongate
solid copper cathode bar 40 is located between the carrier bars
36 and supported by the struts 38. The cathode bar is also
rigidly connected to the end brackets 37 connected to the carrier
bars, and extends beyond these brackets to rest by gravity
r"~, 4'J
within bronze saddleslbolted on a fixed bus system 46. This
system is supported on insulators by the walls 48 of the tank.
The bus system 46 is connected to the negative side of a system
of rectifiers (not shown). Thus the rack carrier is supported
only by the saddles 44 and is at negative potential.
To improve the rigidity of the rack carrier, steel
channel upright brackets 50 are welded to the carrier bars 36,
and steel brace rods 52 are welded to the ends of the carrier bars
and to the brackets.
Lugs 54 are welded on the brackets 50 by means of
interconnecting bridge plates 56 as shown more particularly in
s7
Fig. 4. The lugs 54 cooperate with a hoist ~ of commercially
available construction.
The rack 32 is bolted on the rack carrier 34, and
comprises two vertical copper end rack members 58 and 60 and
one verticalr non-conducting center rack member or support 62.
The end rack members 58 and 60 are bolted to the cathode bar 40
as shown by a bolt 64 in Fig. 4. These connections are secure,
as the current is conducted from the bus system 46 through the
saddle 44, the cathode bar 40 and these connections to the
respective end rack members 58 and 60 to the rods. The center
rack member 62 is not current-conducting, and is preferably
supported by the cathode bar by any convenient means such as a
stirrup hung over the bar and adjustable for different rod
lengths.
-- 10 --
~Q3~t`5~
1 The end rack member 58 has a series of stainless steel
V-notched brackets 66 bolted to it, each adapted to receive a
work piece or rod 68 in such manner that the rod will abut the
rack member 58 upon longitudinal movement in its direction.
The center support rack member 62 has a series of hooks 70 for
receiving the rods. The vertical end rack member 60 has stain-
less steel spring clips 72 welded to it, as shown in Fig. 8.
These clips are adapted to apply pressure to retain the rods in
notches 74 on projections from the end rack member 60.
All immersed surfaces of all parts of the end rack
members 58 and 60 and the center support member 62 are coated
with plastisol or any other inert plastic, except the surfaces
in direct contact with the rods 68, to prevent such surfaces
from receiving deposits of copper.
During the plating process, "treeing" readily develops
at any pinholes or bare metal areas in electrical connection with
the cathode bar, and it is necessary to remove the trees from
the rack members prior to reloading with a new set of rods,
either mechanically or by a nitric acid stripping bath.
Round solid copper anode bars 76 are supported on
suitable insulators on the tank 11 and above the bath. The anode
bars are connected to a bus system 78 connected with the positive
side of the rectifier supply. The anode bars are located
centrally between each pair of rack carriers 34, and additional
anode bars are located between the end rack a rre~ls and the
adjacent walls of the tank 11. Titanium holding baskets 80,
each having a copper hook 82 bolted and silver soldered thereto,
are hung on the anode bars 76 by means of these hooks, thereby
making electrical connection with the positive side of the
3Q rectifier power supply. The hooks are coated with plastisol
~3~
1 except at their points of contact with the anode bars. Each of
these baskets contains a plurality of anodes which are preferably
copper chunks. The anodes preferably have a ~OEp~OU~ content
of between .025 and .06 percent. The titanium anode baskets are
preferably constructed in the manner described in U.S.Patent
No. 3,300,396, dated January 24, 1967 to Charles T. Walker.
Perforated air pipes 81 are located at the bottom of
the tank 11 and extend at least the length of the rods. The per-
forations in the pipes are located so as to cause air bubbles to
pass over and around the anodes as well as the rods for efficient
agitation of the plating bath.
Having thus generally described the steps of the plating
process and certain features of the rack construction as well as
that of the tank 11, we turn next to a more detailed description
of the process. This is described in relation to the plating of
ground rods up to one inch in diameter.
Cold drawn steel rods to C1018 or equivalent in
physical strength and surface condition are placed on a rack
in the loading and unloading station 1. As previously noted,
the connections of these rods to the cathode bar are established
onl~ by the end rack members 58 and 60. In operation, the
current flowing through each end rack member to the cathode
bar 40 may be as high as 3,000 amperes.
A standard programmed hoist system transports the
loaded rack from the station 1 to the station 2, comprising a
tank having a commercial soak cleaner in water at a concentration
of 9 to 11 ounces per gallon by weight at a temperature of 180F.
Aft r at least eight minutes in this tank, the rack is moved
to the tank 3. This tank is of conventional construction, and
contains a commercial electro-cleaner in water at a concentration
- 12 -
6~J9
1 o~ 11 to 13 ounces per gallon by weight at a temperature of
180F. The tank has saddles connected to the positive side of
~ c~ eJ
a rcc~ifie- power supply and steel cathodes connected to the
negative side, as is conventional in such electro-cleaners,
and current passes through the rods between the anode and
cathode at a density of approximately 60 amperes per square
foot of rod surface area. This process continues for at least
eight minutes.
The rack then moves to the tank 4 through which fresh
water at room temperature is circulated.
The rack moves from the tank 4 to a tank 5 which is
also supplied with fresh water at room temperature, this water
being air agitated as shown by a broken line 84 in ~ig. 9.
Air agitation is produced by a perforated pipe placed longitu-
dinally at the bottom of the tank 5 in position to cause the
bubbles to rise up directly underneath the rods. In the
subsequent steps including air agitation,the air is agitated
in a substantially identical manner.
~ rom the tank 5, the rack passes to the tank 6
containing muriatic acid at a concentration of 9 to 11 percent
(.9-1.1 normal) at 120F. The rack remains in this solution
for at least eight minutes.
The rack then passes to the tank 7 where it receives
a fresh water rinse with air agitation at room temperature.
~ he nickel strike bath in the tank 8 is prepared in
the following manner. Nickel chloride hexahydrate is added to
water in the tank 8 to a concentration of 19 to 21 ounces per
gallon ~y weight. Boric acid is also added to a concentration
between 3.9 and 4.1 ounces per gallon by weight. Sufficient
hydrochloric acid is added to adjust the pH to 2.8-3Ø The bath
1 is maintained at a temperature of 120F. This tank is electri-
fied by connections of a negative terminal to the saddles
supporting the cathode bar and a positive terminal to nickel
anodes, and current is passed between the positive and negative
terminals through the rods at a current density of approximately
37 amperes per square foot for three minutes.
The solution in the tank 8 is continuously recirculated
through a filter by means of a pump as shown in the drawing by
conventional symbols F and P, respectively. It has been deter-
1Q mined that the thickness of the nickel strike coating must besufficient to seal t:he surface of the steel, and that it must
be non-porous to prevent the acidified rinse in the tank 10 and
the plating bath in the tank 11 from attacking the steel core.
In practice, the nickel coating is deposited to a thickness of
between 88 millionths and 100 millionths of an inch.
The rack then passes to a tank 9 where it receives a
fresh water rinse with air agitation at room temperature.
The tank lO contains sulfuric acid in solution at a con-
centration of one percent by volume, at room temperature. The rack
is dipped into the tank lO, and immediately removed therefrom to
the tank ll.
The plating bath in the tank ll, having a capacity of
7200 gallons, is prepared as follows. A copper sulfate penta-
hydrate is added to water in the tank to a concentration between
30 and 34 ounces per gallon by weight. Sulfuric acid is added
to the tank to a concentration between 8 and lO ounces per gallon
by weight to produce the necessary conductivity. The bath is
further provided with chloride ions by adding sufficient hydro-
chloric acid to bring the chloride ion concentration to between
50 and 120-milligrams per liter. The tank still further contains
- 14 -
6~9
1 30 gallons of make-up brightener such as "UBAC HS Make-up", and
15 gallons of maintenance brightener such as "UBAC HS Maintenance",
these two brighteners being sold commercially by The Udylite
Company, a division of Oxy Metal Finishing Corporation.
As noted above, the brighteners are consumed during
the plating process and must be periodically replenished by the
monitor device 28. The rate of consumption of each brightener
in this process is approximately one gallon per 48,000 ampere
hours.
It has been observed that the temperature of the copper
plating bath may fluctuate within certain limits above and below
a preferred temperature of 120F., for example between 110 and
130 degrees, without undue interference with the quality of the
plate and without causing the other above-described side effects
of elevated temperatures.
However, to maintain the temperature within this
range, the process will inevitably require the use of a heat
exchanger as described.
A typical current density during operation as des-
cribed in the above detailed example is above 120 amperes per
square foot of rod area. It has been demonstrated that the cur-
rent density can be increased to at least double this figure
provided there is sufficient air agitation, consistent control
over the nickel strike according to the criteria described above,
and consistent use of the acid dip in the tank 10 prior to the
copper plating step.
A measure of the rapidity with which rods can be plated
according to the above-described process is given by the following
example. In equipment constructed and operated as described
herein, rods as large as 15 feet long and 0.542 inch in diameter
* rr~d~ k
-- 15 --
6~9
1 may be plated to a copper thickness of .011 inch in 51 minutes
at a current density of 240 amperes per square foot of rod area.
For the same number of rods 16 feet long and the same diameter,
the same thickness in copper is plated in one hour and 20 minutes
at 150 amperes per square foot. The time, current density and
total current are thus interrelated in an apparent manner.
In the tank 11 comprising five cells or racks of rods,
there are six anode bars upon which 80 titanium holding baskets
80 are hung. With 40 to 50 anodes per basket providing an
average anode surface area of 10.4 to 13 square feet per basket,
operation at a current density of approximately 3~ to 36 amperes
per square foot of anode area occurs at full load.
Throughout the copper plating period, the bath is air
agitated to a maximum extent.
This feature is deemed of major significance in the
achievement of higher current densities according to this inven-
tion. The function of air agitation is to provide maximum solu-
tion velocity over the anode and cathode surfaces, preventing
excessive polarization of either surface which would cause rough
or powdery and non-adherent copper deposits. Further, the vigor-
ous air agitation moves the solution that is contiguous to the
cathode surface in the electrolyte to insure exposure to copper
ions in the bath and to aid in the exposure to fresh brighteners.
A major unexpected advantage of the present process has
been the control of build-up of copper sulfate. It is believed
that this is attributable to a combination of several features
of the p~ocess, notably the presence of a sufficiently high
phosphorous content in the anode copper, the reduced surface area
of the anodes, the close maintenance of the temperature of the
plating bath, and the monitored control over the brighteners
- 16 -
~361"~9
1 consumed during operation.
The tanks 12 and 13 each provide a water rinse with air
agitation at room temperature.
The tank 14 provides a final rinse with a concentration
of 0.1 percent of Cobratec 99, a benzotriazole, sold commercially
by Sherwin Williams Chemical Co. This solution is maintained
at a temperature of 120 F.
The rack containing the plated rods is then unloaded for
final finishing operations. These operations include cutting
the rods to the proper length and forming the driving tips by
machining or other suitable forming operations.
By means of the above-described process and appara-
tus, it has been possible to produce a highly pure, dense and
consistent copper plate on the rods, as shown by photomicrographs.
Thus it has been possible to eliminate the use of a
cyanide plating bath. The nickel strike coating ensures a
highly effective molecular bond to the steel core, and aids in
producing a smooth, bright plated surface. These features have
been attained at a sufficiently high production speed to render
the product commercially competitive as compared with cyanide
copper plated ground rods.
- 17 -
