Mechanical Technology

Mechanical Technology — August 2015

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Proactive maintenance, lubrication and contamination management

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After starting the process manually, the plating is mechanised by attaching

the two plating shoes to a rotating beam. The total electrical energy in kWh

is used to determine the coating thickness for a given area to a thickness

accuracy of better than 99%.

The journal-bearing surface of a shaft coated with a nickel cobalt

hardened layer.

Refurbishment of the Transnet trac-

tion motor casings can be done with

the with field coils intact and the

change in coating area around the

profile (left) is easily accommodated

by the process.

damage will be cut away before a new

section is welded on. This has potential

consequences with respect to distortion

and may potentially affect the current

carrying capacity.

“Using our cold selective electroplat-

ing process, however, we can take all

of the necessary equipment onto site

and complete the repair

in situ

. Without

dismantling anything at all, we will build

up the damaged aluminium section and

we can then coat the surface with silver.

I am certain that we can do this job at a

fraction of the cost of sending the whole

component out for a traditional repair,”

Pienaar reveals.

The equipment needed is relatively

simple: a dc rectifier; the anode ap-

plicator with its copper shoe and felt

covering; a solution tray to capture and

recycle electrolyte; a small variable flow

pump to recirculate the electrolyte; and

the electrolytic solution itself. For coating

circular components, it is also possible

to automate the process to some extent,

by rotating either the component or the

shoe so as to maintain brush-like contact.

The plating control unit is equipped

with an amp-hour meter with a six-digit

impulse counter to ensure precise plat-

ing deposits. Pienaar explains: “The

deposition rate for this process is directly

proportional to the current density. This

is because there is an exact relationship

between the number of electrons flowing

into the cathode and the amount of metal

deposited. The total electrical energy in

kWh therefore relates directly to deposit

volume, so it can be used to

determine the coating thick-

ness for a given area.

“We have developed plat-

ing characteristic data for all

of our electrolytes and, for

any given application, these

can be used to determine

the quantity of electrolyte

required, the plating current

and voltage and the total

energy required to achieve the neces-

sary thickness. On a 100

m thickness,

we will be accurate to within 0.01

or within 99% of the specification,” he

assures, adding that no post finishing is

required once the process is completed.

“The finished surface does not look as

bright as those coated in an electroplating

tank, but measurements show that the

selective electroplating process produces

higher surface smoothness than tradi-

tional electroplating.”

In addition, all the electrolytes are

manufactured in South Africa and the

intellectual property associated with

the characteristic data is South African

owned. “But the idea is not to sit on this

technology as an exclusive service pro-

vider. We aim to help small businesses to

set up local selective electroplating and

refurbishing services all over the country,”

Pienaar continues. “Cash flows in current

times are being squeezed and we believe

that greater access to this process can

save clients significant amounts of money

in the long term.

“On the Transnet traction motor

casings, with field coils intact, it costs

something like R100 000 for a strip out

and repair using fusion-based processes.

We are able to avoid having to remove the

coil while repairing the casing and journal

bearing bores, completing the equivalent

job at a fraction of the cost,” he says.

Of the six main Transnet workshops:

Koedoespoort, Bloemfontein, Durban,

Germiston, Salt River and Uitenhage

all have invested in their own selective

electroplating equipment. “We have

equipped these Transnet facilities with

the rectifier and rotating equipment

required and we supply the electrolytes

for them to refurbish all of their rail axles

for themselves.

“We see this as an ideal model to

take to other industries in South Africa.

Whether as part of small engineering

shops or as mobile service providers op-

erating onsite or out of containers, we see

this process as an ideal entrepreneurial

opportunity. As well as reducing main-

tenance costs for industry, the process

can help to create jobs and improve the

economy,” Pienaar concludes.