In its
simplest form, electroplating is a process that uses electrical current to
reduce dissolved metal cations so that they form a metal coating on the surface
of an electrode. The process is dependent on an effective and consistent power
supply, or source, to produce the required electrical current, normally
introduced into the process line by a device known as a rectifier.
The purpose
of a rectifier is to remove any variation or fluctuation from the power supply,
effectively ‘straightening’ it and making it consistent. Most power supply
devices in metal treatments are set up to convert a standard alternating
electrical current (AC) to a direct current (DC) in order to achieve the
consistent input required for the plating process.
Earliest beginnings
Electrodeposition
of precious metals can be traced back to around 1800, when Italian chemist and
professor Luigi Brugnatelli developed a process for coating gold on to a silver
substrate. He was aided in this project by Allisandro Volta, who was in the
process of developing voltaic electrical batteries.
It wasn’t
until the 1840s that the Elkington brothers of Birmingham, UK, refined the
precious metal plating process and turned it into a proper commercial venture.
From the UK, the technology spread rapidly to Europe and the USA. In Russia,
large scale gold plating for cathedral domes, icons and religious statues were
successfully completed. And as the growth of industrialisation continued
throughout the world, electroplating using DC power based on the Elkingtons’
patents reigned supreme.
In the 20th
and early 21st centuries, the electroplating process has largely
adhered to its original principles, but at the same time developed improvements
in chemical solutions, process plant automation and wave-form technology for
rectifiers, turning electroplating into less of a black art and more of a
sophisticated technical procedure, governed by industrial and international
safety standards.
What is a power supply?
A power
supply is a device that converts AC power from the mains into the appropriate
source of power for, in this case, electroplating. The Power Supply Unit (PSU)
most commonly used in electroplating is the rectifier.
The earliest
type of electrical rectifier used to convert AC to DC was the Mercury Arc
Valve, a type of Cold Cathode gas discharge tube invented by Peter Cooper
Hewitt. As the commercial implications of this breakthrough invention became
more significant, the need for rectification allied to electroplating began. So
dedicated rectifiers were developed to support the new, booming electroplating
industries, fuelled by world wars, consumerism and economic prosperity.
Throughout
the 20th century, original equipment manufacturers such as
Westinghouse, Brentford and Drake exploited the demand for DC power supplies.
In the UK, the aerospace, automotive and general engineering industries were
booming in the period from the 1940s until the 1980s. Along with this surge in
industrial production was a constant need for more sophisticated plating and
coating processes, with a subsequent demand for efficient and reliable power
supplies.
Set of standard rectifiers and transformers for electroplating
Decline in UK sales of standard rectifiers
Riley Surface World was founded in the white heat of this technological revolution, so the
sale and refurbishment of DC power supplies took centre stage, allowing us to
develop our company to the powerhouse that it is today.
The nature
of manufacturing is that it is constantly changing. As products become obsolete
and new ones take over, production lines are continuously being reconfigured,
or in some cases dismantled and rebuilt. In the new globalised economy, these
changes often take place across international boundaries, with the need for
equipment suppliers to be very flexible and able to meet this ever changing
demand.
Over the
past 10 – 15 years, our company has seen a sharp reduction in demand for
standard DC power supplies from the UK metal treatments industry. This decline
is largely due to much of the bulk zinc plating of mass produced products, such
as nuts and bolts or shopping trolleys, moving overseas to lower cost
economies. As Britain moves to a more specialised manufacturing nation,
traditional electrolytic treatments are being replaced by more modern e-coating
and other organic coating processes, allied to the needs of the higher end
aerospace, automotive and general engineering industries. These processes
either do not require rectifiers, or use more compact switch mode units rather
than the older ‘filing cabinet’ models traditionally associated with
electroplating.
A good
example is the power supply used for a powder coating gun. Older models use a
separate, free-standing power supply unit, whilst more modern units have the
power supply built into the device, resulting in a more compact and efficient
unit.
Set of high powered rectifiers adapted from anodising to electrowinning applications
New, growing DC power applications
At the same
time, new high powered rectifiers are being harnessed for a whole new set of
industrial functions. In the oil exploration and construction industries,
rectifiers are being utilised for cathodic protection of metal reinforcements
in offshore platforms, bridges and other kinds of structures subject to
corrosion. The introduction of the appropriate electrical charge to metal can
work wonders for the life expectancy of such structures.
Rectifiers
are also used extensively throughout the world’s mining and metal extraction industries
in a procedure known as electrowinning or electroextraction. This is the electrodeposition of metals from their ores that have been put in solution via a
process commonly referred to as leaching. Electrorefining uses
a similar process to remove impurities from a metal. Both processes use electrolysis on a large scale and are important
techniques for the economical and straightforward purification of non-ferrous metals. The resulting metals are
said to be ‘electrowon’.
Detail of high powered rectifier
The
most common metals to be processed as part of the electrowinning procedure are lead, copper, gold, silver, zinc, aluminium, chromium, cobalt and manganese. The growth of applications
such as cathodic protection and eletrowinning are creating new markets for
power supply manufacturers and resellers, such as our company.
Riley
Surface World has recently won a large order from an Australian metal refining group
for a set of 6 x 500 amp, 0 – 25 volt DC rectifiers formerly used in the UK for
the anodising of surface finished aluminium coil, as used in light diffusers
and other similar products. These high powered units are now being applied to electrowinning
on a very large scale. This is just one example of how DC power supplies for
one process can be adapted to another application in a different part of the
world, providing opportunities for the UK electroplating and power supply
industries.
