Surface World August 2019 Surface World August 2019 | Page 54
ELECTROPLATING, ANODISING & GALVANIZING
eliminating the risk of parts being returned by
the customer if plugs are inadvertently left in
at the time of delivery.
An eco-rinse cycle in town water is performed
in the next three tanks, again with recycling
between the stages. The following process,
which takes place at the far end of the line in
tank 8, is the removal in a mix of nitric acid
and hydrofluoric acid of alloying elements on
the surface of components, especially of
castings, that remain after chemical etching.
Two further eco-rinse immersions in tanks 9
and 10 brings the pre-treatment to a close,
by which time the components have travelled
back past the centre
tank towards the
load/unload
stations.
A fi ght bar being lowered
by one of the transporters
into a tank.
The Turbex line control.
The waste water treatment
plant control system.
program is automatically selected.
There are four load/unload stations at one
end of the line, where components are loaded
onto flight bars that progress to a buffer
station from where they are picked up by one
of two overhead transporters and dipped into
15 tanks sequentially. Up to five jobs can be
processed simultaneously in the line.
Automatic dosing stations are provided for
metered dosing of chemicals into several of
the tanks, the quantity being worked out
automatically according to the amount of
surface area to be anodised on each flight
bar. The working environment is clean and
fume-free, as each tank is hermetically sealed
and the lid is not opened until a transporter is
directly above it. Positive pressure pulls the
fumes through the handling system and
extracts them to a scrubbing unit.
After processing, flight bars are returned to
four load/unload stations adjacent to the
loading area and the test pieces are taken
52
away for analysis, which includes pull and
shear tests after adhesive has been applied.
Following each successful test, the ERP
system is advised that the components are
ready to deliver to the customer.
The anodising sequence
As a conveyor is not involved in transporting
flight bars around the system, the anodising
process starts in the centre of the line and
progresses initially away from the load/unload
stations. Alkaline degrease takes up to one
hour in the first tank for the most soiled
castings and the solution is rinsed off in town
water in the next two tanks, the water being
recycled between the second and third stage.
Tank 4 is a chemical etch using sodium
hydroxide to remove pre-existing aluminium
oxide from the surface of components.
Immersion time is controlled to avoid unduly
changing of the geometry of the
components. It also precludes the need to
plug holes, resulting in a cost saving and
AUGUST 2019
The actual
anodising stage of
the process is in
tank 11, which
contains sulphuric
acid, and lasts
between eight and
10 minutes, during
which time a
nominal 4 to 6
microns film
thickness is
deposited. An
ecological feature of the equipment is
continuous dosing of the acid, instead of
recycling the fluid when the aluminium
content reaches say 20 grams per litre.
Avoidance of waste is made possible by
employing a pump to recirculate the fluid
through a retardation unit, where the
aluminium is filtered out.
A clean rinse in three successive tanks containing
deionised water, which is produced locally within
the line, ends with an ultra-clean rinse to ensure
that conductivity is less than 200 microsiemens.
The last stage, prior to the flight bar being
taken back to the unload station, is
hydrothermal sealing at 96°C in a proprietary
chemical blend. Reserved for high-end
applications and involving 30-micron
particulate filtration, the process seals
microscopically small pores created on the
surface of components as a result of
dielectric breakdown during anodising.
Visit: www.turbex.co.uk
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