African Fusion March 2017

29 / 40

27
March 2017 AFRICAN FUSION
Burnishing is used to improve run-out
measurement reliability, which can
significantly improve the in-service condition-
monitoring accuracy for rotating equipment.
A schematic representation of the burnishing
process, which improves surface strength and
reduces roughness. Plastic deformation occurs
which leads to a smoother surface profile.
The typical arrangement of eddy-current
proximity probes for shaft vibration
monitoring.
cal run-out can be measured using an
electrical run-out indicator apparatus on
a lathe or inspection bench. Electrical
run-out is measured every 1.0° through
360° and plotted on graphs using special-
ised, calibrated equipment andapplicable
software.
Discussing eddy-current proxim-
ity probes for shaft vibration monitor-
ing, Hoosain says that the probes are
positioned over a specially machined
probe track area adjacent to each bearing
journal. The signal from the eddy-current
proximity probe is a function of the gap
between the probe tip and the target ma-
terial. If the run-out changes in service, the
difference is registered by the probes and
will indicate to operators and engineers
that the equipment is damaged – worn,
out of balance or poorly lubricated, for
example.
Surface imperfections such as scratch-
es, out-of-roundness or non-concentricity
with respect to the bearing journal are
mechanical imperfections, which will
appear as vibrations that will result in
measurement errors. Thesewill be picked
the rapid solidificationof small globules,
flattened from striking a cold surface at
high velocities. The different processes
include:
• High velocity oxy-fuel (HVOF): This
process operates on a continuous
steady-state basis with continuous
powder feed. Thermaspray offers
two processes, gas and liquid fu-
elled.
• Wire Arc Spraying: Also known as
the twin-wire arc spray process, in
this thermal spray process a direct
current (dc) electric arc is used to
melt the feedstock. Compressed air
behind the arc is then used to atom-
ising the molten material. Higher
thermal efficiency is achieved as
wires are melted directly. Coatings
are coarse with higher porosity.
• Powder plasma spraying: Plasma,
the 4th state of matter, consists of
neutral and positive atoms and free
electrons. Plasma gases are heated
as they ionise in the arc and high
degrees of melting and relatively
high particle velocities are achieved.
Finely structured coatings with high
adhesion strength can result.
Plasma Transferred Arc (PTA)
welding and hardfacing
This is a versatile method of depositing
highqualitymetallurgically fuseddepos-
its on relatively lowcost substrates. Both
the surface material and the coating
material are melted during the process.
PTApermits precise control of important
welding parameters, such as powder
feed rates, gas flow rates, amperage,
voltage, and heat input, ensuring con-
sistency. Controlled heat input ensures
that weld dilutions can be controlled to
between 5% and 7%.
Polymer applications
• Plasma Coatings (non-stick and
traction coatings): Thermaspray
has undertaken a strategic partner-
shipwithPlasmaCoatings in theUSA
to offer the South African market a
new range of surface technologies
and coatings to tackle the sugar,
food, printing and packaging, tyre
and rubber, paper andpulp, fempro/
diaper and many more industries.
These coatings are designed to
solve many of the above indus-
tries’ problems resulting in reduced
maintenance, higher outputs and
an increase in cost savings. These
coatings combine the advantages of
thermal spray (metal base) coatings
with polymer top coatings to offer
benefits of wear resistance, slip and
traction. These coatings can be ap-
plied to aluminium, steel, stainless
steel, tool steel, copper, ceramics as
well as synthetic materials.
• Diamant Metalplastic (polymeric
solutions): Thermaspray is the
exclusive Southern African repre-
sentative of German-based DIA-
MANTMetallplastic GmbH. DIAMANT
Metallplastic offers the metalwork-
ing industry high-quality polymeric
solutions to restore functionality
to castings, thereby significantly
reduce scrap. The DIAMANT poly-
meric solution includes products for
impregnating and sealing leakages,
repairing of blow holes and surface
treatments as well as wear protec-
tion and services.
Typical applications in sugar industry
include knife and trash plate replace-
ment components in sugar mill, shred-
der hammers, crushers rolls, scrapers,
pump casings, conveyor screws, valves
covers, flanges and bearings and bear-
ing journals.
Thermaspray, in a joint venture with
Cape Town-based Surcotec, offers an
extensive portfolio of engineering and
thermal spray coating solutions that ex-
tend component life cycles to assist OEM
and end-user clients across southern
Africa in reducing costs and increasing
production.
The company’s world-class quality
wear- and corrosion-resistant thermal
spray coatings, Plasma Transferred Arc
(PTA) cladding and Polymer coatings
are augmented by a host of specialised
allied services.
up as signals by the eddy-current proxim-
ity probes.
Typical equipment using probe tracks
includeboiler feedpumps, 50%boiler feed
pumps, turbine rotors, compressor rotors,
blower rotors, pinion shafts and cryogenic
pump rotors.
Burnishing, de-magnetisation and
measuring of electrical run-outs are all
routinely performed in Thermaspray’s
well-equipped workshops according to
the relevant ISO standards.