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Frequently
Asked Questions
New! Click here
for a comprehensive glossary of Thermal Spray terms!
What
is the arc-plasma spray process?
Arc-plasma spray is
the method whereby a hot gas plasma is used to melt a particulate material
and transfer it to a substrate, at which point the material solidifies
to become a coating. The plasma is generated by passing the gas between
two concentric electrodes (water-cooled ) where it is heated by a sustained
high-current d.c. arc. Temperatures within the chamber reach higher then
30,000° F which causes the gas to expand and issue from the front electrode-nozzle
at a very high velocity. At some point downstream from the arc, powder
is injected via a carrier gas and mixed with the plasma. The powder melts
and is carried at the gas velocity to the substrate where it is quenched
and bonds to form a dense coating. Both thermal and kinetic energy in
the particles bring about the high bond strength associated with plasma
spray coatings.
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What
about size limitations?
We have processed
films as thin as 2 µm, and as thick as ½ in. on foils and ceramics
small enough to be held in tweezers and on castings and fabrications with
many hundred square feet of area.
If the substrate will
fit within our 10x11 foot door, we can process it in the shop. For those
larger parts or ones not easily accessible, we have portable equipment
that we can bring to the job.
I.D.'s above 4 inches
can be coated internally; below this diameter, we can reach the depth
equal to the diameter.
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Will
heat distort the part?
No! The heat input
to the substrate is very minimal and even on small substrates, the temperature
will normally be held at 250° F. Thus APS processing will not affect the
geometry nor the hardness of nearby surfaces which have been finished.
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But
won't such coatings flake and peel off?
At APS, the minimum
bondstrength of a properly chosen coating
system should be 7000 PSI or better. There are several methods for constructing
a coating to withstand high loads and even severe impact. Even ceramics
have been graded-diffused bonded on aluminum plate and successfully tested
as armor plate against 30-06 projectiles. Other coatings have been milled,
threaded, ground, and machined--even to feathering against the base substrate.
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How
can I benefit from this technology?
Easily, by saving
time and money! Consider the following suggestions for your use.
Salvage!
Either worn or new mismachined parts. We can bring a worn part back into
spec at a fraction of the new cost and most generally within a two week
period. The part will outperform a new counterpart in most instances!
And how about those
production castings with overbored holes or those shafts with under-size
bearing surfaces? Like another chance at machining them to spec?
Hardfacing!
Use in lieu of distortion-causing heat treats. Or provide a better surface
for that bearing... for slides... for seals. How about lining your pumps
for improved wear? Mixer bodies? How about a coating with a higher hot
hardness than your present part has?
Corrosion!
Repair pumps and valves with linings... patch reactor kettles and mixers...
rebuild those seals... clad those offending parts.
Saving
Material Costs!
Why use that 4000 lbs. of stainless shaft when you can clad a much less
expensive material and save up to half the price! Why use an inch-thick
Hastelloy® casting when it has to be discarded or rebuilt after 0.050
in. of wear? Use a 0.060 in. coating at less than half the cost. Machining
Hastelloy and Inconel expensive? Why not machine a less resistive material
and clad for your corrosion protection?
Production line down?
Delay in getting those parts?
APS Materials offers a 48 hour turnaround (excluding shipping) to machine,
repair, and maintenance departments. This includes coating and finishing
the part to spec ready to use!
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Where
can I find more info about Thermal-Spray Technology?
Easy... the list of
links below are always being updated. Check back often to see the latest
additions
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Glossary
of Terms
A
l B l
C l D l E l F
l G l H l I l J l K
l L I M I N I O I P
I Q I R I S I T I U I V I W
I X I Y I Z
A
Abradable
Seals
A seal made
from mating two soft metal, or metal containing soft graphite, surfaces
together using friction and pressure.
Abrasion
To wear
away by friction.
Adhesion
A binding
force that holds together molecules of substances whose surfaces are in
contact or near proximity.
Alumina
Aluminum
oxide; a ceramic used in powder or rod form in thermal spray operations.
Anode
The electrode maintained
at a positive electrical potential.
Arc
A luminous discharge of electrical
current crossing the gap between two electrodes.
Arc
spraying
A thermal spraying
process using an arc between two consumable electrodes of surfacing materials
as a heat souce and a compressed gas to atomize and propel the surfacing
material to the substrate.
Atmospheric
Plasma Spraying (APS)
A plasma
spray method done in open air.
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B
Bond
strength
The force required
to pull a coating free of a substrate, usually expressed in kPa (psi).
Bio-active
Any material
that encourages growth, such as bone growth, when implanted in the body.
Bio-active material is used as a coating on dental and orthopaedic implants in order
to create a bond to bone in the body.
Bio-inert
Any material that does not harm and is not rejected by the body when implanted.
This material is often used as a surface coating on dental and orthopaedic
implants.
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C
Carbide
A chemical
compound formed between carbon and a metal or metals; examples include
tungsten carbide, tantalum carbide, titanium carbide, chromium carbide.
One of the hardest examples is boron
carbide.
Cathode
The electrode
maintained at a negative electric potential.
Ceramic
Any
of the various hard, heat-resistant, and corrosion resistant coatings
made up of non-metallic materials.
Cermets
A mixture
of ceramics and metals used as a thermal spray material.
Coating
(1) The
act of building a deposit on a substrate, (2) The spray deposit.
Composite
coating
A coating
consisting of two or more dissimilar spray materials which may or may
not be layered.
Controlled
atmosphere chamber
An enclosure
or cabinet filled either with an inert gas or evacuated to below atmospheric
pressure, in which thermal spraying can be performed to minimize or prevent
oxidation of the coating or substrate.
Corrosion
To wear
away gradually, especially by chemical action.
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D
Deposition
rate
The weight
of material deposited in a unit of time.
Dielectric
coatings
A coating that
serves as a non-conductor of electricity.
(see
an example of this application)
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F
Feed
rate
A nonstandard
term for spray rate.
Flame
spray
A thermal spray
process in which an oxyfuel gas flame is the source of heat for melting
the surfacing material. Compressed gas may or may not be used for atomizing
and propelling the surfacing material to the substrate.
Fretting
Surface damage
resulting from relative motion between surfaces in contact under pressure.
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G
Gradated
coating
A thermal
spray deposit composed of mixed materials in successive layers that progressively
change in composition from the constituent material lot to the surface
of the sprayed deposit.
Grit
blasting
The preparation of
a substrate for the thermal spray process by blasting with sharp irregular
shaped grains to produce a pitted surface.
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H
Hardfacing
A surfacing variation
in which the surfacing metal is deposited to reduce wear.
HVOF
(High Velocity Oxygen Fuel)
A high velocity
flame spray process.
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I
Inert
gas
A gas that
does not normally combine with the substrate or the deposit.
Interface
The contact surface
between the spray deposit and the substrate.
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M
Mask
A device for
protecting a substrate surface from the effects of blasting or adherence
of a spray deposit.
Mechanical
bond
The adherence
of a thermal spray deposit to a roughened surface by the mechanism of
interlocking particles.
Metallic
bond
The principal
bond that holds metals together and is formed between base metals and
filler metals in all processes.
Metallurgical
bond (see above)
Molten
metal flame spraying
A thermal
spraying process variation in which the metallic material to be sprayed
is in the molten state. (see flame spray)
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N
Near
Net Shapes
In the thermal
spray process, the substrate is removed after application to leave a seamless,
solid shape.
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O
Overspray
The excess
spray material that is not deposited on the part being sprayed.
Oxide
A chemical
compound; the combination of oxygen with a metal forming a ceramic; ex.
Aluminum oxide.
Oxyfuel
gas spraying
A nonstandard
term for flame spraying.
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P
Particle
size
The average
diameter of a given powder or grit granule.
Particle
size distribution
Classification
of powdered materials as determined by various testing methods, defining
the particle sizes and quantities in a given sample.
Plasma
An electrically neutral, highly ionized gas composed of electrons,
ions, and neutral particles.
Plasma
spraying
A thermal
spray process in which a nontransferred arc is used as the source of heat
that ionizes a gas which, in turn, melts and propels the coating material
to the work piece.
Powder
Material manufactured
into finely divided particles. When blended for thermal spraying, powder
falls within a specific mesh range, usually finer than 120 mesh (125 microns).
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S
Spalling
The flaking
or separation of a sprayed coating.
Splat
A single sprayed
particle that resembles a thin, flattened drop of liquid, under magnification.
Spray-cast
A moving mass
of dispersed liquid droplets or heat softened particles deposited on a
substrate.
Substrate
Any material
to which a thermally sprayed deposit is applied.
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T
Thermal
Barrier Coatings
A group
of ceramic coatings, including Yttria Stabilized Zirconia (YSZ) and Magnesium/Zirconate,
used to protect the substrate in extreme heat environments.The heat rejection
properties of TBCs excel in applications to an excess of 3000 °F. TBCs
have been used successfully on piston tops, valves, exhaust systems, etc.
Thermal
Spraying
A group of processes in which finely divided metallic or nonmetallic surfacing
materials are deposited in a molten or semi-molten state onto a substrate
to form a deposit.
Torch
A device used
for fusing sprayed coatings; it mixes and controls the flow of gases.
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W
Wear
To damage,
erode or consume by long, hard use.
Wire
flame spraying
A thermal spray process variation in which the surfacing materials are
in wire form. (See flame spray)
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