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The Concept |
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Surface Engineering's
Extreme Coatings™ process utilizes emerging
Thermal Spray technologies to apply extremely wear resistant coatings
to virtually any size injection molding or extrusion screw. This process
provides crack free coatings with hardness values ranging from 55-75
on the Rockwell "C" scale in thickness from 0.003"-0.050".
Proprietary compositions of various Carbides, Ceramics, and Alloys are
incorporated to achieve abrasion resistant characteristics unmatched
by any of the conventional hardfacing alloys popular today! This process
completely eliminates the necessity for Chrome Plating, Flame Hardening,
or Nitriding, as the entire screw surface is coated, including the root
and flite sides. The coatings are much more wear resistant than any of
the three aforementioned processes, which makes the process excellent
for screws exposed to fiber filled compounds. Furthermore, the process
requires no preheat of postheat procedure, and during application, components
rarely exceed temperatures of 350°F. The low heat input helps prevent
distortion, minimizing costly straightening and/or machining time. It
also allows for the repair of D-2 Tool Steel components, typically scrapped
when completely worn. Preparation for screw rebuilding requires only
touch up work and the removal of old Chrome before the coating application.
Another unique aspect of the process is the "Dualcoat" concept.
This targets those who require extreme wear resistance through the root
of a screw, but whose barrels may not be compatible with the hardness
of the root coating. In this case, the flights may be coated with a more
traditional product, but will be masked during application of the harder
root coating, thus eliminating compatibility issues and maximizing screw
life. It also must be noted that today’s popular hardfacing alloys
can be applied via the Extreme Coatings process with an improvement in
screw life. This is due to the elimination of base metal dilution inherent
to welded overlays. Other applications where this process is currently
utilized includes Turbine Components, Bushings, Shafting, Mixer Blades,
Chutes, Fan Blades, Conveyors, Slurry Pumps, and many other applications
where extreme conditions of wear exist.  |
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The Process |
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| As the gas mixture
burns, the powder particles are melted and accelerated down the barrel.
Temperatures
above 6000 ºF are attained with the
combustion chamber while the substrate temperature is maintained below
350 ºF by a gas cooling system. Particle velocities of approximately
2,500 ft/s are produced. The kinetic energy released by impingement upon
the substrate contributes additional heat and promotes bonding, high
density, and appreciable hardness values. The coating is built up to
the specified thickness while the workpiece is rotated or passed in front
of the gun. |
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Component Preparation |
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Surface Preparation is the most critical step in a thermal spraying operation. Coating adhesion quality is directly related to the cleanliness and roughness of the substrate surface. The coating material and the substrate type are the major factors in determining what surface preparation is necessary to achieve consistent bonding. Sprayed deposits do not add to the strength of the substrate. The purposes of surface roughening are as follows:
Internal stresses from shrinkage develop in coatings and these
stresses increase with increased coating thickness. The stresses
are more severe in hard metals or ceramics. Roughening is a method
of reducing these stresses by dividing the internal stresses into
smaller components which will cancel each other out. As the layers
are folded up and down, the coating strength is improved. |
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Wear Mode |
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| Surfaces subjected to low stress abrasion show that material
has been removed by hard, sharp particles or other hard, sharp surfaces
plowing material out in the furrows. Grinding with a surface grinder
can be a controlled from of low stress abrasion. The low stress qualifier
means that the abradant is imposed on the surface with relatively low
normal forces. The operating forces must be low enough to prevent crushing
the abradant. Low stress abrasion rates are directly proportional to
the sliding distance and the load on the particles or protuberances and
are significantly reduced by hard microconstituents within the surface
microstructure. |
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Abrasion Resistance Data |
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The Coatings |
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Telar
Corp |
 Phone:
(800) 320-6115 Fax:
(440) 748-0304 |