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WATER BLASTING MEDIA
Hydroblasting,
water jetting or water blasting are terms
commonly used when describing water as the tool
to do surface preparation. The use of water is a
technique for cleaning surfaces, which relies
solely on the energy and force of water striking
a surface to acheive its cleaning effect. In
principel abrasive is not used in
waterblasting equipments, hence, the problems
caused by dust pollution and by the disposal of
spent abrasives are eliminated.
SURFACE CONDITION AFTER WATERBLASTING
Flash rust :
When large areas
are waterblasted, flash rusting which
deminish the original surface standard may
occur, before painting can be carried out. The
degree of flash rusting depends on many factors,
such as humidity level, temperature and the
length of time the surface is exposed.
Degrees of flash
rust :
-
Light flash
rust : small quantities of
light tan-brown rust will partially
discolour the original steel surface. The
discolouration may be evenly distributed, or
in patches, but it will not be heavy enough
to mark an object brushed against the areas.
-
Medium flash rust :
a layer of light tan-brown rust
will cover the original steel surface. This
layer may be evenly distributed or in
patches, but it will be heavy enough to
easily mark objects brushed against the
areas.
-
Heavy flash
rust : a heavy layer of dark
tan-brown rust will be completely covering
the original surface. This layer will be
evenly distributed and will easily mark
objects brushed against the areas.
Temperature rise
:
The use of
waterblasting equipments will cause the temperature of
the steel to rise. The increase of temperature
of the steel surface can be substantial,
depending on the pressure of the equipment used
and will help waterblasted surfaces to
dry off faster, hence reducing the degree of
flash rusting.
Removal of
foreign elements :
The use of water
has the advantage of removing oil and grease
from the surface along with salt deposits. This
is a major plus point of waterblasting.
The grey, brown to black discoloration of
corroded and pitted steel after waterblasting
cannot be removed by further blasting.
Studies shows that this thin film consists of
mainly ferric oxide, which is an inert material.
As it is tightly adherent, it does not present a
serious contamination problem.
SURFACE PROFILE
Waterblasting
equipments
will not produce a surface profile as such.
Weakend steel might erode, resulting in metal
loss, but the surface profile exposed after
blasting will have been produced by earlier
surface preparation or corrosion.
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