Types
of Abrasive Blasting
b) Wet
Wet-abrasive blasting is used to
control the amount of airborne dust. There are two general types of wet
abrasive blasting. In one, water is injected near the nozzle exit into the
stream of abrasive (Figure 2). In the other, water is added to the abrasive at
the control unit upstream of the nozzle and the mixture of air, water, and sand
is propelled through the hose to the nozzle. For both types of wet-blasting,
the water may contain a corrosion inhibitor. Inhibitors are generally sodium,
potassium, or ammonium nitrites, phosphates or dichromates. Inhibitors must be
chosen to be compatible with the primer that will be used. After wet blasting,
the surface must be rinsed free of spent abrasive. (The rinse water should also
contain a rust inhibitor when the blasting water does.) Rinsing can be a
problem if the structure contains a large number of ledges formed by upturned
angles or horizontal girders since water, abrasives, and debris tend to collect
in these areas. The surface must be completely dry before coating. When leaded
paint is present, the water and other debris must be contained and disposed of
properly. This waste may be classified as a hazardous waste under Federal and
local regulations, and must be handled properly.
Schematic Drawing of Cross Section
of Typical Water-Injected Wet Abrasive Blasting Nozzle
c) Vacuum
Vacuum blasting systems collect the
spent abrasives and removed material, immediately adjacent to the point of
impact by means of a vacuum line and shroud surrounding the blasting nozzle.
Abrasives are usually recycled. Production is slower than open blasting and may
be difficult on irregularly shaped surfaces, although shrouds are available for
non-flat surfaces. The amount of debris entering the air and the amount of
cleanup is kept to a minimum if the work is done properly (e.g., the shroud is
kept against the surface). This procedure is often used in areas where debris
from open air blasting or wet blasting cannot be tolerated.
d) Centrifugal
Cleaning by centrifugal blasting is
achieved by using machines with motor-driven bladed wheels to hurl abrasives at
a high speed against the surface to be cleaned. Advantages over conventional
blasting include savings in time, labor, energy, and abrasive; achieving a
cleaner, more uniform surface; and better environmental control. Disadvantages
of centrifugal blasting include the difficulty of using it in the field,
especially over uneven surfaces, although portable systems have been developed
for cleaning structures such as ship hulls and storage tanks. Robots may be
used to guide the equipment. In many cases, the abrasive used is reclaimed and
used again.
Leopad Group a leading provider of corrosion
protection services ranges from the scope of blasting and painting, insulation,
thermal spray application, passive fire protection, refractory and other
services such as scaffolding, cable tray systems and cathode protection.
We are a
Malaysian company with close to 3000 staff and over 10 offices and fabrication
yards throughout the country. Leopad Group is dedicated to being the market
leader for corrosion protection and provide the highest standards in the
industry with the convenience of providing multi-disciplinary services through
a single point of contact.
For further
enquiries on our services, please contact our Business Development Department
at +603-22600200 , website www.leopad.com or email at hq@leopad.com
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