What is Abrasive Blast cleaning?
Abrasive Blast cleaning is mechanical cleaning that makes use of the continuous impact of abrasive particles at high velocity on a steel surface through a jet of compressed air or by centrifugal impellers. The centrifugal impellers require large stationary equipment that is fitted with radial bladed wheels where the abrasive particles will be fed. As the wheels revolve at high speed, the abrasives are thrown into the steel surface. The force of impact will be determined by the size of the wheels and their radial velocity. Modern facilities that offer abrasive cleaning use about 4 to 8 wheels that are configured to treat steel surfaces with 100% efficiency in mill scale and rust removal.
Abrasives used in Abrasive Blast cleaning
A wide range of abrasives are used in Abrasive Blast cleaning from silica sand that is no longer allowed in many countries because of the overwhelming amount of dust that it produces to crushed nut shells and fruits kernels so that underlying material will not be damaged. The abrasives can also be metallic like steel shots or grit and non-metallic like metal slags and aluminum oxide as well as recycled abrasives in the form of plastic abrasives and glass grit. However, aside from the type of abrasive, size is also an important factor to be considered because it can affect the efficiency of cleaning. Generally, fine grades of abrasives are efficient in cleaning new steelwork whereas coarse grades are relatively more efficient in cleaning heavily corroded surfaces. In some cases, a mixture of grades might be required depending upon the condition of the steel surface.
The technology of wet abrasive cleaning
Surface cleaning through Abrasive Blast cleaning presents serious dangers to operators because of exposure to hazardous dust and creation of an explosive atmosphere. The introduction of water in blast cleaning has reduced the hazards of dust particularly in the removal of old lead based paints. The technology of mixing water with abrasives has been developed with the same pressure and equipment that is used for dry blast cleaning. Water is usually introduced behind the nozzle so that it can be atomized and accelerated through the nozzle orifice along with air and the abrasive. Water is also introduced in controlled amounts at the base of the blast pot and then mixed with air and abrasives as it passes through the blast hose. In some wet abrasive processes, inhibitors are used in water to prevent the formation of rust in the surface. However, it is important to determine whether there are traces of the inhibitor left on the surface and whether it will be compatible with coating that will applied.