What is Abrasive Blasting

Abrasive blasting is the process of blasting an abrasive material on a surface with high pressure. In other words, the kinetic energy from the abrasive material is transferred to the metal surface or masonry. This is one of the most effective methods used to remove foreign coating on a surface.

There are various industries like the automobile industry and shipbuilding that use this form of blasting. A portable blast, a blast cabinet, and a blast room is the basic equipment used in this process.

The purpose of propelling a stream of abrasive material on a surface is as follows:

• To roughen a smooth surface
• To smooth out a rough surface
• To remove flash

• To give shape to a surface
• To remove contaminants and other unwanted constituents on a surface
• To give a matte finish
• To eliminate blur on a surface

There are various abrasive materials that we use to coat on a surface. But sand is the commonly used abrasive material. This is called sandblasting. Some of the other material that is used is listed below.

• Staurolite
• Coal slag
• Olivine

• Glass beads
• Copper slag
• Nickel slag
• Hematite
• Aluminum oxide
• Walnut shells
• Crush glass
• Garnet
• Steel grit

Before selecting an abrasive, some of the factors such as size, shape, mass, hardness, color and chemical constituents of the abrasive material should be considered.

There are basically three main components involved in this process.
1. Abrasive Container - It contains the abrasive material.
2. Propelling device - Device that expels the abrasive to the nozzle. e.g. pump
3. Blasting nozzle - The abrasive material comes out from the nozzle.

The composition is forced out from the nozzle using any of the following mediums:

• Air pressure
• Water pressure
• Centrifugal wheel (centrifugal force and inertial force)

The propelling systems are discussed below.

1. Suction Blast Systems
The suction blast system consists of two hoses. One hose is connected to the abrasive container and the other hose is connected to the compressed air system. The high pressure of the compressed air creates a vacuum inside the chamber (blast gun).

Due to this vacuum, the reverse force pulls out the abrasive material from the container and expels it through the nozzle.

2. Pressure Blast Systems
In this system, the abrasive is not drawn from the container, instead, the pressure tank is utilized to expel the abrasive to the nozzle. The abrasive forces out through the blast hose, and reaches the nozzle. The velocity of the expelled abrasive is higher as compared to suction systems and thereby the efficiency and production rate is increased.

* Suction blasting and pressure blasting systems work on air pressure propelling methods

3. Barrel Blasters
Barrel blasters are designed to run continuously for a long time. It is a centrifugal type of system, that uses centrifugal forces to discharge abrasives on a surface. The high pressure required to propel the abrasive material is done by compressed air.

Centrifugal wheel systems use centrifugal and inertial forces to propel the abrasive onto a surface. A rotating impeller is used in the system that combines the mentioned forces and blasts the material. It is used for heavy-duty works and provides good speed and efficiency.

The parts of this system include a barrel, dust collector and a reclaim system (high performance blower expels the material and debris is generated). Once the timer is set and the abrasive is filled in the barrel, the device will start functioning.

4. Wet Blast Systems
A pump is used to agitate the water and the abrasive present inside the blast system. The mixture of water and abrasive makes a slurry, which is used in the system.

The velocity of the slurry comes out of the nozzle in a controlled way, and it is used for peening (improving the surface of the metal) and cleaning the metal surface. Though dry blasting is widely used, some applications demand wet blasting.

Care should be taken while performing the operation as there are chances of introducing contamination on the surface (hammering effect), especially while working with wet blasting systems. Abrasive systems produce a lot of dust and contaminated material after the operation.

The dust, thus produced during the operation is collected inside the dust container present in the blasting system. Lastly, operating abrasive blasting systems can be destructive also. So, it should be carried out with utmost cautiousness.