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06-05-2016
What You Need to Know About Abrasive Blast Cleaning

 

The success of any coating application depends on several parameters that include surface preparation, skills of the coating applicator, film thickness, methods of application and the existing conditions at the time of application. The need for surface preparation varies but it generally depends on the type of substrate. There are substrates that require nothing more than simple cleaning with a dust cloth while other substrates require abrasive blast cleaning.

Abrasive blast cleaning is a process of cleaning a surface through the forceful application of abrasive media to remove unwanted rust, oxide and scale in preparation to industrial coating on the surface. Sometimes, the surface is prepared for other subsequent processes like anodizing and welding that requires a clean surface. Generally abrasive blast cleaning is considered a more economical process of surface preparation compared to electrochemical cleaning, pickling or hard finishing that is why it is mostly used on steel and/or iron substrates.

The methods of abrasive blast cleaning are segregated as dry blasting and air pressure blasting. Mechanical blasting which is considered dry blasting makes use of cabinet-like equipment to prevent the discharge of stray abrasives. The cabinet typically has one or more blast wheels that direct the abrasives at the work piece through centrifugal force. The abrasive blast cleaning pattern is in consideration of the surface design including the direction and shape of delivery. The volume of abrasives that are used in mechanical blasting is typically 250 feet per second to provide a high level of cleaning in a relatively short period of time.

Abrasive blast cleaning through the use of compressed air uses direct pressure or an induction method. Direct pressure blasting makes use of a pressurized container, where the abrasives are fed before it is piped to the blast hose and upper portion of the pressure vessel. Air pressure on the blast hose and upper part of the pressure vessel is usually 80 to 90 psi to allow the free fall of abrasive through an aperture at the bottom of the pressure vessel. As abrasives fall through, compressed air conveys it to the point of operation.

In the induction suction method, a blast gun is connected to an air pipe and a flexible hose that carries the abrasive. The abrasive hose is open to atmospheric air on the base of the machine hopper. As a result, when compressed air passes through the gun and over to the abrasive hose, a partial vacuum is created on the hose that draws or induces the abrasive in the gun to where it is propelled to the nozzle.

In induction gravity method, air and abrasive media is mixed and then gravity fed into an overhead storage. When air supply enters the gun at the point where the abrasive is entrained, a partial vacuum is created. Rapid expansion of compressed air when it emerges plus the force of gravity will provide final acceleration to the abrasives. However, this type of abrasive blast cleaning is only used for specialized applications like shot peening.

 


This works really well in comparison to a manual cleaning.
Posted by: Johnston | May 25, 2016, 1:47 pm
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