We discuss the history of abrasive blasting, what types there are and provide an overview of the abrasive materials used as blast media.
What is Abrasive Blasting?
There are several reasons why abrasive blasting would be used, commonly these are for:
- making a rough service smooth
- making a smooth service rough
- altering the shape of the workpiece
- remove surface contaminants (such as rust or residue)
- remove previous coatings
- clean or prepare a surface
- finish a surface
There are a number of methods of abrasive blasting, each provide a different outcome and require the use of varying blasting materials or “blasting media”.
The type of blasting media used is dependent on the workpiece material and desired effect. Blasting media comes in a range of different densities, materials, hardness, particle sizes and shapes which all need to be considered in order for the desired effect to be achieved.
Abrasive blasting is typically done by using either a centrifugally powered wheel to propel the media at the surface of the workpiece or with compressed air which is the method typically used at ADS Laser Cutting. It can also be done by using a high pressure water jet with high velocity.
History of Abrasive Blasting
Modern abrasive blast cleaning is used in a variety of industries such as (but not limited to) oil and gas, steel fabrication, marine ship building, construction and the automobile industry.
Abrasive corrosion theoretically has been around since the Earth was formed. In the deserts for example sandstorms are a naturally occurring event, with these high-speed winds which carry sand and other particles being capable of altering the surface of an object (known as wind erosion) and have also been known to damage young crop plants.
Abrasive blasting as we know it today however, began with Benjamin Tilgham, who patented the first shot blasting machine in 1870. This was used to clean up painted and/or rusted surfaces. Thomas Pangborn developed this further in 1904 to include compressed air with the blast alongside deep cleaning of metal materials through the use of sandblasting.
A problem with sandblasting during the early 1900’s is the serious health implications as a result of high-risk exposure to silica dust. Water was originally introduced into abrasive blasting in the early 1950’s once silica sand had been banned in sand blasting. This ban was introduced due to the discovery silica fractures upon impact becoming respirable with this posing a high risk of Silicosis and other respiratory diseases to the operator.
Types of Abrasive Blasting
There is a wide range of terms used in abrasive blasting, including:
- Sand Blasting
- Shot Blasting
- Bead Blasting
- Wheel Blasting
- Air Blasting
- Wet Blasting
- Soda Blasting
- Dry-Ice Blasting
- Micro-Blasting or Pencil Blasting
The three most common methods of abrasive blasting are Sand Blasting, Shot Blasting and Wet Blasting.
Sandblasting when used in sheet metal fabrication, is the process of firing a blast media at high velocity typically out of an air-powered pressure gun (known as Air Blasting), towards a metal surface. This is done with two hoses; one which compressed air passes through, creating pressure. This pressure then pulls media from a tank through the second hose, before expelling both the air and sand together out of the gun. Sandblasting can be used to remove paint, residues from oxidation, rust, scratches, casting marks and is widely used for cleaning a surface before applying a finish, such as powder coating.
Shotblasting fires abrasive media like tiny pieces of metal (known as steel shot and steel grit) against a surface to remove impurities and clean it. It is also used to polish or strengthen (known as peen) metal and is often used as a method of preparing a workpiece for metal finishing. This method can be done by pneumatically accelerating the blast media towards the surface using compressed air inside of a blast cabinet (Air Blasting). It is also often done using Wheel Blasting, which instead of being propelled by compressed air, the media essentially ‘throws’ the shot or grit at the workpiece via a centrifugally powered rotating wheel.
Wetblasting is used to remove coatings, residues, corrosion and contaminants from hard surfaces and is similar to sandblasting only the blast media is dampened prior to blasting. Hot water and soap can be used at the same time as fine media such as plastic or steel meaning an operator can simultaneously degrease the surface while blasting. Methods include attaching either a Water Injection Nozzle (WIN) or Halo nozzle to a sandblaster which dampens the abrasive as it leaves the nozzle, by using cabinets or blast rooms, modifying sandblasters to store water and abrasives in a tank prior to them being drawn through using the Venturi Effect and with Vapor Abrasive Blasters where the water and abrasive are stored in a tank before being pushed into the airflow.
Abrasive Materials Used in Blasting
Abrasive materials can be either organic, plastic, metal, silicate, or stone. Each material type performs a particular task well due to a number of its key abrasive properties, which includes a mix of its hardness, shape, particle size and density.
Common abrasive materials include:
- Aluminium Oxide Grit
- Glass Beads
- Plastic Abrasive Grit
- Pumice Grit
- Steel Grit
- Steel Shot
- Walnut Shell Grit
- Silicon Carbide
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