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Abrasive blasting is the operation of cleaning or preparing a surface by forcibly

propelling a stream of abrasive material against it. Usually explained as the use

of a material against another material to make it smoother, remove surface

contaminants or to roughen a surface. It is also the appropriate term for what is

known as glass bead blasting, sandblasting, sand carving, sodablasting or shot

blasting.

Surface cleanliness and roughness

Abrasive-blasted surfaces are characterised by two kinds of information that are both

essential but fundamentally different, although sometimes mistaken for each other:

cleanliness and roughness.

Cleanliness reflects the degree of presence of undesirable residual contaminants on the

surface, whereas roughness refers to the micrometric shape of the surface, called the surface

 profile.

Operations

Abrasive blasting: Abrasive blasting or air blasting is a method of propelling abrasive using

a compressed gas (typically air) or pressuried li!uid (typically water) as the propellant.

"here are numerous generic terms for this application usually related to the abrasive media in

use# common terms include sand blasting, shot blasting, grit blasting, bead blasting and blast

cleaning.

"he large variety of applications creates the need for a diversity of e!uipment:

• Portable blast equipment (aka blast pot): $ry abrasive blasting applications are

typically powered from a diesel air compressor. %ost applications involve a

 pressuried vessel that contains the abrasive and meters it into the compressed air

stream. &et blasting is accomplished by in'ecting the abrasive into a pressuried

water stream or creating a slurry of abrasive and water that is pressuried or

introduced into a compressed air stream. &et blasting is often used in applications

where the minimal dust generation is desired. ortable applications may or may not

recycle the abrasive and portable dry blasting generally does not attempt to contain or

minimie the dust generated from the operation.

• Blast cabinet: A blast cabinet is essentially a closed loop system that allows the

operator to blast the part and recycle the abrasive. A typical blast cabinet consists of

four components# the containment (cabinet), the abrasive blasting system, the abrasive

recycling system and the dust collection. "he operator blasts the parts from the

outside of the cabinet by placing his arms in gloves attached to glove holes on the

cabinet, viewing the part through a view window and, typically, turning the blast on

and off using a foot pedal or treadle. Automated blast cabinets are also used to process

large !uantities of the same component and may incorporate multiple blast noles

and a part conveyance system.

o "here are three types of blast systems used in a blast cabinet. "wo systems(siphon and pressure) are dry and one is wet:

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A siphon blast system (aka suction blast system) uses the compressed

air to create vacuum in a chamber (known as the blast gun). "he

negative pressure pulls abrasive into the blast gun where the

compressed air directs the abrasive through a blast nole.

A pressure blast system incorporates a pressuried vessel. "he abrasiveis stored in the pressure vessel then sealed. "he vessel is pressuried to

the same pressure as the blast hose attached to the bottom of the

 pressure vessel. "he abrasive is metered into the blast hose and

conveyed by the compressed gas through the blast nole.

&et blast cabinets use a slurry system that in'ects the slurry into a

compressed gas stream. &et blasting is typically used to create a

surface profile when the frictional heat of dry blasting would damage

the part.

•

Blast room: "his is a larger version of a blast cabinet with the eception that the blastoperator works inside the room. A blast room always has three of the four components

of a blast cabinet: the containment, the abrasive blasting system and the dust collector.

%ost blast rooms have recycling systems ranging from manual recycling (sweeping

and shoveling the abrasive back into the blast pot) to full reclaim floors that convey

the abrasive pneumatically or mechanically to a device that cleans the abrasive prior

to recycling.

Wheel blasting: &heel blasting or shot blasting is typically categoried as an airless blasting

operation because there is not a propellant (gas or li!uid) used to propel the abrasive. *ather,

a centrifugal wheel is used to propel the abrasive against the substrate. &heel machines are a

high-power, high-efficiency blasting operation with recyclable abrasive (typically steel orstainless steel shot, cut wire, grit or similar sied pellets). +pecialied wheel blast machines

 propel plastic abrasive in a cryogenic chamber# this type of wheel blasting is usually used for

deflashing plastic and rubber components. "he sie of the wheel blast machine, and the

number and power of the wheels vary considerably depending on the parts to be blasted as

well as on the epected result and efficiency.

!dro"blasting: ydro-blasting, commonly known as water blasting, is a common abrasive

 blasting operation because it is very effective and, in most cases, will only re!uire one

operator. ydro-blasting is the process by which a highly pressured stream of water is used to

remove old paint, chemicals, or buildup without damaging the original surface. "his method

is ideal for cleaing internal and eternal surfaces because the operator is generally able to

send the stream of water in places that previously were deemed unreachable. A ma'or benefit

of hydro-blasting is the ability to recapture and reuse the water, thus eliminating waste and

the impact on the environment.

#icro"abrasive blasting: A dry abrasive blasting process. "ypically pressure blast systems

as this allows the feed of abrasive media to be controlled independently of blast pressure but

some systems are siphon blasters. %icro-abrasive blasting uses smaller noles (typically

./ mm to 0./ mm diameter) to provide a fine stream of abrasive accurately to either a small

 part (mm sie) or a small area on a larger part. 1enerally the area to be blasted is from about

0 mm to only a few cm at most as abrasive blasters with larger noles are faster for largerareas. %icro-abrasive blasting uses media with particle sies from 0 micrometres up to

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about 0/ micrometres and usually higher pressures than most of the larger blasters 2 psi

(3 ka) to 0/ pounds per s!uare inch (0, ka) deliver sufficient energy to these small

 particles. "he abrasive media is generally not recycled as the particles either shatter on impact

or lose their sharp edges. Also known as pencil blasting, the fine 'et of abrasive is accurate

enough to write directly on glass and delicate enough to cut a pattern in an eggshell.

Abrasives

Silica sand: +ilica sand is the most commonly used abrasive and typically has the most

negative impact. "he silica sand !uickly breaks up and creates large !uantities of dust, which

when eposed to the operator can cause +ilicosis, a debilitating lung disease. &hen silica

sand is sold for the purpose of blasting, it is often coated with resins to control the dust from

the breaking sand. 4ote: %ost larger silica sand company5s will not sell sand for the purpose

of sandblasting due to high volume of dust creating by the sand breaking when hitting the

ob'ect. i.e. 6.+. +ilica Co.

$oal or smelter slag: Coal or smelter slag contains a low silica content and therefore does

not cause +ilicosis. owever, these abrasives have been reported to release other aardous

Air ollutants (A5s) into the air.

#etallic% s!nthetic% and mineral: "hese other types of abrasives are growing in popularity

due to the low dust creation and reclamation of material. 7ach of these abrasives report

significantly less dust and waste than sand and coal8slag abrasives.

Organic: "ypically ground nut shells or fruit kernels. "hese soft abrasives are used for

cleaning of brick or stone work or the removal of graffiti without damaging the underlying

material. Also used for the removal of conformal coatings from printed circuit boards forrework.

Safet!

Cleaning operations using abrasive blasting can present risks for workers5 health and safety,

especially in air blasting applications. Although many abrasives used in blasting booths do

not have a haardous component (steel shot and grit, cast iron, aluminum oide 9aka

corundum, garnet, plastic abrasive and glass bead), other abrasives (silica sand, copper slag,

nickel slag, and staurolite) have varying degrees of haard (typically free silica or heavy

metals). owever, in all cases their use can present serious danger to operators, such as burnsdue to pro'ections (with skin or eye lesions), falls due to walking on round shots scattered on

the ground, eposure to haardous dusts, heat ehaustion, creation of an eplosive 

atmosphere, and eposure to ecessive noise. ;lasting booths and portable blaster5s

e!uipment have been adapted to these dangers. <+A (<ccupational +afety and ealth

Administration) mandates engineered solutions to potential haards, however lobbying has

allowed silica sand to continue to be used even though most commonly used blast helmets are

not sufficiently effective at protecting the blast operator (respiratory protection is approved

 by 4=<+ - 4ational =nstitute for <ccupational +afety and ealth).

"ypical safety e!uipment for operators that are open air blasting or blasting in a blast room

include the following:

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• ositive pressure blast hood or helmet - "he hood or helmet includes a head

suspension system to allow the device to move with the operator5s head, a view

window with replaceable lens or lens protection and an air feed hose.

• 1rade $ air supply - "he air feed hose is typically attached to a grade $ pressuried

air supply. 1rade $ air is mandated by <+A to protect the worker from haardousgases. =t includes a pressure regulator, air filtration and a carbon monoide alarm.

• 7ar protection - ear muffs or ear plugs.

• ;ody protection - ;ody protection varies by application but usually consists of

gloves, and overalls or apron (minimal), leather coat and chaps, or cordura8canvas

 blast suit.