How to Create an Abrasive Air Blast Room by Eric G. Thomas
Abrasive blasting has been around for as long as man could
throw a mineral abrasive, such as silica sand onto an object.
The reasons for the surface preparation vary from removing
an existing coating to preparing the surface to accept a new
coating. The idea is simple, and the industry was born with
the advent of the air compressor.
An abrasive blast room is the core to any modern abrasive
blast system. Confining the blasting operation to a controlled
clean environment enables efficient abrasive recycling.
The design criteria required for a properly sized blast room
system includes the size of the largest workpiece, the weight
of the largest workpiece, the material handling method, the
number of hours of blasting per day, and the base material
of the workpiece. Each of these items needs to be addressed
in order to finalize the configuration of the blast room.
The size of the largest piece will determine the dimensions
of the blast room enclosure. The width of the room is determined
by adding four to five feet on each side of the workpiece.
This space is required for the blast operator to maneuver around
the part and blast the part from various angles.
The height of the blast room is also determined by the workpiece
height, but the material handling of the part must also be
considered. For example, if a work car on a track is the material
handling method, then the height of the work car must be taken
into consideration to determine proper clearance of the blast
room roof panels. Again, a four- to five-foot clear area will
be required for the blast operator or up to seven feet clear
if the operator will walk on top of the part while blasting
(e.g. a tank in the railcar industry).
The length of the blast room is determined by adding four
to five feet on each end of the workpiece to allow for operator
a blast room can be done by three different methods of
air-flow design. The three air-flow designs are "down-draft," "end-to-center," and "cross-draft" ventilation.
various room air speeds are determined by the abrasive
that will be used in the blast room and the method the room
is to be ventilated. Table I is provided by ANSI and outlined
in ANSI Z9.4-1985, "Abrasive Blasting Operations–Ventilation
and Safe Practices."
most common and economical method of ventilation is "cross-draft." Basically,
the calculation for the dust collector size is determined
by the following formula: width of room x height of room
air speed (fpm) = cfm. Note: The cross sectional air speed
is typically 50 fpm for steel grit abrasive and 60 fpm for
nonferrous mineral abrasives.
For example, the dust collector sizing for a room 16 x 16
x 60 ft. that is using steel grit abrasive is calculated as
follows: 16 x 16 ft. x 50 fpm = 12,800 cfm required for a room
air-flow rate of 50 fpm.
reclaim system adds an additional air volume to the dust
collector that will range between 500 to 1,200 cfm; therefore,
the resultant dust collector will be sized for (12,800 cfm
+ 500 cfm.)—a total of 13,300 cfm.
When selecting the proper abrasive for the blast room, it
is important to look at the entire spectrum of parts that will
be blasted in the facility.
For example, a job shop blasting operation may see one type
of work for a period of time and another type of fabricated
aluminum parts for another period of time. In this type of
application, you would want to select a type of abrasive that
is applicable to both types of base material, i.e. steel (ferrous)
and aluminum (nonferrous), such as garnet, star blast, aluminum
While a mineral abrasive gives you the flexibility to accept
a variety of work into your shop, it does break down at a much
faster rate than steel grit abrasive. Typically, you can recycle
mineral abrasives about three to six times, based on operating
pressures at the nozzle and the initial size and hardness of
Steel grit abrasive also comes in a variety of sizes and hardnesses.
The typical recycle rate for steel grit (G-40) is 150 to 200
times. Again, this can vary based on operating pressure at
costs of spent abrasives are a major factor in abrasive
selection. The amount of waste that must by removed is directly
related to the recyclability of the specific abrasive and
the volume of abrasive that is used. This can result in
quantity of waste material that must be dealt with in regards
to "cost of disposal." This cost will vary based
on the blasting operation and coatings being removed. If
lead paint or zinc primer is being removed, the disposal
be up to $500 per 55-gallon drum of waste. The return on
investment (ROI) for a blast room facility is the key element
the investment in a blast room facility. Recycling abrasives
and minimizing waste disposal costs is the single most important
element in achieving a good ROI on the capital purchase.
The reclaim system is comprised of a floor reclaim and an
abrasive separator. The floor reclaim design can vary from
simple "sweep-in" designs
to "full" floor reclaims, which recover all the
abrasive through a grated floor. Reclaim designs vary based
on the manufacturer
and type of abrasive that is being reclaimed.
When a very light abrasive, such as small glass beads or a
fine aluminum oxide (i.e. 120 mesh or smaller) is being used,
the most common method of reclaim is a vacuum floor and cyclone
separator. This method is also used in most hand cabinets that
use suction or pressure blasting.
Single-screw partial reclaim system.
most reliable and cost-effective method of reclaim floor
is the mechanical screw floor with a belt and bucket elevator,
rotary scalping drum, and air-wash separator. There are four
different designs for a reclaim floor. They are single screw, "H"-shaped, "U"-shaped,
and full reclaim. The selection of the proper design is based
on production needs as well as economic concerns. The following
is a description and plan view drawing of each reclaim floor
partial reclaim system is the most economical floor design
available. The system contains the major components
found in reclaim systems including metering shed plates;
heavy-duty screw, belt, and bucket elevator; airwash separator;
plate rotary scalping drum separator; and abrasive storage
hopper with a caged man ladder and handrail. This reclaim
package can be expanded to an"H," "U," or
full-floor reclaim design. This floor design is for low-
H-Shaped partial reclaim system.
The "H"-shaped partial reclaim system adds two longitudinal
metered screw assemblies along each side wall of the blast
room. The position of the screw assemblies allows the abrasive
delivered from the blasting nozzle, which is either blown or
rebounded off the work piece, to strike the side walls and
fall into the screws, reclaiming approximately 60 to 90% of
the blast media. The remaining abrasive on the floor is pushed
into the screw assemblies at the end of the work shift. The
screws are protected from an overload by metering shed plates.
The "H"-shaped floor design is typically utilized
in a "flow thru" room configuration where heavy
workpieces or material handling devices can drive into the
room and position
the workpiece on the steel-covered concrete floor located
between the screws. This floor design is best suited for
The "U"-shaped partial reclaim system adds two longitudinal
metered screw assemblies along each side wall of the blast
room and positions the cross screw along the back wall of the
blast room. The position of the screw assemblies allows the
abrasive delivered from the blasting nozzle, which is either
blown or rebounded off the work piece, to strike the side walls
and back wall of the blast room and fall into the reclaim system.
A "U"-shaped floor design will reclaim 60 to 90%
of the blast media. The remaining abrasive on the floor is
pushed into the screw assemblies.
U-Shaped partial reclaim system.
screws are protected from an overload by metering shed
plates. The "U"-shaped floor design is typically
utilized in an "in–out" room configuration
where heavy workpieces or material handling devices can drive
into the room and position the workpiece on the steel- covered
concrete floor. This floor design is best suited for medium
to high production.
The full-floor reclaim system utilizes multiple screw assemblies
to create a fully automatic abrasive reclaim floor system.
All the abrasive that is blasted is returned to the separator
system. The full-floor reclaim design requires that the material
handling of the workpiece be intricately designed into the
configuration of the room. Material handling of the workpiece
includes a work car/track system, an overhead monorail crane,
an overhead bridge crane, or heavy-duty floor grating and support
steel sized to allow a forklift to drive onto the reclaim floor.
The full-floor reclaim design can be used with any room configuration.
This system is best suited for high-production requirements.
partial floor reclaim systems will have an added "clean-up"cost
associated with the ROI that must be calculated into the
justification for capital expenditure. Choosing the right
to best meet production and cost requirements will result
in the quickest return on your investment.
The material handling method of moving the workpiece through
your facility or just through the blast room must be considered
so the room is designed for that specific handling device.
As mentioned earlier, the partial reclaim floor designs lend
themselves to forklift trucks or driving the workpiece directly
into the blast room, such as construction equipment or trailers.
Full-floor reclaim system.
The full-reclaim floor design can be configured for a work
car track system, overhead monorail or bridge crane system,
or a combination of both. The blast room configuration will
vary based on your plant layout and the material handling method
for the workpiece.
A "flow-thru" room configuration is designed for
work to enter one end of the room and exit the room on the
opposite end. This configuration is typically used for an "in-line" production
flow of the workpieces. A "flow-thru" design requires
more floor space in your facility, in that you typically
allow for an in-bound and out-bound staging area prior to
production phase, such as paint.
An "in–out" room
configuration is designed for work to both enter and exit
the same end of the blast room.
This configuration is typically used because of space or
production flow considerations. The blast room and paint
booth are usually
side-by-side. This configuration allows for both rooms to
be presented the workpiece from a variety of sources and
while minimizing factory floor space requirements.
The amount of abrasive blasting that is done in an eight-hour
period and the number of blasters required for that production
level is another factor that dictates a blast room design.
For example, if you are currently operating with four blasters
in an outdoor sandblasting operation, you will require a blast
room with enough room, abrasive capacity, and reclaim equipment
to accommodate this production level.
The reclaim systems and room designs will vary in size and
capacity based on production levels.
A properly designed blast room facility will provide your company
the tools it needs to meet the demands for a clean environment
as well as providing a good ROI. Recycling blast abrasives
saves money by reducing waste. The enclosed blast room saves
money by allowing production to continue regardless of outdoor
G. Thomas has been involved in the abrasive air blast industry
since 1987 and oversaw the installation of over 1,500
air blast facilities.
Sandblasting Equipment offers blast equipment, supplies, parts and
accessories for sale and select blast equipment is available for rent.
We service most equipment that we sell or rent. We do not offer blasting
services. Images and content on this web site were created by or for
Norton Sandblasting Equipment. Unauthorized reproduction, distribution,
or attempts to use images or content without written permission will
result in legal action.