Material: Recycled Glass Issue: Processed recycled glass has been sold as an abrasive blasting medium
under several brand names in different
parts of the United States. However, limited public information is available
regarding the performance of finely
sized crushed glass in abrasive applications
because manufacturers have developed
their own proprietary data.
Historically, the predominant
material used for abrasive blasting
was silica sand, hence the common
reference to “sandblasting.”
Other media include garnet,
staurolite and industrial by-products
such as coal slag, copper slag, nickel
slag and steel grit.
Even walnut shells and plastic
beads have been used for abrasive
blasting. Individual abrasive media performance depends
on hardness, shape, size, weight,
and other characteristics. Health- considerations are sometimes significant
in evaluating blasting abrasives.
For example, concerns about silicosis
due to the presence of crystalline
silica have resulted in very little
silica sand now being used in abrasive
blasting. Best Practice: While silica sand is a raw material used in the production
of glass (see Chemical Composition of Container Glass Best
Practice), the manufacturing process converts the crystalline structure
to an amorphous state.
Tests have shown that recycled
container glass contains less than
1% crystalline silica (see
Analysis of Glass Dusts Best Practice). Lower health risk represents a potential competitive
market advantage for recycled glass,
which can be processed to physical
characteristics similar to silica
sand for use as an abrasive. Crushed, graded glass described in this Best
Practice should be distinguished from
glass beads, which have been used
for abrasive blasting for many years.
Beads are spherical in shape
and are often made from post-industrial
recycled glass. Glass beads have been used especially in applications
where fine surface finishing is important. Finely-sized crushed glass is the same raw
material, but has an angular grain
shape, meaning that it does not leave
as fine a surface finish, but removes
paint and scale more quickly. Recycled glass has been successfully substituted for silica
sand and other blasting media in shipyard
trials conducted by Glass Recycling
Inc. of Marietta, GA, and in other
construction projects and equipment
cleaning.
Glass must compete with common
abrasive alternatives as well as niche
materials such as plastic pellets
used on sensitive surfaces.
Generally, coarser blasting
abrasive is used when heavy surface
build-up removal is required, while
finer sizes are used more for industrial
cleaning applications. Because of the tight gradation
requirements, and the need for clean,
dry, dust-free products, most glass
processing facilities are not capable
of generating crushed glass blasting
abrasive.
Blasting abrasive is typically
packaged in 50 and 100 lb. bags or
in bulk supersacks weighing 2,000
lbs. or more.
Recycled glass can be used
in the same blasting equipment used
for any of the common slag, with consideration
to blasting pressure, feed orifice,
and nozzle sizing. While not considered hazardous, glass dust
is an abrasive nuisance dust and every
consideration should be given to minimizing
dust generation in blasting. Tests have shown that various
sizes (12 mesh and finer) of recycled
glass media perform well in preparing
steel to a "white metal"
condition. Glass can be used as a dry blasting media or
combined with water for use in slurry
blasting. While some equipment can recover used media, tests conducted by
KTA Tator, Inc. found medium breakdown
rates during use at a level that would
not be suitable for more than one
use.
Performance results of post-consumer
glass and post-industrial glass as
a blasting abrasive in this same evaluation are illustrated in the table below. The results show that cullet performs favorably
when compared with 16x35 silica sand. Testing showed that, for blast cleaning of tight mill scale bearing
steel at 100 psi, the cleaning rate
of the post-consumer and post-industrial
products was higher than that of the
silica sand cleaning rate data.
Also, the consumption rate
of the post-consumer products is lower
than that of silica sand, while the
post-industrial product tested comparable
to the referenced silica sand in consumption
rate per square foot of blasted surface.
Implementation: The increased use of recycled
glass in abrasive blasting will require
improvements in both the quantity
and quality of public information
on its use. Benefits:
The
beneficial health implications of
using recycled glass instead of silica
sand may be significant.
Recycled glass may also offer
economic advantages over other abrasives,
when efficiently processed, due to
the abundant supplies of recovered
glass in many parts of the country.
While screening contaminants
and fine-sizing glass to appropriate
specifications for blasting media
is not inexpensive, costs of color-sorting
post-consumer container glass can
be avoided since this application
is not color sensitive. By offering an opportunity for mixed color
post-consumer glass as well as other
types of post-industrial glass, this
is an application that may improve
the economic viability of glass recycling. Application
Sites: Blasting shops, shipyards,
aerospace maintenance facilities,
and construction sites. Contact: For more information about this Best Practice, contact
CWC, mailto:info@cwc.org. References: Freas, Don, TriVitro
Corporation, Seattle, WA IMTEK, Inc.,
Blast Cleaning Abrasive Evaluation
Program, prepared by KTA Tator, Inc., 1995. John Hill, Hill Abrasives,
Ontario, New York, 315/946-5100. Small-Scale Recycled Glass-to-Fines Processing
System, CWC, June 1996. Product literature and telecon, Sept. 1996, Wayne McDonald, Glass Recycling
Inc., Marietta, Georgia. |
