 |
Testing
Washed Bottles for
the Creation fof Glass Fusing Kits
|
Report No. GL-98-2
FINAL REPORT
Prepared for:
CWC
A division of the Pacific
NorthWest Economic Region (PNWER)
2200 Alaskan Way, Suite 460
Seattle,
WA 98121
December 1998
Prepared by:
Skookum, Inc.
Copyright © 1998 CWC. All rights reserved.
Federal copyright laws prohibit reproduction, in whole or in part, in
any printed, mechanical, electronic, film or other distribution and storage
media, without the written consent of the CWC.
To write or call for permission: CWC, 2200 Alaskan Way, Suite 460,
Seattle, Washington 98121, (206)
443-7746.
Disclaimer
CWC disclaims all warranties to this report, including
mechanics, data contained within and all other aspects, whether expressed or
implied, without limitation on warranties of merchantability, fitness for a
particular purpose, functionality, data integrity, or accuracy of results. This report was designed for a wide range of
commercial, industrial and institutional facilities and a range of complexity and
levels of data input. Carefully review
the results of this report prior to using them as the basis for decisions or
investments.
LINKS
This report contains links to outside resources and
documents that are pertinent to the context of the information in this
report. The following list will take
you to the point in the report where you can use each link:
CWC (formerly the Clean Washington
Center)
NIST Manufacturing Extension Service
The Pacific Northwest Economic Region (PNWER)
U.S. EPA
A report describing the fusing
process
A manufacturer of fused glass
tile
How to make permanent molds
How to make a shaker table
How to find the best particle density
A manufacturer of glass kilns
A manufacturer of electronic controllers
for kilns
A manufacturer of glass processing
systems
CWC’s Best Practices in Glass
Recycling (INSERT ON PAGE 10)
ACKNOWLEDGMENTS
CWC
is a nonprofit organization providing recycling market development services to
both businesses and governments, including tools and technologies to help
manufacturers use recycled materials.
CWC is an affiliate of the national Manufacturing Extension Partnership
(NIST MEP) – a program of the US
Commerce Department’s National Institute of Standards and Technology. The MEP is a growing nationwide network of
extension services to help smaller US manufacturers improve their performance
and become more competitive. CWC also
acknowledges support from the US Environmental Protection Agency and
other organizations.
TABLE OF
CONTENTS
Page
1.0 INTRODUCTION.............................................................................................................. 1
2.0 SUMMARY OF GLASS FUSING PROCESSES............................................................ 3
2.1
Glass Fusing Process................................................................................................... 3
2.1.1
Collecting and Color Sorting Wine Bottles..................................................... 3
2.1.2
Washing the Bottles in the Wine Bottle Washing Machine.......................... 3
2.1.3
Breaking the Bottles for Volume Reduction and Shipment........................... 4
2.1.4
Having the Broken Glass Ground to Four Mesh Sizes.................................. 4
2.1.5
Testing the Fuseability..................................................................................... 5
2.1.6
Designing the Kits............................................................................................ 6
3.0 COST ANALYSIS.............................................................................................................. 7
3.1 Estimate of Costs........................................................................................................ 7
4.0 INSTRUCTIONS FOR THE FUSING KITS.................................................................. 8
4.1
Colors and Grades....................................................................................................... 8
4.1.1
Glass Particle Sizes and Characteristics......................................................... 8
4.1.2
Combinations of Grades.................................................................................. 9
4.2
Moldmaking................................................................................................................ 9
4.3
Kiln Casting.............................................................................................................. 11
4.4
Recommendations.................................................................................................... 12
5.0 REFERENCES................................................................................................................. 13
APPENDICES
Appendix 1: Firing Schedules A, B1, B2, and B3
Appendix 2: Glass Fusing Project Actual Costs
Appendix 3: Sample Tile Evaluation Sheet
1.0 INTRODUCTION
The use of recycled glass as a raw material for
manufacturing products by fusing finely crushed glass is a growing area of
interest by small
businesses. Glass fusing consists
of placing finely crushed glass into a mold and then heating the glass in a kiln with electronic controls to
approximately 1500° F. At that temperature, the glass particles
fuse, or sinter, into a solid mass and take the shape of the mold.
Skookum, Inc., is a business
in Port Townsend, Washington, employing developmentally handicapped clients in
business enterprises. The company also
operates the Jefferson County Recycling Center, where collected recycled materials are
sorted.
Beginning in 1996, Skookum established a division within the corporation
dedicated to washing wine bottles for resale to the wine industry. That business generates a significant amount
of waste in the form of bottles that have been washed, but cannot be sold
because they are the wrong style or have surface blemishes.
On one occasion, some of
Skookum’s washed waste bottles were crushed and then used by a small glass
fusing company as a raw material. Those
bottles were found to fuse more cleanly than other post-consumer glass bottles. It was assumed that the process for washing
the bottles, which consisted of a caustic (usually sodium hydroxide) soak
followed by several clean
water rinses, resulted in a glass that was cleaner, and therefore contained
less inorganic particles to inhibit the glass fusing process than the unwashed
bottles. In addition, technical
literature established that devitrification of glass requires inorganic sites
around which crystals form. Cleaner
glass may inhibit devitrification, with coincident loss of gloss, as a result
of having fewer sites for initiation of crystal
growth.
This information prompted
Skookum’s management to consider whether it might be possible to find markets
for washed bottles in the nascent glass fusing crafts industry.
In 1997, Skookum responded to
a CWC Request for Proposals with a plan requesting support in assembling and testing glass fusing crafts kits. The target market for the kits would be high
schools and ceramics supply stores.
This report presents a summary
of the glass fusing process used to create the glass fusing kits, instruction
sheets written for inclusion in the kits, and a cost analysis of the materials
used in kit production. The costs are
described both as the project was implemented and assuming production scale.
2.0 SUMMARY OF
GLASS FUSING PROCESSES
2.1
GLASS FUSING PROCESS
The following steps were
necessary to create the glass fusing kits:
·
Collecting
and color sorting the wine bottles.
·
Washing
the bottles in the wine bottle washing machine.
·
Breaking
the bottles for volume reduction and shipment.
·
Having
the broken glass ground into four different mesh sizes.
·
Testing
the fuseability by making tiles.
·
Designing
and testing the kit.
2.1.1
Collecting and Color Sorting
Wine Bottles
Collected recycled materials were sorted at the
Jefferson County Recycling Center (operated by Skookum, Inc.) and some of the
wine bottles used for this study were recovered from this recycling
center. In addition, collections were
made by placing a labeled, public drop-off bin in front of the Skookum
Environmental Services Recycling center in Port Townsend. The drop-off was popular with the public and
produced cleaner containers than those recovered from the recycling center.
Several of Skookum’s developmentally disabled
workers were trained to sort the bottles by color and to remove trash and
unusable bottles; unusable bottles included bottles that were too large for the
washing machine and those that had debris inside the bottles. The colors chosen for the kits were Deadleaf
Green, Emerald Green, Bright Green, and Clear.
2.1.2 Washing the Bottles in the Wine Bottle
Washing Machine
Skookum’s bottle washing machine was manufactured in
Austria. While the machine is fairly
new, it is temperamental and prone to breakdowns, which are expensive and time
consuming. The general washing process
is as follows. First the bottles are
soaked in a hot caustic solution to kill bacteria and remove labels. Then the bottles are rinsed several times
with clean water. The bottles are
carried through the process on a moving belt with "cradles."
Washing bottles for resale to the wine industry has
proven to be more technically challenging than originally expected. The heated, two percent caustic soda soak
does not remove the pressure sensitive labels on many American wine bottles. This necessitates the rewashing of many of
those bottles. In addition, if bottles
are dusty, the machine does a poorer washing job. In general, washing the bottles is highly labor-intensive with
high maintenance costs. For a more
complete description of bottle washing, see CWC report GL-97-12, "A Model
for a Bottlewashing Plant."
If washing glass for fusing became a full-time
operation, washing individual bottles may not be the most efficient procedure.
A more cost-effective method might be to break the bottles first, then
wash them in a continuous process. This
would eliminate the need to handle the bottles individually. It may also be easier to remove labels through
a combination of screening and washing of crushed bottles than washing whole
bottles.
2.1.3 Breaking
the Bottles for Volume Reduction and Shipment
Glass breakers are common in the recycling industry
for volume reduction of recycled glass prior to shipping. For this project, a glass breaker was used
to break the washed bottles into pieces that were approximately one to two
inches in diameter. The pieces were
loaded into fiber bags that hold approximately one ton of glass.
2.1.4 Having the Broken Glass Ground to Four
Different Mesh Sizes
After crushing, the glass was shipped to TriVitro Corporation,
a Kent, Washington, company
specializing in glass grinding for various specialty markets, especially
sandblasting abrasives. To prevent
cross-contamination from other kinds of glass, TriVitro used a separate
crushing line dedicated to fusing glass to process the glass for this
project. Systems are available for
performing this type of glass processing.
TriVitro processed the glass and generated the
following grades (sizes are given in Standard U.S.Mesh):
·
3
x 6 mesh;
·
6
x 20 mesh;
·
20
x 50 mesh; and
·
50
mesh minus.
Each grade was made in the four
colors previously mentioned. In all, 16
separate glass grades and colors were produced.
2.1.5
Testing the Fuseability
The CWC has published four
“Best Practices in Glass Recycling” covering different aspects of the glass
fusing process. Within the Best Practices in Glass Recycling Manual
see the following:
·
Fusing Recycled Glass
·
Permanent Molds for Fusing Glass
·
A Simple Vibratory Compaction Table
·
Simple Particle Packing
These
Best Practices are excerpted in the instruction sheets section of this
report. A number of books have also
been written on glass fusing as an art and a craft (for examples, see
References). However, it is important
to understand that the type of glass that is generally used in arts and crafts
is quite different from recycled container glass. Soda lime glass used for container manufacturing “devitrifies,”
or returns to the crystalline state, very easily upon reheating. This can result in dull and uneven tiles.
Two
individuals with experience fusing container glass were selected to test the
fuseability of the washed, graded glass samples. Samples and test results were to be used to confirm the efficacy
of the glass for fusing and as a basis for the instruction sheets. Tiles measuring 4”x4” were chosen as the
test standard; each tile weighed about 200 grams. Samples of the glass were heated in standard electric
"potter's" kilns with electronic digital controllers at various
heating and cooling rates to a variety of maximum temperatures. This was done to optimize the fusing process
with this particular glass and to develop straightforward instructions for
fusing the washed bottle glass using commonly available equipment.
Following the initial testing, confirmation tests
were run by local ceramic artists and high school ceramics classes with similar
results. The most common concerns
involved temperature control and variations from the suggested firing
schedules. This feedback confirmed the
fact that each kiln performs differently.
Therefore, any person interested in trying kiln fusing should initially
run a number of tests to confirm the best profile for the specific kiln.
There was positive feedback from the high school
testers and many comments concerning how clean the ground glass was; feedback
on the mold material was also positive.
Some of the testers preferred using one-time plaster molds and these
also worked well.
2.1.6
Designing and Testing the Kit
The kits were designed to be sold primarily to high
school ceramic departments and through ceramic supply stores. There are 16 bags in each kit and each kit
contains a different size and color of ground glass. Of the 16 bags, 12 contain two pounds each of the coarsest ground
glass. The other four contain one pound
each of the finest ground grade (of which there is less material produced in
the grinding process). There is also a
three-pound bag of premixed mold material in each kit. An instruction sheet, describing the basic
glass fusing process, is also included in the kit.
3.0 COST
ANALYSIS
When Skookum was washing wine bottles for resale to
the wine industry, the company determined that the sorting and washing process
cost 25 cents per bottle, including labor and facilities expenses. On average, 1,400 wine bottles weigh one
ton. Therefore, Skookum’s cost for
washing is about $350 per ton.
3.1 ESTIMATE OF COSTS
The following is an estimate of Skookum’s direct
expense for each kit, projected to production volumes (See Appendix 2 for
actual expenses of this project):
Washed
glass (.25/pound x 28 pounds) $
7.00
Glass grinding (on contract w/TriVitro)
[$300/ton = .15/pound x 28 pounds] $ 4.20
Glass transport (.10/pound x 28 pounds) $ 2.80
Kit packaging $
3.00
Kit literature $
2.00
Moldmaking
material $
2.00
Kit assembly $
2.00
Direct management $
2.00
Direct kit cost $25.00
Defective kits (20%) $
5.00
Total direct kit
cost $30.00
At 200 grams per 4"x4" tile, each kit will
make 63 tiles. Interviews with retail
sales organizations and crafts people determined a reasonable retail price of
$95. This implies a wholesale price of
$47.50. Given direct costs of $30.00
for kit materials and assembly, $47.50 may be a feasible wholesale cost.
In addition, it may be possible to develop an
aftermarket of people who have learned the process and only want to buy glass
for tilemaking in specific sizes and colors in bulk.
4.0 INSTRUCTIONS FOR THE FUSING KITS
Instructions that would be included in each kit
consist of four sections that cover:
(1) colors and grades; (2) moldmaking; (3) kiln casting; and (4)
recommendations.
4.1 COLORS AND GRADES
Included in the kit are four colors of glass, each
in four grades. The colors are Clear,
Dead Leaf Green, Emerald Green, and Bright Green.
4.1.1 Glass particle sizes and
characteristics:
3x6 Coarse: Tiles made from this grade will have the clearest, most
transparent crystal appearance. Some
tiny air bubbles will be captured inside the tiles. There may be internal cracks and occasional surface bumps. This size is better for decorative objects
than for tiles because the clarity will reveal mounting adhesive through the
tile.
6x20 Medium: Tiles made from this grade will have excellent clarity and good
surface gloss. There will be some
bubbles captured within the tile. This
grade is good for both tiles and art objects.
20x50
Fine: Tiles made from this grade
will have less clarity and will be translucent rather than transparent. The tiles will have excellent surface gloss
and less internal bubbles. This is the
best single size for all-around fusing work.
-50 Extra
Fine: Tiles made from this grade
will be opaque with good surface gloss and have a fine-grained texture. Because it is so fine, any possible
contamination will also be very small. It
will also shrink more in thin tiles.
4.1.2 Combinations of grades
Combining 6x20, 20x50, and -50 is not recommended;
the large 20x50 particles do not flow into the surface, leaving a rough or
mottled look.
Combining 20x50 and -50 is recommended as the best
all-around fusing glass. It combines
the glassy qualities of the 20x50 fine with the fault resistance of the -50
fine (mix a ratio of 2:1 Fine:Extra Fine).
4.2 MOLDMAKING
These are general instructions for making simple
molds (square tiles, simple shapes) out of the mold material provided in the
kit. The mold material is a mix of
calcium aluminate cement and fused silica aggregate, with a ceramic additive to
give a fine-grain texture. These molds
can be reused many times, are lightweight, and easy to clean for reuse. For other mold mixes, see References.
1. Prepare a pattern of the object to be cast in
glass. Make a "master" tile
to be reproduced in glass out of a piece of something soft, like foamboard or
clay, to the shape desired. To make the master, use something soft
because the mold material shrinks as it dries.
Hard materials will get stuck when the mold dries. Also, because the glass sand will shrink
when fused, use a 3/4" thick pattern if you desire a 3/8" thick
finished tile. Make the edge of the
pattern slightly angled to facilitate easy removal of the pattern from the cast
mold. In addition, the master cannot
have any undercuts because the fused glass piece must drop directly out of the
mold. The cast mold is made in the mold
box.
2. A mold box is a
base with four sides that is strong enough to hold wet mold mix and can be
easily disassembled to remove the mold; painted scrap plywood works well. The sides can be nailed, screwed together,
or tightly bound with adhesive duct tape.
Single-use mold boxes can be made out of pieces of cardboard cut, bent,
and taped to make a box. The master
pattern is secured to the bottom of the box; screws work best, but other
methods, like two-sided carpet tape, will work as well. The size of the box should be large enough
so that the center pattern has at least a 1/2" clearance from the outer
walls all the way around, including the top.
Before filling the mold box with cement, coat the inside with vegetable
oil, as this will help with releasing the mold from the master after it
hardens.
3. Measure out enough dry mold mix to fill the mold box, plus a
little extra.
4. In a separate container, add water to the mix
a little at a time and stir until the mix is completely wet. It is important not to add too much water
because this will weaken the mix. Use
just enough so that the mix will work comfortably and settle into the mold.
5. Fill the mold box to the top
with the wet mix. Tap the mold box to
remove any bubbles and trowel the exposed surface to make it smooth; this will
help it to shed less grit later. At
this time, the back of the mold can be inscribed with a name, date, number,
etc.
6. Allow the mold to dry for about eight hours and then remove it
from the mold box.
7. Pre-fire the mold in the kiln
and soak (leave at temperature) at 1700° F for one hour. This proofs the mold
to withstand the fusing temperature of glass.
8. Before filling the mold with
glass, apply a mold release (Self Primer for Glass™) to the mold. Alumina hydrate mixed with water can also be
used; mix it until it is the consistency of paint and then brush on the
mold. The release agent should then dry
before using. These products can be
purchased at ceramic supply businesses.
As these molds can be reused many times, reapply the mold release as
needed. The mold should be cleaned
after use with a putty knife or steel brush.
4.3 KILN CASTING
1. Apply the mold release and fill the mold with
the glass color or color mixtures desired.
The coefficients of expansion for all colors of this glass are well
matched and will generally give no problems of defects. See Section 1 for grade compatibility.
2. Load the kiln with molds,
making sure to leave space around each mold and one or two inches from the kiln
walls.
3. Start the firing using the
established firing schedule and the programmed kiln controller. Four suggested firing schedules, in order of
best test results, are as follows (See Appendix 1):
·
Heat
to 1550° F as quickly as possible; soak for 15 minutes; turn off the kiln and
cool naturally.
·
Heat
at 500° F/hour to 1550 ° F; soak five minutes; turn off the kiln and cool naturally.
·
Heat
at 500° F/hour to 1600° F; soak five minutes; turn off the kiln and cool
naturally.
·
Heat
at 500° F/hour to 1650° F; soak for five minutes; turn off the kiln and cool
naturally.
4. Monitor firing and adjust temperatures as
necessary. It may help the glass to
stay "glassy" if the kiln is manually “crash cooled" from the
highest temperature down to 1050° F if
the kiln and controller are unable to cool quickly. As there are many different types of kilns, operators will have
to determine this.
5. Wait
until the kiln is completely cooled before removing the molds.
4.4 RECOMMENDATIONS
1. After removing the tiles, they can be cleaned
several ways. Rinsing the tiles with
water will remove most of the mold release that may have stuck to the
tiles. If needed, soaking the tiles in
vinegar will also help with mold release.
In addition, abrasive pads may be used to scrub the surface. If there are sharp points around the edges,
they can be removed with a grinding wheel.
Always wear goggles and gloves and follow safe shop practices. Experiment with these tools and processes to
find the one most suitable.
2. For best
results, fire together only those molds filled with glass of the same particle
size, range or combinations.
3. Unused glass should be kept
away from mold mix, ceramic dust, grit, metal, plastic, wood or organic
contaminants. Unused mold mix should be
kept in sealed dry containers; stir dry mold mix before using.
4. Keep kiln and mold mix areas clean to
prevent contamination of glass in open molds or storage containers.
5. Maintain and handle molds carefully to
prevent grit and dust from contaminating the
glass.
6. Keep good records of firing schedules and
results to diagnose problems and improve
skills.
5.0 REFERENCES
1. Cummings,
Keith, Techniques of Kiln-Formed Glass,
A&C Black, London, 1997.
2.
Lundstrum, Boyce, Glass Casting
and Moldmaking, Vitreous Press, 1989.
3. McGregor
and Schoerer, Contemporary Kiln-Formed
Glass, Bullseye Glass, Portland, 1992.
