A new consumable refractory has been developed to reduce
costs and increase production for container glass manufacturers.
Figure 1. In a glass melting furnace, ingredients are
added through the doghouse and glass exits at the gob feeder.
All of us can remember when everyday items such as
ketchup, mayonnaise and beer were found solely in glass containers. Now these
products are packaged not only in glass, but also in plastic and aluminum. The
glass container industry has responded to this competition by producing its
goods as economically as possible, and one way of addressing that goal is to minimize
The manufacture of a glass bottle starts with feeding
ingredients such as silica, soda and cullet (recycled glass) into a melter (see
Figure 1) and fusing them at an average temperature of 2800°F. The glass leaves
the melter through a distribution system and eventually arrives at a gob
feeder, where it is formed into cylindrical "gobs" that then slide
down troughs into molds where they are shaped and blown into bottles. A
bottle-making machine can contain 10 or more molds and manufacture at rates
exceeding 400 bottles/minute.
Figure 2. Feeder refractory assembly.
The Role of the Feeder
A melter can support two or more feeders, with each
feeder providing glass for a single bottle-making machine. The feeder consists
of several carefully designed cast refractory shapes (see Figure 2), which are
known as consumable refractories
since their lifespans are
relatively short as a result of chemical corrosion and mechanical abrasion.
These refractories must be of the highest quality at this stage of the process
to ensure uniformity and consistency in the final product; any flaws that arise
from refractory defects will result in lost production.
A feeder assembly consists of four main parts. The
orifice ring is a disk-shaped refractory located at the bottom, and it contains
one to four cylindrical holes through which the glass is dispensed and shaped
into gobs. With glass flowing over and through the ring, it is subjected to
rapid wear and therefore must be replaced relatively frequently. The spout
contains the glass above the orifice ring and has a service life of about one
The feeder tube is located just above the orifice ring,
thereby creating a gap through which glass flows at a controlled rate. The
feeder tube rotates at a rate set by the glass manufacturer, and this movement
thermally homogenizes the glass. Suspended in the center of the feeder tube are
one to four ceramic plungers (one for each hole in the orifice ring). The
plungers oscillate vertically and force precisely measured amounts of glass
through the orifice ring. The oscillation rate can be quite rapid; plungers
serving a 400 bottle per minute machine using a 3-hole orifice ring will rise
and lower at nearly 135 cycles per minute.
Consumable refractories for the feeder are expensive, but
not in the same way as raw materials or labor costs. The high cost of
consumable refractories is a result of the time required to replace worn
refractory parts, which can result in thousands of dollars in lost production
time. Despite their cost to bottle-making manufacturers, consumable refractories
have not been improved for at least 25 years.
A New Development
Numerous refractory products are manufactured for the
glass industry with zirconia contents ranging from 20 to 50%. Certain
refractory materials,* which contain nearly 30% ZrO2
are offered for applications that require high glass corrosion resistance. The
refractory is made using zircon (ZrO2
and high-purity aluminosilicate materials. Mixes are cast into a mold using
ethyl silicate as a binder, which allows the shapes to set rapidly and allows
the molds to be used more efficiently. The demolded shapes are then dried,
fired well above their expected service temperature, and packed for shipment to
These materials are widely accepted by the glass industry
and provide superior performance in many applications. However, improved glass
corrosion resistance was needed for feeder expendables, and R&D efforts
have sought to develop a new product that would be superior to anything on the
The development required a twofold approach. First, the
amount of ethyl silicate added to the mix needed to be minimized to achieve
higher density and lower porosity. However, reducing the ethyl silicate amount
leads to increased mix viscosity. This, in turn, increases the chances of air
entrapment during casting, which can lead to macroporosity (porosity that can
be seen by the naked eye). Adding liquid to increase fluidity allows air
bubbles to rise to the surface more easily during the casting process, but it
also decreases density and increases the fine porosity, translating to reduced
glass corrosion resistance. The trick then is to minimize liquid demand while
achieving sufficient fluidity to release air bubbles.
The second approach involved the modification of the mix.
To minimize risk to the customer, the goal was to keep not only the same
overall chemistry as the original shapes, but also retain the same chemistries
within the matrix and coarse aggregate portions of the refractory body. These
objectives were achieved, but required substantial raw material adjustments. In
combination with the ethyl silicate work, the raw material changes allowed for
a more fluid mix, and, as a result, almost no macroporosity.
*such as shapes made with ZEDPAVE-CFTM
refractory material, manufactured by MINTEQ International, Slippery Rock, Pa.
Table 1 illustrates the properties of the new refractory
material** in comparison to the previous product. The enhancements in density
and porosity appear to be insignificant; however, the finished product provided
a quantum leap forward in glass corrosion resistance and significantly
increased wear life.
When tested in customer facilities, the results of
expendables made with the new composition have shown performance improvements
of 35 to 60%. Achieved benefits include increased service life, more consistent
gob weights and better temperature uniformity. The consumable refractories'
advancements have translated into improved manufacturing efficiencies-it is now
possible for glass bottle manufacturers to reduce the annual losses normally
incurred during replacement of feeder refractories by up to 50%. Work continues
with many container operations to demonstrate the benefits of cast shapes made
with the new refractory material, and the trials are showing reduced down times
and improved production efficiencies.
shapes, developed by
For more information regarding cast shapes and
other refractory materials for the glass industry, contact Gary Stark at MINTEQ
International, Inc., 395 Grove City Rd., Slippery Rock, PA 16057; (800)
245-1929; e-mail Gary.Stark@minteq.com;
or visit www.minteq.com.