TEXTO EM PROCESSO DE TRADUÇÃO
Bottles, jars, and jugs and ampoules made of glass are
used in the industry for food and pharmaceutical packaging.
Glass packaging is usually formed directly from the
molten raw materials into the package. This means that
material testing generally must be conducted on the
package itself rather than on a sheet or resin pellet as is
an option in papers, metals, and plastics. Most standards
have to do with maintaining production quality and
dimensional consistency (Table 5).
Glass properties are dependent on the composition.
Appropriately equipped analytical laboratories can determine
this, but in glass manufacturing plants, density and
softening point can be substituted for a full analysis.
Strength in glass is not typically measured using a
tensile strength as in most other materials, because it is
extremely strong but extremely brittle. Compressive
strength measurements of glass result in much higher
strength values than tensile strength measurements.
Glass packages generally break at lower values than
the theoretical expectations because of small cracks on
the surface that serve as stress concentration points.
Online application of pressure, at squeezing stations on
glass package-making lines, is used to prevent cracked,
broken, or weak packages from advancing into the process.
Internal pressure resistance is an important property
of glass containers, which will endure pressures
such as sterilizing in the package and carbonation. The
compressive strength of glass packages reflects their
ability to support the load in stacking systems and
when closures are applied. It is generally addressed
during the design stage by selecting appropriate neck
and body diameters and shoulder radius. The heel design
of containers can also improve strength.
== algumas propriedades ==▼
. General dimensions
Thermal shock is a measure of glass’ tendency to crack
under heat. This is important for hot fill, retorting, and
applications in which the product is heated in glass by the
consumer to be served. Finite-element analysis is used to
Glass is often used for its superior optical properties.
Thus, measurement of these properties is important. On
glass production lines, automated inspection stations are
used to verify that the containers are free of sand, dirt,
stones, and other visual defects. Clarity and color, and the
consistency of both, are important in glass manufacture
and use. When printed or when graphics are formed into
the glass surface, the appearance of these aesthetics also
needs to be measured.
The containment capability of a glass container is
dependent not only on the properties of the particular
glass formula but also on the thickness of the container
walls. Additionally, the total weight of each container
must be measured and controlled to assure consistency
of cost, performance, and fill weights. The finish dimensions
must be consistent to assure that the cap/closure
system fits properly, offers correct opening strength, and
provides an appropriate seal of the package.
Glass offers excellent water vapor and gas-barrier properties.
When pigmented, it provides light control as well.