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What
is a Burst Test?
Whole Package Testing
Pressure, Flow, Time Relationship
Connecting the Package to the Instrument
In
pneumatic testing of flexible packages, we are
testing the whole package in the case of closed
product or at least 3 sides of an open pouch.
This is to clearly separate this technique from
the single piece of perimeter seal used in the
tensile/ pull peel test.
There
are three variables in the pneumatic test, pressure,
flow and time.
In
Burst testing, pressure and flow are the controlling
variables of the test. The time is dependent on
the previous two. This plot show the ideal test
characteristic with uniformly increasing pressure
in the package, followed by the rupture at the
maximum pressure followed by a drop in pressure.
The
instrument provides a flow rate into the package
that will overcome any losses and increase the
internal pressure of the package until it reaches
its ultimate strength, at which point it ruptures
and the internal pressure drops rapidly. The maximum
pressure is then the measured analog of that package’s
seal strength.
As
mentioned previously, flow control is an important
variable in the measuring process. Thus in current
generation instruments, flow control valves are
built into the instruments along with pressure
regulation. However, again going back to the need
for consistency in methodology, it is also important
to control the delivery of the air to the package
through the penetration of the package wall. The
operator may cause leaks around the inflation
probe or cause ripping of the material surface
when installing the probe. Since these effects
may cause a change in required flow and pressurization
rate, it is desirable to prevent these leaks as
well. The previous diagram shows our Package-Port
that seals the inflation probe and the package
together in a leak tight manner. While most products
on the market have the capacity to make up for
the air loss, only a leak tight fitting can prevent
the variable flow loss and eliminate yet another
variable from the test process.
Another
characteristic to note is the "Delayed Burst"
test. On this chart you can see the uniform rise
of pressure in the package, but then a steady
holding of the maximum pressure before the final
rupture of the package seal. This curve is not
representative of a pure Burst test since the
holding of a constant pressure begins to approach
a Creep test rather than a uniformly increasing
Burst test.
The
phenomenon of the delayed burst test has been
seen since the implementation of the graphic plot
output available in our instrumentation. This
slide shows the actual pressure vs time curve
of a burst test. I point these characteristics
out to emphasize the importance of using all your
available measuring tools to characterize your
package and the package test. In this way, you
can characterize your package from the validation
phase and compare the curves for process analysis
at a later date.
This paper is presented courtesy
of TM Electronics, Inc.
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