1990 the Federal Aviation Administration (FAA) requested proposals
for the development of an aerosol can with improved fire safety. Two
Small Business Innovative Research (SBIR) contracts were awarded to
Materials Engineering, Inc. in February 1991 to develop of such a
Aerosol cans are
pressure vessels. A typical can is a three piece construction of tin
coated steel ('tin plate'), comprised of a rolled and welded cylindrical
body, a stamped top and bottom. The ends are attached to the body
by a mechanical method known as double seaming. The can safely holds
its contents at pressures of up to 140 psi. Special high pressure
cans (D.O.T. types P and Q) are made which can maintain greater pressures.
When a can
is heated, the internal pressure increases. This will result in mechanical
deformation or buckling of the ends, followed by bursting. A typical
burst event occurs when one or both of the double seams detaches,
releasing the contents. As a considerable amount of energy is released
during a burst, the can components may be propelled as shrapnel, and
if an ignition source is present and the contents are flammable, a
fireball may result. The aerosol industry has discontinued the use
of CFC propellants for environmental reasons, and most propellants
in use today are flammable.
investigating plane crashes, the FAA has found burst aerosol cans
in the wreckage. It is common for luggage to contain deodorant, hair
spray and other personal products in aerosol cans. The presence of
burst cans indicates a fire within or near the cargo compartment can
produce sufficient heat to burst aerosol cans.
were raised by the FAA as to the affect that burst cans would have
on a fire in the cargo compartment. Would the fireball help to sustain
a fire? Would the high energy burst rupture the cargo compartment?
Would shrapnel pierce the cargo compartment? Though no evidence has
ever been found that points to aerosol cans as contributing to an
aviation accident, the FAA continues to be concerned over this issue.
The goal of the
development effort was to improve the can in two regards. First, to
create a can capable of maintaining integrity at a higher pressure.
As the double seams are typically the weakest link, the SBIR effort
developed laser welding technology to create higher strength end and
body seams capable of withstanding higher pressure.
second goal of the development effort was to develop a pressure relief
mechanism causing the can to slowly vent rather than burst, gently
releasing its contents. Based upon these developments, two patents
have been issued covering the invention of an improved aerosol can.
Benefits of the MEi Can:
Our can has addressed
the concerns raised by the FAA. Increasing the maintainable pressure
allows more time to extinguish the fire or heat source in the cargo
compartment before aerosol cans burst. In some instances, this may
prevent bursting from occurring. When the heat of a fire in the luggage
storage compartment causes the internal pressure of the cans to increase
to over-pressurization, the MEi cans will vent in a controlled manner.
No pressure wave, fireball or shrapnel will result. This will eliminate
the risk to the structural integrity of the cargo storage area.
The FAA has performed
testing comparing the performance of the MEi cans to conventional
cans when exposed to a fire under simulated luggage storage conditions.
The testing confirmed the safety benefits of the MEi can.
MEi has completed
the development effort and issued the final report. We are currently
looking for partners to commercialize the technology through licensing
or other business arrangements. Ralph C. Daehn, principal investigator
for the SBIR project, is handling the commercialization phase.
Our customers often
ask us how we conduct an investigation, what equipment and techniques
we use, and what information can be learned from them. There are many
tools which we use to help us gather information about the material
or component as part of an investigation. This article will give a
brief overview of the tools we use.
are necessary to properly conduct a test and to interpret the results
so that the information generated is meaningful. Our technical knowledge
and experience are the most important thing we use to conduct an investigation
and solve a problem.
The tools we use
can be classified into one of two categories: destructive and non-destructive.
As the names suggest, to gain information using destructive tools
requires consumption or alteration of the components. Therefore, their
use must be clearly thought through to insure that no information
is lost in the process.
tools are those which do not alter a component. These include optical
microscopy, hardness measurement, scanning electron microscopy, energy
dispersive x-ray spectroscopy, non destructive inspection techniques,
and dimensional measurement devices. These will be discussed in more
detail in a future issue.
Optical Microscopy: By cross sectioning, mounting, polishing and etching
a sample, the materials engineer can learn about the characteristic
of a material. Metallurgical microscopes, often referred to as metallographs,
allow a sample to be viewed at magnifications ranging from less than
50x to more than 1000x. An understanding of microstructure is the
primary knowledge learned from metallographic examination.
information includes the phases present, grain size, case hardening,
weld or braze joint integrity, decarburization, and the presence of
material defects such as inclusions, porosity, and shrinkage. These
provide insight into the processing history of the material, including
heat treatment, metal working, casting, and forging. In most cases
metallography is the definitive method to determine these materials
and processing characteristics.
examination can also determine coating or plating thickness, although
very thin coatings require other techniques. Metallography is useful
in understanding the nature of cracking, determining whether the crack
propagates transgranularly or intergranularly, and if branching or
secondary cracking is present. Such information provides insight into
the cause of the cracking.
Interdendritic shrinkage porosity
(dark areas) in an aluminum castin, revealed through metallographic
examination (left). Microhardness traverse of nitrided 1144 steel,
showing an increase in hardness (smaller indents) in the nitrided
Testing: Just as the name suggests, microhardness is conducting hardness
measurements on a microscopic scale, using a sample which has been
cross sectioned and metallographically prepared. Microhardness can
determine hardness gradients such as case depth of carburizing or
nitriding, the presence of decarburization, level and uniformity of
work hardening, and the hardness of microconstituents within a microstructure.
It can also measure hardness at a narrow tip or other locations of
a component where it is difficult to take Rockwell hardness measurments.
hardness measurement of components which are difficult to measure
using conventional methods due to size (very small) or geometry (i.e.
Microhardness is measured using many different scales including Knoop,
Vickers and DPH and can be measured at various loads from 10 gram
to 1000 gram. Caution should be taken when examining microhardness
data as ASTM test standards state conversions to the Rockwell C scale
are not exact but approximate.
A component, either in its entirety or in part, is etched to reveal
certain macroscopic features or gross structural details, such as
grain flow, segregation, overheating damage and cracking. Macro-etching
is commonly applied to large polished cross sections of forgings to
determine proper flow lines which indicate proper forging technique.
Testing: This involves extracting material from a component and machining
it into a test bar and applying mechanical loads until failure. As
such, mechanical property testing is not always possible for all components,
especially those which are small or odd shaped. The most commonly
used is the tensile test, where a dogbone shaped sample is pulled
in tension until failure. This test provides tensile strength, yield
strength, elongation, reduction of area and elastic modulus. Similar
testing can determine compression and shear strength.
mechanical test is charpy impact, where the amount of energy absorbed
in a controlled impact is measured. This is a measure of toughness
or brittleness, commonly used for tool steels and structural steels.
testing is used to determine conformance to blueprint or specification
requirements, which usually reveal if the component has been properly
processed. The information is also very useful in comparing materials
to understand processing problems.
mechanical property testing is generally used to characterize a class
of materials. Material property characterization, including fatigue
and creep rupture testing, generates information about materials which
is used in the materials selection process.
The elements present can be measured quantitatively using a variety
of techniques such as spectrographic analysis, atomic absorption (AA),
and wet chemistry methods. These determine if a material is of the
proper composition, or if certain unwanted or 'tramp' elements are
present in excessive amounts. This is used to determine conformance
to procurement specifications, or to compare materials to understand
processing or failure problems.
As important as these tools are, care has to be taken in selecting
which tools will aid in the investigation. Conducting tests which
are unlikely to provide meaningful information is a waste of our time
and your money.
about the tools of the trade will be featured in future issues.
Durako was named as an Outstanding Materials Engineer by the school
of Materials Engineering at Purdue University in West Lafayette, Indiana.
This is the inaugural year of the award, which is presented to graduates
of the school who have shown exceptional achievement in the field
of Materials Engineering. Four awards were issued from the thousands
of alumni of the school. The award was presented to Bill on campus,
Wednesday, March 19, 1997.
part of the award, Bill made a presentation to the students and faculty
in the school of Materials Engineering which was titled "What
Does It Take To Be A Successful Engineer in Today's Marketplace?"
The presentation was aimed at providing the students insight into
what skills, characteristics and traits are most important to be a
success working in industry. The talk emphasized such basic skills
as report writing, oral communication, being able to work with others
and general technical knowledge. The presentation also included (live
from the home office in Virgil, Illinois) Bill's Top ten list of "Things
to Help Your Professional Career".
According to Dr.
Gerry Liedl, head of the School of Materials Engineering, "There
is great value in having successful alumni provide input into the
various aspects of professional life in the field so the students
have a base of information for decision making as they enter their
also met with members of the faculty, renewing friendships and sharing
memories with professors, and meeting the members of the staff.
"I was very
impressed with the new curricula in place at Purdue, which has changed
considerably since my days on campus. Discussing the changes with
the current faculty makes a strong impression that Purdue has moved
significantly toward its goal of graduating students who have the
right mix of skills and abilities to make an immediate contribution
to industry. The new senior design project includes skills such as
proposal writing, budget and schedule estimating, and working together
in teams. As we all know, working successfully with others is a key
to success in today's workplace."
go out to Matt Erickson, Metallurgical Engineer at MEi, whose wife
Debbie gave birth to their first child, Zachary Tyler Erickson, on
April 20, 1997. Zach weighed in at 7 lbs. 12 oz. and 22 inches long.
scanning electron microscope (SEM) is a powerful tool, capable of
magnifications up to 180,000 times. It allows us to reveal information
which is critical to metallurgical investigations, such as fracture
modes and surface characteristics.
SEM can also be fun to play with, because it allows one to view the
surface of anything at high magnification with great depth of field.
All of us have been amazed by the pictures of various insect parts,
especially the eye of a fly.
our contest, we take a look at an object on the SEM that should be
familiar to all of you. In this issue we ask you to identify the object
shown in the two photographs at two different magnifications. This
should be an easy one, as we first got the idea having seen similar
photographs published in magazines.
Please fax, mail
or e-mail us (donít call) with your answer. We will draw a
winner from all correct entries received by June 6. The correct answer
and the winner will be published in the next issue Of Materials Interest.
The prize is a
$50 restaurant gift certificate, so put on your thinking caps.
Last issue, we
had many correct entries, and even more that were very close to being
correct. We also posted the photographs at our booth during the fall
CASMI conference and collected entries from trade show attendees.
showed two types of hair: from a dog and from a human. We found the
differences between the two hairs to be quite fascinating. Notice
the barbed surface on the dog hair. No wonder it clings to your clothes.
Our winner, drawn
at random from the correct entries, was Tracy Lester of Ventaire in
Tulsa Oklahoma. Her efforts earned her a nice dinner at Tony Roma's
designs, manufactures and installs custom steel and aluminum canopies
and building fascia for a variety of industries from convenience stores
to banks located all across the country. Last year, Ventaire celebrated
its 50th anniversary, having started out as a manufacturer of metal
awnings for homes.