Materials Engineering, Inc.
47W605 I.C. Trail
Virgil, IL 60151
Of Materials Interest1997 Spring
Improving a Good Thing: MEi Develops Improved Aerosol Can
How We Do What We Do
MEi President Receives Award From Purdue University
Baby Update
The "What Is It?" Contest

Improving a Good Thing: MEi Develops Improved Aerosol Can

In 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 can.

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.
When 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.
Concerns 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.
SBIR Development:
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.
The 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.

How We Do What We Do
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.
Special skills 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.
Non-destructive 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.
Destructive Tools:
Metallography and 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.
Microstructural 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.
Metallographic 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 case (right).

75X 75X

Microhardness 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.
Microhardness allows hardness measurement of components which are difficult to measure using conventional methods due to size (very small) or geometry (i.e. ball bearings).
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.
Macro-Etching: 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.
Mechanical Property 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.
Another common 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.
Mechanical property 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.
More sophisticated 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.
Chemical Composition: 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.
More information about the tools of the trade will be featured in future issues.

MEi President Receives Award From Purdue University
Bill 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.
As 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 professional careers."
Bill 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."

Baby Update
Congratulations 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.

The "What Is It?" Contest
The 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.
The 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.
In 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.
The photographs 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 in Tulsa.
Ventaire 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.
Congratulations, Tracy!

Next: 1998 Spring Newsletter