bulletproof materials

The Future of Bulletproof Metal

Every day, law enforcement, security officers, and military personnel (along with politicians and movie stars) depend on bulletproof vests for their very lives. The materials used can vary from bulletproof metal plates to man-made Kevlar fabric, to composites, which combine two different types of material together to produce one with superior characteristics.

All of these types of protection rely on the principle of absorbing the bullet’s enormous energy, though they approach this in different ways. And of course, they must do this with the minimal amount of bulk and weight – or they’ll be too uncomfortable to wear.

Current Bulletproof Vest Technologies

Ever since chemist Stephanie Kwolek invented the stronger-than-steel material Kevlar for DuPont de Nemours, other companies have competed to discover even stronger and lighter materials for bulletproof vests. Some of the newer materials for this purpose include Dyneema, Zylon, and Spectra.

Meanwhile, researchers across the globe continue searching for armor materials that are even lighter and stronger – as well as easier and cheaper to make. Some of the proposed materials include ceramic composites with titanium or carbon fibers, and graphene nanowires.

One of the more fascinating new materials that could prove to be the strongest yet is a composite metal foam invented by a team of researchers at North Carolina State University led by Afsaneh Rabiei. This material is much lighter than metal plating, yet can shatter an armor-piercing bullet on contact.

Material Just Like Styrofoam

The new material is a composite made by melting aluminum around hollow steel spheres, which creates air bubbles surrounded by a metal matrix. The result is a metallic “foam.” On impact, the metal spheres squeeze down and the pores collapse – just like squeezing a sheet of bubble wrap or stepping on a piece of Styrofoam.

“What we did is introduce the same concept to metals, and now we have the impact protection, because of the porosity inside,” said Professor Rabiei in a video interview. “But this time you have it against much heavier impact.”

Rabiei’s initial testing showed that the metallic foam could go to 80 percent compression without damage, because the energy is absorbed as the outside force compresses the material.

Later, when a 7.62 x 63 mm M2 armor-piercing round was fired into a sample of metal foam, following standard testing procedures established by the National Institute of Justice (NIJ), the bullet shattered on impact. The round caused an 8 mm indentation on the back – an 80 percent improvement over the 44 mm indentation allowed by the NIJ standard.

But not only is the metallic foam strong, it’s only about 1/3 to 1/2 the weight of sheet metal, due to the air bubbles inside. In fact, the foam is so strong and light, it can stop a bullet even at a total thickness of less than an inch, making an entire bulletproof metal suit not out of the realm of possibility.

Visit www.IndustrialMetalSupply.com for the Southwest’s largest supply of metal and metal tools and accessories.


heat conducting metal

Best Metals for Conducting Heat

Thermal conductivity is the term that describes how quickly a material absorbs heat from areas of high temperature and moves it toward areas of lower temperature. The best heat-conducting metals have high thermal conductivity and are useful for many applications, such as cookware, heat exchangers, and heat sinks. On the other hand, metals with a lower rate of heat transfer are also useful where they can act as a heat shield in applications that generate large amounts of heat, such as airplane engines.

Here’s a ranking of heat conducting metals and metal alloys from lowest to highest average thermal conductivity, in Watts/meter-K at room temperature:

  1. Stainless Steel (16)
  2. Lead (35)
  3. Carbon steel (51)
  4. Wrought iron (59)
  5. Iron (73)
  6. Aluminum Bronze (76)
  7. Copper brass (111)
  8. Aluminum (237)
  9. Copper (401)
  10. Silver (429)

Stainless Steel

With one of the lowest thermal conductivities for a metal alloy, stainless takes much longer to conduct heat away from a source than, say, copper. This means that a pot made of stainless would take much longer to heat up food than a copper-bottom pot (though stainless has other benefits). Steam and gas turbines in power plants use stainless steel because of its heat resistance, among other properties. In architecture, stainless steel cladding can resist high temperatures longer, keeping buildings cooler in sunlight.

Aluminum

While aluminum has a slightly lower thermal conductivity than copper, it is lighter in weight, cheaper, and easier to work with, making it a better choice for many applications. For example, microelectronics such as LEDs and laser diodes use tiny heat sinks with aluminum fins that project into the air. Heat generated by the electronics transfers from the chip to the aluminum and then to the air, either passively or with the help of forced airflow convection or a thermoelectric cooler.

Copper

Copper has a very high thermal conductivity and is much cheaper and more available than silver, which is the best metal of all for conducting heat. Copper is corrosion resistant and resists biofouling, which makes it a good material for solar water heaters, gas water heaters, and industrial heat exchangers, refrigerators, air conditioners, and heat pumps.

Other factors affecting heat conduction

When considering the best metals for heat conduction, you must also take into account other factors in addition to thermal conductivity, which affect the rate of heat flow. For example, the initial temperature of the metal can make a huge difference to its heat transfer rate. At room temperature, iron has a thermal conductivity of 73, but at 1832°F, its conductivity drops to 35. Other influences include the temperature difference across the metal, the thickness of the metal, and the surface area of the metal.

For the largest selection of metals in the Southwest, contact Industrial Metal Supply.

Data taken from Engineering Toolbox.


best metals for welding

Best Metals for Welding

The best metals for welding depend on the project design and budget, the skill and experience of the welder, and the welding process to be used. Almost any metal can be welded, but some are easier than others for creating a high-quality, defect-free weld.

Some types of metal require special equipment, such as a vacuum or gas chamber, limits on heat exposure, or pre- and post-welding heat treatment. Some perform better with different types of welding, whether stick, TIG, or MIG. Choosing the right electrode and filler material for the base metal and following prescribed welding procedures is essential. Each specific situation depends on the base metal’s chemical makeup.

Low Carbon Steel

Also known as mild steel, low carbon steel contains a very small percentage of carbon (less than 0.3%) and up to about 0.4% manganese (AISI 1018 steel). This commonly used steel is very ductile, due to its low carbon content. High ductility means high weldability because it reduces the chance of brittleness in the heat affected zone (HAZ), which can lead to hydrogen cracking. Low carbon steel can be welded using almost any type of equipment and is one of the best metals for welding.

Stainless Steel

Stainless steel can be quite weldable, depending on the grade. Ferritic and austenitic stainless steels can be welded fairly easily, but not martensitic stainless types, which tend to crack. Stainless steel tends to warp under high heat, which can affect the shape and strength of the final workpiece. Another issue is that the chromium in stainless will combine with carbon during the welding process, leaving the piece more susceptible to rust without its chromium oxide protective layer. To prevent this problem, don’t heat the workpiece above the recommended temperature, or choose a low-carbon stainless grade.

Aluminum

Creating a defect-free weld in aluminum is different than welding steel, but can be done by following the prescribed guidelines. Choosing the proper grade is important, as some types are much easier than others to weld. Because of aluminum’s high thermal conductivity, heat is transferred away from the weld very quickly. Equipment with a higher welding current may be required to supply the necessary heat. As it cools, aluminum shrinks significantly more than steel, so special care must be taken to prevent craters and cracking. Finally, the natural aluminum oxide coating on the base metal can add contaminants, and should be removed prior to welding to avoid porosity in the weld.

Other Metal Types

Other metals, including magnesium, copper, cast iron, titanium and superalloys such as Inconel, can be welded. These will typically require special equipment and expert skill, making them less weldable for traditional job shops and hobbyists.

Industrial Metal Supply is your one-stop shop in the Southwest for all things metal. Visit our catalog for a wide selection of metal products, including steel, stainless steel, and aluminum, as well as all the machines, supplies, and accessories you need for welding.