If it's time to replace seals on equipment you use in various industrial or marine applications, you might consider using aluminum bronze. This bronze alloy, sometimes combined with other metals, is proving to be the go-to choice for machinery that requires corrosion and heat resistant seals. Below is a brief description of aluminum bronze, the benefits of use, the various types of the alloy and an explanation on how seals and other parts are usually made.  

What is Aluminum Bronze?

Aluminum bronze is made by combining aluminum with copper to make bronze, rather than combining tin and copper. The aluminum portion makes up between 4 and 15 percent of the alloy. The addition of other trace metals changes the composition, making the alloy stronger and more heat resistant. In some cases, nickel aluminum bronze is even used in landing gear bushings for commercial and other aircraft. The material is able to stand up to the extreme friction created by take-offs and landings as well as the metal stress created when a jumbo jet bounces onto the tarmac.

Benefits of Aluminum Bronze

In addition to being heat and stress tolerant, aluminum bronze is resistant to corrosion. Seals made of this substance hold up to acids such as sulfuric, hydrochloric and hydrofluoric. They are often used in pickling equipment in the food industry, which uses vinegar and other diluted acids in the process.

Aluminum bronze has been compared to mild steel in the strength category. The alloy holds up well in repetitive motion machinery, such as used in paper making. The product is also used in the electronics industry in everything from clamps on welding machines to heavy duty gear wheels. The alloy is also spark resistant, but can be soldered with the use of special fluxes. It may also be welded using a metallic arc welder.

Types of Aluminum Bronze

• The combination of aluminum and copper to create aluminum bronze is called a single-phase, alpha alloy. These are usually made into sheets, tubes, strips and wires.

• Duplex alloys have aluminum and bronze mixed with another metal, such as iron or nickel. The addition of the third metal makes it more suitable for hot casting.

• Other combinations include copper-aluminum-silicon and copper-manganese-aluminum alloys. Both cast well. These combinations were originally developed to make propellers.

Aluminum Bronze Most Used for Seals

UNS C95400, the official designation, is the aluminum bronze alloy most often used for seals and valves. It is made up of 85 percent copper, 11 percent aluminum and 4 percent iron. A special casting process makes the material resistant to seawater corrosion and the end products are often used at nuclear power plants.

Most valves and seals are made by sand-casting, similar to the process used by sculptors and jewelry makers for centuries.It's also known as lost wax casting.  A wax mold is made of the object then covered with a fireproof mold, usually steel reinforced sand. The wax is melted and drained out, leaving the sand-cast. Molten metal is poured in and allowed to solidify, then the sand is removed.

Aluminum bronze is cast using a steel mold in a centrifugal casting machine. Since steel conducts heat better than sand and the rotation of the centrifuge creates airflow, the resulting object cools down much faster than the sand-cast item. The more rapid cooling changes the chemical composition of the aluminum bronze making it more resistant to corrosion. The centrifuge also compresses the metal as it spins, eliminating minute air pockets and further strengthening the product.

Some of the other items C95400 is used for include industrial bearings, wear plates, liners, adjusting nuts and collets. The latter are sleeves that are used to hold router bits in woodworking tools. Go to website for more information.