Know Brass from Bronze and Avoid Costly Mistakes
Knowing exactly what material you need to order and what you are working with can eliminate potential errors or problems when fabricating that metal. This in turn saves you time and money.
By Jack Kruse, Mac Metals Inc.
As a producer of brass and bronze extrusions, we receive numerous calls from people who use inaccurate terms when requesting material. When purchasing brass or bronze, saying "I want to buy some brass bar" without specifying the alloy is like saying "I want to buy a car" without specifying whether you want a Ford Taurus or Chevrolet Malibu. Let’s try to clear up some common misunderstandings about brass and bronze.
If someone handed you a piece of yellow metal and asked you to identify whether it was brass or bronze, could you? Unless you had some psychic ability, the answer is no. The piece would have to be analyzed in a lab to determine whether it was brass or bronze. So, if they can look so much alike, what makes brass and bronze different?
The words brass and bronze encompass many different types of brass or bronze, which are referred to as alloys. The word alloy means to mix together. By mixing various other elements with copper, such as zinc, lead, nickel, silicon, manganese, etc., you come up with many different copper alloys. Brasses are alloys whose primary element is copper and the secondary elements is zinc. Many brass alloys have an additional third or more element in them.
Bronzes are alloys whose primary element is copper and the secondary elements is, take a guess. Did you say tin? If you did you were partially wrong. At one time this was true. Tin was the only secondary element used in bronze. But today there are bronzes which have little or no tin in them. Aluminum bronze’s secondary element is aluminum, and silicon bronze’s is silicon. Neither alloy has tin in it.
There are two categories of brass and bronze—wrought and cast. In general, wrought products are produced by some type of working, such as extruding, and castings are molten metal poured into some type of mold. The physical properties of the two are very different. We will only be concerned with wrought alloys in this article— specifically extrusions. Angles, channels, tee, bar, rod, and handrail are forms of extrusion.
Brass alloys are broken down into three categories based on their composition: copper-zinc, copper-zinc-lead, and copper- zinc-zinc-tin. The 300 series brasses such as C38500 and C36000 have zinc as the second largest element and lead the third, giving you the leaded brasses. The 200 series brasses such as C22000, C26000, and C27000 have zinc as the second largest element and no lead, giving you the unleaded brasses.
Architectural Bronze is a Brass Alloy
Brass alloy C38500, popularly called architectural bronze, is the most commonly used alloy to produce extrusions for the architectural industry. Its color is somewhat more golden than yellow brass alloys and, most importantly, it is the easiest alloy for mills to extrude into complex shapes. You will find some distributor’s catalogs listing it as "Bronze." Keep in mind that it is actually brass alloy C38500. They might also use the old designations of 385 or 360, etc., which were replaced by the newer Copper Development Association six-digit designations, i.e., C38500 or C36000.
Bronze alloys are broken down into five categories: copper-tin, copper-tin-lead, copper-silicon, copper-aluminum, and miscellaneous copper-zinc. Most extruded bronze alloys, such as manganese bronze and silicon bronze, were designated for use in industrial applications, not architectural. They are very strong, hard metals, which are very expensive relative to the common brasses.
Nickel Silver has no Silver
The last alloy to discuss is nickel silver. Nickel silver is very strong and highly resistant to corrosion and wear. Most nickel silver used for extrusions in the U.S. is either C77400 (10 percent nickel) or C77600 (13 percent nickel). The primary element is copper, and the secondary element is nickel. Let’s clarify now that there is no silver in nickel silver! If you mirror polish these nickel silver alloys they will look like chrome with a slight yellow tint. As the nickel content increases, the alloy looks more silvery and less yellow. If the nickel content is low enough, the metal can look like a washed out brass alloy. Left unpolished, nickel silver oxidizes to a dark gray color. Many people use this alloy to achieve the architectural look of stainless steel. The reason being that stainless steel cannot be extruded in complex or thin wall shapes. In addition, the surface quality of stainless steel extrusions is very porous and rough.
Inaccurate Commercial Names
What about popular non-technical names for some of the metals? Names such as Commercial Bronze and Architectural Bronze are inaccurate and misleading. Why? Because neither is actually bronze. They are technically brass alloys C22000 and C38500 respectively, and their colors and properties are worlds apart. The terms German silver and white bronze for nickel silver are also inaccurate, outdated, and rarely used. Using these popular names is fine, so long as you specify the alloy number along with them.
Consult Your Sales Rep
To sum up, the Copper Development Association alloy designations such as C38500 and C36000 are the correct way to specify material when ordering. If you are not sure what the alloy callout is, tell your sales people what you are looking for and have them explain exactly what it is they are
- Offers reliable, fast, very high-quality cut. n High repeatability due to no wear parts. n No deformation of material. (Laser is closer to machining than plasma.)
- Accuracy of cut can be maintained in very thin and pliable materials.
- Cuts up to 3/4" steel, 1/4" stainless, and 1/8" aluminum.
- Fabricators can assemble their finished products, instead of cutting parts.
*This article originally ran in the January/February 2005 issue of O&MM Fabricator.