Chapter 15 Introduction to Nonferrous Metals 343 and set points so parts stay within the required temperature range frequently falls to the technicians and operators closest to the process, since each oven has its own “personality,” or behavioral characteristics. Some alloys have narrow solutionizing temperature ranges, and these alloys need very uniform-temperature furnaces during heating and soaking. Operators must watch these runs closely, and frequent furnace calibrations are usually required. One method for solutionizing and aging nonferrous alloys with narrow temperature ranges is to use a fluidized bed furnace. In this process, a tank is partly filled with dry sand, and hot gas is pumped through from the bottom. This creates a quicksand effect, with very uniform temperature. Open baskets holding small parts slide easily into the bubbling sand. Upon removal, the parts are dry and the sand shakes off. The time to heat is much shorter than in an air furnace. Die cast parts, with much finer dendrite spacing and more uniform composition than sand castings, can be solutionized much faster by fluidized bed processing than by air furnace heating. Part temperature and cycle time can be controlled better than in air furnaces, but the tighter process controls also mean that the technicians and operators must watch the production closely. A two-minute soak in a fluidized bed furnace means exactly 120 seconds, not 150 seconds. 15.5.6 Joining Nonferrous Metals Joining, or forming a metallurgical bond between two workpieces, can be done with most nonferrous metals. To make a true metallurgical bond, some surface oxide on the workpieces must be disrupted. The joint can be formed with or without liquid in the joint volume. Forge Bonding and Roll Bonding Forge bonding, or forge welding, is the traditional way a blacksmith welds pieces of wroug ht iron, as discussed in Chapter 9. Nonferrous metals can also be forge welded, when the workpieces are at the hot-work temperatures. A modern production form of forge bonding is roll bonding. Roll bonding is a method of combining two metal plates with different properties by hot-rolling to join them together. Slabs of an alloy with one set of properties are strapped on one or both sides of a slab with a different composition and properties. The pack is heated to hot-working temperature, then put through a rolling mill. As the thickness is reduced, the length increases, and a metal-to-metal metallurgical bond of the two alloys forms. The result is a single piece of metal with different properties on the outside and the center of the finished sheet. Finished strip can be formed and processed as one piece, yet retain the different properties of the two components. For example, kitchen pans with copper on the outside of the pan and steel on the inside, Figure 15-26, are fabricated from roll-bonded copper and steel slabs. vlaru/Shutterstock.com Figure 15-26. This kitchenware, made from copper roll- bonded to steel, provides more uniform heating of food while keeping the scratch and wear resistance of steel. Copyright Goodheart-Willcox Co., Inc.