Dexmet has been a leader in the heat treating of expanded metal products. The purpose behind the various processes depends on the application. The following is a discussion of some the options you may choose depending on your end requirements.
The most commonly requested process is a full anneal. The temperature to accomplish this depends not only on the alloy of the product but may, in certain cases, depend on the degree of cold work that goes into the metal prior to anneal. Copper is a prime example in that after 100% cold work, a full anneal can generally be achieved at less than 300 degrees Fahrenheit (°F). Since we generally require a fully annealed raw material, with some exceptions, the amount of cold work is rather low. Some say it is in the neighborhood of 20-25%. Under this condition, an annealing temperature of in excess of 600°F is required for full anneal. Sometimes, to get the desired softness, the metal must reach near the sintering point to get the required result. This can occur in several metals but most commonly in copper and nickel.
We have a method to numerically determine the level of softness which we call the BART number. BART stands for Bend Angle Recovery Test and is determined by a proprietary measurement device that we can supply if you desire to have your own. The softer the metal, the lower the amount the metal recovers from being bent 90°F at a distance of 1” from the fulcrum. Values therefore range from just above 0 to just below 90°F but never at the extremes. Values for a particular mesh configuration and alloy can be developed from testing representative samples. We have predictable values for several configurations but we always run into new ones on a regular basis. Once established, the degree of anneal can be easily quantified. As far as I know, no one else has this capability.
The ideal stress relieve will result in a mesh that has the same BART number after heat treatment but lays flatter and feels softer. The ultimate tensile of the product is unchanged. Unfortunately the temperature required to reproduce the ideal situation varies with chemistry and in some cases cold work. It is useful when working the expanded metal around a form without losing the strength of the mesh.
The strand anneal is useful for metals, like stainless steel where it must be brought to a sufficiently low temperature from the anneal temperature in a short amount of time. If this is not done, inter-granular corrosion could develop and deposit carbon in the grain boundaries. This can be an issue in some applications.
Removing Residual Oil
Sometimes it is useful to insure the metal has no residual lubricants on it. Here, after degreasing the metal we put it in an oven to remove the last vestiges of any trace of lubricants. For this a temperature of 400°F will suffice.
Regardless of your needs, Dexmet can accommodate them with our oven and furnace capabilities.
Kirt Griffin, Quality Assurance Manager