Spark testing identifies ferrous metals by generating sparks through grinding or heating the sample. Each alloy has a unique spark pattern, and automatic spark testing eliminates human error. The process is quick and inexpensive but can damage the sample. It can also be used to sort samples by type. Chemical analysis may be used for positive identification.
The spark testing process typically involves using one of two different methods to generate sparks from an iron alloy. These sparks can often be used to identify the type of ferrous metal the object is made of. A person with a well trained eye may be able to identify the overall league through simple observation, or some type of graph may be used. There is also a process known as automatic spark testing, which can use spectroscopy and a few other methods to eliminate the possibility of human error. In cases where positive identification of the metal in question is needed, a process such as chemical analysis may be used instead of spark testing.
There are two main methods of generating sparks to test. The first involves a grindstone, against which the object can be leaned. This wheel will often be made from carborundum or aluminum oxide, which can abrade and heat small pieces of metal into bright sparks. The other method is to heat the sample with a torch or other appliance until it is hot. Compressed air can be blown into it, which will cause the metal to ignite and give off an even shower of sparks.
Each of the different ferrous alloys tends to have its own unique spark pattern. Some metals create a longer stream of sparks, while others can have sparks of different lengths. A practiced eye may be able to tell the difference in these patterns of sparks, or comparisons can be made to known samples or photographs. The automatic spark test can also remove the human element by using methods such as spectroscopy and spectrometry to observe and classify the pattern.
There are a number of benefits to spark testing. The process is typically very quick, requires no specialized equipment, and can therefore be inexpensive compared to other methods. A potential downside is that the process can damage the sample, as the sparks are made from abraded pieces of metal. Scrap is usually used for this reason so as not to damage a piece that will later be used for another purpose.
In addition to its use in determining the specific classification of a ferrous metal, the process can also be useful in sorting samples by type. Rather than comparing the sparks from a piece of metal to a known sample or photograph, this process may simply involve comparing pieces. If the sparks are identical, then the objects are probably made of the same alloy and those with different spark patterns can be sorted into separate groups.
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