Most are well aware that sparks are a common occurrence when dealing with metals like steel, but did you know that sparks may actually serve as indicators that reveal specific qualities or characteristics about a metal? It’s true — and this is typically done through a quick, inexpensive test known as the spark test.
At Wasatch Steel, we’re happy to offer the very best steel products in Utah, from steel sheet to steel bar, tube and more, plus tips on various processes that may be used on steel and other ferrous metals to detect certain qualities. What do sparks have to do with metal properties, and what is the spark test? Here’s everything you need to know.
When steel or other metals come into contact with a grinding wheel during standard operations, the wheel or disk will grab tiny bits of the metal and rip them off of the surface, tossing them aside. When this process takes place with great amounts of energy, the metal that’s cast aside can become hot enough to glow.
This process is known as incandescence, and it’s possible to discern the properties of a metal based on color, shape and intensity of the glow — and of other elements. For instance, the size of pieces that are ripped off can also indicate if a metal is ductile, brittle or somewhere in between.
In general, the more incandescent a spark appears to be, the higher-quality and purer a metal will be. By extension, the less incandescent a metal spark may appear to be, that might indicate it is of lower quality or contains impurities. Read on, however, to learn about the spark test and why it’s used here.
Due to the basic facts above, one of the most common and fundamental tests run on steel and other metals is known as the spark test. By taking a sample of a given unknown metal and grating it over the surface of a grinding wheel, operators can subject that metal to sparks and learn more about its quality, properties and makeup. So how does this work?
To start, a piece of steel is typically shaved off with a grinder or other tool. This shaving must be thin enough so that it will produce a sample of sparks that can be observed. In this shaving process, a shower of sparks will erupt from the grinding wheel as it makes contact with the metal, and these sparks may take on any number of forms or colors.
From here, the metal worker in charge of the test will be able to view the sparks that are created by their metal. And based on the three factors we’ll go over below, they can tell quite a bit about the metal in question.
Generally speaking, spark color tells you the most about the temperature and energy within the metal. When the grinding wheel removes small specks of metal from the test piece, it’s using energy to do so — meaning it has less energy with which to send that speck flying.
Due to this reality, harder metals that require more energy to separate will produce sparks with lower energy levels — and therefore a duller red hue. Softer metals, on the other hand, will produce white or hot sparks, indicating higher energy levels.
In general, red sparks indicate a lower-quality metal that is easier to cut and will have fewer applications in industry. White or hot sparks indicate a higher-quality metal with more potential for commercial use.
Another important quality that a metal worker will be evaluating when performing the spark test is the length of the sparks that are released from the metal. Sparks with a high surface area will cool faster than smaller sparks, and this is due to basic physics that dictate how quickly energy can be transferred.
Therefore, sparks that are smaller in size will maintain their hot temperatures for longer periods of time — this means they’re hotter metals. On the other hand, when larger particles are ripped away from a metal, these sparks will dissipate faster because there is less surface area over which the heat can be dispersed.
Based on this, it’s generally considered standard that shorter-length sparks reveal a metal with a higher content of carbon. Softer, lower-quality metals typically have smaller surface areas because they are more brittle.
Finally, another effect that may take place during the spark test is when sparks actually split in midair, or fork. The visual effect here is similar to a firework in some ways, and this often indicates a metal producing carbon dioxide as a byproduct.
This, in turn, often signals an unequal distribution of carbon in the original steel or metal being tested. Steel, for example, can have carbon evenly distributed throughout its makeup or unevenly spread out — depending on the intended use of the steel. When unequal amounts of carbon are present in a metal, spark fork is more likely to occur during testing because this imbalance adds stress on the material.
It’s important to note that for many metals, there will be no spark forking at all. In these cases, steel generally being one of them, the absence of spark fork is a positive indicator that the metal contains even carbon distribution.
In general, sparks can tell you quite a bit about a metal if you know what to look for. By observing color, length and fork effects in a given set of sparks, a metal worker can learn a lot about their materials even if they’re unknown.
For more on this, or to learn about any of our steel products or steel services, speak to the staff at Wasatch Steel today.