The Spark Test For Identifying Metals. When it is necessary to sort materials, several rough methods may be used without elaborate chemical analysis. The most obvious of these is by using a magnet to pick out those materials that contain magnetic elements. To differentiate various levels of carbon and other elements in a steel bar, hold the bar in contact with a grinding wheel and observe the sparks.
With high levels of carbon, for instance, sparks are produced that appear to split into several bright tracers. Patterns produced by several other elements, including small amounts of aluminium and titanium, for instance, can be identified with the aid of Data Sheet 13, issued by the American Society for Metals (ASM), Metals Park, OH.
The Spark Test
The idea of this test is simple: the spark stream given off during a grinding operation can be used to approximate the grade or alloy of a steel. The equipment used should be a grinder with a no-load speed of 9000 rpm and a wheel size of around 2.5 inches.
The Spark Test, A Semi-Darkened Location is Necessary.
The easiest way to learn the test is to observe the spark streams from various known grades and compare them with this text. As you grind, you will see lines called carrier lines. At the termination of the carrier lines, you will see small bursts called sprigs.
Low carbon (1008) is a very simple stream with few bright sprigs. The higher the carbon content, the more numerous the carrier lines and sprigs. Some alloying elements change the appearance of the test. Sulphur imparts a flame shaped, orange coloured swelling on each carrier line. The higher the sulphur, the more numerous the swellings. A spear-point shape that is detached from the end of the carrier line identifies phosphorus.
The higher the phosphorous content the more numerous the spear points. Nickel appears as a white rectangular-shaped block of light throughout the spark stream. Chromium appears as tint stars throughout the carrier lines, having a flowering or jacketing effect to the carbon burst. The presents of silicon and aluminium have a tendency to depress the carbon bursts.
The safest and most reliable method to check chemical content is to use an Eddy Current test or similar technique performed by a certified laboratory with technicians certified and trained in such matters.