Is it really possible to see what kind of metal is being machined by looking at the sparks?
Yes, it is possible to gain insights into the type of metal being machined by observing the sparks generated during the machining process. This technique, known as spark testing, is a common practice in metalworking industries.
When a metal is subjected to machining operations like grinding or cutting, it generates sparks with distinct characteristics based on its composition. Factors such as the chemical composition, hardness, and heat treatment of the metal influence the color, shape, length, and intensity of the sparks.
Experienced workshop professionals who have acquired knowledge and expertise in spark testing can make informed judgments about the type of metal being machined by carefully observing these sparks. However, it’s important to note that spark testing is not always foolproof and may require additional analysis or confirmation using other methods for complete accuracy.
While spark testing can provide valuable indications about the general type of metal, it should be complemented by other techniques like spectroscopy, chemical analysis, or material identification methods for more precise and conclusive results.
Identification principle
When the machining steel sample is ground on the grinding wheel, the high-temperature fine metal particles are projected along the tangential direction of the grinding wheel rotation, and then rubbed against the air, the temperature continues to rise, and the particles are violently oxidized and melted. Bright streamlines.
The abrasive grains are in a state of high temperature, and the surface is strongly oxidized to form a layer of FeO film. The carbon in the steel is very easy to react with oxygen at high temperature, FeO+C→Fe+CO, so that FeO is reduced; the reduced Fe will be oxidized again, and then reduced again; this oxidation-reduction reaction is cyclical and will continue CO gas is generated, and when the iron oxide film on the particle surface cannot control the generated CO gas, a burst phenomenon occurs and sparks are formed.
If the bursting particles still have FeO and C that have not participated in the reaction, the reaction will continue, and there will be two, three or multiple bursting sparks.
Carbon in steel is the basic element for forming sparks. When cnc steel contains manganese, silicon, tungsten, chromium, molybdenum and other elements, their oxides will affect the lines, colors and states of sparks. According to the characteristics of the spark, the carbon content and other elements of the steel can be roughly judged.
Spark pattern
The sparks produced when steel is ground on the grinding wheel are composed of root sparks, middle sparks and tail sparks to form a spark bundle. The line-like trajectory formed by high-temperature grinding particles is called streamline.
The bright and thick points on the streamline are called nodes. When the spark bursts, several short lines are called awn lines. The sparks formed by the awn lines are called festival flowers.
With the increase of carbon content, the continuous bursting on the awn line produces secondary flowers and tertiary flowers. The bright dots that appear near the awn line are called pollen.
Due to the different chemical composition of steel materials, the sparks of different shapes at the streamline tail are called tail flowers. The tail flowers include bract-like tail flowers, foxtail-like tail flowers, chrysanthemum-like tail flowers and feather-like tail flowers.
Bract tail flower
Foxtail flower
Chrysanthemum tail flower
Pinnate tail flower
Practical application
Spark characteristics of carbon steel
Carbon is the basic element of sparks in iron and steel materials, and it is also the main component determined by the spark identification method. Due to the different carbon content, the spark shape is different.
①The streamlines of low carbon steel are thick and thin, with few popping flowers and mostly one-time flowers, and the awn lines are thick, long and have bright nodes. The sparkle color is straw yellow with dark red.
20# steel
②The streamlines of medium-carbon steel are slender and numerous, and there are nodes at the tail and middle of the streamlines. Compared with low-carbon steel, there are more popping flowers, and the flower shape is larger. There are primary flowers and secondary flowers, with a small amount of pollen attached. Sparkle color is yellow.
45 # steel
③The streamlines of high carbon steel are thin, short, straight, numerous and dense. There are many burst flowers, the flower type is small, and they are mostly secondary flowers, three flowers or multiple flowers, the awn line is thin and sparse, there is a lot of pollen, and the sparkle color is bright yellow.
T10 steel
Spark characteristics of cast iron
The cast iron sparks are very thick, with many streamlines. They are generally secondary flowers with more pollen and burst flowers. The tail gradually thickens and droops into an arc shape, and the color is mostly orange-red. In the spark test, it feels soft.
Spark characteristics of alloy steel
The spark characteristics of alloy steel are related to the alloying elements it contains. In general, elements such as nickel, silicon, molybdenum, and tungsten inhibit spark popping, while elements such as manganese, vanadium, and chromium can promote spark popping. Therefore, the identification of alloy steel is difficult to grasp.
Generally, the spark bundle of chromium steel is white and bright, the streamline is slightly thick and long, and the burst is mostly a single flower, the flower type is larger, in the shape of a large star, the forks are many and thin, with broken pollen, and the spark center of the burst is brighter.
The spark bundles of nickel-chromium stainless steel are thin, the light is dim, and it bursts into a flower, with five or six branches in a star shape, and the tip bursts slightly.
The high-speed steel sparks are slender, with a small number of streamlines, no sparks bursting, dark red in color, intermittent streamlines at the root and middle, and arc-shaped tail flowers.
Advanced Cheats
Spark Identification Table
Carbon Steel Spark Characteristics Table
Effect table of alloying elements on spark
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Post time: Jun-05-2023