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How do you know the type of steel by looking at EDM sparks?

 Some old grinder drivers in the factory are very knowledgeable, and they can know the type of steel by looking at the sparks they produce, and they feel very good.

It is said that this can only be understood, not in words. Is it really? In fact, as long as the essence of things is mastered, not old drivers can still have this skill.

01 Principles of Spark Identification Method

When the steel material is ground on the grinding wheel, the high-temperature fine metal particles are thrown out in the tangential direction of the grinding wheel rotation, and then rubbed with the air, the temperature continues to rise. In the process of contact with air, the carbon element in the steel will chemically react with the oxidized iron oxide to produce iron element and carbon monoxide. Carbon monoxide explodes in contact with air to form sparks, so a bright streamline is formed on the trajectory of the metal particles.

We know that steel not only contains carbon, but also may contain manganese, silicon, tungsten, chromium, molybdenum and other elements. When a spark is formed, the oxides of these elements will produce a flame color reaction, which affects the line, color and state of the spark. According to the color and shape of the spark, the chemical composition of the steel can be roughly determined.

02Various forms of grinding sparks

Although everyone has seen sparks, do you know how to describe the various forms of sparks?

The fire bouquet produced by grinding is composed of root sparks, middle sparks and tail sparks, while the fire bouquet is composed of streamlines, nodes, popcorns and tail flowers.

With the increase of carbon content, the burst on the awn line continues to produce secondary flowers and tertiary flowers. The bright dots near the awn line are called pollen.

03The sparks of different steels have characteristics

When performing spark identification, the grinding wheel speed is generally 46-67r/s. When the steel is in contact with the grinding wheel for grinding, the pressure is moderate, and the spark streamline is slightly higher than the horizontal direction. Carefully observe the color, shape, length, number of knots, and characteristics of the tail to judge the type of steel.

1) Carbon steel

The carbon content of steel will cause the difference in spark shape.

Low-carbon steel with a carbon content of less than 0.25% has thick and thin streamlines, few pops and more one-shot flowers, thick and long awn lines with bright nodes. The color is yellow grass with dark red.


Medium-carbon steel with a carbon content of more than 0.25% has a slender and many streamlines, with nodes at the tail and middle of the streamlines, a large flower shape, primary and secondary flowers, and a small amount of pollen. The color is yellow.

45 # steel

The streamlines of high carbon steel are thin, short, straight, multiple and dense. There are many popcorn flowers, small flowers, mostly secondary flowers, tertiary flowers or multiple flowers, with thin and sparse awn lines and many pollen. The color is bright yellow.

T10 steel

2) Alloy steel

Chromium, manganese, and vanadium can help produce spark bursts, and tungsten, cobalt, nickel, silicon, etc. can inhibit spark bursts.

The alloy steel with 1%-2.5% nickel, the spark does not spread out, and the flower bud is oval.

Tungsten alloy steel sparks resemble fox tails, while silicon alloy steel sparks flared.

The chromium-nickel alloy steel sparks in full bloom and bursts three times. The flower has a multi-layered star shape, and the flower center has bright buds that are red.

3) Chrome steel

Generally, chrome steel fire bouquets are white and bright, with a slightly thicker and longer streamline. The bursting is mostly a one-time flower, with a larger flower shape, a large star shape, multiple and thin branches, with broken pollen, and a brighter spark core.

4) Nickel-chromium stainless steel

The fire bouquet of nickel-chromium stainless steel is thin, with darker luminescence, bursting into a single flower, five or six branches, star-shaped, and slightly bursting at the tip.

5) High-speed steel

The high-speed steel fire bouquets are long and slender, with few streamlines, no spark burst, dark red color, intermittent streamlines at the root and middle, and arc-shaped tail flowers.

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