The ability of the cast iron platform material to resist local deformation, especially plastic deformation, indentation or scratching is called hardness. The hardness index of the cast iron platform is usually expressed by Brinell hardness (HB), and the standard is between HB170-240, according to the specific use of the workpiece The hardness generally does not exceed this range.
Principle of hardness test. Press the steel ball or cemented carbide ball of a certain diameter into the surface of the cast iron platform at the specified test pressure, remove the test force after a certain time, measure the surface indentation diameter, and divide the test force by the indentation surface area to calculate the hardness. The smaller the indentation, the greater the Brinell hardness value, that is, the higher the hardness.
The method of adjusting the hardness of the cast iron platform is the inoculation of cast iron. This is the most commonly used method. Usually, the inoculant is slowly added to the molten iron after the furnace is released. The gray cast iron after the incubation treatment will tend to be uniform and improve the machining. The performance also increases the strength of gray cast iron.
If the hardness of the cast iron platform casting is not enough, then the casting is easily deformed and damaged. Tools such as scribing platforms, cast iron inspection plates, cast iron flat feet, cast iron bent plates, V-shaped brackets and other inspection and measurement tools cannot be used accurately, which directly affects the accuracy of the data of the detected workpieces. Adjusting hardness with chemical composition is the most common method. Generally, the hardness is mainly adjusted by adjusting the content of C. The adjustment range is usually 2.9-3.5 followed by si. The usual range is 1.5-2.4%. The higher the content of these two elements, the lower the hardness, and the lower the content, the higher the hardness.