Difference Between Black Steel Bars and Bright Steel Bars
A common question that is normally asked is regarding the difference between black steel bars and bright steel bars
Black Steel Bars
Black Steel Bars are produced in a rolling mill by heating raw material such as billet, blooms, etc at a temperature around 1200 C through a number of rolls to achieve the desired shape and size. Some of the shapes are rounds, hexagons, flats, bars, etc. Due to the nature of the process and temperatures involved, precise control of tolerances that can be achieved in bright bars cannot be achieved in black steel bars. Therefore they are further processed to make steel bright bars for processes that require more precise accuracies. Therefore black steel bars are less expensive than bright bars.
Bright Steel Bars
Bright Steel Bars are produced from black bars by passing through dies in a cold condition or by turning the bars in a peeling machine and some other processes. They are used where specific tolerance are required such as for use in CNC machines, etc. Some times heat treatment such as annealing is done before cold finishing.
There are five main type of different processes to achieve the desired sizes.
The black steel bars are drawn through dies of the required shape. The raw material is chosen depending on the shape to be drawn. This increases the yield strength and tensile strength. This also eliminates a number of surface imperfections caused due to the rolling process.
The black bars are turned to the desired sizes. This process eliminates all surface imperfections. But internal imperfections if any are exposed. This process does not increase the tensile strength of the bars
The grinding process is used to narrow the tolerances and improve the surface finishes of the above two processes
The polishing process improves the surface finish of the bars
Cold Rolling is typically used to produce complex shapes.
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