Black and Bright Bar
Black carbon steel bars are converted to bright bars by any of the following methods as listed below.
Drawing through tungsten carbide (or sometimes hardened steel) dies.
10-42 mm dia. – usually drawn from hot rolled coil on a Schumag machine.
40-100 mm dia. – from hot rolled bar on a draw bar bench.
Removal of the surface by turning on a lathe or "peeling" the surface away in a bar peeling machine.
Removal of the surface by grinding (special and more expensive applications).
Why do black bars need to be converted to bright bars?
- Closer dimensional tolerances for feeding through collets.
- To make it more attractive to customers
- Improved roundness enabling better gripping in lath jaws to prevent slippng
- To prevent rust formation.
- Removal of surface defects(turning, peeling, grinding only)
- To make it easier for heat treatment.
- Removal unwanted millscale which cause excessive soiling of machines and abrasion of slideways.
- By turning or peeling the risk of heat treatment cracking is reduced.
- To improve subsequent processing.
Bright bar in grades 080m40(En8) and 070m20(En3a)
