Cold drawing is the pulling of a hot rolled steel bar through a die that is slightly smaller in size. So how is cold drawn steel made? The process path that Datong Hydraulic uses consists of first shot blasting the hot rolled bar, then cold drawing it through the die, then rotary (roll) straightening, and finally cutting to length.
This initial operation will clean the surface of the hot rolled bar, essentially removing all scale and rust. This operation also creates a bar surface which will help carry the drawing lubricant into the die.
The main operation, which actually produces the cold drawn steel tube. We use a heavy frame drawn bench which can draw out over 40′ long finished cold drawn bars. The die itself is mounted securely so as not to move during operation. A pusher mechanism will grab the bar and advance the first 12″ of the bar through the die. Next a buggy carriage will grab the portion of the bar that’s sticking out through the die. The buggy is attached to a large endless chain that is power driven and able to pull the buggy and bar all the way through the die.
Rotary (roll) straightening:
After the drawing operation itself is completed, the bars will undergo a straightening operation. Straightness tolerances will vary depending on grade and size, and tolerances are called out in the ASTM A108 specification (see link and citation above). We can also hold tighter than standard straightness depending on the material upon request. The rotary straightening operation also improves surface finish and will help control size slightly.
The final operation before packaging is saw cutting the bars to length. The end gripper marks left from the drawing operation are cut off. The bars are then cut to the required length. Standard cold drawn lengths are 12′, 20′, and 24′ long. We can provide up to 40′ cut lengths upon request.