Procedure for Slitting of Mild-Steel Strips

This is the process of cutting strips of different sizes from a hot rolled mild steel coil. The strips are used for making square rectangular and circular hollow sections or tubes. In this process, width of the strips range from 47/48 millimeters and thickness of 1.0 millimeters for making 12 millimeters by 12 millimeters square hollow sections to width of 670 mm and thickness of 5.9 millimeters to 6.0 millimeters for making 175 millimeters by 175 millimeters square hollow sections or 200 millimeters by 150 millimeters rectangular hollow sections. For this process, the hot rolled mild steel coil is bundled in a 6 to 10 tone-package with a width of 1200 millimeters to 1300 millimeters.

Materials needed for the process are: slitting line machine, overhead crane, weighing scale, micro meter screw gauge, 3 meter steel tape and the mild steel hot rolled coil.

Before the process begins the coil is visually checked for deformities, that is; burrs, dent edges, elongations, lamination and waviness. It should also be checked for supplier tolerance on mechanical properties; thickness and width.

If the coil is okay, the straps which seal the coil are welded off leaving one which would hold the coil preventing it from unfolding or uncoiling before loading it in the slitting line machine.

The coil is then placed in the slitting line machine with the help of an overhead crane and on to the slitting line car at the slitting line bay. At this point the machine is turned on, the coil is pushed forward using hydraulic force and raised up to be sandwiched by cone-shaped mandrel of the plate drums that straightens them. The remaining scrap is scaled off using a pinch roll-up, it is then used to support the coil to penetrate through the rollers. Prior to the material reaching the cutters, the coil width is measured using a 3 meter steel tape and the thickness measured using 0 to 25 millimeters micro meter screw gauge to ensure they are of the required dimensions. These steps should be done thrice; at the start of the process, when the material gets to the mid section and when it gets to the end.

If all is okay, the machine is turned back on and the material passed through the cutters. As the process continues, the strips are moved to the mandrel that straightens them, where the separator shaft is used to prevent the strips from intermingling. The sides - which are part of the additional width - are considered extra material (scrap), they are rolled and attached by the scrap winder unit which moves in a circular motion simultaneously with the machine as the material is being processed. Adjustment screws are fastened to lock the strips so that as the mandrel starts to recoil, the strips would not detach or slip off.

As the process proceeds, speed is gradually increased to allow easy flow of strips that are being cut into slits. The clutch at the main slitting drive is released to ensure the process is continuous. Strips are tightened by inserting short strip straps as the process is ongoing. At the end of the process, the strips are welded. At this point the separator shaft is moved upwards and the mandrel screws are unlocked to access and remove the strips. This point culminates the procedure for slitting of mild-steel strips.