The process of manufacturing mild steel hollow-section structures involves a step-by-step arrangement of cutters, plastic ‘spacers’ and industrial rings in the slitting-line machine to get good quality steel strips. The process results in hollow-section structures that are circular, rectangular and square in shape as well as ‘multi-c’ and flat bar strips.
In this procedure the smallest width used is 25 millimeters; this size of width is applied in the making of flat-structured bars of thickness of 2.8 to 3.0 millimeters. The largest width used is 670 millimeters that has a thickness ranging from 5.9 to 6.0 millimeters, which is commonly used for making 175 by 175 millimeter square-structured hollow-sections. The smallest thickness used in the procedure is 1.0 millimeter.
Before the process begins, one should make sure the cutters, plastic ‘spacers’ and the industrial rings are clean. There are a couple of reasons for this; the first is because of durability of the equipment, the second is that, if left unclean, the cutters may increase in size by a few millimeters due to accumulation of dust particles resulting in incorrect strip sizes. In addition to these two main reasons, in the process of welding or using oxy-fuel to cut off sections of the strip that are damaged during the process, the sparks produced can attach themselves to the cutters if they were not properly cleaned and this can lower the quality of the hollow-section strips being manufactured. For quality results, it is always recommended to clean the cutters, plastic ‘spacers’ and the industrial rings before and after the slitting of strips in the slitting line machine.
Before arranging the cutters, you should have the slitting machine’s setting plan and line up all materials needed. This will make the work easier and also avoid errors that sometimes cause a newly assembled setting not to work properly for the first time. With everything in place you should start by opening the machine. First step is to unscrew and loosen the stand-lock bolt then move the stand away from the shaft by unscrewing the movable stand-stud screw. You should then draw the slitting machine’s top and bottom shafts apart, by turning its hand wheel in an anticlockwise direction till one has access to the overlapping cutters. After that is successfully done, remove the plastic ‘spacers’, cutters and rings then assemble them as per the size of strips to be produced.
The plastic ‘spacers’ with rubbers and those without should be arranged equally in an alternating order. The work of the rubber is to reinforce the strips in the slitting machine to prevent them from moving out of line thus causing damage to the resultant strips. With the plastic ‘spacers’ in place screw back the stand-lock bolt and lock it, then close the shaft-lock nut. Slowly turn the hand wheel to move the slitting machine’s shafts to their original position ensuring the edges of each cutters fit over each other creating a clear overlap. Lastly, after the assembly process is complete, make sure you tighten the slitting machine’s shaft-nut firmly so that the materials in the slitting-machine do not lose alignment once the slitting begins.
The bush, disk and rings must be arranged according to the slitting machine’s setting to allow the strips to evenly recoil at the separator shaft during the slitting process. Also, instead of making a space of exact width between the spacer’s disks, there should be an allowance; strips of thickness as small as 1 millimeter should have an allowance of 1.2 millimeter and those of 5 millimeter should have an allowance of 2 millimeters. This is mainly because strips of light thickness like 1 millimeter tend to get out of alignment easily, thus given that specified margin of allowance to stay in alignment from beginning to end of the process.
With everything set and working, let the process run till the number and shape of hollow-sections are all done. After the process is complete, confirm the accuracy of the setting by measuring the distance between each cutter. If there is a reduction in length between the cutters, insert a plastic shim with the exact required thickness between the ‘spacers’. Normally, plastic shims’ thicknesses range from 0.1 to 0.8 millimeters.
In storing the cutters after the process is completely done, do not mix light gauge cutters with those of heavy gauge, they should be kept in separate places. This is mainly due to the fact that light gauge cutters are used for cutting strips of 1.0 millimeter but can also be used in cutting strips of 5.0 millimeters, but once a light gauge cutter is used in cutting thicker material like 5.0 millimeter, they should never be used as light gauge cutters else this will result in low quality strips. Additionally, you should remember to clean all the materials as earlier mentioned.