In processing metal coils, both ferrous and non-ferrous, slitting lines are used to reduce the width of an incoming coil by cutting it into a series of narrow coils. At the entry end of the line a coil is mounted on a mandrel and unwound. The unwound material is referred to as “strip”. The leading edge of the strip is passed through a slitting machine that slices the strip longitudinally into multiple widths (these portions are often referred to as “mults”) that are then rewound on a recoiling mandrel. The mults are then discharged and dealt with as individual narrow coils. The number of mults can vary from as little as two to as many as thirty or more.
Referring now to FIG. 1, a typical slitting machine A is shown which includes a pair of parallel arbors 10, 11 that are tooled with rotary knives 12. The knives are typically hardened steel discs, having a bore that corresponds to the arbor diameter. The knives are mounted by sliding them onto the arbor face and then spacers 13 are slid onto the arbor between adjacent knives. On a given arbor, the distance between adjacent knives establishes the width of the mult that will be produced in that zone. There is a longitudinal key (not shown) that engages the knives and also a slot in the arbor. The key serves as a way of transmitting the power (i.e., torque) from the arbor to the knives.
The upper and lower arbors 10, 11 are tooled with the same spacing between adjacent knives but the arrangement is such that the upper knives versus the lower knives are offset to each other by essentially the width of a knife. As seen in FIG. 1, all the knives 12 can be the same diameter and width. The spacers 13 between the knives can have additional “rubbers” or rubber sleeves 14 slid over the outer diameter of the spacers. The rubber sleeves 14 serve as strippers that keep the mults from wrapping themselves around the flanks of the knives. The rubber sleeves are essentially the same diameter as the outer diameter (OD) of the knives themselves. Scrap chute C is shown below the slitter knives where trim falls into the scrap chute.
In a parallel fashion, one of the arbors 10, 11 is adjustable relative to the other arbor such that the vertical gap between the knives can be adjusted. Typically to make a cut, the vertical gap between the upper and lower arbors has to be adjusted just right. If the gap is too wide, the strip S will not be cut. If the gap is too small, it may result in poor cut quality (i.e., bad edges). When the strip is “cut” the cut zone includes a zone of penetration and a zone of fracture through the thickness of the strip. The amount of penetration (i.e., knife gap) required to cause the fracture, depends on strip material properties.
When the strip is cut into mults, the leading edge of the strip can cause issues with threading the leading edge through the rest of the line downstream of the slitter.
For example, the individual mult leading edges want to curl up and down, each adjacent mult curls in the opposite direction of its neighbor, thus requiring special handling during the threading of the line.
To avoid this situation, it has become common practice for operators to vary the gap between the slitting arbors. When the leading edge of the strip presents itself to the slitting machine, the gap between the upper and lower knives is adjusted too wide to effect the cut. After the leading edge is through the slitter, one of the slitter arbors is adjusted to close the gap between the upper and lower knives to a point where the material is “cut”. This technique leaves the leading edge of the strip with a length that is uncut and essentially one whole width of material thus making it much easier to thread the line. Once the line is threaded and the leading edge is close to the recoiler, the leading edge “uncut” zone is sheared off. This entire operator practice is often referred to as “plunge” slitting.
Plunge slitting is an improvement in threading the line, but it is an imperfect solution. The purpose of the present disclosure is to further improve the threading of slitting lines. In the process of slitting, in addition to the mults, the slitter also trims the outside edges (two edges) of the parent coil. This edge trimming accomplishes two things: 1) it establishes an exact width for the outermost two mults (one on each edge of the coil); and 2) it trims away bad edges from each edge of the parent coil (examples of bad edges or edges which could have cracks or could have material handling damage from prior handling of the parent coil).
Each edge trim includes a relatively narrow ribbon of scrap material. The scrap is removed from the line just downstream of the slitter. The two ribbons of scrap can be chopped into discrete scrap pieces (such was discussed in U.S. Pat. No. 7,901,271 related to scrap choppers which is hereby incorporated by reference in its entirety) or the scrap could be wound onto scrap winders.
When operators use plunge slitting, the leading edge of the strip remains uncut and includes the “scrap” edges. This requires the operator to stop the line and enter the line to physically and manually cut the scrap away from the uncut zone thus allowing the scrap to be redirected to the scrap chopper chutes or to scrap winders. This practice reduces productivity and introduces an unsafe condition for the operator.
Typically a slitting line would not have notchers. Normal use of notchers are on “coil to coil” lines where the tail of an exiting coil is welded or stitched to the head of an incoming coil. The notches are cut in the weld or stitch zone so that the weld or stitch could be tracked as it goes through the process line (such as a continuous pickle line for example). Tracking the weld or stitch zone allows pinch rolls and like equipment to partially open to pass the weld or stitch zone and close back. Notchers are also used to cut test samples out of the strip such as on a coil to coil line.
However, existing slitting lines do not use notches to reduce the width of its leading end of the strip which enables the trimmed scrap edges to not foul as the scrap chutes near the exit of the slitter.
Plunge slitting without the use of notches would result in the leading edge of the strip crashing against the scrap chutes.
Thus, there is a need for a method of improving the threading of slitting lines including the addition of notches which overcomes the above mentioned deficiencies while providing better overall results.