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How to analyze the choice of slitter knife clearance and the situation of the slitting line from the burr of the strips?

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Author : Mr. Jiang
Update time : 2021-04-22 16:04:07
For coils slitting, we are most concerned about the quality of the strip edges, and the edges of the strip usually appear in the following situations. In this article, we will discuss one by one around the strip burr state and the direction to solve the problem.
State of Burr: The burrs of all strips are completely irregular.
Caution: Check the accuracy of the slitting machine and the slitting tools respectively.
State of Burr: The slats with odd or even numbers cannot be cut off.
Caution: The shaft shoulder of the slitting machine is with big offset, and the first clearance is not good.
State of Burr: The burrs on both sides of the strip are different, but the burrs on each side are regular.
Caution: The shaft shoulder of the slitter is with offset, or the first clearance is not good.
State of Burr: In the length direction of the whole strip, the burrs are good and sometimes bad.
Caution: The shaft shoulders run out greatly, and the parallelism of knives is poor.
State of Burr: When slitting multiple strips, some strips have good burrs and some are bad.
Caution: The cumulative error of slitting tools is not good or there are rust spots on the knife.
State of Burr: The burrs on both sides of all strips are regularly too large.
Caution: Too big slitter knife clearance.
State of Burr: There is a regular squeeze shape on both sides of all strips.
Caution: Slitter knife clearance is too small.
Although the above lists common burr problems and the directions to solve them, in actual production, many problems are often intertwined, and it is difficult to find the real cause. Therefore, the elimination method must be adopted to measure each accuracy index of the machine, each accuracy index of the knife, bonded stripper ring and spacer. After eliminating the accuracy of equipment and tools, the issue of whether the clearance is reasonable can be analyzed. Therefore, the premise of discussing the quality of the strip edge is whether the material edge burr is relatively uniform, and then the value of the knife clearance can be analyzed, and then there can be a direction to adjust, and finally solve the problem. If the burr of the material edge is absent from time to time, or changes periodically in the longitudinal direction, it must be caused by insufficient accuracy of the tool or the accuracy of the machine.
When the clearance is too large, the sheet material is not 100% sheared in the clearance. It has extra space necessary for normal shearing, so that the stretched part of the material is pulled to the outside of the material, thus forming obvious and complete burrs at the tail, and the side of the material strip is flat without light.
When the clearance is too small, the space between the knives is too small to make the sheet material form a complete shear, so it has to squeeze the material to form a second shear, and the material that cannot be sheared will form burrs. This kind of burr is not big, but it is fragmented, intermittent, and filamentous, the whole side is uneven, and the middle part is shiny. The manifestations of these two kinds of burrs are completely different and are easy to distinguish. If you still find it difficult to distinguish, it would be more helpful to analyze the edge side of the strip coil with a 20 x magnifying glass with a light source. For the burr-free edge side of the strip coil, each circle appears as two clear layers. One part of the thickness is completely cut and the other part is tore off. The boundary line is very complete, the layer is very uniform, and the appearance is shiny. It is more obvious under the magnifying glass, and it feels good in hand. The edge sides of the strip coils with too large clearance have a dark appearance and rough hand feeling. While the edge sides of the strip coils with too small clearance have squeezed bright bands with uneven widths. Figure 1 and Figure 2 are the strip edges with too large and too small clearance respectively.

Figure 1 The edge of the strip when the slitter knife clearance is too large

Figure 2 The edge of the strip when slitter knife clearance is too small
Slitting was considered an art, but it is gradually being recognized as a science. Thanks to advances in equipment, tools and software, it is now possible to control variables and improve the slitting process to achieve unprecedented results. For more professional knowledge about slitting, you can read following article.
1.  How to avoid slit-in coil slitting problems - by Jim Wilcox