Common Problems and Solutions of Slitting Lines

Posted by chrisheqi on March 27th, 2019

Today's iron and steel business is not limited to "moving bricks". Providing valuable supply chain services is the way to survive in the future. The requirement of iron and steel man's business ability is also raised to the level of "knowing astronomy from top to bottom to geography".

The most common value-added service in supply chain is shearing processing, which is more difficult to identify and deal with quality or equipment problems than the original defect. Iron and steel friends suffer from inexperience in this respect. They often look for people to negotiate everywhere, but they may not be able to solve it.
Next, the author will solve the puzzles for you one by one.

Common problems in this shearing process are divided into longitudinal shear series, transverse shear series, blanking series and equipment maintenance series.
Brief Analysis of Common Problems in Longitudinal Shearing and Slitting Processing

In the process of sheet slitting line processing and shear production, many processing centers will have some similar common problems (regardless of the differences of equipment itself).

For example, burrs, sickle bending, winding staggered layers, multiple winding irregularities, edge waves after longitudinal shearing, etc., the most common of which are burrs and sickle bending.

1. What are burrs and camber?

Burrs and camber in shearing process are similar to defects of main production line (continuous retreat, hot rolling, etc.) in steel mill, but slightly different.
Following are the physical drawings of common burrs and camber defects in shear processing.
As shown in the figure, a spiral impression appears on the edge. When the coil is unfolded, it will be found that the section at the edge of the strip is inconsistent. One section is all cut-off surface, and the other section is all tear surface. The burr of the whole steel strip section is also very large, and the width tolerance varies greatly, which is essentially a manifestation of sickle bending.
Similar fluctuations in cut-off surface and width do not affect the use of less demanding users. However, it will have a negative impact on the follow-up processing of high precision and high quality (such as high requirements for sickle bending when making shelves, and pits when making punching burrs fall), let alone the production of products with shear accuracy exceeding 0.1 MM.

Analysis of burr and camber defects in longitudinal cutting
The investigation and improvement of longitudinal burr and sickle bend are mainly focused on the longitudinal blade and its accessories. We can check by detecting and controlling some key parameters.
Case: After inserting the blade, the clearance of different angles of the same cutting edge is measured. The clearance of the blade is measured once every 90 degrees of rotation. The structure shows that the difference between the minimum and maximum clearance is 0.12 mm among the four measuring points.
Conclusion: The discrepancy of blade clearance will affect the stress distribution of the slitting blade during shearing and the stability of the long-term operation of the blade. In the shearing process, the cutting edge is in a curved state, which not only causes burrs and sickle bending, but also leads to side waves.

Reason analysis: The reasons for inaccurate positioning are as follows:

1. Damage of longitudinal shear separator working face
The tolerance of the parallelism of the two ends of the longitudinal shear sleeve is positive or negative 0.002 mm, and the smallest errors can be found by naked eyes are more than 0.1 mm. If there is a common damage to the spacer, the accuracy can not be guaranteed basically once there is a collision, which directly affects the accuracy and quality of the product after shearing.
Typical morphology of spacer damage
The main cause of the damage is operation and maintenance. For example, the worker has not developed the habit of light handling, or may fall or bump when lifting or handling.
In addition, the material quality and surface hardness of the separator are also important. Some small processing factories do not meet the shear accuracy standards because they save the cost in places that should not be saved. This makes it easy to cause such problems even if the collision is lighter, which needs to be paid more attention to when choosing and purchasing the material of the spacer.
2. Locking problem of blade and spacer on tool axle
In order to ensure product size, the shearing mill usually combines the axle and blade together to form a complete whole. Once all the blades and spacers on the whole axle are not locked (as shown in the figure below), the external force acting on the strip steel reaction force changes, and the blade rotates with the axle, which directly results in the shearing burr. The solution is very simple, that is, to ensure locking. But whether the locking can be ensured is closely related to the equipment configuration. There are two common locking modes: hydraulic and mechanical.
Although the mechanical locking is easy to operate, the locking effect is general and only the employees with great strength should be selected to operate. The locking effect of hydraulic nuts is good, but we need to have a certain understanding of the equipment, but the effect of blind purchasing is not as good as mechanical locking.

3. Unparallel tool holder
The shearing process is formed by the interaction of upper and lower tool holders. If the upper and lower tool holders are not parallel, one of them is in an inclined state, it will also lead to sickle bending and burrs.
It is relatively easy to solve the problem of non-parallel tool shafts. Equipment experts can quickly solve the problem by adjusting worm gears and using professional testing equipment.

Conclusion

Slitting line production is a typical way of coil processing. With the upgrading of industry and the increasing demands of customers on product quality, higher quality expectations are put forward for the vertical shear production line. Of course, in addition to improving the operation and management level of the vertical shear production line, there are also high requirements for the configuration, maintenance and spot inspection of the vertical shear equipment.
Slitting line defects are not only burrs and camber, but also other common problems in production, such as winding staggered layers, uneven winding, side waves after longitudinal shear, etc.

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