How to Deal with Quality Problems When Slitting Coils

Many problems can occur during the metal slitting process. These include poor edge quality, edge burrs, edge waviness, curvature, knife marks and out-of-spec slit widths.
Slitting has always been considered an art, but it is increasingly 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. Let's look at how to keep these under control.

 

Blade Clearance

Horizontal tool clearance is the most important of these variables. In the past, clearance was almost always set at 10% of the metal thickness. However, 10% is seldom the correct gap. The thinner the metal, the more difficult it is to achieve the correct gap.
Conversely, on thicker metals, the old rule is even less applicable.
Excessive vertical tool clearance or overlap can be the culprit for many strip defects, including edge waviness, crossbows, curvature and deep tool marks. It can also damage tools, such as knives and stripper rings, and can even wear out slitters.
 

Shims

When tools are made and maintained properly, they not only create a good edge, but they keep the tool sharper for longer. If the tool is in poor condition, or if the rubber shims are not manufactured and used to the correct specifications, it can be difficult to obtain accurate clearance between tools.
When shims are damaged (scored and dented) they will not seat correctly. This will result in inaccurate horizontal clearance. In addition, the tool may oscillate, causing clearance variations, which will result in poor or uneven edge quality. Please replace the tools on time.

   

Burrs

Burrs are edge defects that can occur during the slitting process. The main cause of burrs is too tight or too loose horizontal knife clearance. Incorrect clearance automatically leads to poor quality edges. In fact, one of the characteristics of a poor quality edge is a burr.
If the horizontal gap is too loose, the metal will stretch and tear around the knife.
If the horizontal gap is too tight, more force is required to cut the material, which creates a burr.
In addition, a dull knife will automatically create a burr. You are better off using the most wear-resistant knife you can find so that the blade stays sharp for the longest period of time.
 

Knife Marks

Knife marks on strips are almost always caused by improper handling of the stripper ring. In the past, peel-off rings were of the same size and hardness. Even today, some operators wrap tape around the tool so that the non-cutting edge does not leave a mark on the tape. If you do this, stop! Wrapping tape around knives is dangerous; it also leads to poor edge condition, burrs and edge waves.
Proper stripping ring practice includes using male and female rings of different sizes, colors and hardnesses. Size and hardness are not absolute constants and may vary from machine to machine. Size should vary from one metal to another and from thickness to thickness.

   

Slit Width

Some variables that can cause slit width to be out of specification include improper tool clearance, incorrect or worn tools, unmaintained machines, and improper handling of the release ring. If the horizontal clearance is not correct, the width will change. If the release ring is not used properly, the width can change. Different metals react differently to being cut.
Each machine, metal type and tool set may follow different rules. Therefore, you should document the results of each slitting operation and continually improve by monitoring the results.



The more the tool manufacturer knows about your operation, the better they can help you choose the right tool metal grade and advise you on the best tool clearance. If you do not understand good stripper ring practices, it will be difficult to set up your machine correctly. It is also important to consult your supplier GOODKLIFE for the correct application. Training in proper web slitting practices can be helpful, as one scenario does not apply to every setup.