Slitting Cutters

PRIVATE AND CONFIDENTIAL

Issues with horizontal clearance:

Issue Effect on Strip and Slit edge Effect on Knives

Knives set too closely (Insufficient horizontal clearance

• Deeper than normal nick• Small break• Jagged line between the two zones• Burr on bottom edge

• Knives wear off too quickly• Unnecessary forced imparted to slitter

head• Knives often chip

Knives set extremely tight • Nick extending through most of the strip

• Little or no fracture zone• Excessive Burr• Wavy Edges• Double Shear

• Chipping of Knives• Spalled Knives

Knives set too far apart (Excessive horizontal clearance)

• No noticeable nick• Heavy roll over on the top of the strip• Heavy burr on the bottom of the strip

• Knives act like bending dies• Reduced life of knives

PRIVATE AND CONFIDENTIAL

Issue Effect on Strip and Slit edge

Poor Edge condition • Incorrect horizontal knife clearance• Incorrect vertical clearance or overlap• Separator disk - issues

Knives dull too quickly • Incorrect knife grinding practice• Incorrect knife selection• Speed mismatch• Incorrect vertical/horizontal clearance• Incorrect material selection of knives

Chipping of Knives • Too much vertical overlap• Incorrect alignments• Incorrect use of stripper rings• Incorrect material selection of knives

Marking on strip surface • Issues with knife design• Incorrect spacers usage• Issues with the use of coolant

Wavy edges on the strip • Incorrect vertical/horizontal clearance• Incorrect use of stripper rings

Common slitting problems and solutions

Table: Common slitting problems

PRIVATE AND CONFIDENTIAL

Grinding of Slitting Knives

Re-grinding of Slitting knives is a very specialized process and extra care should be taken as improper grinding can cause change in:

• Microstructure of knives• Strength of cutting edge

The above could lead to inferior quality of slitting along with a reduced life of the knives.

For slitting knives, the re-grinding should be done on a cylindrical grinding machine and the Outer diameter of all the knives should be ground at the same time.

Grinding wheel of a coarser particle size will invariable be softer and have a more open structure in order to be self dressing. This is ideal for the re-grinding of the outer diameter of the knives.

Care should be taken while synchronizing the below to obtain the proper surface finish of between 7-10 rms:

• Feed rate (depth of cut)• Grinding wheel speed• Slitting cutter rotation

If the above parameters are not set correctly it may result in:

• Burn marks on the blades• Size variation between knives• Increase in number of re-grindings required

PRIVATE AND CONFIDENTIAL

Issue Effect Solution

Grinding wheel too soft • The wheel loses grain too easily• High wear rate of the grinding wheel

• Reduce the RPM of the knives and increase the wheel RPM

Surface finish of knives after re-grinding is not good

• Slit edge is not of desired quality• Marking on the strip being slit

• Reduce depth of cut while grinding• Decrease knife RPM• Use Grinding wheel of finer particle and

structure

Vibration during grinding • Poor quality surface finish• Decrease in the life of the knives

• Reduce the depth of the cut• Use softer wheel with higher particle

size• Check dynamic imbalance of grinding

wheel

Scratches on the Outer Diameter of the knife

• Slit edge is not of desired quality• Need for frequent re-grinding of the

knives• Marking on the strip being slit

• Check and replace the diamond dresser• Replace coolant as metal particles

within coolant

Burn marks on the knife after grinding

• Decrease in the life of the knives• Marking on the strip being slit

• Decrease grinding wheel rotation• Increase knife rotation• Use of coolant between grinding wheel

and knife

Grinding of Slitting Knives

Table: Common grinding issues