Questions:

1. If I upgrade my slitting knife material from D2 steel to CPM10V, what will I gain in productivity?

Answer: D2 steel is widely used knife blade material that offers good wear resistance. CPM10V is a composite steel made from a blend of alloys in a particle state that has excellent wear characteristic. CPM10V is more expensive than D2 but offers better economy of production run time, given that the knife setup for each is the same. CPM10V slitter blades and tungsten carbide bottom knives offer the ultimate in paper slitting blade metallurgy.

2. Recently I've seen a much shorter sharpness life for our knife blades from what it used to be, and we have changed nothing on the slitter. What could cause the problem?

Answer: There are a number of factors that can influence knife life, including over heating during regrind to alter the metal temper, too much side load force during setup, and knife holder fatigue.

The most common is excessive side-load force, which can be caused by an over zealous operator or a knife holder that has become loose internally (worn and sloppy shaft support, bearing wear, etc.). When a knife holder becomes loose (the knife lower head is allowed to wobble) the blade toe-in, or cant angle, increases and offers more of the sharp blade edge to the harder bottom knife. The sharp edge cannot support the load so it quickly wears away until it has made enough surface area to support the force applied.

3. What are the advantages and disadvantages of crush cutting vs. shear slitting?

Answer: Shear slitting is the use of two sharp edges (knives) against one another with material passing in between, like a pair of scissors. An upper knife and a lower knife make a shear slitting assembly. The upper knife is usually attached to a pneumatic cylinder, which upon command moves the knife into or away from the material passing over the lower knife.

The lower knife is usually mounted on a driven anvil shaft, which can be either inflatable to lock the lower knives, a steel shaft design where the lower knives are set screw locked, or mounted on an electric motor.

Shear slitting is probably the most common because its effective on a wide range of materials from foil to paperboard to heavy sheet plastic. They come in different sizes depending on web material composition and web speed. Blade life is always a consideration for a given application.

The main advantage is cleaner cuts. The main disadvantage with shear slitting is that both knives have to be positioned when making slit width changes. This means removing the web from the knife area. Removing the lower knives for sharpening can be time consuming as well.

Crush cutting has an upper knife that is pneumatically loaded against the material web with a hardened, sleeved anvil roll behind it. The material is actually crushed or split apart.

Set up changes are quicker than shear slitting and can be accomplished with the material web remaining in place. The main disadvantages are that blade life is shorter due to metal-to-metal contact and the final cut is usually rougher than shear slitting.

4. What is the required hardness of anvil rolls, and crush cut blades?

Answer: Hardness of anvil rolls should be 63-65 Rc. Dienes crush cut blades are 59-61 Rc. Blades are softer to prevent scoring of the anvil rolls.

5. What are shear cut blade specifics, i.e. bevel angle, finish?

Answer: Common male knife bevel specifications are:

Single bevel: Strongest, longest lasting cutting edge. For cutting heavy weight materials.

Double bevel: Thinner cross section than single bevel. Cleaner cut edge slitting medium weight materials. Best choice for cutting a wide range of materials with good knife life.

Double hollow bevel: Thinnest cross section. Cleanest cut edge for cutting thin materials. Least knife life.

Finish: Dienes knife edges are circumferentially ground with surface finishes of 8 rms.