Carbide Slitter Rewinder Bottom Knives for Paper & Film Rewinding Lines

Because a shear cut needs a hardness differential to stay a shear cut. When the two knives are close in hardness, the material in the shear zone deforms instead of separating cleanly, and you get a burred slit edge and crushed fibre that becomes dust in the roll. The harder bottom knife holds a stable edge geometry while the softer top knife carries the wear — which is also why the top knife is the one you expect to change more often. Matching the hardnesses is a common and expensive mistake.

At the slit itself, before the web cleaners and static bars. A bottom knife whose edge has rounded or whose face finish has dulled stops shearing and starts crushing, and crushed fibre goes straight into the roll — often showing up as a defect two processes later. The tell is timing: dust that appeared gradually points at the knife, dust that appeared after a grade change points at the substrate. Inspect the edge under magnification and check the face finish, not just sharpness by feel.

Yes, and it is the normal way these are bought. Bottom knives typically outlast top knives by a wide margin, so replacing them on the same cycle wastes serviceable tooling. Give us the bottom knife OD/ID/thickness and the matching top knife specification, and we will match the mating geometry and the hardness differential to what you already run.

Yes, provided the body is straight and true and the braze seats are sound. Re-tipping is substantially cheaper than a new knife and is the reason to choose tipped over solid carbide when the economics are close. Solid carbide cannot be re-tipped — when the edge is spent the knife is spent, which is the trade you accept for the longest single service life.