Sharpness (edge)
Sharpness is a geometric dimension of cutting edges . In idealized form, one thinks of the cutting edge as two planes that approach each other at an acute angle. The idealized cross-section is a triangle. With real cutting edges, the tip of the triangle is more or less flattened. The sharpness is the width of the resulting stump.
Classic objects with the property "sharpness" are the knife and the scissors . However, their operating principles are different: while the knife "cuts" an object by dividing the object with an acute-angled cutting edge and shifting the two parts symmetrically perpendicular to the cut ( wedge cutting ), the scissors shear by moving two right-angled cutting edges past each other and thereby the Move object parts in the cutting direction ( shear cutting ).
The property of sharpness is given by the abrupt transition of the surfaces of the sharp object.
Razors and Nihontō are considered to be particularly sharp .
Basically, it can be stated that the sharpness of a blade is not permanent, but a temporary condition. Even if a blade is not used, various processes (e.g. corrosion ) can reduce its sharpness. How long the sharpness remains under the respective conditions is described by the term “ edge retention ”. In some applications, value is placed on high sharpness with low edge retention (blades are often renewed, re-sharpened), with others, however, the edge retention is more important (no blade change, no re-sharpening possible without effort).
Advertising statements from blade manufacturers that promise “particularly high sharpness” should be treated with caution, as even the sharpest blade loses its sharpness and becomes blunt after more or less long use. Therefore the statement "sharpness is a result of care and not a property" is justified.
Sharpness test
The sharpness tests include, among other things
- the split leather test , in which the notch depth is measured with a defined splitting force,
- the paper cut test , in which a defined force is used to cut into damp or dry paper,
- the attempt to cut into target tissue , in which a biological target tissue is cut and the cutting force or the cutting depth is measured,
- the micro-sharpness test , in which the sharpness of the actual cut edge is measured on closely defined rubber or silicone threads. The macro-frictional forces, which always arise on the cutting tool surfaces, can thereby be completely hidden. This type of measurement also provides information on the cutting edge width or the cutting edge radius and the micro-roughness on the edge itself.
literature
- American National Standards Institute (ANSI), ISO 8442-5: Materials and articles in contact with foodstuffs - Cutlery and table holloware - Part 5: Specification for sharpness and edge retention test of cutlery
Individual evidence
- ^ Roman Landes knife blades and steel. Technological consideration of knife edges. P. 29