Self-sharpening knives and blades – truth or myth?

Self-sharpening knives with a blade that never dulls are the dream of any housewife and owner. This applies to various kitchen equipment (meat grinders, food processors), tools, household appliances and appliances. Manufacturers often use various gimmicks and tricks to sell a product. “Self-sharpening”, “non-dull”, “eternal”, “laser sharpening” – these and many definitions can be used in advertising materials. Is it true? Can knives self-sharpen and not dull, or is this just a marketing gimmick?

A non-dull blade: is it possible?
Those who remember the school physics course know that hard material deforms soft material under pressure. This is the cutting principle that kitchen knives, other cutting tools, and other cutting tools demonstrate. The hardness of metal / alloys and other materials is generally understood to be the resistance to deformation under pressure. The parameter affects characteristics such as wear resistance, pliability during processing and abrasion resistance.

Can the blade not be blunt? Yes, but only if you don’t use it. Blade wear during operation is inevitable, even when it comes to the hardest materials. At the same time, harder materials are able to maintain cutting properties for longer and resist wear. For example, zirconia ceramic knives. Another option is a serrated blade.

Maintaining the sharpness of ceramic knives is due to the properties of the material, and the serrated blade is due to the increase in the length of the cutting edge and its shape. It is worth noting that it is extremely difficult to sharpen all these types of knives at home: skills and equipment are required.

 

Sharpening – processing (grinding) of the cutting part of the tool. During sharpening, an edge angle (sharpening cone) is formed by removing the top layer. The sharpness of the knife is determined by the cutting edge, but gradually this angle changes, and the shape of the blade deforms.
To maintain cutting performance, another important procedure is dressing. This is the alignment and elimination of blade defects: dents, bends, chips. Everything is simple and obvious: a straight and sharpened blade at the right angle cuts well, but a deformed blade with a blunt cutting edge does not.

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High blade hardness is not always the best option
It would seem that the wear problem can be minimized by using carbide steels, but this is not the case. When working with a knife or other cutting tool, it is not always possible to cut at the same angle. The slightest deflection results in lateral loading, and thin, hard metal is brittle. There is always the chance of a blow, a chance of hitting a hard surface or blotches with the blade. The consequence of this is chips, a rapid loss of sharpness due to damage to the blade. An example is cast iron, which is very hard but can burst on impact.

 

Soft material will not burst or chip in similar situations, but the cutting edge deforms quickly. For restoration, dressing without sharpening is often sufficient.

The properties of steel blades depend on alloying additives, which can be used as:

Chromium (Cr) – improved strength and corrosion resistance
Tungsten (W) – increase in hardness, decrease in brittleness
Vanadium (V) – resistance to deformation
Manganese (Mn) – increased impact resistance

In a good knife, a compromise is reached between ductility and rigidity, necessary for comfortable use. Ideally, the problem is solved by a set of knives, each of which is designed for a specific type of food. In this case, the necessary rigidity, as well as the ergonomics of work, are taken into account.

Self-sharpening knives: myth or reality
Self-sharpening knives are called, which are most often made of a plate consisting of several layers of metal of uneven hardness. The softer layers wear out faster and more easily, exposing and cutting out the hard layer. This technology is nothing new.

 

The simplest example is the self-sharpening plows used by our ancestors several centuries ago. The softer metal is subject to intense wear when plowing the ground. Thus, the equipment was able to plow large areas, while maintaining sufficient sharpness.

A similar principle is found in nature. For example, the standard of sharpness is the beaver’s teeth, which consist of hard outer enamel with a high iron content and an inner soft layer – dentin. In other words, in this case, the hard layer serves as the base, while the grinding of the inner soft layer provides the necessary angle for the sharpness of the tooth.
Multilayer alloys are also not new to humanity. A striking example is Damascus steel. In such blades, the number of layers can exceed a hundred. The legendary sharpness and durability are due to the correct combination of materials, and, of course, the complex and painstaking production process. The hardest layer can be less than 0.01 mm thick.

How multilayer knives are made can be seen in the video below.

In one of the following videos, the author of the video answers the question of how self-sharpening occurs (10:50).

It should be noted that uncontrolled surface wear will sooner or later lead to the need to sharpen the blade. At the same time, a self-sharpening blade is able to maintain cutting properties at a high level for longer if the knife is used for its intended purpose.

In addition to the self-sharpening blade, there is a separate self-sharpening function. The sharpening mechanism can be located in the stand or in the handle for folding models. Sharpening occurs every time it touches. With little or no user involvement. If the abrasive elements are installed correctly, then such a knife will really always be sharp. The disadvantage of this function is the rapid wear of the blade during intensive use. Over time, the metal will grind off and will not reach the sharpening elements, and therefore the self-sharpening function will disappear.

Laser sharpening
Laser sharpening is not, in fact, sharpening. Most often, this concept means point hardening of the blade. What does it do? Inhomogeneous cutting edge hardness. To make the blade, relatively soft (or cheap) steel can be used, and zone hardening increases the hardness to the desired level. Transverse stripes are visible on the blade. The soft surface grinds down quickly, while the hard one continues to cut, or rather, saw. This is similar to the microserrator principle.

Laser sharpening can also be called laser control of the sharpening level, which is used in production. In other words, it is not even metal processing, but a measurement of parameters.

Outcomes
There are no non-dull knives – this is contrary to the laws of physics.
But there are knives that can retain cutting properties for many years: ceramic (with zirconium), microserrators.
Self-sharpening knives exist, but they will also have to be sharpened someday.
Laser sharpening is a myth, but it sounds beautiful. The laser is used to control sharpening in production or zone hardening.
A hard, sharp blade is not a guarantee of perfect cutting: plasticity is also important, otherwise such a knife can be damaged even from contact with the board due to fragility.
Intended use is one of the components of the durability of knives of any kind.