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Damascus steel is a composite carbon steel with a visible pattern that has been made by mankind for several millennia. One of the most common and at the same time the easiest to make types of such metal is the so-called “wild damask”. It is made by welding a package of strips from several grades of steel, with multiple bending and forging. The package is heated in a crucible and added on top of various materials (so-called flux), which fuses with the scale formed on the surface of the plates, cleans from it welded surfaces. Dissolving scale, flux simultaneously forms a liquid slag, protecting the surface of the metal from further oxidation. Package with liquid slag heated to white heat and forged. After the first welding of the package it is uncovered on a strip and cut into several pieces, which are again stacked and made a second welding. Welding can be repeated many times until the desired steel characteristics appear. As a result, the layers of metal are mixed randomly and a pattern is formed on the surface of the bar. The appearance of the pattern depends on the number of layers and the grades of steel used. Light lines in the steel pattern give a high level of chromium or nickel. Dark lines show the use of carbon steels.

There are a number of standard problems associated with creating damascus. The main quality of Damascus steel is considered to be the alternating layers of metal with high carbon content, which give an aggressive cut, and low carbon content, which give it strength. However, during forge welding of layers with different carbon content, carbon diffusion occurs and they mix with each other. This degrades the cutting properties of the high-carbon components of the package by depleting the amount of carbon, and the large number of welds can reduce the strength of the blade. Moreover, the amount of carbon can burn out to appreciable amounts during the welding process, weakening the wear resistance of the steel. As a result, the consumer cannot often predict the properties of the resulting blade. It is widely known that damask can for no apparent reason simply stop cutting even on a well-sharpened knife, it can flake out, become very brittle. The fight against these drawbacks and the development of powder steel production technologies pushed knife makers first to artisanal experiments with powder steels, and then to the application of complex high-tech solutions.

The key role in the development of modern damask manufacturing technologies was played by the appearance of new technological equipment in the knife industry. Industrial forging presses, electric arc furnaces with controlled atmosphere, etc. began to be used for manufacturing of knife steel. In particular, specialized vacuum rolling mills, expanded productivity and allowed the development of industrial production of damask on the basis of the latest technologies of powder metallurgy.

The use of vacuum technology for the production of Damascus steel, allows the use of both metal bars and powder method as raw materials.

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The main advantage of the vacuum method for welding plates of traditional damask is the absence of oxidation of metal during heating. This makes it possible to pre-weld high-alloyed, including stainless steels without flux. Connected ground plates are welded by diffusion welding in a vacuum chamber under a press. The package welded in this way is expanded into plates, which are again ground and welded until the required number of layers is obtained. This method can be used to produce damask from stainless and alloy steels. An excellent method of welding high-alloy steels is also rolling a package of ground or otherwise cleaned plates on a vacuum rolling mill.

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The vacuum method is also used in powder metallurgy. A sealed, oxygen-free capsule filled with wire, metal powder or mixtures is placed in an inert gas-filled chamber of a gas-stat. The capsule is heated to 1200-1400°C and the chamber is filled with gas, up to a pressure of approximately 1500 atmospheres. After the pressurized sintering of the composite material is complete, the sintered composite shell is mechanically removed and the cleaned composite is press forged or rolled through a rolling mill. Almost any type of damask can be produced by this method.

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The advent of these technologies made it possible for large steel companies to produce damask in very large quantities. The largest of these companies was the Swedish Damasteel AB, which in 1996 received a patent for the production of powdered damask blanks. Damasteel’s production technology was “hot isostatic pressing”, which turns a rapidly hardening powder into a compact billet. Powders of two or more types of steel are placed in the center of a steel capsule in which a vacuum is created and hermetically sealed. The powders are sintered together under high pressure in a hot isostatic press. Pressing continues until the density reaches 100%. Damasteel produces two types of billets by powder metallurgy – bars with a layered concentric pattern and a multilayer package with parallel layers. The billets can then be used to create more complex patterns in the forging process.

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The advantages of Damasteel steel are high corrosion resistance, predictable heat treatment regimes, pure chemical composition with minimal impurities, very good cutting properties when alloyed with vanadium. It is also important that the hardness of the metal after heat treatment reaches 63.5 HRC. With ordinary damask it is impossible to speak accurately about the hardness, it will be extremely heterogeneous throughout the blade after forging. Powdered damask solves this problem by creating a homogeneous structure. In addition to making knives, Damascus steel is also used to create a variety of jewelry and costume jewelry. Damasteel steel is also used to create items made with the Japanese mokume-gane technique.

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Damasteel is based on RWL34 steel, a powdered, high-carbon steel additionally alloyed with molybdenum and vanadium, with medium corrosion resistance. It is produced by Damasteel AB itself. It has a good combination of cutting edge resistance, corrosion resistance and mechanical properties, and holds a thin cutting edge well. It has a large number of alloying elements, including manganese, molybdenum, vanadium, chromium and sulfur. With its high hardness, the steel is well machinable – ground and polished, it is excellent for blades of complex geometry and is considered one of the best steels for artistic etching. Several damask packages are produced with the use of this steel, the most popular among them are:

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The DS93X package is a martensitic steel with a Damascus steel pattern. It consists of two different hardened knife steel grades. The light component is RWL34 powder steel and the dark component is RMS-27 carbon steel.

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The Damacore DC18N package is also a martensitic steel. It contains three different alloys. The central core consists of N11X, an alloy steel with a high nitrogen content. The outer layers with the damask pattern consist of RWL34 and PMC27. The steel has high hardness after quenching and tempering.

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Both packages have excellent corrosion resistance and high mechanical strength. These steels also have good ductility and are easy to grind and polish.

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Thus, on the example of powdered damask, we see a harmonious combination of ancient technologies of production of beautiful and strong steel, with the most advanced technologies of powder processing.

A fillet knife is a specialized knife for preparing fillets of fish, meat or poultry. It is characterized by a long, narrow and flexible blade. Good sirloin knives can bend almost in a circle. That is, the main distinguishing feature is exactly flexibility. This knife should work superfine, cutting off the thinnest pieces of fish or meat, often less than a millimeter thick. The knife must also pass over the bones, the spine and tendons, to separate the skin from the meat, leaving a minimum layer of meat and subcutaneous tissue. In addition to removing the skin and separating the meat from the bones, a sirloin knife can be used to cut the product into thin slices (slices). That is why filleting knives are in demand among professional masters of European cuisine, and among cooks specializing in making sushi and other Japanese dishes. Often a sirloin fish knife has a serrated edge for tail and fins processing.

The length of the traditional “fillet” varies from 10 to 30 cm. Usually in serial industrial production, the sizes of such knives are 10, 15, 19 and 23 centimeters. The thickness of the blade varies from 0.5 to 1.5 mm. The width of the blade is from 1 to 3 centimeters. In terms of blade profile, a sirloin knife often has a straight edge, sometimes slightly bent upwards. Narrower in width, the knife is used most often to cut off the fillet, a wider blade separates the loin from the bones. It should be noted that a well-sharpened “fillet” should easily cope with cutting across the side (abdominal) bones of medium-sized fish. And at primary blunting it is quite capable of working due to its geometry without much effort.

The optimum angle that is considered the accepted standard for the cutting edge of a “fillet knife” is 23+/-2 degrees. Professional sirloin knife is sharpened usually under the hand of a particular professional. There is also the elasticity of the blade, and whether he is left-handed or right-handed, based on this some of the approaches can be wider or narrower, etc. Usually, factory knives made in-line are sharpened on a grinder rather coarsely and without a micro grip. And knives that are made or sharpened individually are recommended to be sharpened according to the method of sharpening safety razor blades, i.e. with three facets of micro-piping. For example, such a variant is possible: after skinning preliminary sharpening on abrasive grit from 800 to 1000 at an angle of 18 degrees, final sharpening on abrasive 3000 grit at an angle of 20 degrees, finishing with natural stone or blank with paste at 23 degrees. The direction and the combination of the ribs during finishing are also individual. The criterion of a good sharpening of a filleting knife can be a simple test, when only the skin is easily removed from a tomato and the pulp is not affected.

When talking about the difficulty of sharpening a fillet knife, the main factor to consider is its flexibility. It is extremely difficult to maintain the angle when the blade is thin and flexible. It is especially difficult to do it with a long blade. And if at manual sharpening this issue is solved by precise, extremely easy movements of the approach on the stone, then on sharpening machines with a rotary mechanism light movements alone will not be enough. It is necessary to securely fix the knife, preventing the blade from bending on the tip or handle side and preventing sagging in the central part. To solve this difficult task, the Profile K03 sharpener is equipped with so-called “fillet clamps”. These clamps reliably hold any blade shape, ensuring that the jaws are in contact with the planes of the knife edge and that the blade has open access to the blade for machining. The fillet clamps are based on three basic elements: the base, flat springs, and clamping jaws. Powerful jaws are connected to the base through flat flexible springs, which provide a universal fit and when the knife is inserted into the clamp, the springs change from a free state to a tense state, thus the rigidity of the clamp is significantly increased. Also, the fixing and adjusting screws in the clamp bundle, form a rigid geometric system and at the same time, allow a wide range of adjusting the clamp to any shape of the blade and ensure symmetry of installation.

For sharpening of fillet knives Technostudio “Profile” offers two variants of clamps:

1. Fillet full-milled clamps. They are designed for fixing knives with the thickness of the shank up to 3.5 mm. The shape of the outer surface is radially convex, which allows you to set the minimum sharpening angles of 7.2 degrees. The clamps are made of a single piece of aluminum, allowing to adjust the clamp to any shape of the blade and ensure symmetry of installation. The width of the clamps is selected in such a way as to allow up to 4 clamps to be mounted simultaneously on the frame and securely fix even the most flexible fillet knife. It is possible to move the clamps independently along the entire length of the frame. There is no need for calibration. It is possible to sharpen: kitchen knives, filleting knives, keychain knives, dangerous razors, knives with “scandi-slopes” and other narrow long knives. The recommended knife length for these clips is from 30 to 300 mm. The minimum recommended blade width is 10 mm. The width of the clamp jaws is 21mm each.

2. Single Sirloin Clamp -a special clamp for narrow sirloin knives, with a reduced sharpening angle. The thin jaws of the clamp are made of structural spring-spring steel, which provides sufficient clamping force. The clamp with a modified jaw configuration and with the use of special screws has a maximum minimum sharpening angle of 6.5 degrees per side. The minimum width of the knife that can be fixed by the clamp is 10 mm, the maximum thickness of the blade is 2.5 mm. The clamp fasteners are anodized by default. It is recommended to use this clamp for sharpening small fillet knives as well as small knives with descending bevels like Victorinox and other folding knives and multitools. The recommended knife length for this clamp is from 50 to 200 mm. The width of the jaws of the single fillet clamp is 32 mm.

Belgian stones are mined from deposits in the Ardennes Mountains region. Which, in turn, are the western end of the Rhine Slate Mountains – one of the largest mountain systems in Western Europe, passing through the territory of Germany, Luxembourg, France and Belgium. The length of the mountain range is 400 km, with the highest point – the Groser – Feldberg mountain with a height of 880 meters. These mountains are composed mainly of shales, quartzites, sandstones and limestones. On the territory of Belgium, the rocks are mainly limestone and shale, formed about 480 million years ago, clay and volcanic ash.

As a result of geological processes over millions of years, in the thickness of so-called metamorphic rocks, which include crystalline schists, the formation of a rock-forming mineral, a semi-precious stone – garnet. During long-term weathering garnets as chemically resistant structures are not destroyed for a long time, but pass into placers and in the form of small crystals are preserved inside shales and limestones. Garnet is divided into many species: andradite, grossular, almandine, pyrope, etc. Depending on the variety, garnet has different hardness (from 6.5 to 7.5 on the Mohs scale) and density (for example, pyrope has a density of 3.57 g/cm3 and almandine has a density of 4.3 g/cm3). Garnet crystals with grain size from 5 to 25 microns are randomly scattered in the layers of Belgian shales and are an excellent abrasive, confidently working on steels with hardness up to 62 HRC. It is garnet that gives shale, which is ineffective at sharpening, the qualities of a good abrasive.

Shales themselves are a variety of rocks with parallel layered assemblages of minerals such as chlorite, actinolite, quartz, staurolite, etc. Under the influence of strong dynamic impacts, the rocks are transformed into crystalline shales that can be easily delaminated into plates and tiles. The ability to split into separate plates and makes it possible to mine them by simple percussion of a tool, without the use of special machines or explosion engineering.

According to local legend, deposits of slate in the Ardennes region began to be mined in the times of the Roman Empire. Slate was used mainly for building applications, as a facing material. It has become popular as an abrasive material in modern times. And it was mined in this quarry first of all Yellow Belgian Coticule slate, the so-called “Yellow Belgian stone”. And then, much later, similar abrasive properties were discovered in another stone – Belgian Blue Whetstone, abbreviated (BBW) – “Belgian Blue Stone”. Its blue-violet color was determined by the presence of iron oxide in the precipitate. It has even more abrasive power than Yellowstone, primarily because of its larger garnet crystals. Yellow Belgian Stone and Blue Belgian Stone are actually mined together. They are arranged layer by layer in narrow beds, with the Blue Stone being the predominant rock and making up the majority of the material extracted.

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The way both stones are used for sharpening purposes is extremely simple. They are water stones, which do not require immersion in water, but only soaking the surface of the stone and applying a slurry. The garnet crystals in the stones are released from the surface, together with the particles of the stone itself, and begin to work due to a fairly uniform and constant supply of slurry. The very structure of the shale acts as a kind of “binder” for the garnet grains. However, it should be remembered that there is no real binder in this stone and it will be produced rather unevenly and regularly require leveling. Belgian natural stones are best suited for pre-finishing sharpening and finishing polishing of the cutting edge. These stones work equally well on carbon and stainless, Damascus and high-speed steels. They can be used for finishing not only knives, but also woodworking tools and dangerous razors.

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The two main types of Belgian stones are:

1.Yellow Belgian stone(Yellow Belgian Coticule)

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The stone contains a high concentration of small garnet grains ranging in size from 5 to 15 microns. It represents 30 to 42% of the grains from the volume of the stone. The metal removal rate is similar to synthetic stones. Coticule is often compared to 6000-8000 grit according to the Japanese JIS system, but this is a very rough approximation. A major factor in sharpening with this stone is the density of the slurry. The thickest slurry can give about 1000 to 2000 grit, and a pure stone with water 16000 grit. Polishing with this stone gives a matte underwater finish, similar in appearance to the result of Arkansas Black natural stone.

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2. Belgian Blue Whetstone(Belgian Blue Whetstone) has a geometric shape of garnet crystals, the dodecahedron, identical to the Yellow Belgian Whetstone. But Blue Whetstone contains lower concentrations of grains up to 25% of the stone’s volume. However, the garnet grains themselves are significantly larger, ranging from 10 to 25 microns. Bluestone has a higher hardness than Yellowstone. The manufacturer indicates the grit of the stone to be approximately 4000 according to the Japanese JIS system, but as in the case of the Yellow stone, it should be borne in mind that the scale developed for synthetic stones cannot fully correspond to the natural ones.

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These stones are manufactured in both hand sharpening stone format and as small stones that fit the abrasive holders of the Profile K03, Blitz, Kadet and TSPROF PIoneer abrasive sharpening devices.

Ceramic bond is a special mixture of different types of bulk crushed components, which is supplemented with the main abrasive material and subjected to special heat treatment. The main abrasive fillers for ceramic bonds are silicon carbide and aluminum oxide.

As a result of heat treatment, ceramic bonds form two types: fusible (vitreous) and sintered (porcelain). After cooling down, melting bonds turn into glass-like, sintering ones are only partially melted and become close to porcelain in their composition. As a result of processing, the ceramic bond acquires such properties as water resistance, fire resistance, chemical and mechanical resistance. Different abrasive materials require different heat treatment.

Abrasive tools based on aluminum oxide (electrocorundum) are made on fusible bonds, and those made of silicon carbide are made on sintered bonds. Fusible bonds provide greater abrasive tool strength than sintered bonds. The disadvantages of the sintered bond are its brittleness and reduced bending strength. However, both bonds are considered to be hard. Under the hardness of the abrasive tool is understood, the ability of the bond to resist the tearing of abrasive grains from the working surface under the action of external forces.

Various raw materials are used for the production of ceramic binders: refractory clays, feldspars, wollastonite, boron and borlithium glasses, silica, lithium-containing materials (petalite, lithium manganate, molybdenum, etc.). All materials used in the production of binders are pre-dried, ground to a given coarseness (usually less than 100 microns) and mixed in various proportions. In order to increase plasticity, adhesives such as dextrin, soluble glass, etc. are added to the ceramic mass. Masks for abrasive tools are produced depending on the purpose of their use. Ceramic bond is marked with the letter K and has additional alphabetic and numeric designations. All bond varieties have additional indexing. For example, fusible ceramic binders have Russian marking K1, K5, K8.

Ceramic bond with silicon carbide powder is the most common, and is used to make most of the tools used for industrial grinding applications. The composition of the bond includes refractory clay, feldspar, talc, chalk, quartz and liquid glass. In Russia such clay grades as Latnenskaya, Polozhskaya, Novorayskaya are most commonly used. At the same time, the maximum effect is given by the use of coal clay or a mixture of refractory clay and coal-humus substances, which provide maximum strength. These types of raw materials give the binder additional porosity of the structure due to the burnout of carbon and organic impurities. This reduces the amount of carbon and in the final product, increases its strength. To improve wetting of silicon carbide grains with the binder, the method of coating the grains with fine powders, glasses of different composition is also used, as a result of which films are formed on the surface of silicon carbide grains, which, interacting with the binder, contribute to increasing the strength of the tool. In some cases, various modifiers, in particular so-called boron-containing fluxes, are used to increase the strength of such a bond. Manganese sulfate and manganese carbonate may be added to the bond as “modifiers” in amounts up to 2% of the total mass, which also contributes to increasing the strength and hardness of such bonds.

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Examples of ceramic bonded products used for knife sharpening include “Profile” stones based on silicon carbide. They demonstrate a good hardness of the bond and confidently cope with any steel.Also ceramic bond is used in the American Boride stones series T2, which are made on the basis of aluminum oxide and demonstrate a very high hardness of the bond. They also work on any steel, quickly remove metal, are productive and have a long service life. We will tell you more about these stones in a separate article.

Mora, one of the world’s largest knife manufacturers, has come a long way in its development. The beginning of its history dates back to 1891, when master craftsman Eric Frost founded his knife factory. This is how the largest knife company in Mora – Frost Knivfabrik – came into being. In 1912, two other craftsmen from the same town, Lok Anders Mattsson and Krang-Johan Eriksson, founded the company Eriksson & Mattssons Knivfabrik. Both KJ Eriksson and Frost Knivfabrik operated in parallel and were competitors throughout the twentieth century. In the early 2000s, the shares of Frost Knivfabrik were bought out by KJ Eriksson, and in 2005 the two companies merged completely. And there was a single company Morakniv, a large, powerful company with conveyor belt production of knives.

For almost a century, knife makers from the town of Mora produced classic Swedish knives made of carbon steel, with “Scandinavian” blade geometry and a wooden handle. These were mainly work and craft knives. The company Frost Knivfabrik also produced a large number of kitchen knives. And K.J.Eriksson produced a survival knife for Swedish Air Force pilots for several decades. The knife had a classic design, with a carbon steel blade and a birch wood handle. The blade was 10 cm long and 2.4 mm thick. The knife was equipped with a leather sheath with a short hanger, had a well-developed grip and a sling cutter on the edge. It was not intended for use in combat, but for survival of a pilot who had been in an accident. In 1995, the knife was removed from the Air Force and replaced by the legendary Fallkniven F1 survival knife.

Today, Morakniv produces a very large range of products. Among them are hiking, kitchen, work, garden, craft and fishing knives. In addition, axes, flame throwers, diamond and ceramic sharpening stones are produced. There is an opportunity for the buyer to purchase individual blades, and from a variety of steels: carbon, laminated or stainless steel. It is impossible to describe the full number of models of the company Mora, but we can highlight some.

Classic models are not a thing of the past, they are still produced and in demand. These knives have a wooden handle made of Scandinavian birch. The steel of the blades on these knives – classic carbon, with a hardness of about 58 HRC. In addition, laminated steel blades are also produced. The geometry of the blade on these models – drop point, Scandinavian descents brought to zero, the angle of the descents-underslopes about 20-23 degrees. Carbon steel on Mora knives is of good quality, not prone to creases, keeps sharpening well and is very easily corrected with any mousate from ceramic to diamond. However, it rusts very actively and requires maintenance. This problem can be solved by etching the blade in various substances, usually citric acid, vinegar, etc. are used for this purpose. They create a fairly stable film on the surface of the blade, protecting it from corrosion. An example of a classic knife of this company are models without a guard: Mora Classic No. 1, 2,3, as well as knives with a guard: Mora Classic 611 and Classic 612.

In 1976, KJ Eriksson began production of the 510 knife model with a plastic handle without a grip, and later the 511 with a grip. These knives were utilitarian tools designed for heavy work, construction and various industrial needs. The knives were very cheap and were produced in huge quantities. Initially they had a blade made of carbon steel only, but since the 90s they started to use stainless steel Sandvik 12C27. This is a good quality rolled steel, the main advantage of which is high strength, which it shows even in severe frost conditions. In Scandinavian zero descents on very hard wood, this steel can buckle, but there are ways to strengthen it: creating a micro-feed or a micro-lens. In the 2000s, the 510 was upgraded to the Craftline HighQ Allround, which had a rubber coating on the plastic handle and a scabbard with a plastic clip, which was very convenient to carry on the belt, even without a belt. And around 2015, this line of knives underwent changes, turning into the Mora Basic 511, Mora Basic 546 and similar models. Scabbards for these knives received an additional attachment, allowing to “double” the knives in a kind of pair, which can be useful primarily in construction and installation work. The handle of the working knife has been slightly changed, it has got an additional stop on the side of the tip, for more rigid fixation of the hand.

Mora’s most versatile knife model of the last 20 years has been the Companion model. It was a continuation of the popular Moga Clipper line of knives. This model is made with carbon and stainless steel. The knife has a very large number of colors, almost for every taste. It is medium-sized, lightweight, with comfortable and reliable plastic sheath. The knife is suitable for household work, use in construction, use in hiking.

Created in 1991, the Mora 2000 or as it was then called by K.J. Eriksson Mora 2000, almost 10 years later became the most popular outdoors knife in Russia. Fishermen, hunters and tourists bought this knife in mass. What was the reason for such popularity? Obviously, the factors of success of this model were: price, quality and availability for purchase – the knives were sold in almost every hunting store. The Mora 2000 knife is lightweight, with comfortable plunge sheath, grippy handle made of plastic and rubber, with a blade of interesting, original shape. The blade is made of Sandvik 12C27 stainless steel. In 2015, the 2000 model received a sequel in the form of the Mora Kansbol knife. The blade did not change in geometry, but instead of polishing, it acquired a stonevosh treatment. On the handle of the knife there is now a hole for the handle. Mora Kansbol, in addition to the usual sheath, is equipped with an additional multi-mount hanger. This hanger can be attached to Molli slings or backpack straps, which makes traveling in boats or on mountain slopes more convenient.

In 2012, Mora partnered with Light My Fire, a famous Swedish firestick manufacturer, to produce a new camping knife. It was a hybrid of Craftline HighQ Allround model, with a geometrically similar blade to the Mora 2000 knife, and a special notch in the tip of the knife, with FireSteel fire starter mounted there. The knife found its buyer and in time Mora decided to produce similar knives on its own. This model is now called Mora Companion Spark, it has a blade from Mora Companion, a plastic sheath with a hanging clip and a fire starter in the handle. The flame thrower is of good quality and allows you to reliably shoot out a sufficiently dense sheaf of sparks and ignite dry and prepared materials for burning: absorbent cotton, rubbish, small shavings, etc. The model turned out to be very successful, easy to use, lightweight and multifunctional.

Aluminum oxide is a binary compound of aluminum and oxygen. It is common in nature as the main constituent of alumina – a mixture of aluminum oxides and elements such as potassium, sodium, magnesium, etc. Alumina consists of up to 98% of α- and γ-modifications of aluminum oxide and is a white crystalline powder. There are several main varieties of aluminum oxide, but most commonly used in industry is α-oxide or corundum, which is a mineral in the form of large transparent crystals, trigonal singony.

Raw materials for aluminum oxide include bauxite (aluminum ore), alunite (alum stone), and nepheline (potassium and sodium aluminosilicate). For the production of high-strength corundum ceramics, aluminum oxide powder obtained by thermal decomposition of some aluminum salts of varying degrees of purity is used. Aluminum oxide obtained by decomposition of salts is a highly dispersed powder γ-Al2O3 (when calcined up to 1200°C) and has a high chemical activity.

Synthetic α-aluminum oxide (corundum) is used as: an intermediate in aluminum production, for refractory, chemical resistant and abrasive materials, in the production of components for lasers, for the manufacture of synthetic gemstones, etc. Electrocorundum is mainly used for sharpening, both on electric equipment and sharpeners, and for hand sharpening. Electrocorundum (alund, aloxite) is a crystalline aluminum oxide that is artificially produced by melting alumina. This is done in a continuous process in arc furnaces with subsequent crystallization of the substance. After baking, the synthesized corundum acquires a very high hardness, second only to diamond. The Mohs hardness index for electrocorundum is 9, which is practically marginal. The more aluminum oxide is contained in electrocorundum, the harder, stronger and lighter it becomes.

The most commonly used electrocorundum for sharpening is normal (alund). It is a type of electrocorundum containing 91% to 96% Al2O3 in its composition. It is smelted by reductive smelting from bauxite containing aluminum. This electrocorundum abrasive has high hardness and is suitable for grinding a wide variety of metals. The density of electrocorundum ranges from 3.8 g/cm³ to 3.9 g/cm³; the microhardness is approximately 18.6 GPa (Pascal) to 19.6 GPa (1900 kgf/mm² to 2000 kgf/mm²). The color of corundum depends on the impurity content. Unlike silicon carbide, aluminum oxide can have a minimum grain size of less than 1 µm, which allows for more efficient fine finishing of the cutting edge. Sharpening on aluminum oxide abrasives is well suited for most kitchen and hunting knives as well as carpentry tools.

Aluminum oxide is cleaner than silicon carbide works on steels below 58 HRC, leaving a less coarse risk on the approach. Due to the fact that the corundum grains do not split in the process of work, as in silicon carbide, and rolled, reducing in size and losing the sharpness of the edges, this abrasive works softer. At the same time, the difference in working speed between aluminum oxide and silicon carbide depends mainly on the hardness of the bond. Oxide stones are created on a vitreous ceramic bond while carbide stones are created on a porcelain bond, which is much softer. In addition, aluminum oxide stones work with oil, while silicon carbide stones work with an aqueous suspension, which has a greater abrasive effect. However, this does not apply to the stones of Naniwa Professional series, which due to the very high quality of abrasive powder and finely dispersed suspension, are able to work quickly and efficiently on any steel, including those above 58 HRC.

Examples of aluminum oxide sharpening stones include:

1. Boride T2 stones – The Boride T2 series of American Boride stones are made of ceramic vitreous bonded oxide. This results in high performance and a lower than average wear rate. Boride stone manufacturers recommend T2 as the best series for stainless steel. When sharpening with Boride T2 series stones, both oil-based and water-based coolants can be used. The stone is cleaned in water, with a stiff brush and a soap solution. Traces of oil-based coolant are effectively and quickly removed with cleaning oils such as TSPROF abrasive cleaning oil. Stones on thick glass or mirror are leveled with silicon carbide powder.

2. Boride PC (Polisher’s Choice) stones are a series of synthetic aluminum oxide stones of exceptionally high quality. The name of the stones literally translates to “Polisher’s Choice”. PC series stones are designed as finishing stones for the final finishing of metal to a mirror shine. Boride PC stones are used only with the application of coolant.

3. Naniwa Professional stones -an improved series of Japanese Naniwa stones. This series uses magnesia-bonded aluminum oxide. The stones do not require soaking, slow salting and high performance. The stones work gently, yet are fast enough due to their suspension. Naniwa Professional are suitable for virtually all steels.

The first historically known tools resembling knives are obsidian detachments – nuclei. That is, products made of volcanic glass were used by human ancestors several hundred thousand years ago. And having gone a long way in metallurgy, mankind returned to the use of ceramics at the end of the twentieth century. In 1985, the Japanese company Kyocera began production of ceramic knives based on zirconium dioxide. These knives were the result of the most advanced technology at that time. To date, such knives have become very widespread, at an extremely low price.

What a ceramic knife is made of

Ceramic knives are made from zirconium dioxide (ZrO2), which is obtained by special processing of the mineral zircon. Zircon (ZrSiO4) is a material belonging to the class of silicic acid salt minerals, which was discovered by the German chemist M.G. Klaproth in 1789. Zirconium (Latin: Zirconium; denoted by the symbol Zr) is a material of the periodic system, with atomic number 40. It is a lustrous metal, silvery gray in color. It is highly ductile and resistant to corrosion. Zirconium compounds are widely distributed in the lithosphere. In nature, its compounds are known exclusively with oxygen in the form of oxides and silicates. Despite the fact that zirconium is a diffuse element, there are about 40 minerals in which zirconium is present in the form of oxides or salts. The most common in nature are zircon (ZrSiO4), baddeleyite (ZrO2) and various complex minerals.

Zircon is the most common zirconium mineral. It occurs in all types of rocks, but mainly in granites and syenites. In Hinderson County, North Carolina, USA, zircon crystals several centimeters long have been found in pegmatites, and crystals weighing several kilograms have been found in Madagascar. Baddeleyite was discovered in 1892 in Brazil. The main deposit is in the Posus di Caldas region of Brazil. The largest zirconium deposits in terms of size are located in the United States, Australia, Brazil, and India.

Raw materials for zirconium production are zirconium concentrates with mass content of zirconium dioxide not less than 60-65%, obtained by enrichment of zirconium ores. The largest volumes of zirconium production are concentrated in Australia (40%) and South Africa (30%). The main methods of obtaining metallic zirconium from concentrate are chloride, fluoride and alkaline processes.

Zirconium has been used in industry since the 1930s, but its high cost limited its use. Metallic zirconium and its alloys are used in nuclear power. Zirconium has a very low thermal neutron capture cross section and a high melting point. Another application of zirconium is alloying. In metallurgy it is used as a ligature. It is used as a deoxidizer and deazotator. Zirconium alloying of steels (up to 0.8%) increases their mechanical properties and machinability. In industry, zirconium dioxide is used in the production of zirconium-based refractory materials, ceramics, enamels, glasses. It is used in dentistry for dental crowns. It is used as a superhard material. Zirconium dioxide conducts current when heated, which is sometimes used to produce heating elements that are stable in air at very high temperatures. Heated zirconia is able to conduct oxygen ions as a solid electrolyte. This property is used in industrial oxygen analyzers and fuel cells. What distinguishes zirconium ceramics from other materials is its tremendous heat resistance and hardness, which is usually not less than 80 HRC. In addition, zirconium oxide is completely unreactive to most acids, alkalis and other active substances.

Zirconium oxide is obtained from zircon by chemical processing with additives. The resulting powder is mixed with additives. There are sintering additives, which affect the sintering characteristics and quality of the finished ceramics, and auxiliaries, which aid in molding. Accordingly, zirconia blanks are manufactured by various techniques. In particular, it is possible to alloy zirconium dioxide with oxides having a cubic crystal lattice. The most commonly used oxides for this purpose are oxides of the elements – calcium and magnesium, as well as metals – iron, manganese, chromium. In addition, zirconium oxide is often alloyed with aluminum oxide. The alloying oxides can change the color of ceramics from white to black (black color can also be obtained by special treatment). For example, this is used in the coloring of fianites – artificial diamonds based on cubic zirconium oxide.

Zirconium dioxide has a high hardness, which is measured using the Mohs hardness scale of materials. The hardness of zirconium dioxide on the Mohs scale is about 8.5 units, while the hardness of steel on this scale, depending on the heat treatment, from 4 to 7 units, corundum about 9 units, diamond 10 units. Thus, the material from which ceramic knives are made, in terms of hardness is close to diamond. Zirconium ceramics is also used in jewelry, in the aviation industry and mechanical engineering, in dentistry. Zirconium dioxide has more than 80 times the wear resistance of steel.

HOW TO MAKE CERAMIC KNIVES

The technical process of creating zirconium blades is as follows: obtaining alloyed zirconium oxide powders, preparation of press compositions and pressing, firing at high temperature (1350C+, in some cases up to 1700C), hot isostatic pressing at high temperatures and pressure.

The process of making ceramic knives is quite labor-intensive. To produce a ceramic blade, zirconium dioxide powder is first pressed under a pressure of 300 tons per square centimeter, then heat treated at temperatures of 1600-2000 degrees Celsius in special ovens for a long time (from two to six days). At the same time, zirconium dioxide crystals are sintered and the process of forming blanks is underway. The longer the product is kept in the furnace, the stronger it becomes. Depending on the specifics of the technological process, black or white ceramics are obtained. Black ceramics are made by adding a special black dye and keeping the workpieces in the kiln for a longer period of time, as a result of which they become stronger. The quality of ceramic knives varies greatly, as it is highly dependent on the technological capacity of the manufacturer, and the adherence to a complex technological process.

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PLUSES AND MINUSES OF CERAMIC KNIVES

The properties of zirconia ceramics depend significantly on the technology used to produce them, ranging from the purity of the initial zirconia powder, alloying system, powder granulometry, sintering regimes, etc.

In terms of mechanical properties, zirconium ceramics are significantly inferior to the most common steels, in particular, in terms of bending strength by a factor of about two, and in terms of impact strength by several times. This severely limits the versatility of ceramic knives. Because of their brittleness, most manufacturers urge not to use these knives for meat with bones, frozen foods, work on hard surfaces (glass, ceramic), etc. However, it should be noted that ceramics have unique properties that are superior to steel in terms of corrosion resistance and inertness to food.

CHARGING A CERAMIC KNIFE

Due to the fragile nature of the cutting edge, a ceramic knife requires quite large sharpening angles. On average, it is recommended to sharpen it to a full angle between 30-40 degrees. Sharp angles of 20 degrees or less are contraindicated for such knives, as the fragility of the cutting edge at this angle of sharpening becomes very high. Sharpening of ceramic knives is complicated by the fact that in the process is not formed burr and control of the angle must be maintained with the help of special devices, primarily electronic angle meter. Thus the manual sharpening of ceramic knives, without the use of sharpeners, requires an extraordinary, virtuoso skill from the sharpener.

Not all abrasives can handle sharpening a ceramic knife. Budget stones made of silicon carbide and aluminum oxide can’t handle these knives. The quality of the grinding powder and bond plays a key role here. The American Boride CS-HD sharpening stones are very effective in sharpening ceramic knives. The grain size of the stone should not be very coarse, in particular the Boride CS-HD for sharpening ceramics should be started with a 320 grit stone, because a coarser abrasive will cause cracks on the cutting edge. Obviously, the reason for this result is the very high quality of the silicon carbide powder and ceramic porcelain bond used in this American manufacturer’s products.

Electroplated and organic bonded diamond stones also perform well when sharpening knives. A little less active in sharpening them are elboron stones, which do not remove the zirconium layer as quickly as diamonds. However, all these abrasives are suitable for this sharpening and produce a good cutting edge condition.