PLF’s range of filling machines are all built to facilitate the stringent demands of the food, beverage, cosmetics and pharmaceutical industries, i.e. easy to clean with quick changeover, minimum giveaway, gentle product handling. They can be semi or fully automatic and are built so that performance can be enhanced to meet production demands. Each machine can be fitted with PLF’s accumulated or individual head-update weight control systems to ensure maximum accuracy and minimum giveaway.
The machines are also designed to be flexible so as to accommodate a variety of filling machine methods – containers can be filled by vacuum for more static powders, and by volume for free-flowing products. Extensive powder trials are conducted (free of charge) to assess the most appropriate filling method for each. PLF machines can be designed to be ATEX compliant, when required.Traditionally, fill/finish lines have used piston pumps but, in today’s production environment, piston pumps suffer from a number of drawbacks.
Production managers switching from piston pumps to peristaltic pumps are often surprised at the accurate, pulsation- free flow that peristaltic pumps achieve. In addition, sophisticated electronic control of the pump motor enables the flow rate to be ramped up, maximized and ramped down again, thereby reducing aeration and foaming so that very short cycle times to be maintained. It is not unusual for peristaltic pumps to be used on filling machines systems processing up to 150 bottles per minute.With appropriately sized tubing, peristaltic pumps can deliver volumes down to 0.5ml at an industry-standard accuracy of +/-0.5 percent; smaller volumes can be delivered with an accuracy of +/-1 percent. Typical high-speed beverage filling machines use in-process checkweighing to monitor the filling accuracy and, if necessary, the output from this can be used in a closed-loop pump control system.
source: myblog dr-machine
Tungsten (pronounced /ˈtʌŋstən/), also known as wolfram (/ˈwʊlfrəm/, WOOL-frəm), is a chemical element with the chemical symbol W and atomic number 74.
A steel-gray metal, Tungsten Bar is found in several ores, including wolframite and scheelite. It is remarkable for its robust physical properties, especially the fact that it has the highest melting point of all the non-alloyed metals and the second highest of all the elements after carbon. Also remarkable is its very high density of 19.3 times heavier than water, and 71% heavier than lead. Tungsten is often brittle and hard to work in its raw state; if pure, it can be cut with a hacksaw.
The pure form is used mainly in electrical applications, but its many compounds and alloys have many applications, most notably in incandescent light bulb filaments, X-ray tubes (as both the filament and target), and superalloys.
Tungsten is the only metal from the third transition series that is known to occur in biomolecules, and is the heaviest element known to be used by living organisms.
In 1781, Carl Wilhelm Scheele discovered that a new acid, tungstic acid, could be made from scheelite (at the time named tungstenite). Scheele and Torbern Bergman suggested that it might be possible to obtain a new metal by reducing this acid. In 1783, José and Fausto Elhuyar found an acid made from wolframite that was identical to tungstic acid. Later that year, in Spain, the brothers succeeded in isolating Tungsten Rod by reduction of this acid with charcoal, and they are credited with the discovery of the element.
In World War II, tungsten played a significant role in background political dealings. Portugal, as the main European source of the element, was put under pressure from both sides, because of its deposits of wolframite ore. Tungsten’s resistance to high temperatures and its strength in alloys made it an important raw material for the weaponry industry.The name “tungsten” (from the Nordic tung sten, meaning “heavy stone”) is used in English, French, and many other languages as the name of the element. Tungsten was the old Swedish name for the mineral scheelite. The other name “wolfram” (or “volfram”), used for example in most European (especially Germanic and Slavic) languages, is derived from the mineral wolframite, and this is also the origin of its chemical symbol, W. The name “wolframite” is derived from German “wolf rahm” (“wolf soot” or “wolf cream”), the name given to tungsten by Johan Gottschalk Wallerius in 1747. This, in turn, derives from “Lupi spuma”, the name Georg Agricola used for the element in 1546, which translates into English as “wolf’s froth” or “cream” (the etymology is not entirely certain), and is a reference to the large amounts of tin consumed by the mineral during its extraction.
In its raw form, Tungsten Powder is a steel-gray metal that is often brittle and hard to work, but, if pure, it can be worked easily. It is worked by forging, drawing, extruding or sintering. Of all metals in pure form, tungsten has the highest melting point (3,422 °C, 6,192 °F), lowest vapor pressure and (at temperatures above 1,650 °C, 3,000 °F) the highest tensile strength. Tungsten has the lowest coefficient of thermal expansion of any pure metal. The low thermal expansion and high melting point and strength of tungsten are due to strong covalent bonds formed between tungsten atoms by the 5d electrons. Alloying small quantities of tungsten with steel greatly increases its toughness.
Naturally occurring tungsten consists of five isotopes whose half-lives are so long that they can be considered stable. Theoretically, all five can decay into isotopes of element 72 (hafnium) by alpha emission, but only 180W has been observed to do so with a half-life of (1.8 ± 0.2)×1018 yr; on average, this yields about two alpha decays of 180W in one gram of natural Tungsten Rod per year. The other naturally occurring isotopes have not been observed to decay, constraining their half-lives to be
182W, T1/2 > 8.3×1018 years
183W, T1/2 > 29×1018 years
184W, T1/2 > 13×1018 years
186W, T1/2 > 27×1018 years
Another 30 artificial radioisotopes of tungsten have been characterized, the most stable of which are 181W with a half-life of 121.2 days, 185W with a half-life of 75.1 days, 188W with a half-life of 69.4 days, 178W with a half-life of 21.6 days, and 187W with a half-life of 23.72 h. All of the remaining radioactive isotopes have half-lives of less than 3 hours, and most of these have half-lives below 8 minutes. Tungsten also has 4 meta states, the most stable being 179mW (T½ 6.4 minutes).
Elemental tungsten resists attack by oxygen, acids, and alkalis.
The most common formal oxidation state of tungsten is +6, but it exhibits all oxidation states from −2 to +6. Tungsten typically combines with oxygen to form the yellow tungstic oxide, WO3, which dissolves in aqueous alkaline solutions to form tungstate ions, WO2−4.
Tungsten Carbide Powder (W2C and WC) are produced by heating powdered tungsten with carbon and are some of the hardest carbides, with a melting point of 2770 °C for WC and 2780 °C for W2C. WC is an efficient electrical conductor, but W2C is less so. Tungsten carbide behaves similarly to unalloyed tungsten and is resistant to chemical attack, although it reacts strongly with chlorine to form tungsten hexachloride (WCl6).
Aqueous tungstate solutions are noted for the formation of heteropoly acids and polyoxometalate anions under neutral and acidic conditions. As tungstate is progressively treated with acid, it first yields the soluble, metastable “paratungstate A” anion, W7O6–24, which over time converts to the less soluble “paratungstate B” anion, H2W12O10–42. Further acidification produces the very soluble metatungstate anion, H2W12O6–40, after which equilibrium is reached. The metatungstate ion exists as a symmetric cluster of twelve tungsten-oxygen octahedra known as the Keggin anion. Many other polyoxometalate anions exist as metastable species. The inclusion of a different atom such as phosphorus in place of the two central hydrogens in metatungstate produces a wide variety of heteropoly acids, such as phosphotungstic acid H3PW12O40.
source:answers|tungsten
A tungsten powder comprised of macro-spherical particles of tungsten disulfide having an average particle diameter of from about 5 to about 50 micrometers is prepared by successively treating spray-dried powders of ammonium metatungstate with heat in air and sulfidizing the resultant tungsten trioxide in a carbon disulfide-containing atmosphere at about 750° C. The tungsten disulfide powder may also be formed to have a bimodal particle size distribution of the macro-spherical particles and smaller, dispersed micro- to submicron-sized fine particles.
Tungsten is a heavy, gray metal with bluish overtones. When mixed with black carbon, tungsten carbide is created.
The compound is made by heating pulverized tungsten with black carbon, when hydrogen is present. Temperatures range from 2,550 to 2,900 degrees F or 1,400 to 1,600 degrees C. A common method for making the compound was developed in the 1920s in Germany and involves mixing powered tungsten carbide with cobalt. This mixture is then made into the required shape and heated to 2,550 to 2,900 degrees F or 1,400 to 1,600 degrees C. This heat melts the tungsten carbide partially, working as a cement. These Tungsten Carbide Powders are known by the names Carboloy and hardmetal.
Tungsten disulfide is a solid inorganic lubricate typically applied as a dry film to provide lubrication under conditions that are generally unsuitable for most organic-based lubricants, e.g. high loads, high temperatures (to 500° C. in air) and vacuum environments. Tungsten disulfide powders may be used as an lubrication-enhancing additive in various greases, oils, or self-lubricating polymers. Examples of these applications are described in U.S. Pat. Nos. 4,075,111, 4,715,972, and 5,013,466.
The tungsten and carbon is made into a powder using a pulverizer. The materials are then placed into a crucible and heated using an arc of electricity. The two materials then combine creating the tungsten carbide.
Commercially available tungsten disulfide powders are composed generally of irregularly shaped flat platelets as shown in FIG. 1 . It has been postulated that these irregular platelets have chemically reactive edges which cause them to stick to machinery parts and undergo undesirable chemical reactions. Spherical fullerene-like tungsten disulfide nanoparticles have been shown to improve the tribological properties of Tungsten Bar disulfide. Such particles are described in International Application No. WO 01/66462 A2. The fullerene-like nanoparticles were made by sulfidizing WO 3 in a solid-gas reaction with H 2 S. The temperature in the reaction path ranged from 750° C. to 850° C. The size and geometry of the WS 2 particles was found to be determined by the size and geometry of the WO 3 particles being reduced. Larger oxide precursor particles (about 0.5 μm) were slower to convert necessitating the addition of an extra annealing step at 950° C. to complete the conversion. Although larger particles were thought to be a better lubricant in cases where the mating surfaces had higher surface roughness, the process described therein was limited to producing spherical particles up to 0.5 μm.
A gray, inorganic material, Tungsten Carbide Powder functions as a hardener in armor-piercing projectiles, the sharp edges of drills and saws, and cast iron. Besides industrial uses, it is also used to create jewelry due to its hardness and deduced risk of allergic reactions among those with sensitive skin, among other desirable properties.
A gray, inorganic material, tungsten carbide functions as a hardener in armor-piercing projectiles, the sharp edges of drills and saws, and cast iron. Besides industrial uses, it is also used to create jewelry due to its hardness and deduced risk of allergic reactions among those with sensitive skin, among other desirable properties.
In another embodiment, a bimodal distribution of macro-spherical and smaller, dispersed micron- to submicron-sized fine particles of tungsten disulfide are prepared by heating spray-dried powders of ammonium metatungstate in air, mixing the resultant tungsten trioxide with a tungsten metal powder , and sulfidizing the mixture in carbon disulfide at about 750° C. The resultant tungsten disulfide powder contains a bimodal distribution of the macro-spherical tungsten disulfide particles and fine tungsten disulfide particles having an average particle diameter of from about 0.5 to about 5 micrometers. Preferably, the fine particles have an average particle diameter of from about 1 to about 3 micrometers.
Because it retains its strength at high temperatures and has a high melting point, elemental tungsten is used in many high-temperature applications, such as light bulb, cathode-ray tube, and vacuum tube filaments, heating elements, and rocket engine nozzles. Its high melting point also makes Tungsten Bar suitable for aerospace and high-temperature uses such as electrical, heating, and welding applications, notably in the gas tungsten arc welding process [also called tungsten inert gas (TIG) welding].
Because of its conductive properties and relative chemical inertia, tungsten is also used in electrodes, and in the emitter tips in electron-beam instruments that use field emission guns, such as electron microscopes. In electronics, tungsten is used as an interconnect material in integrated circuits, between the silicon dioxide dielectric material and the transistors. It is used in metallic films, which replace the wiring used in conventional electronics with a coat of tungsten (or Molybdenum Powder ) on silicon.
The electronic structure of tungsten makes it one of the main sources for X-ray targets, and also for shielding from high-energy radiations (such as in the radiopharmaceutical industry for shielding radioactive samples of FDG). Tungsten powder is used as a filler material in plastic composites, which are used as a nontoxic substitute for lead in bullets, shot, and radiation shields. Since this element’s thermal expansion is similar to borosilicate glass, it is used for making glass-to-metal seals.
The hardness and density of tungsten are applied in obtaining heavy metal alloys. A good example is high speed steel, which may contain as much as 18% tungsten. Superalloys containing tungsten, such as Hastelloy and Stellite, are used in turbine blades and wear-resistant parts and coatings. Applications requiring its high density include heat sinks, weights, counterweights, ballast keels for yachts, tail ballast for commercial aircraft, and as ballast in race cars for NASCAR and Formula One. It is an ideal material to use as a dolly for riveting, where the mass necessary for good results can be achieved in a compact bar. In armaments, tungsten manufacturer , usually alloyed with nickel and iron or cobalt to form heavy alloys, is used in kinetic energy penetrators as an alternative to depleted uranium but may also be used in cannon shells, grenades and missiles to create supersonic shrapnel. High-density alloys of tungsten with nickel, copper or iron are used in high-quality darts (to allow for a smaller diameter and thus tighter groupings) or for fishing lures (tungsten beads allow the fly to sink rapidly). Some types of strings for musical instruments are wound with tungsten wires. Its density, similar to that of gold, allows tungsten to be used in jewelry as an alternative to gold or platinum. Its hardness makes it ideal for rings that will resist scratching, are hypoallergenic, and will not need polishing, which is especially useful in designs with a brushed finish.
Tungsten compounds are used in catalysts, inorganic pigments (e.g. tungsten oxides), and as high-temperature lubricants (tungsten disulfide). Tungsten Carbide Powder (WC) is used to make wear-resistant abrasives and cutters and knives for drills, circular saws, milling and turning tools used by the metalworking, woodworking, mining, petroleum and construction industries and accounts for about 60% of current tungsten consumption. Tungsten oxides are used in ceramic glazes and calcium/magnesium tungstates are used widely in fluorescent lighting, while tungsten halogen bulbs are frequently used to light indoor photo shoots, and special negative films exist to take advantage of tungsten’s unique disentangling properties. Crystal tungstates are used as scintillation detectors in nuclear physics and nuclear medicine. Other salts that contain tungsten are used in the chemical and tanning industries.
Precautions
The data concerning the toxicity of tungsten is limited, but cases of intoxication by tungsten compounds are known, the lethal dose is estimated to be between 500 mg/kg and 5 g/kg for humans. Tungsten is known to generate seizure and renal failure with acute tubular necrosis.
The effects of Tungsten Powder within the environment are essentially unknown, a concern that has arisen in response to increasingly widespread use of the material as a fishing sinker, some of which are inevitably lost into water bodies. The same unknown variable applies whenever tungsten may be deposited into the environment, either knowingly or inadvertently.
source:answers
A thermal spray powder is formed as a mixture of tungsten carbide granules and chromium carbide granules. The tungsten carbide granules each consists essentially of tungsten carbide bonded with cobalt, and the chromium carbide granules each consists essentially of chromium carbide bonded with nickel-chromium alloy. The powder may be asmixed with self-fluxing alloy powder. The powder preferably is sprayed with a high velocity oxygen-fuel thermal spray gun.
Tungsten is a heavy, gray metal with bluish overtones. When mixed with black carbon, tungsten carbide is created.
The compound is made by heating pulverized tungsten with black carbon, when hydrogen is present. Temperatures range from 2,550 to 2,900 degrees F or 1,400 to 1,600 degrees C. A common method for making the compound was developed in the 1920s in Germany and involves mixing powered tungsten carbide with cobalt. This mixture is then made into the required shape and heated to 2,550 to 2,900 degrees F or 1,400 to 1,600 degrees C. This heat melts the tungsten carbide partially, working as a cement. These tungsten carbide-cobalt creations are known by the names Carboloy and hardmetal.
Wear resistance is a common requirement for thermal sprayed coatings, and carbide powders are frequently used, for example tungsten carbide. British patent specification No. 867,455 typifies cobalt bonded tungsten carbide powder admixed with a sprayweld self-fluxing powder for producing coatings. Often such coatings are subsequently fused. Self-fluxing alloys are nickel, cobalt or iron based alloys with chromium and with small amounts of boron, silicon and carbon which serve as fluxing agents and hardeners. Examples of self-fluxing alloys are disclosed in the aforementioned British patent specification and U.S. Pat. Nos. 3,743,533 and 4,064,608. Iron base alloys with molybdenum, boron and silicon are disclosed in U.S. Pat. No. 4,822,415.
The cobalt- tungsten carbide itself is also sprayed neat, i.e. without the self-fluxing ingredient, best results being with high velocity, particularly plasma spray or a high velocity oxygen-fuel (HVOF) gun or a detonation gun. The granules of a powder typically are formed of subparticles of tungsten carbide and cobalt, spray dried, sintered or fused, the result being crushed and classified into a powder of proper size for thermal spraying.
Another carbide is chromium carbide that is utilized for higher temperature applications. This carbide may be sprayed without any metal binder, but it usually is clad or bonded with nickel or nickel alloy, such as nickel-chromium alloy, such as described in U.S. Pat. Nos. 3,150,938 and 4,606,948.
Tungsten carbide manufacturer and chromium carbide have been combined together with nickel for the detonation process as taught in U.S. Pat. Nos. 3,071,489. In one aspect of this patent, the elemental ingredients are all mixed together, and then sintered and crushed into a powder. In another aspect, separate powders of tungsten carbide, chromium carbide and nickel are blended to form a powder mixture of the three ingredients. In this form there is a tendency for the carbide to lose carbon in the flame. The two carbides also have been combined together with cobalt (without nickel) in a powder formed by casting and crushing, or by sintering, as taught in U.S. Pat. No. 4,925,626. Cobalt does not have as high corrosion resistance as nickel.
The latter patent teaches a method for producing a coating material of WC-Co-Cr alloy for high velocity oxygen-fuel thermal spraying. A mixture is prepared of tungsten carbide, cobalt and chromium, the latter being in the form of chromium carbide. The mixture is alloyed by by spray drying followed by sintering and plasma densification.
U.S. Pat. No. 4,588,608 teaches a powder for the detonation process, in which the powder is a cast and crushed composition of tungsten carbides , chrominum and cobalt. Two proprietary coatings of this nature are LW-45 and LW-15 produced by Praxair, Inc., Danbury, Conn., by the detonation process. LW-45 nominally contains 8% cobalt 4% chromium and balance tungsten carbide. LW-15 nominally contains 84% tungsten, 8% cobalt, 3% chromium and 5% carbon. These coatings have been utilized in specified applications such as petrochemical gate valves.
The tungsten and carbon is made into a powder using a pulverizer. The materials are then placed into a crucible and heated using an arc of electricity. The two materials then combine creating the tungsten carbide.
A gray, inorganic material, tungsten carbide functions as a hardener in armor-piercing projectiles, the sharp edges of drills and saws, and cast iron. Besides industrial uses, it is also used to create jewelry due to its hardness and deduced risk of allergic reactions among those with sensitive skin, among other desirable properties.
An object of the present invention is to provide an improved powder of Tungsten Bar and chromium carbide for the thermal spray process. Another object is to provide improved corrosion resistance in wear resistant carbide coatings. Further objects are to provide improved impact and toughness in such coatings.
The foregoing and other objects are achieved by a thermal spray powder formed as a mixture of tungsten carbide granules and chromium carbide granules. The tungsten carbide granules each consist essentially of Tungsten Carbide Powder bonded with cobalt, and the chromium carbide granules each consist essentially of chromium carbide bonded with nickel-chromium alloy. The powder may be admixed with a self-fluxing alloy powder, advantageously iron based.
Objects are also achieved by a method of producing a carbide coating utilizing a thermal spray gun having a combustion chamber with an open channel for propelling combustion products into the ambient atmosphere at supersonic velocity. The method comprises preparing a substrate for receiving a thermal sprayed coating, feeding through the open channel a carbide powder, injecting into the chamber and combusting therein a combustible mixture of combustion gas and oxygen at a pressure in the chamber sufficient to produce a supersonic spray stream containing the powder issuing through the open channel, and directing the spray stream toward the substrate so as to produce a coating thereon. The carbide powder is formed as a mixture as set forth above.
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