In last part we know how the grade powder is gained by mixing up the grade ingredients in a ball mill and drying them in a spray dryer, which also influences much the final quality of tungsten carbide cutting tools. Here we explain the procedure of compacting.

Compacting or Pressing

The grade powder is consolidated into a compact by two main routes: pressing in rigid dies (uniaxial pressing) and isostatic pressing in flexible molds (compaction under hydrostatic pressure). Other techniques, such as powder rolling, cold extrusion, explosive compaction, slip casting, vibratory compaction, or metal injection molding, have gained no industrial importance.

Tungsten powder is not easy to compact due to its relatively high hardness and difficult deformation. Nevertheless, in most cases compaction is performed without lubricant to avoid any contamination by the additive. The resulting compacts are generally sufficiently strong so that they can be handled without breaking. For machining the part, it must be pre-sintered beforehand.

Take tungsten carbide inserts as an example. The grade powder goes into insert shaped molds specially designed to allow for the shrinkage that will happen later on in the process. The powder is compressed into the molds, in a process similar to how pharmaceutical tablets are formed.

 (To be continued-This article is divided into several parts and this is part 5, for part 4 please refer to http://news.chinatungsten.com/en/tungsten-information/80274-ti-10325; for part 6 please refer to http://news.chinatungsten.com/en/tungsten-information/80276-ti-10329)

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Two types of crystalline (NH) 4) 10[H 2W 12O 42]·10H 2O were precipitated in sequence when an ammonia solution of , peroxopolytungstate was neutralized with hydrochloric acid. It was found by X-ray diffraction that one of them is an unknown phase of ammonium paratungstate, and the other is the reported one. Heating the former, it turned directly to common triclinic WO 3. On the other hand, the latter yielded the hexagonal form of WO 3 (h-WO 3) in the temperature range 350-370 °C. This is a new synthetic method of h-WO 3, though the final precursor is a known compound. The color of h-WO 3 thus formed was pale yellow and contained a small amount of residual ammonia (N/W = 0.017 in molar ratio). Its crystallographic c-axis (7.689 Å) was shorter than than the reported value (7.798 Å) for the same WO 3 phase synthesized from 3WO 3·H 2O. 

 

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In last part we know that tungsten carbide grain size is key to the properties of final tungsten carbide cutting tools, together with additives such as binder cobalt, carbides of titanium, tantalum, niobium, etc. Here we explain the process of mixing up.

Mixing Up

All these ingredients used to make tungsten carbide are blended with a liquid such as alcohol or hexane and placed in a mixing vessel, often a rotating drum called a ball mill. In addition to the grade ingredients, cemented balls 1/4″ to 5/8″ in diameter are added, to help the process of adhering the cobalt to the tungsten carbide grains. A ball mill may be as small as five inches in diameter by five inches long, or as large as a 55-gallon drum.

When the mixing is complete, the liquid must be removed. This typically happens in a spray dryer, which looks like a stainless steel silo. An inert drying gas, nitrogen or argon, is blown from the bottom up. When all the liquid is removed, the remaining dry material is “grade powder,” which looks like sand. The level of mixing up all ingredients affects the uniformity of grade powder and then finally has great effect on the final tungsten carbide cutting tools.

(To be continued-This article is divided into several parts and this is part 4, for part 3 please refer to http://news.chinatungsten.com/en/tungsten-information/80247-ti-10323; for part 5 please refer to http://news.chinatungsten.com/en/tungsten-information/80275-ti-10328)

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Tungsten is almost three times as dense as iron, almost twice that of lead and virtually the same as gold, its high density made itself that earned it is name which is comes from Swedish: tungsten heavy stone.

All sorts of weird applications have evolved to exploit tungsten's unique qualities. As we know, its density could rage from 17.0~18.5g/cm3, and the hardness usually from 24~28HRC, besides, when it comes to be used as the bullet, then the hardness should be controlled at least 40HRC, that is the most important reason why the military has called tungsten into service in another kind of evolutionary arms race, and also it is a prefer material called green bullet for tungsten missiles for it is non-toxic.

Tungsten makes very good bullets, which is the kind of thing that if you fire it at someone else's armour, and it will go right through it and kill it. Just like the creatures of the Cambrian period, once someone starts using teeth (or tungsten bullets and missiles) you need to do something about it. If you introduce tungsten into your bullets you've got to introduce tungsten into your armour. The fascinating balance military engineers have to negotiate between the strength of tungsten and the costs in fuel and manoeuvrability all that extra weight brings.

Now they could put the tungsten on the side of the tank but not on the top. Then people are developing warheads that will fly towards the tank and then at the last minute go up and then drop on it, so then you have to start arming the top of the tank. So tungsten metal is a perfect for bullets and missiles.

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