Spark plasma sintering (referred to SPS) is a kind of progress that put metal powder into the mold made by graphite and other materials, which uses the upper and lower punches to excert energized electrodes and particular sintering pressure to produce high performance material after discharge activation, thermoplastic deformation and cooling. SPS process and hot pressing (HP) have some similarities, but the heating mode is completely different, which uses DC pulse current pressure sintering to sintering directly. In general, DC pulse current plays a significant role in generating discharge plasma, the impact of the discharge pressure, Joule heat and the diffusion of electric field.









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The second is the presence of microwave irradiation decreases the activation energy, and it is not easy to grow grains, resulting, which can achieve more uniform fine grain microstructure, and the internal porosity has been reduced so that the products have better ductility and toughness. In addition, the sintering temperature required is also decreasing. Last but not least, microwave sintering can be alternative for material heating.

Different materials have different capacity of absorbing microwave so that we can not only use alternative heating or selective chemical reactions to obtain new materials and new structures, but also can control the heating zone by adds some wave-absorbing material or take advantage of strongly absorbing  material to preheat the transparent material and other methods. Compared to traditional sintering progress, tungsten carbide nozzle microwave sintering is more easily to control and it is save and pollution-free, which deserves to be popularized.

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Some scientists also found that the microwave field can enhanced the effect of ionic conductivity, and they think high-frequency electric field can promote the transfer of the surface of grain charged vacancy so that the grain is in plastic deformation and promote the sintering of conduct to some extent. In addition, the neck area of sintering that is highly affected by the electric field, which can also make local area ionization for further accelerating the mass transfer process.

The most main advantage of tungsten carbide nozzle microwave sintering is that the microwave was directly coupling with material. Due to the volume of microwave heating, the whole area can receive zero gradient material uniformly heated. The decreases of internal material thermal stress, the decreases of cracking and the deformation occurs, and the material microwave can be absorbed directly into heat so that energy usage has been greatly improved and saved about 80% of energy than conventional sintering.









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Compared to traditional sintering process, microwave sintering technology increases the kinetic energy of interior sintered material molecules, atoms, ions, etc. And the sintered material reduced activation energy, increased diffusion coefficient, which can be fast sintering and getting grain refinement through the interaction of microwave sintering material at low-temperature. Microwave radiation can promote densification specifically due to it is not only heating energy, but also a sintering activation process. To analyze the phenomenon, the structure and the apparent activation energy, microwave radiation was found indeed largely contributed to the diffusion of atoms, and the diffusion coefficient under microwave heating was significantly higher than the diffusion coefficient under conventional heating.

















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Tungsten Carbide drill bits are used in many applications including drill bits for the manufacturing industry. Carbide drill bits come in various sizes and have a multitude of uses within the industry.

Carbide drill bits are usually attached to some sort of tool, usually a drill which forces the drill bit to rotate and provides adequate torque to create a hole for the intended purpose.

Carbide drill bitsTungsten Carbide and carbide mixes are extremely hard and can produce appropriate drilling capabilities in most all materials while holding a sharp edge longer than other bit materials. Because of its durability, Tungsten Carbide can be rather expensive so that is why industries are using more recycled carbide tools. Carbide recyclers are collecting scrap carbide from various industries and machine shops to process through carbide recycling methods.

The use of Tungsten Carbide in drill bits provides a longer lasting, stable, and solid material for use in drilling within numerous industries. Carbide recyclers process the scrap carbide through their facilities and send this cleaned material out to manufacturers who reform the carbide into new products such a carbide drill bits.

Carbide drill bits can be either solid tungsten carbide or merely have the tips covered in a Tungsten Carbide cement.These Carbide drill bits are preferred in construction, mining, farming, automotive and machine shop industries due to their long life. As with any metal of drill bit, there is always wear and tear, dulling, and sometimes breakage. Machine shops can resharpen carbide drill bits in order to further lengthen their usage life. The carbide scraps, filings and sludge can then be delivered to carbide recyclers for the best current scrap carbide pricing. Carbide-USA provides specific instructions on how to keep the carbide scrap separate from other metals and how to properly deliver to their offices.

The major benefit of carbide drill bits is that they provide a longer working life due to their hardness factor. Hardened steel is not able to last as long in steady applications as Tungsten Carbide. By utilizing carbide material, industries can keep their tools on line in the field for longer periods of time preventing down time and loss of time spent on a project.

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This article will go on to describe the affecting reasons that the length of tungsten electrode service life on quality and productivity of pipe welds in “Tungsten Electrode Service Life and Its Value in Stainless Steel Pipe ProductionⅠ”:

(3) Under the sustained action of arc cathode up to thousands of degrees high temperature, the ends of the tungsten electrodes will eventually appear oxidized ablation. When the operator find that the shape of the ends of the tungsten electrode has changed and is not sufficient to ensure penetration quality, it is the time to shut down to replace or re-sharpen the electrode tip during continuous welded pipe production. This downtime often cause some scrap stainless steel tube, thus affecting the rate and productivity of the welded pipe.

(4) In the single pipe production, the length of each pipe is typically 4-6 mm. In order to improve productivity and reduce rework pipe volume, it should be avoided that a half-way stop to replace the tungsten electrodes.

(5) In order to obtain as high welding speed and productivity pipe as possible, the parameter (big tungsten rod diameter and the highest allows use of welding current) is always chosen in accordance with the thickness of welded pipe. The results of a research institute showed that: the burning loss of cerium tungsten electrode (a diameter of 2.4 mm) is slightly larger than lanthanum tungsten electrode and yttrium tungsten electrode only when it’s current is more than 230A. However, if it is less than this current value, the cerium tungsten electrode is better than the above two. The former arc reliability is better than the latter one. This is because: tungsten, lanthanum, thorium electron work function, is respectively 4.5 eV, 3.3eV and 3.35eV, while cerium electron work function is only 2.6eV.



 

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Tungsten electrode service life refer to welding time that after a cutting grinding and under arc conditions, tungsten electrode end shape is stable and allows continuous or accumulated stainless steel pipe welding. Whether during single or continuous welded pipe production, the length of the time will directly affect the quality and productivity of pipe welds, this is because:

(1) In the GTAW(namely Gas Tungsten Arc Weld) production and applications, if the end shape of the tungsten electrode is changed, then its arc shape will change as well, that is to say, current density distribution, the current field shape, the size of Plasma air drag force and electromagnetic force (Lorentz magnetic) field distribution in the arc will change.

(2) In the PAW (Plasma Arc Welding) production and application, if the shape of the tungsten electrode tip is changed, the central position of electrodes material tip and its effective neck-in will produce offset within the plasma welding torch, resulting in a plasma arc is compressed and its flow power fluctuations, thus affecting the keyhole effect, that is to say, it will have an influence on the stability of the weld penetration quality.、


 

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There are several conclusions discussed below on failure research of the tungsten electrodes under high pressure environment:

(1) Failure form of tungsten electrodes are three forms, showed in the following: tungsten electrodes melting, tungsten electrodes erosion and tungsten electrodes tip stick on metals. Among them, tungsten electrode melting account for about 1%; tungsten electrode erosion possesses the largest proportion, which is 90%, the tip will blunt after the tungsten electrode erosion; while the proportion of tungsten electrode tip stick metal is 9 percent, tungsten electrode which sticking to the metal can no longer arc.

(2) Gives the geometric criterion of tungsten electrode failure.

(3) Under high-pressure conditions, there are a lot of factors affecting tungsten electrodes failure, such as, protective gas effects and workpiece surface status. You can use the following methods to study measures to prevent the failure of tungsten electrodes: establish tungsten electrode failure fault tree under high pressure conditions, conduct quantitative and qualitative analysis of fault tree to identify the minimum cut set, and then calculate the structure importance coefficient of the events. Eventually, develop relevant measures to prevent the tungsten electrode failure on the basis of the aforementioned analysis.



 

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Carbide testing can be quick and easy if you follow the steps below

1.The first step to carbide testing is to see if your carbide is heavy? It does not take a lot of carbide for the weight to add up. Carbide is much heavier then steel is.  A coffee can full of carbide will weigh around 50 pounds while the same coffee can full of steel would weigh around 25 pounds.

2.Carbide testing with a magnet is very easy. First question is it magnetic? True tungsten carbide has very little attraction to a magnet. You should be able to easily pull the magnet away from the carbide. If your magnet is hard to pull away from the tool it is steel.

3.spark-test:How much does the material spark? If you place a piece of carbide on a grinding wheel the spark will be close together and the spark will be more orange in color. While a piece of steel will spark like a sparkler and the sparks will be whiter.

These three great ways of carbide testing while allow you to be confident in what you have is carbide.

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Pure tungsten and doped tungsten are common anode material, and thorium tungsten, lanthanum tungsten are acting as cathode material. In order to improve the high temperature strength and the recrystallization temperature of tungsten, lanthanum oxide may be employed as the dispersed reinforcing phase. Therefore, lanthanum tungsten electrodes (W - La₂O₃ alloy) are often used as an electrode material. German KIT researchers had adopted tungsten powder with Fisher particle size (1-3 micron) to conduct MIM experiments of lanthanum tungsten electrodes, after sintering at 1600 ℃, then conducting the hot isostatic pressing to obtain basic fully dense parts. The density of lanthanum tungsten electrodes can be improved by increasing the sintering temperature and hot isostatic pressing treatment, but it is often limited by equipment and cost. On one hand, study more granular tungsten powder to do MIM experiment, on the other hand, use Ni as an activating element, studying its effect on the sintering density, and finally successful use of MIM technology to develop a kind of W - 1.5% La₂O₃ electrode with cuppy shape.

Remarks:

1. Fisher particle size: The average particle size of the powder measured by Fisher method. Fisher method is a relative measurement method; we can not accurately determine the true size of powder, it is only used to control the quality processes and products.

2. MIM, namely, Metal Injection Molding, which is a kind of forming method that injecting the plasticized mixture of metal powder and its binder in the model. 

 

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