In part 7 we know that adhesion wear happens when tungsten carbide cutter surface rubs with another high-pointed contact surface under certain excessive friction and pressure, and with temperature increased the carbide surface is plastically deformed, penetrated by high points and result in material loss. In this part we will talk about which tungsten carbide grade shall we choose when we meet with a concrete failure mode.

The useful life of a tungsten carbide cutter is determined by many factors. These include the composition and properties of the carbide, the geometry of the carbide component, the design of the assembly, and the chemical, physical, and mechanical environments in which the carbide operates. Changes in any of these factors can produce an associated increase or decrease in service life. The chart below considers only one of these elements – the tungsten carbide grade. Here is a table for clearer explanation.

 (To be continued. This article is divided into 9 parts and this is part 8, for part 7 please refer to http://news.chinatungsten.com/en/tungsten-information/79387-ti-10153; for part 9 please refer to http://news.chinatungsten.com/en/tungsten-information/79413-ti-10159)

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Tungsten polymers are used to produce catheters and other devices that are inserted into the body for diagnostic or interventional procedures are commonly filled with substances opaque to x-rays, thereby rendering the devices visible under fluoroscopy or x-ray imaging. These fillers, or radiopacifiers—tungsten(typically dense metal powders)—affect the energy attenuation of photons in an x-ray beam as it passes through matter, reducing the intensity of the photons by absorbing or deflecting them, could be a suitable material for X-ray absorption for many radioan facilities especially medical devices. Because these materials exhibit a higher attenuation coefficient than soft tissue or bone, they appear lighter on a fluoroscope or x-ray film. This visibility provides the contrast needed to accurately position the device in the affected area. Image contrast and sharpness can be varied by the type and amount of radiopacifier used, and can be tailored to the specific application of the device.

For example, a device designed for use near the surface of the skin requires less radiopaque filler to achieve the required level of attenuation compared with one used inside the coronary vasculature. Device design is also a factor: a higher loading of radiopaque material, for instance, is needed for thin-wall catheter tubing than for products with thicker walls. Generally, compounds should contain only the amount of additives absolutely required for the application, since overloading can result in the loss of the polymer's mechanical properties. Blending together several radiopaque materials can produce better results than using only one type in a formulation.

Among the most widely used radiopacifiers for medical devices are barium sulfate, bismuth compounds, and tungsten—metals that are excellent absorbers of x-rays. Selection of the correct fillers in the proper amount requires a thorough understanding of attenuation and how it is affected by various radiopaque compounds. This article discusses those radiopaque fillers commonly used with medical-grade thermoplastic polymers and the factors involved in their selection.

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An x-ray machine, like that used in a doctor's or a dentist's office, is really very simple, but inside the machine is an x-ray tube, then X-rays come from that. An electron gun inside the tube shoots high energy electrons at a target made of heavy atoms, such as tungsten material. X-rays come out because of atomic processes induced by the energetic electrons shot at the target, but tungsten material has good radiation protection ability as its high density raging from 17.0~18.5g/cm3.

As we know, X-ray production whenever electrons of high energy strike a heavy metal target, such as tungsten target. When electrons hit this material, some of the electrons will approach the nucleus of the metal atoms where they are deflected because of there opposite charges (electrons are negative and the nucleus is positive, so the electrons are attracted to the nucleus). This deflection causes the energy of the electron to decrease, and this decrease in energy then results in forming an x-ray, finally reach the wonderful radiation shielding protection.

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In another experiment, researchers use copper (Cu), tungsten (W) and tungsten copper (Cu-W) as electrode for tungsten carbide machining. The result shows that tungsten copper (Cu-W) can remarkably improve the machining efficiency. What’s more, the wastage of electrode is lower under the low voltage so that Cu-W is the most ideal material for tungsten carbide machining. In addition, the researchers also use different content of Cu and ZrB₂ or TiSi as electrode for EDM by PM (Powder Metallurgy). Compared with graphite, copper and tungsten copper, TiSi/Cu has higher wastage of electrode, the machining surface is rough and the efficiency is not so well so that it is not suitable used as electrode. While ZrB₂/Cu can be used as electrode, but the combining power between Cu-base and ZrB₂ is weak, and the content of ZrB₂ will has an effect on EDM properties.












 

More information about tungsten copper electrode and other materials comparison, click here:

http://news.chinatungsten.com/en/tungsten-information/79286-ti-10093 
http://news.chinatungsten.com/en/tungsten-information/79316-ti-10129 
http://news.chinatungsten.com/en/tungsten-information/79338-ti-10130 
http://news.chinatungsten.com/en/tungsten-information/79339-ti-10131 
http://news.chinatungsten.com/en/tungsten-information/79397-ti-10135

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Tungsten copper (Cu-W) not only has high melt point, low coefficient of expansion and spark resistance, but also has good conductivity so that it is a new kind of high-performance electrode material. Tungsten copper electrode is widely used in die steel and WC work-pieces, the common ratio of Cu/W is 25:75. However, the higher price than graphite or copper, tungsten copper spreading has been blocked to some extent.

Some researchers use copper, tungsten copper, brass and aluminum as electrode for hardened steel machining. The result shows that Cu and Al have higher speed and better precision, Cu and tungsten copper (W-Cu) has the lowest electrode wastage and brass electrode wastage is the largest. Therefore, Cu is a kind of ideal electrode for hardened steel machining, which has low wastage of electrode and high MRR (Material Removal Rate).

More information about tungsten copper electrode and other materials comparison, click here:

http://news.chinatungsten.com/en/tungsten-information/79286-ti-10093 
http://news.chinatungsten.com/en/tungsten-information/79316-ti-10129 
http://news.chinatungsten.com/en/tungsten-information/79338-ti-10130 
http://news.chinatungsten.com/en/tungsten-information/79339-ti-10131

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In part 6 we know that catering failure happens when the tungsten carbide cutter’s surfaces are stricken by particulate-bearing liquid or gas, especially when the operating temperatures are much higher and the more fine-grained the carbide is, the easier for the failure to occur.. In this part we will talk about adhesion wear/galling as another failure mode.

7. Adhesion wear/galling 

Adhesion wear occurs when a tungsten carbide cutter’s surface and that of a mating part or the work material rub together or slide past each other with sufficient force to create excessive friction and pressure at high points of contact between the materials. The high temperatures and pressures generated in these contact zones result in plastic deformation at the material surfaces, penetration of one surface by the high points on the other, and finally the transfer of material (welding) of one material to the other. As material builds up on one of the surfaces, the still higher points of contact create more heat, leading to more deformation, penetration, and material transfer. This process is often referred to as “galling”. Failure by adhesion wear can take several forms, but typically the buildup reaches a stage where it eventually is dislodged pulling chunks of the carbide surface with it.

 (To be continued. This article is divided into 9 parts and this is part 7, for part 6 please refer to http://news.chinatungsten.com/en/tungsten-information/79384-ti-10152)

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In part 5 we know that although carbide material is hard, tungsten carbide cutters can still deform plastically due to a high enough temperature to soften the binder metal, and such a tiny thermal deformation can result in the function failure of assembly tools. In this part we will talk about cracking which is also one of the most common failure modes of tungsten carbide cutters.

6. Cratering failure

Failure known as “cratering” is a localized form of erosion in which a depression develops at the point where a continuous stream of metal or particulate-bearing liquid or gas strikes the working surface of the tungsten carbide cutter’s component. At operating temperatures high enough to soften the binder metal (those exceeding about 900° C.) cratering can take place rapidly. Very fine-grained carbides are particularly susceptible to cratering since smaller grains are locked into the carbide surface by a relatively thin layer of binder metal. As the crater increases in size and depth the carbide is weakened to the point where normal operating stresses produce mechanical failure in the area of the crater.

(To be continued. This article is divided into 9 parts and this is part 6, for part 5 please refer to http://news.chinatungsten.com/en/tungsten-information/79348-ti-10146 ; for part 7 please refer to http://news.chinatungsten.com/en/tungsten-information/79387-ti-10153)

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The tungsten-based bucking bar has one or more smooth surface which is held up against the back of a rivet while it is being shot. The energy gets transferred from the source (the rivet gun) through a medium (the rivet) to the receiver (the bucking bar). The gun is on one end, and the bucking bar is on the other. The gun impacts the rivet, which sends the impulse to the bucking bar, which actually bounces off the rivet and "swings" back at it (by virtue of the person holding it firmly in place), smashing the rivet in turn. This happens many times per second - depending on air pressure and trigger operation. The primary skill required when bucking rivets is to hold the bucking bar stable and square to the rivet. Other than that, just let physics do the work. You don’t have to push on the rivet, just hold it steady.

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Tungsten alloy is a kind of composite materials that tungsten whose quality fraction is 80%-98% distributes to Ni-Fe-W sosoloid, as it is wished, tungsten alloy combines with the high density, high strength of tungsten and good ductility of matrix, so it has a series of properties of physics, chemistry and mechanics.

Tungsten alloy has wide usage in military industry with its good properties, one of applications is tungsten alloy anti-material rifle bullet, anti-material rifle continues the thinking of anti-tank rifle which was used in twice World War, it can launch large caliber machine gun bullet cooperating with anti-material rifle bullet, it can penetrate light tank which has thin armor, and kill personnel in the tank, it can also kill sniper hiding behind blindage mainly used for dealing with vehicles, oil depot, radar, telescopic surveillance mirror, copper flying at low altitude and jet landing on the ground. 

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