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What Is a Tungsten Filament?

Details: Category: Tungsten Information; Published on Thursday, 11 September 2014 16:38; Written by jwy; Hits: 576

A tungsten filament is a thin strand of the metal which glows very brightly when an electric current is passed through it. When coiled and sealed inside a glass container filled with an inert gas, a tungsten filament can glow brightly enough to light up a room. It was the inclusion of a tungsten filament in his electrical lighting system that resulted in the world giving Thomas Edison credit for inventing the electric light bulb when in fact dozens of scientists had been experimenting with electric light.

Tungsten is an element (Symbol: W; Atomic Number 74) discovered in the late 18th century. Almost twice as dense as lead, it has the highest melting point of all the metals at 6192 ° F (3422 ° C); of all the elements, only carbon’s melting point is higher. These properties make tungsten very useful not only in electric technology, but also for military applications such as hardening weapons. Another use of tungsten is as a component of jewelry, where it’s combined with other materials to form very hard and lustrous compounds, although they can be brittle.

When Thomas Edison and other scientists were working on developing the electric light bulb, they experimented with a number of materials for the light-producing filament. Until the early 20th century, the most successful incandescent light bulbs utilized a filament of carbonized bamboo, which lasted about 1,200 hours. Edison wasn’t the first to use tungsten, which was introduced as an incandescent light bulb filament in Europe in 1904.

In 1906, Edison's company General Electric (GE) developed a process for making pure tungsten flexible enough to draw into a coiled wire. Using a coiled wire allowed GE to increase the surface area of tungsten that would be inside the bulb. By 1911, the company was manufacturing and selling light bulbs using the new filaments, which outlasted all others. Advances in this technology continued almost uninterrupted, so that the cost of operating an incandescent bulb by the turn of the 21st century was less than 5% of what it was in 1911.

Despite its success as the light source for incandescent bulbs, tungsten filament is remarkably inefficient in producing light. About 90% of the power used in operating an incandescent light bulb is emitted as heat, not light. As more efficient methods of producing light have been developed, most notably fluorescent lighting and light emitting diodes (LEDs), some have called for the banning of incandescent bulbs as an energy conservation measure.

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Industry Specifications for Tungsten Alloys

Details: Category: Tungsten Information; Published on Thursday, 11 September 2014 16:24; Written by jwy; Hits: 533

In August of 1986 the last revision of the “Proposed Military Specification” for Tungsten Base Metal, High Density (MIL-T-21014D) was issued. In use for many years this specification defined the requirements for four classes of machinable, high density tungsten base metal produced by consolidating metal powder mixtures comprised primarily of tungsten. The alloy classes differed in tungsten content and density. The specification defined four slightly magnetic tungsten alloys (containing Ni-Fe binders) and three nonmagnetic tungsten alloys (containing Ni-Cu binders) in terms of their composition, mechanical properties, and machinability. ASTM approved a standard containing essentially the same content in 1987. The most recent revision of the ASTM standard (ASTM B777-07) was published in November of 2007 and is the active standard for tungsten alloys at this time. A third standard was introduced in August of 1998 by the Society of Automotive Engineers (SAE Technical Standard AMS-T-21014). All three of these standards contained the same set of mechanical properties for the various alloy classes. These properties are summarized in the table below.

Class	Nominal Weight of Tungsten (%)	Density (g/cm3)	Hardness (Rc max.) (1)	Elongation (% min.) (2)	Ultimate Tensile Strength (ksi min.)	Yield Strength at 0.2% Offset (ksi min.)
1 – Magnetic	90.0	16.85 – 17.25	32	5	110	75
2 – Magnetic	92.5	17.15 – 17.85	33	5	110	75
3 – Magnetic	95.0	17.75 – 18.35	34	3	105	75
4 – Magnetic	97.0	18.25 – 18.85	35	2	100	75
1 – Non-mag	90.0	16.85 – 17.25	32	2	94	75
2 – Non-mag	92.5	17.15 – 17.85	33	2	94	75
3 – Non-mag	95.0	17.75 – 18.35	34	1	94	75

1. For mechanically worked or aged material, the hardness can be as high as Rc 46.

2. Determine with an extensometer accurate to 0.5% elongation or less.

Tungsten Alloy Applications in the Military Industry

Details: Category: Tungsten Information; Published on Thursday, 11 September 2014 12:45; Written by yewq; Hits: 565

New materials, also known as Advanced Materials, refers to the new materials, which was found in recent successful studies and undergoing researches, with superior features, functions and able to meet the need of high-tech. Development of human history shows that material is the material basis and pilot of social development and the new material is a milestone of social progress.Materials technology has been a very important field in the world's national science and technology development planning, together with information technology, biotechnology, energy technology, are recognized as high-tech in today's society and for a long time dominate human technology. National defense force is often the prior user of new materials technology achievement, and the study and development of new material technology play a decisive role in the development of national's defense industry and weapon equipments.

The melting point of tungsten is the highest in metals, and its outstanding advantages is the high-temperature strength and crossion-resistance, which showing excellent properties inmilitary industry , especially weapon manufacturing.It is mainly used for manufacturing armor piercing bullet in weapon industry.

The armor-piercing bullet that in China's main battle tank 125 Ⅱ type is made of W-Ni-Fe, with variable density of sintering press, the average performance can achieve tensile strength 1200 MPa, elongation of more than 15%, tactical and technical index of 2000 meters homogeneous from the breakdown of 600 mm thick steel armor. Presently, tungsten alloys are widely used in large ratio armor-piercing in main battle tank, small and medium-caliber anti-aircraft penetrators and high-speed anti-piercing material , which makes this kind armor-piercing with more powerful breakdown.

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Brazing Tungsten Carbide Components

Details: Category: Tungsten Information; Published on Thursday, 11 September 2014 16:17; Written by jwy; Hits: 559

Tungsten carbide components are commonly joined to steels and other materials by brazing. Brazing involves placing a metallic braze alloy along with a fluxing agent between the components to be joined and then heating the assembly until the braze alloy melts and flows to fill completely the small gap between the two components. Soldering is similar to brazing, but is performed at lower temperatures with lower melting point alloys. Soldered joints, however, generally lack the mechanical or thermal strength to satisfy the requirements of many applications.

Although many variables determine the quality and strength of the bond between two brazed components, attention to a few important principles usually leads to a satisfactory result. Both the carbide and the steel components must be clean so that the molten braze alloy wets their surfaces completely and forms a strong chemical bond with each. Tungsten carbide components are often grit blasted, sanded, or ground to create clean, new surfaces, or plated or treated in salt baths to prepare the surfaces for brazing. Similarly, steel components are vapor degreased or cleaned with solvents or caustic solutions. The presence of any residual grease, oil, oxidation, dirt, or other surface contaminants adversely affects the wetting of component surfaces by the braze alloy and results in an inferior joint. Various tests of the flow of molten braze alloys over component surfaces are commonly used to assess the “brazeability” of the components. The relative importance of clean surfaces will, however, vary with the design and application of the brazed assembly.

Under the right conditions all common braze alloys from pure copper to silver alloys will readily wet cemented carbide surfaces. The most popular braze alloys (American Welding Society designations shown in parentheses) consist of approximately 50% silver and include alloys with cadmium (BAg-6), without cadmium (BAg-24), with manganese (BAg-22), and with tin (BAg-7). These alloys possess moderate melting points in the range 1150 to 1300ºF and can be purchased in wire, rod, or ribbon form or as a trimetal braze in which a copper shim is “sandwiched” between two layers of silver alloy. Braze alloy manufacturers are a good source of detailed information on the selection and use of these products.

For high temperature applications copper is typically used as the brazing material. Although copper has a lower tensile strength than the silver alloys at room temperature, copper retains much of its strength to temperatures approaching 1000ºF . If brazing is carried out in an oxidizing environment, borax is an effective flux for copper. Normally, however, copper brazing is performed in a hydrogen atmosphere where no flux is needed. Other high temperature brazes include high nickel alloys containing some chromium, boron, and silicon. These alloys flow at temperatures exceeding 1800ºF. It should be noted that high brazing temperatures may cause grain growth or other unwanted changes in the steel component.

Fluxes are generally used in combination with the braze alloy to minimize the oxidation of surfaces to be joined during the heating of the assembly. Both “white” and “black” fluxes are commonly used in combination with the silver alloys listed above. The two are similar except that the “black” flux has a higher boron content and therefore is more effective at higher brazing temperatures.

The basic brazing steps follow.

Lightly apply flux to the steel surface.

Position a precut piece of braze alloy on the steel and lightly coat with flux.

Position the tungsten carbide component and coat the outside surfaces with flux.

Heat the assembly evenly throughout its volume to the proper temperature.

Once the braze alloy is molten, jiggle the carbide slightly to allow any flux or fumes to escape. Do not press too firmly or the braze alloy will be forced out of the joint.

Allow the assembly to cool slowly. Make no attempt to cool the assembly quickly.

Wash off any excess flux with hot water.

The optimal thickness of a braze joint is believed to be about 0.004 inches. This thickness represents a compromise between the high strengths associated with very thin joints and the superior ability of thicker brazes to absorb thermal and mechanical strains acting on the joint. Brazing strains are minimized by brazing only one surface between the carbide and steel components. Cemented carbides expand and contract only about one-half as much as most steels. If the carbide component is constrained during either heating or cooling, excessive stresses can develop and failure by cracking may occur. If the braze joint consists of two or more surfaces, the design of the joint must allow the carbide component adequate room during heating and cooling. The brazing of a carbide ring to a steel core, for example, is a very tricky case. Brazing strains become more significant in larger or longer joints. In such cases, various design considerations are utilized alone or in combination to avoid the problem.

Methods of heating the assembly to be brazed include hand torches, batch furnaces, and high frequency induction coils. Torch flames should be somewhat reducing to minimize oxidation of component surfaces. It is important to heat the entire assembly uniformly to minimize thermal gradients and stresses and to reach, but not exceed the proper brazing temperature. Underheated brazes will not melt and flow properly. Overheating may cause low boiling point constituents in the braze alloy to boil off. This alters the properties of the alloy and may result in entrapped gas bubbles in the braze joint. Any environmental factor that influences the rates of heating and cooling of the braze joint must be controlled to insure that the quality of the braze joint does not vary.

Tungsten Alloys in the Construction of National Defense

Details: Category: Tungsten Information; Published on Thursday, 11 September 2014 11:58; Written by yewq; Hits: 539

1.In the aerospace industry applications. China developed the first generation of tungsten heavy alloy performance good in the 1960s, since immediately after the birth of self-developed China’s first artificial satellite navigation device has been successfully applied, then this new material has the first in China an intercontinental missile and developed by a variety of new fighters, helicopters, has been successfully applied. Developed to meet the needs of Chinese communications satellite, but also successfully developed a new type of density up to 18.5g/cm3 high proportion of tungsten-based alloys. A variety of high-performance W-Cu alloys in the rocket (missile) combustion chamber, nozzle, throat, rudder and other parts of the development of high temperature has been applied.

2.Military industrial applications. China has successful developed the W-Ni-Fe heavy alloy, provides of a variety of wear, shaped charge of the development a key material. W-Ni-Cu heavy alloys also play an important role in doing gyrorotor high proportion of material in China’s first nuclear submarine of the research and development.

3.In the civilian industry and nuclear industrial applications. In the nuclear power industry, used for nuclear reactor insulation and shielding materials, tungsten heavy alloy has a good prospect. In civilian industry, high-density tungsten alloy has been more widely used, mobile phones and golf oscillator rod weight will be a wide range of products. Processing done in the electric performance of the anvil block material to make electrical upsetting of hundredfold increase production efficiency, has significant economic benefits.

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What Is a Tungsten Filament?

Industry Specifications for Tungsten Alloys

Tungsten Alloy Applications in the Military Industry

Brazing Tungsten Carbide Components

Tungsten Alloys in the Construction of National Defense

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