Because tungsten owns a lot of good properties, such as, high melting point, high hardness, high hardness and high purity and the like, which is the main content of tungsten needle. Tungsten needle can be prepared in some way and be used in some fields. The diameter of some tungsten needles is similar to tungsten electrodes. Or we can understand it as when the tungsten electrode is thick enough, the products can be called tungsten needle. And when the tungsten wire is bold enough, the products can be called tungsten needle after cutting into a set length. Therefore, tungsten needle has some similar applications as tungsten electrodes and tungsten wire.

Tungsten needles can be made needles of flash lamp in camera, needles of sodium lamps and needles of halogen lamps and metal halide lamps. They also can be applied to welding. Another important application of tungsten needle is to be used as material to purify the air.

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GTAW - Gas Tungsten Arc Weld, also called Tungsten Inert Gas, TIG for short.

The following part will describe something about results on GTAW Arc Stability Test Results in High Pressure.

(1) To carry out the experiment, GTAW test apparatus for the high pressure environment appliance is designed, the apparatus consists of seven parts, they are: a high pressure gas pipeline system, high pressure gas deployment tank, high pressure welding test chamber, the welding process high-speed picture pick-up system, high pressure gas control system, cabin inner scene and welding process monitoring system and all-position automatic welder.

 (2) The test is arc stability test carried out under high pressure, the results shows that, at the condition of 0.2 / 0.4 / 0.7MPa, GTAW arc can burn steadily.

(3) The test also showed that several factors what influence the arc stability, including the state of the workpiece surface, tungsten electrode, and a shielding gas effect. Tungsten electrode damage will seriously affect the stability of the arc.

Arc stability refers to the degree that arc remains stable combustion without causing broken arc, drift and arc blow.



 

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By GTAW arc stability test under high pressure environment, you can know that many factors can affect the arc stability of tungsten electrodes, including the effect of shielding gas, the tungsten electrode and the workpiece surface condition and other factors. This article is mainly about the effect of shielding gas effect on arc stability.

Shielding gas effect will affect the stability of the arc. Under certain conditions, the gas flow rate and nozzle diameter has an optimum range, shielding gas effect is best at this time, and the effective protection area is also the largest on the weldment. If the gas flow is too low, the air flow exclude the ambient air is weak, so that shielding gas effect will be relatively poor; if the gas flow is too fast, it is easy to form turbulence and involve air when gas exhaust, thereby reducing protection effect. When the gas flow rate is constant, if the nozzle diameter is too small, the protected area is relatively small, and it will lead to the formation of turbulence because of the high air velocity;

 if the nozzle diameter is too large, it will not only hinder observation, and will lead to a too low flow rate, that is to say, the protective effect is not very good. In addition, this test is carried out under high pressure environment, it also needs to consider the environmental pressure (air) impact on the protective gas - argon, and measure can be taken: ensure that the ambient air pressure is less than the argon gas pressure.



 

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GTAW（Gas Tungsten Arc Welding） arc stability test under high pressure showed that there are many factors can affect the arc stability, such as, the surface state of workpiece, tungsten electrodes, a shielding gas effect and other factors. This article describes that workpiece surface state impact on the arc stability.

Workpiece surface state would influence the stability of the arc. GTAW welding method is particularly sensitive to the oil and oxide films on workpiece / wire surface, if there is the presence of the oil or oxide films, the arc is not capable of ignition or stable combustion. So, before welding, the wire surface and the part near the joint weldment must be cleaned to remove the grease, moisture, dirt and other debris oxide film on metal surfaces and to ensure that arc strike stably and bur steadily. Cleanup methods can be divided into the following kinds; you can select one according to the materials.

(1) Chemical cleaning. This method is commonly used to cleanup weld wire, whose effect is good and production efficiency is high. For different metal materials, chemical cleaning agents and process procedures they been used are different, so it should be cleaned according to instructions.

(2) Mechanical cleaning. This method is simple and the results are good.

(3) Chemical - Mechanical cleaning, if it is a large workpiece, it needs twice cleaning. 



 

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Test results of hyperbaric welding experiments (under three different pressure condition)

The above table shows that, it can get a stable combustion arc under three different pressure conditions. By high-pressure environment, GTAW arc stability test can found that, there are many factors will affect the stability of the arc, such as, tungsten electrodes, workpiece surface state, protective gas and other factors. This article is primarily concerned with the impact of tungsten electrodes on arc stability.

Because tungsten electrodes will directly affect the stability of the arc, we select lanthanum tungsten electrodes as the electrodes material, which owns large emission current, good ablation resistance and non-radioactive. The shape of the tungsten tip is important process parameters, under normal circumstances, a different shape should be chosen according to the ends of the welding current species (high current / low current). In the small current conditions, welding select tungsten electrodes with small diameter and the cone angle, which can make arc easier and stable; at high currents, when welding, the melt of the tip end due to overheating can be avoided when the cone angle increased, thereby reducing losses and preventing the expansion of the arc to affect the cathode spots stability. During use, tungsten electrodes require frequently trimming with wheel / special tungsten grinder.

Tungsten electrode damage will affect the stability of the arc, solution: choose better electrode materials; select appropriate welding parameters; with reasonable mechanical structure.



 

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Test material:

(1) Base metal: API 5L X56 pipeline steel tube, dimensions: 168.3mm (outer diameter) × 9.5mm (thickness).

API 5L X56 pipeline steel chemical composition (%)

Mechanical properties of API 5L X56 pipeline steel tube

Electrode is adopting lanthanum tungsten electrode, because it owns good ablation resistance, large emission current and without pollution, and so on. Studies have shown that lanthanum tungsten electrode possesses the most outstanding performance. (1) Owns the best arc performance and its arc voltage value is the minimum ;( 2) when the arcing time is longer, lanthanum tungsten electrode’s working temperature is low,at this time its burning resistance is maximum, keep the shape of the tip long, the highest electron emission ability. (3) 2% lanthanum oxide electrode having good workability.

Environmental conditions: hyperbaric welding test chamber (volume of 5.5m3; maximum working pressure of 1.0MPa; design pressure 1.5MPa); high pressure gas tank deployment (capacity 5.5m3; maximum working pressure of 4.4MPa; design pressure 4.85MPa); CPLMS1000-25K CCD & CMOS high-speed digital camera (up 25000ftp); QWZH - 315 type all-position automatic welding machine, this machine has a control of high precision welding.



 

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GTAW, namely the Gas Tungsten Arc Weld, is one kind of non-MIG welding, also known as tungsten inert gas welding (TIG). It is similar to MIG welding, and their dissimilarity is that the GTAW electrodes are made of tungsten which is tungsten electrode that has high melting point, and can withstand high temperatures. Because it does not melt during welding, so there would be no loss. Protect gas acts as flux, if necessary, the filling bar materials can be used to provide the weld with metal. TIG weld almost can weld all metals, in which includes most of the steel, copper, magnesium alloy, aluminum alloy, and part silver, gold, brass, bronze and titanium. The weldment (sheet or the like) which using this process to weld out having a high quality. The following is the part vocabulary content of what mentioned in this article:

Gas Metal Arc Welding (GMAW) refers to, making use of the arc generated from the welding workpiece and the welding wire as a heat source, thereby welding the metal. It has MAG welding (Metal Active Gas shielded arc welding), MIG welding (Metal Inert Gas arc welding) and CO2 welding.

Protective gas refers to, the gas that protecting the hot metal from the ambient air in the welding process, to protect the metal droplet, puddle and weld area.

Solder flux refers to all the material can be used to reduce the base material and the interfacial tension of the solder, including molten salt, organic, metallic steam and gas activity, i.e., the other substances removed base material and the outer solder.



 

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Generally, grind the taper on the tungsten to a distance of less than 2.5 times the electrode diameter (a 1/8-in, electrode you would grind a surface 1/4 to 5/16-in. long). Grinding the tungsten to a taper eases the transition of arc starting and creates a more focused arc for better welding performance. When welding with lower currents on thinner materials (those ranging from .005- to .040-in.), it is best to grind the tungsten to a point. A pointed tungsten allows the welding current to transfer in a focused arc and helps prevent thinner metals, such as aluminum, from becoming distorted. As a note, using pointed tungsten for higher current applications is not recommended, as the higher current can blow off the tip of the tungsten and cause weld puddle contamination.

Instead, for higher current applications, it is best to grind your tungsten to a truncated tip. To achieve this shape, first grind the tungsten to a taper as explained above, then grind a .010- to .030-in. flat land on the end of the tungsten. This flat land helps prevent the tungsten from being transferred across the arc and/or from balling.

In any application, the type and shape of tungsten you use helps determine the arc quality and welding performance you will achieve. Each of the six types of tungsten discussed here bring with it distinct advantages and disadvantages. That’s why, regardless of type of material you are TIG welding or whether you are using an AC or DC process, it is always important to choose your tungsten wisely for each application. Doing so can maximize your TIG welding success and is one of the best defenses against contamination and rework.

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Balled tips are generally applied to pure tungsten electrodes and are suggested for being used in AC process on sine wave and conventional square wave TIG welders. To ball the end of the tungsten appropriately, simply apply the AC amperage recommended for a given electrode diameter and the ball on the end of the tungsten will form itself. The diameter of the balled end should not exceed 1.5 times the diameter of the electrode (a 1/8-in. electrode should form a 3/16-in. diameter end), as having a larger sphere at the tip of the electrode can reduce arc stability and/or fall off and contaminate the weld.

A pointed and/or truncated tip, for pure tungsten type, ceriated type, lanthanated type and thoriated type, can be used for inverter AC and DC welding processes. To properly grind the tungsten, use a grinding wheel specially designated for tungsten grinding to avoid contamination and one that is made of borazon or diamond to resist tungsten’s hardness. Note: if you are grinding thoriated tungsten, make sure you control and collect the dust, have an adequate ventilation system at the grinding station and that you follow manufacture’s warnings, instructions and MSDS sheets.Grind the tungsten straight on the wheel versus at a 90-degree angle to ensure that the grind marks run the length of the electrode. Doing so reduces the presence of ridges on the tungsten that could create arc wandering or melt into the weld puddle, causing contamination.

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Packaging

1. Marking of packages

The following information, as a minimum, shall be legibly marked so as to be visible from the outside of each package:
a. The number of this Standard, i.e., AWS A5.12M/A5.12:2009 (ISO 6848:2004 MOD);
b. Electrode diameter;
c. Electrode length;
d. Net quantity of electrodes;
e. Supplier’s name and trade designation;
f. Lot, control, or heart number.

2. Packing

Tungsten electrodes shall be packed so that their surfaces are protected from all damage or staining when they are properly transported and stored.

3. Marking of over-packing

Marking of any, or all, over-packing of unit packages with items listed in 11.1 shall be optional with the manufacturer.

4. Warning label

The appropriate precautionary information as given in ANSI Z49.1, latest edition (as a minimum) or its equivalent, shall be prominently displayed in legible print on all packages of electrodes, including individual unit packages enclosed within a larger package.

Electrode quality

The surface of electrodes shall be free of impurities, undesirable films, foreign inclusions, cracks, scale and other defects. Electrodes shall be internally free of foreign inclusions or anything else that would adversely affect the operation of the electrode. Oxide additions shall be sufficiently uniformly distributed throughout the electrode so that the operation of the electrode is not adversely affected.



 

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