Hazelwood has indicated it is targeting ferrotungsten production of 1500 tpa in 2014 and 2600tpa in 2015. Current feedstock for the plant is being obtained from a variety of international sources. Hazelwood has indicated it plans to develop the Big Hill deposit to provide feedstock for the Vietnam ferrotungsten project. The company also is evaluating its wholly owned Mulgine Hill and Trench deposits of its Mount Mulgine Project, 350 kilometres north-northeast of Perth as a potential additional feedstock source. Hazelwood purchased Gindalbie Metal's 30% interest in the deposits in the second half of 2013 and commenced an engineering pre-feasibility study in October 2013. Hazelwood released resource figures for Mulgine Hill in March 2011, which, based on a cut-off grade of 0.05% WO3, included Indicated Resources of 10.16 Mt averaging 0.16% WO3 and Inferred Resources of 5.35 Mt at 0.12% WO3 for about 18 000 tonnes of contained tungsten. Indicated Resources reduce to 2.23 Mt at 0.35% WO3, using a cut-off grade of 0.2% WO3. The company also indicated that 95% of the resource is within 100 metres of the surface. Recent drilling by Minjar Gold Pty Ltd, which has the gold rights for the Mount Mulgine project, resulted in significant tungsten intersections about 300 metres from previous drilling at the Trench deposit. Intersections included 70 metres at 0.167% WO3 and 72 metres at 0.134% WO3. Mineralisation at Mount Mulgine, which includes molybdenum, is thought to represent an Archean porphyry tungsten-molybdenum system (Mulgine Hill) and associated skarn (Trench), related to the Neoarchean Mount Mulgine Granite.

 

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Hazelwood Resources Limited (Hazelwood) released an initial ore reserve estimate for the Big Hill deposit of Proven Reserves of 18.78 Mt averaging 0.11% WO3 and Probable Reserves of 6.43 Mt averaging 0.11% WO3. The deposit's Measured Resources are 22.94 Mt averaging 0.11% WO3, with Indicated Resources of 11.95 Mt grading 0.1% WO3 and Inferred Resources of 12.54 Mt grading 0.08% WO3 for a total resource of 47.43 Mt averaging 0.1% WO3. All the estimates were at a cut-off grade of 0.05% WO3. The deposit is part of the Cookes Creek tungsten project located 70 kilometres from Nullagine in WA. Mineralisation occurs as scheelite veins thought to be related to the spatially-associated Mesoarchean Cookes Creek Monzogranite. Hazelwood is undertaking a definitive feasibility study for the Big Hill deposit, including large scale metallurgical test work on bulk ore samples, which has demonstrated the ability to produce high purity tungsten concentrate. Hazelwood completed an integrated pre-feasibility study in 2010, which incorporated its Big Hill tungsten deposit and its jointly owned ferrotungsten project in Vietnam. In June 2011, Asia Tungsten Products Company Ltd (ATC), which is 60%-owned by Hazelwood (increasing to 100%), completed construction of a ferrotungsten plant in the Vihn Bao district near the Port of Haiphong in northern Vietnam. The plant is expected to have a capacity of approximately 3000 tpa of contained tungsten in the form of 75% grade ferrotungsten. Initial production commenced in April 2013 with 140 tonnes of contained tungsten produced up to August 2013. 

 

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There are some points on how to reduce exposure when using tungsten electrode:

1. Choose tungsten electrodes without thorium, for example, selecting cerium tungsten electrodes, lanthanum tungsten electrodes, yttrium tungsten electrodes, or zirconium tungsten electrodes whenever possible.

2. Read, understand, and follow all information in the Material Safety Data Sheet (MSDS) for the selected tungsten electrode.

3. Use a high-efficiency dust collection system to capture particles created during the grinding of electrodes or disturbed during housekeeping.

4. Evaluate the ventilation system before acceptance and periodically thereafter to minimize personnel and environmental contamination. AWS disclaims liability for any injury to persons or to property, or other damages of any nature whatsoever, whether special, indirect, consequential or compensatory, directly or indirectly resulting from the publication, use of, or reliance on this Safety and Health Fact Sheet. AWS also makes no guaranty or warranty as to the accuracy or completeness of any information published herein. 

5. Develop and implement standard operating procedures for the use of thorium tungsten electrodes, including proper procedures for storage, grinding, use, housekeeping and disposal.

6. Provide training in the operation of the welding and grinding equipment, personal hygiene and safety. 

 

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The following article will describe the other part content of thoriated tungsten electrode radioactivity.

Is there a concern to the user?
The risk of internal exposure during welding is negligible in most circumstances since the thoriated electrode is consumed at a very slow rate. During the grinding of the thoriated tungsten electrodes, radioactive dust is created, posing the potential hazard of internal radiation exposure by inhalation or ingestion unless care is taken to control the dust.

What to do with the collected dust particles?
1. Regularly remove the dust generated by grinding.
2. Properly dispose of the dust and spent electrodes in accordance with federal, state, and local regulations.

Summary
Several of the information sources listed indicate that the risk of occupational exposure to radiation during storage, handling, and welding with thoriated tungsten electrodes is negligible where simple precautions are taken. Special care should be taken to control and collect dust from grinding these electrodes in order to prevent a potential ingestion and inhalation exposure to radioactive dust particles resulting from this operation.



 

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Thoriated tungsten electrode contains thorium, which is a radioactive material that can pose health and environmental risks at elevated exposure levels. Thorium is a low-level radioactive material that primarily emits alpha particles, some beta and gamma radiation as well. The electrode is normally sharpened by grinding as part of the standard procedure while preparing to perform GTAW (Gas Tungsten Arc Welding). Dust particles from this grinding process can cause internal radiation exposure if the dust is accidentally ingested or inhaled, so caution is necessary. Concern regarding radiation exposure to the external body from the electrode is minimal. Thoriated tungsten electrode has a wide application because they make good welds and are long lasting and quite easy to use. A thoriated tungsten electrode operates at a temperature well below its melting temperature compared to a pure tungsten electrode. This result in a much lower rate of consumption of the electrode during welding, which eliminates much of the “arc wander” associated with balled pure tungsten. Other reasons for their use include easier arc initiation, reduced weld metal contamination, higher current carrying capacity, the ability to sharpen the electrode, and a longer life. 



 

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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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