Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten. Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws. 

Etch pits on (001) surfaces of calcium tungstate crystals, formed on treatment with hot dilute solutions of hydrochloric acid, were identified to be dislocationetch pits. The technique is able to follow the motion of dislocations during annealing by the formation of new sharp‐bottomed pits adjacent to flat‐bottomed pits at the initial dislocation positions. Inclusions, both solid and gaseous, are an important source of dislocations in crystals of calcium tungstate grown from the melt.

 

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An etch-pitting technique is described for revealing the points of intersection of dislocations with the (100) and (001) surfaces of calcium tungstate single crystals; each etch pit represents one dislocation. The dislocation configuration that is responsible for the residual strain in as-grown ``a'' axis crystals and the mechanism of its growth from the melt are discussed. Preliminary results concerning the distribution of impurities in doped calcium tungstate crystals and the effect of doping on dislocation density and distribution are described. The solution behavior of calcium tungstate in various solvents and a chemical polishing procedure for calcium tungstate are presented.

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Tungsten copper points’ material is made of tungsten which possesses high melting point, high hardness and other excellent performance and copper which own thermal capacity, high electrical conductivity and excellent performance, which owning good arc-erosion resistance, high strength and anti-welding properties. Tungsten copper points are mainly applied in switching circuit and oil circuit breakers and SF6 high voltage circuit breakers due to their not easily oxidization and less wear and tear. Breaking capacity of tungsten copper points has been greatly improved with improved contact structure recently.

Now, it is reported that the arc-erosion resistance can be improved by adding a certain amount of nickel in copper tungsten points; and the ablative performance of copper tungsten points can be increased if tungsten powder’s particles diameter is down to 5μm around, wherein the burning rate of the copper tungsten points will decrease to a minimum if the content of tungsten is increased to 80% -90%.



 

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Tungsten copper contacts material is an alloy made of tungsten (with high hardness, high melting point and other excellent performance) and copper (with high electrical conductivity, thermal capacity and excellent performance), possessing high strength, good arc erosion resistance performance and anti-welding properties. Because tungsten copper contacts is not easily oxidized, thus they have less wear and tear, so it is mainly used for switching circuit breakers, oil circuit breakers and SF6 high voltage circuit breakers. In recent years, breaking capacity of tungsten copper contacts has been greatly improved with improved contact structure.

Now, it has been reported, adding an appropriate amount of nickel in copper tungsten contacts, their arc erosion resistance performance are improved; if the diameter of tungsten powder particles is down to 5μm or so, you can increase the copper tungsten contacts’ ablative performance, wherein if the content of tungsten is increased to 80% -90%, the burning rate of the copper tungsten contacts will down to a minimum.



 

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The requirements of tungsten points’ material on switches and appliances are shown as follows:

1. Mechanical properties requirements: High temperature resistance, high hardness, good ductility and excellent toughness and other performance requirements.

2. Physical properties requirements:
With low resistivity, high boiling point, low vapor pressure,  good thermal stability, large heat capacity,  high melting point, good thermal conductivity, a high electron work function and other performance requirements .

3. Chemical properties requirements:
With good corrosion resistance; not easily oxidized in the atmosphere, curing, carbonization and difficult to form conductive compounds, if the phenomenon appears, it should have high volatility.

4. The electrical contact properties requirements:
With arc erosion resistance, welding and small metal transfer tendencies, low and stable contact resistance and other performance requirements

5. Processing performance requirements:
With easy brazing and welding performance requirements and others.



 

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The following are some main points of the performance requirements of tungsten contacts material on switches and appliances:

1. Mechanical properties: High temperature resistance, high hardness, good ductility and excellent toughness and other performance requirements.

2. Physical properties: A high melting point, high boiling point, low vapor pressure, low resistivity, good thermal conductivity, large heat capacity, good thermal stability, a high electron work function and other performance requirements .

3. Chemical properties: Good corrosion resistance and they are not easily oxidized in the atmosphere, curing, carbonization and they are difficult to form conductive compounds, if it occurs, they are required to have a high volatility.

4. The electrical contact properties: A low and stable contact resistance, arc erosion resistance, welding and small metal transfer tendencies and other performance requirements

5. Processing: With easy welding performance requirements, brazing and other methods can be used.



 

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6. Overhaul the capacity of capacitor.
Placing the capacitor flatly on the cylinder head and grounding the housing, and then aligning the high voltage bus with capacitor wire head about 5mm. Then you should strike the tungsten points of the distributor, so the high-voltage current can charge in the capacitor by 4-5times. You should move the head of capacitor wire into the housing of 3mm around. If the following phenomenon appears: Flashover, with weak, dark red spark and small sound, it shows that the capacity of the capacitor is small and you should replace it; if the capacity of the capacitor is large, the following phenomenon will appear, and it shows that you don’t need to change it. Phenomenon: flashover, with louder sound and blue sparks.

7. Overhaul the connection of battery wire.
You should eliminate the oxide of each wire connector and tighten the wires.

8. Overhaul the generator.
In order to avoid the situation that the engine is operating in a low speed for a long time, you can increase the contact gap of tungsten points appropriately.



 

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4. Overhaul tungsten points’ ablation on tungsten contact spring arm in distributor.

Check the gap of tungsten points when there are no spring balances. It is a normal value if the gap is bigger than 0.37mm. Close the tungsten points, and then strike tungsten points by hand to test fire. If the tungsten contact spring arm is too soft, there will be a strong high voltage spark.

Or use a spring balance, if you have one, to hook one side of the active tungsten contacts arm. If the indication on the spring balance does not satisfy the standard of tungsten contacts of the car model when the contact is opened, it should changed; On the contrary, it doesn’t need to.

5. Overhaul capacitor ground.

Fastening the capacitor case and tightening the wire point orderly.



 

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2. Overhaul tungsten points’ ablation on riveting loose or bracket set screw loose.

Opening the distributor lid, inspecting the situation of tungsten rivet and points bracket set screw loose condition, then pulling the two tungsten points back and forth. And then removing tungsten points, and re-riveting to make it no loose, or changing tungsten points directly when the tungsten points are loose.
Tightening the tungsten points’ bracket set screw when they are loose.

3. Overhaul the skew and offset situation of contact surface.

Opening the distributor lid, the first thing is to inspect the offset and skew situation.
Adjusting the gasket of active tungsten contact arm when the contact surface offset.
Using pliers for twisting tungsten points frame to correct them when the contact surface of tungsten points has skew or excursion.



 

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Founded in 1973, THE BRITISH DARTS ORGANIZATION (BDO) is recognised globally as the world’s leading darts organization with over 1,000 officials and a calendar that produces in excess of EIGHT HUNDRED darts events annually.
 

The BDO is firmly established as governing body for the sport of darts in Britain, and as such is fully committed to regulating, organizing, promoting, staging, administrating and fostering darts nationally, internationally and worldwide for men, women, boys and girls to ensure the on-going growth of the sport for all participants irrespective of gender, age or ability.
 

The BDO represents darts from grass roots right through to professional standard. As such it is all-inclusive and representative of the sport. The BDO comprises sixty-six member counties in Britain, and has sixty-nine associate countries worldwide. Each BDO county stages its own domestic events, with some staging open events for men, women and youth. Each county has a Super-League for men and women and some have their own youth sections.
 

The BDO is administered by a board of directors, democratically elected annually at its AGM. It is funded by subscription from its member counties, and also receives revenue from various sponsors, etc.
 

As for professional game of dart, we recommend tungsten dart, tungsten is an extremely dense metal. It is also very durable, so a high-density tungsten dart resists wear and the knurling will last much longer.

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