The preparation of silver tungsten points is adopting infiltration method, the calculation should be accurate to ensure that the content of silver in silver tungsten points is qualified and you should not waste silver. The equation between the infiltrating silver’s content and actual density of tungsten skeleton can be seen as follows:

       R1 = Q * R2 / V * R3 * S

In the above equation,
R1 is referring to actual density of tungsten skeleton (g / cm³);
Q is referring to Requirements of infiltrating silver (g);
R2 is referring to theoretical density of tungsten skeleton (g / cm³);
V is referring to Skeleton volume (cm³);
R3 is referring to theoretical density of silver (g / cm³);
S is referring to correction value, and its range is between 0.8 and 0.9.



 

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Mechanical alloying processes for the preparation of silver tungsten contact (W - 35 Ag):

Prepare materials:
Industrial pure tungsten powder, purity> 99.3%, Φ: 1μm - 5μm;
Pure silver powder, purity> 99%, Φ: 1μm - 2μm;
Mixing powder: Batch mixing tungsten powder and silver powder, silver content is of 35%;
Milling: in the air, milling in the milling machine for 0 to15h, the diameter of grinding media is 6.35mm of WC small ball, motor speed is controlled at 250r / min or so.
Pressing: under 300Pa conditions, with one-way presses pressing mixed powder, so that it becomes compact.
Sintering: under hydrogen conditions, the temperature is controlled at 870 ℃ sintering 2h for getting the maximum sintered density.
Cooling: After the completion of sintering, waiting the sintering furnace to be cooled to room temperature.
Hot pressing: Under 600Pa conditions, the temperature is controlled at 850 ℃, heating 1h, then hot-pressing the sintering compact.



 

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Infiltration process for the preparation of silver tungsten contacts: First of all, you should press tungsten skeleton and silver blanks, then pre-sintering tungsten skeleton at high temperature, and then stack tungsten skeleton and silver blanks together into sintering furnace for liquid phase sintering, the temperature should be controlled above the melting point of silver, silver in the molten state will fill the tungsten skeleton pore by capillary action, and ultimately form silver tungsten contacts.

The principle of capillary action of silver tungsten contacts prepared by infiltration process, whose equation expressed as follows:

    H = 2α * cosθ / g * ρ * γ

Among them,
H: height of the liquid infiltrate into the capillary (mm)
α: surface tension (N / m²) between the liquid and gas phases
θ: wetting angle
g: acceleration of gravity
ρ: liquid density (kg / m³)
γ: capillary radius (mm)

As can be drawn from the above equation, if θ is smaller, silver (liquid metal) is easier into the tungsten porous skeleton gaps, that is to say, it is more easily to get desired silver tungsten contacts with high density.



 

Tungsten Metals Manufacturer & Supplier: Chinatungsten Online - http://www.tungsten.com.cn
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When the car is working, result in that the main reasons of tungsten contacts gap misalignment of distributor are shown as below:

1. Tungsten contacts ablation, it will cause the increase of tungsten contacts gap after the surface oxide shedding.
2. The top block of movable arm of contact wears, so the gap of tungsten contacts becomes smaller.
3. The distributor between the shaft and bushing will wear on each other, not only result in the distributor shaft swing phenomenon occurs, but will make the tungsten contact gap volatile, suddenly become small or big.

4. Driver’s improper adjustment. Under normal circumstances, the driver would use visual methods and their experience to adjust the gap of tungsten contacts, rather than through plug inspections and adjustments. This can cause the size misalignment of the tungsten contact gap.

Therefore, in order to improve the engine's power to reduce the consumption amount of fuel and maintain the normal operation of the engine, you should correctly adjust the gap of tungsten contact of distributor.



 

Tungsten Metals Manufacturer & Supplier: Chinatungsten Online - http://www.tungsten.com.cn
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