Application of Molybdenum Materials in Microwave Oven Magnetron Field

A complete magnetron is mainly composed of six parts, namely the cathode, anode resonant system, (microwave energy) output device, input circuit, cooling section and magnetic circuit. The cathode of the magnetron is the electron emitter,The performance of the cathode affects the operating characteristics and longevity of the entire magnetron, and it is considered to be the heart of the magnetron.

The upper end shield and lower end shield of the cathode and the two leads are molybdenum metal parts, the tungsten-thorium Filament on the lead wire(molybdenum wire) between the upper end shield and lower end shield emitted electrons, electrons in the molybdenum end shields produced by the electromagnetic field Oscillation produces a microwave, the molybdenum end shield acts as a constraint on the electromagnetic field. The lead wire is the effect of the output microwave. The structure of the cathode is shown in Figure 1.

Machining process of molybdenum parts in microwave ovens

1. Process diagram of lead line(see Figure 2)

Typically, manufacturers of molybdenum parts for microwave ovens produced with pure molybdenum wire to process leads directly , and the requirements for pure molybdenum wire are usually as follows :

    ● Diameter: 1.3 ~ 1.6 mm

    ● Diameter Tolerance: ± 0.01mm or ± 0.02 mm depending on diameter,

    ● Chemical composition requirements: Mo: 99.95% or more, Fe: ≤0.01%

    ● Physical index requirements: Tensile strength: 750 ~ 1 800 N / mm2

    (Different customers has different tensile strength requirements)

    ● Single molybdenum wire: 15 kg or more; 

Eddy current testing requirements: The depth of the rift more than 5% of the wire diameter is determined as the scars,single scars of 1kg molybdenum wire can not exceed 20 points, requiring 100% eddy current testing detection. After microwave oven magnetron manufacturers receiving qualified pure molybdenum wire products, the processing process of the lead wire is as follows:

    ● Step 1  The molybdenum wire will be cut into the required size;

    ● Step 2  The two ends of the truncated wire will be polished;

    ● Step 3  The heating and reducing treatment of the surface of the wiret;

    ● Step 4  Bending forming;

    ● Step 5  Quality inspection;

    ● Step 6  Qualified goods out of the warehouse.

2. Process diagram of the Molybdenum end shield (see Figure 3)

Typically, manufacturers of molybdenum parts for microwave ovens procured molybdenum powder to process molybdenum end shield directly. The requirements for molybdenum powder are usually as follows:

  ● Chemical requirements: Mo:99.95% (minimum); Fe:0.05% (max); O:0.5% (max); Cd:0.001% (max); Pb:0.005% (max); N V R:0.03% (max).

  ● Physical indicators requirements: loose density:≤1.0g/cm;

  ● Density:2.9g/cm3 min; average particle size:≤ 3wm

After Microwave oven magnetron manufacturers receiving qualified molybdenum powder products,The molybdenum cap is processed as follows:

  ● Step 1, Spray drying treatment for the molybdenum powder;

  ● Step 2, Adding adhesives to the molybdenum powder,use of compression molding process;

  ● Step 3, Do false sintering, the purpose is to remove the adhesive;

  ● Step 4, High temperature sintering;

  ● Step 5, Surface polishing treatment on end shield ;

  ● Step 6, Do surface reduction treatment on qualified molybdenum shields, the main purpose is to remove the oxide on surface and clean the foreign matter on surface;

3. The process of the upper end shield and the lead wire (see Figure 4)

  ● Step 1, To weld qualified upper end shield and lead wire(spot welding);

  ● Step 2, Quality inspection; Finally,the qualified products out of the library.

Brief for the consumption of molybdenum materials in microwave oven industry

The consumption of molybdenum materials for microwave ovens in 2011 is about 150t,and the consumption of molybdenum  products includes molybdenum powder and molybdenum wire, The main consumers of molybdenum materials are microwave ovens magnetron manufacturers,mainly in Korea market and Japan market, these molybdenum  parts and other tungsten components and ceramic parts and other common assembly into a set of magnetron,supplying to the microwave oven manufacturers.

Microwave oven after development of decades, has become necessities for life now. Southern China area has become the world's microwave production base,including the Midea, Galanz, LG, Panasonic, The output of microwave production in China is about 70% of global.In 2011, the demand of core parts of the microwave oven - molybdenum parts on magnetrons (set of molybdenum parts including upper and lower end shields and leads)is increasing.