Molybdenum News Center

The hardness and plasticity of the metal powder pressing process on a large, soft metal powder pressed more easily than the hard metal powder, the powder of molybdenum metal powder flowability than other poor, hard and brittle, the greater the compaction pressure required, thus to ensure suppression performance and uniform distribution of the density of molybdenum powder, be careful when loading powder, uniform, mold should always clean and wipe dipped in a solution of carbon tetrachloride --- paraffin to reduce friction between the powder and the die wall.

 

Coupling force between the powder particles is roughly divided into mechanical engagement force of gravity and the particle surface of the particle and between the atoms. For any metal powder, the

The time of pressing force of the mechanical engagement between the powder particles have a primary connection that the compact power intensity. Therefore, the more complex the shape of the powder particles, the rougher the surface, the particles of the powder between the more closely engaged with each other, the higher the strength of the compact.

 

Passing the billet to suppress and reduce the elastic aftereffect, the pressing process requires a certain dwell time, so that a sufficient pressure transmission, and thus conducive to the various parts of the compact density distribution; the powder body with the air gap sufficient time through the mold wall and the mold or between the punch and the punch mandrel gap escapes to the engagement between the powder and the mechanical deformation of sufficient time. Low-temperature sintering of compacts should be especially careful, because molybdenum brittle, making billet is not cold and hot temperatures, either sintering temperature or cooling should have a buffer, in order to avoid fracture, low temperature sintering time and temperature should be controlled, so that billet exclude both low impurities, but also enhance the strength and electrical conductivity, which is conducive to vertical melt processing.

 

A sintered billet is sintered in a constant current, to a high temperature volatile impurities, to obtain a dense, uniform crystal grains of the molybdenum metal in a reducing atmosphere. Current regulation is a sintered to obtain a sintering temperature, the same molybdenum billet sintering temperature required is the same, but the current is perpendicular to the melt can be different, because the pressure of the cooling water, H2 flow rate, the size of a sintered cap affect the sintering temperature, which leads to different adjustable current. Have done this test: the same batch of billet, large hood needs a sintered current 2900A, while the small cover current needs of a sintered 3400A (because of the cooling water near the small cover clamped molybdenum billet, the cooling effect is more good); same cover, cooling water pressure is different, inconsistent output of molybdenum proportion (cooling water pressure when a small proportion).

 

Vertical sintering must melt under certain reducing atmosphere, partly in order to prevent oxidation of billet, on the other hand is to further the "exclusive polygamous reduction" is a "growth state" and then restore molybdenum powder, which is conducive to improving the purity of the surface of the particles to promote the migration of atoms to accelerate the sintering process. Experience has shown that the particle size of the vertical rows of miscellaneous melt great influence in the vertical melting process, granular powder is not conducive excluder, it should be appropriate to extend the row of miscellaneous time, reduce heat temperature and shorten the holding time; rather coarse granularity miscellaneous powder is easy to row, it should shorten the waiting time miscellaneous, improve thermal currents. Molybdenum bars can be adjusted by the proportion of such controlled within a specific range, in order to get the required number of grains of ideal molybdenum, and then get drawn filaments suitable, high temperature, corrosion boutique molybdenum.

 

In summary, molybdenum production through many complex process influenced by many factors, mainly as powder metallurgy production process, it is very fragile, any little tiny factors can cause fluctuations in quality, thus adjusting the process, careful operation never be empty words, it requires all aspects of cooperation, down efforts need to in order to ensure the stability of molybdenum to improve the quality.

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