Sphéroïdisation des poudres

• Process description
• Applications

Process description

The most important aspect for industrial processes is the transformation of either agglomerated powders produced by spray drying and sintering techniques,or angular powders produced by conventional crushing methods, into spherical powder.

Powder densification and spheroidization is a widely accepted application of induction plasma technology. It essentially consists of in-flight heating and melting of feed material particles followed by cooling and solidification under controlled conditions.

Depending on the size and apparent density of the treated powder, the time of flight of the particle is controlled such that the molten droplets have sufficient time for complete solidification before reaching the bottom of the primary reactor chamber. Finer particles, entrained by the plasma gases, are recovered in a filter downstream of the primary chamber.

Industrial applications benefit already from the unique properties of Tekna’s spheroidization process. The process results in a considerable improvement of the properties of the powder in multiple aspects:
 

Improved powder flow

Spheroidized particles provide a more homogeneous and stable flow while feeding. This allows feeds to run at faster or slower rates without clogging problems.

Decreased porosity

Porosity is removed when the material is melted. Increased particle density translates into better material to use in powder metallurgy applications and denser coatings.
 

Increased powder density

The tap density of the powder is increased by the presence of spherical and dense particles, resulting in denser coating or parts.
 

Reduced powder friability

Wear on parts and coatings can be reduced by lowering the edging, crumbling, chipping or breakup of the powder used before being processed. The treatment removes internal fractures or weak internal bonds with the end effect of a longer life for the coated parts.
 

Enhanced powder purity

The in-flight melting process can also be used to enhance powder purity through the selective/reactive vaporization of impurities. Tekna’s specialized equipment for purification enhancement can easily and rapidly increase the purity of the initial material by a factor of 10 to 100. Contaminant levels can be brought down to the ppm or ppb levels with one, or multiple, passes depending on the precursor's initial composition.

The electron micrographs below show the drastic improvement in the quality of tungsten carbide powder:  

Properties	Before Plasma Treatment	After Plasma Treatment
Particles	WC -100+400 Mesh   /   40-150 um	WC -100+400 Mesh   /   40-150 um
Tap Density	8.1 g/cm3	10.2 g/cm3
Hal Flow Test	19 sec/50g	7 sec/50g
Degree of spheroidization

 Materials Available

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Applications

For many years, Tekna Plasma Systems has promoted and developed powder particle spheroidization/densification for commercial applications, using induction plasma technology.  Industrial fields ranging from powder metallurgy to thermal spray coatings require spherical powder.   The most pressing need is for an industrial process to turn agglomerated spray dried, or crushed angular powders, into perfectly free flowing spherical powders. Spherical powders are ideal for such applications as powder injection molding, thermal spraying of coatings, or near net shape parts.

Powder metallurgy Tekna’s plasma treated powders have superior properties in terms of spheroicity, tap density and purity, making them attractive in many fields of powder metallurgy.
Wear resistance applications Spherical tungsten carbide (WC) is the base material of choice for hard surfacing applications. It is well known that coatings using spherical WC powders provide better resistance to wearing and are less abrasive. Tekna’s unique spherical powder is being used for industrial applications such as: Centrifuge drums Drilling tools Nozzles Cutting edges
Electronic components The electronics industry benefits from the high purity spherical powders produced by Tekna’s induction plasma process for manufacturing high end electronic components such as piezoelectric devices, and hard drives.
Thermal spraying and laser cladding Plasma treated powder considerably improves powder flow, allowing better feeding which results in a more uniform coating. Steady feeding is one of the most important parameters for achieving high quality thermally sprayed coatings and laser claddings.

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