Mixing process should be strictly controlled, as the defects cannot be compensated and new defects will be caused in subsequent steps. For cemented carbide, the mixing time must be extended during mixing, due to that the carbide powder is irregular and the particle is too thin. 

 

Submicron powders with larger forces between particles may produce agglomeration. To obtain uniform feed, polar molecular binders, such as ethylene vinyl acetate copolymer, should be added to reduce particle agglomeration and powder friction. Using high viscosity binders, such as high-density polyethylene can avoid the segregation due to the poor particle size distribution of powder particles.

 

 

When mixing temperature is too low, the viscosity of feedstock will increase, resulting in wear between feeding and mixing device and into the foreign body. And subsequent defects will happen.

 

Mixing Temperature

When the mixing temperature is too low, the viscosity will be too large, which is easy to introduce the foreign body. At the same time, inadequate and uneven mixing will be caused. When feeding in with too much gas, injection green compacts will produce holes. Overtop mixing temperature will deteriorate the adhesive properties and lead to the separation of powder and binder.

 

Rotation of Mixer

The high shear force resulting from the too high rotation of the mixer will lead to abrasion and introduce impurities. When the rotational speed is too low, sufficient shearing force cannot be generated, and the alloy powder aggregate is crushed, so that the viscosity of the binder cannot be properly lowered.

 

Granulation Control

The material used for injection molding usually needs granulation after mixing. There are two purposes of granulation: 1, to obtain particles easy to store and transport, to facilitate feeding when injection; 2, to get easy recycling of recycled materials. Cutting method are usually used for granules. When extruding and cutting, the granulation can be operated with negative pressure or even vacuum, so that the porosity can be effectively reduced.