To achieve successful results in powder metallurgy the metallic powder must be thoroughly homogenized. The term blending and mixing are both used in this content. Blending refers to intermingling powders of the same chemical compositions but possibly different particles size. Mixing refers to combining powder of different chemistries. The mixing or the blending of metal powder before composition is down for the following purposes.
(i) To obtain uniform distribution of particle size.
(ii) To combine two or more metal powder to create desired alloy and
(iii) To coat particle with the lubricant.
Mixing can be done either wet or dry. Lubricants such as graphite or stearic acid are used in the mix to improve flow characteristics of the powder and reduce wear. Binders, which are required in some cases to achieve adequate strength in the pressed but unsintered part. Deflocculants, which inhibit characteristics during feeding. Percise control of the volume of the raw powders and the quantity of lubricants used is essential in blending process.
The best mixing is obtained when all particles have essential in blending process. The best mixing is obtained when all particles have similar size shape and density. The blending and mixing are done by mechanical means and are as follows shown in figure.
(i) Rotation in a drum, (ii) Rotation in double-cone container,
(iii) Agitation in screw mixer, (iv) Stirring in a blade mixer.
The containers are usually designed with internal baffles or other ways of preventing free-fall during blending of powders of different size, because variations in setting rates between sizes result in segregation. Vibration of the powder is undersirable, since it also causes segregation. Best results seem to occur when the container is between 20% and 40% full.