Free-fall tumbling mixer

Fig. 5. Two samples of a nominally 15-p.m calcium carbonate powder, tumbled in the free-fall tumbling mixer/sampler, taken nine minutes apart. The similarity between the two samples demonstrates that these are probably representative of the bulk powder.

Fig. 1 Two devices that can be used to obtain a small representative sample from a larger supply. (A) Systematic representative sampling of a powder can be achieved with the spinning riffler (From Ref. ) (B) the spinning riffler is composed of several removable sample cups (C) chaos-generating devices, such as the free-fall tumbling mixer, can be used for powder homogenization and sampling (From Ref.t f) and (D) exploded view of the sample carrier.

Two important methods are the spinning riffler and the free-fall tumbling mixer. The first has been proven to be the most superior method of sampling in experiments and should be used whenever possible. The second has not been investigated fully but deserves... 

Figure 1.5. In the free-fall tumblii mixer, a powder to be sampled is homogenized in a sample jar which tumbles chaodcally in a rotating drum. After the tumbling, any sample taken at random from the powder is a representative sample. It is convenient to take random samples using a sampling cup mounted to the lid of the jar [43, 44].

For tumbling mixers, there are three main mechanisms for mixing convective mixing, shear mixing, and dispersive or diffusive mixing. " All three mechanisms are present to some extent in free-fall mixers. During scale-up, as the batch size is increased, so are the forces (gravitational, convective, and shear) that... 

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