In the processing of tobacco, there often occurs at various stages a mixture of lighter tobacco fragments and heavier tobacco fragments which require separation to permit further processing of the lighter and/or heavier fragments. Winnowing techniques of various types have been used for this purpose.
Such winnowing may be effected, for example, on threshed tobacco leaves to separate the desirable tobacco lamina from the undesirable tobacco stem material. Such winnowing also may be effected on the final blend of shredded tobacco intended for cigarette manufacture to remove unwanted stem material. Another example of winnowing is in the processing of material resulting from the cutting of whole tobacco leaves, such as described in U.S. Pat. No. 4,233,996 issued Nov. 18, 1980 to Warren A. Brackmann et al and assigned to the assignee herein, the disclosure of which is incorporated herein by reference, to separate heavier shreds of tobacco having stem portions associated therewith from lighter shreds which do not have stem portions associated therewith. Further, winnowing also is effected following threshing of the heavier shreds to separate the lamina shreds from the stem fragments.
In U.S. Pat. No. 4,386,617 issued June 7, 1983 to Warren A. Brackmann et al and assigned to the assignee herein, the disclosure of which is incorporated herein by reference, there is described a procedure for forming shredded tobacco stem material wherein tobacco stem material is fiberized between counter-rotating disc plates. The material which results usually contains heavy fragments and clusters of fibres which are unwanted in the end use of the shredded stem material and need to be removed. There is a need, therefore, for some form of separation or winnowing procedure to remove the unwanted heavy fragments and fibre clusters from the shredded stem material.
One problem which arises with existing tobacco winnowing procedures, which generally rely on gravity-induced separation of heavier particles from lighter particles in air, is that a satisfactory separation of desired material from undesired material often is not achieved, and desirable material may be lost or further processing necessary at a later stage of processing. In addition, when the undesired material is the heavy fraction, which often is the case, some heavier material which comprises agglomerations of desired lighter material forms part of the heavy fraction and hence desirable material may be lost.
One example of such material is the clusters of shredded stem material mentioned above, which are removed from the desired individual shredded stem particles along with the heavy stem fragments upon winnowing. Another example is pods of Oriental tobacco leaves which often result when opening and winnowing Oriental tobacco.
A need, therefore, exists for a tobacco winnowing procedure which will achieve substantially complete separation of lighter particles from heavier particles and will further process heavier particles which are multiple components of desired lighter particles to recover the lighter particles therein.