This invention relates to apparatus of the type commonly known as "deflakers" which are used in the preparation of paper making stock, especially from waste paper materials of widely varying characteristics.
Deflakers are often used to perform a defibering operation on relatively coarse stock which has either been extracted from a pulper without screening, or which has been rejected by a relatively coarse screen after extraction from a pulper. Such stock can therefore be expected to contain not only a high proportion of usable but still undefibered paper material, but also substantial quantities of reject materials such as plastic, tramp metal such particularly as staples, screws, wire, nuts and bolts, and other hard contaminant materials.
A significant problem which has been encountered by deflakers of the prior art has been their inability to handle successfully stock which contains tramp metal. More specifically, the prior art deflakers have shown a tendency to be self-destructive in that they will accept stock containing tramp metal, but their filling or tackle becomes so damaged in attempting to disintegrate the metal that it becomes useless for further defibering action.
Other practical disadvantages of prior art deflakers have included the cost of their filling or tackle, its tendency to wear to the point of unacceptably low effectiveness, and the time and effort required for its replacement, which commonly includes the necessity of disconnecting and reconnecting one or both of the inlet and outlet pipe lines. Further, prior art deflakers often permit stock to flow through grooves in the working face of the rotor or stator without entering the high shear defibering zone between those faces, which results in poorly defibered stock.