Doctor blades are commonly used for effecting creping of paper in papermaking machines; and for other uses in papermaking machines, coating machines, and other machines. Inasmuch as a doctor blade is normally in contacting relation with the surface of a rotating cylinder, the tip of the doctor blade is subject to wear; and, as wear progresses, the doctor blade's effectiveness may diminish. That is, progressive wear of the doctor blade may induce progressive diminution of a particularly important property of the product being made or the material being processed by the apparatus in which the doctor blade is disposed. For example, doctor blades used for creping paper in a tissue paper making machine precipitate progressively greater loss of machine-direction tensile strength of the paper as doctor blade wear progresses. This is particularly true in installations wherein the impact angle progressively changes, as wear occurs, due to the way the doctor blade is mounted. Commonly, in such machines, creping blades are changed (i.e,, replaced by new or newly sharpened blades) after a product property of particular importance (e.g., machine direction tensile strength) has been reduced to a predetermined minimum acceptable level by doctor blade wear, or after other observed deleterious ramifications of abnormal doctor blade performance. It has been discovered, however, that the rate of progressive diminution of such an important product property due to doctor blade wear can be reduced greatly by continually adjusting the impact angle of the doctor blade. Thus, the present invention pertains, in general, to a method of and apparatus for continually adjusting the impact angle of a doctor blade to at least partially offset negative ramifications of progressive doctor blade wear: for example, so adjusting a creping doctor blade in a papermaking machine that the machine-direction tensile strength property of the paper remains more uniform over a greater period of time than were the impact angle of the doctor blade not so adjusted.
USPTO Backgrounds
USPTO Backgrounds