Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Patent
1986-10-31
1988-12-06
Lacey, David L.
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
162374, D21F 154, D21F 148
Patent
active
047894334
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a skimming blade for a papermaking machine for the removal of water from the pulp on the wire of the papermaking machine. The skimming blade has a supporting surface disposed substantially parallel to the wire and supporting the wire, and the supporting surface is adjoined by at least one dewatering surface serving for dewatering by suction and offset from the supporting surface.
Skimming blades, which are also called "foils," have long been commonly used components in papermaking machines; they are distinguished from register rolls by a very high dewatering rate, i.e., the use of foils in papermaking machines has considerably reduced the sheet formation length of the wet end of such machines. In other cases it has been possible by installing foils to increase the rate of production of the machine without changing the sheet formation length of the wet end.
High dewatering rates, however, lead to considerable problems in sheet forming, i.e., at the usual consistencies of the fiber suspension, the fibers and fillers tend to flocculate coarsely. To reduce this flocculation, high-turbulence headboxes have been developed, which provide a well-distributed fiber suspension onto the wire of the papermaking machine with a highly uniform microturbulence.
This turbulence of the furnish decreases again after a relatively short time as it runs onto the papermaking machine wire, the term, "short time," meaning a range of a few milliseconds, i.e., after a wire travel of 20 to 100 cm there is no microturbulence in the fiber suspension to prevent the flocculation of fillers and of fibers. The turbulence itself can be imagined as an accumulation of small eddies, the life of an eddy being shorter as the eddy is smaller.
The production of large eddies is undesirable since, due to the centrifugal forces, they cause separation which in turn leads to poorer sheet formation. As these considerations show, the microturbulence of the fiber suspension provided by the high-turbulence headboxes has already substantially subsided before the suspension reaches the first skimming blade, e.g., the first forming board blade or foil blade.
In DE-A No. 23 37 676, therefore, it has already been proposed to provide a skimming blade with a trough within the bearing area, which is to form a stirring channel. The effect thereby achieved is only very slight, however, since the trough once filled with water is substantially neutral in behaviour, and the wire, which is in contact with both sides of the wire supporting area of the foil blade, seals off the trough once it has been filled with water. The minimal entrainment of water caused by the moving wire is not sufficient to create any microturbulence in the furnish on the wire that would reach as far as the dewatering surface of the foil.
It is therefore the object of the invention to create a skimming blade for a papermaking machine, which will make it possible to sustain the microturbulence within the fiber suspension on the wire, and to control and revive the microturbulence.
This object is achieved by a skimming blade for a papermaking machine for dewatering the furnish on the wire of the papermaking machine, which has a bearing surface supporting the wire and disposed substantially parallel to the wire, the bearing surface being adjoined by at least one dewatering surface serving for dewatering by vacuum and offset from the bearing surface, and which has the distinguishing characteristic that the dewatering surface has at least one trough which extends along the envelope line of the dewatering surface at an angle of 90 to 5 degrees from the direction of movement of the wire.
The offsetting of the dewatering surface from the bearing surface of a foil is disclosed in DE-A No. 24 18 851. The step formed between the the bearing surface and the dewatering surface can apply a suction to the wire, this suction being controllable. The dewatering rate is thus controllable. The good sheet formation based on microturbulence, however, can hardly be affected by controlling the vacu
REFERENCES:
patent: 3496064 (1970-02-01), Scott
patent: 3573159 (1971-03-01), Sepall
patent: 4123322 (1978-10-01), Hoult
Feldmuehle Aktiengesellschaft
Hastings K. M.
Lacey David L.
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