Coating apparatus – Solid member or material acting on coating after application – Running length work
Patent
1984-10-05
1987-01-20
McIntosh, John P.
Coating apparatus
Solid member or material acting on coating after application
Running length work
118123, B05C 1104
Patent
active
046373381
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a scraping device and particularly to an apparatus for scraping off of excess coating composition from a traveling web of material, for instance a web of paper, which is coated with the coating composition. The scraping is effected by means of a doctor which has an elastic blade. This doctor can be developed in two different forms. In one form, it consists exclusively of a elastic blade. In such case the free end of the blade itself is pressed against the web of material. In the other form the doctor is formed of a blade and a metering rod attached to the free end of the blade. In this case the metering rod is pressed against the web of material. In both cases the blade is deformed to a greater or lesser extent when pressed against the web of material.
The purpose of such a scraping apparatus is to obtain thickness of layer which is as uniform as possible upon the coating of a web of material with coating composition. The thickness of the layer is to be adjustable, for instance by changing the force with which the doctor is pressed against the web of material.
At the place where the excess coating composition is scraped off, the web of material can travel over a rotatable roll or over a stationary supporting device. Alternatively the web of material can travel between two symmetrically arranged scraping apparatus if it has been previously coated simultaneously on both sides.
PRIOR ART
British Pat. No. 1,424,150; Pat. No. 4,220,113; 17 274 which corresponds to U.S. Pat. No. 4,375,202; Pat. No. 4,335,675.
From FIG. 3 of Reference 1 it can be noted that the blade, which is deformed under the pressing pressure, forms at its tip the so-called blade working angle with the web of material. Requirement is made of all scraping apparatuses of the type in question here that this blade working angle remain unchanged when the application force is varied. This is important for the following reasons:
(a) If the blade is itself pressed against the web of material, then the blade has at its tip a diagonally ground blade scraping surface. From FIG. 6 of Reference 1 it can be noted that this blade scraping surface must be always parallel to the surface of the web. If only an edge of the blade is pressed against the traveling web the quality of the coating suffers.
(b) If the blade bears a metering rod at its tip, it must be seen to it that the metering rod rests, as is known, in a doctor bed. Thus there would be the danger of the doctor bed coming into contact with the traveling web if the blade working angle were to change upon a change in the application pressure.
The various designs known from the above-mentioned references all have the features in common that the doctor supporting beam can be swung around a first swivel axis which extends transverse to the direction of travel of the web as close as possible to the line of attack of the doctor on the web of material. This swingability is necessary in order to be able to vary the basic adjustment of the doctor so as to effect adaptation to different types of webs, coating compositions or types of doctors. The aforementioned blade working angle thus results from this basic adjustment and the application force applied.
The requirement indicated above that the blade working angle be maintained unchanged upon a change in the application pressure is satisfied in the known designs by means of completely different measures and with varying degree of success.
In the known apparatus in accordance with References 1 to 3, the doctor supporting beam has an additional axis of swing (D)--as seen in cross section--between the point of attack of the doctor on the traveling web and the point of attack of the supporting ledge on the blade. (The supporting ledge is arranged in that case on an extension of the blade clamping device). If the doctor supporting beam is swung around this additional swivel axis, then the application force changes (with deformation of the blade), and the blade working angle remains constant. This favorable effect,
REFERENCES:
patent: 3245378 (1966-04-01), Caple et al.
patent: 4220113 (1980-09-01), Wohlfeil
patent: 4309960 (1982-01-01), Waldvogel
patent: 4335675 (1982-06-01), Waldvogel
patent: 4375202 (1983-03-01), Miller
Wochenblatt fur Papierfabrikation 1980, pp. 781-783, by H. P. Frei.
Leonard Haas, Pulp & Paper International, Apr. 1976, pp. 67-69.
Wochenblatt fur Papierfbrikation 1980, pp. 271-276, by H. Ruckert.
J. M. Voith GmbH
McIntosh John P.
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