US3526204A - Edge thickness control for liquid coating operation - Google Patents

Description

United States Patent Inventors Paul E. Schnedler Middletown, Ohio; James C. Young, Middletown, Ohio App]. No. 667,451 Filed Sept. 13, 1967 Patented Sept. 1, 1970 Assignee Armco Steel Corporation Middletown, Ohio a corporation of Ohio EDGE THICKNESS CONTROL FOR LIQUID COATING OPERATION 12 Claims, 5 Drawing Figs.

U.S. Cl 118/8, 239/597, 239/523, 118/63 Int. Cl B05c 11/06 Field of Search 118/63, 8;

References Cited UNITED STATES PATENTS 2/1888 Simonds 15/307X 12/1933 Sullivan 15/307 12/1935 MarshalL. 239/597X 12/1939 Conn 239/522X 6/1965 Davis 118/8 4/1968 Beall et al. 118/63 7/1964 Jester 118/63X' Primary Examiner-John P. McIntosh Attorney-Melville, Strasser, Foster and Hoffman ABSTRACT: A method and apparatus for continuously coating a web of material and controlling coating thickness at the edges of the web by providing a fluid jet transversely of the web and increasing the jet wiping action in a narrow zone adjacent the edges of the web.

Patented Sept. 1, 1970 l NVENTO R/S PAUL E Jcwvemse & JA/wfsCfJuA/e,

EDGE THICKNESS CONTROL FOR LIQUID COATING OPERATION BACKGROUND OF THE INVENTION An elongated jet of fluid under pressure has long been used in the coating industry for various purposes. For example, particularly in the paper industry, such nozzles or techniques are referred to variously as air brushes or air knives." Without attempting to precisely define these terms, it is sufficient for present purposes to say that according to these techniques, an elongated jet of fluid under pressure is directed transversely of a moving web and used to finish a liquid or semi-liquid material which has been applied as a coating to the moving web. The term finishing is intended to include any action which helps to produce a level, controllable, and uniform coating on the web.

It is believed that the action of the fluid jet on the web produces several effects. On the one hand, it is thought that the jet provides a pressure darn which meters the quantity of liquid coating carried by the moving web past the jet. The pressure dam will cause the excess coating material to flow back for accumulation and re-use. It is also believed that the fluid jet tends to level the surface of the liquid or semi-liquid coating material carried by the moving web.

It has been observed that when a fluid jet of this character is directed at a traveling web of material, excessively heavy coatings occur in a narrow zone adjacent each edge of the web. The essence of this invention resides in the discovery that such undesirable edge build-up may be avoided by a relatively simple and easily controllable method and means, In point of fact, operations in the jet finishing of a steel strip which had passed vertically through a zinc coating bath resulted in excessivecoating thickness within A to 2 inches from the edges to such an extent that the product could not be coiled without damage to the strip.

Careful investigations of this phenomenon have shown that the wiping action of the fluid jet on the liquid coating is substantially uniform across the strip width, except for a narrow zone adjacent each edge of the strip.

While the precise nature of this phenomenon is not fully known, applicants have found that it does not occur if the fluid jet is directed at a web which is passing around a roll or the like which extends beyond the edges of the web. Without intending to be bound by theory, applicants believe that each portion of a jet directed at a moving web will be deflected by the web into vertical components parallel to the surface of the web and to the direction of web travel, and into horizontal components also parallel to the web surface but normal to the direction of movement of the web. Assuming for purposes of orientation that an elongate horizontal jet is directed at a vertically traveling web, each segment of the jet throughout the center portion of the web will be supported laterally or collimated by adjacentjet segments on each side. The horizontal A, component of deflection of each jet segment will substantially cancel each other out, so that throughout the center portion of the web, the jet will be deflected substantially only into vertical components. This effect does not occur near the web edges because of the lack of lateral support and counteracting horizontal components from the jet segments beyond the web edge. It is therefore believed that in the narrow zones adjacent each edge of the web, the vertical components of the deflected jet are somewhat less. It would therefore appear that this reduction in the vertical component permits the build-up of heavier coatings adjacent the edge of the web.

As already indicated, the problem may be alleviated if the web is backed by a roll at the point of impingement, this is frequently impractical because the liquid coating (molten zinc for example) on the reverse side of the web cannot be contacted without damaging the surface of the product. Directly opposed jets have been used with some success but the noise level due to interference is most uncomfortable to workmen. By the use of the present invention, the noise problem can be avoided since the nozzles do not necessarily oppose each other.

SUMMARY OF THE INVENTION Briefly considered, this invention contemplates a method and apparatus for increasing the wiping action of a fluid jet in a narrow zone adjacent the edges of a moving web. Preferably, this is accomplished by means of a nozzle extension which increases the wiping action of the jet on the edges of the web where excessive coating thickness might otherwise occur. The wiping action is increased by either bringing the jet closer to the web or reducing the angle between the jet and the web.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a nozzle extension according to this invention.

FIG. 2 is a cross sectional view showing the main fluid nozzle and the nozzle extension of this invention.

FIG. 3 is a top plan view showing one half of the main nozzle and one nozzle extension, and the relationship of these components to the web being coated.

FIG. 4 is a partial cross sectional view showing a modification of the invention.

FIG. 5 is a perspective view showing another modification of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT This invention relates to a coating process and apparatus wherein a web of material is continuously wetted and coated with an excess of liquid coating material by spraying, dipping or other conventional means. As an exemplary illustration the invention will be described as acting on a web which passes through a bath of liquid coating material and exits vertically upwardly. As is well known in the art, the surface of the web will be coated with the liquid as it emerges from the bath and must be finished before it solidifies or hardens. It should be understood that the invention finds utility in the coating of a paper web as well as in the hot dip coating of metallic strip.

At a point a short distance above the level of the bath, a fluid jet is directed transversely of the moving web, and as already indicated, serves to finish the liquid or semi-liquid coating. The location, size, velocity, and so forth of the jet do not per se form a part of this invention. It is known that these factors must be regulated so that the fluid jet effects a wiping or leveling action on the coating material. For example, when the speed of the web is such that an excess of coating material is withdrawn from the bath, the fluid jet must be arranged so that the excess coating material is returned to the bath.

Referring to FIG. 1, one form of nozzle extension according to this invention has been shown in perspective. It will be seen that this embodiment contemplates in effect a unitary body indicated generally at 10 and having an upper lip 12 and a lower lip 14 defining a slot 16 therebetween. Although parallel lips are illustrated in this figure, a slot which converges toward the front surface may also be used.

It will be observed that the body portion has a rear surface indicated generally at 18 which includes the portion 18a, and the rear edges 12a and 14a of the upper and lower lips respectively. The portion 18a should be in contact with the leading edge of the main nozzle 22 for positioning purposes, but it is not necessary that the rear edges 12a and 14a respectively of the upper and lower lips contact the main nozzle. The rear surface 18 (and particularly the portion 18a) may be flat or shaped to conform to the leading edge of the main nozzle. The front surface 20 of the nozzle extension is substantially defined by the front edges of the upper and lower lips 12 and 14; this surface 20 may be angularly related to the rear surface 18 for reasons set forth in more detail hereinafter.

Referring to FIGS. 2 and 3, a conventional fluid jet nozzle used in the coating industry is indicated generally at 22. One embodiment of such a nozzle is described in detail in U.S. Pat. No. 3,314,163. This nozzle will be supplied with fluid under pressure from a suitable source (not shown) and will direct an elongated jet of fluid under pressure transversely of a moving web 24, through the elongated discharge opening 26.

It will be observed that the nozzle extension of this invention is disposed with its slot 16 aligned with the discharge opening 26 of the fluid nozzle 22.

As a practical matter, the thickness of the slot opening in the nozzle extension should be substantially greater than the thickness of the opening in the main nozzle. For example, in the coating of steel with zinc, it has been found that a dimension of about .045 inches for the opening 26 is desirable. In this same example, the opening of the slot 16 in the nozzle extension should be on the order of l inches. This insures that the upper and lower lips in no way interfere with or cause turbulence in the emerging fluid jet if the centerlines are not precisely coincident.

Referring now to FIG. 3, it will be observed that the nozzle extension in effect serves to reduce the distance between the web 24 and the discharge opening of the nozzle only in a relatively narrow zone adjacent the edge of the web. The front surface 20 in fact defines the effective discharge opening of the nozzle combination at the edge of the web. This increases the wiping action only on the edges of the strip where excessive coating thicknesses have been found to occur. Inasmuch as the wiping action of the fluid jet depends upon the distance between the nozzle opening and the web, the included angle between the rear and front surfaces 18 and 20 respectively of the nozzle extension may be varied as necessary. By the same token, it might be desirable under certain conditions to alter the shape of the front surface of the nozzle extension, such as by making it parabolic or elliptical.

Referring to FIGS. 2 and 3, one manner of mounting the nozzle extensions will be described. It will be seen that the rod 28 is mounted on the supports 30 which are secured in any suitable fashion to the body of main nozzle 22. Slidable upon the rod 28 is the block 32 which carries the arm 34. This arm is in turn secured in any suitable fashion to the lug 36 on the nozzle extension 10.

Secured to the opposite side of the block 32 is the leafspring 38. It will be apparent that this spring tends to bias the rear surface 18 of the nozzle extension into contact with the main nozzle 22, and yet permits the extension to slide longitudinally with respect to the nozzle 22.

It is desirable to provide some means for moving each of the nozzle extensions along the nozzle 22. Such adjustment is desirable when operating procedures contemplated webs of differing widths, and permits adjustment to compensate for lateral movement of the web during operation. In addition, the adjustable feature facilitates the adaptation of automatic positioning equipment, as will be described briefly hereinafter.

As seen in FIG. 3, the adjustment can be accomplished by means of the hand crank 40, which through suitable gearing drives the pulley 42, cable 44, and pulley 46. The cable 44 will of course be connected to the block 32, so that it is moved in response to the crank.

This system is readily adaptable to automatic operation. For example, a suitable device (illustrated schematically at 48 in FIG. 3) can be provided for sensing the position of the edge of the strip. This might conveniently be accomplished by a photocell (not shown). Signals from the photocell would be transmitted as is well known in the art toa reversible motor (not shown) which in response thereto actuates the mechanism for moving the extension. In this manner, a constant relationship can be maintained between the nozzle extension and the edge ofthe strip.

Numerous modifications may be made in the foregoing embodiment. For example, as indicated at the outset of this application, the purpose of the nozzle extension is to increase the wiping action of the fluid jet in a narrow zone at the edge of the coated web. This wiping action can also be increased by changing the angle of impingement of the jet stream on the web. For example, if the fluid jet is directed at an upwardly moving coated web, directing the jet stream downwardly to contact the web at an acute angle increases the wiping effect. Hence, as is schematically illustrated in FIG. 4, the nozzle extension can be utilized to direct the stream downwardly, in addition to bringing the jet stream closer to the strip, to obtain an even greater wiping effect.

Another configuration of nozzle extension is illustrated in FIG. 5. In this embodiment the extension 10 has a uniform projection from the nozzle but has a curved surface 20 so that the angle of impingement becomes more acute as the edge of the web is approached. (The path of the jet stream below the single lip 20 is indicated by the arrow 19 in FIG. 5.) Although a two-lip extension could be made this way, a single lip will usually be adequate to increase the wiping effect. There are various ways in which this curved or warped surface could be shaped and any of them are considered within the scope of the invention if they direct the jet stream more downwardly and/or toward the center of the web.

Another modification within the scope of the invention would be the supply ofa separate or supplementary jet fluid to the nozzle extension.

In cases where the jet nozzles are considerably wider than the web being treated, it may be desirable to block the unused portion of the nozzle by means of an elongated unslotted body on the nozzle extension.

No limitations are to be inferred or implied from the foregoing discussion, except insofar as specifically set forth in the claims which follow.

We claim:

1. In coating apparatus including a fluid nozzle having an elongated discharge opening for directing an elongated jet of fluid at a coated web, means for supplying fluid under pressure to said nozzle, and means for moving said coated web past said nozzle; at least one nozzle extension comprising:

a. an upper lip having a rear edge in close proximity to said nozzle and a front edge angularly related to said nozzle opening; and

b. a lower lip having a rear edge in close proximity to said nozzle and a front edge angularly related to said nozzle opening, said upper and lower lips defining an elongated slot therebetween, the edge portion of said coated web passing said front edges of said' lips.

2. The nozzle extension claimed in claim I wherein the ad jacent surfaces of said upper and lower lips are substantially parallel and congruent.

3. The nozzle extension claimed in claim 1 wherein the adjacent surfaces of said upper and lower lips converge to define an inwardly tapering elongated slot therebetween.

4. The nozzle extension claimed in claim 1 wherein the distance between adjacent surfaces of said upper and lower lips is at least equal to the narrow dimension of said elongated discharge opening.

5. The nozzle extension claimed in claim 4 including means biasing said nozzle extension against said fluid nozzle.

6. The nozzle extension claimed in claim I wherein said front edges of said upper and lower lips are linear, and intersect said respective rear edges.

7. The nozzle extension claimed in claim 1 including a second nozzle extension, said two nozzle extensions arranged at the edges of said coated web and having said angular relations between said rear and front edges oppositely inclined.

8. The nozzle extension claimed in claim 1 wherein said nozzle extension is movable along said discharge opening, and including means to move said nozzle extension.

9. The nozzle extension claimed in claim 8 including means for sensing the position of an edge of said web, and means operative in response to said sensing means to actuate said means for moving said nozzle extension, whereby said nozzle extension automatically remains in a constant position relative to the edge of said web.

10. In coating apparatus including a fluid nozzle having an elongated discharge opening for directing an elongate jet of fluid at a coated web, means for supplying fluid under pressure to said nozzle, and means for moving said coated web past said nozzle; at least one nozzle extension comprising:

a. a body portion having a rear surface, a front surface, and defining an elongated slot extending through at least a portion of both said front and rear surfaces, the opposing walls of said slot being substantially planar;

b. means slidably mounting said body portion with said slot aligned with said discharge opening of said fluid nozzle and with said body portion disposed between said discharge opening and said coated web; and

c. means normally biasing at least a portion of said rear surface of said body portion into sliding engagement with said fluid nozzle.

11. In a coating apparatus including a supply of fluid under pressure, a nozzle for finishing a coated web moving in a path of travel past said nozzle, comprising:

a. a nozzle body having an elongated discharge opening of a length greater than the width of said web; said opening being parallel to the surface of said web;

b. a pair of nozzle extensions associated with said nozzle body for increasing the wiping action of said fluid adjacent the edges of said web, said nozzle extensions being disposed between said nozzle body and said path of travel of said web, each said nozzle extension being substantially shorter than one-half the width of said web; and

c. means to move said nozzle extensions transversely along said discharge opening of said nozzle body.

12. The apparatus claimed in claim 11 wherein said nozzle extensions each comprise at least oneilip having a rear edge in close proximity to said nozzle and a lower surface curved at least over part of its area and disposed between said nozzle and said path of travel of said web to deflect a portion of said fluid jet adjacent the edge of said web, whereby to decrease the angle at which said jet is directed at said web.

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