US 3841557 A
Continuous strip is hot-dip coated and passed between coating control nozzles from which gaseous fluid is projected to form gaseous barriers which wipe excess coating material back into the melt. The width of the gas outlet slot in each nozzle is controlled by thermally expanding at least a portion of the walls of the slot, thereby constricting the slot and thus controlling the flow of gas through the slot, thereby in turn controlling the wiping action of the gaseous barrier on the coating and thus controlling coating thickness. The width of the slot can be selectively controlled at increments in a direction along the length of the slot by a variety of heating means, to produce desired coating thickness at each increment across the width of the strip. The heating means is under remote control and the control system can include structure for displaying slot width and can include automatic control structure. At least a portion of the walls of the slot is of material having a high coefficient of thermal expansion, to enhance the effect of heating. The width of the slot can also be adjusted by cooling at least a portion of the walls of the slot, thereby thermally contracting the walls of the slot and thus enlarging the slot. Cooling can be used to make rapid changes in slot width, to dislodge foreign matter from the slot, to aid the heating means in production of a large temperature differential between intermediate and end portions of the slot, or for other purpose.
Description (OCR text may contain errors)
United States Patent [191 Atkinson [111 3,841,557 Oct. 15,]1974 COATING THICKNESS CONTROL AND FLUID HANDLING  Inventor: Edward S. Atkinson, Michigan City,
 Assignee: National Steel Corporation,
22 Filed: on. 6, 1972 21 Appl. No.: 295,740
 U.S. Cl 239/11, 138/46, 239/597  lint. Cl F23d 15/00  Field of Search 239/11, 13, 133, 135, 597,
Primary Examiner-M. Henson Wood, Jr. Assistant ExaminerMichael Y. Mar Attorney, Agent, or FirmShanley and ONeill  ABSTRACT Continuous strip is hot-dip coated and passed between coating control nozzles from which gaseous fluid is projected to form gaseous barriers which wipe excess coating material back into the melt. The width of the gas outlet slot in each nozzle is controlled by thermally expanding at least a portion of the walls of the slot, thereby constricting the slot and thus controlling the flow of gas through the slot, thereby in turn controlling the wiping action of the gaseous barrier on the coating and thus controlling coating thickness. The width of the slot can be selectively controlled at increments in a direction along the length of the slot by a variety of heating means, to produce desired coating thickness at each increment across the width of the strip. The heating means is under remote control and the control system can include structure for displaying slot width and can include automatic control structure. At least a portion of the walls of the slot is of material having a high coefficient of thermal expansion, to enhance the effect of heating. The width of the slot can also be adjusted by cooling at least a portion of the walls of the slot, thereby thermally contracting the walls of the slot and thus enlarging the slot. Cooling can be used to make rapid changes in slot width, to dislodge foreign matter from the slot, to aid the heating means in production of a large temperature differential between intermediate and end portions of the slot, or for other purpose 13 Claims, 13 Drawing Figures Pmmm WW1 3.841. .557
sum 1 ar 4 v IA 000000 0000000oooocoooooooooooooo000000oooooooooooooooooooo fi COATING THICKNESS CONTROL AND FLUID HANDLING BACKGROUND OF THE INVENTION A revolutionary coating control system for galvanizing has recently come into use. In this sytem, which is described in Mayhew US. Pat. No. 3,499,418, the thickness of a hot-dip zinc coating is controlled by jets of gas issuing from coating control nozzles between which steel strip is passed with the coating still in molten condition. The gas jets, which extend transversely across the strip, form gaseous barriers which wipe excess coating metal back into the zinc pot without contact of the molten coating by any mechanical device. This system produces improved surface and other qualities in the galvanized product.
In operation of such gaseous barrier coating weight control lines, there is a problem in that it is difficult to maintain the thickness of the coating at desired values at all increments across the width of the strip, particularly at the strip edges where there is a tendency for the coating to be thicker than desired. This so-called heavy edge is disadvantageous, inter alia, in producing spooled coils which in turn produce wavy edges in the strip upon uncoiling. Such wavy or pie-crust edges render the strip commercially unacceptable.
It is known that changing the width of the gas outlet slot in a coating control nozzle can change the thickness of the coating, all other operating variables being equal. Prior proposals for changing the width of the gas outlet slot to control coating thickness have included the use of removable shims or inserts to form at least one wall of the gas outlet slot so that, by interchanging the shims with shims of different sizes, the width of the gas outlet slot can be changed. The prior art proposals have also included the use of adjusting screws or bolts to warp the walls of the slot towards one another, or to releasably hold a wall of the slot in any of a plurality of manually set positions which provide different slot widths."
Such slot-width control techniques are deficient in a number of respects. They are slow and require an excessive amount of labor to make the adjustment. And, interruption of what would otherwise be a continuous process for work on the nozzle is usually required, thereby causing expensive downtime on the coating line. Also, the labor required on the nozzle is a hot and unsafe type of work because of proximity to molten metal and other high-temperature materials.
These deficiencies of the prior art are overcome by the present invention, which makes it possible to control the width of the gas outlet means instantaneously, with a minimum of hand labor, without interruption of the coating process, and with safety and comfort.
Other advantages of the invention will appear from the following detailed description which, in connection with the accompanying drawings, discloses several embodiments of the invention for purposes of illustration only and not for defining the limits of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates a coating system embodying principles of the invention.
FIG. 2 is a left side view of structure illustrated in FIG. 1.
FIG. 3 is an enlarged view taken on the section planes designated by line 3-3 of FIG. 2.
FIG. 4 is a view on the cross-section plane indicated by line 44 in FIG. 3.
FIG. 5 is a view of nozzle and cooling details, taken in part on the section planes designated by line 5-5 in FIG. 3.
FIG. 6 is a view on the section plane designated by line 6-6 in FIG. 5.
FIG. 7 is another view of nozzle and cooling details, taken in part on the planes indicated by line 7-7 in FIG. 3.
FIG. 8 schematically illustrates operation of heating and control details of the system of FIG. 1.
FIG. 9 schematically illustrates another form of nozzle heating and cooling structure embodying principles of the invention.
FIG. 10 schematically illustrates another form of nozzle heating structure embodying principles of the invention.
FIG. 1] schematically illustrates still another form of nozzle heating structure embodying principles of the invention.
FIG. 12 schematically illustrates another form of heating control and cooling structure embodying principles of the invention.
FIG. 13 illustrates another form of heating element which can be used in the structure of FIG. 1.
Reference numerals with the letter suffix A, B, C, etc. denote elements which are similar to the elements designated by the corresponding reference numerals having no letter suffix.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS With reference to FIGS. 1 and 2, continuous steel strip 20 follows travel path 22 through galvanizing pot or reservoir 24; Reservoir 24 has walls 26 and contains bath 28 of molten coating metal. The path of travel of the strip is established or defined by a sequence of guide rolls around which the strip is threaded in a conventional manner. The rolls include sink roll 30, around which strip 20 passes to change direction. The guide rolls also include roll 32 which is located in reservoir 24 above sink roll 30, and also include roll 34 which is located far above the melt. The strip travel path extends through reservoir 24 and through coating control zone 36, which is positioned above and contiguous to the bath of molten coating metal. After passing through coating control zone 36, the strip changes direction around guide roll 34 and eventually is coiled on mandrel 38 which is driven by variable-speed motor 40 to pull the strip through the system.
The strip passing upwardly from the coating bath carries on each of its broad, generally planar opposite surfaces a layer or coating of molten coating metal. In coating control zone 36 are provided nozzles 42, 44 which control the shape and thickness of the coatings by wiping excess coating metal back into the melt. This is effected through means of jets or barriers of compressed gaseous fluid, in accordance with the basic principles taught in the above-referenced Mayhew patent. The jets impinge upon the strip at substantially a perpendicular angle, i.e., from about 5 below the perpendicular to about 10 above, and preferably at perpendicularity.
Nozzles 42, 44 form part of a coating control rig which includes frame members 46, 48. The frame members support the nozzles with nozzle 42 on one side of and facing the strip travel path, and with nozzle 44 on the opposite side of and also facing the travel path. Nozzle 42 is apDroximately the same height as nozzle 44. The nozzles are similar to one another, so description of one imparts an Understanding of both.
Nozzle 42 is elongated, and includes upper die member 50 and lower die member 52 (see also FIG. 3). Since the direction of travel of the strip through the coating control zone is upwardly, lower die 52 is upstream and upper die 50 is downstream relative to the direction of travel of the strip. The bottom surface of upper die 50 is flat. An elongated cavity 54 (FIG. 4) is formed in lower die 52 so that, when the dies are assembled as shown in FIG. 3, the cavity defines an elongated gas manifold 56. Gas manifold 56 is supplied with compressed gas through a plurality of branch conduits 58 which communicate between nozzle manifold 56 and gas supply conduit 60 (FIG. 2) which through a flexible connection (not shown) communicates with a source of compressed gas which can be air, steam or other gaseous fluid, and can be preheated or be at ambient temperature. Valve 62 is placed in supply conduit 60, for controlling the pressure of gas in nozzle manifold 56. The manifold in the other nozzle has a similar gas supply system.
Upper die 50 and lower die 52 are assembled by bolts (not shown). Holes 64 (FIGS. 3, 4) are provided in lower die 52, and tapped holes 66 are provided in upper die 50, to receive the bolts. An elongated shim 68 is placed between the rear portions of the dies before assembly to maintain the front portions of the dies spaced slightly from one another. With this arrangement, portion 70 of upper die 50 and portion 72 of lower die 52 respectively define top and bottom walls of gas outlet means in the form of a slot or passageway 74. Gas outlet slot 74 faces the strip for passage of gas out of the nozzle and projection against the strip. Gas outlet slot 74 extends along a line in a direction which is transverse to the path of travel of the strip. Slot 74 is very small in its width dimension W (FIG. 3), which is taken in a direction along the travel path. Shim 68 extends around the ends of the gas manifold in the nozzle and forms end-walls for slot 74 so that gas can escape from the manifold only through the gas outlet slot. Slot 74 extends substantially the entire length of the nozzle.
The strip-facing edge of each of dies 50, 52 is rectilinear, and parallel to the surface of the strip. Gas outlet slot 74 extends outwardly on each side of the longitudinal centerline of the nozzle to and slightly beyond the edges of the path of travel of the strip. For any given galvanizing line, the width of the travel path is established by the width of the widest strip which is to be processed by the line, plus an additional amount for normal wandering or tracking of the strip to either side of a centered pass line position. Gas outlet slot 74 is considered to have an intermediate or central portion 76 (FIGS. 2, which is centered on the nozzle centerline, and an end portion 78 on each end of intermediate portion 76.
Heating means collectively designated 82 (FIG. 2) are provided contiguous to gas outlet slot 74 for selectively controlling the width W (FIG. 3) of the gas outlet slot at increments along the length of the gas outlet slot. This is effected through thermal expansion of material of the walls of the gas outlet slot (principally the upper wall, to which the heating means is contiguous). Such wall expansion constricts the slot and thus reduces the flow of gas from the nozzle.
In the embodiment of FIGS. 1-7, heating means 82 takes the form of a plurality of selectively operable electrical resistanceheating elements 84 (FIGS. 3, 6) which are spaced at intervals or increments in a direction along the length of the gas outlet slot. In this embodiment of the invention, heating elements 84 are provided at equal intervals all along the length of the nozzle from one end portion of the gas outlet slot to the opposite end portion of the gas outlet slot.
Each heating element 84 includes a U-shaped resistor 86 and a terminal 88 and can be of a type such as the Calrod Electrical Heating Elements manufactured and sold commercially by the General Electric Company. Each heating element 84 is received in a separate cavity 90 in upper die 50. Cavities 90 extend from the rear face of the die toward the front of the die so that the tips of resistors 86 are located at the front end portions of the respective cavities. With this arrangement, heating elements 84 are in excellent heat exchange relationship with upper wall of gas outlet slot 74 for application of heat to that wall with minimum thermal losses and with maximum thermal expansion of the wall per unit of heat generated by the heating elements. It will be understood that the heating elements can be inserted through the top face of the die instead of the rear face.
Selective energization of heating elements 84 to heat the top wall of the gas outlet slot at the increments of length affected by the respective heating elements to respectively differing temperatures thereby thermally expands the material of the top wall of the gas outlet slot to different degrees and thereby constricts the slot to different widths along the length of the slot by, in effect, lowering the top wall of the slot by different amounts. This in turn adjusts the flow of gas through the slot at each increment so that the desired wiping action by the gas jet and thus the desired coating thickness can be obtained at each increment along the slot length.
For operation of the heating means in the manner just described control means collectively designated 92 (FIG. 8) are provided. The control means includes operating means or control panel structure 94 for selective energization and deenergization of heating elements 84, and includes the necessary electrical connections between the heating elements and operating means 94. Operating means 94 is at a location which is spaced remotely from the coating pot and the nozzle structure to make it possible for workmen to manipulate the operating means with freedom from interruption of coating of the continuous, moving substrate. The remote location of the operating means allows it to be manipulated without interference from the substrate itself, and without unsafe or uncomfortable proximity to hot materials. Stated differently, heating elements 84 are operated from a position such that the width of the gas outlet slot is under remote control. No interference with, or interruption of, the process of coating the substrate is necessary, and no unsafe or hot work is required, in order to make coating thickness adjustments.
The control system for each heating element 84 is like that for each of the others, so description of the structure for controlling one heating element imparts an understanding of all. In FIG. 8, electrical current flows from power line 96 and through conductors 98 and 99 to sliding contact 100, the position of which along resistor 102 is controlled by handle so that resistor 102 is in effect a variable resistor. From resistor 102, current passes through one of the conductors in a multi-conduct'or cable 106 to the leftmost heating element 84 and the circuit is completed from the heating element through a common ground conductor 108. Movement of sliding contact 100 along resistor 102 by vertical movement of handle 104 changes the amount of heat generated by the heating element. Since handle 104 is rigidly connected to sliding contact 100, since conductor 99 is flexible, and since each heating element along the length of the gas outlet slot is connected for operation by a handle 104, the width of the gas outlet slot is displayed all along its length by the position of the handles. Note in FIG. 8 how the handles define a profile or curve which progressively lowers to the unit centerline on each side, since the sliding contacts 100 are progressively lower on the resistors in directions approaching the centerline. With this arrangement of the contacts, the central heating elements are progressively hotter than those in the end portions in directions to ward the center. Hence, the width of the gas outlet slot in the intermediate portion is constricted, and progressively so, relative to its width in the end portions where less heat is applied and therefore less thermal expansion takes place. It will be understood that finely indexed electrical and electronic display systems can be used in lieu of the handle-positioning system illustrated to display slot width.
Heating elements 84 are received in the upper die in the embodiment illustrated in FIGS. ll-7, but it will be understood that the heating elements can be placed in either the upper or lower die, or both. With the heating elements in the upper die as illustrated, essentially all of the thermal expansion is undergone by the upper wall 70 (FIG. 3) of the slot because of the close heat exchange proximity of that wall to the heating elements. Lower wall 72 remains essentially rectilinear or flat. Thus in FIG. 8, the curve depicted by the positions of the handles in essence displays the profile of the upper wall of the gas outlet slot. With heating elements in the lower die in addition to the upper die, the lower wall of the slot also undergoes thermal expansion. And, with heating elements in the lower die only instead of in the upper die, the lower wall of the slot undergoes essentially all of the thermal expansion and the upper wall of the slot remains essentially rectilinear.
In order to enhance the effect of the heating elements in constricting the gas outlet slot, upper die 50 is made of material having a high coefficient of thermal expansion, so that the top wall of the gas outlet slot will undergo maximum expansion per unit of heat input. Aluminum is one preferred material for fabrication of the upper die because of its coefficient of thermal expansion of at least about 1 l X 10' inches per inch per degree Fahrenheit between 32 and 2l2F., see e.g. Perrys Chemical Engineers Handbook (fourth Ed.) by John H. Perry et al., published by McGraw-HilL New York, 1963, page 23-40. As used herein the term aluminum embraces aluminum-base alloys in addition to the pure metal. Austenitic stainless steels, which have coefficients of thermal expansion of at least 6 X 10 inches per inch per degree Fahrenheit between 32 and 212 F. (Perrys Handbook, pp. 23-35, 23-36), are other preferred materials.It is desirable to employ austenitic stainless as the die material in operations where high temperatures are involved (e.g. where superheated steam is used to form the gaseous barrier), to withstand the high temperatures which are established by the fluids and which are required to effect expansion of the top slot wall for control purposes. Aluminum is used for low-temperature operations. It will be understood that coefficients of thermal expansion vary somewhat with temperature and coefficients for varying temperatures are published in standard reference works including Aluminum, published by the American Society for Metals, Metals Park, Ohio, 1967, Vol. I, pp. 280-282 for Aluminum, and the Metals Handbook (eighth Ed.) also published by the American Society for Metals, 1961, Vol. I, pp. 422423 for austenitic steels.
Exemplary slot widths are of the order of about 0.015 inches with the nozzle at ambient temperature. With such widths, the heating elements need only have capabilityfor effecting a change in slot width of about 0.003 inch, and preferably about 0.005 inch in order to provide satisfactory control. It is desirable to have a gas outlet slot that can be provided with a 0.005 inch width differential between the end portions and the interme diate portion. The temperatures which are necessary to produce the requisite expansion will depend upon a number of variables, including the: operating temperature of the nozzle and including the material of the nozzle because as noted above, coefficients of thermal expansion vary among materials, and vary with temperature within a given material. Die design is also a variable which must be considered, because the height of wall determines how much overall elongation by thermal expansion the wall will undergo along a vertical line, and because not all of the expansion will be in the desired direction (i.e., downwardly, or into the slot). The die is preferably designed such that at least one-half of the wall expansion is into the slot (except in areas contiguous to the end portions of shim 60, where expansion of wall 70 is constrained to some extent but not significantly detrimentally so because less expansion is needed at the ends of the gas outlet slot). The more of the expansion which occurs in the direction into the slot is the better, from the standpoint of thermal efficiency. In the embodiment illustrated in FIG. 3, wall 70 has a height as measured at dimension H of 1 inch. It will be understood that heights H of larger values will produce larger absolute values of expansion. In order to determine the necessary temperature (over and above the operating temperature) which is necessary to produce the desired change in slot width, it is only necessary to determine the number of Fahrenheit degrees which are required to elongate wall 70 about twice the amount of the desired change in slot width (assuming that one-half of the expansion will be vertically upwardly, and one-half vertically downwardly into the slot). This number of degrees is calculated from the coefficient of thermal expansion for the particular material at the particular temperatures involved, from the particular required elongation of the wall, and from the height H of the particular wall.
The nozzle support structure includes a holder ll10 (FIGS. 1, 2) for each end of each of nozzles 42, 44. Each nozzle holder includes a generally U-shaped nozzle mounting bracket 112, the back of the bight of which is secured to a rig frame member, as 08. Each bracket 112 includes upper and lower mounting slides 114, 116 respectively and the slides at the ends of each nozzle define a guideway for the nozzle to move toward and away from the strip travel path. Nozzle 42 is moved along its guideway to adjust the spacing of the nozzle from the travel path by an adjustment screw 118 at each end of the nozzle. Each screw 118 is rotatably secured to nozzle 42, and is threaded through a stub cy lindrical sleeve 120 which is rigidly secured to plate 122 which extends between upper and lower slides 114, 116 of the respective holder 110. Rotation of screw 118 in one direction moves nozzle 42 toward the travel path, and rotation of screw 118 in the opposite direction moves the nozzle away from the travel path.
Movement of nozzle 44 in its guideways is effected by an adjustment screw 124 at each end of the nozzle. Each screw 124 is rotatably received in a fitting 126 which has a projection 128 which extends downwardly through a slot 130 formed in the respective upper mounting slide. Each projection 128 is rigidly secured to nozzle 44 and each screw 124 is threaded through stub cylindrical sleeve 132 which is fixed to a rig frame member, as 48. Rotation of screws 124 in one direction moves nozzle 44 toward the strip travel path, and rotation of screws 124 in the opposite direction moves the nozzle in the opposite direction, away from the path of travel of the strip.
In one mode of operation of the system thus far described, continuous steel strip is passed through coating bath 28, and molten coating metal adheres to eachof the opposite surfaces of the strip. The coated strip emerges from the coating bath and passes upwardly into coating control zone 36 with the coatings still in molten condition. The strip passes between coating control nozzles 42, 44 and gas under pressure is projected from the gas outlet slot of each nozzle against the respective coated surface of the strip. The gas projected against the coated substrate controls the molten coating thickness by wiping excess coating metal back into the melt in accordance with teachings of the Mayhew patent. When coating thickness on either coating at any increment across the strip is found to be less than desired, the heating element 84 at that increment is energized to heat and thereby expand the top wall of the gas outlet slot and thereby constrict the gas outlet slot at that increment. This decreases the wiping action of the gas jet at that increment, resulting in less coating material being wiped back into the melt and thus a thicker coating. It will be understood that it can be necessary to energize a plurality of mutually contiguous heating elements in order to make the required slot width adjustment, as where, for example, the region of thin coating extends past a plurality of heating elements. If coating thickness on either coating at any increment across the strip is found to be greater than desired, the heating elements of the associated nozzle are energized at all increments other than the location of the excessively thick coating to constrict the gas outlet slot at all locations other than that of the excessively thick coating. The gas pressure, nozzle spacing and/or strip speed are adjusted in known fashion to bring the wiping action of the gas jet up to the pre-constriction magnitude at all such other increments, with the result that the wiping action is increased at the increment where the slot width was not constricted. The increased wiping action at this location reduces the thickness of the coating from the excessive value. As the coating line continues to operate, the thickness across the strip is monitored and heating elements selectively ener gized and/or deenergized as necessary to constrict or increase the width of the slot to maintain desired coating thickness at all increments across the strip.
Occasionally, as mentioned hereinabove, the coating tends to become excessively thick at the strip edges, forming the so-called heavy edge and associated problems. To overcome this condition, heating elements 84 are selectively energized to progressively constrict the width of the gas outlet slot from the end portions of the gas outlet slot in directions toward the center of the slot in the manner displayed by the handle positioning of FIG. 8. This technique, when accompanied by an increase in the gas pressure, nozzle spacing and- /or strip speed to bring the wiping action in the intermediate portion up to its preconstriction magnitude in order to maintain desired coating thickness in the center, results in an increased wiping action at the strip edges and thus a reduction in excessive coating thickness or heavy edge. In fact, if it is not desired to possess capability for incremental control of the gas outlet slot along the entire length of the slot, the heavy edge problem can be overcome and economies effected by positioning heating elements at increments along only the intermediate portion of the gas outlet slot.
In the embodiment of FIGS. 1-7, there are two cooling systems for each of nozzles 42, 44. Each cooling system is provided for adjustment of the width of the gas outlet slot by action in a different way to thermally contract material of the walls (as with the heating means, principally the top wall) of the gas outlet slot. These cooling systems are generally designated 134 and 136 in FIGS. 5, 6, and 7. Cooling system 134 includes passage 138 (FIGS. 5, 7) for a coolant fluid, e.g. water. Passage 138 extends from one end portion to the other end portion of the gas outlet slot in close heat exchange relationship to top wall 70. A coolant fluid inlet passage in the form of a conduit 140 which is controlled by a valve 142 is provided at one end portion of passage 138, and a coolant fluid outlet passage in the form of a conduit 144 (FIG. 2) is provided at the other end portion. By opening inlet valve 142 (FIG. 7) and passing coolant fluid through passage 138, preferably with the heating elements deenergized, the top wall of the gas outlet slot can be thermally contracted in rapid fashion. This is advantageously done, e.g., when it is desired to make a general change in slot profile, since the thermal contraction of the top wall which is caused by cooling all along the slot causes the width of the slot to increase toward values extant before constriction by thermal expansion, i.e., toward the rectilinear shape which the top wall possesses at ambient temperature. This in effect erases the profile of the top wall which is provided by a particular pattern of energization of the heating elements so that a new profile produced by a new pattern of heating element energization can be instituted. Or, cooling of the die by cooling system 134 can be used to dislodge specks of scale or other foreign matter which can become stuck in the gas outlet slot. Cooling system 134 can be used for this latter or any other desired purpose by itself without any heating elements in the die and/or without the presence of cooling system 136.
Cooling system 136 (FIGS. 5, 6) includes a coolant fluid passage 146 which extends along each end portion 78 of the gas outlet slot. A second passage 148 controlled by a valve 150 is provided at the outer end region of each passage 146 for inlet of coolant fluid. Passage 146 does not extend completely through the die but rather, terminates in the intermediate portion of the die. A plurality of spaced-apart fluid outlet passages 152, 154, 156 are provided along each passage 146. Valves 158, 160 are provided for controlling flow through outlet passages 154, 156.
With cooling system 136, cooling can be employed to aid the heating elements in production of a larger temperature differential between end portions and intermediate portion of the gas outlet slot than can be provided by heating elements alone. In this mode, the heating elements in the intermediate portion are energized to provide high temperatures and the heating elements in the end portions are energized for low temperature or deenergized, and the transition heating elements between these extremes are energized to progressively move from one to the other. With valves 158, 160 at each end open and with water circulating through each passage 146, cooling of the maximum length of the gas outlet slot is achieved. By throttling each valve 160 to minimize flow through the associated outlet passage 156, cooling along a lesser length of the gas outlet slot is effected, and similarly, throttling each valve 158 decreases cooling along a still longer length of the slot. Care should be taken not to completely close valves 160 or valves 158 so as to permit escape of vaporized coolant liquid entrapped upstream of the respective valves.
It will be appreciated that if desired either or both of cooling systems 134, 136 can be dispensed with and heating means alone used to control the width of the gas outlet slot. It will further be appreciated that, as with the heating means, the cooling means can be used in the lower die in addition to or in lieu of the upper die.
It has been said herein above that the heating elements are spaced at increments along the gas outlet slot, and an example of spacing for the heating ele ments is on one-inch centerlines. This provides a control system having capability for fine adjustments along the length of the gas outlet slot. However, where less precise control is acceptable, larger spacings (e.g., 2 inches or 3 inches) can be used. And, where it is not desired to have equal selectivity all the way across the strip but it is desired to have capability for producing greater constriction in the intermediate portion of the gas outlet slot than in the end portions, the heating elements can be spaced at closer increments along the intermediate portion of the gas outlet slot than along the end portions. Such a construction is illustrated in the embodiment of FIG. 9. Also in FIG. 9 is depicted a slightly different form of cooling system which combines capabilities of the two cooling systems of FIGS. 5-7, along with a further modification in which flexibility for cooling along the length of the slot is somewhat reduced. In FIG. 9, an additional passage 162 is provided to connect the two passages 146A. Also, a twoway valve 164 is provided at one end of the nozzle for selective connection of right-side passage 146A with a coolant fluid supply conduit 166 or a coolant fluid discharge conduit 168. In one mode of operation, valve 164 is operated to connect supply conduit 166 to rightside passage 146A and valve 150A is opened to admit coolant fluid to left-side passage 146A and the two end portions of the gas outlet slot are cooled in the manner discussed in connection with the cooling system of FIG. 5. Coolant vapor generated in stagnant-flow central passage 162 escapes through outlet conduits 152A, 154A. In another mode of operation, each valve 158A is throttled down to eliminate liquid flow to the extent possible while allowing for escape of entrapped vapor, and reduce the length of slot which is cooled.
In still another mode of operation, all of valves 158A and 176 are throttled down to eliminate liquid flow to the extent possible while allowing for escape of vapor. Valve 164 is switched to communicate right-side passage 146A with coolant discharge conduit 168. Coolant fluid passes from inlet valve A through the entire length of the die and is discharged through conduit 168 to erase the existing slot profile, to dislodge a foreign particle, or for other purposes as discussed above in connection with the cooling system of FIG. 7.
All valves herein disclosed are solenoid-operated and controlled in a conventional manner from the remote control panel at which is located the operating structure for the heating means.
If desired, and if the great flexibility of control which is provided by individual heating elements is not required, a capability for producing a higher temperature in the intermediate portion of the gas outlet slot than in the end portions can be realized by heating means such as depicted in the embodiments of FIGS. 10 and 11. In these embodiments, the heatingmeans take the form of elongated electrical resistors which extend along the respective gas outlet slots and which have greater electrical resistance in the intermediate por tions than in the end portions so as to produce progressively high temperatures (and therefore progressively constrict the slot) inwardly on each side toward the center. In FIG. 10, the heating means takes the form of a wound nichrome ribbon 172 having progressively increasing numbers of turns as it approaches the center of the gas outlet slot from each side, so that the electrical resistance of the ribbon is greatest in the intermediate portion of the gas outlet slot. It will be understood that, instead of increasing the number of turns, progressively increasing the thickness of the ribbon in the intermediate portion could achieve the same result. Also, a wire could be used in lieu of a ribbon. With the form of heating means illustrated in FIG. 10, passage of current of different values through the heating means produces different temperatures at increments along the length of the gas outlet slot in accordance with the different values of electrical resistance along the length of the heating means and with the value of the current passed through.
In FIG. 11, the heating means takes the form of a plurality of electrical resistors 174 which are elongated and extend in a direction along the length of the gas outlet slot. Resistors 174 progressively decrease in length so that the resistance of the heating means considered as a whole is greatest in the intermediate portion of the gas outlet slot. Resistors 174 can be individually or gang-controlled, with individual control increasing the flexibility of the heating means with respect to providing given temperatures at particular increments along the length of the gas outlet slot.
FIG. 12 depicts still another embodiment of the invention which employs an automatic control system for the heating means. In this embodiment, the control means includes sensing means in the form of a thermocouple 176 for selectively detecting the temperature at the walls of the gas outlet slot at each increment along the length of the gas outlet slot. The control means also includes a controller 178 which is responsive to each thermocouple for selectively actuating the heating element 84D which is associated with the respective thermocouple to maintain a temperature which is preset on the controller for each increment along the die. It will be appreciated that there is a thermocouple 176 at each heating element 84D along the die length. Thermocouples 176 can also be used to record the slot profile, because temperature is related to the size of the slot. Note also that the embodiment of FIG. 12 includes only one cooling system, which corresponds to that designated 136 in FIG. 5.
FIG. 13 depicts another form of heating element 179, which is similar to that of the embodiment of FIGS. 1-7 but which has a resistor 180 of greater effective length, for production of more heat. The resistor is folded upon itself, for compactness.
Operations in accordance with the invention are highly advantageous. Coating thickness can be controlled at increments across the width of the strip so that the coating thickness is as desired at all increments across the strip. Uniform coating thickness can be provided if desired, or the coating can be shaped to be thinner at the edges than at the center to facilitate coiling, if that is desired. In any event, heavy edge and resultant spooled coils can be avoided, as can coatings with undesired thin or thick areas.
Control over the coating thickness effected by control over the width of the gas outlet slot in accordance with the invention is effected instantaneously, with only the labor required to adjust the heater controls and with absolute comfort and safety. No interruption of coating or downtime on the coating line is required. Further, cooling in accordance with the teachings of the invention makes it possible to rapidly change die profile, to dislodge foreign objects, and to maintain high temperature differentials between end portions and intermediate portion of the gas outlet slot.
The invention has been described in connection with embodiment of its principles in a galvanizing environment. However, the coating need not be zinc; other materials, metals and nonmetals, can be applied. And the substrate need not be steel or even metallic; other materials, e.g. paper, can be coated. Further, control of flow of fluids through slots or other passageways in other than coating environments can advantageously be had with use of thermal expansion and/or contraction principles of the invention. Accordingly, for definition of the principles and the scope of the invention, reference will be made to the appended claims.
1. Coating control apparatus, comprising elongated nozzle means for projecting a gaseous barrier against a coated surface of a continuous substrate to wipe excess molten coating material from the continuous substrate to control the thickness of molten coating on the surface of the continuous substrate,
the nozzle means including walls defining linearly extended gas outlet means for projecting gas from the nozzle means,
the gas outlet means having length in a direction along the nozzle means,
the gas outlet means having width in a direction transverse to the length and transverse to the direction of projection of gas from the nozzle means,
heating means contiguous to the gas outlet means for controlling the width of the gas outlet means by thermally expanding at least a portion of the walls of the gas outlet means, and
control means for the heating means,
the control means including means for operating the heating means from a location spaced remotely from the nozzle means.
2. Apparatus as defined in claim 1,
in which the heating means includes means for selectively controlling the width of the gas outlet means at increments in a direction along the length of the gas outlet means.
3. Apparatus as defined in claim 1,
the heating means including a plurality of spacedapart, selectively operable heating elements.
4. Apparatus as defined in claim 1,
the heating means being electrical heating means.
5. Apparatus as defined in claim 1,
at least the portion of the walls of the gas outlet means being of highly expansible material having a coefficient of thermal expansion of at least about 6 X 10 inches per inch per degree Fahrenheit between 32 and 212 F.
6. Apparatus as defined in claim 5,
the nozzle means including a pair of die members,
one of the die members being of the highly expansible material,
the heating means being mounted on the one die member.
7. Apparatus as defined in claim 1, including cooling means contiguous to the gas outlet means for adjusting the width of the gas outlet means by thermally contracting at least a portion of the walls of the gas outlet means.
8. Apparatus as defined in claim 7,
the cooling means including coolant fluid passage means in the nozzle means.
9. Coating process, comprising the steps of passing a continuous substrate having opposite surfaces along a travel path through a bath of coating material to form a coating on at least one of the surfaces of the substrate,
passing the coating substrate through a coating control zone contiguous to the bath,
providing nozzle means in the coating control zone for controlling the thickness of the coating on at least the one surface of the substrate,
each nozzle means including walls defining linearly extended gas outlet means,
the gas outlet means having length in a direction transverse to the travel path,
the gas outlet means having width in a direction along the travel path,
projecting a gaseous barrier under pressure from the gas outlet means against the coated substrate to wipe excess coating material into the bath, and
controlling the width of the gas outlet means by thermally changing the volume of at least a portion of the walls of the gas outlet means,
thereby controlling the flow of gas through the gas outlet means.
10. The process of claim 9,
in which the volume is thermally changed by heating.
13. The process of claim 9,
in which the volume is thermally changed at increments in a direction along the length of the gas outlet means.