05/159703

02/19/1974

07/06/1971

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427/315

493/328, 427/420, 427/377, 427/331, 427/374.400

D21H23/68; D21H17/60; D21H23/30; D21H23/46; D21H23/00; D21H17/00; B05B13/02; B44D1/08

118/63,64,66,69,72,324 117/105.3,158,168,59,68,60,119.2,119.8 229/3.1 93/36PC

2809129	Method of coating sheets with lubricant for draw dies	October 1957	Peterson
3132968	Curtain coating machine	May 1964	Wandtke
3267902	Impregnating and coating apparatus	August 1966	Pritchard et al.
3524759	PROCESS FOR CURTAIN COATING ARTICLES WITH A MOLTEN COMPOSITION	August 1970	McConnell et al.
3635193	APPARATUS FOR COATING AND/OR IMPREGNATING SUBSTANTIALLY PLANAR ARTICLES	January 1972	Stease
3205089	Method and apparatus for flow coating objects	September 1965	Kinzelman
3603219	METHOD FOR IMPROVING THE BENDING QUALITY OF WATER RESISTANT CORRUGATED PAPERBOARD	September 1971	Hallis

Katz, Murray

Sofocleous M.

Wood, Herron & Evans

This application is a divisional of U.S. application Ser. No. 881,239, filed Dec. 1, 1969. The parent application issued as U.S. Pat. No. 3,635,193 on Jan. 18, 1972.

Having described the preferred embodiment of my invention, what I desire to claim and protect by letters Patent is

1. A method of applying a liquid composition to a series of discrete, substantially planar articles in order to coat or impregnate said articles comprising the steps of

2. A method as set forth in claim 1 including the steps of

3. A method as set forth in claim 2 including the step of

4. A method as set forth in claim 3 wherein said substantially planar articles include corrugated paperboard and wherein said liquid composition is a molten wax, said method including the step of

5. A method of applying a liquid composition comprising molten wax to a series of discrete, substantially planar articles in order to coat or impregnate said articles comprising the steps of

6. A method as set forth in claim 1 wherein said substantially planar articles include corrugated paperboard and wherein said liquid composition is a molten wax, including the steps of

7. A method as set forth in claim 6 including the step of

8. A method as set forth in claim 6 wherein said articles are, precut, knockdown carton blanks.

9. A method of applying a liquid composition to a series of elongated articles in order to coat or impregnate said articles comprising the steps of

This invention relates to a method and apparatus for coating and/or impregnating articles. In preferred form, this invention relates to a method and apparatus for producing wax impregnated, planar, corrugated paperboard in either wet waxed or dry waxed form.

Generally speaking, regular corrugated paperboard has one serious drawback, and that is it rapidly loses strength with increased moisture content of the paperboard itself or its environment. For Example, if a box has 1,000 lbs./in. of compression strength at 50 percent relative humidity it may well have less than 500 lbs./in/ compression strength at 90 percent relative humidity. Of course, loss of board strength in high humidity environments is not desirable, but the disadvantages of regular corrugated board are even more serious when the board actually gets wet. If regular corrugated paperboard is made with non-waterproof adhesive it literally falls apart upon being subjected to water. On the other hand, if regular corrugated paperboard is made with highly sized wet strength liners, medium and waterproof adhesive, it may not fall apart upon getting wet, but a box having a typical original 1,000 lbs./in. compression strength will have only about 150 lbs./in. after getting wet.

Therefore, one of the primary reasons for impregnating and/or coating corrugated paperboard with wax is to improve the strength performance of that board under wet and/or humid conditions. The wax impregnation or coating alters the strength properties of the board so that it will perform under conditions where regular corrugated paperboard, without wax coating or impregnation, fails. Further, impregnation, and to some extent wax coating, also improves the dry compression strength of the corrugated paperboard.

Wax impregnated and/or coated corrugated paperboard is mainly used in the formation of boxes for the shipment of fruits, vegetables, poultry, and seafood. Such foods are cooled prior to packing in the box but, once packed, a layer of ice is provided on top of the food products to maintain a chilled environment during shipment. Such boxes are generally stacked five or six high during delivery to distributors and during delivery to retail or institutional outlets. It is apparent that a high degree of wet compression strength is required under these moisture conditions because it is desired that such boxes have a useful life under such moisture conditions of at least about four to seven days or more. Further, wax impregnated and/or coated corrugated paperboard can be used in advertising displays, play houses for children, portable fishing shacks and duck blinds, picnic boxes, refuse containers for public events, and the like, all because of its high compressive strength when dry, as well as its high compressive strength when wet, relative to similar paperboard not coated or impregnated.

There are three basic methods known for wax impregnating and/or coating corrugated paperboard, all of which are in some degree of commercial use. These three basic methods are (a) a dip process which is capable of impregnating the board as well as providing a coating, (b) a sheet fed roll waxing process which is used during manufacture of the board but which can only provide very limited impregnation, and (c) a so-called curtain coating process which is only capable of coating the board's surface. Thus, only the dipping process is capable, from a practical standpoint, of impregnating corrugated paperboard to high degrees of wax pickup, e.g., about 40 percent to about 50 percent by weight. The other two methods are limited to low degrees of wax pickup, e.g., about 10 percent to about 20 percent by weight.

The curtain coating method provides a sheet of wax that is discharged in a vertical plane and the board to be coated is passed in a horizontal plane through the falling curtain. The curtain coating process if very similar to applying wax to the board's surface with a printing roller, except in place of a printing roller a falling curtain is used. But only one side can be coated during a single pass, and if the other face of this board is to be coated a second pass is required. Further, it is only possible to coat the outside surface of the paperboard with this method, i.e., it is not possible to obtain maximum impregnation or saturation of the board, which results in a relatively low percentage wax pickup for the board. Such a low degree of wax pickup does not give sufficient added rigidity to the final corrugated board, nor does it give adequate water resistance to the final board, as may be desired for numerous end uses.

The method of waxing the board during manufacture generally involves roll or spray coating the inside faces of the liners for the board, and roll or spray coating the fluted medium, prior to their adhesion together into final board form. This method also can provide only a relatively low percentage wax pickup. If it is attempted to put on a great deal more wax than the approximate 12 percent to 15 percent by weight usually used in practice, a major problem of adhesion occurs during formation of the final board configuration. Also, because the board has been impregnated during manufacture the board is not yet cut to final useful size, such as, for example, a box blank; the scrap produced by the subsequent cutting step is quite difficult to reprocess in that the wax must be eliminated prior to the paper being recycled.

The dipping process is the only known practical method, to the best of my knowledge, for impregnating sheets of corrugated paperboard with wax at relatively high wax pickup percentages. In the dipping process the sheets or box blanks are simply dipped in a bath of molten wax, the board being retained in the wax tank from on the order of 5 seconds to 15 seconds or more. While the board is immersed in the wax bath, the air and moisture in the board is replaced by the molten wax. The corrugated board is then removed from the wax bath and maintained in an oven, or in open air, for a period of time to drain off the excess wax. The board may be turned top to bottom as desired to provide a more uniform distribution of wax if required, but generally speaking there is more wax at the bottom of the blank than at the top. The dip process is capable of providing wax impregnated board of either wet or dry waxed type at high wax pickup levels, e.g., about 40 percent to about 50 percent by weight.

But there are a number of disadvantages of the dipping or immersing method in impregnating corrugated paperboard with wax. In the first place, the corrugated board tends to build up a high latent heat, i.e., a good deal of heat is retained in the board, due to immersion in a very hot bath of molten wax. This latent heat provides operator handling problems in that the board is quite hot when it reaches the end of its processing cycle; further, a definite fire hazard is created because the board is processed at or near its combustion temperature. Also, the high latent heat causes moisture to be boiled out of the board with the result that the final product is relatively brittle, thereby providing forming or folding problems in certain end uses. Further, the dipping process is not conductive to the production of coated or wet waxed board because the wax is generally still in the molten state as it comes out of the bath; of course, blocking of the boards one with the other occurs if the boards are stacked at this point. Also, the dipping process does not admit of control over percentage wax pickup in that it is not possible to manufacture boards with less than maximum wax impregnation with any consistant degree of accuracy.

Thus, the prior art methods either produce wax impregnated board by dipping, i.e., board saturated with wax to obtain 40 percent by weight or more wax pickup, or produce wax treated board by curtain coating or waxing during manufacture, i.e, board with wax pickup of only about 10 percent to about 20 percent by weight. The wax board properties obtained by these methods of waxing are, of course, quite different. Wax impregnated board, either wet or dry waxed, imparts dry strength as well as greatly improved performance under wet and humid conditions. The amount of strength improvement depends on type of board used, the corrugating adhesive, amount and type of wax used, and distribution of wax throughout the board. At wax pickup levels around 45 percent by weight it is possible to obtain 60 percent or more increase in compressive strength at standard conditions. At 90° F. and 90 percent relative humidity, impregnated board may exhibit compressive strength of about three times the compressive strength of unwaxed board. Strength retention of impregnated board, when water enters the flutes, is far better after immersion in water than for curtain coated board or board waxed during manufacture. Thus, the main advantages for wax impregnated board are greatly improved dry strength, greatly improved wet strength when exposed to liquid water, and maximum strength retention at high humidity.

On the other hand, board treated with wax to a level of 10 percent to 20 percent by weight pickup, such as by curtain coating or waxing during manufacture of the board, does not have the strength properties of wax impregnated board. The main reason for wax treating corrugated board is to stop, or at least greatly retard, the wicking of water. Regular corrugated paperboard will absorb water rapidly if one end of a sample is wetted; wax treated board will not. Otherwise, board treated with wax does not approach the maximum strength and water resistance properties exhibited by impregnated board although wax treatment does impart some added strength or ridigity to the board.

Therefore, it has been one objective of this invention to provide a novel method and apparatus by means of which substantially planar articles can be impregnated and/or coated.

It has been another objective of this invention to provide a novel method and apparatus by means of which corrugated paperboard may be impregnated with wax, i.e., either dry waxed or wet waxed.

It has been another objective of this invention to provide a novel method and apparatus adapted to impregnate corrugated paperboard which substantially eliminates the problems cited above which are associated with the main prior art method known for impregnating corrugated paperboard, namely, dipping.

By dry waxed corrugated paperboard, for the purpose of this application, is meant board that is impregnated with wax, but with substantially no coating of wax on the faces or exposed surfaces of the board. By wet waxed corrugated paperboard, for the purposes of this application, is meant board that is impregnated with wax, but with a coating of wax present on the faces or exposed surfaces of the blank.

As used in the wax impregnating and/or coating of corrugated paperboard, i.e., the preferred embodiment, the method and apparatus of this invention requires the board first to be vertically disposed, and a plurality of the boards are then arranged side-by-side with at least minimal gaps between their faces to form a group so that multiple boards can be processed simultaneously. Each board of a group is inserted into one of a first series of ajustable slots at the input end of a processing tunnel. The input end slots cooperate with a second series of adjustable slots at the output end of the processing tunnel. A plurality of lines of travel one for each board in a group are formed by bands which cooperate with the two series of slots, which extend from one tunnel end to the other, and which are adjustable in height relative to the board height, thereby providing flexibility in the handling of varying width boards. The group of boards is disposed on a powered conveyor and is advanced by that conveyor through the processing tunnel, the boards being guided in their movement through the tunnel by the bands which define the lines of travel. The processing tunnel is of sufficient length that at least two or more groups of, e.g., corrugated paperboard knockdown carton blanks may be subjected to different stages of the process at the same time within the tunnel.

Upon entering the tunnel the group of boards is first subjected to a steam preheat for raising their temperature prior to flooding with molten wax. The group of vertically positioned boards is then passed under a cascade or free fall in a manner similar to a waterfall of molten wax, each board following its own individual line of travel. The plane of each board, as it passes beneath the molten wax cascade, is substantially perpendicular to the plane of the free falling, unrestrained waterfall or cascade of molten wax. The corrugated boards are preferably fed with flutes perpendicular to the group's line of travel, i.e., parallel to the cascade or waterfall of molten wax, when it is desired to achieve maximum wax impregnation and wax percentage pickup. However, if only minimum impregnation and/or wax coating of the boards' faces is required, the boards may be fed so that the flutes are parallel to the group's line of travel. The cascade of molten wax is provided by at least one weir interconnected with a molten wax circulating system.

The weir is disposed substantially transverse to the line of travel of the group within the processing tunnel, and one weir releases two cascades, one from each lip, that fall freely toward the top edges of the board. The weir is structured so that it can be raised or lowered as required depending on the width of the upright boards.

Thereafter, the group of boards passes at a controlled rate through the tunnel's conditioning section which is maintained at an elevated temperature with a constantly changing hot air environment, thereby providing a residence time within which the desired degree of impregnation occurs. The tunnel's conditioning section is provided with a top air knife adjacent the weir and a bottom air knife adjacent the end of the section, the air knives functioning to blow off excess molten wax from the face or liner of the corrugated paperboard and, when the flutes are disposed vertically during processing, to blow out excess wax from within the flutes. Subsequently, the boards pass into a cooling section having a constantly changing cool air environment, the cooling step being the last processing step carried out within the tunnel. The forced, cool air is directed up through the boards to draw heat therefrom so that, when the boards exit from the processing tunnel, they are sufficiently cool for handling by an operator and for stacking.

The advantages of the novel method and apparatus of this invention, when utilized to impregnate corrugated paperboard with wax, are numerous over the prior art wax impregnation method of dipping. The method and apparatus of this invention are much more versatile in that they can easily handle knockdown box blanks with vertical or horizontal flutes, unlimited board lengths, assembled box partitions, odd sizes and shapes at the same time, bundled or corrugated items with flutes vertical, and board widths limited only by the height of the inlet and outlet openings of the processing tunnel. Further, the board can be packaged as it exits from the processing tunnel, whether it is wet waxed or dry waxed, i.e., blocking of the boards is not a problem as it is cooled during processing. Also, the percentage wax pickup within the processing tunnel and the type wax impregnation, i.e., either wet or dry waxed, can be readily controlled.

Further, operation of the method and apparatus of this invention is relatively clean in that the board is cooled when it exits from the processing tunnel, no wax reclaiming is required, and recycling of the cascade overflow is completely within the machine. Further, less drying out of the board occurs during waxing because the mass of wax contacting the board is substantially less than that during dipping, and because the temperature of the molten wax and conditioning temperature after waxing is lower than in typical dipping methods. Also there is very little fire hazard involved with this machine in that a minimum of latent heat is retained by the board and its does not even approach its combustion temperature; also, the machine can be quickly enclosed if fire does develop and the entire processing tunnel area filled with steam to suffocate the fire. Further, a greater throughput per unit time, whether the board is wet waxed or dry waxed, can be achieved for corrugated paperboard impregnated with wax according to the method and apparatus of this invention.

Other objectives and advantages of this invention will be more apparent from the following detailed description of the method and apparatus as utilized with the wax coating and/or impregnating of corrugated paperboard. The detailed description is presented in conjunction with the drawings in which:

FIG. 1 is a partially broken away diagrammatic perspective view illustrating the method and apparatus of this invention;

FIG. 2 is a more detailed perspective view illustrating a corrugated paperboard carton blank held in a vertical or upright attitude, i.e., positioned on edge, in a line of travel formed by vertically adjustable bands as the blank is processed through the method and apparatus of this invention;

FIG. 3 is a view similar to FIG. 2 illustrating preconditioning of the blank with steam prior to applying wax;

FIG. 4 is a view similar to FIG. 3 illustrating passing of the blank through a cascade or waterfall of molten wax from weirs positioned above the blank's line of travel;

FIG. 5 is a greatly enlarged cross-sectional view of one end of the carton blank taken generally along line 5--5 of FIG. 4 illustrating deposition of the molten wax after the blank passes from beneath the weirs when the flutes of the board are vertically positioned relative to the boards' line of travel;

FIG. 6 is a view similar to FIG. 4 illustrating passing of the blank beneath a top air knife for more evenly distributing the wax on the faces of the blanks, both inside and outside, and for blowing out wax from the flutes of the blank when the flutes are vertically disposed;

FIG. 7 is a view similar to FIG. 6 but illustrating a bottom air knife;

FIGS. 8A and 8B are diagrammatic cross-sectional views of the apparatus of this invention incorporating the method of this invention;

FIG. 9 is a cross-sectional view taken along line 9--9 of FIG. 8A;

FIG. 10 is a cross-sectional view taken along line 10--10 of FIG. 9;

FIG. 11 is a cross-sectional view taken along line 11--11 of FIG. 9;

FIG. 12 is a flow diagram illustrating the hot melt system incorporated with the apparatus of this invention;

FIG. 13 is a cross-sectional view taken along line 13--13 of FIG. 8A;

FIG. 14 is a cross-sectional view taken along line 14--14 of FIG. 8B;

FIG. 15 is a cross-sectional view taken along line 15--15 of FIG. 8B;

FIG. 16 is a cross-sectional view taken along line 16--16 of FIG. 8A;

FIG. 17 is a cross-sectional view taken along line 17--17 of FIG. 8B;

FIG. 18 is a partially broken away, fragmentary perspective view illustrating the wax pan and air discharge plenum in the cooling section of the apparatus; and

FIG. 19 is a partial perspective view of the tie rods of the transport conveyor.

This invention, as mentioned, may be adapted for use with different coating and/or impregnating compositions and may be used for coating and/or impregnating different substantially planar articles. However, in the detailed description of the method and apparatus of this invention, as set forth below, the substantially planar article to be processed and the liquid material to be applied is a prescored, corrugated paperboard carton blank, and a wax, respectively. Further corrugated paperboard may easily be coated and/or impregnated by the method and apparatus of this invention with other liquid materials such as, e.g., asphalt or tar-based bituminous materials.

THE METHOD

In accordance with the preferred method steps of this invention, a preformed, scored, corrugated paperboard carton blank 10 is vertically supported, i.e., positioned, on its bottom edge 11 on a powered conveyor 49, see FIG. 2. The plane of the blank 10 is disposed parallel to the axis 12 of a processing tunnel 14. A number of such blanks 10 are preferably established in side-by-side relation with gaps between faces 13 of respective blanks, see FIG. 1, to form a group 8 thereof; thus, in each group there are a series of blanks aligned parallel one to the other and disposed across the width of the processing tunnel 14. Each blank 10 of the group is guided in its individual line of travel through the processing tunnel 14 by group alignment means in the form of flexible guide wires or narrow bands 15 stretched between input 16 and output 17 ends of the tunnel. A number of blanks 10 equal to or less than the number of lines of travel established by the guide bands 15 may be processed all at once in each group 8, and the blanks 10 in any one group may be of the same or different sizes and/or configurations. The lines of travel defined by guide bands 15 for the blanks 10 are generally of a width substantially greater than the thickness of a knockdown carton blank 10, so more than one blank may be sandwiched between a pair of related guide banks if desired. But it is generally desirable to process only one blank 10 within one pair of guide banks 15 in any given group 8 so as to allow the blank to accordian open, see FIGS. 3-7, compared to FIG. 1, as it receives heat from the preconditioning and waxing steps, thereby making its inner faces readily accessible to the molten wax cascade; because the bands 15 are resilient such a feature is possible. The blanks 10 remain on edge or vertically disposed through the wax impregnating method of this invention by means of guide bands 15 as they are subjected to the various processing steps in tunnel 14. The flutes 18 of the blanks 10 are also preferably vertically disposed, i.e., perpendicular to the blanks' line of travel, when the blanks are being processed if up to maximum impregnation of the paperboard is desired, see FIG. 5. Thus the carbon blanks 10 are supported by conveyor 49 for travel through a processing environment in the form of processing tunnel 14 while retaining the blanks in a substantially vertical attitude by group alignment means in the form of bands 15. Although carton blanks 10 are illustrated, other substantially planar articles such as assembled box partitions, cardboard pallets and planar sheets of all shapes and sizes, may also be processed by this method.

After the blanks 10 have been vertically disposed on their bottom edges 11, and positioned between restraining means such as flexible guide bands 15 to form a group 8 thereof, the group is subjected to a preheat step whereat steam is directed upwardly between the spaced, vertically disposed blanks from the bottom edges 11 thereof, see FIG. 3; the steam functions to raise the temperature of the blanks and to provide them with a little additional moisture.

Subsequently, the group 8 of corrugated paperboard box blanks 10 is passed underneath a cascade 21 or free fall of molten wax, the cascade falling in a substantially vertical plane that extends angularly relative to the group's axis of movement through the processing environment and is preferably positioned substantially transverse to the blanks' lines of travel, see FIG. 4. The cascade 21 is of a width to insure contact of the molten wax with all blanks 10 in a group 8. The wax cascade 21, when it contacts the blanks 10, is under substantially free flow conditions as it floods the faces 13, both inner 20 and outer 22, of the blank. Such a free flooding step substantially aids in elminating residual or latent heat in the blanks 10 because such heat is permitted to escape therefrom. Further, when the flutes 18 of the blanks 10 are disposed vertically, i.e., parallel to the cascade 21 of wax, the wax can readily flood the intersticies 24 of the blank between the medium 25 and the liner or faces 13 of the board, thereby permitting maximum penetration of wax into the liners and medium, see FIG. 5. Preferably, the cascade 21 is created by at least one weir 27 full of molten wax 28 which creates a head of the molten wax, the weir being positioned immediately above the top edges 29 of the blanks 10 so as to reduce agitation or splashing or spraying of the wax within the curtains; preferably the weir is no more than about six inches above the widest blank 10 being processed to avoid undesirable splashing of the wax. The weir 27 provides as close to a vertical cascade 21 as is possible when large volumes of wax, e.g., 200 gal./min., must be controlled and provided under very low pressure conditions. Also, the weir 27 is preferred because substantially no spray or splash patterns are created, and because substantially no air is entrapped within the wax cascade 21. Preferably, the wax temperature is on the order of about 170° F.-240° F.; this is a substantially lower temperature than that normally used with the dipping method and allows the final waxed blanks 10 to retain a realtively high degree of moisture, thereby providing a more flexible product with less chance of cracking or bending at score lines. Such a mode of depositing or coating or impregnating wax on corrugated paperboard is indeed novel and unique, and provides a number of advantages which have been discussed heretofor.

After the group 8 of blanks 10 have passed through and underneath the molten wax cascade 21, they are subjected to an initial blast of air 31 from the top edges 29 thereof, see FIG. 6. Such an air blast 31 or air knife is provided substantially immediately downstream of the molten wax cascade and tends to blow the excess wax 32 from the sides or faces 13 of the blanks 10, thereby aiding in controlling the percentage wax pickup. The top air blast 31 permits a lesser percentage wax pickup to be achieved, yet permits wax impregnation to be maintained, than with any other impregnating method. Further, when the flutes are vertically disposed such an air blast 31 also tends to clean out exeess wax 33 from the flutes, see FIG. 5, thereby providing a more efficient process. Thereafter, the blanks are subjected to a slightly elevated temperature, for example, from about 140° F. to about 180° F., for a limited period of time, for example, from about 1 minute to about 15 minutes, which depends on the blanks' throughput rate. The function of this ovenizing or conditioning step is to permit the molten wax 28 to bite into or impregnate the blanks 10. After the conditioning step the blanks are then subjected to a bottom air blast 34 which is directed up against the bottom edges 11 of the carton blanks 10, thereby removing from the blanks 10 any beads or drips of excess wax which have run down the sides or faces of the blanks as those blanks were subjected to the conditioning step, see FIG. 7. Although the air blasts 31, 34 do not insure 100 percent symmetrical distribution of wax coating or wax impregnating of the box blanks, generally speaking such a lack in completely even distribution is beneficial when the bottom flaps 19 of the potential carton are positioned toward the bottom of the blanks' vertical position as processed. This for the reason that it is generally desired to have a higher wax content for the bottom flaps 19 of the carton, as well as toward the bottom of sides 35, and as opposed to top flaps 36, so as to make the ultimate carton as resistant to water from the bottom as possible when it is in final carton configuration. Thus, the graduation of wax distribution of the carton blanks 10 fits the use requirements quite well as highest wax content for strength and for waterproofing is not needed in the top flaps 36 but is beneficial in the vertical side walls 35 and bottom flaps 19.

Whether the blank 10 is wet waxed or dry waxed is regulated by controlling the molten wax temperature and the throughput rate or speed of the blanks 10 through the preconditioning, waxing and conditioning steps. Generally speaking, throughput rate affects the amount of surface wax but does not appreciably affect wax pickup. For example, higher throughput rates result in more surface wax but about the same total wax pickup; this is probably because the higher the throughput rate results in a shorter conditioning time which results in less "soak in" of the wax. With all else constant, the percentage wax pickup will be higher the higher the wax melting point. Thus, the higher the wax temperature and the lower the throughput rate, the higher the degree of wax impregnation to the blanks 10 and the less the surface coating of the corrugated paperboard, and vice versa. For example, with a standard coating wax at a temperature of about 225° F. - 250° F. with a throughput rate of about 3-4 fpm through the cascade and a residence time of about 4 min. - 5 min. in the conditioning section at about 160° F., a standard corrugated paperboard would probably be substantially totally saturated with very little face coating, i.e., would be dry waxed, at approximately a 45 percent by weight wax pickup. On the other hand, at that same wax temperature and at the same wax percentage pickup, but at an increased throughput rate of about six fpm through the cascade and a residence time of about 21/2 minutes in the conditioning section at about 160° F., a standard corrugated paperboard will have substantially less than total saturation and be provided with a good surface coating, i.e., would be wet waxed, at about a 45 percent by weight wax pickup. If the wax temperature is lowered further, the surface coating is increased. Generally speaking, wax impregnated board can be produced within a wax percentage pickup range of about 30 percent to about 60 percent by weight with the method and apparatus of this invention, although it is preferred to operate within about 40 percent to about 50 percent by weight. Further, a tolerance of about 3 percent can be maintained within these ranges.

Once the box blanks 10 pass the bottom air blast 34 they are thereafter cooled to handling temperature, for example, about 120° F. or less, so that the blanks can be handled by an operator and stacked without blocking together. Such a cooling step is accomplished simply by directing cool air from outside the processing tunnel 14 up through the vertically disposed box blanks 10.

THE APPARATUS

The apparatus for carrying out the method of this invention is illustrated in FIGS. 1, 8A, 8B, and 9-19. The apparatus is basically comprised of the processing tunnel 14 with a feed platform 23 and a take-off platform 26. The processing tunnel 14 is provided with a hot section 30 and a cool section 37, the hot section including a preconditioning section 38, a wax application section 39 (which is fed by a hot melt wax system 40), and a conditioning section 41. Typical dimensions may include a tunnel length on the order of 30 ft. with inlet 16 and outlet 17 openings about 8 ft. square, the hot section 30 being about 23 ft. long. A transport system 42 conveys the blanks 10 from the input or front end 16 through the tunnel 14 and out the rear end 17. It will be noted that a number of groups 8 of blanks 10 may be undergoing processing at any one time in the tunnel with the groups, of course, being subjected to different processing steps in different areas of the machine, see FIG. 1.

The tunnel 14 is an enclosed, elongated chamber which is essentially open at each end 16, 17. The feed end 16 of the tunnel 14 and the output end 17 of the tunnel are each provided with a series of upstanding or vertical bars 43 which are part of the transport system 42 and which extend substantially the entire height of the openings, to define a series of slots across the openings 16, 17 at each end of the tunnel, see FIGS. 8A, 8B, 16 and 17. The bars are mounted to the tunnel ceiling 44 at their top and to superstructure which is part of the tunnel floor 45 at their bottom in a manner that permits the distance between bars to be adjusted laterally to provide wider or narrower slots as desired. The series of upstanding bars 43 spaced at intervals across the tunnel openings 16, 17 cooperate with the series of straps or wires or guide bands 15 which run the length of the tunnel 14 and which are held in tension by being wrapped around the bars at each end, note FIGS. 16 and 17, to define the multiple lines of travel for multiple carton blanks 10 (preferably one blank to each line of travel for one group 8 of blanks) through the tunnel. Each pair of bars 43, one at each end 16, 17 of the tunnel 14, is thus provided with at least one, and preferably two or more, continuous wire loops 46 which extend around the ends of the bars. When two or more loops 46 are provided in the same vertical plane (by being looped around the same pair of bars 43 one above the other) the blanks can then be provided with a guide band 15 on each side at the bottom, one or two in the middle, and one at the top to maintain the blanks 10 on edge as they progress through the tunnel, see FIG. 2. At the tunnel's take-off end 17 each loop is provided with tension adjustment means 47. The tension adjustment means 47 includes a fork 48 having tines 78 slidably received about a bar 43, the bands 15 being fixed to the tines by rivets 64. A bolt 79 is threaded in the head of fork 48 and is adapted to engage compression spring 80, the compression spring biasing a stud 91 against the bar 43. Further the forward end of each bar 43 at the tunnel's take-off end 17 is provided with a deflector 70 that prevents blanks 10 from getting hung up on the transverse edge 100 if the bands 15 are not tightly tensioned. Thus, when the bolt 79 is adjusted the tension on straps 15, i.e., on loop 46, extending between vertical bars 43 can also be adjusted. To raise or lower each loop relative to its pair of supporting bars 43, the tension in the loop is relieved and the loop moved to its newly desired position, tension thereafter being returned by tension adjustment means 47.

The wires or straps 15 cooperate to establish a series of lines of travel across the width of the tunnel 14, for maintaining the blanks 10 upright or on edge as they proceed through the tunnel. Thus, at any given point in the tunnel 14 there may be a group of blanks 10 positioned transverse to the axis or machine direction 12 of the tunnel. But, also within any given line of travel there may be multiple blanks 10 positioned one in front of the other to provide a number of groups 8 in process at the same time so that, for example, while one group is being subjected to the waxing step the other may be subjected to the conditioning step, thereby providing optimum leading of the tunnel 14 with blanks 10, see FIG. 1. Further, because of the tension adjustment means 47 associated with the guide straps 15, the straps may be easily adjusted vertically relative to the height of the tunnel 14 so as to efficiently define the lines of travel no matter what height sheet or box blank 10 is being processed. Thus, the bands 15 in cooperation with the series of upstanding vertical bars 43 at each end of the tunnel 14 provide wide flexibility to the apparatus in that it permits the equipment to handle a great variety of paperboard shapes and sizes either at the same time or separately. Further, such multiple shapes or sizes may either be in the same group 8 or end to end within the same line of travel. Thus, substantially any height paperboard up to the height of the tunnel inlet 16 and outlet 17 openings, and substantially any length paperboard, can be handled because of the lines of travel defined by the novel apparatus.

A further part of the transport system 42 is the powered conveyor 49 which includes a conveying plane 50 positioned in the floor 45 of the tunnel 14, see FIGS. 8A and 8B. The conveyor 49 is comprised of a link chain 51 on each side, see FIG. 19, which runs the entire length of the tunnel 14 from the input end 16 to the take-off end 17, and which carries a series of transverse or tie bars 52 interconnecting the two link chains one to the other. The link chains 51 pass about suitable sprockets, not shown, mounted on an idler shaft; not shown, at the take-off end 17 of the tunnel 14, and also pass about suitable sprockets, not shown, mounted on a drive shaft, not shown, at the input end 16 of the tunnel. The drive shaft, not shown, of the conveyor 49 is interconnected with a drive motor, not shown, through a variable speed gear box, not shown, so as to provide the desirable range of transport conveyor speeds. The crossbars 52 of the conveyor, as seen in FIG. 19, are provided with serrations 53 along their lengths and are also burred toward the machine direction so as to assist in gripping the bottom edge 11 of each box blank 10 as it merely rests on top of the conveyor and is not clamped thereto. The transport conveyor 49 preferably is adapted to operate between about 1 fpm and 15 fpm.

The feed platform 23, see FIG. 8A, is provided to arrange a series of blanks 10 in a group before starting them through their respective lines of travel in the tunnel 14. The platform 23 includes a table 191 vertically movable relative to frame 192, the table being guided in its vertical movement by pins 193. The table 191 is moved up and down by turning crank 194 which causes pin 195 fixed to the crank to rotate the eccentric cam 196, the table resting on the cam 196. In use, the table 191 is raised by crank 194 to that level where its top surface 197 is above the conveying plane 50 of conveyor 49. Each blank 10 of a group 8 is then stood on its bottom edges 11 while protruding over a rubber covered take-up roll 198 and the conveyor 49, thereby slightly extending at its leading end into its line of travel defined by bands 15. When a group 8 is established the table 191 is lowered by crank 194 and rubber covered take-up roll 198 draws the group 8 of blanks 10 off the table onto the conveyor 49 (the take-up roll is driven by a chain, not shown, connected to powered conveyor 49).

The take-off platform 26, see FIG. 8B, is provided to receive the impregnated blanks 10 from the output end 17 of the tunnel. The take-off platform includes, immediately adjacent the take-off end, a powered belt 201 driven by a chain 202 from drive motor 203 fixed to the underside thereof. The belt 201 moves around drums 204 at each end. The belt 201 also cooperates with table 205 of the platform 26 to deliver the blanks 10 to the table from the apparatus. In use, as the blanks 10 reach the end of the powered conveyor 49 they are simply picked up by belt 201, which moves at the same rate as conveyor 49, and extracted completely from the processing tunnel 14.

The processing tunnel 14 itself basically includes the top 44, two sides 54, and the floor or bottom 45. The floor of the processing tunnel 14, as far as the blanks 10 are concerned, is comprised of the conveying plane 50 of the chain bar conveyor 49. However, the chain bar conveyor 49, and the lines of travel defined by the tension straps 15, do not extend the entire width of the tunnel 14, note FIG. 9. On either side of the conveyor 49 and lines of travel, there is provided a walkway 55 between the conveyor 49 and the side walls 54 of the tunnel 14 which extends the entire length of the tunnel. The walkway 55 is supported by suitable angle members 56 positioned therebeneath which are fixed to channel members 57 extending below the bottom 44 of the tunnel. Within that area defined by the depth of the channel members 57, i.e., below the conveying plane 50 of the transport conveyor 49, there is provided a wax drip pan 58 that extends substantially the entire length of the tunnel 14, and a cooling air discharge plenum 59 that is positioned only in the cool section 37 of the tunnel 14, see FIGS. 8A, 8B, 9, 13 and 15. The cooling air plenum 59 is positioned between the wax drip pan 58 and the conveying plane 50 of the transport conveyor 49, see FIGS. 8B, 15 and 18. Beneath the wax drip pan 58 along the entire length thereof there is provided a series of steam coils 61 fed by a steam source, not shown, so as to maintain the wax in that pan 58 molten to permit recycling through the hot melt system 40. The wax pan 58 is also provided with a drain outlet 62 in one side thereof adjacent to the waxing section 39 of the processing tunnel 14, see FIG. 8A. Basically, the wax pan 58 is configured to drain toward that outlet 62 as from that point the wax is recycled through the hot melt system 40. Thus, the wax pan 58 is supported by the channel 57 depending from beneath floor 44, the walkways 55 and the wax pan extending from the inlet end 16 to the outlet end 17 of the tunnel. Further, it will be noted that the return plane 63 of the transport conveyor 49 runs along the bottom of and within the wax pan 58, thereby running through molten wax. This helps to keep the conveyor's crossbars 52 at operating temperatures to prevent undue chilling of the blanks' bottom edges 11. Also, the wax pan 58 serves not only to receive drippings from the blanks 10 as they pass through the tunnel 14, as well as excess from the waxing section 39, but the molten wax therein also serves as a major source of heat to warm the environment within the tunnel's hot section 30 to that temperature level desired.

The inlet end 16 of the tunnel 14 is provided with a roll door 65 fixed to the top 44 of the housing, see FIG. 8A. The roll door 65 is adapted to be pulled down from its own housing 66 until the lower edge 67 is positioned at the height desired above transport conveyor's conveying plane 50. In use, the roll door 65 will preferably be pulled down until the bottom edge 67 thereof is just a couple of inches above the top edge of the blanks 10 being processed. Further, the inlet end 16 of the tunnel 14 is provided with an air door 68 comprised of a fan 69 fixed to the housing's ceiling 44 within the tunnel 14, and which is interconnected by conduit 71 with a plenum 72 which extends across the tunnel's mouth and is also fixed to the housing's ceiling. The plenum 72 is provided with a series of air intakes along its width, and is provided to aid in maintaining environmental temperature conditions within the tunnel, i.e., to prevent substantial cold air from entering with each group 8 of blanks 10. The output end 73 of fan 69 is connected by flexible conduit 74 to top air knife 75, the top air knife's function being explained subsequently.

The preconditioning section 38 of the tunnel 14 is comprised of a steam manifold 76 fixed to steam pipes 77 that extend transversely of the apparatus' machine direction 12, see FIG. 8A. The steam pipes 77 are positioned underneath the transport conveyor's conveying plane 50 and are provided with suitable nozzles to direct steam against the bottom edges 11 of the blanks and up through the vertically positioned blanks as they come through the inlet end 16 of the tunnel 14. The main function of such a preconditioning is to quickly get the blanks 10 to temperature whereat the molten wax can most efficiently impregnate same.

The waxing section 39 is immediately downstream of the preconditioning section 38 in the processing tunnel 14. The waxing section is basically comprised of two weirs 27 which are fixed between parallel sides 81, see FIGS. 8A and 9-11. The downstream end of the sides 81 mounts a top air knife 75 that is connected by flexible conduit 74 with the output end 73 of fan 69. The air knife 75 and the weirs 27 extend transverse to the tunnel's axis 12, and the weirs and the air knife are each of the length substantially equal to or greater than the width of the transport conveyor's conveying plane 50. The weirs 27 are fed with molten wax from the hot melt system 40 by a feed conduit 82 which terminates in separate weir pipes 83 positioned adjacent the weir bottoms.

The top air knife 75 is simply a tubular manifold extending between the side plates 81 that defines a slit 116 in the bottom thereof running axially of the manifold. The weirs 27 and air knife 75, being mounted between sides 81, are vertically adjustable relative to the height of the processing tunnel 14 because of their mounting structure 84, see particularly FIGS. 9-11. The side plates 81 mounting the weirs are each provided with a roller 85 at each end, the rollers being adapted to cooperate with vertical struts 86, 87 positioned toward the front of the leading weir and toward the rear of the trailing weir, respectively. Thus, as the weirs 27 and air knife 75 are adjusted vertically they are guided in their vertical movement, and prevented from undue cocking, by means of rollers 85 which cooperate with the other edges of each pair of vertical struts 86, 87. The apparatus for moving the weirs and air knife vertically includes two weights 88, one disposed on each side of the tunnel 14 and each of which is carried by a pair of chains 89 fixed at one end to side plate 81, as at 90. The chains 89 pass up and over sprockets 92 carried on idler shaft 93, the shaft 93 being mounted by bearings 94 to suitable support members 95 at the top of the tunnel's housing.

The weirs 27 and air knife 75 are raised and lowered by means of drive motor 96 mounted on top of the tunnel's ceiling 44. The drive motor shaft 97 is connected with an idler shaft 98 by means of chain 99 and sprockets 101, 102, see FIGS. 9-11. The idler shaft 98 mounts an intermediate sprocket 103 which is interconnected with weir drive shaft 104 by chain 105 and sprocket 106. Weir drive shaft 104 mounts a sprocket 107 on each side of the weirs 27 which is disposed to cooperate with a drive chain 108 positioned on each side of the weirs 27, see FIG. 9. Further, an idler sprocket 109 is mounted at floor level 45 of the housing on each side of the weirs 27, each sprocket 109 cooperating with a drive chain 108. Each drive chain 108 is an open loop chain which is fixed at end 111 to a side plate 81 by finger 112, and is also fixed at other end 113 to a weir side plate 81 by finger 114. Thus, as weir drive sprockets 107 are rotated through the sprocket train 101, 102, 103, 106 from drive motor 96, the drive chains 108 are caused to move clockwise or counterclockwise (see FIGS. 9 and 10) in loops about sprockets 107, 109, thereby raising or lowering the weirs 27 and top air knife 75 fixed between side plates 81. The weights 88 permit use of a smaller drive motor 96 to lift and lower the weirs 27 and top air knife as desired, and also permit the weirs and top air knife to settle gently toward the bottom or floor 45 of the tunnel 14 if the drive chain 108 should happen to break.

Each weir 27 is preferably configured in channel form with an outwardly protruding lip 117 on each edge thereof. The weirs 27 are preferably sized to meter about 180 to 200 gal./min. As the molten wax is fed into the weir 27 it fills up the channel and overflows over the lips 117 at the top of the channel in free fall or cascade fashion down over the top edges 29, downwardly on the faces of and between the blanks 10 passing therebeneath on transport conveyor 49. Because the weirs 27 and top air knife 75 are adjustable vertically relative to the blanks 10, and because the conveying plane 50 of the transport conveyor 49 is in a substantially constant horizontal plane, the weirs 27 and top air knife 75 may be raised or lowered as desired depending on the width of the blanks 10 being processed (which blanks 10 are, of course, being processed on edge). Such an adjustability feature is quite advantageous in that it reduces the turbulence in the molten wax cascade such as might be created if the weirs 27 were positioned too far above the top edges 29 of the blanks 10, thereby preventing substantial splashing of the molten wax as it passes downward between the vertically disposed blanks which splashing and spraying has been found to be undesirable. The bands or wires 15 which define the lines of travel do not break up this vertical flow of molten wax, either, because of their sharp edges on top. Further, the vertical adjustability feature permits the air knife 75 to be positioned immediately above the top edge 29 of the vertically disposed blanks 10 and allows it to perform in a more efficient manner in its function which, as mentioned, is to blow off excess wax from the outer and inner surfaces or faces of the blanks 10 and, if the corrugated board flutes are disposed vertically, to blow out excess wax from within the flutes. Preferably the air knife may function with about 500 cfm.

The conditioning section 41 is positioned immediately downstream of the waxing section 39 and, with the preconditioning section 38 and waxing section 39, forms the hot section 30 of the tunnel, see FIGS. 8A and 8B. The conditioning section 41 basically provides an open tunnel environment at an elevated temperature for an extended conveyor run to allow impregnation of the molten wax into the blanks 10 to occur. In this conditioning section 41 the hot air is just recirculated with an even distribution of air pickup being provided throughout the length and width of the section by means of air discharge occuring at floor 45 level throughout the section. Further, such a recirculatory hot air system is preferred so that hot air is not blown directly onto the board so that the board does not dry out, i.e., lose moisture, such a moisture loss causing cracking in the final coated blanks 10.

Hot air is essentially recycled within this conditioning section 41 by means of a fan 118 positioned at each side adjacent the tunnel's ceiling 44 and inside the housing. The input end 119 of each fan 118 communicates with an intake plenum 121 fixed to the inside ceiling of the tunnel and discharge plenums 122 communicate with the outlet end 123 of the fans 118 through distributing chamber 124. The intake plenum 121 extends the width of the transport conveyor 49 and is provided with a series of slots 126 having downwardly angulated lips 127 which are angled downstream of the machine direction 12. The intake plenum 121 extends between the waxing section 39 and the cooling section 37, as illustrated in FIGS. 8A, 8B.

There is a discharge plenum 122 on each side of the tunnel 14. The discharge plenums 122 are positioned along floor 45 to discharge hot air at floor level through orifices 125 along the entire length of the tunnel's hot section 30 from the input end 16 to the cooling section 37, see FIGS. 8A and 8B. The discharge plenums 122 are connected with fans 118 by the distributor plenums 124, as mentioned, and the distributor plenums are fixed to side walls 54 of the tunnel 14. The fans 118 are mounted above the walkways 55 on each side of the processing tunnel by brackets 131 fixed to ceiling 44, each fan being interconnected with a separate drive motor 132 mounted to the outside of the tunnel housing's sides 54. Within the discharge plenums 122 there is provided a series of heat fins 134 mounted on a steam pipe 135, the steam pipe being interconnected with a high temperature steam source, not shown. The fins 134 and pipe 135 extend substantially the entire length of discharge plenums 122, see FIGS. 8A and 8B, and are positioned adjacent the orifices 125 of those plenums. Preferably, the air recirculatory fans 118 in the conditioning section 41 are able to transmit on the order of about 8,000 cfm.

At the end of the conditioning section 41 there is provided another fan 138 mounted toward the tunnel's ceiling 44 see FIG. 8B. The outlet of fan 138 is interconnected by conduit 137 with a bottom air knife 139 positioned beneath the conveying plane 50 of conveyor 49, i.e., beneath bottom edges 11 of the blanks 10 as they are transferred thereover by the transport conveyor. The bottom air knife 139 is similar to the top air knife 75 in that it is simply a tubular chamber provided with a slot 141 in its surface which directs the air against the blanks' bottom edges 11. The bottom air knife 139 serves to remove drips or beads of wax at the blanks' bottom edge as well as to clean out the bottoms of the flutes 18 if the flutes are vertically disposed. It will be noted that the bottom air knife 139 is angulated relative to the conveying axis 12 of the transport conveyor 49 and this for the reason to prevent undue vibration and noise in the boards as caused by the high velocity directed air. The bottom air knife 139 cooperates with an air pickup plenum 143 positioned transverse to the axis 12 of the transport conveyor 49 and mounted between tunnel sides 54 along the ceiling of the processing tunnel 14. The pickup plenum 143 is connected with the inlet of fan 138 through conduit 144. The bottom air knife 139 and the pickup plenum 143 cooperate together to form an effective air curtain between the hot section 30 of the tunnel 14 and the cooling section 37 of the tunnel.

As is illustrated in FIGS. 8B and 14, the hot section 30 of the apparatus may be partially closed off from the cool section 37 of the apparatus by means of a dropleaf door 151 hinged to provide three sections 152, the top section 152 being hinged, as at 153, to a top panel 154 extending downwardly from and fixed to the processing tunnel's ceiling 44. The dropleaf door 151 may be adjusted to three different heights simply by changing the configuration of the door, thereby providing a height adjustable door which can be raised or lowered as desired depending on the width of the blanks 10 (the blanks standing on edge) being processed. It is preferred to maintain a minimum clearance between the top edges 29 of the blanks 10 and the bottom edge 150 of the door to preclude undue movement of hot air into the cooling section 37 from the hot section 30 and cool air into the hot section 30 from the cooling section 37. The walkways 55 on both sides of the tunnel are closed by doors 161 hinged as at 162 to vertical supports 163 to further establish definiation between the hot 30 and cool 37 sections at this point in the processing tunnel.

The cooling section 37, below floor level, is provided with a series of air diffuser elements 155, note FIG. 18, which are positioned transverse to the axis of the transport conveyor 49. The air diffuser elements 155 are angulated to open upward and are mounted between sides 156 of an air pan 157, the pan 157 and elements 155 cooperating to form the cooling air discharge plenum 59. The air pan 157 itself is mounted on top of sides 158 of the wax pan 58, and, thereby, separates the molten wax in the wax pan as it extends underneath the cooling section from the cooler air in the cooling section 37 when the cooling section is being used to cool the blanks 10.

As is illustrated in FIGS. 8B and 15, the cooling section 37 is basically comprised of an air input plenum 164 on each side thereof which accepts air from and communicates with, the atmospheric environment outside the processing tunnel 14. Within each air plenum 164, which extends substantially the entire length of the cooling section 37, there are positioned two blower fans 165 that pull in the air from outside and direct it down through a distributor plenum 166 fixed to the interior of the housing's side walls. The distributor plenums 166 are also of a length substantially equal to the length of the cooling section 37 and communicate at their bottom end, through elongated openings 167, with the cooling air discharge plenum 59. The diffusers 155 function to distribute the cool air equally throughout the cooling section 37 so as to provide adequate air flow contact up through the blanks 10 as the blanks pass through the cooling section.

Within the distributor plenums 166 on each side wall 54 of the cooling section 37 there is provided a humidity control means in the form of water spray heads 178 connected to a water source, not shown, which exhaust a fine water spray to raise the relative humidity of the cooling air contacting each group 8 of blanks 10. Such humid cool air tends to restore some of the moisture level in the blanks 10 lost through its processing in the hot section 30 of the apparatus.

In the ceiling of the cooling section 37 there is provided a centrally located discharge fan 168 which is mounted on struts 169 between sides of a faring 171. The fan 168 is driven by motor 172 through belt 173. Louvers 174 are positioned in the exhaust path of the fan 168 so the fan can only exhaust air from the cooling section and so no outside air is accessible to the cooling section when it is desired to close off that section. A screen 175 is positioned above the fan 168 so as to preclude debris from falling into the cooling section 37. Thus, the fan 168 draws air directly out from the cool section through the ceiling of the processing tunnel 14 into the environment surrounding the tunnel; the normal air flow pattern 176 in the cooling section is as illustrated in FIG. 8B. Preferably the fans 165, 168 in the cooling section 37 are able to move about 20,000 cfm.

It is highly preferred that a static, slightly negative pressure be maintained throughout the processing tunnel 14 during its use. This for the reason that a hot section 30 and a cool section 37 are within the same processing tunnel and it is easier to maintain a pressure equlibrium between such sections at slightly negative pressures than at slightly positive pressures. A pressure equilibrium must be established so that hot air does not flow into the cooling section 37 from the hot section 30 and so that cool air does not flow into the hot section from the cooling section. To aid in keeping hot air out of cooling section 37, and vice versa, there is provided the air curtain created by bottom air knife 139 and plenum 143.

As the hot blanks 10 exit from the hot section 30 of the apparatus and pass through the cool section 37 of the apparatus, oftentimes wax drips off the lower edges 11 of the blanks an is caught by the air diffuser elements 155 as well as in the air pan 157. After a prolonged run of the machine it oftentimes becomes necessary and desirable to clean out these structural elements and this is accomplished by first closing the roll doors 65, 180 at the ends 16, 17 of the apparatus and raising the dropleaf door 151 to make the entire tunnel one long hot section. Thereafter the inlets have their air supply shut off by closing a damper 182 (FIG. 8B) in the air supply duct to the air plenums 164 on each side of the cooling section and a slide damper 183 (FIG. 15) over exhaust fan 168 is closed, thereby completely sealing the tunnel from its outside environment. Subsequently, the doors 181 on each of the inlet air plenums 164 associated with fans 165 is tilted to the open position, see phantom lines of FIG. 15, and the fans 165 are energized, thereby providing an interior recirculation path within the cool section 37 as illustrated in phantom lines in FIG. 15. At this point, hot steam is interjected into the bottom of each distributor plenum 166 through side 184 of T-fittings 185, thereby creating a steam environment within the cooling section 37. Such a steam environment, accompanied by the heat from the molten wax in wax pan 58 positioned beneath the cool air discharge plenum 59, causes the wax in the air diffuser to melt and run through holes 186 at each end of each air diffuser element 155 (FIG. 18) and into the air pan 157. Any wax and condensation in the air pan, the wax therein now being in the molten state, then runs out drain ports 187 of T-fittings 185.

At the outlet end 17 of the cooling section 37 there is provided a roll door 180 mounted to the top of and outside of the tunnel's housing, the roll door 180 being housed in housing 179. This rear roll door 180 is also height adjustable and is preferably positionable immediately above the top edge 29 of the blanks 10 as they exit from the tunnel 14 so as to disturb the air equilibrium conditions within the tunnel as little as possible.

The hot melt system 40 utilized with the apparatus of this invention is illustrated in FIG. 12. The hot melt system 40 includes the wax pan 58 and the weirs 27, the weirs discharging the molten wax into a free falling cascade or free fall type flow over the top edges 29 of the blanks 10 into the wax pan. From the wax pan 58 the molten wax is recycled through a coarse particle filter into a minor reservoir. The minor reservoir is maintained at a preselected level from a large reservoir which, of course, provides the main source of wax supply. The minor reservoir maintains the volume of molten wax in process at a predetermined level and compensates for loss of wax through impregnation on the blanks 10 being processed. The wax in the minor reservoir is maintained in a preselected temperature level by a heater, and is subsequently cycled through a fine particle filter by pump P, driven by electric motor EM, into the weirs.

While the method and apparatus of this invention is particularly adapted to the coating and/or impregnating of substantially planar articles, it may also be used to process extended length articles where the cross-section thereof is other than substantially planar, for example, where the cross section is angular as in the case of angulated corrugated paperboard which may be used to protect edges and corners of e.g., a desk, during transit. In such use the elongated member is aligned parallel to the axis 12 of the processing tunnel 14 and is disposed on the transport conveyor 49 in tent-like fashion. Thereafter the member is subjected to the same process steps as discussed above. The undercut surfaces of the angular member, as it lies on the transport conveyor 49, may be coated with molten wax by spray heads, not shown, located beneath the conveying plane 50 of the transport conveyor which directs a molten wax spray up against the underside of the angular member.