US3668369A

US3668369A - Heat sealing apparatus for closure of paperboard package flaps

Info

Publication number: US3668369A
Application number: US54079A
Authority: US
Inventors: William J Howe
Original assignee: Georgia Pacific LLC
Current assignee: Georgia Pacific LLC
Priority date: 1970-06-02
Filing date: 1970-06-02
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06

Abstract

Apparatus for heat-sealing paperboard package closure flaps having a heat sealable coating. While the package moves, two flaps are brought into proximity along two planes diverging at an acute angle, and upon the facing flap surfaces, are impinged one or more high-volume, low-velocity streams of very hot air, each along a controlled narrow area to heat one or more critical strips of each flap above the heat-sealing temperature.

Description

Howe

[ 1 June 6, 1972 HEAT SEALING APPARATUS FOR CLOSURE OF PAPERBOARD PACKAGE FLAPS Inventor: William J. Howe, Los Altos, Calif. Assignee: Georgia-Pacliic Corporation, Portland,

Oreg.

Filed: June 2, 1970 Appl. No.: 54,079

Related US. Application Data Division of sei. No. 795,786, Feb. 3, I969, abandoned, which is'a continuation-in-part of Ser. No.

' 696,794, Jan. l0, I968, abandoned.

[56] References Cited UNITED STATES PATENTS 3,509,68l 5/1970 Sass ..53/3 75 X 3,340,777 9/ I967 l-littenberger et al. ..53/375 X 3,249,024 5/ l 966 Shiu .93/36 Primary Examiner-C. L. Albritton Attorney-Owen, Wickersham & Erickson [57] ABSTRACT Apparatus for heat-sealing paperboard package closure flaps having a heat scalable coating. While the package moves, two flaps are brought into proximity along two planes diverging at an acute angle, and upon the facing flap surfaces, are imp- 'inged one or more high-volume, low-velocity streams of very U.S. Cl. ..219/243,53/375, 22l9/374, hot air each along a controlled narrow area to heat one or 19/375 more critical strips of each flap above the heat-sealing temlnt. CI. ..H05b 1/00 peramm Field of Search ..2l9/243, 374, 375; 53/375,

53/387, 388 11 Claims, 16 Drawing Figures AMBIENT AIR 1 2 '57 AMBIENT AIR PATENTEDJUH 6 I972 SHEEI 2 OF 3 FlG 2 Q /O OOO R m o wmww J M m. f w M a O- Q m G F g FlG ll ATTORNEYS PATENTEnJun sum 3,668,369

sum 30F a Rik 76 mm 7 77 I l I02 FIG..14

INVENTOR. WILLIAM J. HOWE FlG 15 ATTORNEYS HEAT SEALING APPARATUS FOR CLOSURE OF PAPERBOARD PACKAGE FLAPS This application is a division of application Ser. No.

795,786, filed Feb. 3, 1969 (now abandoned in favor of streamline continuation Ser. No. 101,126, filed Dec. 23, 1970), which was a continuation-in-part of application Ser. No. 696,794, filed Jan. 10, 1968 now abandoned. This invention relates to improvements in apparatus for heat-sealing paperboard packages and the like. It relates to a novel heating apparatus and a novel manifold for emitting hot air against a pair of package flaps that are to be scaled together.

Paperboard packages often have their flaps provided with heat-scalable (usually thermoplastic) coatings which are heated, and then the package is closed and sealed by forcing the heated flaps together and holding them together until the heat scalable material is cooled sufficiently to provide a tight seal. I-Ieretofore, there have been difficulties to accomplishing this heat-sealing operation efiiciently without damaging the carton or marring its outside surface coating, and, as a result, apparatus for accomplishing it automatically has tended to be very expensive. Also, whenpackaging frozen goods, it has often been difficult to employ heat sealing without damaging the goods themselves by subjecting them to too much heat. Further, prior art apparatus is not readily adjustable to changes in types of coatings or to speed changes in packaging machinery. A feature of the present invention is that relatively simple apparatus costing only about one-tenth or one-twentieth as muchas comparable prior-art apparatus can do the job efficiently and well, without any damage to the frozen contentsinsi'cle the package or to the package itself, and can do so in a verysirnpleand foolproof manner. Installation costs and maintenance costs are much lower, too, and changes in coating types or in the speed of the packaging machinery are readily made.

Some of the better prior-art systems have required special air driersfor drying the air before it is heated, because moist air damages their heater elements, and they have required a supplemental air-compressor system in addition to the normal compressed air system of the packaging plant. The present invention operates without any special driers and uses normal plant' compressed air. No supplemental system is needed. In fact, my 'new system uses much less air than do the prior-art systems.- I

An important feature of the invention is the provision of a manifold and heater system in which heated air'at high temperature is evenly distributed at low-velocity and high-volume over a relatively short distance to quickly heat the plastic coating on the flaps to the temperature at which it becomes tacky or otherwise heat sealable. The present invention does this in a single manifold without necessarily having separate compartments in the manifold. An even flow of air throughout the manifold is provided by spacing the discharge holes to balance the naturally uneven input to those holes. At the holes, the manifold is independently positioned away from the flaps to enable flow of air. Also, by using separately controlled multiple heaters the system (with or without a partition in the manifold) can be used to provide a different temperature at one end or one portion of the manifold than at another end or portion thereof for quick adaptability to various coating types and machine speeds. I

The heater housings of the invention prewarm and predry ambient air without any supplemental warmers or driers being required, and they provide a swirl-type of air flow through the double jacket in the first two of the three passes through the heater, thereby getting the greatest efficiency in air heating. Also, less heat is lost between the heaters discharge into the manifold and the manifold discharge than is lost in conventional apparatus, partly because the outlet from the heater elements is large and located quite close to the manifoldss discharge openings and partly because of the low velocity of the heated air, a major feature of this system. As a result, the

device uses less wattage than conventional systems and wastes less heat.

In this invention no insulation of any kind is needed over or around the heater housings, yet their outer walls are actually barely warm to the touch, although extremely hot air (typically 1,000 to 1,200" F) is sent from the heaters into the manifolds. It is the only system in use today without insulation.

Another feature of the invention is that the air stream flow from the manifolds is designedto contact the flaps only where it is needed and not over their full surfaces. The low velocity of the air stream helps here. The flaps do not touch the manifold while they are being heated, and when they are being cooled, they do not require back-up pressure.

This invention employs much less air than conventional systems and uses it efiiciently at the flaps and at low velocity; so it does not inflate the packages, as do many prior-art systems, and as a result, there is no time and space wasted in waiting for packages to deflate before packing them in cases. Also, no temperature correction of the product is necessary and there is no product deterioration.

To summarize theinvention briefly, the apparatus includes a hot air manifold having two surfaces meeting at a sharp acute angle, each such surface having at least one row of openings along it for emitting the heated air. These openings are positioned away from the flaps, so that the air can move away. A novel air heater connected to the manifold comprises a long slim cylindrical ceramic heater with a plurality of circumferentially spaced long air passages, an inner shell surrounding and against the outer wall of the ceramic heater. Around the inner shell and spaced from it to provide a passage is an intermediate shell, and an outer housing surrounds the intermediate shell and is spaced from it to provide a passage; this outer housing has a tangential air inlet. Hence, the air gets three passages through the heater. The ends of the intermediate shell and outer housing are closed, while the ceramic heater is connected directly to the manifold at one end and is s aced at its other end from the closed end of the intermediate shell. The intermediate shell has aperture means at the end opposite the inlet, so that air entering the tangential inlet is swirled between the outer housing and the intermediate shell for its first passage, then goes through the aperture in the intermediate shell and is swirled around the inner shell in its second passage, goes through the heating passages in the ceramic heater for its third passage, and then enters the manifold through a large outlet. At the manifold the outlet holes are so spaced that the air flow is longitudinally even, and thearea of the air flow is balanced to the area of the inlet so that no excess pressure is generated by the expansion of heated air and so that the outlet holes supply the air at the same low velocity as that of the entering air.

Other objects and advantages of the invention will appear from the following description of some preferred embodiments.

In the drawings:

FIG. 1 is a fragmentary top plan view of a package closure system of this invention, including a conveyor system along which paperboard cartons (which may contain frozen food or any other contents) are moved through the flap-heating and heat-sealing stages, which embody the principles of the invention.

FIG. 2 is an enlarged view in section taken along the line 22 in FIG. 1.

FIG. 3 is an enlarged view in section taken 33 in FIG. 1.

FIG. 4 is an enlarged view in side elevation taken line 44 in FIG. 1.

FIG. 5 is a view in section taken along the line 5-5 in FIG. 4.

FIG. 6 is a view of aportion of FIG. 5, shown with holding along the I rollers bearing against the outer major carton flaps to hold it closed against the inner major flap, during cooling and congealing of the heat-sealing coating.

FIG. 7 is an enlarged view in elevation and in section taken along the line 7-7 in FIG. 1 showingthe air heating of the coating on the outer major and inner major flaps by a manifold of this invention.

along the line FIG. 8 is an enlarged view takenin section along the line 88 in FIG. 1, showing closure of the heated flaps of FIG. 7.

FIG. 9 is a view taken along the line 9-9 in FIG. 2, showing the structure of the air heater.

FIG. 10 is a view in perspective of a double manifold unit of the invention, used for closure of wide flap systems with overlap.

FIG. 11 is a fragmentary view in section taken along the line 11-11 in FIG. 10.

FIG. 12 is a fragmentary view in section of a modified form of manifold also embodying the principles of the invention,

j'employing a somewhat different shape and two double rows of discharge openings.

FIG. 13 is a view similar to FIG. 5 of closing rollers for use with the manifold of FIG. 12.

FIG. 14 is a similar view of another form of closure device for bearing on four areas of the closure flaps.

FIG. 15 is a front elevational view of another modified form of manifold having slots and flow-enabling recesses, with a portion cutaway to show the rear wall.

. FIG. 16 is an enlarged fragmentary view in section taken I along the line'l6-16 in FIG. 15. As shown in FIG. 1, a paperboard carton 20 is moved along a conveyor 21. The carton 20 has outer major flaps 22 and 22a and inner

major flaps

23 and 23a. These

flaps

22, 22a and 23, 23a are to be closed against each other and sealed. At least one of the

flaps

22 and 23 has been coated on one of the two facing surfaces 24 and 25 (FIG. 7) with a suitable thermoplastic or other material enabling heat sealing. Often both flaps are so coated. For example only, a frozen food product, such as a pie, may have been placed inside the carton 20, and the .operation is to be conducted without in any way overheating that frozen food product or marring the outer surface of the carton. On each side of the package, the closure is'to be accomplished simultaneously, in order to maintain alignment of the carton 20, so that there are duplicate apparatus, one on each side of the conveyor 21, comprising identical flap-

heating units

26 and 27 and identical flap-closing

units

28 and 29.

A narrow plow 30 precedes each

heating unit

26 and 27 and bends the inner major flap 23 up to perpendicular position at the end of the carton 20, and a rod plow 31'then bends the outer major flap 22 over to a suitable acute angle, as shown in FIG. 7, as the carton 20 approaches the

heating unit

26 or 27.

The

plows

30 and 31 immediately precede and continue alongside of a manifold 32 and are made so that they correctly position the

flaps

22 and 23 but are not themselves subject to heat build-up when no'carton is running through the machine; they stay cool while the machine runs empty. The manifold 32 is a very important element of each

heating unit

26, 27 of the invention, and each manifold 32 is provided with at least one or more heaters; in the embodiment shown in the drawings there are a pair of

such heaters

33 and 34. The manifold 32 emits very hot (e.g., l,000 to l,200 F.) air at high volume and at low velocity; this air heats the plastic coating of certain narrow areas on the flaps 22 and 23'above the temperature where the coating becomes tacky, and then the outer major flap 22 is closed against the inner major flap 23 by a closing roller 35 or a plow and is held closed against it under pressure by the

closure system

28 or 29, while cool air is blown against the carton 20 and flaps 22 and 23 from a cool-air manifold 36.

All these will be now discussed in more detail.

In the form of the invention shown in FIGS. 1-11 each hotair manifold 32 is provided with two walls and 41 meeting at a vertex 42 of a sharp acute angle. This makes it possible to bring the flap 22 close to the flap 23 at the manifold 32. Each

wall

40 and 41 is provided at suitable locations with a row of

discharge openings

43 and 44 at different distances from the vertex 42 and not opposite each other, to assure correct overlap of the heated areas in the flaps. As shown in FIGS. 2 and 7, the heated air through the

openings

43 and 44 is directed against the

flaps

22 and 23, the inner major flap 23 being perpendicular to its main carton walls, while the outer major flap 22 is at an acute angle, as set by the plow 31 and held in position, as by a rod 37, the resistance of the flap 22 to folding keeps it against the rod 37 without any spacing member having to be between the

flaps

22 and 23. The manifold 32 may be generally triangular in cross section, as shown in FIGS. 2 and 7, with a third generally vertical wall 45 provided with one or

more openings

46 and 47 to receive the output from the

heater units

33 and 34; in this instance two

heater units

33 and 34 are shown, but there may be only one heater or there may be more than two. Thelength of the manifold 32 depends partly on. the number of heaters and partly on the speed of the conveyor. For packaging closure it may be about 3 to 8 inches long, typically, but may be longer; for providing a manufacturers joint at very high speeds, it may be a couple of feet long, e.g., 16 to 48 inches long for a speed of 1,200 feet per minute.

As shown in FIG. 3, the openings 43 leading from the manifold 32 are spaced apart, not evenly but in a pattern which gives an even distribution of the discharge air, and the openings 44 are similarly spaced, so that the container flaps 22 and 23 are properly heated within a'very short travel, a few inches travel only. As shown in FIG. 7, the

manifold walls

40 and 41 are spaced from and lie at an angle to the flap surfaces 24 and 25 which they are to heat, thereby spacing the manifold from the flap surface 25 in the vicinity of the openings 44, to enable flow of air, and only a

small area

48, 49 of each

flap surface

24, 25 is heated. The total area of the

openings

43 and 44 is made sufiicient to give high-volume, low-velocity air flow, so that the hot air impinges against the flap surfaces 43, 44 to heat them without causing high velocity in toward the vertex 42 and sending air. into the inside of the package being closed. Also, the

openings

43 and 44 are not spaced the same distance from the vertex 42 but are instead spaced toimpinge with flaps at areas '48 and 49 that lie at the same distance from where the flaps 23 and '24 meet; this means that the openings 43 lie closer to the vertex 42 than do the openings 44, and it means that very

narrow areas

48 and 49 can be heated and the heat confined to them, since they will mate accurately.

As shown especiailyin FIGS. 2, 3, and 9, each

heater unit

33 or 34 comprises an outer metal housing 50, an intermediate" metal shell 51, and a ceramic heater 52 with a close-fitting metal inner shell 53 around the outer circumference of the heater 52. The housing 50, intermediate shell 51, and inner shell 52 are all cylindrical tubes and are radially spaced from each other to provide cylindrical

annular passages

54 and 55 on each side of the intermediate shell 51. The outer housing 50 is provided with an inlet 56 leading generally tangentially into it adjacent the end distance from the manifold 32, to induce swirling of the air around the intermediate shell 51. A suitable air supply tube 57 supplies ambient air under low pressure to the inlet 56. A pair of

end closure members

58, and 59 connect the outer housing 50 to the intermediate shell 51, the member 58 closer to the manifold 32 being also used to provide spacing, not only between the intermediate shell 51 and housing 50 but also between the intermediate shell 51 and the inner shell 52 and also a connection fitting 60 to the

manifold opening

46 or 47. The intermediate shell 51 is thus fully supported at both ends, to maintain accurate spacing and prevent movement during operation, and it is provided with an outer and closure member 61 through which may extend an electrical power line 62 for the heater 53. The ceramic member 53 and its outer sheath, the shell 52, is held and spaced away from the intermediate shell 51 by the member 58 and by spacing and supporting screws 63. Thus, there is an outer swirl passage 54 between the housing 50 and the shell 51, an inner swirl passage 55 between the shell 51 and the shell 52, and there is a plurality of straight-flow passages 64, each containing a helical heater element 65, running through the ceramic heater 53. The heating elements 65 extend the length of the ceramic body 53, and provide intense air heating for the air passing through the passages 64, which are the only airflow passages through the heater 53. What appears to be a cylindrical passage 66 is blocked intentionally and merely serves to lessen the amount of ceramic body.

with resultant forcing of the air to retain the flaps in their closed Asa result of this structure, air enters tangentially through the inlet 56 and swirls around in the first passage 54, going toward the manifold 32. Near the end wall 58 closest to the manifold 32 it passes through a slot or other aperture or apertures 67 in the shell 51 and then swirls back inside the second passage 55 to the opposite end 61 most distance from the manifold 32. Then it turns in and goes by the space 68 in through the plurality of third passages 64 and from there directly into the manifold 32 through the opening 47, which is the full size of the heater 53, so that there is no restriction between the heater 53 and the manifold 32 but rather an enlargement there. In the manifold 32 it goes up and goes out the two series of

discharge openings

43 and 44 impinging upon the thermoplastic coated

flaps

22 and 23 as shown in FIG. 7. The accumulated total of the areas of the

openings

43 and 44 in the manifold 32 is about 1 percent of the accumulated open cross-sectional area of the passages 64 through the heater 53. This enables a rise in ambient air temperature to about 1,000 to 1,150 F. to take place without increasing the velocity of the heated air. The purpose is to send a volume of hot air at low velocity through the

openings

43 and 44 and against the

areas

48 and 49, rather than to send high-velocity air through them unwanted places and and unwanted rapidity in the cooling of the air. The velocity of the air issuing from the

openings

43 and 44 is actually lower than that going into the inlet 56. It has been found that this system heats the

flaps

22 and 23 quite rapidly to a temperature enabling their closing. Therefore, such a manifold 32 need only be a few inches long. Most of the housing 50 is merely warm to the touch, though the air inside is rapidly dried and heated and may emerge from the

heater

33, 34 at temperatures up to l ,000l ,200 F., for example. 7

Right beyond the end of the manifold 32 are the closing rollers, which preferably comprise a pair of

hemispherical rollers

70 and 71 contacting the opposite faces of the carton 20, as shown in FIGS. 4 and 8, and the hemispherical roller 35, which engages the outer major flap 22 and closes it against the inner major flap 23. While the hemispherical shape is preferred, it is not essential in all cases. The low-friction roller 35 is mounted with its fiat portion 72 parallel to the main walls of the carton and perpendicular to the flap 23. The

other rollers

70 and 71 are mounted perpendicular to this roller 35 and engage the

walls

73 and 74 of the carton 20, retaining the cartons shape and squareness while the flap 22 is pushed against the flap 23; these

rollers

70 and 71 serve no other purpose than the prevention of distortion of the carton from friction of the closing roller 35; they, thus, insure that the edge of the flap 22 seals parallel to the score line of the flap 23.

Just beyond the closing

rollers

35, 70, 71 are the hold-down

roller systems

28 and 29, each of which in the illustrated embodiment comprises two staggered rows of

cylindrical rollers

75 and 76 and mounted to be free running and to engage the carton 20 as the carton 20 is moved along them by the conveyor 21. They provide sufficient pressure for retaining the closure without putting so much pressure that it becomes difficult to move the carton 20. They do not seal the carton; they position while they cool and seal themselves. These

rollers

75 and 76 are adjustably mounted, as shown in FIG. 5, between a lower plate 77, which holds the shaft 78 for the lower roller 76, and an upper manifold 36 which holds the shaft 79 for the upper roller 75, the plate 77, the manifold 36 and plate 77 being held together by a bolt 80 and spaced apart by a spacer 81 which may be changed to give different spacing. The manifold 36 has an inlet 82 for a supply of cold air, which can be simply ambient atmospheric air, and is provided with a series of discharge openings 83 in a face 84, which are made to. point down against the carton 20 at approximately the level where the horizontal faces meet the convex faces of the

roller

70 and 71. By this means, the carton flaps 22 and 23 are rapidly cooled, and in only about 2 feet the carton can be released from the

rollers

75 and 76, and it will remain tightly closed without any additional pressure being necessary.

As shown in FIGS. 10 and 11, the system may be applied as well to a system having two outer flaps which overlap by using a staggered pair of manifolds 32 and 32a each with their heaters. First one outer flap is sealed and then the other.

FIG. 12 shows a modified form of manifold with a rhom boidal shape, having a vertical wall 91 meeting an inclined upper wall 92, a rear vertical wall 93 and a lower inclined wall 94. This shape is often desirable, and for purposes of example is shown with two rows of discharge openings on each of the two

upper walls openings

95 and 96 in the wall 91 and

openings

97 and 98 in the wall 92. There could, of course, be single matched rows of openings or more than two rows per wall. The rows are, of course, matched to cause the impinged surfaces to meet when the flaps are closed. Two rows of openings enable more sealing area and sealing strength than does one row. Double rows are not generally practical with the manifold 32, for the divergency between rows would render the two rows different in the temperatures they impart. The rhomboidal shape does enable this, and positive spacing may be obtained by

rods

99 and 37, that enable air flow, which are not mounted on the manifold but beside it, to enable free adjustment relative to the manifold.

With double rows of discharge openings, as in FIG. 12, the holding

assemblies

28 and 29 are preferably modified as shown in FIG. 13 to replace the bolt 80 and spacer 81 with a longer bolt 100 and a large spacer 101.

With even wider flaps and more rows of sealing plastic, the structure of FIG. 14 may be used, with a bolt 102 and a bar 103 inserted between two

spacers

104 and 105 and supporting on shafts

additional rollers

106 and 107. Many other modifications are possible.

The manifold may be varied in many ways. A manifold 110 is shown in FIGS. 15 and 16. It may have the rhomboidal shape of the manifold 90 but has vertical slits 111 instead of double rows of openings to heat a wide band on the flaps. This wider hot-air path gives a broader seal that is feasible with drilled holes. By way of illustration, there are also shown two recesses or slots 112 and 1 13 that intersect the slits 111. With these, themanifold 110 can be quite close to the flaps to be heated even touching them and still the

slots

112 and 113 let the hot air flow freely in a direction which prevents heating of undesired flap areas. Horizontal slots may be used in staggered formations, and various other opening patterns may be used. A single heater may be attached to the single fitting 114 of the manifold 110.

To those skilled in the art to which this invention relates, many changes in constmction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. In heat sealing apparatus for closure of paperboard package flaps having heat-scalable coatings, a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, each surface having a row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold, and air-heating means for supplying said manifold with heated air, the total area of said manifold openings being large enough relative to said air-heating means so that the heated air issues from said manifold openings at lower velocity than that at which it passes through said air-heating means, so that low velocity air issues in large volume from said openings.

2. In heat sealing apparatus for closure of paperboard package flaps having heat-scalable coatings, a hot air manifold having two' surfaces meeting and terminating at a sharp acute angle, each surface having a row of openings therealong for sending hot air against two flap surfaces facing and on op posite sides of said manifold, and air-heating means for supheated air, said manifold openings in said rows being spaced apart from each other at varying distances so that, having substantially identical areas, all

openings, regardless of their proximity to said air-heating means, send out substantially the same flow of heated air.

3. In heat sealing apparatus for closure of paperboard package flaps having heat-scalable coatings, a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, each surface having a row of openings therealong for sending hot air against'two flap surfaces facing and on opposite sides of said manifold, the row of one said surface lying at a difi 'erent distance from the vertex of said sharp acute angle than the row on the other said surface but at the same distance relative to the flaps they are heating, so that they gently heat narrow strips on said flaps that coincide when the flaps are urged together, and air-heating means for supplying said manifold with heated air.

4. In heat sealing apparatus for closure of paperboard package flaps having heat-scalable coatings, a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, said manifold having a shape that is generally triangular in cross section, with a vertical rear wall connecting the walls providing said two surfaces, and each said surface having a row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold, and airheating means for supplying said manifold with heated air thereto generally horizontally to said vertical rear wall.

5. in heat sealing apparatus for closure of paperboard package flaps having heat-scalable coatings, a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, said manifold having a shape that is generally rhomboidal, with a vertical rear wall, a vertical front wall providing one of said two surfaces and the other walls being inclined, each of said two surfaces having a row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold and air-heating means lying generally horizontally and leading into said rear wall for supplying said manifold with heated air.

6. Heat-sealing apparatus for closure of paperboard package flaps having heat-scalable coatings, including in combination:

a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, each surface having at least one row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold, and

at least one air heater connected to said manifold for supplying hot air thereto, each heater comprising an outer.

metal tubular housing having first and second closed ends and a tangential air inlet near said first closed end, an intermediate tubular metal shell inside and spaced from said outer housing except at said closed ends and having near said second closed end radial aperture means, said intermediate shell being closed and fully supported at both its ends, and a ceramic heater body having a surrounding shell on its outer surface lying inside and spaced from said intermediate shell, said ceramic heater body having a plurality of lengthwise passages each with a heating element inside said passages leading through an enlarged outlet through said housing, larger in cross-section than the total cross-sectional area of said lengthwise passages, into said manifold at one end and said'body stopping short of said first closed end of said intermediate shell at the other end, whereby air enters said tangential inlet, swirls around in a passage between said housing and said intermediate shell, flows through said aperture means, swirls toward said second closed end in a closedend passage between said intermediate and surrounding shells and then flows back through said lengthwise passages into said manifold at high volume and relatively low velocity, the total area of said manifold openings being greater than the total cross-sectional area of said lengthwise passages through said body, so that air issues from said manifold openings at low velocity and gently, though in great volume.

7. The heat-sealing apparatus of claim 6 wherein said manifold openings are substantially identical in size and are spaced apart at varying distances to secure substantially the same flow rate through each.

8. The apparatus of claim 8 wherein said manifold is unpartitioned and has a plurality of spaced heaters spaced apart said manifold and distribution of the heated air therealong.

9. The apparatus of claim 8 wherein said manifold openings are substantially identical in size and are spaced apart at vary ing distances depending on the location of the outlets from said heaters into said manifolds, such that, regardless of the proximity of the openings to the heater, the flow is substantially identical.

10. An air heater for heat sealing apparatus having a manifold to which said heater supplies hot air, said heater comprising I an outer metal tubular housing having first and second closed ends and a tangential air inlet near said first closed end,

an intermediate tubular metal shell inside and spaced from said outer housing except at said closed ends and having near said second closed end radial aperture means, said intermediate shell being closed at both its ends and positively supported at both its ends to assure accurate radial positioning along its full length,

40 a ceramic heater body having a surrounding shell on its outer surface lying inside and spaced from said intermediate shell, said body having a plurality of lengthwise passages, each with a heating element inside, said passages leading through an enlarged outlet of said housing into said manifold at one end and said body stopping short of the closed end of said intermediate shell at said first closed end of said housing, said outlet being larger than the cross-sectional width of said passages through said body, to prevent an increase in velocity of air passing through said outlet, 7

whereby air enters said tangential inlet, swirls around in a passage between said housing and said intermediate shell, flows through said aperture means, swirls toward said second closed end in a closed end passage between said intermediate and surrounding shells and then flows back through said lengthwise passages and into said manifold at relatively low velocity.

11. The air heater of claim 10 wherein said outer tubular housing, said intermediate shell and said heater body are 0 detachable from each other and from a said manifold.

from each other to provide a desired flow rate of heated air for.

UNITED STATES PATENT ()FFICE QETTFTCATE F CGRECTTUN Patent No. 3,668,369 Dated June 6, 1972' I Inventor(s) William J. HGWe It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

T- Column 1; line 19, "to" should read -in--.

Column

5, 7 line 18, "l,OOO" should read --l,O00F.--. Column 8, line 18, which is line 1 of claim 8, 'claim 8" should read --claim 7-",

Signed and sealed this 11 th day of November 1972.

l as AL) Attast:

EDWARD MQFLETCHER JR 6 ROBERT GOTTSCI-LALK attesting Officer Commissioner of Patents PO-1050 UNITED STATES PATENT OFF ICE 6 CERTIFICATE OF CORRECTIUN Patent No. 3,668,369 Dated June 6, 1972' Inventor(s) William J. Howe It is certified that error appears inv the above-identified pater 1t and that said Letters Patent are hereby corrected as shown below:

1- Column 1, line 19, "to" should read --in--. Column 5, "1

line 18, "1,000" should read --l,OOOF.--. Column 8, line 18, which is line 1 of claim 8, "claim 8" should. read --claim 7----s Signed and sealed this lhth day of November 1972.

EAL) Att-est:

EDWARD PLFLETCHERJR. BUBEJRT GDTTSCEALK ltte sting Officer Commissioner of Patents

Claims

1. In heat sealing apparatus for closure of paperboard package flaps having heat-sealable coatings, a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, each surface having a row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold, and air-heating means for supplying said manifold with heated air, the total area of said manifold openings being large enough relative to said air-heating means so that the heated air issues from said manifold openings at lower velocity than that at which it passes through said air-heating means, so that low velocity air issues in large volume from said openings.

2. In heat sealing apparatus for closure of paperboard package flaps having heat-sealable coatings, a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, each surface having a row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold, and air-heating means for supplying said manifold with heated air, said manifold openings in said rows being spaced apart from each other at varying distances so that, having substantially identical areas, all openings, regardless of their proximity to said air-heating means, send out substantially the same flow of heated air.

3. In heat sealing apparatus for closure of paperboard package flaps having heat-sealable coatings, a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, each surface having a row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold, the row of one said surface lying at a different distance from the vertex of said sharp acute angle than the row on the other said surface but at the same distance relative to the flaps they are heating, so that they gently heat narrow strips on said flaps that coincide when the flaps are urged together, and air-heating means for supplying said manifold with heated air.

4. In heat sealing apparatus for closure of paperboard package flaps having heat-sealable coatings, a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, said manifold having a shape that is generally triangular in cross section, with a vertical rear wall connecting the walls providing said two surFaces, and each said surface having a row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold, and air-heating means for supplying said manifold with heated air thereto generally horizontally to said vertical rear wall.

5. In heat sealing apparatus for closure of paperboard package flaps having heat-sealable coatings, a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, said manifold having a shape that is generally rhomboidal, with a vertical rear wall, a vertical front wall providing one of said two surfaces and the other walls being inclined, each of said two surfaces having a row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold and air-heating means lying generally horizontally and leading into said rear wall for supplying said manifold with heated air.

6. Heat-sealing apparatus for closure of paperboard package flaps having heat-sealable coatings, including in combination: a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, each surface having at least one row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold, and at least one air heater connected to said manifold for supplying hot air thereto, each heater comprising an outer metal tubular housing having first and second closed ends and a tangential air inlet near said first closed end, an intermediate tubular metal shell inside and spaced from said outer housing except at said closed ends and having near said second closed end radial aperture means, said intermediate shell being closed and fully supported at both its ends, and a ceramic heater body having a surrounding shell on its outer surface lying inside and spaced from said intermediate shell, said ceramic heater body having a plurality of lengthwise passages each with a heating element inside said passages leading through an enlarged outlet through said housing, larger in cross-section than the total cross-sectional area of said lengthwise passages, into said manifold at one end and said body stopping short of said first closed end of said intermediate shell at the other end, whereby air enters said tangential inlet, swirls around in a passage between said housing and said intermediate shell, flows through said aperture means, swirls toward said second closed end in a closed-end passage between said intermediate and surrounding shells and then flows back through said lengthwise passages into said manifold at high volume and relatively low velocity, the total area of said manifold openings being greater than the total cross-sectional area of said lengthwise passages through said body, so that air issues from said manifold openings at low velocity and gently, though in great volume.

8. The apparatus of claim 8 wherein said manifold is unpartitioned and has a plurality of spaced heaters spaced apart from each other to provide a desired flow rate of heated air for said manifold and distribution of the heated air therealong.

9. The apparatus of claim 8 wherein said manifold openings are substantially identical in size and are spaced apart at varying distances depending on the location of the outlets from said heaters into said manifolds, such that, regardless of the proximity of the openings to the heater, the flow is substantially identical.

10. An air heater for heat sealing apparatus having a manifold to which said heater supplies hot air, said heater comprising an outer metal tubular housing having first and second closed ends and a tangential air inlet near said first closed end, an intermediate tubular metal shell inside and spaced from said outer housIng except at said closed ends and having near said second closed end radial aperture means, said intermediate shell being closed at both its ends and positively supported at both its ends to assure accurate radial positioning along its full length, a ceramic heater body having a surrounding shell on its outer surface lying inside and spaced from said intermediate shell, said body having a plurality of lengthwise passages, each with a heating element inside, said passages leading through an enlarged outlet of said housing into said manifold at one end and said body stopping short of the closed end of said intermediate shell at said first closed end of said housing, said outlet being larger than the cross-sectional width of said passages through said body, to prevent an increase in velocity of air passing through said outlet, whereby air enters said tangential inlet, swirls around in a passage between said housing and said intermediate shell, flows through said aperture means, swirls toward said second closed end in a closed end passage between said intermediate and surrounding shells and then flows back through said lengthwise passages and into said manifold at relatively low velocity.

11. The air heater of claim 10 wherein said outer tubular housing, said intermediate shell and said heater body are detachable from each other and from a said manifold.