US3118041A - Web heater for vacuum packaging machine - Google Patents

Description

Jan. 14, 1964 w. E. mum 3,118,041

WEB HEATER FOR VACUUM PACKAGING MACHINE Filed March 6, 1959 4 Sheets-Sheet 1 INVENTOR. MLL/HM E you/vs Jan. 14, 1964 w. E. YOUNG WEB HEATER FOR VACUUM PACKAGING MACHINE 4 Sheets-Sheet 2 Filed March 6, 1959 Hmmn! Hm.

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/ IIIIIIIIIIII.' MILL/4N rray/vars United States Patent 3,118,041 WEB HEATER FGR VACUUM PACKAGING MAtCHiNE William E. Young, Believiiie, N1, assignor to Standard Packaging Corporation, New York, N.Y., a corporation of Virginia Filed Mar. 6, 1959, Ser. No. 797,805 Claims. (Cl. 219-19) The present invention relates generally to electrical heaters for plasticizing web material, and more particularly to a heater adapted to operate in conjunction with a vacuum packaging machine in which thermoplastic web material is plasticized and vacuum-formed into containers for packaging food and other products.

Vacuum packaging machines are known which make use of rolled webs of thermoplastic film such as Saran, Polyethylene and Mylar. The material is formed into containers enveloping the commodity being packaged, the containers being evacuated and heat sealed. In one such machine, which is disclosed in the copending application of Mahafiy et al., Serial No. 653,084, filed April 16, 1957, (now Patent No. 2,935,828) for Continuous Vacuum Packaging Machine, the web is fed over a rotary drum having mold cavities formed therein. The moving web is first plasticized by a heater unit such that by applying suction to each cavity, the web material is drawn therein to form a pocket conforming to the shape of the mold.

In order efiectively to plasticize the web material so as to form pockets of good quality, it is important that the heat be uniformly distributed throughout the surface of the web. Otherwise where differential heating occurs there is a tendency for the material to thin out in localized areas which are overheated. The various defects which are encountered as a result of poor web heating are known in the trade as poor draw, blow outs and popping, these terms being descriptive of the nature of the defect.

Another problem which arises in the web heater is in connection with film webs having printed matter thereon which may be colored. The printed areas tend to absorb more heat radiation than the clear regions, and if the re sultant heat intensity is excessive, the film may burn through. For example, blue printing absorbs heat at a much greater rate than unprinted areas.

Still another problem commonly encountered relates to residual heat in the web heater. It is customary to provide the web heater with a reflector on the side of the lamps away from the film surface, the reflector concentrating the infra energy in the direction of the film. When the machine and the lamps are turned off, the residual heat in the lamps and the reflector may be sufficient to burn the film, thereby wasting packaging material.

Another drawback of conventional heaters is that the physical arrangement of heating elements is such as to produce hot spots in localized areas, particularly when the lamps are placed in an intersecting grid pattern. It is found that an excessive heat concentration occurs at the points of intersection.

In view of the foregoing, it is the principal object of this invention to provide an improved web heater adapted to plasticize a moving web of thermoplastic material, the heat being applied uniformly across the surface of the web such that the temperature thereon is equalized during the film forming operation.

More specifically, it is an object of the invention to provide a web heat in which the lamps are all arranged in staggered relation transversely relative to the direction of film travel, whereby an evenly diffused heating action is produced to uniformly plasticize the web.

Another object of the invention is to provide a heater element including a water-cooled reflector of improved r. CC

design which acts quickly to remove residual heat when the lamps are turned off.

Yet another object of the invention is to provide a circuit arrangement for any array of heater lamps as above described, which circuit is adapted temporarily to boost the voltage through the lamps to permit rapid warm-up of the lamps and thereby reduce waste of packaging material when the machine is started.

For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description to be read in conjunction with the accompanying drawings, wherein like components in the various views are identified by like reference numerals.

In the drawings:

FIG. 1 is a perspective view of a vacuum packaging machine which includes a web heater in accordance with the invention.

FIG. 2. is a plan view of the web heater unit, per se.

FIG. 3 is a transverse section taken through lines 33 in FIG. 2.

FIG. 4 is an end view of the heater unit looking in the direction of arrows 4-4 in FIG. 2.

FIG. 5 is a side view of the unit looking in the direction of arrows 55 in FIG. 2.

FIG. 6 is a plan view of the reflector incorporated in the heater unit.

FIG. 7 is a side view of the reflector before it is curved into shape.

FiG. 8 shows the curved reflector.

FIG. 9 is a section taken through lines 9-9 in FIG. 6.

FIG. 10 is a schematic diagram of the electrical circuit for operating the heater unit elements.

Referring now to FIGS. 1 and 2, the vacuum packaging machine which incorporates the web heater in accordance with the invention is provided with a feeding conveyor 10 on which are placed the products 11 to be packaged. These products may be of any type which benefits from vacuum packaging, such as sliced luncheon meats, cheese and other perishables. Most bacteria which cause food discoloration and deterioration are nourished by oxygen. When oxygen is removed, bacterial growth is inhibited and the color and flavor 0f the food are retained for a long period.

The products 11 in slab form are arranged in double rows on the conveyor 10. At the other end of the machine opposite to the conveyor there is mounted a roll of thermoplastic web material 12 which is fed onto a vacuum forming drum 13 having a double row of circumferentially arranged mold cavities 14. The drum acts to form the web into double rows of pockets surrounded by flange portions. At the input end of the machine there is mounted a roll of web material 15, this roll having a width permitting it to be superimposed over the flanges of the vacuum formed pockets so as to define an enclosure, the interfaces of the webs from rolls 12 and 15 being heat scalable in character.

The web 15 feeds upwardly to the exit end of the conveyor in where the products are transferred to the web, the latter then travelling downwardly over a supporting structure 16 to the lower portion of the drum 13 where the vacuum formed pockets, now inverted, are fitted over the products. The superimposed webs with the products enclosed between them are next sealed together around the peripheries of the pockets, excepting for small passageway areas, by a heat sealing unit at the lower end of the drum. The now partly completed packages continue under the drum '13 to an evacuating and final heatsealing head. If desired, the packages may be gassed while in the final head subsequent to the evacuation and prior to the heat-sealing. Appropriately arranged knives 3 sever the packages to form individual packages which fall down a chute 17 to an output conveyor 18.

The web heater unit, generally designated by numeral 19, is mounted above the drum 13 against the control panel 29, the unit having an arcuate shape conforming to the curvature of the drum. The web material from roll 12 is carried over the cavities lid in drum 13 and passes under the heater unit 19. A vacuum system communicating with the cavities is so operated that when the web material is plasticized by the heater, the suction is made operative to draw the softened material into the cavities.

The general arrangement of drum and heater as well as the other machine components is disclosed in the abovementioned copending application. The present invention is concerned only with the structure and operation of the heater unit and will now be described in connection with FIGS. 2 to 10.

Referring now to FIGS. 2 to 5, the heat unit is con stituted by a rectangular metal frame constituted by two trapezoidal side plates 21 and 22 and two angle bars 23 and 24. Mounted against the side plates 21 and 22; are two channel members 25 and Secured by brackets to the ends of the channel members are arch-sha ed insulating mounts 2'7 and 23 of Teflon or similar dielectric material, the mounts lying in spaced parallel relation to the end pieces 23 and 2 2. Attached to the end pieces are arch-shaped insulators 29 and 3% which dimensionally match the insulation mounts. The heater is mounted in position over the drum by means including brackets 31 and 32.

As best seen in 1G. 3, the mounts 27 and 28 are each formed with a series of equi-spaced radial slots a, b, c, a, e, etc., for receiving the terminal pins of heat lamps. Seventeen heater lamps L to 1 are provided, the slots being alternately long and short in length whereby when the lamp pins are inserted, the lamps are caused to occupy staggered positions.

The lamps L to L all extend transversely relative to the direction of film movement, as best seen in FIG. 2. The lamps act as infra-red radiators comprising transparent tubes enclosing resistance elements terminating in connecting pins P and P which are received in the slots of the mount.

In practice the elements may each have a 500 watt rating. The distance between slots is smaller than the diameter of the lamps but because of the staggered arrangement it becomes possible to crowd the seventeen lamps within a relatively small are such that radiation is produced throughout the area without the existence of open or non-radiating spaces between the lamps. The pins P and P extend into the insulated space between the mounts 27 and 28 and the insulators and 3b, and are thereby isolated from the metal frame. Connecting leads are attached to the pins for applying voltage thereto.

The water-cooled reflector 33 is generally rectangular in form and is curved to rest on top of the mounts. The reflector, as best seen in F168. 6 and 7, is preferably made of two sheets of aluminum and 3322 by the roll bond method in which a silk screen pattern is laid out sinuously in the path of the water passageway 33c on the two sheets. The passageway is coated with a substance which prevents bonding, such that when the two sheets are rolled and bonded together as one piece, fusion occurs only in the non-coated areas. Pressure is then applied to the unbonded passageways and this serves to open up the duct area 330, as best seen in FIG. 9. Input and output pipes 34 and 35 are connected to the ends of the water passageway. The reflector, which is initially in fiat form as shown in FIG. 7, is curved to shape as shown in FIG. 8.

It will be seen in FIG. 2 that when the reflector is in position over the lamps, the parallel main passages therein are perpendicular to the lamps for most effective cooling. The fiow of water in the reflector removes heat quickly therefrom, this flow being maintained even after the lamps are turned off to dissipate any residual heat from the lamps and the reflector.

Referring now to FIG. 10, the electrical circuit for the lamps L to L is shown, the voltage source being a three-phase line 1 I and 1 which is connected through a suitable switch 36 to a three-phase voltage control variac 37 having three adjustable impedance branches and sliding contacts 38, 39 and 4t? therefor.

The lamps L to L are connected in an unbalanced delta circuit. Lamps L to L, are serially connected as a string in one branch of the delta, lamps L to L are serially connected in another branch, and lamps L to L are serially connected in the third branch. Shunted across the lamps L to L in the third branch are the serially-connected lamps L to L Therefore each series string consists of four lamps except for the string of lamps L13 to L17.

Sliding contact of the variac is connected to junction 1 in the delta, contact 39 to junction 1 and contact 4% to junction 3 Thus tie same magnitude of voltis applied across each string of lamps in the delta and one-fourth of this voltage appears across each lamp in the series string, save for the five lamp string L to L where only one-fifth of the total voltage is developed across the lamps therein.

Consequently since the lamps L and L are arrayed one after the other in staggered relation in the direction of film travel, the lamps L to L are uniformly heated, whereas the remaining lamps L to L are all heated to a relatively lower temperature. This is desirable in order to reduce the temperature somewhat on the exit side of the heater unit.

In order to reduce waste of packaging material when the packaging machine is started, circuit means are provided to permit rapid warm-up of the heater lamps. This is accomplished by a manually-operated booster switch '41 which is arranged to connect variac contact 40 to the midpoint of series string L to L variac contact 39 to the midpoint of series string L to L and variac contact 38 to the midpoint of string L to L In addition, variac contact 38 is connected between lamps L and L in the five lamps string L to L This booster action doubles the voltage across all lamps, with the exception of lamps L to L where the increase is not quite as great. Since the lamps are operated above their rated value when the booster switch 41 is turned on, this causes a rapid warm-up and as soon as the desired temperature is reached, the switch 41 is cut oil and the lamps revert to their normal operating voltage.

While there has been shown what is considered to be a preferred embodiment of the invention, it will be manifest that many changes and modifications may be made therein Without departing from the essential spirit of the invention. It is intended, therefore, in the annexed claims to cover all such changes and modifications as fall within the true scope of the invention.

What is claimed is:

1. A web heater unit adapted to plasticizc a web of film travelling on a vacuum molding drum, said heater unit comprising an arcuate array of tubular heater lamps disposed in alternately staggered relation over the drum transversely relative to the filmmovement to provide uniformly diffused radiation of heat, means electrically to energize said lamps at given voltages for normal operation, and switch means momentarily to boost said voltages to effect rapid warm-up of said heater unit.

2. A web heater unit adapted to plasticize a web of film travelling on a vacuum molding drum, said heater unit comprising an arcuate array of tubular resistance heater lamps disposed in alternately staggered relation over the drum transversely relative to the film movement to provide uniformly dilfused radiation of heat, and means electrically to energize all lamps in said array with the same voltage, except for the lamps in the end portion of the array at the exit side of the film, said end portion lamps being energized at a lower voltage.

3. A web heater unit, as set forth in claim 2, further including booster means temporarily to increase the voltages across said lamps to effect rapid warm-up thereof.

4. A web heater unit adapted to plasticize a web of film travelling on a vacuum molding drum, said heater unit comprising a rectangular frame supportable over said drum, a pair of arch-shaped insulating mounts mounted within said frame adjacent the ends thereof and having radial slots formed therein at equi-spaced positions, said slots being alternately short and long, a plurality of tubular resistance heating elements supported between said mounts transversely relative to the direction of film movement and having terminal pins receivable in corresponding slots in said mounts whereby said elements are arrayed in staggered relation over said drum.

5. A heater unit, as set forth in claim 4, wherein the distance between radial slots is smaller than the diameter of said tubular elements.

6. A web heater unit adapted to plasticize a web of film travelling on a vacuum molding drum, said heater unit comprising a rectangular frame supportable over said drum, a pair of arch-shaped insulating mounts mounted within said frame adjacent the ends thereof and having radial slots formed therein at equispaced positions, said slots being alternately short and long, a plurality of tubular heating elements supported between said mounts transversely relative to the direction of film movement and having terminal pins receivable in corresponding slots in said mounts whereby said elements are arrayed in staggered relation over said drum, and a curved watercooled reflector supported on said mounts above said lamps.

7. A web heater unit adapted to plasticize a web of film travelling on a vacuum molding drum, said heater unit comprising a rectangular frame supportable over said drum, a pair of arch-shaped insulating mounts mounted within said frame adjacent the ends thereof and having radial slots formed therein at spaced positions, said slots being alternately short and long, a plurality of tubular heating elements supported between said mounts transversely relative to the direction of movement and having terminal pins receivable in corresponding slots in said mounts whereby said elements are arrayed in staggered relation over said drum, and means selectively to energize said lamps with voltages producing normal heating and relatively large booster voltages effecting rapid warm-up.

8. A web heater unit adapted to plasticize a web of film travelling on a vacuum molding drum, said heater unit comprising a rectangular frame supportable over said drum, a pair of arch-shaped insulating mounts mounted within said frame adjacent the ends thereof and having radial slots formed therein at spaced positions, said slots being alternately short and long, a plurality of tubular heating elements supported between said movements transversely relative to the direction of film movement and having terminal pins receivable in corresponding slots in said mounts whereby said elements are arrayed in staggered relation over said drum, and a curved watercooled reflector supported on said mounts above said lamps, said reflector including a sinuous water passageway providing parallel paths extending perpendicularly relative to said lamps.

9. A web heater unit, as set forth in claim 6, further including a three-phase circuit for energizing said lamps comprising a delta each branch of which includes a like given number of serially-connected lamps, and an additional string of series connected lamps connected in shunt relation across one of said branches and provided with a greater number of lamps than said given number, and means to connect a three-phase source to the junctions of said delta whereby all lamps are heated to the same degree except those in said additional string.

10. A web heater unit, as set forth in claim 9, further including booster switch means connected to an intermediate point in each string of lamps in said delta to increase the operating voltage thereof momentarily.

References Cited in the file of this patent UNITED STATES PATENTS 1,492,595 Edmands May 6, 1924 1,646,010 Clover Oct. 18, 1927 1,896,398 Gay Feb. 7, 1933 1,960,697 Cochran et a1 May 29, 1934 2,028,453 Hoffman Jan. 21, 1936 2,3 69,803 Sardeson Feb. 2 0, 1945 2,561,092 Bell July '17, 19:51 2,655,802 Ravich Oct. 20, 1953 2,956,149 Dowell et al Oct. 11, 1960 3,008,029 Davis et al. Nov. 7, 1961 FOREIGN PATENTS 795,921 France Jan. 13, 1936 180,573 Austria Dec. 27, 1954

Claims (1)

1. A WEB HEATER UNIT ADAPTED TO PLASTICIZE A WEB OF FILM TRAVELING ON A VACUUM MOLDING DRUM, SAID HEATER UNIT COMPRISING AN ARCUATE ARAY OF TUBULAR HEATER LAMPS DISPOSED IN ALTERNATELY STAGGERED RELATION OVER THE DRUM TRANSVERSELY RELATIVE TO THE FILM MOVEMENT TO PROVIDE UNIFORMLY DIFFUSED RADIATION OF HEAT, MEANS ELECTRICLLY TO ENERGIZE SAID LAMPS AT GIVEN VOLTGAGES FOR NORMAL OPERATION, AND SWITCH MEANS MOMENTARILY TO BOOST AND VOLTAGES TO EFFECT RAPID WARM-UP OF SAID HEATER UNIT.

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