US3622750A

US3622750A - Heating element and packaging machine equipped therewith

Info

Publication number: US3622750A
Application number: US726513A
Authority: US
Inventors: Ridley Watts Jr
Original assignee: American Packaging Corp
Current assignee: AMPAK Inc A CORP OF DE
Priority date: 1968-05-03
Filing date: 1968-05-03
Publication date: 1971-11-23
Anticipated expiration: 1988-11-23

Abstract

A skin-packaging machine has a plurality of heaters which are connected in series during product loading portions of a cycle and are connected in series-parallel for the heating part of the cycle. The heaters each includes a tubular quartz core which support a Nichrome resistance heating element. In one form, the element comprises a thin ribbon corrugated transversely of its length with the ribbon wound in loose convolutions around the core so that it is free to expand and contract. In another form, a ribbonlike heating element is corrugated transversely of its length and circularly bent about a longitudinal axis to define a generally C-shaped cross section. The open side of the C-shaped ribbon is of smaller extent that the diametric extent of the core. The core extends within the element and the edges of the Cshaped ribbon engage the core. Because of the corrugated configuration of the heating element, physical contact between the core and element is minimized. Apparatus for directing air into heat-transfer relationship with the heating element may be provided. The air-directing apparatus may include means for passing air through the core. The interior of the core may have a radiant heat-absorbing coating to aid in heating the air passing therethrough. Alternatively, a reflector may be provided within the core to reflect incident radiation back to the heating element.

Description

United States Patent [72] lnventor Rldley Watts, Jr.

Cleveland, Ohio [21 Appl. No. 726,513

[22] Filed May 3, 1968 [45] Patented Nov. 23, 197 l [73] Assignee The American Packaging Corporation [54] HEATING ELEMENT AND PACKAGING MACHINE EQUIPPED THEREWITH 18 Claims, 11 Drawing Figs.

[51] lnt.Cl 05b 3/10, 1365b 31/00, F24h 3/04 [50] Field of Search 219/342, 343, 347, 353-358, 374-376, 377, 380, 381, 542,

FORElGN PATENTS 26,704 8/1914 Great Britain 338/321 491,765 3/1954 ltaly 219/542 Primary Examiner-A. Bartis Attorney-Watts, Hoffman, Fisher & Heinke ABSTRACT: A skin-packaging machine has a plurality of heaters which are connected in series during product loading portions of a cycle and are connected in series-parallel for the heating part of the cycle. The heaters each includes a tubular quartz core which support a Nichrome resistance heating element. 1n one form, the element comprises a thin ribbon corrugated transversely of its length with the ribbon wound in loose convolutions around the core so that it is free to expand and contract. 1n another form, a ribbonlike heating element is corrugated transversely of its length and circularly bent about a longitudinal axis to define a generally C-shaped cross section. The open side of the C-shaped ribbon is of smaller extent that the diametric extent of the core. The core extends within the element and the edges of the C-shaped ribbon engage the core. Because of the corrugated configuration of the heating element, physical contact between the core and element is minimized. Apparatus for directing air into heat-transfer relationship with the heating element may be provided. The airdirecting apparatus may include means for passing air through the core. The interior of the core may have a radiant heat-absorbing coating to aid in heating the air passing therethrough. Alternatively, a reflector may be provided within the core to reflect incident radiation back to the heating element.

' PAIENTEBunv 231921 'f 'QT FIG.2

HEATER B uf ztts, H01 mannr i Shun/ i Hei nu,

INVENTOR R IDLEY WATTS JR.

ATTORNEYS.

INVENTOR. RIDLEY WATTS JR.

UYqiisJ-{ofimann Hakka,

ATTO RN EYS Watts, .Ir. entitled FILM relatively high resistance CROSS-REFERENCE TO RELATED PATENT U.S. Pat. No. 3,501,886, issued on Mar. 24, I970 to Ridley PACKAGING MACHINE AND METHOD.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to electric heaters and to mechanisms utilizing electric heaters and more particularly to a skinpackaging machine equipped with a novel and improved heater.

In packaging operations transparent plastic films are frequently used which are relatively transparent to radiant energy. Accordingly, it is necessary to heat these films by convectionfTypically this is accomplished with a flow of hot air.

Modern skin-packaging machines are designed for use in many applications other than retail display packages. For example, they may be used in protectingproducts for shipment or storage. In such applications the machines may be used intermittently and sporadically. Because of this sporadic or cyclic use, skinpackaging and other machines normally use electricity as a source of energy for heat.

For this and other applications there has been a need for an electrical heater which: (a) has quick response when turned on; (b) is a good source of radiant energy; and (c) is efficient for use as a heat source for convection heating.

2. The Prior Art Prior electric heaters have had a number of disadvantages. One is that a heater for a relatively large area must be made of wire and for mechanical strength these wires have been of relatively large cross section. This results in excessive usage of electricity. Another disadvantage is that sections of the heater are allowed to sag-in order to allow sufiicient room for expansion and contraction of a heater element. Sagging elements are susceptible to snagging and shorting, have poor appearance, andthe like.

One attempt to increasethe life of electric heaters has been to encase a resistance wire in a quartz tube. These quartz tubes have considerable disadvantages including very slow response time for convection .heating. They are not good sources of heating a passing flow of air or the like because'effective heating is not accomplished until the quartz tube itself has become hot.

In order to overcome the problems of burning outof heating elements resulting from'thermal expansion, the prior art has proposed restraining the elements against excessive expanding movement. These proposals have resulted in overstressing and breakage of the elements and supports have often increased conductive heat losses to the supports.

Accordingly, prior electric heaters have had slow response times, have had short lives, have been slow and poor in convection heating and have been inefficient in that excessively heavy wire has been required for mechanical strength and the excessively heavy wire utilizes excessive amounts-of electrici- SUMMARY OF THE INVENTION The heater of the present invention has an extremely high surface area per unit volume. It has outstanding characteristics both as a source of radiant energy and a source of convection heating with'very quick response times. It also has long life and uses very thin efficient ribbon.

In preferred form, a core in the form ofquartz tube is used as a support for the electric heater. A thin Nichrome ribbon is crimped so that it is corrugated with the corrugations running transverse of an elongated strip of the ribbon is then wound in loose convolutions around the quartz tube so that it is free to expand and contract and slide along the tube. Since the convolutions are loose, heater element to core contact is minimized. This minimizes heat losses into the core.

In another preferred form of the invention the ribbonlike heater element is corrugated transversely of its length and circularly bent about a longitudinal axis to define a generally C- shaped cross section. The open side of this C-shaped ribbon is of smaller extent than the diametric extent of the support. The element engages the support at spaced locations or points of contact because of the corrugated or ribbed configuration of the element. The engagement of the ribbon is at small, spaced essentially point contacts along the top of the core tube. The

ribbonlike heater element becomes a weak spring so that it Since the quartz is essentially transparent to radiation, for radiant energy purposes the heater acts as if it were a spiral of resistance wire suspended in air. when backed by a reflector, sources of radiant energy either directly radiating the object being heated or radiating against the reflector and thence to the object being heated.

The extremely quick heat generation of this heater and the rapidity with which it reaches relativelyhigh temperatures is believed to be a result of the large area of the element relative to its mass. Additionally the construction of the ribbonlike heater which is corrugated and of small thickness is believed to contribute to the heat generating effect.

In the skin-packaging machine of this inventionlair flows by convection or can be blown over a series of these heaters to provide effective convection heating. The heaters of this invention are outstanding for this purpose in that there is high unit surface'area per unit volume, turbulence is created along the tubes and, while supported mechanically for long life, the heaters are nonetheless in direct contact with the flowing air.

The machine cycle time is further reduced through the provisionof a novel circuit. When the machine is in the load" portion of the cycle the-heaters are in series with low electric potential applied. This warms or preheats, the heater wires. When the film-softening part of the cycle is reached the heaters are switched to a series-parallel relationship and full potential is applied to provide substantially instantaneous high levels of heat energy and very short cycle times.

Another feature of the heaters of this invention is that the heat distribution can be controlled. Expressed another way the watt density'along the heater can be varied according to the needs of a given application. Thus variation is accomplished by varying the spacing of convolutions of the wound heater ribbon and the spacing and shape of the corrugations in the ribbon.

In other applications the heater is placed within a surrounding tube. Air is passed between the tubes and out the inner tube, or vice versa, to provide a stream of hot air.

In another form a radiant-energy-focusing element is provided so that radiant heating of an object, as well as heating by an air flow, is accomplished.

Accordingly a principal object of the present invention is the provision of a new and improved electrical heat source.

Other objects and advantages of the present invention will become apparent from the following detailed description made with reference to the accompanying drawings which form a part of the specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a film-packaging machine embodying the present invention;

FIG. 2 is a circuit diagram showing heater connections;

FIG. 3 is an elevational view of a heater element embodying the present invention having portions shown in cross section and portions removed;

FIG. 4 is a crosssectional view as seen from the plane indicated by the line 55 of FIG. 4;

FIG. 5 is across-sectional view of a portion of a modified heater embodying the invention having parts shown in section;

FIG. 6 is a perspective view of a portion of a heater similar to FIG. 5;

FIG. 7 is an elevational view of a modified heater embodying the invention and shown partly in cross section;

FIG. 8 is a cross-sectional view seen from the plane indicated by the line 88 of FIG. 7; and,

FIGS. 80, 9 and 10 are views of modified heaters similar to 5 the heater of FIG. 7.

DESCRIPTION OF PREFERRED EMBODIMENTS reference U.S. patent to Ridley Watts, .lr., and accordingly it will be described only briefly. The machine 10 has a rectangular base 12 with a control panel 14 on a front surface of the base. A generally rectangular vacuum platen 16 is supported on the base 12 and, in use, supports a panel or supporting board B on which articles A can be placed for packaging. Two

spaced upright support columns l8, 19 extend from two rear corners of the base 12. A heating unit 20 is supported by the support columns l8, 19 extending forwardly in cantilever fashion and spaced above the base 12 and vacuum platen 16.

In use a sheet of card stock and products to be packaged are mounted on the base 10. A sheet of thermoplastic film is secured to the frame 24. The heating unit 20 heat softens the film. The frame is then lowered, a vacuum is drawn and ambient air pressure forces the film onto the card stock.

The heating unit 20 includes a rectangular hood 26 and a rectangular oven 28 carried beneath and surrounded by the hood 26. A blower and motor unit 29 at the rear of the oven 28 and hood 26 also forms a part of the heating unit. The hood 26 has a top surface 26a and a peripheral depending flange 26b. The hood is supported by the support columns l8, 19 for 3 vertical adjustment and pivotal movement relative to the base 12.

The oven 28 includes a heating element supporting plate 30 that functions as a reflector and has a depending flange 300 at its periphery. Apertures 32 are provided in the plate 30 to receive supporting brackets 34 for heating elements, and to provide passageways through the plate 30 for air circulation. The heating elements, 36 are supported on the lower surface of the plate 30 by the brackets 34. The specific construction of the heating elements 36 is described in considerably greater detail presently.

The oven 28 fits within the hood 26 and is spaced below the upper surface 26a of the hood so that a plenum chamber is provided between the hood 26 and oven 28. The plate 30 is secured in this position within the hood 26 by suitable brackets which have not been illustrated.

A partially cylindrical blower housing 40 extends between the columns l8, 19 at the lower side of the hood. The blower housing 40 is perforated so to provide openings 42 (see FIG. 5 5

l) to serve as air inlets to the blower housing. The housing outlet (not shown) opens into the plenum chamber between the oven 28 and the hood 26. The blower and electric motor unit 29 are located within the housing 40. When the motor is operated, the blower draws air from beneath the

oven

28 and 0 introduces the air under pressure to the plenum chamber, between the hood and the oven. From the plenum chamber the air flows through the openings 32 in the plate 30 past the heating elements, and to a zone directly beneath the oven and hood. This air flow aids in heating film for the packaging operation as well as cooling the heating unit between heating cycles in a manner which is described in greater detail presently.

The frame 24 is manually opened by unlocking the frame members and raising the upper frame member 48 away from In some instances sealing between the article-supporting panel P, and the film F, is enhanced by the application of heat, and in such cases the heaters 36, may be maintained energized while the film is drawn onto the card stock by the vacuum. A suitable heat-hold" control switch, not illustrated, may be provided to maintain the heaters energized after the heater timer has timed out and the frame moved to its lower position. Thus heat can be supplied from the oven 28 to the film F as the vacuum draws the film about the articles on the panel P.

Refem'ng now to FIG. 2 a novel energization circuit C for the heaters 36 is illustrated. As seen in FIG. 2 the machine 10 includes nine heaters 36ai connectable across the lines L1, L2 of a 440-volt three-wire single-phase AC power supply. When the machine 10 is turned on but is not operating to heat the packaging film, the heaters 36a-r' are connected in series across the power supply and hence are heated. At this time the elements are not heated to the high temperatures required for heating the film to its draping temperature.

When the packaging cycle is initiated, the circuitry C is effective to connect the heaters to the power supply so that the temperature of each heating element is elevated almost instantaneously to approximately L700 F. Thus when the film-supporting frame is in its raised position, the blower unit directs a flow of air over the high-temperature elements 36a-i to heat the film F to the draping or therrnoforming temperature.

More specifically when the packaging cycle is initiated, three groups of three heaters each are connected across the power supply. Thus the heaters 360-0 are connected in a series circuit across the power supply, the heaters 36a-f are connected in a series circuit across the power supply and the heaters 36g-i are connected in a series circuit across the power supply. Each of these series circuits are in parallel with the others. Hence the total voltage across the lines L1, L2 is 5 applied across the three heaters in each series circuit and the heaters are heated to the desired high temperature extremely quickly. The low-heat connection of the heaters is effective to maintain the oven components at elevated temperatures during intervals'when the film is not being heated for packaging. Thus the thermal response of the heaters is increased since the heated oven components do not pick up large amounts of heat when the film is being heated.

Operation of the circuitry C is governed by a control circuit 92 for the machine 10, only a part of which is illustrated in FIG. 2. The control circuit 92 is connected across the power lines Ll, N and hence is operated on 220 volts AC.

When an on-ofi' switch S1 for the machine 10 is closed, the control circuit 92 is connected across the power supply and a relay R1 is energized from the line L] through the switch S1 and to the neutral or common line N. Energization of the relay R1 closes relay contacts RC1, RC2 in the circuit C and establishes and energization circuit for the heaters 36a-i.

This energization circuit connects the heaters in series across the power supply. The series energization circuit can be traced from the line L1 through the closed contacts RC1, a conductor 93, heaters 36a-c, a conductor 94, heaters 36f, e, d, and through the heaters 36g, h, i to the line L2 through a conductor 96 and the contacts RC2.

When the heaters 36a-i are connected as described the voltage drop across each heater is approximately one-ninth of the voltage across the lines L1, L2. Because of the high impedance of the nine serially connected heaters the current flow through the heaters is relatively small and resistance heating of each element is limited. Hence the heaters are heated to a temperature above room temperature, but not to the temperature level required for heating film to its draping or thermofonning temperature.

When an article is to be packaged, a cycle switch S2 in the control circuit 92 is closed to energize a relay R2. This relay is energized through a circuit established from the line LI, through the switch S2, the relay SR2, a timer operator switch TS and to the common line N.

Energization of the relay R2 closes relay contacts RC3, RC4 in the circuit C so that the heaters 360-! are heated to high temperature, i.e. about l,700 F. More specifically the heaters 36a-c are connected in a series circuit across the power supply from the line L1 through the contacts RC1, conductor 93, a conductor 97, and to the line L2 through the relay contacts RC4, RC2. The heaters 36d-f are connected in a series circuit from the line Ll through the contacts RC1, RC3, a conductor 98 the heaters 36df,

conductors

94,97 and to the line L2 through the contacts RC4, RC2. The heaters 3634 are energized through a circuit traced from the line L1 through the contacts RC1, RC3,

conductors

98, 95 the heaters 36g-i, -the conductor 96, contacts RC2 and to the line L2.

The timer operated TS is operated from a suitable tuner (not shown) and after a desired interval this switch opens to deenergize the relay R2. Deenergization of the relay R2 opens the relay contacts RC3, RC4, and the heaters 36a-i are again connected in series across the power supply, as previously described, so that their temperature is reduced. The heaters are preferably maintained at the reduced temperature until the cycle start switch S2 is reclosed, or the machine is turned "bfif The cycle time for a machine 10 of the type described depends upon the material and thickness of the film. The machines such as the machine 10 have produced a cycle time of approximately seconds utilizing a film of polyethylene material having approximately a 4-mil thickness. in the past, about half of the total machine cycle time has been devoted to heating the film so that, in the case of 4-mil polyethylene film, 12-15 seconds have been devoted to heating. One reason for the relatively long heating cycles is that polyethylene or similar film is essentially transparent to infrared radiation and accordingly the heat transfer from the heating elements to the film must take place primarily by convection.

in certain prior art constructions the heating elements have been in the fonn of calrods or fine Nichrome wire or ribbons which when connected across an electric power supply reach an operating temperature of approximately 1700 F. in not less than 4 to 6 seconds. The heating elements are cooled by operation of the blower 29 when the heater is turned off and the cooling process takes place over a period of 6 to 8 seconds. Accordingly the heating elements are subjected to substantial temperature ranges in a cycle of operation of the machine 10 and are often subjected to relatively large thermally induced stresses as a result. Previously known machines of the type referred to have also had the problems noted previously in connection with resistance heated elements for heatmg arr.

According to the present invention a new and improved air heater is provided which minimizes radiation losses and conductive heat losses from a heating element so that both radiant and convective heat transfer is maximized. The heating element is supported through its length by a member which is transparent to radiation. This provides a very large surface area of heating element per unit volume of relatively thin, resistance material. Further since the element cooperates with its support so that failure-due to thermal stressing of the element does not occur yet burning out of the element due to shorting is avoided.

One preferred form of a heater embodying the'present invention is illustrated in FIGS. 3 and 4. As shown in FIG. 3 the heater 36'includes a supporting body 101 including a tubelike support 102 and end

caps

103, 104. The end caps 103, 104 are formed by an electrically conductive material and are connected to the plate 30 by the electrically conductive springlike brackets 34 similar to fuse clips.

A ribbonlike resistance heating element 105 is helically wound about the support 102 and extends between the end caps 103, 104. The element 105 is preferably constructed of Nichrome material and has a relatively small cross-sectional area. Corrugations or ribs 106 are formed in the ribbon 105 transversely of its length and when the ribbon 105 is wound about the support 102 the corrugations extend at a slight angle with respect to the axis of the helix.

Each of the end caps 103, 104 includes a peripheral groove receiving an end of the ribbon 105. A snapring 111 is disposed in the groove 110 and tightly engages the ribbon to insure electrical contact between the opposite ends of the ribbon and each end cap. As noted previously the end caps are formed by a suitable electrically conductive material so that a circuit through the ribbon 105 is established when the end caps are connected across an electrical poser supply.

As is best seen in FIGS. 3 and 4 the ribbon 105 is loosely coiled about the support 102 so that the diametrical extent of the helix fonned by the ribbon 105 is greater than the diametrical extent of the support 102. Thus the helix is supported only at spaced locations along the tube. Because the corrugations are skewed relative to the helix axis and because the tube is cylindrical, the locations at which the ribbon 105 engages the supportare defined by points of contract, or at most, relatively short linesegments. Thus the total area of engagement between the ribbon 105 and support 102 is extremely small and-minimizes heat sink effect of the support.

The helical coils of the ribbon 105 are loosely wound about the support 102; however'the Nichrome material forming the ribbon 105 is sufiiciently stiff due to the corrugations or ribs 106 so that should the heater 36be disposed in a vertical orientation during use, adjacent convolutions of the ribbon 105 do not contact each other.

When the ribbon 105 is connected across a power supply to elevate the temperature of the ribbon to approximately 1700 F. thermal expansion of the ribbon occurs. Expansion of the ribbon essentially results in increasing the diametrical extent of the helix, however axial movement of convolutions of the helix relative to the support 102 alsooccurs. In essence, then, thermal expansion is absorbed by spiral movementof coil on the tube. The windings of the helix are spaced sufficiently far apart that contact between adjacent convolutions does not occur as a result of the thermal expansion.

The support 102, as noted previously, is elongated, preferablygenerally tubelikeor rodlike and is preferably constructed of a material, which is substantially transparent to infrared radiation, i.e. radiant heat. The exterior surface of the support-102 is smooth so that engagement between the convolutions of theribbon 105 and the support is characterized by relatively low frictional forces. This permits free axial movement of the ribbon relative to the support 102 during thermal expansion and contraction without stressing the ribbon.

Because the ribbon 105 is relatively closely coiled, the convolutions at opposite sides of the support 102 confront each other. Since the support 102 is largely transparent to radiant energy the inwardly facing surface of the ribbon 105 reradiates to itself without substantial radiant heat loss to the support. The noted reradiation of the interiorlyfacing surface of the ribbon 105 provides increased availability of heat for convective heat transfer to air flowing across the ribbon.

In addition to the previously noted functions of the corrugations-in the ribbon 105 it should be noted that these corrugations additionally encourage turbulence in the air which flows across the heater 100. Furthermore the corrugations provide radiating ribs and thus greater heat transfer areas than would be available utilizing a helical ribbon of the same size without corrugations.

FIG. 5 illustrates a modified air heater embodying the present invention. The heater'l20 is shell and tube type counterflow heater. The internal tube includes a supporting body 121 and a tubelike support 122 having

end caps

123, 124. Corrugated .ribbon is helically wound about the support 102 in the same manner as described in reference to FIGS. 3 and 4. The end caps 123, 124 are substantially the same as the end caps 103, 104 described previously except that bores 127 are formed in the end caps 123. 124 so that a flow of air is directed throughthe tube 122 from an air supply pipel26. The bore 127 in the end cap 123 is associated with the supply pipe 126 andthe bore and the end cap 124 opens into the shell [30 so that the air emergingfrom the tube 122 is counterflowed along the outside of the support 102 and within the shell 130.

The shell 130 is constructed to provide an opening for the pipe 126 which is sealed so that heated air does not leak from the shell along the pipe. An outlet nozzle 131 is provided in the shell for directing hot air away from the heater. The tube 122 is supported in the shell 130 by suitable members 132 which maintain the tube centered in the shell and provide electrical connections between the element 125 and the power supply.

The air which flows through the support 122 is heated by the interior surface of the tube 122 to make use of heat which is conducted to the tube from the element 125 and the heated air flowing on the outside of the support 102. Preheating of the air in this manner reduces conductive heat losses which might otherwise occur through the tube.

The air in the shell is heated by convection as it flows along the element 125 axially of the tube 122. In the preferred embodiment the shell 130 is a generally cylindrical member constructed from a reflective material or having a reflective coating 1300 on its interiorallyfacing surface so that radiant heat loss from the element 125 is minimized. Thus, the facing surfaces of the element 125 reradiate to each other through the support 102, while radially outwardly directed radiation from the element 125 is reflected by the shell 130 back to the element.

FIG. 6 illustrates a modification of the heater 120 in which a plurality of tubes 122a-c are supported in the shell. A radiant heat absorbing, or black" coating 134 is disposed on the in terior of the tubes so that the interior surface of each tube is heated to additionally preheat the air flowing through the tubes. A single heater element 125a surrounds the tubes.

FIG. 7 illustrates a modified air heater 140 embodying the present invention. The heater 140 is constructed in essentially the same manner as the heater 34 except that the ribbonlike heater element 141 is formed from a generally rectangular sheet of Nichrome which is circularly curved about its longitudinal axis to define a C-shaped cross section. The diametrical extend of the element 141 is substantially larger than its support tube 142 but the distance between the edges 141a, l4lb of the element 141 is less than the diametrical extent of the tube 142 so that the element 141 is supported on the the tube.

The element 141 is corrugated generally transversely of its length so that the edges 141a, b of the element undulate toward and away from the periphery of the tube proceeding along the length of the element. Due to these corrugations the element engages the tube essentially at points of contact spaced axially along the tube.

The ribbonlike element 141 is connected to end

caps

143, 144 on the tube by conductor wires 145 which are helically wound about the tube between the ends of the element 141 and an adjacent end cap. The wires 145 are maintained in electrical contact with the end caps by snap rings 146.

The end caps 143, 144 are substantially the same construction as described above in reference to FIG. 4 except that the end cap 143 includes a bore 150 which communicates with the interior of the tubelike support 142. Additionally, the tube 142 includes a series of slots or holes 151 through its wall. These slots are spaced along the tube. Air to be heated is introduced into the tube through the bore 150 in the end cap 143. The air is under pressure and passes through the slots 151 and impinges on the interior surfaces of the ribbon 141. The air flowing between the ribbon 141 and tube 142 is exhausted between the edges 141a, b of the ribbon and the adjacent periphery of the tube (see FIG. 8). The slots 151 may be of similar shape and cross-sectional area; preferably, however, these slots increase in size proceeding away from the bore 150 so that the flow rate of air through each slot is about the same. The differing sizes of the slots thus minimize nonuniform temperatures along the ribbon. As seen in FIG. 8 an additional air flow can be provided along the exterior of the ribbon 141 in a manner similar to that described in reference to FIG. 3.

Because of the point contact between the corrugated edges 141a, b and the tube 142, the ribbon is capable of unrestrained expansion and contraction along the tube 142 in response to changes in its temperature. The helical conductors 145 are of relatively flexible material so that the electrical connection between the ribbon and end caps is not interrupted due to breaking of the conductors during thermal expansion or contractions of the heating element. The conductors are of a highly conductive material so that the wire itself does not heat appreciably doe to electric resistance during heating of the element.

The ribbon 141 is, as in the case of the helically wound ribbon 105, of extremely small cross-sectional area so that the ribbon heats at a high rate when connected across the power supply. The sectional thickness of the ribbon 141 is exaggerated in FIG. 8 in order to clearly show the relationship of the illustrated parts. It is to be understood that the sectional thickness of this ribbon is extremely small so that the crosssectional area through which current flows in the ribbon is likewise of minimum size.

In the illustrated embodiment, the element 141 is shown suspended from the tube 142. However, the tube 142 is provided with spaced ridges 142a, b which may contact the edges 141a, b at spaced locations along the tube. These ridges can support the element 141 relative to the tube so that the tube can be oriented as desired. For example the tube can be positioned so that the slots 151 open upwardly and the element 141 extends over the upper side of the tube. The edges 141a, b in such an orientation face downwardly and are supported on the ridges 1420, b.

FIG. 8a is a modified heat exchanger similar to the-heat exchanger of FIGS. 7 and 8, except that the inside of the tube 142 is provided with a coating of radiant heat-absorbing material. The coating 157 heats the air 157 heats the air introduced into the tube prior to the air impinges on the element 141 by way ofthe slots 151.

FIG. 9 illustrates a modified heater which is similar to the heater 140 described in reference to FIGS. 7 and 8 except that the interior of the tube 142 is provided with a reflective coating which extends between the edges 14lab of the element 141. The reflective coating 155 prevents any substantial amount of radiation loss from the interior of the element 141 and through the tube 142 between the sides of the ribbon. The reflective coating thus reflects incident radiant energy back to the element 141 so that radiation heat loss through the tube 142 is minimized.

Fig. 10 illustrates a further modified heater including a tube 142 which supports a rodlike prism 160. The prism 160 extends axially within the tube 142 form one end of the tube to the other. The prism 160 is effective to focus radiation from the element 141 and directs the focused radiation between the edges of the element 141 through the wall of the tube. The radiant energy which is not focused as described is reradiated to the interior of the element 141 to reduce radiation losses which might otherwise occur from scattering.

An external air flow is provided around the heater which is heated by convection. The internal air flow in the tube 142 cools the prism 160 before being exhausted from the tube 142 through the slots. As noted previously the ridges can support the element 141 to permit a desired orientation of the tube. Thus objects can be selectively heated both by radiation and convection be proper orientation of the tube and direction of the air flow.

Although the invention has been described in its preferred forms with a certain degree of particularity, it is understood that the present disclosure of the preferred forms has been made only by way way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

lclaim:

1. A heat exchanger comprising:

a. an elongated electrically insulative support member;

b. an electrical resistance heating element substantially coextensive with and supported on said member and connectable across an electric power supply;

0. said element comprising an elongated sleeve of resistance material which is longitudinally split to define spaced edges, said support member extending within said element and said edges formed to define a plurality of spaced locations contacting said support member over relatively small contact areas;

(1. means for directing a heat-transfer medium into heat transfer relationship with said member and said element;

e. said contact locations between said member and said element providing minimal forces opposing relative movement therebetween; and,

f. said element defined by a sleevelike metallic sheet having longitudinally extending spaced sides, with said element engaging said member at spaced locations on said sides; and,

g. electrical conductors connected to opposite ends of said element for connection across an electrical power supply.

2. A heat exchanger as defined in claim 1 wherein said member is generally tubular and further including at least an opening defined in said member, at least part of said element supported in spaced relation to said opening and said means for directing said heat-transfer medium operable to direct said medium from said member through said opening for impingement on said element, said heat-transfer medium flowing along said element and between said edges and said member between said spaced contact locations for transferring heat away from said heat exchanger.

3. A heat exchanger as defined in claim 1 wherein said element comprises a ribbonlike sheet of electrically conductive material which is corrugated substantially transversely to its length.

4. A heat exchanger as defined in claim 1 wherein said electrical conductors are helically coiled about said member to permit relative longitudinal movement between said member and said element in response to thermal expansion and contraction.

5. A heat exchanger as defined in claim 1 wherein said member is generally tubular and comprises a radiant-energyabsorbing interior surface portion, and further including means for directing a heat transfer medium along said interior surface for transferring heat from said member.

6. A heat exchanger as defined in claim 1 wherein said member is tubular and further including a radiant energy focusing structure in said member.

7. A heat exchanger as defined in claim 6 wherein said focusing structure includes a rodlike member for refracting radiant heat.

8. A heat exchanger as defined in claim 7 wherein said rodlike member is a prism.

9. A heat exchanger as defined in claim 7 wherein said heattransfer medium directing means includes means for directing heat-transfer medium across said rodlike member to transfer heat therefrom.

10. A heat exchanger as claimed in claim 6 wherein said focusing structure comprises a reflective surface portion on said tubular member, said surface portion located to reflect incident radiation from said element and radiation at said element.

11. A heat exchanger as defined in claim 1 wherein said element includes generally transversely extending corrugations and said edges are nonlinear.

12. A heat exchanger as defined in claim 11 wherein the spacing between said edges is substantially smaller than the diametrical extent of said member so that only said edges engage said member.

13. A heat exchanger as defined in claim 12 wherein the difference between the diametrical extend of said member and the spacing between said edges is sufliciently large that said edges remain engaged with said member regardless of differences in thermal expansion between said element and said member.

14. A heat exchanger as claimed in claim 1 wherein said member is tubular and defines at least an opening providing a heat-transfer medium passageway between the interior and exterior of said member, said heat-transfer medium flowing between said member and said edges of said element between said spaced contact locations.

15. In a packaging machine for enclosing articles at least in part by a film:

a. a heating structure for heating an air flow directed onto said film, said heating structure including at least a heater comprising; an elongated electrically insulative support member constructed from a material which is substantially nonabsorbent of radiant heat;

c. an electric resistance element loosely disposed about said support member and connectable across an electric power supply;

. said element comprising an elongated sleeve of resistance material which is longitudinally split to define spaced edges, said support member extending within said element and said edges being formed to define a plurality of spaced locations contacting said support member over relatively small contact area;

e. apparatus for directing air into heat-transfer relationship with said element and thence into heat-transfer relationship with a packaging film.

16. A heating structure as defined in claim 15 wherein said element is a ribbonlike sheet of material having corrugations extending generally transversely of its length, said corrugations defining said spaced contact locations engaging said member.

17. A heating structure as defined in claim 15 and further including electrically conductive end structures on said member and means for electrically connection said end structures to said element.

18. A heating structure as defined in claim 15 including a plurality of said heaters, and circuitry controlling energization of said heaters, said circuitry including first circuit means providing for heating of said resistance elements to a temperature between ambient and a predetermined film-heating temperature and second circuit means for effecting energization of said resistance elements to said predetermined temperature from said intermediate temperature substantially instantaneously.

focus said reflected I t l i t P0405) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION N 3,622,750 Dated November 23. 1971 Inventor) Ridley Watts, Jr. Q

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 71 after "ribbon" insert The ribbon.

Column 4, line 23 after "F" insert line 72 after "relay" delete "S" and "operator" should be operated--.

Column 5, line 12 "tuner" should be -timer-.

Column 6, line 8 "poser" should be --'power--.

Column 7, line 41 "extend" should be extent-.

Column 8, line "doe" should be --due;

line 33 after "coating insert --l57--; line 34 delete "heats the air line 35 "impinges" should be --impinging-;

line "form". should be --from--.

Column 9, lines 15-18 delete the entire subsection "f."

Column 10-, line ll "extend" should be extent--;

line 49 "connection" should be -connecting--.

Signed and sealed this 27th day of June 1972.

SEAL) ttest:

DWARD M.F'LETCHER,JR. ROBERT GOTTSCHALK ttesting Officer Commissioner of Patents

Claims

1. A heat exchanger comprising: a. an elongated electrically insulative support member; b. an electrical resistance heating element substantially coextensive with and supported on said member and connectable across an electric power supply; c. said element comprising an elongated sleeve of resistance material which is longitudinally split to define spaced edges, said support member extending within said element and said edges formed to define a plurality of spaced locations contacting said support member over relatively small contact areas; d. means for directing a heat-transfer medium into heat transfer relationship with said member and said element; e. said contact locations between said member and said element providing minimal forces opposing relative movement therebetween; and, f. said element defined by a sleevelike metallic sheet having longitudinally extending spaced sides, with said element engaging said member at spaced locations on said sides; and, g. electrical conductors connected to opposite ends of said element for connection across an electrical power supply.

5. A heat exchanger as defined in claim 1 wherein said member is generally tubular and comprises a radiant-energy-absorbing interior surface portion, and further including means for directing a heat transfer medium along said interior surface for transferring heat from said member.

9. A heat exchanger as defined in claim 7 wherein said heat-transfer medium directing means includes means for directing heat-transfer medium across said rodlike member to transfer heat therefrom.

10. A heat exchanger as claimed in claim 6 wherein said focusing structure comprises a reflective surface portion on said tubular member, said surface portion located to reflect incident radiation from said element and focus said reflected radiation at said element.

13. A heat exchanger as defined in claim 12 wherein the difference between the diametrical extend of said member and the spacing between said edges is sufficiently large that said edges remain engaged with said member regardless of differences in thermal expansion between said element and said member.

15. In a packaging machine for enclosing articles at least in part by a film: a. a heating structure for heating an air flow directed onto said film, said heating structure including at least a heater comprising; b. an elongated electrically insulative support member constructed from a material which is substantially nonabsorbent of radiant heat; c. an electric resistance element loosely disposed about said support member and connectable across an electric power supply; d. said element comprising an elongated sleeve of resistance material which is longitudinally split to define spaced edges, said support member extending within said element and said edges being formed to define a plurality of spaced locations contacting said support member over relatively small contact area; e. apparatus for directing air into heat-transfer relationship with said element and thence into heat-transfer relationship with a packaging film.