WO1997047160A1

WO1997047160A1 - Liner compound curing apparatus with rf induction heating

Info

Publication number: WO1997047160A1
Application number: PCT/US1997/010077
Authority: WO
Inventors: Alan Eastwood; Andrew E. Mojden
Original assignee: Fleetwood Systems, Inc.
Priority date: 1996-06-06
Filing date: 1997-06-05
Publication date: 1997-12-11
Also published as: AU3386497A

Abstract

A liner compound curing apparatus (20) which includes a conveyor which passes through a high frequency or radio frequency ('RF') induction heating system (22). The induction heating system (22) includes at least one elongated coil and may use a pair of spaced apart elongated coils. The curing apparatus (20) passes the container ends (24) in close proximity to the induction heating system (22) for maximizing the inductive coupling between the heating system (22) and the container ends (24). The conveyor uses a foraminous belt (26) which is positioned between induction coils of the RF heating system (22). The foraminous belt (26) is driven generally co-axially relative to the elongated coils. A vaccum system is coupled to the curing apparatus (20) to draw a vacuum (48) on the container ends (24) positioned on the belt (26) to pull air through the foraminous belt (26) allowing sufficiently close positioning of the container ends (24) relative to the heating system (26). The curing apparatus (20) provides a substantially shorter operating length compared to prior art thermal oven systems and provides the benefit of minimizing detrimental thermal effects on the container end (26) and the liner compound.

Description

LINER COMPOUND CURING APPARATUS WITH RF INDUCTION HEATING

Inventor

Alan Eastwood

208 Langley Road

Slough

Berks SL3 7EE

United Kingdom

A citizen of the United Kingdom

Andrew E. Mojden

747 Taft

Hinsdale, Illinois 60521

A citizen of the United States

Cross Reference

This patent application claims benefit of domestic priority of co- pending U.S. Provisional Application Serial No. 60/019,191, filed June 6, Background

The present invention relates to a device for drying liner compound on articles using a radio frequency induction heating system. More particularly, the present invention is shown in a preferred embodiment as a curing apparatus which is used to cure liner compound on container ends.

The apparatus of the present invention may find utility in other applications. The disclosure provided herein will make particular reference to the handling of container ends during fabrication operations as well as subsequent use of such container ends during packaging operations. In the manufacture and filling of containers, for example beverage containers, vast numbers of container ends are required. Present fabrication and filling operations require handling such large quantities of container ends at a high rate of speed in a generally continuous process. The fabrication or filling facility may have several lanes of can ends streaming to or from various processing steps. Throughout the description of the present invention, groups of container ends generally will be referred to as "sticks of ends" as commonly used in the industry.

By way of background, many fabrication steps may be involved in the fabrication of container ends including stamping a blank end, conversion by which the stamped blank end is formed with a lip or curl, and, perhaps, application of a pull tab. Additionally, a suitable liner material, compound or coating may be applied to an inside surface of the curl of the container end. The curl is an annular groove around the outer edge of the container end in which an upper edge of the container body is mated with the container end. The liner compound provides a seal between the container end and the container body. A final step of the fabrication process may involve placing a predetermined number of container ends in a suitable bag or tray.

The liner compound may be applied in a powdered or liquid spray form, and often requires a period of heat curing prior to further processing of the container end. In the prior art, it has been the practice to deliver container ends, following the coating or spraying operation, to a generally large thermal oven. In general terms, the container ends are conveyed at a relatively low speed through such an oven. The speed of the conveyor through the oven, the overall length of the oven and the temperature inside the oven arc all selected to cure the liner compound while the container ends move therethrough. Numerous ovens and processing lines are used to maintain a desired rate of container end processing.

Use of these thermal ovens, however, has given rise to a number of problems and shortcomings. For example, the relatively large ovens consume considerable energy, thus adding considerable cost to the production of container ends. Further, these ovens can create a considerable amount of heat energy which must be dissipated from the surrounding working environment.

Additional problems include the length, the amount of space occupied by the ovens, and generally slow conveyor speed of such ovens. These ovens take up a relatively large amount of floor space within the container end processing facility. Floor space in such a facility commands premium cost and the use of numerous ovens can add considerable costs to the facility and correspondingly the production of container ends. The relatively long length of these conveyors create additional maintenance and operating problems. Container ends which arc displaced from the conveyor may become lodged in the conveyor or in the oven creating additional problems.

Objects and Summary

A general object satisfied by the present invention is to provide a liner compound curing apparatus which minimizes the cost associated with the production of container ends and the application of liner compound to such container ends.

Another object satisfied by the present invention is to provide a liner compound curing apparatus which minimizes the facility space required to cure liner compound on container ends in a process work flow.

Still another object satisfied by the present invention is to provide a liner compound curing apparatus which minimizes the thermal affects to the metal used to form the container end while curing the liner compound thereon.

Briefly, and in accordance with the foregoing, the present invention envisions a liner compound curing apparatus which includes a conveyor which passes through a high frequency or radio frequency ("RF") induction heating system. The induction heating system includes at least one elongated coil and may use a pair of spaced apart elongated coils. The curing apparatus passes the container ends in close proximity to the induction heating system for maximizing the inductive coupling between the RF induction heating system and the container ends. The conveyor uses a foraminous belt which is positioned between induction coils of the RF heating system. The foraminous belt is driven generally co-axially relative to the elongated coils. A vacuum system may be coupled to the curing apparatus to draw a vacuum on the container ends positioned on the foraminous conveyor belt to pull air through the foraminous conveyor belt. Such a vacuum may be used to facilitate holding the container ends against the conveyor belt allowing sufficiently close positioning of the can ends relative to the RF induction heating system. The curing apparatus provides a substantially shorter operating length compared to prior art thermal oven systems and provides the benefit of minimizing detrimental thermal effects on the container end and the liner compound.

Brief Description of the Drawings

The organization and manner of the structure and function of the invention, together with further objects and advantages thereof, may be understood by reference to the following description taken in connection with the accompanying drawings, wherein like reference numerals identify like elements, and in which:

FIG. 1 is a diagrammatic, perspective view of a curing apparatus of the present invention also showing a heat station and a power supply used with a radio frequency (RF) induction heating system and a protective barrier in phantom line;

FIG. 2 is a partial fragmentary, cross-sectional, side elevational view taken along line 2-2 in FIG. 1 showing a cross-section of the apparatus and the position of induction heating coils of the induction heating system relative to container ends traveling on a conveyor belt positioned in close proximity thereto;

FIG. 3 is a partial fragmentary, cross-sectional, top plan view showing the configuration of the upper induction coils used in the present invention;

FIG. 4 is a partial fragmentary, cross-sectional perspective view of a lower body portion over the top surface of which the conveyor belt moves and in which are formed air outlet apertures of a vacuum system; and FIG. 5 is an enlarged, partial fragmentaiy, cross-sectional side elevational view similar to that as shown in FIG. 2 to the relevant position and spacing of the coil with regard to a surface heated as a result of inductive coupling with the coils.

Description

While the present invention may be susceptible to embodiment in different forms, there is shown in the drawings, and herein will be described in detail, an embodiment with the understanding that the present description is to be considered an exemplification of the principles of the invention and is not intended to limit the invention to that as illustrated and described herein.

A curing apparatus 20 is shown diagrammatically in FIG. 1. The curing apparatus 20 includes an induction heating system 22 which provides high frequency or radio frequency induction heating of workpieces, such as container ends 24, which are carried on a conveyor belt 26, formed of a non-conductive material, passing therethrough. The induction heating system 22 includes a heat station 28 and a power supply 30. The induction heating system 22 provides inductive coupling to the material of the container ends 24 passing in close proximity thereto to provide a desired depth of penetration of heating and generally uniform heating. Induction heating is used to cure liner compound material applied to a surface of the container end 24. The liner compound material is generally applied to a curl 31 of the container end 24 in a known manner.

Curing of water based compound is similar to the drying process of any coating material such as paint. If excessive heat is applied to the surface of the compound being cured, the compound will form a skin over the top surface which will thereby trap moisture under the skin surface. As the moisture becomes heated it will tend to cause a blistering of the skin surface which will be unacceptable for various applications. The RF induction heating used in the present invention only heats the metal substrate of the container end 24. As such, drying is effectively promoted from the portion of the compound directly abutting the substrate of the can end 24 and preventing the formation of a skin over the exposed surface of the compound. In this manner, moisture may be driven off as the heat is conducted through the compound towards the surface.

The induction heating system 22 further includes an upper coil section 32 and a lower coil section 34. With reference to FIGS. 2 and 3, a generally continuous induction coil 36 is assembled and positioned in a serpentine pattern in at least the upper coil section 32. The coil 36 is a continuous hollow copper tube positioned in two serpentine paths on the upper coil section 32. As shown in the drawings, the coil sections 32,34 are molded into upper and lower body portions 35,37.

As shown in the FIGS., the coil 36 is subdivided into the upper coil section 32 and the lower coil section 34. Each of the upper and lower sections 32,34 include a pair of segments identified in the drawings as a first segment 39, a second segment 41 , a third segment 43 and a fourth segment 45. As shown in FIG. 3, the first and second segments 39,41 follow a serpentine path. The third and fourth segments 43,45 may follow a serpentine path or may follow a straight line path.

The coil 36 includes an inlet end 38 and an outlet end 40. Water flows through the center of the coil 36 to remove heat which might otherwise build up in the copper coil material. The cooling of the copper coil material improves the efficiently of the inductive coupling between the induction heating system 22 and the container ends 24 passing in close proximity thereto. Water flows from the first end 47 of the apparatus into the inlet end 38 and through the first segment 39 towards a second end 49 of the apparatus. The water then flows through an elbow 57 which connects the first segment and the third segments at the second end of the apparatus. Water then flows towards the first end of the apparatus and into the elbow 57 whereupon it is connected to the second segment 41 and flows towards the second end of the apparatus 49. The water then flows through a final elbow 57 which connects the second segment to the fourth segment which returns the water to the first end of the apparatus. At the first end of the apparatus, the water then flows out through the outlet end 40.

The coil 36 is formed in the dual path in at least the upper coil section 32 in order to heat the entire container end 24 and prevent heating only around the periphery of the container ends 24. The present invention provides greater and more uniform distribution of heat energy through the container end 24 by use of the serpentine dual paths on at least the upper coil section 32. As such, the more uniform distribution of heat energy in the container ends 24 provides more uniform, efficient and rapid curing of the liner compound applied thereto.

As more clearly shown in FIG. 2, the upper and lower coil sections 32,34 arc spaced apart and form a passage 42 therebetween. The conveyor belt 26 with container ends 24 positioned thereon travels through the passage 42. It can be seen that the vertical dimension 44 of the passage 42 is only slightly larger than the combined vertical dimension of the conveyor 26 and the container end 24. This close positioning of the upper and lower coil sections 32,34 relative to the container ends 24 promotes more efficient inductive coupling with the container end material and more rapid heating.

Adjustment mechanisms in the form of adjustable clamps 60 and spacers 62 provide adjustment and secure the relative position of the upper coil 32 relative to the lower coil 34 to accommodate a range of vertical container end dimensions. Fasteners 61 in elongated holes 63 in the clamps and spacers 60,62 provide a degree of adjustability and are tightened to secure the clamps and spacers 60,62 to the body portions 35,37.

Additionally, adjustable coils 32,34 allow the system to be customized to the specific dimension of each container end passing therethrough and to adjust the strength of the RF field of the coils relative to the container ends passing therebetween.

This adjustment system may accommodate a range of container ends which may be produced by the same facility thereby providing one curing apparatus to accommodate essentially all of the needs of any container end production facility. When adjusting the coils, shims are placed or removed in the area 51 between the surfaces 53,55 of the upper and lower body portions 35,37. The shims alter tubing elbows 57 between the upper and lower body portions 35,37 provide a degree of flexibility when making adjustments and generally are not adversely affected, especially because such adjustments are small.

In order to assure the close positioning of the coil sections 32,34 relative to the container ends 24 and prevent interference between the container ends and the upper and lower body portions 35,37, a vacuum system is employed to draw a vacuum through the passage 42 via a vacuum plenum 50. The vacuum (shown generally by arrow 48) is used to maintain the container ends 24 against the conveyor belt 26. It should be noted that the conveyor belt 26 is a foraminous material through which air may pass. As shown in FIGS. 1 -3 and particularly in FIG. 2, a plurality of air inlet apertures 52 are provided in the upper body portion 35 of the upper coil section 32. A plurality of air outlet apertures 54 are provided in the lower body portion 37 of the lower coil section 34. The upper air apertures 52 communicate with the ambient atmosphere and the passage 42, whereas the air outlet apertures 54 communicate with the passage 42 and the vacuum plenum 50.

The vacuum system provides its greatest effect with container ends 24 which are formed from a generally light material such as aluminum.

Movement of the conveyor may tend to jostle or move the generally lighter aluminum container ends if there are any vibrations or other effects which might move the container ends relative to the belt. However, the vacuum system maintains the container ends in a generally consistent position along the path of travel of the conveyor belt thereby providing predictable location and placement of the container ends relative to the coils.

As such, when the vacuum 48 is operated, the vacuum pulls air through the vacuum plenum 50. The vacuum plenum 50 pulls air from the ambient atmosphere through the air inlet apertures 52 through the passage

42 and through the air outlet aperture 54. Air passes through the conveyor belt 26 and the vacuum forces retain the container end 24 against the conveyor belt 26.

In FIG. 1, the heat station 28 and the power supply 30 of the curing apparatus 20 are shown diagrammatically positioned away from the coils

32, 34 of the induction heating system 22. Generally, the overall induction heating system is of the type such as is provided by Ameritherm Inc. of Scottsville, New York. The power supply operates in the RF range to provide power in the range of 50-200 kHz. The power supply constantly tunes the frequency of the power on a one microsecond loop to deliver maximum power to the load, the container ends, at all times to increase the efficiency of the operation of this system.

As further shown in FIG. 2, the upper section 32 and the lower section 34 are held together by means of the clamp 60 and a spacer 62. The coil 36 in the upper and lower sections 32,34 is embedded or molded in a suitable material which encapsulates the coil 36 to maintain the serpentine pattern of the coil and to isolate the coil from direct contact with a container end 24 passing thereby.

A protective barrier 68 (shown in phantom line in Fig. 1 and in cross- section in Figs. 2 and 3) is provided to protect workers from the induction heating system 22. The barrier 68 is formed of an ultra-high molecular polyethylene which helps guard workers and keep their hands away from the field created by the induction heating system. The barrier 68 is spaced a desired distance away from the induction heating system as required by the operating limitations of this system. The present invention substantially reduces the floor area required to cure container ends and substantially reduces the time. Prior art systems may have required several minutes in order to cure container ends in a flat orientation. The container ends in the present invention are cured quickly as they travel through the length of the induction heating system 22. The container ends 24 are cured in the flats.

In use, the present invention provides rapid and reliable curing of liner compound on container ends. At least one elongated coil is positioned in close proximity and generally coaxial with a path of travel 70 (See FIG. 1 ) through which the conveyor belt 26 moves the ends 24. Container ends 24 are moved by the conveyor belt 26 along the path of travel 70. A high frequency field is established through the coil 36 to produce inductive coupling between the coil 36 and the material of the container ends 24. The container ends are moved for a predetermined period of time to produce a desired inductive coupling characteristic to produce desired heating effects and drive off moisture from the liner compound disposed on the surface of the container ends.

A vacuum is applied to the apparatus in order to retain the container ends in a flat condition against the conveyor belt. A foraminous conveyor belt is provided to allow air to pass therethrough as a result of the vacuum which is induced from the upper body portion through the chamber to the lower body portion.

The coil may be adjusted relative to one another to produce a desired heating effect on container ends moving relative thereto. In this manner, the relationship between the power applied to the coils and the heating of the container ends thereby can be fine-tuned to produce desired effects.

While a preferred embodiment of the present invention is shown and described, it is envisioned that those skilled in the art may devise various modifications and equivalents without departing from the spirit and scope of the invention.

Claims

The Invention Claimed Is:

1. An apparatus for curing a compound on at least one workpiece, said apparatus comprising: an induction heating system including an upper coil section and a lower coil section, said coil sections defining a generally continuous single path coil and being spaced apart defining a passage therebetween; and a conveyor moving through said passage between said upper and lower coil sections for transporting said at least one workpiece in close proximity to said upper and lower coil sections.

2. An apparatus as recited in claim 1 , further comprising: a vacuum system for creating a vacuum between said upper and lower coil sections to promote retention of said at least one workpiece on said conveyor passing through said passage between said upper and lower coil sections.

3. An apparatus as recited in claim 2, further comprising: said conveyor being foraminous for allowing air flowing through said cavity as a result of said vacuum system to flow through said conveyor.

4. An apparatus as recited in claim 1, wherein said conveyor is a non-conductive material to prevent inductive coupling with said upper and lower coil sections.

5. An apparatus as recited in claim 1 , wherein at least one of said upper and lower coil sections is adjustable with respect to said at least one workpiece passing in close proximity thereto.

6. An apparatus as recited in claim 1 , wherein at least one of said upper and lower coil sections include a pair of elongated serpentine segments.

7. An apparatus as recited in claim 1 , wherein said upper and lower coil sections include a first segment extending from a first end of said apparatus to a second end of said apparatus; a second segment extending from said second end to said first end; a third segment extending from said first end to said second end; and a fourth segment extending from said second end to said first end, whereby said first, second, third and fourth segments define a continuous coil which starts and ends at said first end of said apparatus.

8. An apparatus for curing a compound material on a workpiece, said apparatus including an inductive heating system for producing a heating effect on workpieces passed in close proximity thereto, said apparatus comprising: at least one elongated, single path induction heating coil; a conveyor positioned in close proximity to said coil and generally extending coaxially with said elongated coil for defining a path of travel relative to said coil, said conveyor moving workpieccs generally parallel to said coil.

9. An apparatus as recited in claim 8, further comprising: a vacuum system for creating a vacuum between said upper and lower coil sections to promote retention of said at least one of on said conveyor passing through said passage between said upper and lower coil sections.

10. An apparatus as recited in claim 8, further comprising: said conveyor belt being foraminous for allowing air flowing through said passage as a result of said vacuum system to flow through said conveyor.

1 1. An apparatus as recited in claim 10, wherein said conveyor is a non-conductive material to prevent inductive coupling with said upper and lower coil sections.

12. An apparatus as recited in claim 8, wherein at least one of said upper and lower coil sections is adjustable with respect to said at least one workpiece passing in close proximity thereto.

13. An apparatus as recited in claim 8, wherein at least one of said upper and lower coil sections include a pair of elongated serpentine segments.

14. A method of curing a compound liner material on a workpiece, said method including providing at least one generally elongated, single path induction heating coil, providing a conveyor being driven in a path generally parallel and generally proximate to said elongated coil for conveying workpieces relative to said induction heating coil, said method including the steps of: inducing a high frequency energy through said coil; and moving said workpieces in close proximity to said coil generally coaxial with said elongated coil.

15. A method as recited in claim 14, further comprising the step of: applying a vacuum relative to said conveyor for retaining said workpieces on said conveyor.

16. A method as recited in claim 14, further comprising the step of: providing a foraminous conveyor material for facilitating movement of air through said conveyor material under the influence of said vacuum.

17. A method as recited in claim 14, further comprising the step of: adjusting the relative position of at least one section of said coil with respect to said conveyor for adjusting the energy transfer from said induction heating coil to said workpieces carried on said conveyor.

18. A method as recited in claim 14, said method including providing an upper coil section and a lower coil section, said coil sections being spaced apart, said method further comprising step of: conveying said workpieces on said conveyor between said upper coil and said lower coil.