JPH092432A - Inducing/heating mechanism to harden coating of can body at 360× - Google Patents

Abstract

PROBLEM TO BE SOLVED: To heat a can body all parts of its periphery alike and uniformly so as to cure or partially cure the protective coating thereon by placing the can body at the center of an induction coil and subjecting it to induction heating by use of a medium-frequency magnetic field. SOLUTION: An induction heating device 100 comprises a housing 104, an insulating tube 106 passed through an interior chamber 109 defined by the housing 104, and an induction coil 108. A can body 102 is conveyed by a chain 118, enters the heating device 100 from the front end 105, and goes out through the rear end 107. The heating device 100 is furthermore equipped with a power source 110, a control circuit 112, and a blower 114 which circulates air throughout the chamber 109. Into the induction coil 108 a current oscillating in a frequency range of approximately 500Hz to 50kHz is injected so as to produce an oscillating magnetic field along the heating path, heat the can body 102 throughout the full range of 360 deg. by induction heating, and evenly cure the protective coating applied on the can body 102.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to methods and apparatus for heating or treating a metal object, and more particularly to induction heating a metal can body and drying the coating thereon, partially cured. A method and apparatus for causing or curing and for transporting a can body through an induction heating device.

[0002]

BACKGROUND OF THE INVENTION In a method of making a three-piece metal can for storing food and perishable items, a cylindrical can body is generally formed from a precoated metal sheet and the ends of the can body are precoated. Attach the two lids. The precoat protects the contents of the can from contamination and prevents corrosion of the metal by the contents of the can. After forming the can body into a cylinder, the edges of the sheet are welded along the seam. At least in the area of the seam, it is necessary to apply side stripes of the protective coating, since welding damages the protective precoat around the seam.

After welding the seam, during the process of processing the can,
It is known to provide a protective coating around 360 ° around the can body.
This can be done instead of using a pre-coated can material or in addition to the pre-coated can material when an additional layer of protective coating is desired. Furthermore, by welding the seams and then applying a 360 ° coating, the work of applying protective side stripes to the welded seams can be omitted. Such a protective coating is in the form of powdered resin,
Alternatively, it can be applied to the can as a solvent-based liquid.
After applying the protective coating to the can body, the coating is cured onto the can body by a heating process that generally involves both heating and time.

Since the protective coating applied around the can body may separate before curing, it is important to heat the coating as soon as possible after application so that the coating adheres to the can body. It is also important to heat the can body uniformly to ensure that all parts of the coating are fully cured without overheating in only one place. If the heating of the can is too little,
Inadequate curing of the coating on the can body and overheating of the can body can cause the coating to blister and even melt the metal forming the can. If the coating bulges, the protective coating becomes non-uniform and the appearance is poor.

In conventional can processing and assembly lines, the can body is typically transported from the coating process to a heating oven where the coating is cured by a generally convective air flow. Such a mechanism is
It is large and tends to take up space, and requires a large space in the processing plant. Moreover, much of the heat generated by such ovens is absorbed by the walls of the heating chamber and into the air, with only a small fraction of the heat generated (most often about 20%) actually heating the can body. is there. Therefore, such a mechanism has low operating efficiency and is expensive.

Can bodies typically exit the coating process in a single row. To increase the throughput of the processing steps, the can bodies are removed from their single row and aligned, typically 10-20 cans side by side, before being placed in a curing oven. After the heating step, the cans are realigned into a single row again. Such a procedure has double drawbacks. First, it requires equipment and additional processing steps to align and realign the can bodies before and after the heating step. This increases the processing time and costs. Second, the can body must be touched in order to line the can bodies in several rows before the protective coat is cured, which contact may result in loss or damage to the protective coat.

Another problem with convection heating, especially for curing liquid coatings, is that such conventional heating mechanisms heat the coating from the outside to the inside. Thus, the outer surface of the coating forms an epidermis that traps the liquid beneath it and tends to swell in an attempt to break the outer epidermis.

Another problem arises when the can body stays in the heating chamber for longer than intended, such as when the conveyor mechanism that carries the can body fails. In this case, even if the convection oven is switched off, the heat in the oven continues to heat the can body, and the can body may be overheated and destroyed.

Induction heating devices for overheating electrically conductive workpieces are known. In induction heating, an oscillating current is basically passed through an induction coil to create an oscillating magnetic field, and a conductive processed product is placed therein. Heat is generated in the work piece due to the eddy current loss due to the circulating current induced in the work piece by the magnetic field. It is important that the heat generated in the work piece is directly related to the distance between the work piece and the induction coil. The smaller the distance between the work piece and the induction coil, the more heat is generated in the can body, given the other parameters of the system.

Prior art induction heating mechanisms generally have 10
It operates at high frequencies on the order of 0 kHz to 250 kHz. High frequencies tend to minimize the depth of current generated below the surface of the workpiece (skin effect). As a result, the heat generated in the work piece by the high frequency current is concentrated near the surface of the work piece.

Operation at high frequencies has several drawbacks with respect to heating the can body. The first drawback is related to the heating uniformity in the can. Factors such as deformed parts in the work piece and unexpected movement of the work piece relative to the conveyor path change the spacing between the work piece and the induction coil, which is why
As described above, the amount of heat generated in the processed product varies. The problem with high frequency currents is that due to the high concentration of heat near the workpiece surface, such currents increase this heating non-uniformity. Therefore, depending on the proximity to the coil and other factors, the degree of heating of each part of the processed product changes greatly. As a result, localized overheating can easily and frequently occur before other parts of the workpiece are heated to the desired temperature.

Moreover, high frequency currents flow in the induction coil and also near the surface of the conductor which carries the current in the induction coil, which causes the conductor to overheat. Therefore, a water cooling mechanism for sufficiently cooling the conductor is required. Typically, these conductors are constructed using copper tubing with water flowing through their center.

Although the general induction heating method and apparatus do not necessarily solve the special problem of the can body, the following US patent, Miller No. 4,339,645:
No. 4,481,397 to Maurice, 4,296,294 to Beckert, 4,849 to Nozaki,
598, No. 4,160,891 to Scheffler, Ku
No. 4,307,276 to rata, No.4,5 to Curtin
82,972, No. 4,673,781 to Nuns, Ca
No. 4,531,037 to mus, No. 4,775,772 to Chaboseau, No. 4,810,84 to Wicker
No. 3 and 3,727,982 to Itoh.

Conventional induction heating mechanisms are known for welding can body seams and are described, for example, in US Pat. No. 4,783,233 to Yasumuro. Induction heating welding does not have many of the problems associated with induction heating drying and hardening, and there are some important differences between the two methods. For example, welding methods do not require the workpiece to be heated too quickly. Appropriate welds are formed as long as a sufficient amount of heat is generated in the work piece within a certain period of time. However, with the curing method, if the workpiece is heated too quickly,
Liquid paint blisters may occur (as above),
The powder may harden before flowing evenly around the surface of the can body.

Another important difference between welding and 360 ° can body perimeter hardening is that induction heating welding has a one-dimensional alignment problem. That is, as shown in the cross-sectional view of FIG. 1, at some instant during the welding process, the induction heating device may follow a seam passing under it to become a single point on the workpiece, as indicated by the arrow. It is heating. As mentioned above, the amount of heat generated in the work piece is directly related to the distance between the work piece and the induction heating element. Therefore, to control the amount of heat generated at a point on the weld seam, the position of the induction heating device relative to that point need only be adjusted.

In contrast, in the case of 360 ° induction hardening around a cylindrical workpiece such as a can, there is a two-dimensional alignment problem. That is, as shown in the cross-sectional view of FIG. 2, at the moment when the curing step is performed, the induction heating device is placed around the workpiece by the arrow B.
All points indicated by ₁ , B ₂ , ... B _i must be heated. Therefore, in order to control the amount of heat generated at each point around, it is necessary to adjust the position of the induction heating device with respect to each such point. To the Applicant's knowledge, there has hitherto been no mechanism to achieve 360 ° cure around the can body.

[0017]

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a method and apparatus for heating a can body of 360 ° which overcomes some or all of the above disadvantages.

[0018]

SUMMARY OF THE INVENTION The present invention relates to 360 ° induction heating of a can body for heating, drying, curing and / or partially curing a protective coating applied to the can body.
The can body is induction heated by placing the can body in an oscillating magnetic field of medium frequency (500 Hz to 50 kHz) generated by a multi-winding induction coil preferably spirally wound around the transportation path of the can body. . By using a medium frequency magnetic field and centering the cans in the induction coil, the cans can be heated uniformly around their 360 ° and evenly.

The cans are conveyed longitudinally end-to-end through an induction heating device on a conveyor that receives the cans from the protective coating process. The can body and conveyor pass through the induction heating device in a non-conductive insulating tube. To prevent the circulating air in the device from blowing off the coating in the can,
And the insulation tube insulates the can body from the induction coil so that the coating remote from the can body is retained in the tube and does not fall onto the inside of the induction coil, electrical component or device.

The induction coil is spirally wound over the length of the insulating tube so that a magnetic field for heating the can is created in the insulating tube. The diameter of the insulating tube is only slightly larger than the diameter of the can so that the can body moves through the heating device in a relatively constant central position relative to the insulating tube and the induction coil. Thereby, the can body is uniformly heated over the entire circumference thereof.

As mentioned above, an air circulation mechanism for cooling the induction coil can be provided in the heating device. Since medium frequency currents are used, the current travels deeper in the conductors leading to and in the induction coil so that the conductor does not become too hot. Therefore, the electrical components and the induction coil can be cooled in a relatively simple and inexpensive convection airflow mode.

Further, as a result of using the medium frequency current, a tube for cooling water through a conventional center in the coil,
It can be replaced by a wire with a smaller diameter. Such a coil is cheaper to use than conventional copper tubing, and can be wrapped around a length of insulating tubing with more turns if desired, thereby providing the required current. The advantage is that the amount can be further reduced.

A temperature sensor is provided in the insulating tube, the temperature of the can body passing therethrough can be monitored, and the power can be turned off when the temperature exceeds a predetermined threshold value. The conveyor mechanism cured after leaving the device,
Alternatively, the partially cured can is conveyed to an adjacent processing area or other conveyor mechanism.

[0024]

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIGS. 1-9, the present invention generally relates to an induction heating apparatus and conveyor mechanism for curing or partially curing a protective coating on a can during the can manufacturing process. Will be explained. The present invention can be applied to food or other,
Although described with respect to making cans containing such perishable items, the present invention can be used in a wide variety of applications where it is desirable to cure or uniformly heat the 360 ° circumference of a cylindrical workpiece. Further, while the invention is described with respect to ferromagnetic steel cans, it should be understood that the invention can be used to heat other electrically conductive workpieces such as aluminum cans.

As explained in the section of the prior art, it is generally desirable to coat the circumference of the cylindrical can body 360 ° with a coating of dry resin powder or solvent-based liquid. Methods and apparatus for applying such protective coatings are owned by the assignee of the present invention and are incorporated by reference herein in US Patent Application entitled "Methods and Apparatuses for Powder Coating Welded Cans". No. 08 / 393,150. As described in that application, the protective powder coating is electrostatically charged during the coating process to attract and deposit the powder coating particles inside the electrically grounded can body. The protective coating then needs to be cured on the can body. In accordance with the present invention, an induction heating mechanism is used to dry, melt, cure and / or partially cure the protective coating on the can body.

In the preferred embodiment, the protective coating is fully cured in the induction heating apparatus of the present invention, thereby eliminating the conventional convection oven. However, it goes without saying that the induction heating device according to the invention can also be used in addition to a conventional convection oven, in which case it is carried out before (pre-curing) or after (post-curing) the heating of the can in the convection oven. , An induction heating device partially cures the protective coating. As production speeds have increased and paints have changed over the years,
Existing ovens may sometimes achieve only minimal cure. Therefore, the quality of curing can be improved by the pre-curing or post-curing method of the present invention. further,
Partially curing or preheating immediately after applying the protective coating eliminates the need for careful handling of the can body and increases the line speed between the coating area and the conventional convection oven. Can be increased.

Referring now to FIG. 3, an induction heating apparatus 100 for heating a plurality of cans 102 is shown. The can enters the heating device at the front end 105 and exits through the rear end 107. The chain 118 conveys the can body longitudinally through the heating device, i.e. the central axis of the can body cylinder is essentially parallel to the direction of movement of the can body, the can bodies being end to end but end to end or almost It may be a match. The device 100 includes a housing 104, which is cut away in FIG. 3 to show an insulating tube 106 and an induction coil 108 through an inner chamber 109 defined by the housing 104. (The winding interval of the induction coil 108 shown in FIG. 3 is provided for the sake of clarity and does not limit the present invention). The device 100 also has a power supply 1
10, a control circuit 112, and a blower 114 for circulating air throughout the chamber 109.

The housing 104 preferably encloses the induction coil 108 on all six sides of the heating device 100 and shields the power and control circuits from medium frequency oscillating currents flowing through the coil 108 to protect personnel. It is preferably made of a conductive metal material. As described in detail below, the oscillating magnetic field created by the induction coil 108 is concentrated in the tube 106. Therefore, the housing 104 is hardly heated.

Vents (not shown) may be provided in the top and / or sides of the housing 104 to circulate the air heated by the induction coil 108 and remove it from the housing. In a preferred embodiment, the heating device 100 has a length of about 13 to 20 feet parallel to the direction of travel of the can, a height of about 3 feet, and a width of about 2 feet. As will be apparent to those skilled in the art, these dimensions can be varied in other embodiments of the invention. As described in detail below, the length of the device 100 can vary depending on the extent to which the can body 102 is heated and / or the speed at which the can body moves through the device 100. That is, at a constant velocity, the longer the device, the more heat is generated inside the can body passing through it. Can body 1
02 passes through the insulating tube 106 and the heating device 10
It is transported through 0. The tube 106 extends the length of the chamber 109 and is sealed to the wall of the housing 104 by hubs at both ends of the tube. Thus, since the can body passing through the tube 106 is physically isolated from the chamber 109, the cooling air circulating in the device does not blow off the paint in the can body and is separated from the can body. The paint is held in the tube 106 and does not fall on the heating coil 108 or the room 109.

When heating a cylindrical workpiece such as the can 102, in order to ensure uniform heating over the entire circumference of the workpiece, the workpiece is essentially concentric with the induction coil throughout the heating process. It is important to be in a shape. Therefore, the insulating tube 106 preferably has a diameter that is only slightly larger than the diameter of the can body 102. For example, the can body 102
If the diameter of the tube is 4-1 / 4 inch, the inside diameter of the tube 106 may be about 4-3 / 4 inch. Therefore, the tube 10
Of the six, only about a quarter inch is off center. Of course, the gap between the can body 102 and the tube 106 may be larger or smaller depending on the respective implementation. When curing liquid paints, air is the tube 1
The tube 106 and the can body 10 are circulated in the can body traveling direction 06 or in the direction opposite to the can body traveling direction.
It is advantageous to leave about a quarter of the gap between the two. In such an embodiment, heated air may be circulated from the chamber 109 through the tube 106 to promote uniform heating by air convection and carry away evaporated solvent from the protective coating.

The insulating tube 106 is an induction coil 108.
It is non-conductive so that it is not heated by. Moreover, in order not to disturb the magnetic field formed by the induction coil 108,
The tube 106 is magnetically non-electrically driven. Any of several materials can be used for the insulating tube 106, but Pyrex® is the preferred material because it has high heat resistance, is visibly transparent, and inexpensive. Although not critical to the invention, the wall thickness of tube 106 may be about 0.2-0.4 inches. Such a tube
Available from FJ Gray Company, Jamica, New York, 11435.

As shown in the side view of FIG. 4 and the cross-sectional view of FIG. 5, the can body 102 is supported within a tube 106 on a chain 118, which chain comprises the tube 106.
Supported in a channel 120 on the bottom of the. In the channel 120, the chain 118 has an insulating tube 106.
The purpose is not to wear or wear the bottom of the.

The chain 118 is preferably made of stainless steel. Although stainless steel is a conductor,
It does not overheat as only part of its entire path of travel is in the heating device (as shown in FIG. Furthermore, chain 1
The cross-sectional diameter of 18 is preferably on the order of about 0.125 to 0.25 inches, which is small compared to the cross-sectional area of the induction coil. As will be apparent to those skilled in the art, if the cross-sectional area of the conductor is small compared to the cross-sectional area of the induction coil, the heat generated in the conductor will be very small. Therefore, the chain 11
8 does not overheat. Of course, in other embodiments of the invention, the chain 118 can be made of other materials. Channel 120 is preferably made of a non-conductive material such as ceramic or high density plastic.

In the preferred embodiment of the invention, the width of channel 120 is about 0.7 inches and the combined height of chain 118 and channel 120 is about 0.35 inches.
However, as will be apparent to those skilled in the art, these dimensions can be varied in other embodiments of the invention. As shown in FIG. 7, the channels 120 may extend along the entire upper surface of the conveyor mechanism 124.

As described above, it is important that the can body has a relatively small gap in the tube 106. Since can manufacturing often involves cans of various sizes, the tube 106 is removable so that tubes of various diameters can be used. When replacing the tube 106, first remove the chain 118 and remove it from the tube. The channel 120 is then removed and the induction coil 108 is disconnected from the power supply. Next, the tube 106 is attached to the housing 10.
The hub supporting in 4 is removed, the tube 106 is slid sideways and removed from the coil 108 and the device 100. In the position embodiment of the invention, the coil 108 is also removed at this point. Then insert the new diameter coil and tube. After placing the new coils and tubes, reconnecting the hubs, coils, channels, and chains allows the device 100 to operate again. In the preferred embodiment, the tube 106 is selected so that there is always about a quarter of the clearance with respect to the can body 102.

As noted above, in the preferred embodiment, the coil 108 is also replaced when the tube 106 is replaced so that the coil is wound tightly, essentially concentrically, around the tube of all diameters used. Exchange. In another embodiment of the present invention, a single tube and coil are used for can bodies of various diameters to raise or lower the entire upper surface of the conveyor mechanism 124, including the channel 120, relative to the tube 106 and the coil 108. The space between the can body 102 and the can body 102 can be maintained concentrically.

The power supply 110 is connected to the induction coil 108 via a wire 152 (FIG. 10), and the coil 108 has about 50
It provides an AC current oscillating at a medium frequency of about 6 kHz to 18 kHz for a can body wall thickness of 0 Hz to 50 kHz, optimally on the order of about 10 to 15 mils. This oscillating current produces an AC eddy current around the can body 102 that also oscillates at the same frequency, heating the can body as it moves through the tube 106.

As explained in the section of the prior art, the high frequency current tends to concentrate the heat generated in the work piece near the surface of the work piece, which causes a relatively small variation in the distance between the work piece and the induction coil. It causes a large temperature change. But,
The present invention uses medium frequency currents which tend to generate currents deeper in the can 102. The deeper current distributes the heat generated across the larger cross-sectional area of the can body 102. Therefore, when the distance between the coil 108 and the can body 102 changes, the variation in heat generated is shared by the larger cross-sectional area of the can body. By sharing the generated heat fluctuations over a larger cross-sectional area, the overall temperature change at all points within the can body cross-sectional area is reduced. Thus, the present invention minimizes temperature changes due to undesirable spacing variations between the coil 108 and the can body 102.

In addition, the medium frequency current through the wires connecting to the coil 108 and the wires in the coil is more evenly distributed through the wires. Therefore, the heat generated in the coil 108 is relatively small, and the coil 108 can be formed by an inexpensive standard 8-gauge winding. However, of course, other materials can be used for the induction coil if desired, such as multi-strand litz wire. The coil 108 extends substantially the entire length of the heating device 100, with each turn of the coil being spaced about 0.125 to 0.25 inches from the next adjacent turn and wound about 4 to 8 turns per inch. You can However, of course, the winding spacing of coil 108 may be greater or less than the above range in other embodiments of the invention. For example, the wires can be wound without spacing between adjacent turns so that the wires are wound in contact with each other. As will be appreciated by those skilled in the art, by using a low frequency current, the coil 108 can be formed of a small diameter wire, such as that provided by a winding of 8 gauge or less. Therefore, if no space is provided between the adjacent windings, the number of windings per unit length of the tube 106 can be increased, and thus the current required to heat the can body 102 can be reduced.

In the preferred embodiment of the invention, 8.5 k
At 100 Hz, the power supply 110 delivers about 3.5 kW to the coil 108.
To produce a tank current of about 150-200 amps RMS. In one embodiment of the invention, the current, frequency, 1
By combining the number of turns per inch, the spacing between the coil 108 and the can body 102, the can body thickness, and the length of the heating path, the can body 102 is heated from room temperature when it enters the device 100 to the device 100.
Can be heated up to about 220 ° C. at the outlet of about 4 seconds.

Of course, the values given for power, current, frequency, spacing and temperature are merely examples and may be varied in different embodiments of the invention. Moreover, different protective coatings cure at different temperatures. In a preferred embodiment, the heat generated in the can body 102 can be adjusted by changing the length of the induction heating device 100. Alternatively, two or more induction heating devices 10 of the present invention
The 0s can be aligned vertically adjacent to each other to increase the path length of the can body 102 through the induction heating process.
As will be appreciated by those skilled in the art, by changing other mechanical parameters such as the spacing between adjacent turns of coil 108, the output of power supply 110, and / or the processing speed of the can body 102. It is also possible to change the heat generated in.

Depending on the heating application, it may be desirable to apply more heat at the beginning of the heating cycle than at the end of the heating cycle. Therefore, in another embodiment of the present invention, an induction coil. The tube 106 can be wound more tightly at the front end than at the rear end. Further, as will be appreciated by those skilled in the art, the number of turns of coil 108 per unit length can be increased or decreased at any point along the length of coil 108, thereby increasing or decreasing heating in that portion of the coil. You can also let it.

Since the power required to cure the coating on the can body 102 is relatively low, a relatively simple air cooling scheme can be used to prevent overheating of the induction coil 108. As shown in FIG. 3, the blower 11 is placed on the control circuit 112.
4, cooling air may be circulated over or around the coil 108. Since an induction coil with a large cross section is used to pass the oscillating current, the capacity is about 300-5.
One blower that circulates cooling air at room temperature at 00 cfm
Sufficient to cool the entire length of the induction coil. But,
Those skilled in the art will appreciate that more than one blower 114 may be provided along the length of the coil 108 to cool the airflow in the chamber 109 prior to circulation. Furthermore, the blower 11
4 at various positions in the chamber 109 and the induction coil 108
Can also be cooled.

In the present invention, the can body 102 is a tube 1.
A closed loop temperature controller is included to monitor the temperature of the can body 102 as it passes through 06. As shown in FIG. 3, one or more temperature sensors 119 in the tube 106.
And can detect the temperature of the can body 102. The sensor 119 is manufactured by Watlow Electric Manufacturing Co.,
Infrared (I commercially available from St. Louis, MO, 63146
R) A conventional temperature sensor such as a sensor may be used. Can body 1
If the temperature of 02 is higher than the predetermined temperature, the sensor quickly senses this condition and a signal is sent to the control circuit 112 to turn off the AC current source. This stops all current in the can body 102, thereby preventing the can body 102 from becoming hotter almost immediately. When the temperature sensor 119 senses that the temperature of the can body 102 has returned to a predetermined temperature, the sensor 11
9 sends another signal to the control circuit 12 to turn on the AC current source again. However, since a medium frequency current is used as described above, in another embodiment of the present invention the temperature sensor 1
19 may be omitted.

Although omitted in FIG. 3 for the sake of clarity, the front end 105 or the rear end 107 of the heating device 100 is shown.
Is an emitter 121 and a sensor 1 as shown in FIG.
A linear motion sensor mechanism consisting of 22 may be included.
Emitter 121 may be, for example, a conventional light source for emitting light beam 125, in which case sensor 122 may be a conventional optical sensor. The can body when the can body enters the heating device 100 (when the sensor mechanism is located at the front end portion) or when the can body exits the heating device 100 (when the sensor mechanism is located at the rear end portion). Is the sensor 1 of the ray 125
Periodically prevent transmission to 22. If the sensor 122 does not receive a signal, or if the sensor 122 receives a constant signal after a longer time than the predetermined time, this means that the can body 102 has a predetermined processing speed. This is an indication that the process has not progressed and the device 100 is stuck. In this case, sensor 1
22 sends a signal to the control circuit 112, and the induction coil 108
The power supply to the heating device 100 is stopped, thereby preventing overheating of the can body in the heating device 100. As described above, turning off the power prevents the can body from becoming hotter than almost instantly. Thus, using both the temperature sensor 119 and the linear motion sensor mechanism, the heating device 100
It is possible to prevent overheating of the can body inside. In addition, the linear motion sensor mechanism can also be used to detect conveyor mechanism stalling and turn off the current to the induction coil 108.

The power supply 110 is an alternating current power supply having a current output section connected to both ends of the coil 108 via a wire 152 (FIG. 10). The frequency of the current oscillation is essentially the same as the strong seismic frequency of the coil in combination with the tank capacitor (not shown) in the power supply 110, on the order of 8 kHz. Other frequencies can be used, if appropriate tank capacitors are used. Preferably, when powering up the power supply 110 for the first time, the power supply will have a given tank capacitance and inductance,
Automatically optimizes the frequency of power transfer into the work piece,
However, it is decided according to the standard.

The current output of the power supply 110 should be relatively constant and have a low harmonic content. The subharmonic content reduces the skin effect on the leads 152 to the tank capacitors and coils, thereby allowing thinner leads to be used. It should also be as close as possible to the tank capacitor coil 108.

The output of the power supply 110 is preferably not only adjustable by the low frequency duty cycle, but continuously adjustable during start up and shut down. This is because the duty cycle pulse may cause the can body to vibrate, which may cause some of the protective coating to vibrate and delaminate. Starting and stopping the power supply 110 can be accomplished, for example, by gradually increasing and decreasing the DC voltage to the power supply 110, respectively. General notes about power supplies are included in Lowdon's "Practic," for example
al Transformer Design Handbook ", 2nd ed. (TAB Book
s, 1989).

As shown in FIG. 10, the control circuit 112 preferably includes a conventional central processing unit (CPU) for monitoring the operation of the power supply 110 and for monitoring temperature, as described above, temperature sensor 119 and temperature sensor 119. The feedback signal coming from each of the linear motion sensors 122 can control the entire device 100. The control circuit further includes a power output,
Screen display of system parameters such as current frequency and body temperature and connection to conventional input / output devices (not shown) for dynamically controlling and modifying such system parameters. be able to.

7-9, there is shown a conveyor mechanism 124 for transporting the can body 102 from the protective coating process through the heating device 100 to the next processing zone. The conveyor mechanism 124 includes an endless chain 118 and a can guide portion 126.
a and 126b, drive wheels 128-134, and tensioning wheel 136. The chain 118 is preferably made of conventional stainless steel, generally 0.10, with a generally flat surface profile.
It is a 125-0.25 inch chain. But of course,
The can body 102 can be carried on any of various conveyor mechanisms such as linear motors, belt drives, pushers, pullers, gravity slides, etc.,
However, the conveyor loop must be able to be disconnected and reconnected in order to replace the insulation tube 106 through which the conveyor passes. In a preferred embodiment,
The total loop length of chain 118 is about 50 feet.

In a preferred embodiment, the induction heating device 10
The inlet to 0 is about 3 inches to 3 feet, preferably about 1.5 feet away from the spray coater. During operation, the cans coming from the spray painting process are carried in one row to the zone 138 of the conveyor mechanism 124 and then to the chain 11
8 is conveyed through the heating device. Heating device 100
After exiting, the can body 102 is transported along the zone 140 to the next processing step. At the end of the induction heating step, a conventional magnetic elevator can be used to pull the can body 102 away from the chain 118. If the can body 102 is not ferromagnetic, a mechanism such as a mechanical arm conveyor can be used to move the can body.

As shown in FIG. 9, the chain 118 includes a plurality of hooks 142 arranged at intervals slightly larger than the length of the can body 102. The can body is placed on the chain 118 from the spray painting process and is maintained on the chain 118 at predetermined intervals by the hooks 142. In another embodiment, the hook 142 can be omitted and the can body 102 held in place by contact with the chain 118. As shown in FIGS. 7 to 9, the can body has the conveyor mechanism 1
A pair of can guides 126 attached to both sides of the upper surface of 24.
By a and 126b, it does not roll in the direction perpendicular to the processing direction. Can guide portions 126a and 126
b preferably extends along the entire upper surface of the conveyor mechanism 124 except within the heating device 100.

Those skilled in the art will appreciate that friction wheel 128
~ 134, the chain 118 can be advanced by friction or mesh engagement between the chain 118 and the wheels 128-134. One or more of friction wheels 128-134 may be rotated by a drive motor (not shown) to advance chain 118. As will also be apparent to one of ordinary skill in the art, the conveyor mechanism 124 further includes a tensioning wheel biased away from the friction wheels 130 and 132 mounted for translation to maintain tension in the chain 118. 136 may be included.

As noted above, in embodiments that include a single tube 106 and coil 108, the chain 118 and channel 120 can be raised or lowered to accommodate cans of various diameters in a concentric relationship with the coil 108. . Thus, the wheels 128 and 130 can be vertically adjusted to raise or lower the height of the chain 118 relative to the heating device 100. Similarly, the channel 120 is adjustably mounted to raise or lower with the chain 118. Chain 11
The looseness of No. 8 can be absorbed by the parallel movement of the tensioning wheel 136 as described above. In a preferred embodiment of the invention, the conveyor mechanism 124 moves the can body 102 at about 135 minutes per minute.
With speeds up to 0 cans, optimally about 600 cans per minute can be advanced.

[0055]

As described above, the induction heating mechanism described above is used for the periphery 36 of the can.
The 0 ° coating can be dried, pre-cured, post-cured or cured. As mentioned above, various coatings and line speeds can be accommodated by adjusting the amount of heat generated in the can body 102. The heating and conveyor mechanism of the present invention provides several advantages over conventional convection heating mechanisms for curing the 360 ° perimeter of the can body. For example, the induction heating mechanism disclosed herein can heat a can body with an efficiency of 80-90%, as compared to a conventional convection oven with an efficiency of about 20%. Moreover, the induction heating device of the present invention is a collective handling device or 1 for aligning a row of cans in several rows and then realigning them in a row again.
No need for row alignment equipment. Furthermore, the induction heating device of the present invention is extremely small, occupies only a small portion of the space occupied by a conventional convection heating oven, and is more efficient than conventional convection ovens in terms of operating costs.

The preferred embodiments of the present invention have been described above for purposes of illustration and description. The invention is not limited to the precise form described above. Many modifications and variations can be made as will be apparent to those skilled in the art. For example, the frequency can be changed within an allowable range. The embodiments best explain the principles of the invention and its practical application, so that those skilled in the art can understand the invention in terms of various embodiments and make various modifications that are appropriate for the particular application intended. Selected. The scope of the invention is defined in the claims.

[Brief description of drawings]

FIG. 1 is a diagram showing a one-dimensional position adjustment necessary for induction heating of a welding seam.

FIG. 2 is a diagram showing a two-dimensional position adjustment necessary for induction heating of a cylindrical object.

FIG. 3 is an overall view of the induction heating device of the present invention with a part cut away.

FIG. 4 is an enlarged side view showing a part of the insulating tube and the induction coil of the present invention.

5 is a cross-sectional view of a portion of the insulating tube and induction coil taken through line 5-5 of FIG.

FIG. 6 is a diagram showing a line movement sensor for detecting the presence or absence of a can body along the processing path of the can.

FIG. 7 is a side view showing an induction heating device and a conveyor mechanism of the present invention.

8 is a cross-sectional view of a portion of the conveyor mechanism taken through line 8-8 of FIG.

FIG. 9 is a side view showing a part of the conveyor mechanism of the present invention.

FIG. 10 is a diagram schematically showing a control circuit of the present invention.

Claims (9)

[Claims] 1. A method of curing a coating applied to a conductive cylindrical workpiece at 360 ° around the workpiece by induction heating, comprising: (a) at a frequency of about 500 Hz to 50 kHz along a heating path. A step of generating an oscillating magnetic field; (b) a step of conveying the processed product through the magnetic field generated along the heating path in the step (a); and (c) a length of the heating path is adjusted so that A method comprising at least partially curing the coating. 2. The method of claim 1, further comprising the step of aligning the periphery of the workpiece with the center of the magnetic field during step (b). 3. The step of centering the perimeter of the work piece to the center of the magnetic field comprises physically limiting movement of the work piece on all sides of the work piece perimeter during step (b). The method of claim 2 characterized. 4. The step (a) of generating an oscillating magnetic field
Includes (i) spirally providing an induction coil along the heating path and around the heating path, and (ii) generating an electric current that oscillates in the induction coil at a frequency of about 500 Hz to 50 kHz. The method of claim 1 wherein: 5. The step (c) of aligning the periphery of the work piece with the center of the magnetic field comprises supporting the work piece in a substantially concentric manner with the induction coil. Method 4 6. A device for curing a coating applied to a conductive cylindrical work piece by induction heating at 360 ° around the work piece, the cylindrical shape having a diameter larger than the diameter of the work piece in the device. A tube, an induction coil spirally wound around the tube, means for generating a current that oscillates in the induction coil at a frequency of about 500 Hz to 50 kHz to generate an oscillating magnetic field in the tube, So as to be essentially concentric with the induction coil, supporting a work piece in the tube in cooperation with the tube and controlling conveyor means for conveying the work piece through the tube, and the current generating means. A device comprising control means. 7. The method further comprising means for controlling the current generating means if the temperature of the workpiece exceeds a predetermined value while the workpiece is in the tube. 6 devices. 8. The apparatus of claim 6, further comprising circulation means for circulating air around the induction coil to prevent overheating of the induction coil. 9. The diameter of the tube is about 0.5 inch greater than the diameter of the work piece.
Equipment.