JPS5829592B2 - A device that applies microwave energy to a workpiece - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for applying microwave energy, namely:
The present invention relates to an apparatus for applying microwave energy to a workpiece.

More specifically, the present invention relates to an apparatus for applying microwave energy designed to substantially uniformly distribute hot spots caused by reflected standing wave patterns.

From a commercial standpoint, microwave energy is commonly applied in one of three ways: resonant cavity ovens, waveguide applications, and horn antenna applications.

In a resonant cavity oven, energy in the form of microwave radiation is pumped into a completely sealed metal box.

This metal box has dimensions suitable for supporting standing waves.

The material to be heated is placed in an application device, which necessarily has smaller dimensions than the box.

This type of application equipment does not heat uniformly, does not conveniently apply pressure to the workpiece, and during oven operation
A disadvantage is that workpieces can only be continuously added to and removed from the oven.

In a waveguide application device, a slot is cut into the side of the waveguide to allow a workpiece to be introduced into the waveguide.

It is common to have slots on both sides of the waveguide to allow workpieces to pass through the waveguide continuously.

Although this type of equipment is useful for heating thin webs of preshaped material, it cannot be conveniently used to apply pressure to a workpiece.

Additionally, there are limitations on the size of the workpiece that can be passed through the slot, and this type of device is generally not useful for heating thick workpieces.

In horn antenna applications, a horn antenna is used to convert microwave energy from TE or TM modes to free space or transverse electromagnetic modes.

With this type of application, the energy is difficult to control and it is not possible to uniformly heat thick workpieces or to apply pressure to the workpiece during heating.

Canadian Patent No. 836,140 describes a microwave energy applicator similar in basic form to embodiments of the present invention, but the microwave energy applicator of this patent does not support the workpiece. There is no attempt to distribute the hot spots resulting from the reflected standing wave pattern inside the center tube substantially uniformly across the center tube.

In this invention, as a device for applying microwave energy to a workpiece, a first device having an inlet end and an outlet end receives the workpiece through the inlet end and applies microwave energy to the workpiece. having a hollow tube, the workpiece passes through the first tube, where microwave energy is applied, and then exits from the outlet end of the first tube; first and second hollow waveguide sections disposed in the first tube and communicating with the first tube for introducing microwave energy therein; and a width of the first tube measured between the frequency of the microwave and the second section. , and the angle of inclination of the first and second portions with respect to the first tube is such that the reflected standing wave generated by introducing microwaves into the first tube through the first and second portions, respectively, A device is provided in which the peak amplitudes are chosen to be staggered, thus distributing the hot spots caused by the standing waves substantially uniformly across the width of the first tube.

This invention will become more clear from the detailed description given below with reference to the drawings.

A source 10 of microwave energy is shown in FIG.

Source 10 may be any conventional microwave energy source, and for industrial microwave applications, D, 0. T, and F, C, C, 915 ■ h or 2450 M according to regulations
It typically operates at Hz.

This is for example the EIMAC(TM) Power Pack PPL
-25.

Also shown is what may be called an application device 11.

This application device consists of a hollow central tube 12 and two hollow waveguide sections 13, 14 arranged on either side of the central tube 12.

The central tube 12 has an inlet end 15 and an outlet end 16 through which it receives a workpiece to which microwave energy is applied.

The workpiece passes through the central tube 12 where microwave energy is applied and exits through the outlet end 16.

The central tube 12 may conveniently be a waveguide section itself, but in any case propagates to a workpiece (not shown) that passes continuously through the central tube 12. It is configured to receive microwaves from waveguide sections 13 and 14 that can be used.

In the embodiment of the invention shown in FIG. 1, the center tube 12 and waveguide sections 13, 14 are all rectangular, having two long sides and two short sides.

The long sides of the central tube and the two waveguide sections lie in the same two planes, and the waveguide sections 13, 14 are fixed to the short sides of the central tube 12.

However, it is also possible to rotate the waveguide 12 through 90° and fix the sections 13, 14 on its long sides.

In a preferred embodiment of the invention, as shown in FIGS. 1-3, the waveguide sections 13, 14 are both inclined at an acute angle to the longitudinal axis of the central tube 12 and are directly opposite each other. It is located.

Although less preferred, in another embodiment the waveguide sections 13, 14 can be provided perpendicular to the longitudinal axis of the central tube 12.

In another embodiment of the invention, the waveguide sections 13, 14 are
Instead of being placed directly opposite each other, they may also be placed in a staggered manner.

Additionally, more than one waveguide section may be secured to each short side of the central tube 12, if desired.

Waveguide sections 13 and 14 each provide a microwave energy source 10
connected to.

This connection method is common and is omitted for clarity of illustration.

Microwaves may be supplied from the source 10 to the waveguides 13, 14 either alternately or continuously.

The embodiment of the invention shown in FIG. 2 differs from the embodiment in FIG. 1 in that two microwave sources 10a, 10b are provided.

These sources are connected to waveguide sections 13 and 14, respectively.

Although this embodiment of the invention is the preferred embodiment, in this case source 10a.

The frequencies of the microwaves generated by 10b are different.

This modification will be explained later. As previously mentioned, waveguide sections 13, 14 are preferably inclined at an acute angle to the longitudinal axis of central tube 12, but may also be perpendicular thereto.

An acute angle is the preferred embodiment of the invention.

This is because the dimension A shown in FIG. 3 is considerably larger than the dimension B, and therefore the energy density over the area of A multiplied by the depth of the central tube 12 is the energy density over the area of B multiplied by the depth of the central tube 12. This is because the arc has a lower tendency to blow if the waveguide sections 13, 14 are both inclined at an acute angle to the longitudinal axis of the central tube 12.

Furthermore, if the waveguide sections 13, 14 are each inclined at an acute angle to the longitudinal axis of the central tube 12, the waveguide sections 13, 14
microwave energy passing through the workpiece will also tend to propagate into the waveguide on the opposite side of the center tube 12, such as when the becomes smaller.

When carrying out this invention, it is necessary that n be an arbitrary number and that the microwave propagate through the waveguides 13 and 14 in the TEno mode.

In an experiment conducted to test the ability to implement this invention, T.
Success was achieved using E1o mode.

Note that in the notation used above, in TEno mode the electric field vector is parallel to the short sides of the waveguide sections 13, 14 and therefore perpendicular to their long sides.

The aim is to obtain an electric field inside the central tube 12 that is as uniform as possible.

The microwave energy supplied from the waveguide sections 13, 14 to the workpiece in the center tube 12 is attenuated as it passes through the workpiece, and the magnitude of the vector E is such that the microwave energy decreases logarithmically as it propagates through the medium.

Of course, since the microwave energy is applied to both sides of the central tube 12, there are two logarithmic attenuation curves.

In terms of the overall heating effect, these two curves add up to produce a general heating across the workpiece.

The center tube 12 is preferably made long enough so that substantially no energy is reflected at the outlet end 16.

This helps to minimize the generation of standing waves inside the center tube 12 due to the propagation of microwaves therein.

Even though the center tube 12 is designed to minimize reflections and thus reduce the generation of standing waves, the center tube 12
There is of course a reflected standing wave pattern inside the waveguide, and there are two such reflected standing wave patterns associated with each respective waveguide section 13,14.

The location of the point at which the peak width of the reflected standing wave pattern associated with waveguide section 14 occurs is indicated in FIG. The location where the head amplitude occurs is indicated by point 18 in FIG.

The locations of the points 1γ and 18 closest to the sidewalls of the central tube 12 opposite the waveguide sections 14, 13 are located l/L from the respective sidewalls of the central tube 12, measured along the line joining these points. Four wavelengths apart, the remaining points 17 and 18 occur half a wavelength apart.

At points where peak amplitudes of the reflected standing wave pattern occur, hot spots are created in the workpiece being processed.

In this invention, the frequency of the microwave, the waveguide portion 13,
By selecting the width of the central tube 12, measured at 14 degrees, and the angle of inclination of the waveguide sections 13, 14 with respect to the longitudinal axis of the central tube 12, microwaves can be introduced into the central tube 12 via the waveguide sections 13, 14. The peak amplitudes of the resulting reflected standing wave patterns can be staggered, and the hot spots created by the reflected standing wave patterns can be distributed substantially uniformly across the width of the central tube 12. It turned out that.

The location of the hot spot is determined by experimental observation of temperature changes across the central tube 12.

When the frequency of the microwave, the constant dielectric constant of the workpiece and the geometric shape of the microwave application device are known, the waveguide section 1
Point 1 closest to the side wall of the central tube 12 facing 4 and 13
7°18 is also known, and the remaining points 17 and 1B are also known, so the waveguide section 13, relative to the longitudinal axis of the central tube 12,
By changing the inclination angle of 14 or the width of the central tube 12,
When points 17 and 18 are projected onto a plane parallel to the longitudinal axis of the central tube 12 and perpendicular to the longitudinal axis, as shown in FIG. You can make it appear in the middle.

In practice, experimental observations are required to locate the hotspots and their varying positions are varied according to the above parameters.

This causes a hot spot created by the reflected standing wave pattern to spread across the center tube 12 and thus across the workpiece.
Uniformly distributed.

It should be recognized that the nature of the workpiece itself will have some influence on the location of the reflected standing wave pattern and this needs to be taken into account in order to achieve the desired staggered relationship. .

If desired, the waveguide sections 13, 14 are fixed to the central tube 12 by means of flexible sections, so that the angle of inclination of the waveguide sections 13, 14 relative to the longitudinal axis of the central tube 12 can be varied. Good too.

Similarly, the center tube 12 can be provided with an expansion joint to change its width.

When using the apparatus shown in FIG. 1, the hot spots are first adjusted to be uniformly distributed across the width of the central tube 12.

A workpiece is inserted into the inlet 15 and passed continuously through the central tube 12 and out through the outlet 16.

Waveguide sections 13, 14 from source 10 or source 10at10b
Applying microwave energy via.

By passing through the central tube 12, various workpieces can be heated.

The cross-sectional area of the workpiece should be the same as the cross-sectional area of the central tube 12, otherwise the electric field E will be distorted.

For this purpose, plywood sections were treated with equipment of the type described above.

Microwave energy was used to cure the resin used in plywood veneer laminations, but it could be used in many other ways.

For example, this device can be used to cure rubber.

When manufacturing plywood, it is necessary to apply pressure to the plywood before the resin hardens.

In a device embodying the invention, this can be accomplished by introducing a press into the central tube 12.

The press can be in the form of two suitably supported moving belts, between which a gap is defined, into which the plywood is inserted.

In practice, the belt can be made of metal and the central tube 1
It may constitute a part of 2.

In a preferred embodiment of the invention, two microwave energy sources 10a each operate at different frequencies.

10b was used.

When microwaves are applied to the central tube 12 from both sides, an interference standing wave pattern is created even when the microwave is in use.

With two microwave sources operating at slightly different frequencies, the interfering standing wave pattern is not stationary, but moves back and forth across the central tube 12.

Therefore, hot spots caused by this interfering standing wave pattern do not remain stationary and do not cause problems such as bumps.

Even when applying microwave energy alternately to the waveguide sections 13, 14 from a single source 10, no interfering standing wave pattern is generated.

However, in embodiments of the invention in which microwaves of the same frequency, e.g. from a common source, are simultaneously applied to the waveguide sections 13,14, a stationary interfering standing wave pattern results, which cannot be compensated for. .

Therefore, this is a less preferred embodiment.

Although preferred embodiments and other embodiments of this invention have been described, it will be apparent to those skilled in the art that various modifications may be made within the scope of this invention.

This invention may take the following embodiments in relation to the claims.

b) The means for supplying microwaves is a single microwave energy source communicating with both the first and second parts; and 2) The means for supplying microwaves is in communication with the first part. a first microwave energy source and a second microwave energy source in communication with a second portion, the energy sources generating microwaves at different frequencies.

→The first and second parts are designed to propagate microwaves primarily in the TEno mode, where n is an arbitrary integer.

2) In the above item 3), n is 1.

e) The tube and the section are rectangular, each having two long sides and two short sides, the long sides of the tube and the section lie in the same two planes, and the first and second sections are rectangular. Be fixed to the short side of the first tube.

f) In the above e), the first and second parts are mainly TEn, where n is an arbitrary integer.

be designed to propagate in mode.

g) In the above item), n is 1.

h) In the above item e), the means for supplying microwaves is
a first microwave energy source in communication with the first portion;
a second microwave energy source in communication with the second portion, said energy source generating microwaves at different frequencies.

h) In the above item H), the first and second parts are mainly TEn, where n is an arbitrary integer.

be designed to propagate in mode.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a microwave energy application device embodying the present invention, FIG. 2 is a view showing a preferred embodiment of the present invention, and FIG. 3 is a hot spot in a microwave energy application device embodying the present invention. FIG. Explanation of main symbols, 10: Microwave energy source, 12:
Hollow central tube, 13, 14: Hollow waveguide portion, 15: Inlet side end, 16: Outlet side end.

Claims (1)

[Claims] 1. A device for applying microwave energy to a workpiece, which has an inlet end and an outlet end, and is adapted to receive the workpiece to which microwave energy is to be applied through the inlet end. a first hollow tube, the workpiece passing through the first tube, where microwave energy is applied, and exiting from the outlet end; first and second hollow waveguide sections disposed on both sides of the tube and communicating with the first tube to introduce microwaves into the first tube; means for supplying microwaves to propagate through the first and second portions and to be introduced into the first tube, the frequency of the microwaves, the first and second portions; the width of the first tube measured between and the angle of inclination of the first and second portions relative to the first tube; The peak amplitudes of the reflected standing waves caused by the introduction of the microwaves are chosen to be staggered, so that the hot spots generated by the standing waves are approximately uniform across the width of the first tube. A device for applying microwave energy to a workpiece, characterized in that it is distributed in a uniform manner.