US20060101755A1

US20060101755A1 - I-beam curing system

Info

Publication number: US20060101755A1
Application number: US11/274,559
Authority: US
Inventors: George Harris
Original assignee: RF Tech LLC
Current assignee: RF TECHNOLOGIES -- A FERRITE Co LLC; RF TECHNOLOGIES LLC--A FERRITE Co; RF Tech LLC
Priority date: 2004-11-15
Filing date: 2005-11-15
Publication date: 2006-05-18

Abstract

An I-beam curing device having microwave waveguides with slots on the broad side thereof. The flanges of the I-beam pass through the slots in the waveguides to be subject to the microwave fields therein so as to allow the treating of any material passed through the slots.

Description

RELATED APPLICATION

The present application claims priority from U.S. Provisional Application No. 60/627,588 filed Nov. 15, 2004, herein incorporated by reference in its entirety.

FIELD TO WHICH THE INVENTION RELATES

Solid structural wood of more than nominal lengths is becoming more and more restrictive, both in availability and in cost. The present invention is directed to providing structural, composite, laminated I-beams, and other products to serve as alternatives and/or replacements for solid structural materials.

BACKGROUND OF THE INVENTION

The present application relates to a microwave curing system. Laminated and/or solid end I-beams are increasingly finding favor in the construction and repair of residential and/or commercial buildings. However, the cost and the time to manufacture these beams limit their application to higher-cost and better-designed buildings.

OBJECTS OF THE INVENTION

It is an object of the present invention to lower the cost of heat-manufactured products;
It is another object of this invention to increase the availability of non-solid wood I-beams;
It is a further object of this invention to lower the cost of manufactured wood products;
It is still a further object of this invention to increase the reliability of manufactured wood and/or synthetic structural products;
It is yet another object of this invention to avoid a discontinuity of a microwave field in a manufacturing operation;
It is another object of this invention to allow the transfer of power from a microwave source to multiple wood products;
It is a further object of this invention to retain microwave energy within a product treatment device;
Other objects and a further understanding of the invention may be had by referring to the detailed description, specification, and drawings of the invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective drawing of an exemplary embodiment of the invention utilizing three pairs of waveguides;
FIG. 2 is a longitudinal cross sectional view of the bottom half of the cell of a single pair waveguide like FIG. 1 taken generally along lines 2-2 in FIG. 4;
FIG. 3 is a longitudinal cross sectional view of the top half of the cell of a single pair waveguide;
FIG. 4 is a cross sectional view of the waveguide of FIGS. 2 and 3 taken generally along lines 4-4 of FIG. 2;
FIG. 5 is a perspective view of a single waveguide cell showing the cooperation of slotted waveguides with a laminated beam;
FIG. 6 is a demonstrative figure highlighting the cooperation of a single slotted waveguide to a treated product; and,
FIG. 7 is a demonstrative figure highlighting the orientation of a treated product with a slotted waveguide.

DETAILED DESCRIPTION OF THE INVENTION

Microwaves are an efficient means to transfer physical energy to a product.
On a consumer level, the most familiar is the ubiquitous microwave oven wherein by adjusting the time and power level, a single device can be utilized for differing foods.
However, on the industrial level, things get more complicated: A single unit is typically unsuitable for differing products. Some of this is due to the fact that in a production-type application, lost energy can both cause lower energy efficiency as well as cause thermal problems in the device itself. The former typically increases cost of production, while the latter increases the cost of the device. Normal attempts to bring both parameters into a commercially acceptable level create specialized devices.
The present invention provides both high-energy efficiency and multiple purpose utilization in a single device.
In the exemplary embodiment disclosed, a slot in the center of the broad side of a microwave waveguide allows an I-beam of from 6″ to 24″ wide to pass through a microwave field. This causes the energy of the microwave generator to be concentrated on the flange/web glue joint to expeditiously cure such glue. Field retention pins along the sides of the slotted waveguide retain the microwave energy within the waveguide, while field stop pins at either end of the device allow the passage of the I-beam into and out of the microwave field.
The exemplary embodiment of the present invention includes a microwave generator 10, a material transport guide 20, and a waveguide 50. The particular device 11 is utilized to cure the glue in a wood product 100. In the embodiment disclosed, the wood product is a laminated wood beam 101 including glue holding two flanges 105, 106 to a central web 110. The beam 101 itself has a width 115, which width 115 (together with the sizing of the flanges and web) may change from beam to beam. The present invention can be utilized to heat treat these varying beams in a single device, as will be hereinafter described. Other rectangular wooden/composite beam products could also be treated in this embodiment. The purpose of the exemplary embodiment microwave device is to cure the glue attaching the two flanges 105, 106 to the central web 110. The glue being cured is a therma-set adhesive, preferably a phenolic adhesive. In the preferred example shown, it can be combined with formaldehyde. For example, the adhesive used can be a phenol-formaldehyde, phenol-resorcinol formaldehyde, or any therma-set adhesive.
The microwave generator 10 provides the thermal energy necessary to treat the product that is passing through the device 11. The power, number, and location of the microwave generator(s) are chosen in order to provide the pertinent power necessary to treat the particular product produced by the device 11. In the embodiment disclosed in FIG. 1, there are six microwave generators (not shown) located as the input into three sequential units 12, 13, 14 and 15, 16, 17, respectively, in pairs on the lateral sides of the device 11 (12, 15; 13, 16; 14, 17). These energy sources provide for symmetrical heat in a series-type of orientation. This can allow, for example, energy to be spread out over a longer time, more energy, or other advantages.
In the embodiment disclosed in FIGS. 2-6, a single pair of microwave generator units 12, 15 are shown. This is to facilitate the explanation of the invention as well as recognize that even the parameters of a single-slotted waveguide are variable in the invention claimed herein. For example, the microwave generator 10 used is a commercially-available industrial microwave generator.
The material transport guide 20 is designed both to physically support the product 100 passing through the device 11, in addition to physically locate the microwave waveguide 50 and provide the appropriate field stops to retain microwave energy within the device.
The particular material transport guide 20 disclosed is a cell assembly 21 having two ends 25, 26 with end field stop pins 29 and center and side field retention pins 30, 31.
The ends 25, 26 of the material transport guide 20 are for the input and output of the product 100 being treated within the device 11. To provide for this in the exemplary embodiment, the product 100 is moved parallel to the guide longitudinal axis 28 of the device. The field stop pins 29 and side field retention pins 30, 31 serve to mechanically support the product. This allows movement of the product through the guide 20. Teflon slide covers 36 (FIG. 4) over the individual field stop pins 29 and side field retention pins 30, 31 along the longitudinal axis of the guide facilitate this physical movement. Due to the fact that the top assembly 40 and bottom assembly 41 of the cell assembly 21 each provide a physical location for the waveguide 50, it is not necessary to locate the field pins 29, 30, 31 where the waveguide is located (as subsequently described, the pins and waveguide retain the microwave energy within the device 11 following the confines of the cell assembly). A conveyor (not shown) could be utilized to facilitate the movement of the product through the device 11.
The waveguide 50 itself consists of a generally rectangular waveguide 31 extending between an open input end 60 and an open output end 61. A rectangular waveguide 31 is preferred as specified since it can reliably provide the most energy to the desired location. In the preferred embodiment, this location is the edges of the I-beam 101 (i.e., the flanges 105,106). Further, the rectangular waveguide 31 retains a single waveguide dominant mode (TE₁₀preferred). These both are preferred as concentrating the heat in the device where it is needed in the product. Typically, the product being manufactured is from 8″ to 24″ wide.
To accomplish this, the slots 70, 71 in the broadwalls 52, 53 are from 40% to 50% of the broadwall dimension. In general, they are 20% larger than ½ wavelength in free space of the lowest frequency. It is noted that due to the invention there is no obstruction as the travel of the I-beam through the waveguide.
The open input end 60 of the waveguide 50 interconnects each waveguide to the microwave generator 10 as previously described. For example, the products being manufactured range from less than 8″ wide and 9″ thick up to greater than 25″ wide.
The open output end 61 of the waveguide 50 allows for the passage of the product 100 through the physical cross section 62 of the waveguide 50 as hereinafter described.
The field stop pins 29 at either end of the cell assembly 21 allow for the passage of the product 100 into and from such assembly.
The center and side field retention pins 30, 31 retain the energy of the microwave generator 10 within the waveguide 50 irrespective of the slots 70, 71 in the sides thereof.
The particular waveguide disclosed is rectangular having two broad sides 52, 53 extending between a top 54 and a bottom 55. In pertinent aspect to this invention, the broad sides 52, 53 of the waveguide 50 include two slots 70, 71 therein, which slots retain the microwave energy within the device while also providing for the passage of the product 100 through the cross section 62 of the waveguides, thus transferring the energy from the microwave generator 10 to such products. A rectangular waveguide 31 is preferred having a broadwall dimension from 60% to 90% of half of the wavelength of the frequency in use (generally the lower the frequency, the bigger the units). In the exemplary waveguide disclosed, the rectangular waveguide 31 is about 300 mm×125 mm, and the microwave energy follows Gauss Law converting E to H (electric to magnetic) and Faraday's Law from H to E. The TE₁₀mode, has one-half period in x direction to 0 in y. This forms a parabola/sin wave form along the long edge of the waveguide, with maximum energy at the middle (see FIG. 7).
The exemplary slots 70, 71 are placed exactly along the center of the broadwalls 52, 53 of the waveguide 31. They are placed with their center on the longitudinal center of the waveguide. The slots 70, 71 in turn allow the entry and movement of the product 100 being treated through the microwave field. This is provided without the movement of the microwave components (i.e., generator and waveguide). This provides the energy to the product being exposed to the field. The electrical fields in the waveguide are perpendicular to the broadwalls. As the glue provides the path of least resistance, it heats and thus is cured during the travel of the I-beam down the length of the waveguide 31.
The field at the slot is always ++ of − and never ± due to the symmetry of beam placement in combination with the placing of ¼ wavelength field retention pins outside of the waveguide. The pin current displacement magnetic field interaction act to further maintain isolation and reduce standing ware interaction between the two slotted waveguide application. The changing wave polarity within the waveguide provides the desired heat for product treatment.
To facilitate the transfer of this energy, the longitudinal axis 58 of the waveguide 50 is located at an acute angle 59 to the guide longitudinal axis 28 of the material transport guide 20 (see FIG. 6). The acute angle 59 provides for the gentle entry of the product into the microwave field. It also provides for the appropriate residence time within the slots 70, 71 thus to transfer the appropriate energy to the product 100 passing therethrough.
The actual angle 59 of the waveguide 31 is dependent on the length 56 of the slotted portion of such waveguide together with the spacing between waveguides 81, 82. An angle of 10° to 20° between waveguides is preferred. In general, a shallower angle is preferred to avoid any discontinuity or reflections in the microwave field (10° to 15° further preferred).
The length 56 of the waveguide 50 is selected to provide for the necessary resonance time of the microwave energy to the product 100 being treated. This is a function of the speed of the product through the device as well as the total energy to be applied to the product 100. In general, the length 56 of the line is dependent on the product speed, the angle between the guide 31 and the beam 101, together with the power available from the generator 10. This produces the desired resonance time in the slots 70, 71. The microwave energy itself applies as a cloud in dielectric loss heating rather than ionic conduction, which is radio frequency. (The web is also incidentally exposed to the microwave energy so it should cure, if not already done.)
The spacing between lateral waveguides preferably has a maximum spacing 81 and a minimum spacing 82. These spacings 81, 82 are chosen in consideration of the nature of the product passing through the device 11. For example, the particular device disclosed is used to treat laminated beams 101, which beams may have a variable width from 6″ to 24″.
Further, it is desired to heat the glue on the joints within the flange 105, 106 between such flanges and the central web 110. This also warms the outer edges of the central web 110 so as to avoid cold joints. For this reason, the minimum spacing 82 between the lateral waveguides is selected in recognition of the minimum spacing 82 of the product 100 (6″), while the maximum spacing 81 of the lateral waveguides is selected in accord with maximum spacing 81 of the product (24″). This allows a single device 11 to cure the product, irrespective of the significant differences in widths 115, and thus the use of a single device 11 to treat multiple products. The width of the waveguide, its inside dimensions, is dependent on the width of the products to be treated therein. Still, this width is in turn dependent on the range of treated products.
The device 11 disclosed has a cell assembly 21, which cell assembly is 36″ wide and 11″ high. The length 56 of the slots 70, 71 are approximately 75% (50% to 90% preferred) of the straight length of the waveguide 50. Note that the outer slot 71 is preferably shorter than the inner slot 70 due to the angle 59 between the waveguide 50 and the longitudinal axis 28 of the guide 20. Straight through movement of the product does not require more.
Although the invention has been described in its preferred form with a certain degree of particularity, it is to be understood that changes may be made without deviating from the invention as hereinafter claimed.
For example, symmetrical, paired waveguides are utilized in the preferred embodiments. If desired, a single waveguide on one side of the product could be utilized (or other non-symmetrical variations such as two to three opposing waveguides). The waveguides on opposing sides could be staggered, on the waveguide sizing and the generators could differ (i.e., to differentially treat a product).
Although a wood I-beam is utilized as the product, any product having an aggregate width and length, either singularly or by congregation of multiple products, can be treated in the device. This would include other solids and liquids.
Other objection and a more complete understanding of the invention may be had by referring to the following claims as hereinafter claimed.

Claims

1. A microwave curing device for a product, said device comprising a material transport guide, said material transport guide having two ends and a guide longitudinal axis,

means to move the product along said longitudinal axis of said guide from one end to the other,

a waveguide, said waveguide having two ends, a longitudinal axis, and a broad side, said broad side of the other end of said waveguide being slotted along the length of said longitudinal axis of said waveguide,

said waveguide being connected to said guide with said waveguide longitudinal axis having an acute angle in respect to said longitudinal axis of said guide,

said slotted other end of said waveguide overlapping said guide,

a microwave generator, and said microwave generator being connected to one end of said waveguide.

2. The microwave curing device of claim 1 characterized by the addition of retention stops beside said waveguide along said waveguide.

3. The microwave curing device of claim 1 characterized in that there are multiple waveguides.

4. The waveguide curing device of claim 3 characterized in that two of said multiple waveguides are laterally located in respect to said guide.

5. The microwave curing device of claim 4 wherein the product may vary in a maximum width extent and characterized by said multiple waveguides being spaced by a maximum spaced distance in their slotted sections, and said maximum spaced distance being substantially equal to the maximum width extent of the product.

6. The microwave curing device of claim 3 characterized in that said multiple waveguides include two that are sequentially located in respect to said guide.

7. The microwave curing device of claim 6 characterized in that said two ends of said guide both include microwave field stops.

8. A microwave curing device for a product, said device comprising a material transport guide, said material transport guide having two ends, two lateral sides, and a guide longitudinal axis,

two waveguides, each said waveguide having two ends, a longitudinal axis, and a broad side, said broad side of a first end of each of said waveguide being slotted along the length of said longitudinal axis of said waveguide,

said waveguide being connected to said guide with said waveguide longitudinal axis having an acute angle in respect to said longitudinal axis of said guide with one waveguide being on one lateral side of said guide with the second waveguide being on the second lateral side of said guide,

said slotted other end of each of said waveguides overlapping said guide,

a microwave generator means, and said microwave generator means being connected to a second end of each of said waveguides.

9. The microwave curing device of claim 8 characterized by the addition of retention stops beside said waveguide along said waveguide.

10. The microwave curing device of claim 8 characterized in that there are multiple waveguides on each lateral side of said guide.

11. The waveguide curing device of claim 8 wherein the product may vary in a maximum width extent and characterized by a first end of said two waveguides being laterally spaced by a maximum spaced distance for their slotted sections, and said maximum spaced distance being substantially equal to the maximum width extent of the product.

12. The microwave curing device of claim 8 wherein the product may vary in a minimum width extent and characterized by a second end of said two waveguides being laterally spaced by a minimum spaced distance for their slotted section, and said minimum spaced distance being substantially equal to the minimum width extent of said product.

13. The microwave curing device of claim 8 characterized in that said two ends of said guide both include microwave field stops.

14. The microwave curing device of claim 8 characterized by the addition of field stops beside said waveguide along each of said two waveguides.

15. The microwave curing device of claim 8 wherein the product may vary in length and height and characterized in that said minimum sizes of the two waveguides being greater than all of these dimensions.

16. The microwave curing device of claim 8 wherein a single unit is used to treat multiple devices during a particular production run and characterized in that said microwave waveguide is sized as a minimum size to be greater than the minimum size of the largest of all of the multiple dimensions.