Microwave curing system

• US 5,228,947 A
• Filed: 07/30/1991
• Issued: 07/20/1993
• Est. Priority Date: 07/23/1990
• Status: Expired due to Term

• Current Assignee: Weyerhaeuser NR Company (Weyerhauser)
• Original Assignee: Trus Joist Macmillan A Limited Partnership
• Inventors: Churchland, Mark T.
• Primary Examiner(s): Simmons, David A.
• Assistant Examiner(s): SELLS, JAMES D
• Application Number:
  US07/736,951
• Time in Patent Office: 721 Days
• Field of Search: 156/580.1, 156/580.2, 156/379.6, 156/380.9, 156/583.1, 156/583.5, 219/10.55 R, 219/10.55 A, 219/10.55 F, 333/137
• US Class Current: 156/580.1
• CPC Class Codes: B27N 3/086 Presses with means for extracting or introducing gases or liquids in the mat
• CPC Class Codes: B27N 3/14 Distributing or orienting the particles or fibres
• CPC Class Codes: B27N 3/143 Orienting the particles or fibres
• CPC Class Codes: B27N 3/146 Controlling mat weight distribution
• CPC Class Codes: H05B 6/78 Arrangements for continuous movement of material

Abstract

A system for the simultaneous application of pressure and microwaves to a thick mat of curable assemblies. As the curable assemblies are conveyed through a belt press, microwaves are applied to them through an adjacent, rapidly expanding applicator horn. A microwave-transparent ceramic dam or window across the outlet of the horn blocks the compressed assemblies from entering the horn. To minimize any heat cracking of the window it is formed of a number of pieces. These pieces are held in place at the horn outlet by one or more fins secured within the horn and extending into the window. The fins extend across the interior of the horn and divide it into a number of different microwave paths. The ceramic window pieces at the ends of the paths are carefully shaped, with a cylindrical rear surface, to act as lenses and to act on the microwave energy from each of the different paths so that the microwaves from all of the paths are in phase at the product interface. Air is pumped through a serpentine path in the window to cool it and help prevent cracking thereof. Applicator horns having different heating patterns can be advantageously used at different locations along the press bed.

Claims

1. For curing assemblies, a microwave assembly comprising:

an expanding microwave waveguide having a microwave inlet which is communicable with a microwave source, an outlet, a first pair of opposite walls flaring away from each other from said inlet to said outlet, and a second pair of opposite walls connecting ends of said first pair of walls;

a microwave transparent dam closing said outlet; and

at least one fin extending between said second pair of opposite walls and from said dam toward said inlet and dividing said expanding waveguide within said first and second pairs of walls into a plurality of discrete expanding waveguide passages, said waveguide passages being sized to maintain microwave energy travelling in through said microwave inlet and through said waveguide in substantially the same mode in each of said waveguide passages;

wherein said dam has a rear surface facing toward said inlet, said rear surface forming a lens structure shaped to retard the advance of microwave energy adjacent the center of said dam more than the microwave energy adjacent the edges of said dam at said first pair of walls so that the microwave energy leaving said dam is in substantially the same mode and same phase relationship across substantially the full area of said outlet.

2. The microwave assembly of claim 1 wherein said lens structure comprises a plurality of planar surfaces defining angles at their junctures.

3. The microwave assembly of claim 2 wherein said straight surfaces include an outer edge surface, a planar center surface and a middle connecting surface directly connecting said edge and center surfaces, such that a first angle is defined between said center and connecting surfaces and a second angle is defined between said center and edge surfaces.

4. The microwave assembly of claim 3 wherein the second angle is twice as large as the first angle.

5. The microwave assembly of claim 3 wherein the second angle is nine degrees and the first angle is four and a half degrees.

6. the microwave assembly of claim 3 wherein the second angle is six degrees and the first angle is three degrees.

7. The microwave assembly of claim 3 wherein the second angle is between five and a half and six and a half degrees and the first angle is between two and a half and three and a half degrees.

8. The microwave assembly of claim 3 wherein said fin means comprises a fin extending rearwardly from said center surface.

9. The microwave assembly of claim 8 wherein said at least one fin includes outer fins extending rearwardly at the juncture of said edge and connecting surfaces.

10. The microwave assembly of claim 9 wherein said outer fins are held in slots in said rear surface.

11. A microwave curing and pressing system for curable assemblies, said system comprising:

a press chamber including a side wall assembly;

press belt means for continuously advancing curable assemblies through said press chamber;

first microwave applicator means for applying, through said side wall assembly, microwaves in a first heating pattern to the curable assemblies in said press chamber and as they are advanced therethrough at least in part by said press belt means; and

second microwave applicator means for applying, through said side wall assembly and downstream of said first microwave applicator means, microwaves in a second heating pattern to the curable assemblies in said press chamber and as they are advanced therethrough, the second heating pattern being different than the first heating pattern to accommodate the fact that being downstream the curable assemblies have already been partially heated by the first heating pattern.

12. The system of claim 11 wherein the first heating pattern has average top and bottom surface temperatures at least ten degrees Fahrenheit greater than those of the second heating pattern compared to their respective averages.

13. The system of claim 11 wherein the first heating pattern has average top and bottom surface temperature which are thirty degrees Fahrenheit greater than those of the second heating pattern compared to their respective averages.

14. The system of claim 11 wherein the first heating pattern has average temperatures in generally the middle thirds of the top and bottom surfaces thereof at least ten degrees Fahrenheit greater than those of corresponding locations of the second heating pattern, each compared to their respective averages.

15. The system of claim 14 wherein the first and second heating patterns are spaced approximately eighteen inches apart along the press bed.

16. The system of claim 11 wherein said press belt means defines a nip region and said second microwave applicator means is downstream of the nip region.

17. The system of claim 16 wherein said first microwave applicator means is downstream of the nip region.

18. The system of claim 16 wherein said first microwave applicator means is upstream of the nip region.

19. The system of claim 11 wherein the microwaves from said first and second microwave applicator means have the same frequency and power.

20. The system of claim 19 wherein the applicators'"'"' frequency is 915 MHz and the power is 25 KW per applicator.

21. The system of claim 11 wherein said side wall assembly includes first and second side walls on opposite sides of said press belt means.

22. The system of claim 21 wherein both said first and second microwave applicator means apply their microwaves through said first side wall.

23. The system of claim 21 wherein said first microwave applicator means applies microwaves through said first side wall and said second microwave applicator means applies microwaves through said second side wall.

24. The system of claim 21 wherein said first microwave applicator means includes a first applicator horn in said first side wall and a second applicator horn in said second second wall, opposed to and aligned with the first applicator horn.

25. The system of claim 11 wherein the second heating pattern has an average temperature in the central region thereof which is ten degrees greater than that of the first heating pattern with respect to their average temperatures.

26. The system of claim 11 wherein said first and second applicator means include first and second, respective, microwavetransparent dams in said side wall assembly.

27. The system of claim 26 wherein said first microwave applicator means includes a single fin only assembly extending rearwardly from said first dam and dividing all of the microwaves passing through said first dam into a pair of wave paths, and said second microwave applicator means include three spaced fins extending rearwardly from said second dam and dividing all of the microwaves passing through said second dam into four wave paths into the curable assemblies.

28. The system of claim 26 wherein both said first and second dams have the back surfaces thereof shaped as cylindrical lenses.

29. The system of claim 11 wherein the first heating pattern is more uneven than the second heating pattern.

30. The system of claim 29 wherein the difference in unevenness between the two patterns is greater than ten degrees Fahrenheit.

31. The system of claim 29 wherein the first heating pattern has an unevenness of approximately 20°

F. and the second heating pattern has an unevenness of approximately 20°

F.