Electric heating – Microwave heating – Field modification
Patent
1997-01-15
1999-11-30
Leung, Philip H.
Electric heating
Microwave heating
Field modification
219756, 219701, 219750, H05B 680
Patent
active
059946865
DESCRIPTION:
BRIEF SUMMARY
The present invention pertains to a device for heat-treating products by microwave radiation with a heating chamber for accommodating the products, wherein the microwaves can be coupled into the heating chamber by a device, and the heating chamber has at least one reflecting wall reflecting the microwaves.
Such a device (hereinafter also called furnace) has been known for drying, heating or firing (sintering) a great variety of products.
Difficulties arise if the physical/mechanical properties of the products change during heating, which happens, e.g., during the heating and firing of ceramic products. The term "ceramic products" comprises all types of prior-art ceramic materials, e.g., porcelain, but also special ceramic products, such as carbon products, ferrites, or refractory ceramic products.
Devices of the class described in the introduction have become known to date predominantly as so-called intermittently operating furnaces, in which the products are introduced into the heating space, which is subsequently closed (DE-B 1 097 594). The furnace, which is spherical according to DE-B 1 097 594, is again opened after the heat treatment, and the products are removed.
However, there also are continuously operating furnaces, especially for industrial production, such as tunnel furnaces, in which the products are guided to a furnace outlet via a furnace inlet on a conveying device. The products are heat-treated, e.g., initially heated up, then fired (sintered), and subsequently cooled again, on their way through the heating chamber.
Such a device is described in FR-A 911 170. The furnace has a tubular shape. A likewise tubular reflecting wall with radially arranged devices for coupling microwaves limits the furnace on the inside.
Special measures are to be taken at the furnace inlet and outlet of such a furnace to prevent microwaves from escaping. So-called "microwave traps," which are designed as a "door" according to FR-A 0 911 170, have been known for this purpose. However, even if these "microwave traps" are used, the door must be opened from time to time to feed in new products or to remove the products from the heating chamber, and an undesired escape of microwaves may thus occur. In addition, these measures make such a furnace expensive.
The basic object of the present invention is to design a device of the class described in the introduction such that possibly optimal utilization of the microwave energy within the heating chamber is guaranteed, especially even in continuously operating furnaces and regardless of the shape and size of the products to be treated.
The present invention is based on the discovery that this object can be accomplished in an astonishingly simple manner by a special design and geometric arrangement of reflecting surfaces for the microwaves within the heating chamber.
The present invention is based on the consideration of designing and arranging corresponding reflecting surface(s) such that the microwaves coupled to the heating chamber via a device are reflected exclusively in the space limited by the reflecting surface(s), so that optimal utilization of the microwave energy can be achieved, while corresponding losses are avoided.
In its most general embodiment, the present invention specifically suggests for this a device of the class described in the introduction, in which the reflecting wall has, when viewed from the interior space of the heating chamber, at least two concave curved sections, which are arranged such that the microwaves coupled in via the device are reflected exclusively in the space limited by the reflecting wall.
The partial feature of a concave curvature of the reflecting wall is of particular significance, because the reflecting wall can thus be designed, especially in a continuously operating furnace, such that microwaves reflected in the direction of the inlet and outlet of the furnace are also reflected back and cannot escape via the furnace inlet and outlet.
In other words, the reflecting wall used to reflect the microwaves in the device according
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patent: 2543053 (1951-02-01), Parker
patent: 3281727 (1966-10-01), Niebuhr et al.
patent: 4631380 (1986-12-01), Tran
patent: 5498857 (1996-03-01), Jacquault
patent: 5532462 (1996-07-01), Butwell et al.
Earley John F.A.
Earley III John F.A.
Leung Philip H.
Riedhammer GmbH
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