Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2000-06-23
2001-11-27
Pelham, Joseph (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S400000, C034S224000, C034S225000, C034S226000
Reexamination Certificate
active
06323462
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to conveyor ovens and, more particularly, to ovens in which a plate or the like is baked by directing hot air downwardly onto the upper surface of the plate from above so as to heat the upper surface of the plate uniformly. The invention is particularly useful as a pre-bake oven in a print plate imaging and processing system. The invention additionally relates to a method of using a pre-bake oven.
2. Discussion of the Related Art
So-called conveyor ovens are well known for baking plates and other relatively flat articles. Conveyor ovens are characterized by an oven having an opening through which extends a conveyor. The conveyor transports the article to be baked through the oven at a designated rate such that the article is heated to a desired temperature as it is conveyed through the oven. Conveyor ovens are used in a variety of applications.
For example, in direct print plate imaging and processing systems, conveyor ovens are used to heat print plates prior to development in order to render the background areas of the image soluble in the downstream alkaline developer of the system while simultaneously rendering the image areas insoluble. Precise and consistent heating of the print plate is essential. If the pre-baking or pre-heating step results in more than about a 2° C. temperature variation across the print plate's surface, adverse effects will occur. For instance, if any portions of the plate are overheated, a thermal fog, having an appearance similar to so-called “light fog” found in conventional plates, will form in the overheated areas. Conversely, if uneven or imprecise heating leads to unacceptably low temperatures on portions of the plate, polymers in the portions of the plate which are insufficiently heated will fail to cross-link sufficiently, resulting in a weakened or removed image. Many conveyor ovens which were heretofore available did not provide adequate precision and uniformity of heating to operate acceptably as pre-bake ovens.
Conveyor ovens are also widely used in other applications such as post-bake ovens in print plate imaging and finishing systems. One such oven is manufactured by Wisconsin Oven Corporation of East Troy, Wis. and marketed as the SPC-HTS/109 Series. This oven works quite well as a post-bake oven but exhibits a relatively high profile because the heating elements, blower, and associated ductwork are all located above the conveyor. In addition, the configuration of the ductwork linking the heat source to the conveyor is less than optimal for height minimization purposes. As a result, this oven and others of its type have an overall height on the order of 74″ or more. The relatively high profiles exhibited by these ovens render them somewhat unattractive in applications in which space constraints mandate ovens having the lowest-possible profile.
Many conveyor ovens which were heretofore available also were somewhat inefficient because they employed little or no air recirculation such that all or at least a substantial portion of the air used to bake the subject article was heated from ambient temperature to the working temperature.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore a primary object of the invention to provide a conveyor oven which is capable of precisely and uniformly heating an article to be baked as that article is conveyed through the oven at a designated speed.
Another object of the invention is to provide a conveyor oven which is well-suited for use in applications where space constraints mandate an oven with a relatively low profile.
Another object of the invention is to provide a plurality of insulated oven cabinets permitting multiple and substantially discrete regions of temperature control.
Still another object of the invention is to provide a conveyor oven that recirculates its working air and which therefore is relatively efficient to operate.
In accordance with a first aspect of the invention, these and other objects are achieved by providing a conveyor oven comprising a plurality of cabinets, each having at least one supply/return duct assembly, at least one source of heated air, and a conveyor extending through two cabinets. Each of the plurality of cabinets includes a plurality of sidewalls and a top wall bridging the sidewalls, an entrance being formed in a first one of the sidewalls, and an exit being formed in a second one of the sidewalls. Wherein the exit of an upstream cabinet is disposed adjacent to, and feeds, the entrance of another cabinet. The conveyor extends from the entrance of the upstream cabinet to the exit of the downstream cabinet and has an upper surface along which travels an article to be baked. Each supply/return duct assembly is positioned above the conveyor and has a lower surface which faces the upper surface of the conveyor. Each duct assembly includes a plurality of supply ducts and a plurality of return ducts. Each of the supply ducts has (a) a heated air inlet in fluid communication with the source of heated air and (b) a plurality of downwardly-opening discharge orifices formed in the lower surface. Each of the return ducts has at least one wall formed by a wall of an adjacent one of the supply ducts and has (a) a lower inlet which faces the upper surface of the conveyor and (b) an upper outlet which is in fluid communication with the source of heated air. Each cabinet is equipped with at least one, and preferably at least two facing supply/return duct assemblies. These facing assemblies define a heater source space for each cabinet.
Preferably, in order to facilitate assembly, promote uniform and efficient airflow, and render the oven more compact, the oven further comprises a plenum which houses at least part of the source of heated air. The plenum has an upper portion formed by the duct assembly, a supply passage assembly being formed within the plenum for conveying heated air from the source of heated air to the inlets of the supply ducts, and a return passage assembly being formed between the plenum and the cabinet for conveying air from the outlets of the return ducts to the source of heated air.
In a particularly preferred configuration, each supply passage assembly comprises a first supply passage extending at least generally in parallel with a first one of the sidewalls of the cabinet. A second supply passage is disposed opposite the first supply passage on the opposing side of the conveyor and extends at least generally in parallel with a second one of the sidewalls of the cabinet upward and around the opposing side of the conveyor. The source of heated air includes a blower having an axial inlet, a first radial outlet in fluid communication with the first supply passage, and a second radial outlet in fluid communication with the second supply passage.
Seals are preferably disposed at the interfaces between each plenum and its associated cabinet and at the entrance and exit of the cabinet so that ingress of ambient air is minimized and most of the air used to bake the articles in the oven is recirculated in a closed loop, thereby rendering the oven more efficient and increasing uniformity of heating.
The supply duct discharge orifices are preferably generally H-shaped to further promote uniform air distribution and to reduce whistling noises that might otherwise occur during oven operation.
Still another object of the invention is to provide an improved print plate imaging and processing system employing an improved pre-bake oven.
In accordance with another aspect of the invention, this object is achieved by providing a print plate imaging and processing system that includes a thermal imaging unit, a pre-bake oven, a developer unit, and a finishing assembly. In the thermal imaging unit, an image is thermally imposed on selected areas of the print plate to create image areas and non-image areas on the print plate. The pre-bake oven is located downstream of the thermal imaging unit. The print plate is heated in this oven sufficiently to partially cross-link polymers in the non
Nilles & Nilles SC
Pelham Joseph
Wisconsin Oven Corporation
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