Obviousness

Based on the provided prior art analysis for US Patent 5,708,678, here is an analysis of the obviousness of the patent's claims under 35 U.S.C. § 103.

Standard of Obviousness

An invention is considered obvious if the differences between the claimed invention and the prior art are such that the subject matter as a whole would have been obvious at the time the invention was made to a person having ordinary skill in the art (a "POSITA"). This analysis considers not just what the references explicitly teach, but what they would have suggested to a POSITA, including the motivation to combine their teachings to arrive at the claimed invention.

Analysis of Independent Claims

Claim 1 (Method)

Claim 1 describes a method of using a strongly oxidizing atmosphere to create a desired and controllable layer of scale that is easily removable, by ensuring the atmosphere surrounds the whole periphery of the slab.

Obviousness Combination: The method of Claim 1 would have been obvious over US Patent 5,235,840 ('840 patent) in view of the general knowledge of a POSITA regarding steel metallurgy and furnace engineering.

1. Base Reference - US 5,235,840 ('840 patent): The '840 patent teaches the core of the method: conveying a slab through a furnace and using a controlled, oxidizing atmosphere to intentionally form a "thin, tenacious and adherent" layer of scale. This establishes the principle of using oxidation as a tool to control scale properties for a downstream purpose (in its case, lubrication during rolling).

2. Motivation to Modify the '840 Patent's Method: The '678 patent identifies a known problem in the art: scale formed in neutral or reducing atmospheres (primarily FeO) is very hard to remove. The '840 patent aims for an adherent scale. A POSITA, facing the problem of difficult descaling, would be motivated to create a scale that is intentionally non-adherent or friable. It was well-known in metallurgy that different iron oxides have different physical properties. Specifically, Fe₂O₃ is more voluminous and less adherent than FeO.
   A POSITA would have been motivated to modify the "mildly oxidizing" atmosphere of the '840 patent to a "strongly oxidizing" one. This would predictably shift the chemical composition of the scale towards Fe₂O₃, thus achieving the goal of a more easily removable scale. This is not an inventive leap but rather an optimization of a known process variable (oxidation level) to achieve a predictable result (different scale properties).

3. Element of "Surrounding the Slab": The '840 patent teaches creating a controlled and uniform layer of scale. A POSITA would understand that achieving a uniform result requires a uniform application of the process conditions. Therefore, ensuring that the oxidizing atmosphere evenly contacts or "laps" the entire slab surface is an obvious and necessary condition for achieving the uniformity taught by the '840 patent. Directing gas flow to ensure even heating is a fundamental and routine aspect of furnace design.

Conclusion for Claim 1: A POSITA would have been motivated to modify the controlled oxidation process of the '840 patent by increasing the oxidation level to solve the known problem of difficult-to-remove scale, thus arriving at the method of Claim 1.

Claim 8 (Apparatus)

Claim 8 describes a furnace with upper burners, lower aspiration intakes, and, crucially, diversion baffles extending from the top towards the slab to force the hot gases to flow down and around it.

Obviousness Combination: The apparatus of Claim 8 would have been obvious over a standard roller hearth furnace, such as that generally described in US Patent 5,528,816 ('816 patent), in view of the well-known engineering principle of using baffles to direct fluid flow.

1. Base Reference - A Conventional Furnace (e.g., '816 patent): The '816 patent, from the same assignee, establishes the state-of-the-art context: a roller hearth furnace used to equalize the temperature of slabs. This provides the basic structure of an insulated chamber with rollers and burners.

2. Motivation to Add Baffles: The '678 patent explicitly states the problem this structure solves: "the fumes and gases...tend to be kept in a high position far from the product," resulting in uneven heating. This was a known problem. For a POSITA tasked with solving this issue, the most direct, common, and predictable solution is to physically direct the gas flow downwards. Installing baffles is a textbook method for controlling fluid/gas flow in any thermal or chemical system. The motivation is clear: to solve the known problem of uneven heating by forcing the hot gases to circulate more effectively. The placement of the baffles between the upper burners and extending down towards the product is the most logical and effective configuration to achieve this goal.

Conclusion for Claim 8: Combining the known structure of a roller hearth furnace with the fundamental engineering principle of using baffles to solve the known problem of uneven gas distribution would have rendered the apparatus of Claim 8 obvious to a POSITA.

Analysis of Dependent Claims

Claims 7 and 11 (Roller Cleaning Mechanism)

Claim 7 adds the step of removing scale from the roller rings, and Claim 11 adds the apparatus for doing so (a scale removal means cooperating with funnel-shaped intakes).

Obviousness Combination: These claims would have been obvious over the apparatus of Claim 8 in view of JPS5931819A.

1. Base Reference - JPS5931819A: The prior art analysis identifies that this Japanese reference explicitly teaches a "Removing method of build-up on hearth roll" using a grinding or scraping tool that operates within the furnace.

2. Motivation to Combine: The '678 patent background identifies scale buildup on the support rings as another known shortcoming that can damage the product surface. JPS5931819A provides a direct solution to this exact problem. A POSITA would have been directly motivated to integrate the roller-cleaning mechanism taught by JPS5931819A into the heating furnace of Claim 8 to solve this well-recognized problem. This is a straightforward combination of known elements to achieve the sum of their known functions.

Conclusion for Claims 7 and 11: The subject matter of these claims would have been obvious by incorporating the prior art roller cleaning system of JPS5931819A into a reheating furnace.