T 0855/13 13-06-2017

I. European patent No 1 868 748 (in the following: "the patent") concerns a process and a plant for the manufacture of steel strips or sheets, without interruption between continuous casting and rolling.

II. The patent as a whole was opposed on the sole ground of lack of inventive step (Article 100(a) EPC).

III. The opposition division decided to reject the opposition.

IV. This decision was appealed by the opponent (in the following, "appellant").

V. With the summons to oral proceedings, the Board sent a communication pursuant to Article 15(1) of the Rules of Procedure of the Boards of Appeal (RPBA) indicating its preliminary opinion of the case.

VI. Oral proceedings before the Board were held on 13 June 2017.

VII. Requests

The appellant requested that the decision under appeal be set aside and the patent be revoked.

The patent proprietor (in the following, "respondent") requested that the appeal be dismissed (main request), alternatively that the decision under appeal be set aside and the patent be maintained on the basis of one of the first to eighteenth auxiliary requests filed with letter dated 18 December 2013.

VIII. Claims of the main request

Independent method claim 1 is directed to the following subject-matter (the feature numbering is introduced by the Board for ease of reference):

(a) A process for manufacturing metal strips of thickness in the range between 0.14 and 20 mm and metal sheets of thickness in the range between 10 and 100 mm

(b) from slabs having thickness comprised between 30 and 300 mm and width comprised between 600 and 4000 mm obtained through continuous casting,

(c) with a high quantity of material or mass flow passing in the time unit at the outlet thereof,

(d) wherein the continuous casting (10) is bow-shaped from a mould and

(e) directly connected with a rolling step (11) in a single manufacturing step without solution of continuity,

characterised by

(f) providing a thickness reduction, increasing step by step from its beginning in the mould and continuing in the single step of casting and rolling,

(g) as well as a secondary cooling for obtaining at the outlet of the continuous casting a slab with an inverted temperature gradient in its cross-section,

(h) with an average surface temperature of the slab < 1150 °C and an average temperature at the core > 1350 °C,

(i) an induction heating (12) between casting and rolling,

(j) a cutting and withdrawal (14') of the sheets (20), upon controlled cooling, in alternative to the coil winding (15) of the rolled strip,

(k) as well as providing a speed regulation system in cascade in the downstream direction starting from the continuous casting,

(l) wherein said feeding speed of the casting at the rolling end is step by step increasing in correspondence with the thickness reduction of the desired end product,

(m) with the distance between casting and rolling being the least one admissible by the process.

Independent claim 4 for a plant reads as follows:

"4. A plant for manufacturing metal strips with thickness in the range between 0.14 and 20 mm and metal sheets with thickness in the range between 10 and 100 mm from a continuous casting comprised of mould and subsequent bow caster with means for liquid core reduction starting from slabs (1) of thickness between 30 and 300 mm and width between 600 and 4000 mm, characterized in that said mould has a ratio >= 1.1 between its surface SM at the meniscus, subtracted the area ST interested by the submerged nozzle, and the cross-section area Sb of the slab (1) at the outlet of continuous casting, there being provided a secondary cooling system for obtaining at the outlet of continuous casting a slab having an inverted temperature gradient and a cross-section with an average surface temperature of the slab < 1150°C and with an average core temperature >1350°C as well as a finishing mill (11) directly connected with the continuous casting at a maximum distance of 50 m, further comprising an induction heating furnace (12) between the continuous casting outlet and the rolling-mill (11) and at the outlet of the latter, either a cutting device (14) of coils, wound on an end reel (15), after a final cooling system (13), or a cutting device (14') for the withdrawal of sheets (10) also cooled by said cooling system (13)."

IX. Prior art

In the statement setting out the grounds of appeal, and in the reply to it, the parties relied among others on the following prior art documents which were filed in the opposition proceedings and are cited in the decision under appeal:

D1: WO 2004/026497 A1

D2: EP 0 013 539 A1

X. The arguments of the parties, insofar as relevant for the present decision, can be summarised as follows:

(a) Main request - Inventive step

Appellant's case:

The opposition division's decision that the subject-matter of method claim 1 involved an inventive step starting from D1, was based on a wrong assessment of the teaching of D1 and of common general knowledge in the field of continuous casting.

As acknowledged by the opposition division, D1 discloses all the features of claim 1, with the exception of features (i) and (k). In particular, feature (f) is implicitly disclosed in D1 because, as is generally known in the field of continuous casting, the mould must be funnel-shaped to compensate for the natural shrinkage of the slab upon casting. Further, the two alternatives defined in feature (j) are anticipated by the teaching of D1 because it discloses the step of coil winding of the rolled strip (see coiling stations 19 and 20 in figure 1b) as well as the alternative steps of cutting and removing plate-shaped sheets after rolling (see shearing device 10 and transverse transportation device 11 in figure 1a), upon controlled cooling (by means of tiltable cover 12), in case of a breakdown in the finishing mill 18 (see figure 1b).

With respect to distinguishing feature (i), D1 already discloses the step of heating the strip, between casting and rolling, with a compensation furnace, preferably a continuous roller furnace (see paragraph bridging pages 6 and 7 of D1). The replacement of this compensation furnace by an induction furnace would be an obvious modification, in particular because it is generally known in the art as being more compact and energy-efficient. Contrary to the respondent's view, it does not follow from the wording of claim 1 that the induction heating of feature (i) is aimed at maintaining the inverted temperature gradient defined in features (g) and (h) until the rolling starts. In practice, this effect may or may not be achieved, depending on parameters of the induction heating such as frequency and penetration depth.

With respect to distinguishing feature (k), D2 discloses a continuous casting and rolling plant similar to that of D1, and comprises a system for controlling the speed of the casting machine and of a downstream rolling stand, wherein the speed of the rolling stand is controlled on the basis of the cast strip's temperature between casting and rolling. This renders feature (k) obvious. Contrary to the respondent's view, claim 1 does not exclude that the casting speed varies while the speed of the rolling stand is controlled in the downstream direction, as is the case in D1.

In the event that the Board decides that D1 fails to disclose that the reduction of the slab thickness begins in the mould, as is required by feature (f), this would be an obvious modification falling within the realm of routine design. The mould of D1 is implicitly funnel-shaped to compensate for slab shrinkage. Casting moulds are typically at least 900 mm long, which in light of the aim of reducing the plant length, would encourage a thickness reduction taking place already in the mould.

In conclusion, the subject-matter of method claim 1 lacks an inventive step in light of D1 and D2.

The same arguments apply, mutatis mutandis, to the subject-matter of independent claim 4 for a plant.

Respondent's case:

In addition to features (i) and (k) of claim 1, D1 also fails to disclose features (a), (b), (f) and (j), for the following reasons.

The ranges for the slab thickness (70 to 100 mm), the slab width (800 to 1200 mm) and the strip thickness (0.4 to 12 mm) as disclosed in D1 do not anticipate the broader ranges defined in features (a) and (b).

With respect to feature (f), D1 does not disclose that the thickness reduction begins in the mould 2, but rather downstream of it, in the roller table 3 (page 3, lines 10 to 12 and page 18, lines 7 to 9). Even though it was common practice at the filing date of the patent (7 April 2005) to use a funnel-shaped casting mould to compensate for natural slab shrinkage, it cannot be derived from D1 that the mould 2 is shaped for actively reducing the slab thickness beyond normal shrinkage compensation.

Feature (j) defines two alternatives, namely the cutting and withdrawal of finished sheets and the coil winding of a rolled strip, whereby the user can freely choose between the two alternatives, depending on the required end product. Although D1 discloses the steps of cutting and removing sheets (page 7, lines 12 to 15), this is only an emergency measure taken in the event of a breakdown of the finishing mill 18, and is not a normal processing step in the production of finished sheets. The sheets thus obtained are of low quality, being twisted and bent since they have not passed the finishing mill 18, and hence are not finished. Further, D1 fails to disclose the steps of cutting and removing sheets "upon controlled cooling". Although the tiltable cover 12 is designed to insulate the sheets and limit temperature losses, it does not actively cool the sheets by water jetting, as is the case in the invention.

The claimed invention takes advantage of the inverted temperature gradient of the slab resulting from casting and maintains it by induction heating until rolling begins, as is required by feature (i). This is clear from the wording of features (g) to (i) and is confirmed by the teaching in paragraphs 10 and 22 of the patent specification. D1 does not disclose that the slab is heated, let alone induction heated, between casting and rolling in order to maintain the inverted temperature gradient. In contrast, D1 teaches that the distance between the casting machine 1 and the roughing mill 5 is preferably short, e.g. between 0.5 and 4 m, whereby the slab is fed directly from the casting machine 1 to the roughing mill 5, without being re-heated (page 6, lines 8 to 18). On the other hand, it is mentioned in the paragraph bridging pages 6 and 7 of D1 that, in prior art plants with a larger distance of up to 350 m between casting machine and roughing mill, a compensation furnace is used to homogenise the temperature throughout the thickness of the cast slab, and hence suppress the inverted temperature gradient.

Starting from D1, the technical problem solved by all distinguishing features is how to improve the properties of the end product, while saving energy and maintaining a compact lay-out of the plant (paragraph 11 of the patent specification).

The claimed solution to this problem is neither part of common general knowledge of the skilled person, nor is it disclosed or suggested in D2.

With respect to feature (f), the appellant has provided no evidence supporting its allegation that it was a standard design option to reduce the slab thickness in the mould itself, beyond normal shrinkage compensation.

With respect to feature (i), as explained above, D1 teaches away from heating the slab between casting and rolling to maintain the desired inverted temperature gradient defined in features (g) and (h).

D2 cannot direct the skilled person towards feature (k) for the following reasons. This feature must be construed in the sense that the casting speed is preset and the possible speed corrections have effect on the speed parameters of the downstream rolling stands. D2 discloses a plant comprising a continuous strip casting machine and a rolling mill, wherein the speed of the cast strip between casting and rolling is detected and used to control the motor driving the casting machine, thus permitting operation of the plant without any strip loop (page 5, lines 13 to 21 and claim 1). The skilled person would not consider the teaching of D2 because it concerns a different kind of plant than that disclosed in D1. Moreover, even if he were to consider the teaching of D2, it could not lead him to a speed control system in cascade in the downstream direction, as is required by feature (k), since D2 only discloses a conventional speed control system in cascade in the upstream direction. As shown in the drawing of D2, a speed measuring device 6 is used to control the speed of the casting machine 3 on the basis of the cast strip's speed between casting machine 3 and rolling mill 7. A temperature measuring device 5 is used to control the motor 10 driving the rolling mill 7 on the basis of the cast strip's temperature between casting machine 3 and rolling mill 7, to maintain the temperature within narrow limits (page 8, lines 22 to 36). This eventually also results in an upstream control of the casting speed (page 7, lines 7 to 13).

The subject-matter of claim 1 thus involves an inventive step.

The same arguments apply to claim 4 for a plant. In addition, the appellant has failed to address the specific features of claim 4 that the mould "has a ratio >= 1.1 between its surface SM at the meniscus, subtracted the area ST interested by the submerged nozzle, and the cross-section area Sb of the slab (1) at the outlet of continuous casting" and that "a finishing mill [is] directly connected with the continuous casting at a maximum distance of 50 m".

(b) Main request - Insufficient disclosure

Appellant's case:

The feature of claim 1 that the slab thickness is actively and purposively reduced in the casting mould itself (see feature (f)) is insufficiently disclosed within the meaning of Articles 100(b) and 83 EPC for the invention to be carried out by the skilled person.

Respondent's case:

The ground of lack of sufficiency constitutes a fresh ground of opposition in the appeal proceedings. Since the patent proprietor does not approve the discussion of this ground, it cannot be considered in the appeal proceedings, pursuant to G 10/91.