Method for Hot Rolling Z-Sections Sheet Piles

BACKGROUND ART

Steel sheet piles are long structural sections provided with an interlocking system that allows building continuous retaining walls. The most common sheet pile sections are: Z-sections, U-sections, Ω-sections, flat-web sections and H or double-T sections.

Z-section sheet piles include a first flange, a second flange, which is substantially parallel to the first flange, an inclined web, a first corner joining the web to the first flange, a second corner joining the web to the second flange, wherein each of the corners has an opening angle α greater than 90°, preferably in the range of 110° to 140°. The longitudinal edges of the flanges are generally equipped with coupling means for interlocking purposes. In distinct contrast to other sheet pile sections, Z-section sheet piles do not have a plane of symmetry.

It is well known in the art to produce Z-section sheet piles by a hot rolling process, starting from slabs or, more recently, from beam blanks.

U.S. Pat. No. 5,671,630 discloses a method for rolling such Z-section sheet piles from a beam blank. According to this method, a preform of the sheet pile is rolled with curved preforms of the web and the flanges. The curved preform of the web comprises: two web/flange transition sections, which are substantially flat sections parallel to the rolling plane; a middle section, which is a substantially flat section defining an angle of about 60° with the rolling plane; and two connecting bows, connecting the web/flange transition sections to the oblique middle section. The substantially “J”-shaped preforms of the flanges allow rolling the coupling means close to the neutral rolling plane. In a last rolling step, the curved preforms of the web and the flanges are straightened to form the finished Z-section sheet pile.

It is well known in the art that grooved rolls used for rolling Z-section sheet-piles have a relatively short lifetime. Due to the absence of mirror symmetry in their section, one has to produce one side of the Z-section sheet pile in a deep groove of the upper roll and the other side in a deep groove of the lower roll. Such extreme roll gap contours result in that the roll surfaces are rapidly worn out and in that possibilities for their reworking are rather limited. They also increase the risk of a roll fracture.

There is consequently a need for a method for rolling a Z-section sheet pile in which the rolls have a longer lifetime and are less exposed to a roll fracture.

SUMMARY OF INVENTION

The invention proposes a method for hot rolling a Z-section sheet pile having a first flange, a second flange, which is substantially parallel to the first flange, an inclined web, a first corner joining the web to the first flange, a second corner joining the web to the second flange, wherein each of the corners has an opening angle α greater than 90°, preferably in the range of 110° to 140°. The proposed method comprises the steps of: (1) rolling a curved preform of the web in successive roll gaps defined by at least one roll pair comprising a grooved upper roll and a grooved lower roll, wherein a preform of the first corner and an adjoining first part of the curved preform of the web are formed in a first groove of the upper roll, in which the latter has e.g. its minimum diameter, and a preform of the second corner and an adjoining second part of the curved preform of the web are formed in a first groove of the lower roll, in which the latter has e.g. its minimum diameter; and (2) subsequently straightening the curved preform of the web between an upper straightening roll and a lower straightening roll. In accordance with one aspect of the present invention, at least in the last roll gaps rolling the curved preform of the web, the diameter of the lower roll decreases in a discontinuous manner in the interval between the first groove in the upper roll and the first groove in the lower roll, and the diameter of the upper roll increases in a complementary manner. Decreasing in a discontinuous manner means that the diameter of the lower roll does not continuously decrease; i.e. there are intermediate portions of the lower roll in the concerned interval, in which the initially decreasing diameter stays substantially constant, and/or in which it increases before it decreases again. In other words, in the interval between the first groove in the upper roll and the first groove in the lower roll, the diameter of the lower roll decreases e.g. in a stepped manner and/or in an undulated manner. It follows that less vertical space is required for rolling the preform of the web; i.e. the minimum diameters of the two rolls may be bigger than with any prior art method of rolling Z-shaped sheet-piles. Consequently, the roll gap contour can be reworked more often, before the minimum diameters of the rolls decrease beyond a limit value. Furthermore, less deep grooves in the rolls also result in smaller rolling torques and in more equal surface speeds along the roll gap contour, i.e. in less mechanical wear of the surfaces of the rolls. In summary, with the proposed method, the rolls wear out less faster and must be reworked less often, but—due to a bigger minimum diameter—can even be reworked more often than with any prior art method for rolling Z-section sheet piles. Last but not least, less deep grooves in the rolls also substantially reduce the risk of a roll fracture. Consequently, with the proposed method, expected total life-time of the rolls can be substantially increased. Finally, it will further be appreciated that the proposed method allows using a relatively thin slab as a starting product for rolling a Z-section sheet pile.

In a preferred embodiment, the diameter of the lower roll decreases, in the interval between the first groove in the upper roll and the first groove in the lower roll, in a an undulated manner, so as to have in this interval at least one intermediate maximum value and one intermediate minimum value. This means e.g. that a third part of the curved preform of the web, which is located between the first part and the second part, is formed partly in a second groove of the lower roll, and partly in a second groove of the upper roll. Due to the fact that rolling of the curved preform of the web is allotted onto at least two grooves in the upper roll and at least two grooves in the lower roll, these grooves may be less deep, i.e. the minimum diameters of the two rolls may be bigger.

In a further embodiment, in the interval between the first groove in the upper roll and the first groove in the lower roll, the diameter of the lower roll decreases then stays constant, before further decreasing. This means e.g. that a third part of the curved preform of the web, which is located between the first part and the second part, is formed between substantially cylindrical portions of the upper roll and the lower roll. Due to the fact that the middle section of the curved preform of the web is rolled—at least partly—between substantially cylindrical roll sections, less vertical space is required for rolling the preform of the web; i.e. the minimum diameters of the two rolls may be bigger than with any prior art method of rolling Z-shaped sheet-piles.

If the centre line of a roll is defined as being the axis (line) about which the roll rotates (i.e. the line passing through the centres of the two bearing journals of the roll) and the nominal diameter of a roll in a roll pair is defined as being the minimum vertical distance between the centre lines of the rolls of the roll pair, the minimum diameter of the lower roll in its—aforementioned—second groove is preferably smaller than the nominal diameter of the lower roll and preferably bigger than the minimum diameter of the lower roll in its first groove; and/or the minimum diameter of the upper roll in its—aforementioned—second groove is preferably smaller than the nominal diameter of the upper roll and preferably bigger than the minimum diameter of the upper roll in its first groove.

(This article comes from FreePatentsOnline.com editor released)

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