Method and device in the press section of a paper machine for detaching the web from the face of the press roll

Claim 2

Method in the press section of a paper machine for detaching the web (W) from the smooth face (10ʹ) of a press roll (10), characterized in - that in the method, within the area of the detach­ing point (R), a momentary and local heating effect is directed at the web (W) from outside the roll (10), - that in the method, as the mantle or outer coating of the said smooth-faced (10ʹ) roll (10), a material is used which is magnetically at least to some extent conductive, - that to the said roll mantle, an induction heating effect of such a high frequency (f,f s ) is applied free of contact that the depth of penetration (δ) of the heating effect remains sufficiently low in view of its local and momentary nature, and - that, by means of the said heating effect, the water present between the web (W) and the roll face (10ʹ) is heated, preferably vaporized, locally within the area of the detaching point (R) so as to detach the web (W) from the said roll face (10ʹ).

Claim 3

Method as claimed in claim 1, char­acterized in that in the method, as the electric frequency of the induction heating, a frequency is used that is within the range of f = 0.5 to 2 MHz, preferably f = 0.8 to 1.5 MHz.

Claim 4

Method as claimed in claim 1 or 2, characterized in that in the method the temperature of the roll from which the detaching takes place, preferably the central roll in the press section, is within the range of 60°C to 90°C, preferably about 70°C.

Claim 5

Method as claimed in any of the claims 1 to 3, characterized in that in the method such a heating capacity is used that the temperature of the roll surface rises within the detaching area locally and momentarily maximally by about 40°C...60°C, pre­ ferably by about 50°C.

Claim 6

Method as claimed in claim 4, char­acterized in that the heating capacity per metre of length of the roll (10) is about P = 30 to 50 kW/m, preferably P = 40 kW/m.

Claim 7

Method as claimed in any of the claims 1 to 5, characterized in that the heating effect is arranged adjustable in the axial direction (K-K) of the roll (10).

Claim 8

Method as claimed in any of the claims 1 to 6, characterized in that the level or the axial distribution of the induction heating effect is adjusted by means of adjustment of the air gap, adjust­ment of the frequency, adjustment of the current, adjust­ment of the voltage, or by means of a combination of the adjustments mentioned above.

Claim 9

Method as claimed in any of the claims 1 to 7, characterized in that in the method a closed draw is used for the transfer of the web (W) from the roll (10) in the press from which the web (W) is detached by means of the induction heating in accord­ance with the invention.

Claim 10

Method as claimed in claim 8, char­acterized in that in the method the drying wire (70) or any other, corresponding transfer fabric is passed to the detaching point (R) and that the web (W) is, after the detaching, made to adhere to the drying wire (70) or to a corresponding transfer fabric by means of a suction effect or equivalent and passed either onto the first drying cylinder (68) or onto a corresponding lead-in cylinder or, over the suction sector (71a) of a suction roll (71), onto the first drying cylinder (68) (Fig. 2).

Claim 11

Method as claimed in claim 8, char­acterized in that in the method the guide roll (66) of the drying wire (70) or of any other, corres­ponding transfer fabric is arranged to form a transfer nip with the smooth-faced central roll (10) or equivalent of the press section.

Claim 12

Device intended for carrying out the method as claimed in any of the claims 1 to 10 for being applied in a press section which includes a smooth-faced press roll (10), preferably a central roll (10), from whose smooth face (10ʹ) the web (W) can be detached and thereinafter be passed to the drying section of the paper machine, preferably onto its drying wire (70) or a corresponding transfer fabric, char­acterized in that in connection with the said smooth-faced (10ʹ) press roll (10), at the proximity of the transfer point (R), an electroinductive heating device (20) is provided, whereat the front face of the core of the said heating device forms an air gap (V) at the detaching point with the roll face (10ʹ), which is made of a magnetically conductive, preferably ferro-­magnetic material, and that the said induction heating device (20) comprises one or several magnetically con­ductive coil cores as well as one or several electric coils (30), and that the device further includes high-­frequency apparatuses by means of which an electric current of such a high frequency can be passed to the said coil or coils that, in view of the momentary and local nature of the heating effect, a sufficiently low depth of penetration is obtained for the induction heating effect at the roll face (10ʹ).

Claim 13

Device as claimed in claim 11, char­acterized in that the inductive heating devices (20) comprise a series of magnetic cores (20₁...20 N ) fitted at the proximity of the roll face (10ʹ) to be heated, each of the said cores having an excitation wind­ing of its own or all of the said cores having a common excitation winding (30), that both the basic level of the heating effect and the distribution of the heating effect in the axial direction (K-K) of the roll (10) are controlled by adjusting the air gap (V) between each core and the roll face (10ʹ) to be heated and/or by adjusting the magnetization current and/or by adjusting the frequency of the magnetization current.

Claim 14

Device as claimed in claim 11 or 12, characterized in that in the method, as the supply circuit of electric power, a LC resonance circuit is used, the frequency (f) of the electric power fed into the said circuit having been chosen at a certain safety distance above or below the resonance frequency (f r ) of the said LC resonance circuit.