Method for assembling an improved Yankee cylinder

Abstract

A method for producing a Yankee dryer cylinder, or Yankee cylinder, comprises the steps of disposing of a first and of at least a second cylindrical portion of shell. These are made of steel, have the same diameter and are provided with a plurality of grooves at an internal surface. In particular, the portions of shell, at a respective end, are provided of respective flange portions. The method provides to coaxially position the portions of shell up to arrange respective coupling surfaces of the flange portions adjacent one to the other. Then the engagement of the portions of shell is provided by means of a plurality of clamping members, each of which arranged to clamp the adjacent flange portions. Then, it is provided the circumferential welding of the cylindrical portion of the shell that are opposite to the flange portions, and the removal of the clamping members and of the flange portions.

Claims

1. Method for producing a Yankee dryer cylinder, or Yankee cylinder, comprising the steps of: disposing of a first and at least a second cylindrical portion of shell of said Yankee dryer cylinder, said first and second cylindrical portion of shell being made of steel and having a same diameter, said first and second cylindrical portion of shell having a respective internal surface provided with a plurality of circumferential grooves and of a respective flange portion at a respective end; coaxially positioning said first and second cylindrical portion of shell up to arrange respective coupling surfaces of said flange portions adjacent one to the other; engaging said first and second cylindrical portion of shell by means of a plurality of clamping members, each clamping member of said plurality being arranged to clamp said adjacent flange portions; circumferential welding of said engaged first and second cylindrical portion of shell at the opposite side of said flange portions; removing said plurality of clamping members; removing the flange portions.

2. Method for producing a Yankee dryer cylinder, or Yankee cylinder, according to claim 1, wherein said coupling surfaces of the flange portions of said first and second cylindrical portion of shell are configured in such a way to provide a fixed joint.

3. Method for producing a Yankee dryer cylinder, or Yankee cylinder, according to claim 1, wherein, before the positioning step of said first and second cylindrical portion of shell, a step is provided of making a circumferential housing between said coupling surfaces of said flange portions, said circumferential housing being arranged, in use, to house an annular body, which is removed once said flange portions are removed.

4. Method for producing a Yankee dryer cylinder, or Yankee cylinder, according to claim 3, wherein the annular body is made of ceramic.

5. Method for producing a Yankee dryer cylinder, or Yankee cylinder, according to claim 1, wherein, once said removing step of said flange portions has been carried out, a step is provided of making at least a circumferential groove between said coupled ends of said first and second cylindrical portion of shell.

6. Method for producing a Yankee dryer cylinder, or Yankee cylinder, according to claim 5, wherein said removing step of said flange portions and/or said step of making said groove between said coupled ends of said first and second cylindrical portion of shell, and/or said step of removing said annular body is carried out by means of a removal machine comprising an engagement portion engaging said shell and a working portion provided with a tool.

7. Method for producing a Yankee dryer cylinder, or Yankee cylinder, according to claim 1, wherein both said first and said second cylindrical portion of shell are obtained through the steps of: disposing of un tubular semifinished product made of steel having a side wall provided with an internal surface and an external surface; forging said tubular semifinished product up to obtain a first predetermined thickness s1 at a central portion of said side wall and predetermined thickness greater than said first thickness s1 at the enlarged terminal portions; making a plurality of circumferential grooves at said internal surface of said tubular semifinished product obtaining said first, or said second, cylindrical portion of shell.

8. Method for producing a Yankee dryer cylinder, or Yankee cylinder, according to claim 7, wherein, at said enlarged portion of said cylindrical portion of shell opposite to said terminal portion provided with said flange portion, a step is provided of making a plurality of longitudinal dead holes and wherein, furthermore, the steps are provided of: positioning a head at each enlarged terminal portions of said cylindrical shell, each head being provided with a plurality of through holes, at the end of said step of positioning, each through hole of said plurality being aligned with a respective blind hole of said enlarged terminal portion of said cylindrical shell; fixing each said head to a respective enlarged terminal portion of said cylindrical shell by screwing a stud at each couple of aligned blind hole and through hole.

9. Method for producing a Yankee dryer cylinder, or Yankee cylinder, according to claim 8, wherein, furthermore, the steps are provided of: disposing of a hollow shaft within said cylindrical shell; disposing of a first bearing journal at said first head disposing of a second bearing journal at said second head; fixing by bolt coupling said hollow shaft to said first head, to said second head, to said first bearing journal and to said second bearing journal.

10. Method for producing a Yankee dryer cylinder, or Yankee cylinder, according to claim 7, wherein said step of making a plurality of grooves at said internal surface provides to make an end group of grooves at said first, or second, terminal portion of said first, or second, cylindrical portion of shell, said end group of grooves comprising at least a first and at least a second circumferential groove having a width l that increases and a depth d that decreases going towards said enlarged terminal portion of said cylindrical portion of shell, in such a way to uniformly distribute, in operating conditions, the loads along the final shell.

11. Method for producing a Yankee dryer cylinder, or Yankee cylinder, according to claim 7, wherein at the end of said forging step, said enlarged terminal portion has a tapered internal surface arranged to delimit a circumferential groove having a width greater than the width of the adjacent end groove and a depth that is less than its depth.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be now shown with the following description of its exemplary embodiments, exemplifying but not limitative, with reference to the attached drawings in which:

(2) FIG. 1 shows a flow diagram illustrating the main steps of the method, according to the invention, for producing a Yankee cylinder;

(3) FIG. 2 diagrammatically shows a part of a Yankee cylinder produced by the method, according to the invention;

(4) FIG. 3 shows an enlarged view of the contact zone between the 2 portions of shell of the Yankee cylinder of FIG. 2 in order to highlight some characteristics;

(5) FIG. 4 diagrammatically shows a cross section view of the shell during a production step of the same in order to highlight some characteristics;

(6) FIG. 5 shows an enlargement of FIG. 4 in order to highlight some characteristics;

(7) FIG. 6 diagrammatically shows, in section view, a Yankee cylinder produced with the method, according to the invention;

(8) FIG. 7 shows an enlarged view of the contact zone between the shell and the head of the Yankee cylinder of FIG. 6 in order to highlight some characteristics;

(9) FIGS. 8 and 9 diagrammatically show 2 instants of the production step of the shell, according to the invention, in particular the coaxially positioning step of the 2 portions of shell and the step of disposing them adjacent one to the other;

(10) FIG. 10 diagrammatically shows a removing step of the flange portions carried out by a working machine;

(11) FIG. 11 diagrammatically shows a part of a Yankee cylinder produced with an exemplary embodiment of the method, according to the invention;

(12) FIG. 12 shows an enlarged view of the contact zone between the two portions of the shell of the Yankee cylinder of FIG. 11 in order to highlight some characteristics;

(13) FIG. 13 diagrammatically shows a step of making at least a groove at the coupling zone of the 2 portions of the shell and of breaking of the annular body carried out by the same working machine;

(14) FIG. 14 diagrammatically shows a flow diagram illustrating a possible sequence of steps for obtaining each cylindrical portion of shell;

(15) FIGS. 15 and 16 diagrammatically show 2 instants of the rolling step to which the starting semifinished product is subjected for obtaining the portions of the shell;

(16) FIG. 17 diagrammatically shows in an exploded view, the connection zone between the shell and the head of the Yankee cylinder produced by the method, according to the invention;

(17) FIG. 18 diagrammatically shows the connection zone between the shell and the head of the Yankee cylinder of FIG. 6 in an assembled configuration;

(18) FIG. 19 shows an enlarged view of the circumferential groove that is the closest one to the enlarged terminal portion of the shell;

(19) FIG. 20 diagrammatically shows in a section view the contact zone between the shell and the head of an exemplary embodiment of the Yankee cylinder that can be produced using the method, according to the invention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION

(20) As diagrammatically shown in the block-scheme of FIG. 1, the method, according to the invention, for producing a Yankee dryer cylinder, or Yankee cylinder, provides a starting step of disposing of a first and of a second cylindrical portion of shell 10a and 10b, block 301. More in detail, the portions of shell 10a and 10b are made of steel and have the same diameter, in particular, the same internal diameter in and the same external diameter nest. Both the first portion 10a and the second portion 10b are provided with a plurality of grooves 15 at a respective internal surface 112a and 112b. These are provided with flange portions 19a and 19b at respective ends 11a and 11b. More in detail, the flange portions 19a and 19b protrudes towards the inside of the respective portion 10a and 10b. In the embodiment illustrated, for example, in FIG. 2, the flange portions 19a and 19b are substantially dovetail shaped. Each flange portion 19a and 19b can be made in a single piece, or can comprise many circular sectors. Furthermore, the flange portions 19a and 19b do not necessarily cover all the circumference of the portions of the shell 10a and 10b.

(21) Then, a step of coaxially positioning the first and the second cylindrical portion of shell 10a and 10b follows up to arrange adjacent respective coupling surfaces 29a and 29b of the flange portions 19a and 19b, block 302.

(22) The first and the second cylindrical portion of the shell 10a and 10b are, then, mutually engaged by means of a plurality of clamping members 90, block 303.

(23) As it is shown in detail in the figure, each clamping member 90 is arranged to clamp the adjacent flange portions 19a and 19b. More in detail, each clamping member 90 can comprise a first part 90a that is adjacent, in use, to the flange portion 19a of the first portion 10a of the shell, and a second part 90b that is adjacent, in use, to the flange portion 19b of the second portion 10b of the shell. The 2 parts 90a and 90b of the clamping member 90 are, then, fixed to the flange portions 19a and 19b by means of a bolt 95.

(24) Once the 2 portions of shell 10a and 10b have been clamped to the flange portions 19a and 19b, a circumferential welding is made, block 304. More in detail, the circumferential welding 190 is made at the opposite side of the flange portions 19a and 19b (see for example FIG. 3).

(25) Once the circumferential welding 190 is completed, the clamping members 90 are removed, block 305. Then, the flange portions 19a and 19b are removed, block 306.

(26) This step can be carried out by means of a tool 505, for example a cutter. More in detail, as diagrammatically shown in the figure, a removal machine 500 is provided for removing the above disclosed flange portions 19a and 19b that is equipped with the above disclosed tool 505. The machine 500 can be provided, in particular, with an engagement portion 501 arranged to engage the shell 10 keeping determined relative positions, and with a working portion 502 provided with the tool 505. More precisely, the engagement portion 501 can be provided with shaped members 503 arranged to engage with the grooves 15 of the shell 10 in order to keep the machine 500 in position during its operation.

(27) The working portion 502 can be rotatably connected to the engagement portion 501, in such a way that the tool 505 can be moved with respect to the shell 10. More precisely, during the removing step of the flange portions 19a and 19b, the tool 505 can be oriented along a substantially axial direction to the shell (FIG. 10), whilst during the step of making of at least a circumferential groove between the coupled ends 11a and 11b, the tool 505 is oriented along a direction that is substantially orthogonal to the longitudinal axis of the shell 10 (FIG. 13).

(28) According to an exemplary embodiment of the invention, in order to make a very short circumferential welding 190 and avoid shrinkage stresses, before coupling the first and the second cylindrical portion of shell, a step is provided of making a circumferential housing 98 at the coupling surfaces 29a and 29b of the first and of the second cylindrical portion of the shell 10a and 10b. Then, a step is provided of positioning an annular body 198, preferably made of ceramic, within the circumferential housing 98.

(29) More precisely, the circumferential housing 98 can be made at one of the 2 ends 11a, or 11b, of one of the 2 portions 10a, or 10b, or otherwise can be obtained by making circumferential grooves 97a and 97b at both the coupling surfaces 29a and 29b. In this case, the circumferential housing 98 is obtained drawing one end 11a near the other end 11b, i.e. positioning the 2 circumferential grooves 97a and 97b facing each other.

(30) The annular body 198 is removed, for example crushing it, once removed the flange portions. More precisely, for crushing the annular body 198 it is possible to use the same tool 505 that is used for removing the flange portions 19a and 19b.

(31) As shown in detail in the figure, the first and the second cylindrical portion of shell 10a and 10b have different axial dimensions. More precisely, the length l1 of the first portion 10a is different, for example, greater than the length l2 of the second cylindrical portion of shell the 10b, i.e. l1l2. This, in order to avoid that the welding is carried out along the centre line 115 of the shell 10 of the Yankee dryer cylinder 1.

(32) According to what is provided by the invention, each cylindrical portion of shell 10a, or 10b, is obtained through the steps indicated in the block-scheme 400 of figure.

(33) As shown in the block-scheme 400, each cylindrical portion of shell 10a, or 10b, is made starting from a tubular semifinished product 110 made of steel. This is provided with a side wall 111 having an internal surface 112 and an external surface 113, block 401. A forging step follows of the tubular semifinished product 110 up to obtain a first predetermined thickness s1 at a central portion 111a of the side wall 111 and a second predetermined thickness s2, with s2>s1, at opposite terminal portions 111b, 111c of the side wall 111, block 402. The two opposite ends can have a different thickness, that means a thickness s2 at the portion 11a, or 11b, where they are provided with the flange portions 19a and 19b, and a thickness s3, which is different from s2, at the opposite portion 12a, or 12b that has to be coupled to the head 30, or 20, respectively.

(34) In this way a tubular semifinished product 110 is obtained that has enlarged terminal portions 111b, 111c. Then, a step is provided of making a plurality of grooves 15 at the internal surface 112 of the tubular semifinished product 110, obtaining a cylindrical portion of cylindrical shell 10a, or 10b, of the shell 10 of the Yankee dryer cylinder 1, block 402. In particular, the circumferential grooves 15 are made by machining. As known, in use, in the circumferential grooves 15 collects the condensate, which is formed for the transfer towards the outside of the latent heat of vaporization from the steam that has been introduced inside the body of the Yankee cylinder 1.

(35) According to the invention a step is, furthermore, provided of making a plurality of longitudinal dead holes 17 at the external surface 14, 16 of the enlarged terminal portions 111b, 111c of the cylindrical shell 10, block 403.

(36) Then, the heads 20 and 30 are positioned at the opposite enlarged terminal portions of the cylindrical shell 10, and fixed to the shell 10 by means of studs 50, block 404. More precisely, each head 20,30 is provided with a plurality of through holes 27 each of which, in use, is aligned with a respective blind hole 17. Therefore, the coupling of the heads 20 and 30 to the shell 10 is carried out by screwing the studs 50 in the holes 17 and 27 positioned aligned, block 405.

(37) Once the fixing of the portions 10a and 10b has been carried out, and the shell 10 is obtained, the dryer cylinder 1 is, then, completed positioning a hollow shaft 40 within the cylindrical shell 10, coaxially to it, a first bearing journal 70, at the first head 20, and a second bearing journal 80, at the second head 30. In particular, a first end of each bearing journal 70, 80 is housed, in use, in a hole of a respective head 20, or 30, whilst the opposite end is mounted within a bearing 75, or 85. The hollow shaft 40 is then fixed to the heads 20 and 30 and to the bearing journals 70 and 80 by bolt coupling.

(38) As shown in detail in the FIGS. 17, 18 and 20, the studs used for fixing the shell 10 to the heads 20 and 30 are preferably conical studs 50. More precisely, each stud 50 is clamped to a respective head 20, or 30, by means of a clamping nut 52. Between each clamping nut 52 and the surface of head 20, or 30, a step is provided of interposing a washer made of annealed copper 51. This particular solution allows, in operating conditions, to compensate any play.

(39) The technical solution provided by the present invention allows to distribute more uniformly the stresses, in particular the thermoelastic stresses, the pressure stresses and the stresses that are due to the centrifugal force, allowing to increase the performances and the service life of the Yankee cylinder.

(40) In fact, in operating conditions, the pressure tends to deform differently both the shell and the heads. Therefore, the contact zones between the shell and the heads are the most stressed zones.

(41) For the above discussed reasons, at the connection zones between the shell and the heads the stresses, to which the Yankee cylinder is subjected, concentrate and, therefore, in operating conditions, cracks and slits can happen that can cause, over time, the structure to be broken.

(42) The solution provided by the present invention, instead, allows to increase the thickness of the shell at the terminal portions and at the same time to avoid to introduce elements that weaken the structure as for example welds, or protruding portions of screws. Therefore, in operating conditions, a more uniform distribution of the loads is achieved. A further advantage of using the studs, with respect to the using of the traditional through screws, is to avoid trapping of the air in the hole within which the screw is screwed. In fact, the presence of air within the holes, or the hollows, of the structure can cause cracks and slits, because of the high temperatures at which the Yankee cylinders work, the pressure of the air increases thus producing concentrated stresses.

(43) As diagrammatically illustrated in FIGS. 15 and 16, the above disclosed forging step provides a rolling carried out by means of at least a first bending roll 210 and a second bending roll 220 arranged, in use, to rotate about respective rotation axes 215 and 225 in order to exert their action at the respective opposite surfaces 112 and 113 of the wall 111 of the tubular semifinished product 110. More precisely, the bending rolls 210 and 220 are configured in such a way that, during the rolling step, the thickness s of the tubular semifinished product 110 is reduced to a first value s1 at a central portion and to a second thickness. Alternatively, using specific bending rolls, it is possible to obtain, as above disclosed in detail, a second thickness s2 and a third thickness s3, at the opposite terminal portions 11a and 11b, or 12a and 12b.

(44) As diagrammatically shown in particular in FIG. 20, the step of making a plurality of grooves 15 at the internal surface 112 provides to make an end group of grooves at the terminal portion 12a, or at the terminal portion 12b, of the first, or of the second, cylindrical portion of shell 10a, or 10b. In particular, the end group of grooves comprises at least a first and at least a second circumferential groove 15a, or 15b, and 15a, or 15b having a width l which increases. More precisely if with l.sub.1 is indicated the width of the groove 15a and with l.sub.2 is indicated the width of the groove 15b, it is l1>l.sub.2. Furthermore, the circumferential end grooves 15a, or 15b, and 15a, or 15b have a depth d that decreases going towards the enlarged terminal portions 12a and 12b of the shell 10 obtained by coupling the 2 portions of shell 10a and 10b. Therefore, if d.sub.1 is the depth of the groove 15a and d.sub.2 is the width of the groove 15b, it is d1>d.sub.2.

(45) This particular geometry of the circumferential grooves 15 together with the absence of welds, or flange portions at the side of the shell 10 of screws, or bolts, allows to optimize the performances of the Yankee cylinder 1 with respect to the Yankee cylinders of prior art.

(46) Between the first and the second end group of grooves of the final shell 10, a group is provided of central grooves 15 all having the same width l, that is less than the width of the end grooves, and the same depth d that is greater than the depth of the end grooves.

(47) At the end of the forging step, the enlarged terminal portion 111b, 111c has a tapered internal surface 14, 16 arranged to delimit a groove 18 having a width l that is greater than the width of the adjacent end groove and a depth d that is less than its depth.

(48) An embodiment of the invention provides, furthermore, the step of making the plurality of grooves 15 at the internal surface 112 provides to make a first 15a, 15a, a second 15b, 15b, and at least a third circumferential groove 15c, 15c having a width l that increases and a depth d that decreases going towards the enlarged terminal portion 12a, or 12b, of the final shell 10.

(49) According to an advantageous exemplary embodiment of the invention, each head 20, 30 comprises a central lowered portion 21, 31 that is lowered towards the inside of the Yankee cylinder 1 and an terminal portion 22, 32 connected to the central lowered portion 21, 31 by means of a connection portion 23, 33. This can be substantially flat, or curvilinear, i.e. substantially concave. At the connection portion 23, 33 of a head 20, 30, at least one inspection aperture 25 can be provided for example 2 inspection apertures. These ensure that, during the assembling, or maintenance, operations, the staff can work in safety. In a possible embodiment, each connection portion of each head is provided with 2 inspection apertures arranged at 180.

(50) In particular, each inspection aperture 25 has a tubular shape. The tubular shape of the inspection apertures 25 to simplify and improve dynamic balancing of the whole structure and to help the staff to enter inside the Yankee dryer cylinder 1. The tubular entrance of the inspection apertures, furthermore, increases the structural stiffness of the head and therefore of the whole Yankee cylinder.

(51) As shown in detail in FIG. 8, at least the end circumferential grooves 15 have a curvilinear profile. According to another aspect of the invention, at least these circumferential grooves 15 have a radius of curvature r that is greater than the radius of curvature r of the circumferential grooves 15 positioned at the central portion 11 of the cylindrical shell 10, i.e. r>r. More in detail, the radius of curvature r of the first and of the second circumferential groove 15a, 15b and 15a, 15b of the first and of the second group is set between 9.5 and 10.5 mm, e.g. r=10 mm.

(52) As shown, for example in FIG. 9, between each group of circumferential end grooves 15 and the central grooves 15, a group is provided of intermediate circumferential grooves 15. In particular, the group of intermediate grooves 15 comprises at least a circumferential groove having a width l that is equal to the width l of the grooves 15 of the central portion 11, but a depth d that is set between the depth of the end circumferential groove 15b, or 15b, to it adjacent and the depth of the circumferential central grooves 15. In a foreseen embodiment, also the circumferential grooves 15 of the group of intermediate grooves have a curvilinear shape. In particular, the circumferential grooves 15 of the group of intermediate grooves can have a radius of curvature r set between 6 and 7 mm, preferably r=6.4 mm. Also the circumferential grooves 15 positioned at the central portion 11 of the cylindrical shell can have a radius of curvature r set between 6 and 7 mm, preferably r=6.4 mm.

(53) Concerning the depth of the first circumferential end grooves 15a and 15a, it has been demonstrated that the best conditions are obtained with a depth d1 set between 25 and 27 mm, preferably d1=26 mm. Analogously, the second circumferential grooves 15b, 15b of the first and of the second group have preferably a depth d2 set between 30 and 32 mm, preferably d2=31 mm.

(54) According to an exemplary embodiment of the invention, the circumferential grooves 15 of the group of intermediate grooves have a depth d set between 31 and 33 mm, preferably a depth d=32 mm.

(55) As shown, for example, in FIG. 2, the depth increases along the first 4 grooves, i.e. d>d>d2>d1. All the grooves 15 of the central portion 11 have the same depth d, for example d=33 mm.

(56) The foregoing description exemplary embodiments of the invention will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such embodiment without further research and without parting from the invention, and, accordingly, it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiments. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology that is employed herein is for the purpose of description and not of limitation.