Yankee dryer cylinder with controlled thermal expansion

Abstract

Yankee dryer cylinder (1) having a cylindrical shell made of steel (10), having a first and a second end opposite each other (11, 12) and provided with a plurality of circumferential grooves (15). The cylinder (1) includes a first and a second head (20, 30) made of cast iron and fixed respectively to the first and to the second end (11, 12) of the cylindrical shell made of steel (10). It is, furthermore, provided a hollow shaft (40) mounted inside the cylindrical shell (10) and connected to the first and to the second head (20, 30) at a first and a second end (41, 42), respectively. The cylinder is also provided with a first and a second bearing journal (50,60) fixed to the hollow shaft (40) at a respective end (41, 42).

Claims

1. Yankee dryer cylinder (1) comprising: a cylindrical shell made of steel (10) having a first end (11) and a second end (12) opposite to said first end (11), said cylindrical shell (10) having a longitudinal axis (101) and being, furthermore, provided with a plurality of circumferential grooves (15); a first head (20), or first end wall, fixed to said first end (11) of said cylindrical shell made of steel (10), said first head (20) being made of cast iron; a second head (30), or second end wall, fixed to said second end (12) of said cylindrical shell made of steel (10), also said second head (20) being made of cast iron; a hollow shaft (40) mounted inside said cylindrical shell (10) and connected to said first and to said second head (20,30) at a first and a second end (41,42), respectively; a first bearing journal (50) fixed to said hollow shaft (40) at said first end (41); a second bearing journal (60) fixed to said hollow shaft (40) at said second end (42); wherein said cast iron in which said first and said second head (20,30) are made has the following composition by weight %: C: between 3.0 and 3.5%; Si: between 1.5 and 2.7%; Mn: between 0.3 and 0.7%; P: between 0.05 and 0.10%; V: between 0.20 and 0.50%; S: between 0.05 and 0.10%; Mg: between 0.06 and 0.20%; Cu: between 0.10 and 0.80%; Cr: between 0.05 and 0.10%.

2. Yankee dryer cylinder, according to claim 1, wherein said hollow shaft (40) is made of a cast iron having the same composition by weight % of said cast iron of said first and said second head (11,12).

3. Yankee dryer cylinder, according to claim 1, wherein said first and said second bearing journal (31,32) are made of a cast iron having the same composition by weight % of said first and said second head (11,12).

4. Yankee dryer cylinder, according to claim 1, wherein each of said first and of said second head (20,30) comprises: a central portion (21,31) that is lowered towards the inside of said Yankee dryer cylinder (1); an end portion (22,32) connected to said central lowered portion through a connection portion (23,33).

5. Yankee dryer cylinder, according to claim 4, wherein said connection portion is substantially flat.

6. Yankee dryer cylinder, according to claim 1, wherein said hollow shaft (40) that is mounted coaxially inside said cylindrical shell (10) has a substantially cylindrical shape.

7. Yankee dryer cylinder, according to claim 1, wherein each end (41,42) of said hollow shaft (40) is connected by means of screw bolts to a respective bearing journal (50,60).

8. Yankee dryer cylinder, according to claim 1, wherein an end of each bearing journal (50,60) is housed, in use, in a respective hole of a respective end (41,42) of said hollow shaft (40), each bearing journal (50,60) being provided with a respective portion (55,65) mounted within a respective bearing (71,72).

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 diagrammatically shows in a view according to a longitudinal section, one of the possible embodiments provided for a Yankee dryer cylinder of mixed type steel and cast iron that can be produced using the cast iron, according to the invention;

(3) FIG. 2 diagrammatically shows, in the range of temperatures of interest, the trend of the coefficients of linear thermal expansion for the examined samples, i.e. a sample made of cast iron according to the invention, a sample made of a different type of cast iron and 2 samples made of steel.

DETAILED DESCRIPTION OF THE INVENTION

(4) As diagrammatically shown in FIG. 1, a possible structure of Yankee dryer cylinder 1, according to the present invention, comprises a cylindrical shell made of steel 10 having a longitudinal axis 101, a first head, or end wall, 20 and a second head, or end wall 30. In the embodiment of FIG. 1, each head 20, 30 has a central portion 21, 31 lowered towards the inside of the Yankee dryer cylinder 1, and an end portion 22, 32 that is connected to the respective lowered central portion 21, 31 through a connection portion 23, 33.

(5) The cylindrical shell 10 is provided, in particular at the internal surface 14, with a plurality of circumferential grooves 15 having a predetermined depth. As known, the condensate that is formed for the transfer of the latent heat of vaporization from the steam, that has been introduced in the Yankee dryer cylinder 1, towards the outside, is collected inside the grooves 15.

(6) The 2 heads 20 and 30 are fixed by means of a bolting to the shell 10 at the opposite ends 11 and 12.

(7) The Yankee dryer cylinder 1 comprises, furthermore, a first bearing journal 50 and a second bearing journal 60 that are fixed at the opposite ends of a hollow shaft 40.

(8) The fixing of the bearing journals 50 and 60 to the hollow shaft 40 is carried out by means of screw bolts. The ends 51 and 61 of the bearing journals 50 and 60 are respectively housed, in use, in the holes 41 and 42 of the hollow shaft 40 and have respective portions 55 and 65 mounted inside respective bearings 71 and 72. Each end 41 and 42 of the hollow shaft 40 is, furthermore, fixed to a respective head 20 and 30 by means of screw bolts.

(9) As diagrammatically shown in the example of FIG. 1, for safety reasons, 2 inspection apertures 25 are provided at each head.

(10) According to the present invention, the shell 10 is made of steel, preferably SA-516-70 steel with reference to the ASME nomenclature, whilst the first and the second head 20 and 30 are made of cast iron having the following composition by weight %: C: between 3.0 and 3.5%, Si: between 1.5 and 2.7% Mn: between 0.3 and 0.7%, P: between 0.05 and 0.10%, V: between 0.20 and 0.50%, S: between 0.05 and 0.10%, Mg: between 0.06 and 0.20%, Cu: between 0.10 and 0.80%, Cr: between 0.05 and 0.10%. This particular type of cast iron, more precisely of spheroidal cast iron, named SA-476-80 with reference to the ASME nomenclature, shows, as will be discussed in detail later on, a trend of the linear thermal expansion that is very similar to that one of the steel that is used for the shell 10 (see in this respect FIG. 2). In a particular particularly advantageous embodiment, also the bearing journals 50 and 60 and the hollow shaft 40 are made of the same cast iron of the heads 20 and 30, i.e. the spheroidal cast iron having the above indicated composition.

(11) In the following some experimental data are shown that demonstrate that the cast iron, according to the present invention, hereafter Cast iron-80, having the composition indicated in the following table 1, has a volumetric answer with respect to the temperature that is similar to that of the steel.

(12) TABLE-US-00001 TABLE 1 qualitative and quantitative chemical composition of Cast iron-80 Chemical Intervals of composition Element Symbol by weight (%) Carbon C 3.0-3.5 Silicon Si 1.5-2.7 Manganese Mn 0.3-0.7 Phosphor P 0.05-0.10 Vanadium V 0.20-0.50 Sulphur S 0.05-0.10 Magnesium Mg 0.06-0.20 Copper Cu 0.10-0.80 Chromium Cr 0.05-0.10

(13) In particular, it has been carried out a comparative analysis of the samples of Cast iron-80 (sample 1 of tab.2), with samples made of steel (samples 3 and 4 of tab. 2) and with samples of a different type of cast iron, in the following Cast iron-60 (sample 2 in tab. 2).

(14) The materials have been sampled in a cylindrical shape with a length of 10 mm and an area of 25.5 mm.sup.2.

(15) TABLE-US-00002 TABLE 2 Description of the samples of cast iron and steel examined in respect of the thermal expansion. ASME Sample Type Nickname corrispondente 1 Spheroidal cast iron- 1-Cast SA-476-80 80% ferrite iron80 2 Cast iron-60% 2-Cast ferrite iron60 3 Sample B- 3-Ac-NormB SA-516-70 normalized steel- direction orthogonal to rolling 4 Sample A- 4-Ac-NormA SA-516-70 normalized steel- direction orthogonal to rolling

(16) The results of the measure of the linear thermal expansion coefficients of the samples made of cast iron and steel that are shown in table 1 have been measured in the range of temperature of 45-245 C.

(17) The results obtained are shown in the graph of FIG. 2.

(18) All the samples show a trend of the linear thermal expansion coefficient that increases with the temperature.

(19) The trend is not rectilinear, but there are some regions of differentiated temperatures. In fact, the increasing with the temperature is much higher from 45 to 120 C. and then decreases in the range of 120-245 C.

(20) In general all the materials show similar trends and not very different values with the only exception of sample 2 (Cast iron 60) that shows a higher expansion coefficient (up to about 10%) in the zone from 50 to 90 C.

(21) The average values of the thermal expansion coefficients have been computed and indicated in table 3.

(22) Analysing these values we have an indication of the different behaviour of the thermal expansion between cast iron and steel that in the samples that have been examined is overall very low.

(23) In fact although the cast irons, in all the range that has been examined, have an expansion that is proportionally higher than the expansion of the steels, the differences in the average values lambda are always low in the change of the first decimal, with linear changes comprise between 1 and 2%. A higher interest is however raised by the composition of CAST IRON 80 the thermal expansion curve of which well approximate the curve of the samples made of steel in the whole range of temperature that has been examined.

(24) TABLE-US-00003 TABLE 3 average coefficients of thermal expansion of the samples made of cast iron and steel in different ranges of temperature .Math. 10.sup.6 .Math. 10.sup.6 .Math. 10.sup.6 corresponding 45 45 100 Sample Nickname ASME 245 C. 200 C. 200 C. 1 1-Cast SA-476-80 10.14 9.73 10.30 iron80 2 2-Cast 10.01 9.65 10.46 iron 60 3 3-Ac-NormB SA-516-70 10.05 9.60 10.21 4 4-Ac-NormA SA-516-70 9.95 9.50 10.10

(25) It has been also determined the behaviour of the volumetric expansion of Cast iron-80, that has shown good performances as linear expansion.

(26) The volume expansion coefficient of volume psi can be approximately computed as the triple of the linear one, that is:
Psi=3.Math.
And therefore the volumetric expansion of volume V0 of the material from temperature T1 to temperature T2 (with T2>T1) is:
VtV0=3V0.Math.(T2T1)
and the percentage variation:
V %=100(VtV0)/V0=3.Math.100(T2T1)

(27) TABLE-US-00004 TABLE 4 volumetric change in the samples of Table 1 with respect to temperature V % V % V % Corresponding 45 45 100 Sample nickname ASME 245 C. 200 C. 200 C. 1 1-Cast SA-476-80 0.6 0.45 0.31 iron80 3 3-Ac-NormB SA-516-70 0.6 0.45 0.30 4 4-Ac-NormA SA-516-70 0.59 0.45 0.30

(28) As we can see from the data shown in table 4, in all the ranges of temperature that have been examined the volumetric changes are very low and practically equal to the innovative Cast iron-80 according to the present invention and the steels that have been examined.

(29) In particular in the temperature range comprises between 100 and 200 C. the volumetric changes are only of 3%.

(30) The data above shown and discussed demonstrate that the cast iron, according to the present invention, shows a volumetric expansion vs. the temperature that is very similar to that of the steel. Therefore, a difference of the cast irons that are normally used in the state of the art for producing mixed Yankee cylinders made of steel and cast iron, the use of the cast iron, according to the invention, allows to avoid problems of stability and working, in the zones of contact between the parts made of steel and the parts made of cast iron, when the Yankee dryer cylinder is subjected to thermal stresses.

(31) 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.