Patent Application
20140068961
The present invention relates to a Yankee dryer made of steel for drying a pulp web, with a cylindrical steel shell that is connected to a first and second cylinder end cover at either end, where the cylinder end covers each have an opening at their centre, and to a process for manufacturing a Yankee dryer.
In production of paper webs, particularly for tissue, it is common practice to use so-called Yankee dryers in the drying process. Yankee dryers usually have a very large diameter. They are heated with steam and are difficult to manufacture because there are high demands to be met concerning internal pressures, leak tightness, and the large diameters.
Yankee dryers customary in the trade have the following dimensions, for example:
These cylinders are made predominantly of cast iron, however Yankee dryers made of steel are also already known from U.S. Pat. No. 4,196,689 and DE 2707923. Normally a Yankee dryer consists of a cylindrical shell surface that is closed off at the ends by cylinder end covers of various shapes. The two covers can be bolted or welded to the cylinder shell.
A Yankee dryer rotates in bearings by means of journals and contains a hollow shaft or axle through which the steam for heating can be fed to the cylinder and the waste steam and condensate can be removed.
WO2008/105005 discloses a Yankee dryer made of steel with a central shaft in several sections. This means that the two bearing journals of the Yankee dryer are attached to the end covers separately from a hollow shaft inside the dryer, using bolts for example (see
Conventional Yankee dryers, as illustrated in WO2008/105005, are manufactured in the following assembly sequence:
Due to the safety regulations for manufacture of pressure vessels, the end covers must be welded to the shell on both sides, i.e., on the inside and on the outside. The conventional assembly sequence has the disadvantage that the root weld between the second cover and the cylinder shell on the inside of the cylinder can only be made by entering the cylinder through the manhole in the end cover. This leads to more difficult working conditions for the welders on the one hand (lack of air, light, and space) and presents a much higher risk of accidents on the other hand.
The object of the invention is to provide a Yankee dryer made of steel that is easier to manufacture.
According to the present disclosure, the Yankee dryer has a one-piece central shaft with a first and a second connecting flange to join the central shaft to the end covers. The diameter of the first connecting flange is smaller than the diameter of the opening in the second end cover so that the central shaft can be pushed through this opening into the Yankee cylinder.
Due to the one-piece central shaft, the steel shell of the Yankee dryer can be joined first of all to the two end covers, preferably welded. Thus, the inside of the Yankee is easily accessible because the two openings in the covers are quite large (approx. 1500 mm), making it easy to perform welding work inside the Yankee.
The one-piece central shaft is not inserted into and joined to the cylinder until the end covers have been joined to the steel shell. In addition, handling is easier during assembly because there are fewer components.
Advantageously the diameter of the first connecting flange is larger than the opening in the first end cover. The first connecting flange is thus on the inside of the first end cover after the central shaft has been inserted and can be joined to it easily, by bolting for example.
It is also favorable if the diameter of the second connecting flange is larger than the opening in the second end cover because the second connecting flange then rests on the outside of the second end cover when the central shaft has been inserted and can be joined to it easily (bolted for example).
Thus, the central shaft has connecting flanges at both ends, but with different diameters. It is an advantage if the connecting flange at the operator-side end has a larger diameter than the connecting flange on the drive-side end. Due to this special design of the central shaft and with an appropriate screw joint between the central shaft and the end covers, a facility is also created for changing the central shaft in a non-destructive process. The current state of the art does not disclose any embodiments that make it possible to remove the shaft, if there is a leakage problem for example, without ruining the end covers and usually also the cylinder shell.
It is another objective of the invention to provide a simpler manufacturing process for a Yankee dryer.
The manufacturing process according to the present disclosure for a Yankee cylinder made of steel comprises the following steps:
Thus, the central shaft is not placed inside the cylinder until both end covers have been joined firmly to the cylinder shell. Welding work to join the shell to the covers need no longer be performed through the manhole.
As a practical matter, only the two finish-machined components—the central shaft and the cylinder with end covers—have to be assembled. This also reduces the risk of errors during assembly compared to dryers consisting of several components.
The connecting flanges of the central shaft can either be bolted or welded to the end covers. If they are bolted, this provides the option of making the central shaft easy to replace.
In the following, an embodiment is described with the reference to the accompanying drawing, wherein
In the manufacture of this Yankee dryer 11, the steel shell 12 is first joined to one of the two end covers 13. Then the connecting piece 17 (hollow shaft) is placed inside the cylinder and bolted to the end cover 13. After this the second end cover 13 is placed on the top end of the steel shell 12 and welded to the cylinder shell or bolted to the connecting piece 17. The steel shell 12 must be welded to the end covers 13 from the inside and the outside of the cylinders, thus the second end cover 13 has to be welded to the steel shell 12 through a manhole in the end cover. Subsequently the two bearing journals 15 are bolted to the respective end covers.
The one-piece (unitary) central shaft 7 is shown in
In a further assembly step, the pre-assembled, one-part central shaft 7 is placed inside the steel shell 2 through the opening 6 in the second end cover 4. The diameter of the first connecting flange 8 of the central shaft 7 must be smaller than the opening 6 here so that the central shaft 7 can be placed inside the cylinder.
In the present example,-the diameter of the first connecting flange 8 is slightly larger than the opening 5 in the first end cover 3. As a result, the connecting flange 8 rests on the axially inner side margin of the first end cover 3 after the central shaft 7 has been inserted (see
Similarly, the diameter of the second connecting flange 9 is slightly larger than the opening 6 in the second end cover 4. As a result, the connecting flange 9 rests on the axially outer side margin of the end cover 4 after the central shaft 7 has been placed inside the cylinder and can therefore be bolted to it without any difficulty. This special design also allows the central shaft 7 to be removed easily. The pipes 22 are not mounted until after the central shaft 7 has been installed.
The same principles of construction and manufacturing method can be applied even if the openings in the covers are not circular, so long as the shapes of the flanges have the described relation for the areas of the openings.
| Number | Date | Country | Kind |
|---|---|---|---|
| A 763/2010 | May 2010 | AT | national |
