There are two primary basic constructions of godets heated by means of steam for drawing units, for example. One construction is the hollow-space godet wherein the superheated steam is fed into the inner space thereof without any guidance. During the cooling of the steam, a condensate is formed which, with the godet being rotated, is distributed as a liquid film over the entire inner surface of the godet. Since the water prevents the further heating of the godet, and even cools the wall surface, a continuous discharge possibility must be provided. For discharge purposes, a kind of siphon pipe is arranged; several of these siphon pipes extend, in most cases, distributed over the length of the roll up to the close proximity of the inner wall surface of the godet, and they do not rotate together with the godet. The suction openings of the pipes are arranged at the lower apex of the godet and discharge the condensate even if the godet is at a standstill. If the thickness of the film reaches the mouths of the pipes, the condensate is removed up to a residual minimum by a pressure differential under the effect of the steam which is fed to the unit. Thus, it is quite impossible to remove the condensate entirely by means of this construction; especially the condensate cannot be discharged laterally or between the individual siphon pipes. Furthermore, a large amount of steam escapes also by way of the condensate discharge pipe and thus is lost for heating the godet. An increase in steam consumption is the consequence thereof. Another disadvantage of this hollow-space godet is the low flow velocity of the steam so that, in any event, a uniform heating of the wall surface to a high temperature is impossible.
In addition, to the hollow-space godet, the more advantageous double-walled godet is conventional, consisting of an outer shell and an inner shell, between which a free annular space is provided for receiving the heating medium. In parallel to the godet axis, bars, partitions, or the like are arranged in the free annular space, subdividing the annular space into several parallel-disposed flow channels; preferably, respectively two adjacent flow channels are in communication with each other at one end. At the other end, the heating medium is then fed to one of these longitudinal chambers and is removed from the other longitudinal chamber. This results in a uniform temperature distribution over the wall surface of the godet. The flow velocity of the steam through the channels is high, so that a high godet wall temperature can also be attained.
A disadvantage in this godet construction is that the condensate, which is formed in all cases, can be forced out or removed by suction essentially only through the action of the subsequently fed steam along its way through the adjacent flow channels, and must then be conducted to the central discharge conduit by way of bores in the end wall of the roll associated with each longitudinal chamber and being of a smaller cross section. Under unfavorable conditions during operation, there is thus the danger that temporarily differing resistances are built up in the individual flow channels, which impede the flow of the steam in the channels, and this, in turn, can interfere with the homogeneity of the temperature distribution. Besides, there is the further disadvantage that, when the godet is at a standstill, the condensate, which has formed, accumulates in the lower half of the annular chamber and fills the latter to a maximum. The condensate can be discharged only after the godet has once again commenced its operation.
The ideal, constituting a genuine combination of the favorable features of the hollow-space godet, namely the arrangement of a stationary condensate discharge pipe, with the advantages of a double-walled godet, namely a uniform temperature distribution and a high steam flow velocity, has not as yet been attainable, because the arrangement of a stationary condensate discharge pipe is impossible if the free annular space between the two shells is to be subdivided into individual flow channels.
This invention is based on the problem of maintaining the idea of combining the conventional double-walled godet, if at all possible, with flow channels and a single heating medium discharge pipe, and of finding a solution for this combination.
Starting with the roll as described above, the simple solution, which has so long been searched for, resides in that a single discharge conduit is provided in the roll for removing the heating medium flowing through all flow channels. Preferably, as in the hollow-space godet, the discharge conduit is a pipe stationary with respect to the roll, the suction opening of this pipe being arranged in the immediate vicinity of the outer roll shell or wall. In this connection, the suction opening of the discharge conduit should be arranged vertically below the roll axis, so that even if the roll is at a standstill the entire amount of the thus-formed condensate can be continuously removed.
It would also be advantageous to provide a godet wherein the condensate can be continuously and completely removed without a stationary condensate discharge pipe, while the godet is rotating and also while the godet is at a standstill, namely without the necessity of feeding an increased amount of steam.
In a development of the basic idea of the present invention, this object is attained by providing that the operative heating medium discharge conduit consists of a single, rotating condensate conduit which connects the annular space with a central backflow line. The basic idea, therefore, resides in arranging only a single conduit for the removal of the condensate -- just as the siphon pipe in case of the hollow-space godet-- but this conduit is now to rotate together with the roll and is to collect, during its travel, the thus-formed condensate. In a preferred embodiment, there is not only a single condensate conduit, but a plurality of bores arranged in a stellate pattern in the bottom of the roll, among which, however, only the respectively operative condensate conduit is in communication with the central backflow line. The respectively operative conduit should always be arranged on the underside of the roll, so that even with the roll at a standstill the condensate formed over the entire wall surface can be removed without difficulties.
The advance in the art provided by the present invention is clearly apparent. The aforementioned advantages of the double-walled godet have been retained, namely a good temperature distribution at a high steam flow velocity in the free annular space, namely unchanged over the entire length of the roll. The removal of the condensate, however, has now been made independent of the velocity of the subsequently fed steam; rather, the condensate will collect in the individual heating medium discharge conduits arranged in a stellate pattern while the conduits are rotating, and the condensate will be discharged only when the individual conduit is connected to the central backflow line. Thus, the condensate is forced out of each discharge conduit in a short period of time by the steam pressure and the thus-operative condensate conduit is immediately subsequently closed off again, so that steam still unused for heating purposes cannot escape through the conduit which has been cleared of condensate. Accordingly, in addition to ensuring a flawless temperature distribution, a minor steam consumption is likewise attained.
A very essential further advantage resides in the possibility of being able to discharge the condensate basically entirely during the operation of the roll, i.e., during rotation, as well as during its standstill. If the operative condensate conduit is always provided at the bottom, by arranging only at that location a constant communication with the central heating medium backflow line, the condensate forming along the entire wall or shell surface will flow downwardly into the zone of the operative condensate conduit and will be removed continuously through the action of the pressure differential of the steam. Thus, the inner wall of the roll is always free of condensate, namely also free of a condensate film, so that the temperature distribution is always constant.
In a further development of this idea of constructing an internally heated roll, the present invention furthermore provides that a sealing cap or head is arranged for concomitant rotation at the end of the central backflow line in the region of the plurality of rotating discharge conduits radially disposed in the bottom of the roll; this sealing cap has only on the underside a connecting line which connects the discharge conduit respectively located at the bottom with the central backflow line. This sealing cap thus represents the control element for the discharge of the condensate at the desired location in the roll. By means of this sealing cap, all other backflow lines except for the operative condensate line are sealed off, but one after the other is opened for removing the thus-collected condensate.
The connecting line in the sealing cap must have a cross section ensuring the uninterrupted discharge of the condensate, even in those cases when the opening of a heating medium discharge conduit is covered only partially by the associated opening of the connecting line in the sealing cap. For this reason, the opening of the connecting line in the sealing cap should in any event be larger than the cross section of a discharge conduit. It is most advantageous to fashion the cross section of the opening of the connecting line approximately equally large as the cross section of a discharge conduit plus the area between two adjacent heating medium discharge conduits. In such a case, a discharge conduit will definitely be always in communication with the connecting line and thus with the central backflow line. The most unfavorable case occurs if a discharge conduit is not as yet entirely sealed off by the sealing cap, while the subsequent discharge conduit is already in communication with the opening in the sealing cap. However, with such a size of the opening of the connecting line, a removal of the condensate through the central backflow line is ensured at any position of the roll selectively to the stationary sealing cap.
In order to be able to discharge the condensate formed in the unit in its entirety in the zone of each heating medium discharge conduit, it is advantageous to make the diameter of the free annular space in the zone of the discharge conduits larger than the diameter in the zone of the remaining wall surface. Thus, an annular groove is milled into the shell of the roll in the region of the discharge conduits; this groove will be entered by the condensate and the latter will be completely removed by suction therefrom through the discharge conduits, which have a greater length. A still stronger siphon is produced if the annular space of the roll is conducted by way of a siphon-like elbow in the shell of the roll with the respective discharge conduit. Thereby, the steam always exerts pressure on the surface of the condensate collected at the end of the roll. A consequence of this construction is a total removal of the water without any residue.
The suction opening of the heating medium discharge conduit can be arranged on the flange side of the roll if the roll is mounted in an overhung position. However, it is more advantageous to provide the suction opening of the heating medium discharge conduit on the free end face of the roll. For this purpose, a wall is advantageously arranged at the end of the roll, extending at right angles through the roll and separating the flow channels, i.e., the substantially active portion of the roll, from a heating medium discharge chamber. The heating medium discharge conduit in this discharge chamber is then to penetrate this wall to be able to remove the taken-in condensate from the godet though a central heating medium discharge line.
A particular advantage of the construction of this invention is the possibility of being able to form flow channels in the free anular space between the two roll shells. This can be accomplished, for example, by providing the heating medium feed lines for a plurality of flow channels along the roll shell in the zones of this wall penetrated by the heating medium discharge line. One embodiment could reside in fashioning the individual feed lines for the flow channels as radial bores in the wall. Starting at the openings of the heating medium feed lines, a flow channel is extended in each case along the godet shell surface up to the flange side of the godet. From there, a connection must make it possible for the heating medium to continue its flow in parallel to the first-mentioned flow channels in so-called backflow channels. The backflow channels then terminate freely in the heating medium discharge chamber. Thus, in spite of the flow channels present in this arrangement, the thus-formed condensate will always collect in the heating medium discharge chamber, no matter whether the roll is rotating or at a standstill. Also, the conveyance of the condensate does not require an oversupply of steam, since the cross sections for the discharge of the condensate can be made of a very large size.
The above-defined roll construction is not only suitable for steam as the heating medium, but also, without alterations, for liquid heating media.