Heating – Advancing structure flexing – looping or coiling sheet – web...
Reexamination Certificate
2001-02-14
2002-08-13
Lu, Jiping (Department: 3749)
Heating
Advancing structure flexing, looping or coiling sheet, web...
C432S008000, C034S641000
Reexamination Certificate
active
06431858
ABSTRACT:
PRIORITY CLAIM
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 100 07 004.3, filed on Feb. 16, 2000, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to a method for stably guiding and supporting a web of goods, and preferably a non-air-permeable or air-tight material web such as a thermoplastic web that can be stretched to form a film, between the inlet or entrance gap and the outlet or exit gap of a heat treating apparatus. The invention further relates to an arrangement that forms the entrance and exit gaps of a heat treating apparatus, so as to reduce air losses therethrough.
BACKGROUND INFORMATION
Various thermal treatment processes are known, in which a web of goods, such as a thermoplastic web that may be expanded or stretched to form a thermoplastic film, is guided through a heat treating apparatus. The-web enters the apparatus through an inlet or entrance gap, and leaves the apparatus through an outlet or exit gap. The inflow of cold outside air and the outflow of heated process air through the entrance gap and the exit gap cause undesirable energy losses from the apparatus and from the heat treating process. Additional energy must be supplied to the apparatus and the process in order to make up for the lost heat energy.
The extent of this energy loss is essentially dependent on the vertical size of the entrance gap and the exit gap, and the transport velocity with which the material web travels through the heat treating apparatus. The energy losses are further dependent on the prevailing pressure difference between the interior space of the heat treating apparatus and the atmospheric environment outside of the heat treating apparatus. In other words, the positive pressure that is typically developed inside the heat treating apparatus will constantly seek a compensating path to the lower atmospheric pressure outside of the heat treating apparatus, so that hot process air will constantly flow out of the apparatus through the entrance and exit gaps. It is further understandable that the energy losses increase with the size of the entrance and exit gaps, as well as with an increasing web transport speed. The crosswise width of the entrance and exit gaps is determined by the width of the material web to be processed or to be achieved, so that it is conceptually not possible to reduce or limit this width of the gaps, and the present specification will not further discuss the energy losses resulting therefrom.
The height or the vertical size of the entrance and exit gaps can be influenced or adjusted, and thereby the energy losses may be reduced, as is known from a variety of prior art solutions in this context. For example, it is known to carry out a corresponding control or regulation of the pressure within the heat treating apparatus. As an example, by maintaining a slight under-pressure or negative pressure inside the heat treating apparatus relative to its surrounding environment, energy losses arising from the above mentioned static pressure difference can be avoided. In such a case, however, it is disadvantageous that the surrounding atmospheric air, which is much colder than the temperature of the hot process air within the apparatus, is constantly sucked into the heat treating apparatus through the entrance and exit gaps due to the reduced pressure inside the apparatus.
The quantity of air that is sucked into the apparatus.must then correspondingly be removed from the apparatus in a precisely controlled manner, in order to maintain the intended reduced or negative pressure level within the heat treating apparatus. Simultaneously, additional energy must be introduced, in order to heat the in-flowing, relatively cold surrounding atmospheric air to a temperature level that is sufficiently high so as not to interfere with the heat treating process being carried out within the heat treating apparatus. At the typical high temperatures, for example approximately 240° C. for treating a polyester film, the required continuous supply of additional energy can lead to a considerable energy consumption and increased cost of the process.
The dynamic energy losses that arise due to the quantities of air being carried or pulled along with the web of goods out of the heat treating apparatus at the transport speed of the web cannot be avoided by the above described measure of establishing a reduced or negative pressure within the treating chamber. Instead, other means are necessary to avoid or reduce this type of as energy loss. One possibility is to make the entrance and exit gaps as narrow as possible. To achieve this, for example, partitions or bulkhead members are arranged above and below the material web across the entire width of the heat treating apparatus, along the upper and lower portions of the entrance and exit gaps. Such partition or bulkhead members can be embodied as hanging metal plates or flap doors with a great variety of configurations. In any event, these partition or bulkhead members reduce the vertical height of the open gap.
Such measures are only effective, however, as long as the material web remains stably supported on the intended web transport plane. In this regard, very wide webs and particularly such webs of heavy, limp or slack materials, will hang and bow downward. On the other hand, webs of very thin or delicate materials, which cannot be adequately tensioned, will flutter or billow up and thus away from the intended web transport plane. Webs of material with such characteristics thus come into direct contact with the above described partition or bulkhead members along the entrance or exit gaps. This direct physical contact can cause damage or even tearing of the material web. Thereupon, such a damaged or torn material web leads to a stop or interruption of the heat treating process, which in turn triggers various undesired results, and particularly a slow down or loss of production output, and increased costs.
Another possibility of reducing energy losses is the use of an air curtain or air sluice. In this context, a vigorous air stream is directed in the form of an air curtain substantially perpendicularly against the material web, above and below the material web at the entrance gap and the outlet gap, in order to thereby form a barrier that is intended to block the inflow or outflow of air past or through this air curtain. A disadvantage of such air curtains is that the additional quantities of air that are used for forming the blocking air curtains must again be removed from the heat treating apparatus, insofar as they are sucked into the apparatus. Also, the air curtains directed substantially perpendicularly against the material web do not support the web, but instead are rather difficult to control in order to avoid a billowing or fluttering of the material web.
For the above reasons, there must be a sufficiently large spacing distance between the material web and the nozzles that are necessary for establishing the air curtain. A physical contact between the material web and the nozzles must absolutely be avoided. This in turn requires a sufficiently high air flow velocity and a sufficiently high air flow volume in order to form an effective air curtain spanning this relatively large spacing distance and still achieving an effective blocking or separation of an airflow through the respective gap. As a result, disadvantageous turbulences arise directly in or along the web plane, which can lead to fluttering or billowing of the material web. Such an unsteady travel of the material web is especially disadvantageous for the process reliability when rather sensitive material webs are being treated.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the invention to provide appropriate measures at the entrance and exit gaps of a material web heat treating apparatus, to minimize the loss of energy in the form of hot air out through the entrance and exit gaps, while essentially completely avoiding physical contact bet
Fasse W. F.
Fasse W. G.
Lindauer Dornier Gesellschaft mbH
Lu Jiping
LandOfFree
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