US2946476A - Sealing device - Google Patents

Description

H. J. Ross 2,946,476

SEALING DEVICE 2 Sheets-Sheet 1 July 26, 1960 Filed Aug. 20, 1956 Fm. l..

July 26, 1960 H. J. Ross 2,946,476

SEALING DEVICE Filed Aug. 20, 1956 2 sheets-sheet 2 United States Patent C) y2,346,476 snALrNo DEVICE Herbert John Ross, Runcorn, England, assigner to Imperial Chemical Industries Limited, London, England,

a corporation of Great Britain Filed Aug. 2i), 1956, Ser. No. 604,873

Claims priority, application Great Britain Aug. 29, 1955 4 Claims. (Cl. 2ML-45) This invention relates to a sealing device for vessels or chambers through which materials are continuously passed in sheet form and in which they are subjected to treatments that involve or give rise to evaporation of volatile, substantially water-immiscible, organic solvents. Among such processes are, for example, solvent degreasing of strip metal and of textile materials.

A particular instance is the process and apparatus for dewaxing and degreasing of textile materials described in copending British applications Nos. 1,600/53 (Serial No. 747,481), 22,852/53 (Serial No. 749,705) and 13,149/ 55 which process involves treatment of the textiles with a volatile substantially water-immiscible organic solvent, for example, trichloroethylene or perchloroiethylene, which is subsequently evaporated and recovered. 'In the preferred form of this process the cloth is passed at open width through a series of baths of the solvent 2,9%,476 Patented lluly 26, 1960 lighter material. iAs it is preferable to constructjthis envelope of stainless steel, it is for economicV reasons so arranged in a common containing vessel or chamber that solvent vapour condensed on cooling devices in the upper part of the chamber is returned to the last solvent bath and thence overflows successively into the earlie'r baths of the series, thus moving through the chamber counter-current to the cloth. The cloth, having dipped successively into each of the baths of the series, passe's out of this chamber and into a second chamber where it is passed through water held at such a temperature as causes vaporization of the solvent which again lis recovered and returned to the system.

Each of these treatment vessels thus comprises one or more baths containing the appropriate liquid, a`series of rollers, guides and tensioning devices to cause the cloth to dip into the bath or baths and an external envelope, the primary function of which is to contain the vapours given off from the treatment liquids and enable them to be recovered. Preferably also the envelope carries seals on the orifices by which the cloth enters and leaves to assist in containing these vapours, such as shown and described in my co-pending application Serial No.'489,l89, iled February 18, 1955, which was issued April 22, 1958, as U.S. Patent 2,831,332. Frequently also the containing envelope is made to serve as a structural support for the guides, rollers and tensioning devices that determine the path of the cloth but we have rfound that in some circumstances this may cause considerable inconvenience.

We have found that it is advantageous, in both these chambers, if the framework to which the rollers, guides and tensioning devices are iixed is supported entirely from above. This permits the easy removal of the framework and the rollers and other devices supported thereon from the chamber. Thus mechanical lining up, threading of the cloth, adjustment and cleaning may all be done outside the chamber and in the event of breakage of the cloth, jointing and rethreading can take place externally, thus saving the time that would otherwise be required to free the chamber of solvent so that entry could safely be made to carry out this work. Another advantage, which accrues if the conveying structure is supported from above, is that the envelope may be constructed of desirable that-the minimum amount of such steel should be used. If therefore the conveying structure for the cloth is supported externally and not carried on the envelope,` the latter, having no external load to support may be constructed of comparatively thin sheet stamless steel. Conveniently the structural members that support the cloth-conveying mechanism also support the cover of the chamber which, in this case, is preferably entirely separate from the base and side walls. Bolting or otherwise clamping the cover to the side walls is in these circumstances attended by various inconveniences. For instance, unless the positioning is very accurate distortion or undue straining of portions of the envelope can very readily occur and in any case dismantling for adjustment or maintenance is laborious and time-consuming. In practice it is preferable to make the walls and cover entirely independent andk to provide a seal of some kind to close the gap. it is the purpose of this invention to provide a liquid seal adapted to serve this and analogous purposes.

Such a seal is provided by arranging that a septum constituted by the down-turned edge of the cover of the treatment chamber, or by a skirt or collar depending from the cover, dips into a body of liquid contained in a box-like or channel-shaped vessel attached to and conveniently made integral with the side-walls of the chamber, preferably near the upper extremities thereof, this liquid consisting of two phases, namely Water and the solvent the vapour of which is` to be contained, these phases being maintained in hydrostatic balance by the provision of suitably disposed overows. When the pressure in the treatment chamber is substantially atmospheric, the relative heights of these overflows above the water-solvent interface are, of course, inversely proportional to the relative densities of the two liquids; the case Where the treatment chamber works under superatmospheric pressure is more fully discussed hereinafter.

One embodiment of the invention, appropriate to a case where the solvent is denser than water, is illustrated in Figure 1 of the accompanying drawing. This shows a vertical section through a part of the annular seal wherein 1 represents a portion of one of the structural members that support the cloth-conveying mechanism, which member also supports the cover 2 of the chamber, the down-turned edge or rim of the cover forming the septum 3. The box-like or channel-shaped vessel dened by the walls 4 and vthe base 5 is carried on the upper extremity of the side-wall 6 of the treatment charnber, a small gap 7 being left between the side-wall 6 and the cover 2 of the chamber. The overows for lwater and for solvent are shown respectively as 8 and 9. Provided that in the case where the solvent is denser than water (as, for example, with trichloroethylene) the overdiow 8 -is at a higher level than overiiow 9 and in the case where the solvent is less dense than water' (as, for ex` ample, with White spirit) overow 8 is'lower than overiiow 9, the system is self-adjusting. if, however, the mean working pressure in the treatment Achamber is Substantiallygreater than atmospheric,1then overow Y up ,where water from the feed passesV away by overflow Spend' solvent, or in many cases amixture of solvent with a little water,passes away'by overflow 9. The

mixture is conveniently passed to a water-separator or solvent recoveryrunit and eventually returned to the system.

The above embodiment of the invention may be used on either the chamber where the clothis treated with solvent, or the chamber where entrained solvent is removed by vaporising the solvent from the cloth. In the latter case the mixture of solvent vapour and water vapour condensing in the seal has a much higher water content than the trace which is present in solvent vapour coming from a dewaxing or degreasing chamber. In the case where the solvent is trichloroethylene, for instance, the ratio of water to solvent is frequently vas much as 1 part by weight of water to each 14 parts of trichloroethylene and in some circumstances has been as high as 1 part of water to 3 parts of trichloroethylene. In such a case a further embodiment of the invention may be preferred.

This form (illustrated in Figure 2) enables the seal to function also as a yseparator and so allows the overow of solvent from the seal to be obtained substantially free of water. it also enables both overows to be placed on the same side of the septum with the result that the device can more readily accommodate major pressure changes than can the embodiment described above. In Figure 2, wherein like parts are numbered as in Figure l, i represents a portion of one of the structural members that support the cloth conveying mechanism, which member also supports the cover 2 of the chamber, the down turned edge or rim of the cover forming the septum 3. The box-like or channel-shaped vessel defined by the walls 4 and the base 5 is carried on the upper extremity of the side wall 6 of the treatment chamber, a small gap 7 being left between the side-wall 6 and the cover 2 of the chamber. The overflows for water and for solvent are shown respectively as 8 and 9, both being placed, in this form of the invention, on theY same side of the septum 3. This form oi the invention, as will be apparent from the figure, is only applicable to the case where the solvent is denser than water, hence the overliow `S is placed at a higher level than the overilow 9.

The relative positions of overflows 8 and 9 determine the position of the water-solvent interface since the watercolumn beyond the septum must balance the column of solvent between vthe interface and overllow 9. It the system is to work under a substantial positive mean worm pressure then the water level on the inner side of the.- septum will tall so that the sum of the height of this column and the positive pressure in the chamber balances the Water column on the outer side of the septum. Therefore the seal must be so constructed that the difference in level between the water overflow 8 and the lower extremity of the septum is somewhat greater than the highest pressure that is likely to be builtrup in the treatment chamber.

In operation a relatively small amount of the vapour of the solvent or of mixed vapours of solvent and Water penetrate through the gap 7 and condenses, separating into two layers. Provided a suiciency of water is maintained in the seal, preferably by means of continuous slow feed (not shown) to the outer portion of the channel, the equilibrium position is built up, where water passes away from the overow 8, and the solvent denser than water sinks to the bottom of the seal and is displaced through the outlet 9. There is thus no need to provide a solvent recovery unit as the solvent can be passed back directly into the system. Pipe 10 is a vent pipe to prevent siphoning of liquid ifrom the seal.

In the ease where a seal according to the present invention is provided on the chamber where solvent is vaporised from the cloth, the vapours entering the seal may in some cases be at a suliciently high temperature to cause boiling at the solvent-water interface unless sulicient cooling is provided. This is suitably done by adjustment of the water fed to the outer portion of the channel.

Figures 1 and 2 show the seal tted to the exterior of the treatment chamber. lf desired, of course, the body of the seal can be housed within the chamber.

What I claim is:

1. In an apparatus for the continuous treatment of materials in sheet form with volatile substantially waterimmiscible, organic solvents, means including a cover and independent side wall means defining a chamber within which the materials are subjected to treatments that give rise to evaporation of the solvents, and liquid seal means between said cover and said independent side Wall means for preventing escape of the solvent vapors, said seal means comprising an annular channel-shaped vessel carried by said side wall means and having liquid therein, and an annular skirt on said cover extending downwardly into said vessel, said liquid including water and a water-immiscible solvent, iirst overflow means directly communicating with said water, and second overllow means directly communicating with said solvent.

2. Apparatus as defined in claim l wherein said first and second overiiow means are on opposite sides of said skirt, said water and solvent defining a solvent-water interface disposed on one side of said skirt above the lower end thereof, the relative heights of the rst and second overow means being inversely proportional to the relal-tive densities of the water and solvent.

3. Apparatus as dened in claim 1 wherein said solvent is denser than water and defines with said Water a References Cited in the file of this patent UNITED STATES PATENTS 1,209,465 Matter Dec. 19, 1916 1,874,742 Harnsberger Aug. 30, 1932 2,029,985 Clark Feb. 4, 1936 2,170,579 Sperry Aug. 22, 1939

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