Cascade dam

Abstract

Claims

Dec. 29, 1970 J, PH|| L|P$ 3,550,4-0? CASCADE DAM Filed March 6, 1969 INVENTOR. JEkRY R. PHILLIPS flwf w ATTORNEY United States Patent O 3,550,407 CASCADE DAM Jerry R. Phillips, Huntsville, Ala., assignor to Monsanto Company, St. Louis, Mo., a corporation of Delaware Filed Mar. 6, 1969, Ser. No. 804,939 Int. Cl. B05c 8/04 US. Cl. 68-181 3 Claims ABSTRACT OF THE DISCLOSURE In the Wet spinning process for washing tow it has been discovered that a more effective removal of solvent can be accomplished by positioning a darn within the cascade whereby residual solvent is effectively stripped from the tow and the solvent so stripped is confined to an area before the dam resulting in a solvent-free area after the dam where the tow is passed before removal from the cascade. BACKGROUND OF THE INVENTION This invention relates to a practical and inexpensive apparatus for removing solvent from a filamentary tow with more solvent control during the rinsing process. More particularly, this invention relates to an apparatus for effectively stripping solvent from the tow and preventing the stripped solvent from advancing with the tow. In wet spinning, a polymer solution or dope is extruded through a spinnerette directly into a coagulating bath. The speed of spinning is regulated to maintain certain speeds and the composition and temperature of the coagulating bath is carefully regulated in order to set up the freshly-spun filaments and remove the proper amount of solvent therefrom. The filaments that are formed as the coagulating fluid comes in contact with the dopes are collected, the aggregation of which comprises the tow, and then drawn up a cascade or trough by any suitable means. Generally, coagulating fluid comprises water and an organic solvent, one that is substantially soluble in water and is the same or substantially similar to the solvent employed in the dope. In the rinsing process, water brought up to a given temperature is allowed to flow down the cascade where it comes in contact with the advancing tow whereupon solvent is removed from the tow. A current problem in the washing or rinsing process of filamentary tows is that the solvent in the fiber is not reduced to an acceptable level. The industry has experienced difficulty in removing solvent since the tow as it travels up the cascade carries a boundary layer around each filament that is rich in solvent. It is found that this solvent-rich layer impedes the rinsing process for the hot water flowing down the cascade cannot effectively reach the freshlyspun filaments. The prior art shows a number of stripper devices that help remove or strip boundary layers from the tow. Although the course of the stripped solvent is dictated by the movement of the wash water toward the bottom of the cascade, there are a number of eddies and countercurrents set in motion which result in solvent dissipation toward the top of the cascade, i.e., along the direction of tow movement. Thus, the dissipation of the solvent and the ineffective rinsing of the tow result in a number of problems in the subsequent handling and cut ting thereof. In short, the manufacture of filamentary tow via wet spinning requires that the solvent be effectively removed since tows having high residual solvent exhibit poor textile processing characteristics. A number of immersion devices used individually or in tandem have been employed such as guide rods, rotatable cylinders, squeezers, stripper bars, and the like, to assure submersion and removal of solvent from freshly coagulated filamentary material. Nevertheless, the efficiency of such devices in conjunction with washing cascades commonly employed in the art leave much to be desired. SUMMARY OF THE INVENTION This invention provides an apparatus for effectively stripping solvent from filamentary tow and confining the stripped solvent from advancing therewith. Briefly, in accordance with this invention, in. the wet spinning process for washing tow in a cascade having a fluid stream issuing downward from the upper portion thereof and counter to the tow, an apparatus for stripping solvent from the tow and preventing any dissipation of the stripped solvent from advancing beyond said apparatus and toward said upper portion comprising a stationary dam transversing the width of the cascade, the base of said dam being in contact with the floor of the cascade, and the height of said dam being at least the height of the fluid stream whereby the tow is impinged against the dam as it advances thereover and the tow is subsequently immerged in the upper portion of said cascade upon its advance therefrom. The cascade dam comprises a wall which fully extends transversely of the interior of the cascade and from the floor thereof to at least the level of the wash water and defined at its upper level by a straight and leading edge over which the tow is drawn and defined at its topmost side of said edge with a flat portion extending substantially parallel to the cascade upon which the tow is sup ported in its advance thereover. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a sectional view of the apparatus set within a cascade; FIG. 2 illustrates a view of the cascade darn. DESCRIPTION OF THE. PREFERRED EMBODIMENTS With reference to the drawings wherein my apparatus is shown in FIG. 2, and comprises a cascade dam 18 having a leading edge 10 formed by a top portion 16 and a dam wall 11. Mounted on the sides of the dam 18 are fastening or supporting means which comprises plates 14 with holes 15. In FIG. 1, the darn 18 is shown in position within cascade 19. In general, the dam 18 is placed from approximately to of the distance of the cascade from the top thereof. The base of the dam is allowed to rest flatly upon the cascade floor 12 and the dam is secured to the cascade walls 13. Depressor bar 22 may be employed to submerge tow 20. In operation, the tow 20 is advanced up the cascade 19 while being submerged in the descending wash water 21 until it is impinged against the leading edge 10 of the darn 18 and drawn over the top portion 16 thereof. The wash water 21 flows counter to the tow 20 and the solvent layer surrounding the tow is stripped by the leading edge 10 whereby the solvent so-stripped is confined to the area A before the darn. After the tow 20 is drawn over the darn, it is re-submerged in a solvent-free area B prior to leaving the cascade. The cascade dam presents an arrangement not heretofore known or appreciated in that the solvent is stripped and restricted in any further travel toward the top of the cascade. Thus, the dams cause the tow to be stripped and do not allow solvent-rich water to be carried past it to the upper portion of the cascade. As a consequence of the use of the cascade dam, the tow is washed in a solventfree wash water just prior to leaving the cascade and results in a tow with substantially improved handling and cutting characteristics. Also, by the use of such a dam, there is a reduction of solvent loss in the overall processing of filaments. The height of the cascade dam should at least extend to the level of the wash water; preferably the dam height should be from 5 to 20 mm. above the level of the wash Water. Nonabrasive and corrosion-resistant materials should be used in the cascade dam. Satisfactory materials for forming the dam are glass, glazed ceramic material, stainless steel, etc. Although the general shape shown in the drawing is that of a rectangular solid, it is understood that other shapes are also adequate so long as a dam structure is positioned within the cascade and the top portion of said dam is smooth and presents no interfering surfaces to the tow that would cause filament breakage. I claim: 1. In the wet spinning process for washing tow in a cascade having a fluid stream issuing downward from an upper portion of the cascade and counter to the tow, an apparatus for stripping solvent from the tow and preventing the stripped solvent from advancing beyond said apparatus toward said upper portion comprising a darn transversing the width of the cascade, the base of said darn being in contact with the floor of the cascade, and the height of said dam being at least the height of the fluid stream, whereby the tow is impinged against the dam as it advances thereover and the tow is subsequently resubmerged in the upper portion of said cascade upon its advance therefrom. 2. The apparatus as recited in claim 1, including the following support means to connect and secure the same within the cascade. 3. The apparatus as recited in claim 1 wherein the height of the dam is from about 5 to 20 mm. above the height of the fluid stream within said cascade. References Cited UNITED STATES PATENTS 3,166,924 1/1965 Marsello 68-181X 3,230,747 1/1966 Leonard et al. 68-18lX FOREIGN PATENTS 661,941 4/1963 Canada 68-181 WILLIAM I. PRICE, Primary Examiner

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