US2056982A - Extrusion device - Google Patents

Description

Patented Oct. 13, 1936 UNITED STATES PATENT OFFICE EXTRUSION DEVICE ration of Delaware No Drawing. Application January 6, 1934, Serial No. 705,570

5 Claims. (Cl. 18-57) This invention relates to a mouthpiece for the extrusion of liquids into corrosive baths. It also relates to an improvement in the manufacture of non-fibrous cellulosic pellicles. The invention 5 also relates to an alloy having high resistance to corrosion. The invention will be described as embodied in a hopper lip for use in the extrusion of viscose into a setting bath, but this particular description does not limit the invention.

10 In one method of manufacturing regenerated cellulose sheeting, a cellulose xanthate solution (viscose) is forced beneath the surface of a coagulating bath through an elongated mouthpiece. From this bath it is led in the form of a thin, continuous pellicle through several subsequent operations including purification, washing, finishing, and drying, whence it is finally obtained in the form of a glass-clear, smooth, dense, nonporous, flexible pellicle of regenerated cellulose. 20 It is desirable that this regenerated cellulose pellicle shall have uniform thickness and appearance, a desideratum which can be accomplished only if the opening in the extrusion mouthpiece is of precisely uniform width and 25 can maintain that width over long periods by virtue of the extrusion mouthpiece resisting corrosion and by its not collecting particles from the viscose or coagulating bath. If the lips of the mouthpiece become roughened even minute- 30 1y by the adherence of particles or by corrosion of the lip surface, a streaked, inferior pellicle will be produced and repairs to the mouthpiece will have to be made. The mouthpiece is usually formed by a pair of parallel metal bars, usual- 3 1y called hopper lips, which are attached to the hopper adjustably to regulate the thickness of the formed sheet. The removal and repair of a mouthpiece or lip stop the operation of an expensive machine, require time and labor for correction of the defects, and in these and in other ways increase the cost of production. In addition, the discovery of such defects is usually delayed and a substantial amount of defective sheeting may be produced prior to such discovery. 45 The hopper lips are provided with a high polish in order that they may be perfectly smooth and free from any irregularities which may cause streaks or blemishes in the pellicle, but the viscose contains about 6% sodium hydroxide in 5 the ordinary case, the usual coagulating bath contains approximately 12% of sulfuric acid, and these solutions meet on the'hopper lip, tending to corrode it, impairing its smoothness and inducing streaking of the cast pellicle. The corroding effect of these solutions acting simul- 5 taneously on the hopper lip is so great that hopper lips constructed of materials of the prior art have been incapable of long use, five or six weeks being considered good performance and a five or six hours performance being by no means an unusual occurrence.

Heretofore, substantially pure nickel has been used for the fabrication of hopper lips. This material is not Without defects, however, since the nickel hopper lips corrode quickly, they pick up particles from the solution, and require frequent honing and grinding.

It is an object of this invention to prepare extruded cellulosic structures substantially free from streaks and to provide means for accomplishing this end. It is also an object of this invention to provide a device for the extrusion of an aqueous cellulosic solution such as viscose into a coagulating bath, the said device having high resistance to corrosion, 10w tendency to collectadhering particles, and long operating life. It is more specifically an object of the invention to provide a mouthpiece of high corrosion resistance capable of consistently casting substantially streak free films of regenerated cellulose from viscose. Other objects of the invention will be'in part apparent and in part hereinafter set forth.

The objects of the invention are accomplished by the use as an extrusion mouthpiece of an alloy of particular composition and metallurgical characteristics.

If the full benefits of the invention are to be realized, the alloy should contain particular metals in percentages within definite bounds and should have particular crystalline structure. The first desideratum is that the alloy should contain nickel, chromium, copper, molybdenum, tungsten, manganese, silicon, iron, and carbon. Generally speaking, each of the said elements should be present in an amount preferably within the limits indicated in the following table, but, of course, it is to be understood by one skilled in the art that the mutual relationship of the several constituents will require appropriate balancing and this is indicated specifically in the example set forth:'

alloys which come within the scope of the preceding table: 7 J

Example I Exairliple Exifiple The proportions given in the above two tables are parts by Weight.

p The alloy should also have certain metallurgical characteristics which can be satisfactorily described from the appearance of satisfactory alloys under the microscope. r

The alloy should be of austenitio structure, The name austenite is given to a solid solution of carbon in iron, with or without other elements which in themselves have the property of forming solid solutions with iron. Theories difier on whether the carbon is present as carbide or as elemental carbon, but these theories are unimportant as far as this specification is concerned, the term austenitef being well understood by metallurgists. The methods by which austenitic structures are obtained are known to all persons skilledin the art, and, save to say that the alloy should be cooled slowly, and not quenched, a detailed description of it in this place is unnecessary.

The grain of the alloy should preferably be fine and the grains should be of approximately equal size. A coarse grained structure will serve but must be of purer metal than a fine grained structure. It is, consequently, most advantageous to obtain a fine grain.

The alloy should have few, or practically no, voids. Voids are small cavities occurring presumably, between adjacent crystals on freezing. Their presence in considerable number is a sure indication that the alloy will be much less satisfactory in use than an alloy WithOllt'VOidS.

The alloy should be substantially free of any impurities which are insoluble in the solid solution. For example, any impurities which, upon freezing of the alloy, would be imprisoned between adjacent crystals, are most undesirable. Onthe other hand, small amounts of impurities which are soluble in the solid solution are not of obvious disadvantage.

The alloy should be practically devoid of grain boundary segregations. These boundaries, under the microscope, have the appearance of lines running more or less haphazardly across the face of a polished cross section. The presence of large numbers of these indicates an inferior structure.

The alloy should be substantially devoid of free oxides. The presence in the casting of free oxides decreases the solubility of the carbide phase and induces decreased resistance to corrosion under Working conditions. It is, consequently,.recommended that deoxidation be carried to completion, in the ladle and that the ratio of scrap used be low. Dissolved oxides do not appear to be particularly harmful but, if free oxides are to be avoided, the percentage of total oxide must be kept as low as possible because the presence of an appreciable quantity of oxide results in' a portion of it being insoluble in the solid solution.

The carbide should be present in particles of approximately equal size because the presence in different portions of the casting of particles of considerably different size results in unequal resistance to corrosion, The particles of carbide should also be distributed equally throughout the casting in order that the matrix of softer material may be protected by them. 1

A hopper lip or other mouthpiece made in accordance with my invention resists corrosion for a much longer period and requires less frequent cleaning than hopper lips of pure nickel.

An alloy which may be formed to satisfy the requirements of this specification is marketed under the trade name Illium G and is manufactured and sold by the Burgess-Parr Company of Moline, Illinois. r

I have discovered, additionally, that the resistance of such a hopper lip to corrosion can be materially increased by the use of buffer hardware. By the term hardware is meant the bolt, nut, and the like, which hold the hopper lip in place on the hopper. be made of a metal or alloy which is electro-positive with respect to the metal of the hopper lip and be immersed in the coagulating bath, it will be found that the hardware is preferentially attacked by the corrosive material and consequently, the hopper lip metal'is left substantially free from corrosion over long periods of time. This discovery is not, of course,limited to use with the particular hopper lips which have been described but finds equal application to hopper lips of any material. Thus, for example, extrusion devices or hopper lips made according to my invention, when held in place in the coagulating bath by means of nickel hardware which is itself immersed in the coagulating bath, lasts a much longer time without need for reho-ning than a hopper lip of the same material held in the bath by hardware made of the hopper lip metal. It is advantageous, in certain cases, to increase the size of the hardware over the size of that which is ordinarily used. Thus, elongated bolt heads and nuts present a greater surface to the corrosive liquid than the bolts, nuts, or other hardware, ordinarily used, and for this reason exhibit a greater buffering action. The term buffer as it is used in this paragraph signifies the ability on the part of the metal referred to to inhibit or to lessen the tendency of the hopper lip or other extrusion device to corrode.

The hopper lips of my invention, whether used alone or with'electro-positive hardware, improve performance greatly in the manufacture of regenerated cellulose sheeting from viscose. Thus,

there has been produced a 20% improvement in streak ratings over an extensive period of time. By streak rating is meant the frequency at which streaks appear in the finished film due to imperfections in oraccumulations on the mouth- If this hardware piece. There was a reduction in the neighbor- 75 hood of in breaks of film occurring in the wet end of the casting machine. This represents a great saving in labor and material. In a plant operating several casting machines, interruptions and delays in the casting schedule caused by streak formation in the sheet material produced were reduced in the neighborhood of 80% by the use of hopper lips embodying my invention.

Pure nickel hopper lips require honing about every four and one-half days. With the new type of hopper lips, the length of time between honings is more than doubled.

A nickel hopper lip requires grinding about every six or eight weeks. With my invention grinding is required only about every five or six months.

Another advantage of hopper lips made in accordance with my invention is in respect to interchange of coagulating baths. In the production of thin films of regenerated cellulose, for example, the coagulating bath normally contains sulfuric acid as the active coagulating agent while in the production of heavier gage film an ammonia bath, in which slightly alkaline ammonium sulfate is the active coagulating agent, is used. It has been found that nickel hopper lips, once used in an ammonia bath, can never again be used in a sulfuric acid bath. For example, a nickel hopper lip used in a sulfuric acid bath may be transferred to an ammonia bath without greatly increased corrosion. If, however, after the use of the ammonia bath, an acid bath is brought into contact with the nickel lips, so great a corrosion takes place that within two or three hours the lips must be removed and reground and reserved for use with ammonia baths only. It is not only difiicult and troublesome to maintain proper segregation along these lines, but it is costly and requires a comparatively large investment in hopper lips. This type of corrosion does not occur when my material is used in the fabrication of the hopper lips; hopper lips made in accordance with my invention can be used interchangeably with either type of bath. The interchangeability of the hopper lips of my invention avoids this necessity for segregation and materially reduces the investment in hopper lips.

Among other advantages which flow from my invention are the production of a better quality film having fewer streaks, breaks, and bad edges; longer life of all hoppers and hopper parts with a consequent reduction in investment; reduction in the cost of hopper and mouthpiece maintenance; reduction in the frequency of hopper lip adjustments; and production of film having a more even gage.

The alloy of my invention is capable of use both as a mouthpiece for the extrusion of pellicles, including tubes, caps, and bands, and as a mouthpiece or spinneret for the extrusion of artificial fibers; it is useful both in the viscose and the cuprammonium cellulose processes. Drums constructed of the alloy to which my invention pertains may also be used beneficially in the drum casting process for making regenerated cellulose pellicles. The alloy may also be used in constructing drums used in a casting process which comprises, broadly, extruding viscose solution through an elongated mouthpiece, which is formed by two co-acting hopper lips, into a coagulating bath, then drawing the formed pellicle over said drum of large diameter, mounted for revolving so that the lower portion of the drum is immersed in the coagulating solution; Drums made of this alloy, being highly resistant to the corrosive influence of the coagulating solution and to the building up of adhesions thereon, maintain their smooth, regular surface over an extended period of time and assist in the formation and protection of a smooth, streak-free pellicle.

As many apparently widely diiferent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. A method of forming regenerated cellulose film which comprises extruding viscose into a coagulating bath from a hopper through a mouthpiece attached to said hopper, which mouthpiece is formed by means of two co-acting hopper lips spaced to provide a narrow elongated orifice, said hopper lips comprising an alloy containing parts by weight between about 55 and 60 of nickel, 19.5 and 23.8 of chromium, 7.5 and 9.52 of copper, 2.46 and 4.23 of molybdenum, 1.57 and 3.64 of tungsten, 1.55 and 2.22 of manganese, 0.56 and 1.05 of silicon, 2.79 and 4.16 of iron, and 0.10 and 0.29 of carbon.

2. A method of forming regenerated cellulose film which comprises extruding viscose into a coagulating bath from a hopper through a mouth piece attached to said hopper, which mouthpiece is formed by means of two co-acting hopper lips spaced to provide a narrow elongated orifice, said hopper lips comprising an alloy containing parts by weight between about 55 and 60 of nickel, 19.5 and 23.8 of chromium, 7.5 and 9.52 of copper, 2.46 and 4.23 of molybdenum, 1.57 and 3.64 of tungsten, 1.55 and 2.22 of manganese, 0.56 and 1.05 of silicon, 2.79 and 4.16 of iron, and 0.10 and 0.29 of carbon, and disclosing under the microscope austenitic structure, few voids, substantial absence of impurities insoluble in the solid, substantial absence of grain boundary segregations, being substantially devoid of undissolved oxides and having carbide uniformly distributed.

3. A method of forming regenerated cellulose film which comprises extruding viscose into a coagulating bath from a hopper through a mouthpiece attached to said hopper, which mouthpiece is formed by means of two co-acting hopper lips spaced to provide a narrow elongated orifice, said hopper lips comprising an alloy containing parts by weight between about 55 and 60 of nickel, 19.5 and 23.8 of chromium, 7.5 and 9.52 of copper, 2.46 and 4.23 of molybdenum, 1.57 and 3.64 of tungsten, 1.55 and 2.22 of manganese, 0.56 and 1.05 of silicon, 2.79 and 4.16 of iron, and 0.10 and 0.29 of carbon, and disclosing under the microscope austenitic structure, few voids, substantial absence of impurities insoluble in'the solid, substantial absence of grain boundary segregations, being substantially devoid'of undissolved oxides, and having carbide protectively distributed in particles of approximately equal size.

4. A method of forming regenerated cellulose film which comprises extruding viscose into a coagulating bath from a hopper through a mouthpiece attached to said hopper, which mouthpiece is formed by means of two co-acting hopper lips spaced to provide a narrow elongated orifice, said hopper lips comprising an alloy containing parts by weight between about 55 and 60 of nickel, 19.5 and 23.8 of chromium, 7.5 and 9.52 of copper, 2.46 and 4.23 of molybdenum, 1.57 and 3.64 of tungsten, 1.55 and 2.22 of manganese, 0.56 and 1.05 of silicon, 2.79 and v4.16 of iron; and 0.10 and 0.29 of carbon, and disclosing under the microscope austenitic structure, few voids, substantial absence of impurities insoluble in the solid, substantial absence of grain boundary segregatio-ns, being substantially devoid of undissolved oxides, and havingcarbide protectively distributed in particlesiof approximately equal size, such hopper lips being attached to the hopper by means vof metal hardware electro-positive with respect to the metal of the hopper lips.

5. The method of claim 4 characterized in that said hardware is composed of nickel.

OVID S. PETRESCU.