US2377335A - Structural material - Google Patents

Description

June 5, 1945. I D, HNLAYSON A| 2,377,335

STRUCTURAL MATERIAL File d Sept. 4, 1941 "VI/EN TORS lw/Aluysolv fic- HALE I .9 ATTORNE YS Patented June 5, 1945 don, near Derby, England, assignors to Celanese Corporation of America, a corporation of Delaware Application September 4, 1941, Serial No. 409,520

, In Great Britain September 28, 1940 7 Claims. (Cl. 154-43) This invention relates to structural materials and particularly to materials of a composite character. 1

According to the invention stress-resistin members having such a size or shape of crosssectional area as to be rigid or relatively rigid comprise a fabric base embedded in plastic ma-- terial, the fabric comprising at least one set of heavy parallel yarns lying close to each other. The parallel yarns may be bound to each other by interlaced lighter threads that not only hold the heavy yarns parallel and close to each other but permit them to lie straight, giving a woven structure in which any waviness arising from the interlacing is substantially confined to the light binding threads. The close packing of the heavy yarns coupled with the straight formation of those yarns provides a base fabric in which the maximum tensile strength is obtained; and, with the rigidity imparted by embedding the yarns in plasticmaterial (which should have low elasticity), a rigid or relatively rigid structure can be formed suitable for a variety of uses, such as ties, beams, torsional members, and like members having a length that is substantial as compared with their cross-sectional dimensions. Where the use of any such member might produce a tendency to splitting along lines parallel to the heavy yarns, it may be advantageous to employ fighter binding threads as indicated above. Such a tendency may, however, be resisted by providin a mor elaborate fabric structure, for example, one in which one or more other sets of heavy parallel yarns are provided to give layers in which the heavy yarns of one layer cross those of another layer at a. substantial angle, e. g., at rightangles. Provision of the kind just mentioned may also be desirable where the structural material is intended to be used as a. strut,

It is particularly advantageous to form the' base fabric from yarns of exceptional tensile strength. Outstanding yarns in this respect are continuous filament yarns of regenerated cellulose produced, for example, by the complete sa- 7 'ponification of yarns of cellulose acetate or other plete saponification of such materials may even further increase tenacity. Stretched, or stretched and saponified filaments of this character have a relatively low extensibility, e. g., about 6%, and for some purposes this is an advantage in producing relatively rigid structural members of the kind with which the invention is concerned. The extensibility may,,however, be improved by subjecting the yarns, after stretching, to a shrinking treatment; for example, strong yarns of cellulose acetate may be shrunk by treatment in a bath containing methylene dichloride or ethylene dichloride diluted. with benzene or toluene. The shrinking is accompanied by some loss of tenacity but can be so controlled that the tenacity still remains high, e. g., between 2 and 4 or 5 grams per denier. Other high tenacity yarns suitable for use according to the invention can also be made by wet-spinning organic esters of cellulose under such conditions that the materials are stretched considerably, for example, by several hundreds per cent of their extruded length. In this case also, the-original tenacity of the materials ca still further be increased by saponification. Again, regenerated cellulosic yarns of high tenacity can also be made directly by spinnin solutions of viscose or cuprammonium cellulose under suitable conditions, for example, under such conditions that a considerable stretch is efiected.

Among other materials of which the heavy yarns may be composed are cellulose ether materials that in their manufacture have been subjected to similar processes to those referred to above for ensuring high tenacity, and yarns of the so-called super-polyamides and like linear polymers, e. g., those containing in their structural unit ester groups or anhydride groups.

per denier can be obtained in this way and com- Natural silk yarns .are also suitable for the production of base fabrics of high tenacity.

By the use of high tenacity materials relatively rigid composite structural materials of high strength can be obtained, which may be used in -substitution for metallic structural elements, and,

in many cases, enable a saving in weight to be ob tained. Where, however, high strength is not of the greatest consideration, other textile materials may be used for the heavy yarns, e..g., cotton, wool, jute, hemp and linen, and likewise staple fibre yarns produced from continuous filaments of the character already mentioned, provided that the close packed parallel arrangement of the heavy yarns is adhered to. Where lighter binding threads are employed in the fabric structureto hold the heavy yarn close toeach other it is generally advantageous to employ as these binding threads the stronger types of textile materials referred to above in order to keep the relative proportion of binding thread to heavy yarn as low as possible.

Various forms of plastic material may be used for embedding the base fabric. In order to provide the necessary rigidity highly elastic plastic materials should be avoided. Substances of thermoplastic charactermay be used, for example, cellulose esters and ethers, e. g., cellulose acetate, cellulose acetate-propionate, cellulose acetatebutyrate, cellulose acetate-stearate, cellulose acetate-palmitate, cellulose nitrate, cellulose nitrate-acetate, ethyl cellulose, benzyl cellulose and ethyl cellulose acetate; and of polymerised unsaturated artificial filamentor film-forming substances, for example, polymethyl acrylate, polyethyl acrylate, polymethyl methacrylate, po yvinyl esters and ethers, synthetic resins of the polystyrene class of co-polymers of one or more of such polymerised unsaturated compounds. It is advantageous that the plastic material should have a relatively high melting point and from this point of view simple polymerised vinyl esters,

. for example, polyvinyl acetate and polyvinyl chloride are less satisfactory than co-polymers of these esters with unsaturated compounds of the acrylic series. Cellulose nitrate should not be used where its inflammable nature might be a disadvantage.

Thermosetting plastics may also be used, for example the synthetic resins obtained by condensation of an aldehyde such as formaldehyde with urea or like acting nitrogenous substances, for example, thioureas, guanidine or dicyandiamide, or with a phenolic compound, for example, phenol m-cresol or 3:5 xylenol. Other plastics such as casein and soya bean protein plastics may likewise be employed.

The plastic may be, applied to a base fabric already shaped to correspond to the shape of the structural element desired or the plastic may be incorporated in-the fabric prior to, or during a preliminary shaping of the fabric. In either case a moulding operation is generally desirable to bring about the final shaping of the element, especiallywhere smooth external surfaces are desired. A simple form of light structural element according to the invention is a plain rod having as its basis a cord woven or braided from a number of heavy yarns held together :by a light binding thread. Such a cord may for example consist of a number of heavy, parallel core yarns surrounded by a sheath of similar yarns woven together by a single light weft thread. The cord is impregnated with' plastic material and finally moulded into rigid form by the application of heat and pressure. The amount of plastic material may be such as just to permit the rod to have a smooth surface after moulding or, if desired, additional (ill plastic material may be applied externally of the Structural elements of other cross-sections may be formed by suitably shaping base fabrics prior to embedding them in the plastic material; for example, a ribbon or tube of base fabric may be folded lengthwise into the form of an L, U, T, or H for insertion into a correspondingly shaped mould. In the case of such sections as T's or H's,

stitching may be employed to impart strength I where one portion of the section branches from another.

Composite elements of the kind described may be pierced or drilled for attachment to each other or to other elements of any structure in which they are incorporated. It is desirable, however, to ensure that under the stress to be withstood, splitting between the heavy yarns does not arise. By reason of the method employed for attaching the elements, suitable reinforcement such as a whipping which may be fltted before the final moulding or the application of a ferrule may be employed. For the production of time members, however, strips or flattened tubes of fabric may be wound round a pair of pins spaced to correspond with the desired positions of attachment holes at the two ends of the element and the free ends of the strip or tube may be secured by stitching or whipping prior to moulding, the element as it leaves the'mould already having attachment holes provided in the positions determined by the pills.

The moulded elements need not have the same cross-section throughout their length. For example, the base fabric may be thickened, especially at the ends or other parts where provision is to be made for attachment to other members. Thus, in the case of tubular elements, the end of the tubular base fabric may be folded back on itself. The elements may also be flattened or thickened during the moulding operation. Metal insertsor other pieces may be secured in or on to the fabric/plastic structure by the moulding operation. For example, eyes, bushes, or ferrules may be moulded in place.

As already stated, plastic material may be incorporated into the fabric structure prior to the final moulding in which the structure becomes rigidly embedded in the plastic material. In the case of thermosetting resins for example, the base fabric may be impregnated with an aqueous solution of the resin components so that on the subsequent application of heat and pressure in the moulding operation the condensation of the synthetic resin is completed within the fabric. It is generally advisable, however, to apply moulding powder externally of the base fabric in order to produce a smooth surface on the element. Where thermoplastic embedding materials are employed, e. g., cellulose acetate, impregnation of the base fabric may be assisted by incorporating cellulose acetate yarns in the 'fabric structure. By the application of heat and pressure either in the preliminary shaping of the base fabric or in thefinalmouldingthecelluloseacetateyarnsbecome plastic and bring about the adhesion of the non-thermoplastic yarns in the fabric, aided if necessary by a plasticiser in the cellulose acetate threads or by the application to the threads or the woven fabric of a plasticiser, solvent or latent solvent causes the cellulose acetate threads to fuse.

The weight of the heavy threads will depend somewhat on the type of element to be constructed and in the case of tubular or other thin-walled sections, on the thickness of the walls. In general, however, heavy yarns of say 2,500 or 5,000 denier are convenient; for the lighter binding threads a denier of about 275 maybe employed.

Various forms of members according to the invention will now be described with reference to the accompanying drawing, in which Fig. 1 shows a woven sheath surrounding a number of core yarns all embedded in plastic material; I 4

Fig. 2 shows a tubular fabric embedded in plastic material to form a tubular member;

Fig. 3 shows the formation of another kind of tubular member;

Fig. 4 shows a member similar to Fig. 1 fitted with a ferrule;

Figs. 5 and 6 are front and side elevations of the end of a member fitted with a perforated ferrule;

Figs. '7, 8 and 9 show stages in the manufacture of an eyeletted member;

Figs. 10, 11, 12 and 13 are cross-sections of different types of light-sectioned members; and

Fig, 14 is a cross-sectional view showing the application of a cored member to the reinforcement of a laminated fabric sheet.

In Fig. 1, heavy yarns I are woven with light threads 2 to form a sheath surrounding heavy core yarns 3. The heavy yarns I, 3, may be 3/3/5230 denier yarn produced by stretching times in wet steam) and saponifying cellular acetate continuous-filament yarn. The light threads 2 may be of similar material of 275 denier. The solid cord thus formed is embedded in plastic material 4, this material being shown stripped from the upper half of the figure. The plastic.

material impregnates the whole of the cord assembly so as to add substantial rigidity to the strong structure formed by the cord elements themselves. For example, the cord may be impregnated with liquid urea-formaldehyde before being subjected to a moulding operation in a cylindricalmould of circular section and having a length appropriate to that of the cylindrical member to be formed. In general, the amount of plastic material should be just sufllcient to impart a smooth surface to the cord, the thickness being somewhat exaggerated in Fig. 1.

In Fig. 2, a woven tube 5 similar to the sheath formed by the yarns I and threads 2 of Fig. 1 is embedded in plastic material 6, the moulding operation being efiected after the impregnated tube has been inserted on a mandrel closely fitting the bore 'l of the tube.

In Fig. 3, strips 8 of fabric comprising heavy yarns 9 lightly woven together with threads [0 are wound helically on'a mandrel II to form an inner layer covered by a similar layer formed by strips l2 wound helically in the opposite direction. The assembly is embedded in plastic material l3 by the use of a cylindrical mould as described with reference to the production of the member shown in Fig, 1.

Fig. 4 shows a rod-like member ll of the type shown in Fig. 1, but fitted with a metal ferrule I! which may provide for the anchoring of the member ll. Thus, the outside of the ferrule may be tapered as indicated at IS, the larger end of the ferrule being at the free end of the member.

The ferrule can thus be threaded through a correspondingly tapered hole in some member to which the member I 4 is to be attached. Aferrule of this kind may also be externally screwed to provide a fixing; it may likewise be drilled similarly to the ferrule shown in Figs. 5 and 6. To provide for a firm connection between the member I4 and the ferrule l5 the end of the woven tubular sheath I! may be turned back on itself,as indicated at 18, so as tofill the taper bore of the ferrule. When the ferrule is moulded in position the setting of the plastic material in the portion of the braided cord lying within the. ferrule produces an enlarged end that resists any tendency of the ferrule to pull away from the end of the member under tension. The surface IQ of the plastic material may run smoothly into the surface of the ferrule.

The ferrule 20 of Figures 5 and 6 is flattened and pierced within a hole 2| which enables the member 22 fitted with the ferrule to be used as a tension member with a pin-joint connection to another member generally indicated at 23.

Fig. 7 shows the first stage in the building up of a tension member from a length 24 of heavy yarn fabric which may either be formed by flattening a tube of the kind used in forming the member shown in Fig. 2 or a strip or tape of the kind shown in Fig. 3. The length 24 is wound over a pair of eyelets 25 and the parallel portions of the lengthare sewn or whipped, as indicated in Fig. 8. The assembly, including the eyelets, is placed in a mould diagrammatically indicated at 26, in which the fabric layers and the eyelets are embedded in plastic material to produce a tension member, the eyelets of which provide for ready attachment. A moulded tension member of this kind is shown in Fig. 9; in this case, however, pear-shaped eyelets 21 have been used.

In Figs. 10-13 is a tube of fabric of suitable diameter has been flattened to form a double layer of fabric and manipulated into various sections suitable for light compression members. The double layers 28 are held together by stitching 29 before placing the fabric in the mould in which the plastic material 30 is set.

Fig. 14 shows the application of a stress-resisting member, according to the invention, as the reinforcement of a fabricskln, e. g., of the type described in British No. 514,442. The skin 3| comprises layers 32 of woven fabric each consisting of a set of heavy parallel yarns bound to each other by light threads that permit the heavy yarns to lie straight, the waviness arising from the woven structure being substantially confined to the light binding threads. The heavy yarns in adjacent layers cross one another at a sub-' stantial angle, e. g., at right-angles. The layers 32 are assembled over a mould 33 and suitably impregnated with plastic material. To provide for the reinforcement of the -skin the mould is provided with a groove 34' into which is inserted a braided cord of the kind described. in Fig. 1, the cord comprising a number of heavy core yarns 35 and one or morewoven sheaths 36 to provide for thefirm attachment of the reinforcement to the skin 3|. One or more layers 36 of fabric, similar to that used for the layers 32,are

laid in the groove 3| prior to the insertion of the reinforcing cord, the layers 21 extending over the surface of the mould 33' for some distance on each side of the groove 34. Recesses 38 may be provided to accommodate the layers 31 and enable the outer surface of the skin 3| to have a smooth uninterrupted curvature. The reinforcing cord may be suitably shaped to fit closely into the groove. When heat and pressure is applied to the assembly of fabric and cord on the mould 33, the plastic material with which the fabric and cord is impregnated welds the layers 32 into a.solid skin and also welds the reinforcement to the skin to provide a structure capable of withstanding substantial tension and tearing stresses, and also having considerable rigidity arising from the low-density of the material (e. g., 1.10 to 1.15) as well as from the stifiening imparted by the reinforcing rib.

Having described our invention, what we desire to secure by Letters Patent is:

l. A stress-resisting member having a crosssection enabling it to have substantial lateral rigidity, said member comprising a basis of textile yarns embedded in plastic material of low elasticity, the textile yarns comprising at least one set of parallel yarns lying close to one another and containing artificial filaments that have been stretched while in a softened condition so as to increase their tenacity and reduce their elasticity.

2. A stress-resisting member having a crosssection enabling it to have substantial lateral rigidity, said member comprising a basis of textile yarns embedded in plastic material of low elasticity, the textile yarns comprising at least one set of relatively heavy parallel yarns bound close to each other by being interlaced with relatively light yarns to which the waviness arising from the interlacing is substantially confined, said relatively heavy yarns containing artificial filaments that have been stretched while in a softened condition so as to increase their tenacity 40 and reduce their elasticity.

3. A stress-resisting member having a crosssection enabling it to have substantial lateral rigidity, said member comprising a basis of tex- 4. A stress-resisting member having a crosssection enabling it to have substantial lateral rigidity, said member comprising a basis of textile yarns embedded in thermosetting material 01 low elasticity, the textile yarns comprising at' least one set of parallel yarns lying close to one another and containing artificial filaments that have been stretched while in a softened condition so as to increase their tenacity and reduce their elasticity.

5. A stress-resisting member having a crosssection enabling it to have substantial lateral rigidity, said member comprising a basis of textile yarns embedded in plastic material of low elasticity, the textile yarns comprising at least one set of parallel yarns lying close to one another and containing artificial filaments of an organic ester of cellulose that have been stretched while in a softened condition and then saponified so as to increase their tenacity and reduce their elasticity.

6. A stress-resisting member having a crosssection enabling it to have substantial lateral rigidity, said member comprising a basis of textile yarns embedded in thermoplastic material of low elasticity, the textile yarns comprising at least one set of relatively heavy parallel yarns bound close to each other by being interlaced with relatively light yarns to which the waviness arising from the interlacing is substantially confined, said relatively heavy yarns containing artitile yarns embedded in thermoplastic material of low elasticity, the textile yarns comprising at least one set of parallel yarns lying close to oneanother and containing artificial filaments that have been stretched while in a softened condition so as to increase their tenacity and reduce their elasticity.

ficial filaments of a cellulose ester that have been stretched while in a softened condition and then saponified so as to increase their tenacity and reduce their elasticity. V

7. A stress-resisting member having a crosssection enabling it to have substantial lateral rigidity, said member comprising a basis of textile yarns embedded in thermosetting material of low elasticity, the textile yarns comprising at least one set of relatively heavy parallel yarns bound close to each other by being interlaced with relatively light yarns to which the waviness arising from the interlacing is substantially confined, said relatively heavy yarns containing artificial filaments of a cellulose ester that have been stretched while in a softened condition and then saponified so as to increase their tenacity and reduce their elasticity,

DONALD FINLAYSON. FRANK CORBYN HALE.

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