US 3758247 A
Crosshead die for coating flat cables, in which the melt flow is split into two partial flows and two diversion rollers with helical grooves are provided to guide and divert the partial flows after conversion of their cross-sections.
Description (OCR text may contain errors)
ijnite States Patent 1 1 Deegen Sept. 11, 1973  APPARATUS FOR MAKING FLAT CABLES 3,252,183 5/1966 Bronzert 425/114 BY EXTRUSION 3,383,736 5/1968 Brandt 425/114  Inventor: Axel W. Deegen, Boeblingen,
Germany FOREIGN PATENTS OR APPLICATIONS 168,488 6/1951 Austria 425/114 [731 Assgneef Bus'ness Mach'nes 238,080 1/1965 Austria 425 114 Corporation, Armonk, NY.
 Filed: Apr. 23, 1971 Primary Examiner-R. Spencer Annear 1 Appl' 136934 Attorney-Hanifin & Jancin and John S. Gasper  Foreign Application Priority Data Apr. 23, 1970 Germany P 20 19 629.6
 ABSTRACT  U.S. Cl 425/114, 425/192, 264/172  Int. Cl 829i 3/10 Crosshead die for coating flat cables, in which the melt  Field of Search 425/ 114, 188, I90, flow is split into two partial flows and two diversion 425/192; 264/172 rollers with helical grooves are provided to guide and divert the partial flows after conversion of their cross-  References Cited sections.
UNITED STATES PATENTS Wermine 425/114 X 8 Claims, 8 Drawing Figures 1 PAIENTmsm 1 ma SHEET 1 0F 3 Fl INVENTOR AXEL W. DEEGEN A TTORNE Y APPARATUS FOR MAKING FLAT CABLES BY EXTRUSION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to apparatus for making flat cables, and particularly to an apparatus for coating multiple wires with plastic, or the like, by extrusion.
2. Description of the Prior Art In crosshead or angled dies for wire and cable coating the flow of the plasticized or molten compound entering the die from the screw channel must be diverted to a new axis which is inclined or extends at right angles to the screw axis. The axes of the screw and the diverted melt flow may form an angle of 30, 45, or 90. However, any change in the direction of a melt flow extending in a transverse plane results in different flow path lengths for individual cross-sectional elements. These flow path differences, after diversion, lead to differences in the physical characteristics such as compound pressure, velocity, temperature and viscosity of the material in a plane perpendicular to the direction of movement. It is known from experience that the pressure on the discharge end of the inner arc of the diverted flow path is invariably higher than that on the discharge end of the outer arc, of the diverted flow path, so that the melt flow leaves the exit gap on the side of the die connection with the extruder at a higher speed than on the opposite side..Thus, the wall thickness and the inner stresses of the removed strand increase in the direction of the die connection, which is disadvantageous for the manufactured product. The problem of diversion has been solved in many ways. Path and pressure compensation is, for exampleQobta'ined by extending the inner arc of the flow path and all paths between the border arcs by compensating elements such as core pieces or deceleration fittings which lengthen the flow paths so that the total path of the material in the inner arc is similar to that in the outer arc. From the publication by G. Schenkel, Rheologische Formgebung einfacher Spritzwerkzeuge fur Extruder (Rheological construction of simple dies for extruders) pp. 201 to 207 in the journal Kunststoffe." 49 (1959) it is known to guide the melt flow after division by a knife along the peripheral length of a core piece (inner are around the core) which is centrally fitted into the die-casing. Another design of crosshead dies, which is described in the same publication, is provided with adjustable decel eration fittings 'on the inner arc in lieu of stationary core pieces. The latter design has the disadvantage that a melt flow that is balanced over its full circumference may only be obtained under certain conditions. From a rheological standpoint, deceleration fittings are less favorable than core pieces and lead to stagnation in the melt flow In the crosshead die described in 'French Pat. No. l,024,205, the melt entry is not central but in a plane tangential to the core so that the material flow is not split into two portions. The flow over the whole crosssection is spread around the core by a spiral guide surface. The special design of this surface ensures that the original helical movement changes gradually to an axial one. Crosshead dies of this type have so far failed in gaining ground owing to their elaborate design and long flow paths. I
The above publication also describes crosshead dies with distributors for the extrusion of rubber insulations.
In these, the melt flow coming from the screw is first of all split into two partial flows which are then resplit into two partial flows from two diametrically opposite points. This improves thedistribution of the melt flow over the whole circumference. Designs comprising distributors, similar to crosshead dies with core pieces, have the disadvantage that the repeated division of the melt flow as a result of the reduced velocity in the vicinity of the guide cores leads to undesirable markings in the extruded cable sheath.
SUMMARY OF THE INVENTION It' is an object of this invention to provide an improved apparatus for making flat cable.
It is an additional object of the invention to provide an apparatus for making flat cable having a crosshead die for a screw extruder for coating a plurality of parallel coplanar cores such as conductive wires with rubber or plastic in which the above-mentioned diversion problem of melt flows is solved rheologically satisfactorily.
In accordance withthis invention, the above, as well as other objects, are obtainable by providing a flat cable making apparatus having a die which extrudes dual rectangular plastic melt flows onto an array of a plurality of cores, such as conductor wires from opposite sides of the array. It is a feature of this invention that the die is a crosshead die in which a single melt flow is split into two partial flows and the cross-sections of the partial flows are made rectangular before extrusion onto the array. It is a further feature of the die that channel means including two helical paths is provided in the die for guiding and diverting the melt flows of rectangular cross-section.
It is also a feature of this invention that the die comprise dual block members through which the plurality of cores and the plastic melt flows are moved separately and then extruded at a common point. The die members are preferably hinged together so as to be separable to allow repair, cleaning, changing of wires in the die, with a minimum of effort. Each block is provided with a separate wire guide means which preferably takes the form of flat plates which are attached to the blocks in cantilever fashion and which coact therewith to form a rectangular flow channel means in the region proximate the wires where extrusion takes place; With this arrangement, the wire guides are very slightly deflectable towards each other due to pressureof the plastic in the channels thereby causing the wire guides'to hold the wires firmly and precisely in their predetermined relative locations as the melt flows extruded thereon. I
In the preferred embodiment of this invention, the helical paths mentioned above are designed as helical grooves of rectangular cross-section in the surface of two cylindricaldiversion pins or rods mounted to the die block members and coacting with the channel means therein. The groove in the surface of each diversion pin extends over an arc portion of the periphery thereof, the are being less than a full pitch. The base region of each groove tapers off tangentially in its two end regions from which the melt flow leaves and into which it enters, respectively.
The-diversion pins are set at half the angle of diversion for the entry of the melt flow into the die. The melt flowsare preferably diverted by For this angle of diversion, the pins are set at an angle of 45 to permit are entry of the melt flow. Less acute diversions of the material by say 45 and 60, respectively, are equally favorable. For the diversion of melt flows of rectangular cross-section by means of the arrangement in accordance with the invention, the path length for each individual cross-sectional element is identical.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective drawing which represents a diagrammatic version illustrating the spatial relationship of the melt flows between the extruder exit and the crosshead die exit;
FIG. 2a is a perspective view of the diversion pins used in the crosshead die of this invention;
FIG. 2b is a cross-sectional view of the diversion pins shown in FIG. 2a;
FIG. 3 is a sectional view of a crosshead die in accordance with this invention and whichprovides the plastic melt flow arrangement illustrated in FIG. 1;
FIG. 4 is a section taken along line 44 of FIG. 3;
FIG. 5 is a section taken along line 5-5 of FIG. 4;
FIG. 6 is a section of the crosshead die taken along line 6-6 of FIG. 5; and
FIG. 7 is an enlarged fragment of the die of the preceding Figures witha portion shown in sections taken along lines 7--7 of FIG. 6.
DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawings, the melt flow 18 in FIG. 1, which consists of rubber or plastics such as polyethylene, polypropylene or their copolymers, or polyvinyl chloride and the like, and which comes from the screw extruder, is continuously forced through the die, as is hereafter described by means of FIGS. 3 and 4. Simultaneously, the non-preheated wires 19, which are to be coated, enter the die from the left. Flat cable 20 is hauled off at a speed of about 10 m per minute. In the die the melt flow 18 is split into two symmetrical partial flows 18a, 18b. The circular cross-sections of these partial flows are changed to rectangular ones by correspondingly shaped channels in the die, as is hereafter explained in greater detail. The extrusion cross-section of the melt flow decreases uniformly between the exit of the screw extruder and the die exit. By means of the cylindrical diversion pins 8, 9 shown in FIGS. 2a and 2b the two partial flows 18a, 18b are diverted to a new axis which is inclined or arranged at right angles to the axis of the melt flow 18, and after diversion the two partial flows converge from above and below against the parallel guided wires 19 to form the flat cable 20.
The crosshead die in accordance with the invention is shown in FIGS. 3 and 4. The crosshead die is fixed to the extruder housing with the threaded part of flange 3 by means of cap screws 2.
The thermoplastic material, or the rubber, is forced by a screw extruder through the crosshead die. The distance between the exit of the screw extruder and the crosshead die exit must be as short as possible. The melt flow initially distributes itself in the annular channel 6 between the conical end of extruder screw 1 and a corresponding conical recess of the forming block 4. The tip of extruder screw 1 is chamfered to generate a tumbling motion in the melt flow, thus preventing an overheated zone at the end of the screw. When using polyethylene the temperature of the screw end is, for example, 175 C. For converting the tumbling motion of the melt flow into an axial motion the flow is forced through a filter set 5 consisting of four wire mesh filters of different mesh number, for example, 80, 3,500, 900, and meshes/cm. In the V-shaped channel 7, which is embedded in the distributor 10, the melt flow is symmetrically split. The V-shaped channel 7 is followed by channel portions 70, 7b between cover plate 13a (top) and forming block (top) and cover plate 13b (bottom) and forming block 12b (bottom), respectively. The cross-section of the channel portions 7a, 7b decreases continuously in the direction of the diversion pins 8, 9 and to the location identified by reference lines 21 and 22. By suitably shaping the forming blocks 12 and cover plates 13, the circular cross-sections of the symmetrically split melt flows 18a, 18b (FIG. 1) are changed to rectangular ones.
The thermoplastic material flows through V-shaped channel 7 into channel portions 7a, 7b up to the diversion pins 8, 9 which are provided to guide and divert the melt flows 18a, 18b of rectangular cross-section. The surface of each diversion pin 8, 9 is provided to this end with a helical shallow groove 81, 91 which accommodates the melt flow of rectangular cross-section.
A wire strand 19 consisting of sixty wires with a diameter of 0.18 mm each, and which enters thecrosshead die from the left is guided in between the upper and lower wire guide 11a, 11b. The two partial flows 18a, 18b of rectangular cross-section, which are diverted by means of diversion pins 8, 9, converge from above and below against the parallel guided wires 19, densely surrounding the latter with plastic material. The coated flat cable leaves the crosshead die through an orifice 17 formed by orifice blocks 27 and 29 which are provided at the exit of the crosshead die. By suitably shaping this orifice, grooves are generated in those parts of the surface of flat cable 20 in which there are no wires. The width of the cooled flat cable is 29.2 mm and the thickness 0.7 mm. The cross-sectional dimensions of the orifice exceed those of the finished flat cable by the volumetric shrinkage some 10 per cent in height and width. Cover plate 13a (top) and forming block 120 (top) are pivotable on hinge bolt 15 by means of handle 16 of a locking device, which retains the cover plate 13a and the forming block 120 in the folded down state. This hinge construction permits cover plate 13a and forming block 12a to be opened to permit cleaning the arrangement as well as to replace wires and internal parts. The temperatures are measured by thermocouples 14. The maximum temperature in the crosshead die is 240C when using polyethylene. Heating devices and design details thereof have been omitted for clarity's sake.
For guiding and diverting the partial flows 18a, 18b 'of rectangular crosssection the diversion pins 8, 9 as best seen in FIGS. 20 and 2b include in their surface a helical shallow groove of rectangular cross-section to accommodate the shallow melt flow. The helical grooves 81, 91 do not extend over the full pitch of their respective cylindrical diversion rollers and taper off in their end regions 82, 92 into which the melt flows enter and from which they leave, respectively. The die comprises longitudinal grooves 83, 93 for locking the diver sion pins 8, 9 in position in forming blocks 12a and 12b.
For maintaining the wires 19 precisely spaced and in parallel as the melt flows 18a and 18b are extruded thereon, the wire guides 11a and 11b are specially designed to clamp the moving wires firmly in the positions they are to occupy in the finished cable. For this purpose, the wire guide 11a takes the form of a rectangular plate and is mounted within a recess in the bottom of forming block 12a. Wire guide 11a has a base portion 23 fixedly attached to block 12a by means such as screws 24. The front end of guide 11a has an extension portion 25 which terminates in a taper and forms a channel 26 with block 12a and upper orifice block 27. Likewise, wire guide 11b has a base portion 28, attached by screws 29 into a recess of forming block 12b, with an extension 30 which terminates in a taper and which coacts with forming block 12b and orifice block 29 to form a channel 31. As best seen in FIGS. 6 and 7, the tapered ends of the extension portions 25 and 30 of wire guides 11a and 11b engage the wires 19 of FIG. 1 as plastic is extruded from channels 26 and 31 onto the wires and through the orifice. As seen in these Figures, grooves 32 are formed in the upper surface of ex-. tension portion 30 of guide 11b while extension portion 26 of guide 11a is substantially flat. When pressure is applied by plastic in channels 26 and 31, these two surfaces are pressed tightly together so that wires 19 are firmly held in grooves 32.
The crosshead die in accordance with the invention, in which the melt flow on its way to the orifice is symmetrically split into two partial flows which after conversion of their cross-section to rectangular form are diverted and converge against the wire strand from above and below, has the advantage that the distance between the exit of the screw extruder and the die exit is identical for all cross-sectional elements of the melt flow. Moreover, there is no stagnation zone in which the material might be retained unduly long and thus be decomposed or charred. The manufacturing speed of flat cables by means of the crosshead die in accordance with the invention is essentially higher than that obtainable by known laminating processes wherein plastic tapes are applied to the wire strand from opposite sides and are welded together by heating.
While the invention has been particularly shown and described with reference to a preferred embodiment thereof, itwill be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
We claim: v 7
1. In apparatus for making flat cable by extruding a sheath of plastic material onto a plurality of parallel coplanar moving cores including extrusion means for producing a single melt flow of circular cross-section and a crosshead die,
said crosshead die comprising die block means,
guide means associated with said die block means for guiding said plurality of coplanar cores at an angle across the direction of motion of said single melt flow,
channel means formed insaid die block means havinga first channel portion connected to said extrusion'means for splitting said single melt flow into two separate melt flows and for directing said two separate flows to' opposite sides of and at said angle to said coplanar cores,
said channel means in said first channel portion hav ing successively circular then rectangular crosssections said channel means having a second channel portion formed in said die block means for directing said two separate flows on opposite sides of and in a direction parallel with said coplanar cores,
said channel means in said second channel portion having a rectangular cross-section and diversion means associated with said die block means and coacting with said channel means thereof for diverting said separate melt flows from said angular to said parallel directions of flow,
said diversion means comprises cylindrical diversion pins locatable in said die block means,
said diversion pins having helical groove means con necting said first portion of 'said channel means at the rectangular cross-section thereof with said second portion of said channel means of said die block channel means.
2. In apparatus for making flat cables, a die in accordance with claim 1 in which said diversion pins have helical grooves in the periphery thereof.
3. In apparatus for making flat cable, a die in accordance with claim 1 in which said die block means comprises:
first and second die block members located on opposite sides of said array of cores,
said die block members being relatively movable to permit opening of said die for removal or insertion of one or more of said cores, said die block members being in spaced apart relation to form a passage for said cores therebetween,
guide means carried by each of said die block members within said passage and mutually coacting to hold said plural moving cores in predetermined parallel coplanar array,-
said guide means coacting with said die block members to form rectangular cross-sectional channels on opposite sides of said cores for extruding said dual fiat plastic melt flows onto said cores as they move through said passage and said wire guides.
4. In apparatus for making flat cable, a die in accordance with claim 3 in which said guides comprise:
first and second guide plates, said guide plates having a base portion and an extension portion, said base portion being attached to said die block members and said extension portions extending in cantilever fashion relative to said die block members, i
members toforrn said rectangular channel means for said dual melt flows.
5. In apparatus for making flat cable, a die in accordance with claim 3 in which said die block members are hingedly connected for relative movement to permit opening of said die. 7 i
6. In apparatus for making flat cable, a crosshead die in accordance with claim 2 in which said diversion pins have helical grooves of rectangular cross-section.
7. In apparatus for making flat cable, a crosshead die in accordance with claim 3 in which said helical groove in said diversion pins is formed over an arc of the periphery of said pins.
8. In apparatus for making flat cable, a crosshead die in accordance with claim 4 in which said diversion pins are arranged in said die block means such that the axis of said diversion pins relative to the axis of the single melt flow forms an angleqno greater than 18 i i i t said extension portions coacting withsaid block