1. Technical Field
The field of art to which this invention pertains is that of a coextrusion apparatus and method, particularly for use in manufacturing annular seamless components of elastomeric materials such as used in the production of pneumatic tires, specifically body plies for radial tires. More particularly the invention relates to such a coextrusion apparatus and method in which the outer profile of the tubular extrudate is varied by varying the amount of elastomeric material applied to the outer surface of the extrudate by an elastic die.
2. Background Information
Tubular components or articles such as pneumatic tire body plies, have previously generally been built by utilizing woven fabric and calendering the same with rubber stock which, when cut to size, entails wrapping the sheet component around a tire building drum and overlapping the ends of the sheet to produce an annulus with a generally axially parallel extending seam. In order to avoid this lapped or seamed construction, extrusion has been employed in the prior art whereby a tubular extrudate is produced containing reinforcement cords disposed therein.
Many of the problems with such lapped or seamed construction have been resolved by our previous invention of a coextrusion apparatus and method disclosed in U.S. Pat. Nos. 4,578,024 and 4,657,718, as well as a related product disclosed in U.S. Pat. No. 4,776,909, all of which are incorporated herein by reference in the interest of full disclosure. These earlier inventions provide a solution to the noted prior art problems by producing a generally tubular elastomeric ply or extrudate made up of first and second concentric tubular streams of elastomeric material having interposed adjacent their common interface, a closely and uniformly spaced array of parallel reinforcing elements.
In the building of a tire, the carcass or first stage body, consists of six elements namely, a body ply which is the reinforcing cord and skim, two sidewall bands or annuli, two body ply insert annuli and an inner liner. Heretofore assembly or placement of these six bands on a tire building drum required six separate manually performed steps wherein the individual strips were placed on the tire building drum. These various individual strips of rubber usually were formed of different elastomeric compositions in order to achieve different results when assembled into the final tire. The innerliner is formed of a highly air impervious material and is applied to the body ply to provide the barrier for retaining the air within a tubeless pneumatic tire. The particular compound of the inner liner provides such impermeability characteristics.
The present invention described below pertains particularly to the formation of the sidewall component or part thereof on the tubular body ply component of the vehicle tire, which also may contain the inner liner thereof when forming a first stage tire, wherein the body ply is extruded as a tubular extrudate and the innerliner, preferably of a permeable characteristic supplied by the inner flow channel is joined with the outer flow channel, the profile of which is varied to form the sidewall component or part thereof at distinct locations on the innerliner portion of the tubular extrudate.
The most pertinent prior art with respect to applying and varying the outer profile of a tubular extrudate are shown in the following U.S. patents.
U.S. Pat. No. 3,134,832, discloses a method for extruding articles which comprises an extrusion die having a body and a cylindrical exterior sleeve. A central circular hole is provided and an elastomeric constrictive annulus which defines the extrusion aperture is positioned directly behind a flange. The annulus is held against the interior surface of the flange by a ring. As a gear is turned a follower is screwed into the exterior sleeve, pressing against the ring and annulus so that the annulus can expand inwardly under the compressive force in order to uniformly reduce the size of the hole in the annulus, i.e., reduce the size of the extrusion aperture.
U.S. Pat. No. 3,840,311, discloses an extrusion nozzle for manufacturing a plurality of frozen food type articles. This patent discloses an extrusion chamber having an inlet supply and terminating in an outlet orifice. A flexible wall formed from neoprene rubber can be attached to the casing wall adjacent the outlet in a conventional fashion. Five air cylinders are mounted on a frame which serve to indent a flexible wall so as to vary the shape of the wall and alter the dimensions of the exit orifice U.S Pat. No. 3,940,221, discloses a die with a controllable lower lip opening. A metal die block is provided with a passageway for receiving flowable material which has a lower lip portion and an upper lip. The opening between the lips can be adjusted by moving an elongated metal rod having a head. The metal rod extends through a heater block, so that when the temperature is increased, the elongated rod increases in temperature and expands. A lower end of the heated rod will then be forcibly displaced in an axial direction, to press upon flexible lip and bend downwardly slightly to narrow the gap between the lips and decrease the thickness of the sheet which is being extruded.
U.S. Pat. No. 4,279,857, discloses a shaping nozzle having a core member surrounded by a two part sleeve to define an annular passageway which terminates in an exit passage around an outwardly and downwardly flared central pin or mandrel. An outer fixed ring surrounds an inner, elastic ring which has a substantially crescent shaped interior. A wedge engages an element and an outer ring, and movement of the wedge can determine the shape of the passageway at a given axial position. An axially displaceable piston defines the size of the passageway. An elastic ring having a cylindrical inner surface defines a part of flow passageway. Also, axial displacement of a piston causes movement of a frustoconical surface that defines a wall of the passageway and is capable of changing the thickness and shape of the passageway adjacent the nozzle.
U.S. Pat. No. 4,432,718, discloses an extrusion head comprising a die core and a casing ring located within a head housing. Each die ring section is axially adjustable by positioning screws so that the lower edge boundary of the die gap will be changed. In this fashion the extruded tube material will have walls of variable thickness at predetermined points and the thickness of the extruded tube will increase or decrease as a result of changes in the outer circumference of the tube while its interior contour remains the same.
It is also desirable that when varying the outer profile that the pressure within the stream of elastomeric material remain relatively constant throughout the varying of the size of the extrusion orifice to prevent the elastomeric material from "squirting out" onto the outer surface of the tubular extrudate upon the orifice forming die moving towards and away from the open and closed positions which results in an uneven transition area and smearing of the material along the tubular extrudate. It also is desirable that the die and components thereof be formed of rigid material to enable the extrusion apparatus to have a relatively long operational life eliminating constant repair and replacement of parts due to them being subjected to the high internal pressure and friction of the moving elastomeric streams.
Certain of the prior art patents discussed above disclose an extrusion head which include means of varying the flow of material through an extrusion orifice to regulate the profile of the extrusion material. However, none of these patents disclose the specific configuration and use of a rigid metal die element having two opposed tapered surfaces, one of which regulates the size of the outer extrusion orifice and the other automatically compensates for pressure changes in the stream of elastomeric material adjacent the extrusion orifice to provide a smooth, controlled variable outer profile of a tubular extrudate as in applicants' apparatus and method steps set forth below.