Apparatus and method for handling extruded tubes

The present invention relates generally to the manufacture of extruded tubes and, more particularly, concerns an apparatus and method for handling freshly extruded tubes in order to avoid damaging them or distorting their shape.

Optical fiber is produced by drawing a glass structure known as a “preform.” The preform may include a substrate tube and an over cladding tube, which need to have a precise size and shape in order to assure the quality of the ultimate fiber. These tubes have typically been manufactured by high-temperature deposition, drill, and draw or by a casting process, but such processes are relatively slow and the latter requires the simultaneous casting in hundreds of molds to produce a sufficient quantity of tubes to make the process commercially feasible.

It would therefore be desirable to manufacture these silica tubes by an extrusion process which would be relatively continuous and, therefore, faster and more efficient than the casting process.

The extrusion process, however, introduces its own complications. The relatively thin-walled tubes (about 40 millimeters in diameter with a wall thickness of about 5 millimeters) are extruded to a length of about 6 feet in order for the process to be practical, and are in a relatively soft state when first extruded. Moreover, the tubes must be handled extremely carefully in order to avoid damaging their surface or distorting their shape. In particular, the tube must not only be supported as it leaves the extruder, but must be supported on a moving surface which draws it away from the nozzle of the extruder. This is necessary in order to assure that the tube exiting by the extruder does not stick to the supporting surface and thereby become distorted or damage. Ceramic extruded tubes have been handled on inclined conveyor belts, but the silica tubing is too delicate and must meet far too stringent structural requirements to be subjected to such treatment. In addition, it is then necessary for each extruded length of tube to be supported and protected while it is carried away to a dryer. In the dryer, the tubes are typically supported on rotating rollers and dried for one or two days. The rotating rollers not only assure uniform drying, but guarantee that flat spots are not formed in the tubing.

In accordance with the present invention, a tube take-up apparatus is provided to handle a length of extruded tube. The apparatus includes an elongated housing which is removably securable to the extruder nozzle at a near end and extends away from it. A pair of parallel, spaced-apart rollers of a diameter approximately equal to the diameter of the extruded tubing extend along the length of the housing in a position just below the extruded tubing. The housing is removably mounted on an elongated supporting fin which is secured to the extruder at its near end and extends upwardly between the two rollers and substantially along the entire length of the housing. The supporting fin is, in turn, mounted on a fixed supporting base at its remote end. In operation, a fin ribbon made of a non-stick material, such as teflon, is supported on the upper edge of the supporting fin, and the tube is deposited on top of the ribbon as it is extruded. Simultaneously, the ribbon is drawn away from the extruding nozzle, so as to assist in drawing the extruded tube away from the nozzle and to prevent it from scraping along the supporting surface. The housing is dimensioned so that a full length of extruded tubing will fit in it. After the full length has been extruded, the housing and rollers as a unit are lifted from the supporting fin and are carried away as a unit to a dryer, with the extruded tube supported on the two rollers. Preferably, the axles of the rollers extend from the remote end of the housing and are adapted to be coupled to a motor which will drive them into rotation. The tube may therefore be dried directly within the housing, without any additional handling. In order to accommodate the next extruded tube, another housing/roller assembly is mounted on the supporting fin as the original one is removed, and the next tube is extruded.

The preceding brief description, as well as other objects, features and advantages of the present invention will be understood more completely from the following detailed description of presently preferred embodiment, with reference being had to the accompanying drawings, which:

FIG. 1 is a perspective view of a preferred embodiment of an apparatus for handling extruded tubing in accordance with the present invention;

FIG. 2 is an exploded view of the apparatus of FIG. 1, further including an extruded tube; and

FIG. 3 is an edge view, on enlarged scale with the housing removed, showing the relationship between the rollers, an extruded tube, and the support fin when the housing is mounted on the support fin.

Turning now to the details of the drawings, FIG. 1 is a perspective view of an extruded tube take-up and handling apparatus 10 embodying the present invention, and FIG. 2 is an exploded view thereof. Apparatus 10 broadly comprises a supporting fin 12 , a pedestal 14 , and a housing/roller subassembly 16 . In use, the near end of supporting fin 12 is secured to the tubular nozzle of an extruder through an appropriate clamping fixture 20 , and the remote end is supported on pedestal 14 . Housing subassembly 16 is constructed to fit over fin 12 and to be mounted thereupon with the fin extending upwardly between rollers 30 , 30 (see FIG. 3 ). In this manner, housing subassembly 16 is secured and retained in position upon fin 12 .

Fin 12 and pedestal 14 are preferably made of a sturdy metal material, such as steel or aluminum. The near end 12 a of fin 12 has a clamping fixture 20 mounted thereon by conventional means, such as rivets or screws. Similarly, the remote end 12 b of the fin is mounted to an upright component 14 a of pedestal 14 , also by conventional means, and component 14 a is secured upon a base component 14 b . For reasons to be explained further below, clamping fixture 20 is provided with a through-notch 20 a , which provides clearance above fin 12 . In the drawings, fixture 20 is shown with a top portion 22 pivoted to an open position. However, those skilled in the art will appreciate that the top portion 22 may be pivoted forward and downwardly to a closed position around the nozzle of an extruder and securely retained in place by conventional means, not shown. It will be appreciated that the cylindrical recesses in the two parts of clamping fixture 20 must be shaped to receive the extruding nozzle. For reasons which will become apparent below, the upper edge 12 c of fin 12 is perfectly formed so as to be cylindrically concave, with a curvature that matches the outside curvature of the extruded tube 50 .

Housing/roller subassembly 16 includes a housing 40 , preferably fabricated from sheet metal. The rollers 30 , 30 are mounted for rotation lengthwise in the housing by having their axles 32 protrude through bearings in appropriate bores 40 a in housing 40 . At its remote end, each roller 30 has a gear 34 mounted thereon exterior of the housing. For example, the end of spindle 32 could be made square and the gear 34 provided with as conforming square opening allowing for a press fit. In addition, a gear 36 is mounted for rotation on the exterior of housing 40 so as to be in engagement with the gears 34 , 34 . As best seen in FIG. 3, the rollers 30 , 30 are spaced far enough apart to permit fin 12 to slip freely there between.

As best seen in FIG. 2, housing 40 is provided at its forward end with a keyhole-shaped cutout 42 . The upper portion of cutout 42 is a circular opening 42 a positioned to align with the extruder nozzle. The lower portion 42 b of cutout 42 is dimensioned to be received snugly over fin 12 , and above portion 42 b , the width of the opening is reduced. Cutout portion 42 b and the reduced width portion are repeated at the remote end of housing 40 .

In use, housing 40 is slipped over fin 12 and pressed down thereupon, with cutout portions 42 b limiting the downward movement of the housing. In this position, the extruder nozzle is aligned with cutout portion 42 a and the clamping fixture 20 is secured thereupon. The apparatus 10 is then ready to take-up the tube 50 during extrusion.

As best seen in FIG. 3, the upper surface 12 c of fin 12 is formed so as to be cylindrically concave and to confirm to the curvature of the extruder tube 50 . A ribbon 15 , preferably made of a non-stick material, such as teflon, is provided on the upper edge 12 c of fin 12 and is moved along the top edge, away from the extruding nozzle at the same rate that the tube 50 is extruded. Preferably, ribbon 15 is provided as a closed loop and is driven into movement by conventional means, or by movement of the tube 50 itself.

In operation, the extruding nozzle deposits tube 50 upon ribbon 15 , and the forward end of tube 50 is moved gently towards the remote end of the housing as it is extruded. After the full length of tube 50 has been extruded, the housing/roller assembly 16 may be lifted from fin 12 , whereby the rollers lift the tube off the ribbon, and replaced by another, empty housing. Extrusion of another tube may then begin immediately. The housing with the extruded tube in it may then be conveniently carried to a dryer and left within the dryer for a period of days. During that time, a motor drive would be coupled to gear 36 , whereby tube 50 is gently rotated during drying.

It will therefore be appreciated that subassembly 16 provides a protective environment for tube 50 from the moment that its extrusion begins until the moment that it is fully hardened. During that time, subassembly 16 makes it possible to handle and transport the tubing without danger of damage or distortion to it. Furthermore, the tubing is conveniently placed within a dryer and subjected to the usual rolling action without handling it at all. Best of all, the present invention permits relatively continuous extrusion of the silica tubes.

Although preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that many additions, modifications and substitutions are possible, without departing from the scope and spirit of the invention as defined by the accompanying claims.