Expandable collet
BACKGROUND OF THE INVENTION 
     Strand material is typically collected on a winder by winding the strands around a tube carried by a rotating collet. In the case of glass strads, glass filaments are attenuated through bushing tips or orifices at the bottom of a heated bushing containing molten glass. The filaments as they are attenuated are coated with a binder and/or size by passing the filaments across the surface of an applicator, which is constantly wetted with the binder and/or size to be applied. The filaments are then gathered into a unified strand by a gathering shoe, which is typically a grooved wheel or cylinder. The resulting strand may then be traversed in a vehicle riding in a cam or across the face of a roatating spiral and collected as a forming package on a forming tube carried by a rotating collet. 
     It is necessary to firmly hold the forming tube onto the face of the collet to avoid slippage of the tube as the collet is rotating. This is necessary, since the rotation of the tube with the forming package thereon provides the attenuative forces for the formation of the filaments. Filament diameter is directly proportional to the tension on the filaments from the rotating collet. Should the forming tube slip, uneven tension will be transmitted to the filaments and thus uneven strand diameter results. This produces an unacceptable product. 
     Several solutions to this problem have been employed by the prior art. A first solution is to form the face of the collet of a plurality of fingers which ride within slots or grooves and which are designed to expand outwardly from the collet due to centrifugal force when the collet is rotated. Thus, the face of a collet itself expands to firmly grasp the forming tube. An example of such a collet can be found in U.S. Pat. Nos. 2,891,798; 3,544,016 and 3,871,592. While this solution is satisfactory for collets having a large diameter, as, for example, 12 inches (30.5 centimeters) or more and rotated at high speeds, such a solution is unsatisfactory for collets of smaller diameter, i.e., in the order of 5 inches (12.7 centimeters) and rotated at slower speeds, as is often the case with larger diameter filaments, since the centrifugal forces necessary to expand the fingers is often insufficient. Further, when centrifugal force alone is employed to expand the collet surface and gravity is employed to retract the fingers forming the collet surface, it is clear that the fingers below the horizontal center line of the collet will not retract, due to the gravitational forces pulling downward on these fingers and thus maintaining these fingers in an expanded state. 
     A second possible solution which is commonly employed is to form the collet, or a portion thereof, of an expandable material and &#34;blow-up&#34; the collet by fluid pressure. This solution takes two forms. In one form, a bladder or hollow tube of expandable material forms at least a portion of the outer part of the collet and is expanded to firmly grasp the tube placed thereon. Typical of this form are U.S. Pat. Nos. 2,289,453; 2,621,867; 3,139,242; 3,394,902 and 3,834,257. 
     The other form which this solution may take is to form the collet having an interior tube or bladder which is expanded by air pressure to cause a plurality of protrusions located at the surface of the collet to be forced beyond and protrude from the surface of the collet by the bladded or tube when it is expanded. Typical of this solution are U.S. Pat. Nos. 2,215,069; 3,104,074 and 3,127,124. 
     A problem common to both forms of the fluid pressure solutions is that these collets tend to be unevenably balanced when expanded. This results in an eccentric rotation of the collet and the forming package and tube being carried thereon and thus the forming package will produce an uneven tension on the strand and an uneven diameter strand. This effect becomes even more pronounced as the collet speed is increased and thus the collet readily becomes unacceptable for the collection of glass strands. Further, if gravity alone is employed to retract the collet fingers, when they are employed in combination with a bladder, once again those fingers below the horizontal center line of the collet will not retract. 
     In U.S. Pat. No. 2,801,858, an expandable collet is disclosed which has a single expandable element which is expanded by compressing it at its ends to expand its diameter as its width is decreased. This is accomplished by manually forcing compaction elements towards each other to compress the expandable element therebetween. This type of collet is evenly balanced when expanded. This solution is useful, however, it requires an operator to manually force the compaction elements together, which has been found to be a time-consuming and thus inefficient operation. This method is also employed in U.S. Pat. No. 3,165,279, where the expandable element is extended by forcing a compaction element into it to expand its surfaces outwardly. This, too, requires a manual operation to accomplish the result. 
     In copending U.S. application Ser. No. 701,394, a winder is disclosed in which a plurality of expandable rings are interleaved interleaved with a plurality of unexpandable spacers, with fluid pressure being employed to expand and contract the diameter of the rings and firmly grasp a forming tube. This winder has an uneven surface along its length due to the fact that the forming tube only contacts the outer surface of the expanded rings when they are in their expanded state. Because of this, the forming tubes which must be employed are heavy cardboard tubes which, in order to remove the forming package from the tube after winding, must be destroyed, such as by unwinding the spirally wound cardboard employed to form the tube, crushing the tube, and the like. 
     It is desirable, therefore, to produce a collet having a relatively even surface so that thin-walled forming tubes, such as paper forming tubes, which can easily be removed from the forming package by folding the tube and which may thus be reused several times before discarding, may be employed. 
     It is also desirable, therefore, to produce an expandable collet having the advantages of being evenly balanced to produce a uniform rotation, having the quickness of expansion found in the &#34;blown-up&#34; collets to conserve time in doffing and replacing the forming tube and thus reduce costs and increase efficiency, and to produce a collet which has a relatively smooth surface of the expandable finger type to allow thin-walled forming tubes to be placed thereon for collection of the strand while providing for complete retraction of the fingers when the collet is not being rotated to allow the forming tubes to be placed thereon and removed therefrom easily. 
     THE PRESENT INVENTION 
     The present invention combines the ease of operation of airoperated expandble collets with the precise rotation found in the manually expanded collets, while providing a relatively smooth surface and allowing the use of thin-walled forming tubes by employing expanding fingers. The collet of the present invention comprises a sealed chamber into which a fluid may enter under pressure, a piston which reacts to the fluid pressure, a plurality of expandable rings, a plurality of spacers between the rings and at the end of the rings opposite the piston, a plurality of expandable fingers surrounding the rings and spacers and means for connecting the fingers to the rings. The piston, rings, spacers and fingers are all carried along a common shaft around which they are rotated and are so arranged that, upon introducing a fluid under pressure into the sealed chamber, the piston and spacers transfer this pressure to the expandable rings. This pressure on the rings causes the rings and the fingers to expand and the fingers to firmly grasp a tube, such as a thinwalled paper forming tube. Upon release of the fluid pressure, the pressure is relieved from the expandable rings, causing the rings to return to their original size and shape, with the means connecting the rings and the fingers exerting a force on the fingers to return them to their unexpanded state and release the tube. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The expandable collet of the present invention can best be described with reference to the accompanying drawings in which: 
     FIG. 1 is a side elevational view, partly in section, of the collet of the present invention; and 
     FIG. 2 is a cross-sectional view taken through line 2--2 of FIG. 1, illustrating the expandable collet of the present invention both in its expanded and unexpanded states. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Turning now to the figures, the expandable collet of the present invention is generally illustrated as 10. The collet 10 is connected to a winder 12 through shaft 19 around which the collet 10 rotates. The shaft 19 is connected to a motor, not shown, within the winder 12, the motor supplying the rotational forces for the collet 10, and surrounds a stationary supporting shaft 17. The collet 10 includes a fluid inlet 16, such as a sealed valve, which is detachably connected at one end to a source of fluid under pressure, not shown, and at its other end to a fluid chamber 18. The fluid chamber 18 is internally sealed. As th fluid under pressure enters the sealed chamber 18, and the internal pressure within the chamber 18 increases, piston 20, due to the fluid pressure within the chamber 18, presses against expandable ring 30. Piston 20 is connected to a spring 24 which returns piston 20 to its original position upon release of fluid pressure. Stop 26 limits the unexpanded position of the piston 20. 
     Adjacent to piston 20 are a plurality of expandable rings 30 which are separated by spacers 32 between them and at the end of the collet 10 opposite piston 20. As the fluid pressure builds, forcing the piston 20 toward the expandable rings 30, these rings, which are typically solid rubber rings or doughnuts having a central opening with metal rings 28 fitted therein, increase in diameter and decrease in width. This also decreases the distance between the outside ends of the outermost rings 30. The spacers 32, which are typically formed of a material such as brass, stainless steel or aluminum, are unable to expand, and thus distribute the force equally on the rings 30. As can be seen in FIG. 1, the spacers 32 are designed in shape to exert pressure only on the rubber rings 30 and not on the metal insert rings 28. Thus, as shown, the spacers 32 may be cut out in the area of the metal rings 28. As the rings 30 expand, they exert an outward force on the metal fingers 40 and expand these fingers to tightly grasp a forming tube 34 which is surrounding them. As can best be seen in FIG. 2, the outward expansion of each of the fingers 40 is limited to the height of the opening or slot 46 in the spacers 32 through which connecting members 42 pass minus the diameter of the connecting members 42. The purpose of these connecting members will be more fully described below. The tube 34 may be a relatively thick-wall tube formed of a material such as cardboard, but is preferably a thin-walled tube formed of a material such as paper, which tube may be reused several times to form a plurality of packages before being discarded. The spacers 32 and the expandable rings 30 are carried by the shaft 19 and rotate with it. The piston 20, the spacers 32, and the rings 30 are slideably mounted on shaft 19, except for the spacer (not shown) at the end opposite the piston 20, which is preferably fixed in position. 
     As previously mentioned, as the rings 30 expand in diameter, they decrease in width. Thus, gap 50 is provided between adjacent fingers 40 to allow for this contraction. When the collet 10 is expanded, this gap 50 decreases and, in fact, the fingers 40 could meet, aiding in providing a smooth surface to the expanded collet 10. However, a small gap 50 between adjacent fingers 40 during winding will not adversely affect the operation of the collet 10. Likewise, the longitudinal slots or gaps 52 between adjacent fingers 40 do not adversely affect the operation of the collet 10. 
     When a complete forming package has been formed and it is desired to remove the forming package from the collet 10, fluid pressure is released from the fluid inlet 16, thus equivalently decreasing the pressure on the piston 20, the spacers 32, and the expandable rings 30. The spring 24 forces piston 20 into its unexpanded position, further relieving pressure on the expandable rings 30 and allowing them to return to their unexpanded state, i.e., with an increased width and decreased diameter. 
     When the rings 30 are retracted, the fingers 40 are also retracted. This is accomplished by means of connecting rods 42. These rods pass through the fingers 40 and spacers 32 and are embedded within or otherwise attached to the rings 30. As the rings 30 return to their unexpanded state, the rings 30 exert a pulling force on the connecting rods 42, which force is then transferred to the fingers 40 to return them to their unexpanded state. This loosens the grasp on the forming tube 34 and allows the operator to remove tube 34 with the accompanying forming package of strand thereon. 
     Further pressure to retract the fingers 40 may be placed on the connecting rods 42 by means of O-rings 44. These rings, which are typically formed of elastomeric materials, such as rubber, also expand as the rings 30 expand and the connecting rods 42 push against these rings. When, however, the rings 30 are retracted, the elastic force of the O-rings 44 against the connecting rods 42 aid in retracting these rods and the fingers 40. 
     The complete pressurization of the collet to grasp the forming tube 34 may take place in a time period of about 0.5 to 1.5 seconds, with a fluid pressure ranging from about 30 to about 55 psig (204,082 to 374,150 pascals). The depressurization may take place in about 1 to 3 seconds. The fluids which may be employed to pressurize the system include liquid fluids, such as water, but preferably are gaseous fluids, such as nitrogen, oxygen, helium, carbon dioxide, and especially air. 
     From the foregoing, it is obvious that the collet of the present invention provides an effective means for collecting strand materials, such as glass strands, which is free from the problems encountered in the collets of the prior art. 
     While the invention has been described with reference to certain specific embodiments thereof, it is not intended to be so limited thereby, except insofar as in the accompanying claims.