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 "blow-up" 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 "blown-up" 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.