Fixed-width towpreg apparatus and process

Description

RELATED APPLICATION

This application claims benefit from U.S. Provisional Application No. 60/641,749, filed Jan. 7, 2005, entitled “FIXED-WIDTH TOWPREG APPARATUS AND PROCESS,” which is incorporated herein by reference.

FIELD OF INVENTION

This invention relates to an apparatus and method for manufacturing constant-width tow fibers (“tow” or “towpreg”), which are preferably resin-impregnated.

BACKGROUND OF INVENTION

There are a number of challenges involved in manufacturing a constant-width towpreg. Conventional processes of manufacturing a resin-impregnated towpreg require that the towpreg be oscillated back and forth for spooling onto a core of a spool. As a result of handling the towpreg in this way, one of the problems is that that the resin-impregnated fiber tow tends to vary its width, particularly because it is oscillated back and forth for spooling onto the core. The present invention avoids most of the problems that typically tend to vary the tow width.

SUMMARY OF THE INVENTION

An embodiment of this invention is an apparatus for winding a towpreg, comprising a spool winding machine comprising a rod-shaped body for mounting a core of a spool, wherein the core is shuttled on the rod-shaped body to allow the towpreg to maintain a straight path substantially normal to an axis of the rod-shaped body. The apparatus could further comprise a spool shuttling carriage. The apparatus could further comprise a towpreg delivery head. The apparatus could further comprise a grooved roller that allows control of a width of the towpreg. The apparatus could further comprise a towpreg cooling device. The apparatus wherein the towpreg cooling device is a towpreg cooling tunnel. Preferably, the towpreg cooling device is a towpreg chiller. The apparatus could further comprise a towpreg width measurement device. The apparatus could further comprise a towpreg speed regulation device for regulating a travel speed of the towpreg. Preferably, the grooved roller has a groove of a desired width and rotates in a direction of travel of the towpreg at a rotational speed resulting in a surface speed at the groove that is slower than the travel speed of the towpreg.

Another embodiment is a method for winding a towpreg, comprising impregnating the towpreg with a resin and winding the towpreg on a core of a spool while simultaneously shuttling the core on a rod-shaped body to allow the towpreg to maintain a straight path substantially normal to an axis of the rod-shaped body.

DETAILED DESCRIPTION OF THE INVENTION

One of the features of the spool winder of this invention is that the packaging spool core is shuttled back and forth on a rod-shaped body, e.g., a spline-type support shaft, in a pattern-controlled motion, allowing the fiber to proceed in a straight-line substantially normal to the axis of the rod-shaped body, through the impregnation and spooling process. This facilitates accurate width control of the product, an important benefit for material that is to be used in precise fiber placement operations.

In a preferred embodiment of the towpreg process of this invention, fibers are brought from a creel through an impregnation zone. Once impregnated with resin, the towpreg is shaped to a desired width by passing the towpreg over one or more grooved rollers, with the grooved rollers rotating in the direction of fiber travel, but at a slightly slower surface speed than the travel speed of the towpreg. This differential speed provides the benefits that one could achieve by passing the towpreg over a fixed bar for width control of the towpreg, but further provides a self-cleaning feature that is absent in a fixed bar due to the rotation of the grooved rollers. Optionally, the towpreg could be passed over and under a number of fixed impregnating bars to assist impregnation of the resin between the fibers of the towpreg and, at the same time over the grooved rollers to establish a width in accordance with the dimension of the grooves of the grooved rollers.

With the towpreg at a desired width after being impregnated with resin and traversing through the groove of the grooved rollers, in one embodiment the towpreg then passes through a refrigerated tunnel where its temperature is lowed by air convection. This chilling step substantially fixes or freezes the towpreg width as it goes into the next stage of the process which could be a puller. The puller could include two or more relatively large rotating drums having grooves and sidewalls. The rotating drums could be liquid chilled and could pull the towpreg through the entire process up to the location of the rotating drums. Sidewalls on the rotating drum grooves fix the final width of the towpreg by restricting width-expansion due to fiber tension normal forces.

Variations of the preferred embodiment of this embodiment of the claimed apparatus could include a tow sizing unit, tow width measurement unit, tow heating unit, flattening/guide rollers, tow sizing wheel and pressure roller and cooling devices as those disclosed in U.S. Pat. No. 5,397,523, which is incorporated in entirety herein by reference.

The claimed apparatus could potentially be used for any fiber including glass, carbon, aramid, boron, ceramic, and basalt. With shape variations in the drum and roller grooves, the towpreg cross-section may be varied from a rectangular to an oval, each of various dimensions.

EXAMPLES

The spool winder itself could be a programmable filament-winding machine that is programmed to rotate the spool winder in a particular winding configuration. In the preferred embodiment of this invention, the oscillating carriage of the winder does not move the delivery head of the towpreg, but rather it shuttles the towpreg spool core back and forth on a spline. Shuttling of the spool core allows the towpreg to maintain a straight path. An axial stationary rotating eye head orients the fiber band properly for winding it on the traversing core.

A diagram of the apparatus of the preferred embodiment of this invention is shown in FIG. 1, wherein a resin impregnated towpreg travels from the right to the left during the process of winding the towpreg. In particular the details of the component of the towpreg winding apparatus of FIG. 1 are provided below:

(A) Width-control impregnation rollers: Heated and rotating at a slower surface speed than that of the fiber travel.

(B) Towpreg cooling tunnel: Air refrigerated and thermostatically controlled with fans to create air turbulence for increase heat transfer.

(C) Towpreg chiller/puller and fiber-length measurement: Puller has width and shape control grooves. Length measurement is accomplished with the attachment of a revolution counter or encoder.

(D) Laser micrometer tow-width measurement and/or mass measurement with commercially available gamma or beta gage mass measurement systems and data logging.

(E) Machine take-up speed-regulation dancer wheel to maintain tow tension between puller and winder.

(F) Rotating eye delivery head to orient the fiber at a proper angle for helical winding at the spool.

(G) Spool winding machine and splined shaft spindles for traversing core spooling. Multiple spindles may be used by incorporating a slip-clutch drive to all but the master spindle, to maintain tension in all spooling.

(H) Spool shuttling carriage controlled by a winding pattern for a programmed helical or circumferential wind.

Test Methods and Results

Controlled tow properties include tow width, height, density, and fiber resin ratio. Quality issues include non-wrinkling of the fibers and non-breaking of the fibers in the process. These various properties are measured by the following tests:

• • A) Weighing and measuring specific lengths of processed towpreg. With a known fiber weight per length before impregnation, this test determines fiber resin ratio as well as a towpreg density when coupled with dimensional data.
  • B) Solvent washout of the uncured resin by hanging a tow section in a laboratory cylinder of solvent. This test is used to observe fiber breakage since broken fibers will fall down in the cylinder as the supporting resin is dissolved out with a solvent such as acetone.
  • C) Panel testing. This test involves manufacturing of test panels using the produced material and then running various tests such as tension, bending, and impact, to determine strength translation of the fibers into finished products.
  • D) Fiber wet-out observation. For a towpreg to effectively function as intended, good wet-out must occur at the impregnation part of the process. Wet-out can be observed by manually pulling samples of the towpreg apart to observe dry streaks if they exist.

E) Width of the towpreg is measured with a laser micrometer and the resultant data may be recorded and analyzed. Typical data from quality control procedures is listed in the table below:

Manufacture	Process	Spool	Width	Standard
Date	Batch #	Identification	(mm)	Deviation
Aug. 30, 2005	117	1A	16.75	0.162
Aug. 30, 2005	117	1E	16.39	0.188
Aug. 30, 2005	117	2A	16.67	0.125
Aug. 30, 2005	117	2D	16.47	0.166
Aug. 31, 2005	117	3A	16.65	0.066
Aug. 31, 2005	117	3C	16.47	0.204
Sep. 1, 2005	117	4A	16.63	0.082
Sep. 1, 2005	117	4B	16.61	0.079
Sep. 1, 2005	117	5A	16.6	0.104
Sep. 1, 2005	117	5E	16.43	0.143
Sep. 12, 2005	118	1A	16.486	0.217
Sep. 12, 2005	118	1E	16.368	0.242
Sep. 12, 2005	118	2A	16.536	0.087
Sep. 12, 2005	118	2D	16.477	0.171
Sep. 13, 2005	118	3A	16.578	0.105
Sep. 13, 2005	118	3C	16.56	0.145
Sep. 13, 2005	118	4A	16.604	0.096
Sep. 13, 2005	118	4B	16.542	0.174
Sep. 13, 2005	118	5A	16.597	0.154
Sep. 13, 2005	118	5B	16.447	0.203
Sep. 14, 2005	118	6A	16.63	0.108
Sep. 14, 2005	118	6D	16.376	0.172
Sep. 14, 2005	118	7A	16.62	0.111
Sep. 14, 2005	118	7C	16.59	0.113