Title:
Continuous filament mat and method of making
Kind Code:
A1


Abstract:
The present invention provides an improved method of forming continuous filament mat (CFM) at greater through-put while maintaining or improving product quality by use of a synchronized draw process. The synchronized draw process provides CFM having improved weight variation, structure and tensile strength is capable of operating at increased mat line speed. CFM produced may have controlled mat density, MD density variation, CM density variation, MD tensile strength and CM tensile strength by controlling the period, frequency and interval of the deposited fiber strands. Using the synchronization technology of the present invention it is possible to control the tensile strength ratio (MD/CD) to meet a specific customer need by adjusting the LFR, frequency, period, and line speed. The method of the present invention provides for increasing the throughput of specialized and costly CFM manufacturing equipment without substantial expenditure.



Inventors:
Lin, Jeng (New Albany, OH, US)
Galloway, Eugene V. (Anderson, SC, US)
Peel, Frank (Fergus, CA)
Larsen, Axel (Guelph, CA)
Application Number:
11/014387
Publication Date:
06/22/2006
Filing Date:
12/16/2004
Primary Class:
Other Classes:
442/351, 442/348
International Classes:
D04H13/00; D04H1/00
View Patent Images:



Primary Examiner:
BOYD, JENNIFER A
Attorney, Agent or Firm:
OWENS CORNING (GRANVILLE, OH, US)
Claims:
We claim:

1. A continuous filament mat having a predetermined fiber lay down pattern.

2. The continuous filament mat of claim 1, wherein the predetermined fiber lay down pattern comprises: a plurality of fiber groups laid in a pattern having a predetermined interval.

3. The continuous filament mat of claim 2, wherein the predetermined fiber lay down pattern further comprises: a plurality of fiber groups laid in a pattern having a period (P) on a forming conveyor from a number (N) forming positions, wherein the interval is equal to P/N.

4. The continuous filament mat of claim 3, wherein the predetermined fiber lay down pattern comprises: a plurality of fiber groups laid in a pattern having a number of plies, each ply having a predetermined interval.

5. The continuous filament mat of claim 4, wherein the predetermined interval is equal among all plies.

6. The continuous filament mat of claim 4, wherein the predetermined interval of a first ply is not equal to the predetermined interval of a second ply.

7. The continuous filament mat of claim 4, wherein the predetermined fiber lay down pattern comprises: a number of plies (X), each ply having a period P on a forming conveyor from N/X forming positions, wherein the interval is equal to P/(N/X).

8. The continuous filament mat of claim 1, wherein the predetermined fiber lay down pattern comprises: a plurality of fiber groups laid in a pattern having a number of plies, each ply having a predetermined interval.

9. The continuous filament mat of claim 1 wherein the predetermined fiber lay down pattern comprises: a plurality of fiber groups laid in a pattern having a predetermined period and interval.

10. The continuous filament mat of claim 1, wherein the continuous filament mat has a tensile strength in the machine direction (MD) and in the cross machine (CM) direction and the MD tensile strength is at least 70% of the CM direction tensile strength.

11. The continuous filament mat of claim 1, wherein the continuous filament mat is formed of glass fibers.

12. The continuous filament mat of claim 1 1, wherein the glass fibers are selected from the group consisting of A-type glass fibers, C-type glass fibers, E-type glass fibers, S-type glass fibers, ECR-type glass fibers.

13. The continuous filament mat of claim 1, wherein the continuous filament mat is formed of fibers selected from the group consisting of mineral fibers, glass fibers, carbon fibers, basalt fibers, polymer fibers, nylon fibers, polyester fibers, polyamide fibers, aramid fibers, PVC fibers, PVAC fibers, melamine fibers, acrylic fibers, visil fibers, natural fibers, staple fibers, chopped fibers and mixtures thereof.

14. A continuous filament mat having a tensile strength in the machine direction (MD) and in the cross machine direction (CM), wherein the MD tensile strength is at least 70% of the CM tensile strength.

15. The continuous filament mat of claim 14, further comprising: a predetermined fiber lay down pattern.

16. The continuous filament mat of claim 15 wherein the predetermined fiber lay down pattern comprises: a plurality of fiber groups laid in a pattern having a predetermined interval.

17. The continuous filament mat of claim 16, wherein the predetermined fiber lay down pattern comprises: a plurality of fiber groups laid in a pattern having a period (P) on a forming conveyor from a number (N) forming positions, wherein the interval is equal to P/N.

18. The continuous filament mat of claim 17, wherein the predetermined fiber lay down pattern comprises: a plurality of fiber groups laid in a pattern having a number of plies, each ply having a predetermined interval.

19. The continuous filament mat of claim 18, wherein the predetermined fiber lay down pattern comprises: a number of plies (X), each ply having a period P on a forming conveyor from N/X forming positions, wherein the interval is equal to P/(N/X).

20. The continuous filament mat of claim 14, wherein the continuous filament mat is formed of glass fibers.

21. The continuous filament mat of claim 20, wherein the glass fibers are selected from the group consisting of A-type glass fibers, C-type glass fibers, E-type glass fibers, S-type glass fibers, ECR-type glass fibers.

22. The continuous filament mat of claim 14, wherein the continuous filament mat is formed of fibers selected from the group consisting of mineral fibers, glass fibers, carbon fibers, basalt fibers, polymer fibers, nylon fibers, polyester fibers, polyamide fibers, aramid fibers, PVC fibers, PVAC fibers, melamine fibers, acrylic fibers, visil fibers, natural fibers, staple fibers, chopped fibers and mixtures thereof.

23. A method of manufacturing a continuous filament mat comprising the steps of: drawing plurality of groups of fibers from a plurality of fiber sources, and depositing a plurality of fiber groups in a predetermined fiber lay down pattern on a forming conveyor.

24. The method of manufacture of claim 23, further comprising the step of: determining an interval between the plurality of fiber groups on the forming conveyor, and depositing said plurality of fiber groups on said forming conveyor, each of said fiber groups being spaced from an adjacent fiber group by said interval.

25. The method of manufacture of claim 24, further comprising the step of: altering the predetermined interval.

26. The method of manufacture of claim 24, further comprising the step of: measuring a material property of the continuous filament mat and altering said interval in order to alter said material property.

27. The method of manufacture of claim26, wherein said material property is selected from the group consisting of mat density, MD weight variation, CM weight variation, MD tensile strength and CM tensile strength.

28. The method of manufacture of claim 23, wherein the predetermined fiber lay down pattern comprises: a plurality of fiber groups laid in a pattern having a period (P) on a forming conveyor from a number (N) forming positions, wherein the interval is equal to P/N.

29. The method of manufacture of claim 28, wherein the predetermined fiber lay down pattern comprises: a plurality of fiber groups laid in a pattern having a number of plies, each ply having a predetermined interval.

30. The method of manufacture of claim 29, wherein the predetermined fiber lay down pattern comprises: a number of plies (X), each ply having a period P on a forming conveyor from N/X forming positions, wherein the interval is equal to P/(N/X).

31. The continuous filament mat of claim 23, wherein the continuous filament mat is formed of glass fibers.

32. The continuous filament mat of claim 31, wherein the glass fibers are selected from the group consisting of A-type glass fibers, C-type glass fibers, E-type glass fibers, S-type glass fibers, ECR-type glass fibers.

33. The continuous filament mat of claim A23, wherein the continuous filament mat is formed of fibers selected from the group consisting of mineral fibers, glass fibers, carbon fibers, basalt fibers, polymer fibers, nylon fibers, polyester fibers, polyamide fibers, aramid fibers, PVC fibers, PVAC fibers, melamine fibers, acrylic fibers, visil fibers, natural fibers, staple fibers, chopped fibers and mixtures thereof.

34. A method of manufacturing a continuous filament mat comprising the steps of: drawing plurality of groups of fibers from a plurality of fiber sources, and depositing a plurality of fiber groups in a predetermined fiber lay down pattern on a forming conveyor, said fiber lay down pattern including pattern having a predetermined period, frequency and interval.

35. The method of manufacture of claim 35, further comprising the step of: measuring a material property of the continuous filament mat and altering said predetermined pattern in order to alter said material property.

36. The method of manufacture of claim 35, wherein said material property is selected from the group consisting of mat density, MD weight variation, CM weight variation, MD tensile strength and CM tensile strength.

37. The method of manufacture of claim 35, wherein one or more of the predetermined period, frequency and interval are altered in order to alter said material property.

38. The method of manufacture of claim 37, wherein the frequency is altered in order to alter the ratio between MD tensile strength and CM tensile strength.

Description:

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates to an improved continuous filament mat (CFM) having improved weight variation along the length of the mat and a method of making such a mat.

BACKGROUND OF THE INVENTION

Continuous Filament Mat (CFM) is a continuous reinforcement fiber, non-woven mat containing a resin compatible binder. CFM is used with polyester, vinyl esters urethanes and other compatible resin systems. It includes continuous fibers randomly oriented in multiple layers with a suitable bonding resin and typically contains a silane coupling agent. CFM is particularly suitable for compression molded electrical and non-electrical laminates, as well as for use in pultrusion processes or any process in which a smooth surface is desired. CFM is used in many fiberglass reinforced plastic (FRP) structural applications such as: compression molding, infusion molding, filament winding, pultrusion, reaction injection molding (RIM), resin transfer molding (RTM), and vacuum bagging. The finished molded products have high equiaxial strengths. Typical products are marine railings, window frames, boat parts, high voltage transformers and corrosion resistant pipes. CFM may also be combined with a woven roving to make a combination mat that has superior processability and structural properties. The reinforcing filaments typically thermoplastic fibers such as glass or polymeric fibers; however, any fiber such as carbon and aramid fibers may be used. For the purposes of the present application, the invention will be described using glass fibers as an example.

Compression molding is a mass production method where molding compounds and other resin glass combinations are compressed in matched metal tools located between platens in a press. Typically, pressures of 150 lbs/in2 and temperatures between 265° F. (130° C.) and 340° F. (170° C.) are used to achieve cycle times of 2-3 minutes. Molding compounds of a thermoset resin, chopped roving, fillers and a catalyst are used in sheet molding compound (SMC). SMC is placed in the tool and covered with a layer of CFM to produce a Class A surface on parts such as automotive body panels, appliance housings and composite doors,

Infusion molding processes such as vacuum assisted resin transfer molding (VARTM) use a single-sided mold that is covered with CFM and other reinforcements and sealed with a flexible vacuum bag or film. A vacuum is drawn on the space between the mold and the seal containing the reinforcements, and a thermoset resin is allowed to infiltrate the reinforcements. The resin flows through the reinforcements and cures to form the finished composite. Large high reinforcement content structural composite parts can be produced to make parts such as boat hulls and windmill blades.

Pultrusion is a continuous process for making lightweight lineal profiles such as reinforcing rods, I-beams and tubing. Pultruded parts incorporate a variety of reinforcements ranging from TYPE 30 single-end roving (available from Owens Corning of Toledo, Ohio), bulky roving, surfacing veils, CFM and woven glass fabrics. After the reinforcement is impregnated with resin, the material is pulled through a heated die that gives it a cross-sectional shape, and is then cured to create the composite profile.

Resin Transfer Molding (RTM) is a liquid molding process where a thermosetting resin is injected into a closed mold cavity to make moderate volume semi-structural or appearance parts. CFM, fabrics, multi-end preform rovings, veils, chopped strand mat and directed fiber preforms can be used in resin transfer molding as reinforcements. In RTM, the dry fiber reinforcement is placed in the bottom half of matching molds, the mold is closed and sealed, and then resin is slowly pumped into the mold. The resin wets through the reinforcement fibers and solidifies to form a composite part such as semi-truck parts and electrical cabinets. The molding pressure is typically lower in RTM than in the compression molding process, therefore, tooling and equipment capital costs are lower than high volume compression molding, but higher than open molding processes.

Vacuum bagging is used to tightly consolidate composites used in windmills, aerospace parts and other applications. Materials that are pre-impregnated with resin are typically laminated with vacuum bagging. The components include a film or fabric, breather medium and plastic film that is applied in sequence on top of a laminate stack in an airtight mold. Air between the mold and film is extracted with a vacuum pump, resulting in a positive-pressure force. This compression forces air and excess resin from the composite laminate or components. Vacuum bagging is also used in conjunction with other processes such as infusion molding and wet lay-up.

CFM is formed by reciprocally depositing continuous reinforcing filaments across the width of a moving conveyor. Typically, a CFM line includes 6-20 fiber draw positions from a source that randomly deposit the fibers across the width of the conveyor. The fiber draw positions may include an idler wheel, a pull wheel and an oscillating finger wheel within the pull wheel. Fibers are drawn from the fiber source, around the idler wheel and over the pull wheel. The oscillating finger wheel penetrates the pull wheel to determine the angle at which the fibers are thrown from the wheel and hence, the position across the width of the conveyor. As the finger wheel oscillates, the fibers are deposited on the conveyor in a saw-tooth pattern having defined period (P). The fibers are thrown from the pull wheel faster than the fibers traverse the width of the conveyor so that the fibers form loops on the conveyor. As shown in EQ. 1, the loop formation ratio (LFR) is proportional to the pull speed (Sp) of the fibers divided by the throw length (L) and the frequency (f). As shown in EQ. 2, the period (P) is proportional to the mat line speed Sml, divided by the frequency (f). LFR=Sp/(2Lf)(1)P=Sml/f(2)

In prior art CFM processes each draw position deposits the fibers independently of the other draw positions in the line. FIG. 1A shows a graph of the relative weight verses the location in the machine direction of a CFM mat produced on a 12 draw position line at a frequency of 60 oscillations per minute (OPM), a line speed of 33 feet per minute (FPM), and a period of 6.5 inches. The peak to valley weight variation along the length of the mat ranges from 8-18 % by weight.

As the LFR approaches 10, the fibers are deposited in random loops on the collection conveyor. With a decreasing LFR, the loops become less random and the fibers tend to lie transverse to the length of the collection conveyor. At an LFR of 3.25 a distinct transverse array becomes visible and at a LFR of less than about 2.5 the fibers are substantially transverse to the collection conveyor. A high LFR is preferred in CFM because the random loop pattern increases the tensile strength of the mat. A lower LFR provides a mat having a higher tensile strength in the cross-machine direction and a decreased tensile strength in the machine direction.

In the prior art CFM processes, weight distribution in the mat was related to the mat line speed (Sml) and period. Increased mat line speed increased the variation in weight distribution. In order to control the variation, frequency (f) was increased; however, with increased frequency the loop formation ratio decreases and hence the fibers are deposited on the collection conveyor in relatively straight arrays rather than being deposited in loops. In the prior art processes, a period in excess of about 180 mm causes a standard deviation of the weight of the mat in the machine direction to increase above about 2.2, which a variation that is not acceptable for use in a number of composite fabrication processes. Since an increased mat line speed (Sml) increases the oscillation period (P), the maximum line speed is governed by the weight distribution acceptable for use in the composite fabrication process.

FIG. 1A shows the weight distribution in the machine direction of CFM manufactured in accordance with the prior art process. The CFM line includes 12 draw positions each operating at random, the frequency (f) is 60 OPM with a line speed of 33 FPM with a period of 6.5 in. The mat is built up from the 12 draw positions which are independent of one another and provide a peak to valley variation in weight that ranges from 8% to 18%. This variation in weight is increased when fiber draw positions are taken off-line due to equipment failures or for maintenance.

The limitations on frequency (f), LFR and mat line speed (Sml) prevent the prior art CFM process from producing mat having a suitable tensile strength at commercially desirable high speeds. New technologies in the composite glass industry, such as gas-oxygen fired furnaces, have increased the melting capacity of furnaces used to produce glass fibers. The increased melting capacity has created a bottleneck in the production line at the CFM line. Additional CFM lines require substantial capital and it is desired to utilize the additional melting capacity while avoiding the capital cost of building new fiber forming and CFM lines.

SUMMARY OF THE INVENTION

The present invention provides an improved method of forming continuous filament mat at greater through-put while maintaining or improving product quality by use of a synchronized draw process. The synchronized draw process provides CFM having improved weight variation is capable of operating at increased mat line speed (Sml) and provides CFM having improved structure and tensile strength.

The synchronized draw process may be performed on a standard CFM line with little additional hardware and hence at low cost. The additions to the CFM line include a master PLC 50 that is in communication with forming position 12 via PLC linkage 52. The synchronized draw process may also include a master encoder 54 downstream from the forming position 12 to provide conveyor speed and position data to the master PLC 50 so that the forming position 12 may be individually controlled.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1A is a graphical representation of the weight distribution in the machine direction of CFM manufactured in accordance with a prior art process.

FIG. 1B is a graphical representation of the weight distribution in the machine direction of CFM manufactured in accordance with one aspect of the present invention.

FIG. 2 is an elevation view of a forming position of the present invention including an oscillating servo drive.

FIG. 3 is a schematic view of the CFM line of the present invention including a master PLC in communication with forming position via PLC linkage.

FIG. 4A and 4B are of the profile of fibers deposited on a forming conveyor in the manufacture of a CFM in accordance with the present invention.

FIG. 4C is a graphical representation of the pattern of the fibers on the forming conveyor which is built up to form the CFM of the present invention.

FIG. 5 is a graphical representation of the standard deviation of the weight distribution in the machine direction versus the period (P) of CFM manufactured in accordance with the prior art process and in accordance with the present invention.

FIG. 6A is a graphical representation of the cross machine and machine direction tensile strength of CFM manufactured, at various periods, in accordance with a prior art process and in accordance with the present invention in both a 2×6 synchronized process and a 1×12 synchronized process.

FIG. 6B is a graphical representation of the cross machine and machine direction tensile strength of CFM manufactured, at various oscillation frequencies, in accordance with a prior art process and in accordance with the present invention in both a 2×6 synchronized process and a 1×12 synchronized process.

DETAILED DESCRIPTION AND PREFERED EMBODIMENTS OF THE INVENTION

The improved continuous filament mat of the present invention as shown and described herein provides a lower weight variation and is capable of increased and less expensive manufacture by increasing the through-put of a CFM line. The improved product quality and line speed is achieved by use of a synchronized draw process. The synchronized draw process provides CFM having improved filament structure and tensile strength.

The synchronized draw process may be performed on a standard CFM line with little additional hardware and hence at low cost. As shown in FIG. 3, the additions to the CFM line include a master PLC 50 that is in communication with forming position 12 via PLC linkage 52. The synchronized draw process may include a master encoder 54 downstream from the forming position 12 to provide conveyor speed and position data to the master PLC 50 so that the forming position 12 may be individually controlled.

The fibers used in the manufacture of the CFM may be any type of glass fibers, such as A-type glass fibers, C-type glass fibers, E-type glass fibers, S-type glass fibers, ECR-type glass fibers (such as., Advantex® glass fibers commercially available from Owens Corning), or modifications thereof. In addition to glass fibers, any suitable fibers such as, but not limited to, mineral fibers, carbon fibers, basalt fibers, polymer fibers, nylon fibers, polyester fibers, polyamide fibers, aramid fibers, PVC fibers, PVAC fibers, melamine fibers, acrylic fibers, visil fibers, natural fibers, staple fibers, chopped fibers and mixtures thereof may be used.

Glass fibers may be formed by attenuating streams of a molten glass material from a bushing or orifice to form glass fibers. The molten glass may be attenuated rollers which pull the fibers before they are fed to the forming position 12. An aqueous sizing composition may be applied to the fibers after they are drawn from the bushing to protect the fibers from breakage during subsequent processing, to retard interfilament abrasion, and to ensure the integrity of the strands of glass fibers, that is, the interconnection of the glass filaments that form the strand. Sizing compositions are well-known in the art, and typically include a film forming polymeric or resinous component, a coupling agent, and a lubricant. The film forming component of the size composition is desirably selected to be compatible with the matrix resin or resins in which the glass fibers are to be embedded. The sizing composition used in the present invention is not particularly limited, and may be any sizing known to those of ordinary skill in the art or developed hereafter.

The binder composition may optionally contain conventional additives such as dyes, oils, fillers, thermal stabilizers, emulsifiers, anti-foaming agents, anti-oxidants, organosilanes, colorants, UV stabilizers, and/or other conventional additives. Other additives may be added to the binder composition for the improvement of process and product performance. Such additives include coupling agents (for example, silane, aminosilane, and the like), dust suppression agents, lubricants, wetting agents, surfactants, antistatic agents, and/or water repellent agents.

FIG. 1B shows the weight (on a relative scale) of a CFM manufactured in accordance with one aspect of the present invention. FIG. 1B shows the weight of a CFM manufactured using 6 position synchronization where the frequency is 30 OPM and the line speed is 33 fpm (10 m/min). The lower curves represent the weight from each fiber forming position. The curves have a predefined interval and the sum of the individual curves provides a substantially stable weight across the mat. The CFM shown in FIG. 1B has a period of 333 mm and a peak to valley variation of 1.6%. Comparing FIG. 1A to FIG. 1B it can be seen that the CFM of the present invention provides a predetermined fiber lay down pattern in a pattern having a predetermined interval. FIG. 1B shows the use of 6 fiber groups laid down at a predetermined interval, in this case the interval is equal among all plies, but is possible to manufacture a mat having a 1×5 synchronization and a 1×6 synchronization pattern where the periods of the two patterns is unequal.

As seen in FIG. 2, the forming position 12 includes a fiber draw position 30 from which fibers 32 are drawn. The fibers 32 are drawn around idler wheel 28 and around fiber pull wheel 14. The fiber pull wheel 14 is mounted on drive shaft 16 which is connected to oscillating servo drive 22 and suspended from support structure 26. The forming position 12 includes a shield 24. The oscillating servo drive 22 is linked to master PLC 50 via PLC linkage 52. The oscillating servo drive 22 also controls oscillator 20 which drives oscillating finger wheel 18 across a portion of the circumference of fiber pull wheel 14 to control the angle at which the fibers 32 leaves the fiber pull wheel 14 and hence the position of fibers 32 on forming conveyor 10.

FIG. 3 is a system overview showing one embodiment of the synchronized continuous filament mat line according to the present invention. The CFM line includes a series of N forming positions 12. Typically N may range from 2-20 forming positions 12 or more. Preferably, the CFM line includes between 12 and 20 forming positions 12. Each forming position 12 lays fibers 32 on forming conveyor 10 in a V-shaped pattern as controlled by oscillating servo drive 22. The oscillating servo drive 22 is linked to the master PLC 50 via PLC linkage 52. The PLC linkage 52 may be an electrical communications cable, an optical link, a radio frequency connection or any other suitable data transfer device. Each forming position 12 is also linked to master encoder 54 via encoder linkage 56. The encoder linkage 56 may be an electrical communications cable, an optical link, a radio frequency connection or any other suitable data transfer device. The master encoder 54 may continuously monitor the conveyor speed and position and provide feedback to the master PLC 50 to control the oscillation of the fiber pull wheel 14. The master PLC 50 is programmed with algorithms that enable the deposition of fibers to be altered in the event that a forming position 12 goes off-line so that production of the CFM 60 may continue with little or no density variation.

The master PLC 50 is typically linked to a Human Machine Interface 50A such as a CRT or video touch screen to provide monitoring, control or override of the master PLC 50.

FIGS. 4A-4B show the profile of the mean fiber position of fibers 32 from forming position 12 as deposited on the forming conveyor 10. The mean fiber position shown as a line equal to the center position of the loops of fibers 32 formed on the forming conveyor 10. The profile is controlled by the speed of the forming conveyor 10 as well as the movement of the oscillating finger wheel 18. The x-axis is along the length of the forming conveyor 10 and the y-axis is across the length of the conveyor. The profile definition variables are typically defined by the period, frequency and interval. A cycle is one complete motion of the oscillator back and forth across the width of the line. The period is the distance in millimeters along the x-axis of one complete cycle. The frequency is number of cycles completed in one minute and is expressed in oscillations per minute (OPM). The interval is the distance between the mean fiber positions of two fiber strands 32.

Prior to formation of a CFM 60, the lay-down pattern from the forming positions 12 are typically calibrated. Calibration determines the mean fiber position of each position 12 and allows for the determination of the profile definition variables. Two potential calibration techniques include forming position calibration and fiber position calibration.

In forming position calibration, the distance between successive forming positions is calibrated and the skew angle of the pull wheel is calibrated so that the position of the fiber strands 32 on the forming conveyor can be calculated. Forming position calibration presupposes careful measurement and calibration between each of the banks of forming positions 12 and between each fiber draw position 12 in the individual banks.

In fiber position calibration, the distance and skew angle of each forming position 12 is not measured but rather the fiber strands 32 are projected onto the forming conveyor and the pull wheel is adjusted, either mechanically or electronically through the master PLC, so that an interval of a known value is achieved. Typically, the interval is set to zero during calibration so that an operator can easily observe the fiber strand 32 position and control the mean fiber position of each fiber draw position 12 so that the mean fiber position from each fiber draw position 12 is overtop the mean fiber position on the first fiber raw position 12 in the bank. The opposed banks are then calibrated each to the other, typically so that they are 180° out of phase.

After calibration, the master PLC 50 is programmed to control the profile definition variables so that a CFM 60 having predetermined properties is produced. Typically, the master PLC 50 linked to the oscillating servo-drive 22 controls the oscillator 20 to drive oscillating finger wheel 18 across a portion of the circumference of fiber pull wheel 14. The position of finger wheel 18 controls the angle at which the fibers 32 leaves the fiber pull wheel 14 and hence the position of the fiber strand 32 on the forming conveyor 10. The master PLC 50 controls the speed and relative positions of finger wheel 18 to control the interval between fiber strands 32. Typically, a the master PLC is preprogrammed with a variety of product specific algorithms for the profile definition variables by controlling the speed of forming conveyor 10, speed of the pull wheel 14, frequency (f), the position of the finger wheels 20 and a time offset between servo-drives 22.

The interval between two forming positions 12 is shown in FIG. 4B. The interval is the distance in millimeters between the mean fiber positions of one forming position 12 with respect to another forming position 12. Typically the interval is defined by the distance between the mean fiber positions of adjacent forming positions 12 in a 1-3-5-7-9-11 pattern. However, it is possible to group the forming positions 12 such that the interval is defined between non-adjacent forming positions 12. For example, fibers 32 from forming positions 1, 3, and 5 may be deposited with an interval greater than the desired interval of the finished product and fibers 32 from positions 7, 9 and 11 may be deposited over the top so that fibers 32 from position 7 lie between the fibers 32 of positions 1 and 3; fibers 32 from position 9 lie between the fibers 32 of positions 3 and 5; and fibers 32 from position 11 lie between the fibers 32 of positions 5 and 1. In this example the interval between fibers 32 would lie in a 1-7-3-9-5-11 pattern

FIG. 4C shows a CFM profile of a four oscillator synchronization pattern including first fiber position 62, second fiber position 64, third fiber position 66, and fourth fiber position 68. As the succeeding forming positions 12 are deposited, the density variation of the CFM 60 is reduced. As the number N of forming positions 12 increases, it is possible to control the interval of the forming positions 12 to form a substantially uniform density CFM 60. It is possible to substantially increase the period to allow for faster speeds forming conveyor 10 and increased machine output while controlling the weight variation and the interval so that the sum of the intervals is equal to the period.

It is also possible to control the interval such to form a multi-ply CFM 60 being built up from multiple patterns, such as that shown in FIG. 4C, including first fiber position 62, second fiber position 64, third fiber position 66, and fourth fiber position 68, so that the each ply includes four fiber strands 32. For example, on a CFM line having 12 forming positions 12, a CFM mat 60 having 4 plies of 3 forming positions 12, or in a CFM line having 20 forming positions 12 a CFM mat 60 having 4 plies of 5 forming positions 12 may be formed. The mean fiber position of the first fiber position 62 of each succeeding ply may be deposited substantially on top of the mean fiber position of the first fiber position 62 of the preceding ply or, optimally, it may be spaced apart from the mean fiber position of the first fiber position 62 of the preceding ply.

Typically, the fiber draw positions 12 are numbered consecutively down the line, that is, in a twelve position line, position one at the east end of the line while position twelve is at the west end. The positions are typically not centered over the forming conveyor 10 but the even positions (2-4-6-8-10-12) form a bank that is offset to the north side and odd positions (1-3-5-7-9-11) form a bank that is offset to the south side (the ordinal directions are used for the purposes of example only).

In operation, the line operator may select a desired preprogrammed pattern or establish a unique pattern for a desired CFM configuration through Human Machine Interface 50A. Based on the number of on-line forming positions 12, the master PLC 50 then calculate the intervals to lay down the fibers 32 in the desired pattern. The master PLC 50 may then monitor the output of each forming position 12 and, in the event that a forming position 12 goes offline due to a fibers 32 breakout, a mechanical failure or for scheduled maintenance, the master PLC 50 can control the cycle, period, frequency, interval as well as the speed of forming conveyor 10 and the pattern of the forming positions 12 to minimize or eliminate any flaws in the CFM mat 60 and to maintain the product base weight. The algorithms used to control the lay down pattern may include fixed period, fixed frequency or any other suitable algorithm to provide suitable lay down pattern.

In the event that a fiber draw position goes off-line, a PLC 50 using a fixed period algorithm will decrease the frequency (f), reduce the mat line speed (Sml), maintain a fixed oscillation period (P), and increase the interval of the forming position bank to account for the loss of one or more forming position 12.

In the event of a fiber draw position goes off-line, a PLC 50 using a fixed frequency algorithm will decrease the period (P) and the mat line speed (Sml) in order to maintain a fixed frequency and maintain the interval of the forming position bank to account for the decreased period (P) due to the loss of one or more forming positions 12.

FIG. 5 shows a plot of pooled standard deviation (PSD) of machine direction (MD) weight variation versus period in millimeters. The pooled standard deviation of machine direction is measured by taking 80 samples from each of 6 sections of CFM, determining the standard deviation (σ) of each section and subsequently determining the pooled standard deviation of the 6 sections, where (n) denotes the number of sections, using EQ. 3: PSD=(i=1n σi2n)(3)

FIG. 5 shows the PSD MD weight variation of a non-synchronized mat of the prior art, the PSD MD weight variation of a synchronized mat of the present invention formed on a twelve position line where the banks are separately synchronized but are not synchronized to one another, and the PSD MD weight variation of a synchronized mat of the present invention formed on a twelve position line where the banks are separately synchronized and are synchronized to one another. FIG. 5 also shows that it is possible to manufacture CFM within a wide manufacturing process window based upon fiber generation capacity, the number of forming positions 12, line speed, period (P), and frequency.

By using the inventive method, a synchronized CFM may be formed having reduced weight variation and at increased line speeds. Further, through control of the oscillation rate, it is possible to control the loop formation ratio (LFR) and hence the CM and MD tensile strength of the CFM. Specifically, it is possible to control the CM/MD tensile strength ratio. It is desirable to have a CFM with an increased MD tensile strength in products such as pultrusion. In other products, such as compression molding, infusion molding and resin transfer molding, equiaxial strength may be desired. As shown in FIG. 6A and 6B, it is possible to control the CM/MD tensile strength ratio and therefore to tailor the CFM to the desired properties.

EXAMPLES

Having generally described this invention, a further understanding can be obtained by reference to certain specific examples illustrated below which are provided for purposes of illustration only and are not intended to be all inclusive or limiting unless otherwise specified.

Table 1 shows theoretically determined properties of four continuous filament mats (examples 1-4). Examples 1 and 2 are based on the CFM technology of the prior art. Examples 3 and 4 are based on the CFM technology of the present invention. As seen in Table 1, Ex. 3 has the same basis weight and mat line speed as Ex. 1, but with significantly lower frequency and peak to valley weight variation and at a higher loop formation ratio (LFR) and period. Similarly, Ex. 4 has the same basis weight and mat line speed as Ex. 2, but with significantly lower frequency and peak to valley weight variation and at a higher loop formation ratio (LFR) and period.

Tables 2A-2C show the data used to create FIG. 5 and shows the pooled Standard Deviation of the MD weight variation of CFM having a density of 28.4 g/ft2. Table 2A shows that the weight variation for a non-synchronized CFM increased dramatically for a period above 165 mm. The weight variation is typically unacceptable to the composites industry and limits the overall throughput of a CFM. Table 2B shows that the weight variation for a 2×6 synchronized CFM was initially lower than that of the non-synchronized CFM and increased at a lower rate with increased period. Table 2C shows that the weight variation for a 1×2 synchronized CFM was initially lower than that of both the non-synchronized and the 2×6 synchronized CFM and increased at a substantially lower rate with increased period. FIG. 5 shows that the PSD weight variation is lower at a period of 350 mm than at 160 mm and 165 mm for the 2×6 synchronized and the unsynchronized CFM. The higher period and lower PSD weight variation allows a CFM line to run at a substantially increased throughput without the cost of additional forming positions.

TABLE 1
Mat LinePeak to
SpeedFrequencyvalley
Product(Sml)(f)PeriodVariation
Example(oz/ft2)(MPM)(OPM)LFR(mm.)(Wt %)
11.510.0603.7165 8-18
21.014.3872.616510-22
31.510.0307.43330.4
41.014.3435.23330.5

TABLE 2A
PSDPeriodFrequency (ƒ)
Examplewt. variation(mm)(OPM)
51.83815416584
61.88863716584
72.37664418575
82.05679218575
92.57286219870

TABLE 2B
PeriodFrequency (ƒ)
ExamplePSD(mm)(OPM)
101.7388416091
111.7414516091
121.7898116091
131.6326620371
141.7195820371
151.8511220371
162.1256925457
172.1474925457
182.1528125457
192.161725457
202.2131625457

TABLE 2C
PeriodFrequency (ƒ)
ExamplePSD(mm)(OPM)
211.048820273
221.0550220273
231.1114720273
241.1889828052
251.240928052
261.2180130049
271.2506130049
281.2561230049
291.2802528052
301.6235042
311.6435042
321.6735042

The data from FIG. 6A and 6B is shown in Table 3. As can be seen, the oscillation rate is related to the ratio of the cross machine tensile strength to the machine direction tensile strength (CM/MD). The examples were produced and tested for tensile strength in both the machine direction (MD) and in the cross-machine direction (CM). As can be seen in Table 3, Ex. 30 has improved MD tensile strength over Ex. 31-33, as expected, due to the decreased frequency and the increased LFR. The MD tensile strength is 81% of the CM tensile strength which is very desirable in certain composite applications. Using the synchronization technology of the present invention it is possible to control the tensile strength ratio (MD/CD) to meet a specific customer need by adjusting the LFR, frequency, period, and line speed. It is possible to produce a MD/CM ration greater than 60% and approaching 100%. Preferred MD/CM ratios are typically in the 70-80% range, although the desired ratio may be greater due to the desired properties of a finished composite article. The drop in the CM tensile strength is also expected due to the increased LFR. Typically, any increase in the MD tensile strength is accompanied by a drop in the CM tensile strength due to the orientation of the loops.

TABLE 3
MD/CM/
OscillationMDCMCMMDLine
Exam-Freq.PeriodTensileTensileRatioRatioSpeed
ple(OPM)(mm)(KSI)(KSI)(—)(—)(m/Min)
305825319.023.50.811.2414.7
318816716.626.90.621.6214.7
3211313015.627.90.561.7914.7
338816715.225.30.601.6614.7

The invention of this application has been described above both generically and with regard to specific embodiments. Although the invention has been set forth in what is believed to be the preferred embodiments, a wide variety of alternatives known to those of skill in the art can be selected within the generic disclosure. The invention is not otherwise limited, except for the recitation of the claims set forth below.