FR3056142A1 - CARBON FIBER CUTTING SYSTEM FOR SMC PROCESS - Google Patents

Abstract

System (10) for cutting at least one carbon wire (20), comprising at least one transverse cutting means (50) for the carbon wire, characterized in that it comprises successively from upstream to downstream in a direction of unwinding of the carbon wire (20), and upstream of the transverse cutting means (50): - at least one spreading means (60) of the carbon wire (20) in order to reduce its thickness and to increase its width; and - at least one opening means (70) of the carbon threads (20) thus spread.

Description

056 142

58797 ® FRENCH REPUBLIC

NATIONAL INSTITUTE OF INDUSTRIAL PROPERTY © Publication number:

(to be used only for reproduction orders)

©) National registration number

COURBEVOIE © Int Cl ⁸ : B 29 C 70/54 (2017.01), B 29 C 70/18, B 26 D 9/00, 7/27, B 65 H 51/005, B 29 B 15/08

A1 PATENT APPLICATION

©) Date of filing: 20.09.16. © Applicant (s): COMPAGNIE PLASTIC OMNIUM ©) Priority: Public limited company - FR. @ Inventor (s): TO BE COMPLETED. ©) Date of public availability of the request: 23.03.18 Bulletin 18/12. ©) List of documents cited in the report preliminary research: The latter was not established on the date of publication of the request. (© References to other national documents ® Holder (s): COMPAGNIE PLASTIC OMNIUM related: Anonimous society. ©) Extension request (s): ©) Agent (s): LLR.

PA CARBON FIBER CUTTING SYSTEM FOR SMC PROCESS.

FR 3 056 142 - A1 (Pp) System (10) for cutting at least one carbon thread (20), comprising at least one cross cutting means (50) for the carbon thread, characterized in that it comprises successively from upstream to downstream in a direction of unwinding of the carbon wire (20), and upstream of the transverse cutting means (50):

- At least one spreading means (60) of the carbon wire (20) in order to reduce its thickness and increase its width; and

- At least one opening means (70) of the carbon threads (20) thus spread.

The invention relates to the technical field of products and semi-products for molding a piece of reinforced plastic.

In particular, the invention relates to equipment for cutting into shorter strands continuous carbon fibers wound in the form of wires around a spool, in order to be used in a process for manufacturing a sheet of reinforced plastic material intended for molding room.

In the automotive sector, for example, many parts must combine mechanical strength and low weight.

To do this, it is known to replace steel parts with parts made of reinforced plastic (thermosetting or thermoplastic). These materials are made up of reinforcing elements mixed with a polymer resin. For example, reinforced plastics of the SMC type (from the English term "sheet molding compound") are known.

In the most common case, an SMC sheet is made of thermosetting resin (polyester for example) which impregnates reinforcing elements based on fibers (short fibers, unidirectional, mat, fabric ...), such as glass. It generally comprises a catalyst (hardener) and possibly fillers or other additives.

An SMC sheet is produced by impregnating reinforcing fibers deposited, during manufacturing, sandwiched between two resin films.

The manufacturing process for an SMC sheet is called the "SMC process".

In the so-called “compounding” step of the SMC process, that is to say in the step of mixing a thermosetting resin with reinforcing fibers, the fiber is received in the form of a coil, then it is cut. online on a machine using so-called conventional cutters.

These conventional cutters are made up of a blade roller which cuts the fiber by pressure against a roller generally made of polyurethane (PU). The rotation of the cutter drives the fiber and consequently causes the reels of reinforcement thread to unwind

The SMC process mainly uses fiberglass as reinforcement. The glass fibers generally used are in the form of a coil, known as an "assembled roving" of glass fiber. Such a coil is a set of several individual strands. Each unitary strand, of 50 to 100 tex (g / km) each and of width approximately 0.5mm, comprises a set of elementary glass filaments of 12 to 20 micrometers in diameter. Generally a fiberglass coil has a linear mass of 2200 to 4800 tex.

This so-called "assembled roving" structure thus allows this structure to burst well during the cutting phase, that is to say good separation of the individual strands. This structure thus allows, after cutting into sticks (strand cut in its length), a relatively homogeneous distribution of a mat of glass fiber sticks from 50 to 100 tex, 0.5mm wide, and of length defined by l '' blade spacing, usually 12, 25 or 50mm.

Reinforced plastic parts are also known, the reinforcing elements of which are carbon fibers. Carbon fiber is made up of extremely fine fibers (filaments), about 5 to 10 micrometers in diameter,

To manufacture such parts, using an SMC process, carbon fiber is also presented in the form of a coil but not in the form of "assembled roving", but in the form of "direct roving".

A “direct roving” is a set of several thousand filaments forming the equivalent of a strand (single strand) of 12K, 24K, 48K for example (respectively 12000, 24000, 48000 filaments of carbon fibers), corresponding to masses respective lines of approximately 800, 1600 and 3200 tex. Thus, each “direct roving” (or single strand) wire is a set of carbon filaments.

However, using current systems, intended for cutting strands of glass fibers, for cutting carbon fiber threads, the cut does not generate separation (opening, disassembly) of the elementary filaments constituting the carbon thread: thus, after cutting, strands in the form of flat and rectangular sticks are obtained, which remain compact, about 10mm wide, and of defined length (generally 12, 25 or 50mm), made of carbon fibers of at least 800 tex ( 800 tex in 12K, 1600 tex in 24K, 3200 tex in 50K).

Therefore, during the step of mixing the thermosetting resin with reinforcing fibers, it is not possible to obtain a sufficiently homogeneous distribution from a carpet of carbon coil sticks making it possible to manufacture a sheet of SMC whose mechanical characteristics are homogeneous enough to produce a structural part.

Furthermore, to obtain a reinforced plastic sheet having homogeneous properties, it is necessary to have good impregnation of the reinforcing fibers with the resin. The quality of the impregnation is conditioned by good penetration of the resin through the layer of reinforcing fibers. However, the lack of openness of the "direct rovings" of carbon fibers during cutting into a stick, hinders the penetration of the resin between the fibers, and therefore the quality of impregnation.

The lack of openness of the "direct rovings" of carbon fibers when cutting into sticks, also has an impact on the material's creep capacity during its molding phase as well as its level of mechanical performance.

The object of the invention is to remedy these drawbacks by providing equipment making it possible to cut coils of carbon fibers, into sticks the fibers of which have a degree of disassembly making it possible to manufacture sheets of reinforced plastics having homogeneity of distribution and an impregnation of the carbon fibers with the plastic material (resin), suitable for molding structural parts.

The cutting system achieves this by integrating in particular a longitudinal separation means (that is to say a separation parallel to the direction of advance) making it possible to create carbon wires having a width of the order of 10 to 20 times less than that of the initial carbon thread, preferably substantially equivalent to that of the strands of fiberglass (of the order of 0.5 mm).

Thus, the subject of the invention is a system for cutting at least one carbon thread, comprising at least one means for transversely cutting the carbon thread. The system successively comprises from upstream to downstream (according to the direction of unwinding of the carbon wire in the system) and upstream of the cross cutting means:

at least one means of spreading the carbon wire in order to reduce its thickness and increase its width; and at least one means for opening the carbon wires thus spread.

The system according to the invention makes it possible to improve the quality of the reinforcing mat, that is to say: the homogeneity of the areal mass of deposited reinforcing fibers; better isotropy of the fiber distribution (the fibers are randomly oriented in all directions); an improvement in the quality of impregnation and thus significantly increase the mechanical characteristics and the flowability during the transformation phase by molding.

The system may also include one or more of the following characteristics, taken alone or in combination:

the spreading means comprises a set of spaced successive rollers, the carbon thread passing alternately above and below the rollers in order to distribute the filaments constituting the carbon thread over a greater width; the opening means comprises alone or in combination at least one of the following means: a longitudinal cutting means; at least one roller provided with pins; at least one roller with streaks.

the longitudinal cutting means comprises at least one set of blades substantially aligned on the same axis;

the longitudinal cutting means comprises several sets of blades, the axes of alignment of the sets of blades being parallel to each other, and the blades being offset, in the width of the wires, from one set to another;

the alignment axis is perpendicular to the direction of unwinding of the wires; the blades are substantially circular in rotation about the alignment axis; the carbon wire is wound around at least one coil, the means for cross cutting carbon wires also allowing the unwinding of the carbon thread in a direction of unwinding;

several coils of carbon fibers are used and the system comprises, upstream of the wire spreading means, a wire guiding device, adapted to guide each wire unwound from a coil so that at the input of the means spreading, the son are parallel to each other, and regularly spaced; the comb is dimensioned so as to calibrate this distance so that, at the outlet of the spreading means, the spread threads form a single homogeneous sheet of given surface mass.

The invention also relates to a system for manufacturing a reinforced plastic sheet for molding, comprising at least one conveyor movable in one direction, a first system for supplying plastic onto the conveyor positioned at the upstream end of the conveyor, at least one fiber supply means making it possible to deposit reinforcing fibers on the plastic material deposited on the conveyor by the first plastic material supply system; the fiber supply means comprises a system for cutting carbon threads according to the invention.

The invention also relates to a method for cutting carbon fiber rods wound into rods around at least one coil, the rods being usable in a SMC type process, in which the following steps are carried out:

at least one carbon fiber wire is unwound from the coil; spreading the carbon fiber wire;

the carbon fiber wire thus spread is opened into several carbon wires having a width less than the wire to be cut;

each wire of carbon fibers thus obtained is cut transversely.

According to the invention, the wire can be cut longitudinally so as to obtain wires having a width not exceeding 2mm, and preferably substantially equal to 0.5mm.

The invention also relates to a process for manufacturing a reinforced plastic sheet for molding, in which the plastic is set in motion by a conveyor while carrying out the following steps:

a) a first layer of plastic material is deposited on the conveyor; then

b) carbon rods wound around a coil are cut into sticks, using the method according to the invention for cutting carbon fibers into sticks;

c) a layer of carbon fiber rod is deposited on said first layer of plastic material; then

d) a second layer of plastic is deposited on the layer of sticks;

e) the sticks are impregnated with the two layers of plastic material in order to obtain a homogeneous distribution of the sticks in the thickness of the sheet.

The invention will be better understood on reading the appended figures, which are provided by way of examples and have no limiting character, in which:

Figure 1 schematically illustrates, in a side view, an embodiment of a system according to the invention for cutting carbon son; Figure 2 schematically illustrates, in a top view, the embodiment of the system according to the invention of Figure 1;

FIG. 3 illustrates a so-called conventional cutter;

FIG. 4 illustrates, in a side view, an embodiment of a system according to the invention for cutting carbon wires;

Figure 5 illustrates a 3D view of the embodiment of the system according to the invention of Figure 4;

FIG. 6 illustrates a 3D view of an embodiment of a system according to the invention for cutting carbon wires, comprising a longitudinal cutting means;

Figure 7 illustrates a longitudinal cutting means;

FIG. 8 illustrates a detail of FIG. 7, illustrating the blades and the associated striations;

FIGS. 9A and 9B illustrate examples of means for longitudinal cutting of the carbon wires;

FIG. 10 illustrates an opening roller comprising pins; Figure 11 illustrates a pin as shown in Figure 10; FIG. 12 illustrates an opening roller provided with striations; Figure 13 illustrates in detail the streaks of Figure 12; and FIG. 14 illustrates an embodiment of a system according to the invention for manufacturing a reinforced plastic sheet for molding.

In FIGS. 1, 2, 5 and 6, the thick arrows indicate the direction of advance of the carbon threads 20. Thus, in FIG. 5, the arrow at the top right indicates the arrival of the carbon threads 20; the center arrow (at an angle) indicates the exit of the carbon threads 20 after spreading and opening, but before the cross section; finally, the vertical arrow at the bottom indicates the exit of the sticks 40.

Referring now to Figures 1 and 2 which schematically illustrate an embodiment of a system 10 according to the invention for cutting carbon fibers wound in the form of carbon wire 20 around at least one coil 30, in rods 40, of smaller size, which can be used in an SMC type process. A stick is a piece of carbon wire, made from a cross section of a carbon wire.

Rods can be used in an SMC type process, when the rods have geometric properties making it possible to manufacture SMC sheets having perfect impregnation of the carbon fibers by the plastic material (resin). This type of sticks has in particular a width not exceeding 2mm (preferably substantially equal to 0.5mm).

The system 10 according to the invention comprises at least one cross-cutting means 50 of carbon wires also allowing the unwinding of the carbon wires 20 in a direction of advance (indicated by an arrow in FIGS. 1 and 2). It successively comprises from upstream to downstream and upstream from the cross-cutting means 50:

at least one transverse spreading means 60 of the carbon threads 20 in order to reduce their thickness and increase their width; and at least one opening means 70 of the carbon wires 20 thus spread.

The system 10 according to the invention makes it possible to cut carbon wires 20 having dimensions substantially equivalent to the strands of glass fiber used in an SMC type process.

The cross-cutting means 50 (FIG. 3)

As illustrated in FIG. 3, the cross-cutting means 50 can be a so-called conventional cutter. It can be composed of three rollers.

The function of a pressure roller 51 is to press the wire 20 against a polyurethane (PU) roller 52. A blade roller 53 has the function of cutting the wire 20 perpendicularly to its length, that is to say into sections of given length, by pressing against the polyurethane (PU) roller.

The rotation of the blade roller drives the wire 20 and therefore the unwinding of the reels.

The means for spreading the wires 60 (Figures 4 and 5)

The spreading means 60 of the carbon threads has the function of deploying the threads 20 across their width, crushing them so as to distribute the filaments over a greater width, and making the thread as flat as possible. However, the threads remain "integral" with each other, they are not separated because the spreading means does not have the function of opening the carbon threads.

Thus, the spreading means 60 of the carbon threads makes it possible to reduce the thickness of the threads 20 and to increase their width. It has a set of rollers, which can be made of aluminum.

According to an embodiment illustrated in Figures 1 and 2, the spreading means 60 comprises at least three successive spaced rollers. The wires pass alternately above / below the rollers. The spacing and positioning of the rollers relative to each other are adjustable (at the start of production, or continuously following a control loop) to adjust the thread tension, and therefore its spreading. It is thus possible to adjust the degree of spreading, that is to say the thickness and the width of the carbon wires leaving the spreading means 60.

The wires 20 are then spread out in this spreading means 60, that is to say that the wires pass alternately at least above / below at least three rollers to be spread out.

According to one embodiment, the cylinders can be regulated in temperature and in vibration in order to promote the spreading of the wires 20.

According to one embodiment (Figures 1 and 2), the spreading means 60 comprises a set of smooth rollers (for example three in Figures 1 and 2), parallel to each other, whose axes are perpendicular to the direction of advanced. The wires 20 pass alternately over one roll and then below the next. The wires 20 pass successively between two rollers whose spacing is adjusted. The rollers of the means 60 are adjusted so that at the outlet, the thickness of the wires 20 is substantially equal to a given thickness.

According to an embodiment illustrated in FIGS. 4 and 5, the spreading means 60 comprises six successive spaced rollers, for example:

a roller R1 provided with housing forming grooves (grooves of 20mm width each centered on the roller); the inside diameter is 30mm, and the outside diameter is 40mm; the roller is made of anodized aluminum, and it is mounted fixed; a wire is placed in each 20mm groove, the number of grooves being defined as a function of the tolerance of the desired surface area of carbon; a smooth R2 roller, diameter 30mm, in anodized aluminum, and fixed mounted; an R3 roller fitted with grooves (grooves 20mm wide each centered on the roller); the inside diameter is 30mm; the roller is made of anodized aluminum, and it is mounted fixed;

an R4 roller provided with grooves (grooves 25mm wide each centered on the roller), Se inner diameter is 30mm; the roller is made of anodized aluminum, and it is mounted fixed;

possibly a smooth R5 roller, diameter 30mm, in anodized aluminum, and fixed mounted. The roller R5 is provided with an axial vibrator; the axial vibration improves the spreading;

a smooth R6 roller, diameter 30mm, in anodized aluminum, on a bearing and rotatably mounted.

The radii, spacing, material, finish of the rollers can be adapted as required by a person skilled in the art.

In order to guarantee optimal spreading, the first rollers are mounted fixed.

Preferably, the grooves of the R1 / R3 / R4 rollers are facing each other to keep the alignment of the carbon wires.

The opening means 70 of the wires (FIGS. 9A and 9B, 4, 5 and 7 to 13)

The opening means 70 of the threads has the function of separating groups of filaments along the entire length of the thread, in other words dividing its width, a thread into several threads of smaller width. Advantageously, all the wires of smaller width have the same number of filaments.

At least three embodiments of the opening means 70 are described below:

i. the opening means 70 is a longitudinal cutting means;

ii. the opening means 70 comprises rollers 72 provided with pins 74;

iii. the opening means 70 comprises rollers 76 provided with ridges 78.

A combination of two or three of these embodiments may be advantageous. For example, according to the embodiment illustrated in Figures 4 and 5, the opening means 70 successively comprises a pin roller, then two streak rollers.

i. Longitudinal cutting means 70 (Figures 6 and 7 and 8)

The longitudinal cutting means 70 of the threads has the function of cutting along its length a thread into several threads of smaller width. Advantageously, each smaller width yarn has the same number of filaments.

FIG. 6 illustrates an exemplary embodiment of a system 10 provided with such a cutting means 70.

As illustrated in FIG. 7, the longitudinal cutting means 70 may comprise at least one set of blades 80, for example circular in rotation around the same shaft 82 perpendicular to the direction of advance of the wires. The blades 80 are thus positioned along the length of the wire 20, in contact with the latter. Any other cutting means can be considered such as: water jet, laser, non-rotating knives ...

The blades 80 cut the wires lengthwise by pressing against a counter roller 84, made of polyurethane (PU) for example. Preferably, the counter-water ripple comprises ridges 86, making it possible to guide the longitudinal section of the blades 80.

The spacing L between the blades determines the final width L of the carbon fiber rods 40. Each blade is spaced to obtain a set of wires of width not exceeding 2mm. Preferably, the blades are spaced about 0.5mm apart to obtain a set of wires close to 0.5mm in width.

According to the example of Figures 7 and 8, the longitudinal cutting means 70 comprises: a shaft 82 provided with twelve blades 80 spaced two by 2mm; a cutting counter roller 84 with twelve ridges 86 spaced 2mm apart.

Preferably, the blades 80 do not come into contact with the bottom of the ridges 86 as illustrated in FIG. 8. The shaft 82 and the counter-roller 84 are motorized.

FIG. 9A illustrates the example of a longitudinal cutting means 70 for wires comprising a single set of blades 80.

According to another embodiment illustrated in FIG. 9B, the longitudinal cutting means 70 of the wires comprises several sets of blades 80 located on two different rolls, the blades of the ^1st roller being positioned alternately with respect to the blades of the ^2nd roller . In this way, the spread wires are cut by a first set of blades 80, and have a first width, then they are cut again by a second set of blades. As the blades are offset, the wires are cut and have a second width less than the first width.

In this way, the spacing between the blades can be greater than L, for example 2L, but the wires cut by all the sets of blades thus ultimately have a width L (see FIG. 9B).

Preferably, several coils of carbon fibers are used as illustrated in FIGS. 4 and 5.

In this case, the system 10 comprises, upstream of the spreading means 60 of the wires, a guide device 65 (see FIGS. 1 and 2), such as a comb. This guide device has the function of guiding each wire unwound from a spool so that at the inlet of the spreading means 60, the wires are parallel to each other and regularly spaced (the distance between each wire is identical ). Advantageously, the comb is dimensioned so as to calibrate this distance so that, at the outlet of the spreading means 60, the wires 20 spread out form a single homogeneous sheet and of controlled surface mass.

A sheet thus constitutes a set of carbon threads spread out and arranged edge to edge. There is therefore no space between the wires forming the sheet, so that the sheet has mass homogeneity.

ii. Rollers with pins (Figures 10 and 11)

The opening means 70 may comprise a set of rollers 72, fixed or rotary, provided with pins 74. The pins 74 of the rollers 72 have the function of separating groups of filaments according to the length of the wire, in other words to be separated in its width, a wire in several wires of smaller widths.

An example of a roller used is illustrated in FIG. 10. FIG. 11 illustrates in detail a pin geometry 74 which is particularly well suited to the opening of the wires. Indeed, the pointed and thin head allows you to position yourself between two filaments and to separate them from each other, when the roller rotates, or when the thread advances on the roller.

In one example, a picot 74 measures 7mm in height, the pointed portion measures 4mm, the tips of the pins are spaced 2mm apart, and the base of a picot 74 can be 2mm in diameter.

According to a particular embodiment illustrated in FIG. 4, the opening means 70 comprises a roller R7 provided with 5700 spikes distributed all around a portion of roller of 300mm. The roller can be made of 304 stainless steel. Preferably the roller is rotary. In this FIG. 4, a means A for adjusting the spacing between the alternating rollers (to adjust the tension).

iii. Rollers with ridges (Figures 12 and 13)

The opening means 70 may comprise a set of rollers 76, fixed or rotary, provided with ridges 78. The ridges 78 of the rollers have the function of separating groups of filaments according to the length of the thread, in other words to be separated in its width , a wire in several wires of smaller widths.

An example of a striated roller 76 used is illustrated in FIG. 12. FIG. 13 illustrates in detail a groove geometry particularly well suited to the opening of the wires. In fact, each streak is separated by a pointed edge which makes it possible to position itself between two filaments and to separate them from one another, when the roller rotates, or when the thread advances on the roller.

According to one example, a streak at a depth of 3.5mm.

According to a particular embodiment illustrated in Figure 4, the opening means 70 comprises two rollers R8 and R9 provided with ridges.

The first R8 roller has an inside diameter of 30mm, and an outside diameter of 40mm. Each streak is 3.5mm deep. The streaks are spaced at a pitch of 2mm.

The second roller R9 has an inside diameter of 30mm, and an outside diameter of 40mm. Each streak is 1.75mm deep. The streaks are spaced at a pitch of 2mm.

The rollers can be made of stainless steel. They are preferably rotary.

Advantageously, the opening means 70 comprise at least one roller provided with pins, followed by at least one roller provided with ridges. Indeed, the pins make it possible to burst the carbon thread to improve the opening of the filaments by the striated rollers.

The invention also relates to a production installation 90 (FIG. 14) for manufacturing a sheet of reinforced plastic material for molding.

Such a system 90 comprises at least one conveyor 91, or conveyor, movable in one direction, then successively from upstream to downstream according to the direction of advance of the conveyor, various depositing stations:

a first means of supply 92 of resin on the conveyor comprising means 93 making it possible to ensure a thickness of resin on the conveyor, constant over the entire width of the conveyor;

a means for distributing carbon fibers 94, making it possible to deposit, in a homogeneous manner, carbon fibers, originating from the system 10, on the resin layer; a second means of supplying 95 of resin over the fibers comprising a doctor blade 96 making it possible to ensure a thickness of resin on the conveyor constant over the entire width of the conveyor.

Generally, a protective film (for example polyethylene) is used for the two stages of depositing resin, so that the assembly is sandwiched by two protective films. The first resin supply means thus deposits the resin on a first protective film avoiding contact between the conveyor and the resin, then the second resin supply means deposits the resin on a second protective film covering all of the layers deposited on the conveyor.

The system 90 comprises a system 10 according to the invention for cutting carbon fibers, and making it possible to supply carbon fibers to the means for distributing carbon fibers 94.

The invention also relates to a method for cutting carbon fiber rods wound into rods around a coil, the rods being usable in an SMC type method.

The method uses the system 10 according to the invention in order to obtain carbon fiber rods having dimensions (length, width and thickness) compatible with an SMC type method. It is said that the carbon fibers are compatible, when their dimensions allow a homogeneous distribution on a conveyor and a quality impregnation, substantially identical to the impregnation obtained with the glass fibers from assembled roving.

Thus, it is desired to cut carbon wires wound in the form of a coil, in order to obtain rods having a width less than 2mm, preferably close to 0.5mm.

The cutting method according to the invention comprises the following steps: at least one carbon wire is unwound from a coil;

we spread the carbon wire to make it as flat as possible, that is to say that we distribute the filaments constituting the wire over a greater width (we aim for all the filaments to be parallel to each other );

the carbon fiber thread thus spread out in several carbon threads having a width less than 2mm, preferably a width close to 0.5mm, is opened (longitudinal section, separation by striated or spiked rollers);

each wire of carbon fibers thus obtained is cut transversely.

The system 10 is calibrated so that the carbon fiber wires have a width of less than 2mm, preferably of the order of 0.5mm.

Preferably, the system is calibrated so that the carbon fiber wires have a length of between 13 and 50mm.

This process makes it possible to manufacture rods allowing the formation of a carpet of carbon fibers similar to those currently obtained with fiberglass, and which can, in fact, allow good impregnation of the reinforcing layer.

Preferably, several coils of carbon fibers are used as illustrated in FIGS. 1 and 2.

In this case, before the spreading step, the unwound threads of each reel are guided by means of the comb 65, so that at the inlet of the spreading means 60, the threads are parallel to each other and evenly spaced (the distance between each wire is identical).

Preferably, the comb is dimensioned so as to calibrate this distance so that, at the outlet of the spreading means 60, the wires 20 spread out form a single homogeneous sheet and of controlled surface mass.

The invention also relates to a process for manufacturing a reinforced plastic sheet for molding, in which the plastic is set in motion by a conveyor while carrying out the following steps:

a) a first layer of plastic material is deposited on the conveyor; then

b) carbon rods wound around a coil are cut into sticks, using the method according to the invention for cutting carbon fibers into sticks;

c) a layer of carbon fiber rod is deposited on said first layer of plastic material; then

d) a second layer of plastic is deposited on the layer of sticks;

e) the sticks are impregnated with the two layers of plastic material in order to obtain a homogeneous distribution of the sticks in the thickness of the sheet.

We can also promote the impregnation of the sticks by passing the whole through a calendering machine.

Claims (14)

1. System (10) for cutting at least one carbon thread (20), comprising at least one cross cutting means (50) for the carbon thread, characterized in that it successively comprises from upstream to l downstream in a direction of unwinding of the carbon wire (20), and upstream of the transverse cutting means (50): at least one means for spreading (60) the carbon wire (20) in order to reduce its thickness and increase its width; and at least one opening means (70) for the carbon wires (20) thus spread. 2. System (10) according to claim 1, in which the spreading means (60) comprises a set of spaced successive rollers, the carbon thread (20) passing alternately above and below the rollers in order to distribute the constituent filaments. carbon wire (20) over a greater width. 3. System (10) according to one of the preceding claims, in which the opening means (70) comprises, alone or in combination, at least one of the following means: a longitudinal cutting means; - at least one roller provided with pins; - at least one roller with streaks. 4. System (10) according to one of the preceding claims, in which the longitudinal cutting means (70) comprises at least one set of blades (80) substantially aligned on the same axis. 5. System (10) according to claim 3, in which the longitudinal cutting means (70) comprises several sets of blades (80), the axes of alignment of the sets of blades being parallel to each other, and the blades (80) being offset, in the width of the wires, from one set to another. 6. System (10) according to one of claims 4 and 5, wherein the alignment axis is perpendicular to the direction of unwinding of the son. 7. System (10) according to one of claims 4 to 6, wherein the blades (80) are substantially circular in rotation about the alignment axis. 8. System (10) according to one of the preceding claims, in which the carbon wire (20) is wound around at least one coil (30), the cross-cutting means (50) of carbon son also allowing the unwinding of the carbon thread (20) in an unwinding direction. 9. System (10) according to claim 8, in which several coils of carbon fibers are used and the system (10) comprises, upstream of the spreading means (60) of the wires, a device for guiding (65) the wires, adapted to guide each wire unwound from a spool so that at the inlet of the spreading means (60), the wires are parallel to each other, and regularly spaced. 10 System (10) according to claim 9, wherein the comb is dimensioned so as to calibrate this distance so that at the output of the spreading means (60), the son (20) spread out form a single homogeneous sheet of mass given area. 11. System (90) for manufacturing a reinforced plastic sheet for molding, comprising at least one conveyor (91) movable in one direction, a first plastics supply system (92) on the conveyor (91) positioned at the upstream end of the conveyor (91), at least one fiber supply means (93) making it possible to deposit reinforcing fibers on the plastic material deposited on the conveyor (91) by the first supply system (92 ) of plastic material, characterized in that the fiber supply means comprises a system (10) for cutting carbon wires (20) according to one of claims 1 to 10. 12. Method for cutting carbon fiber rods wound into rods around at least one coil, the rods being usable in a SMC type process, in which the following steps are carried out: at least one carbon fiber wire is unwound from the coil; spreading the carbon fiber wire; the carbon fiber wire thus spread is opened into several carbon wires having a width less than the wire to be cut; each wire of carbon fibers thus obtained is cut transversely. 13. The method of claim 12, wherein the wire is cut longitudinally so as to obtain son having a width not exceeding 2mm, and preferably substantially equal to 0.5mm. 14. Method for manufacturing a reinforced plastic sheet for molding, in which the plastic is set in motion by a conveyor while carrying out the following steps: a) a first layer of plastic material is deposited on the conveyor; then b) carbon rods wound around a coil are cut into sticks, by implementing the method according to one of claims 12 and 13 for cutting carbon fibers into sticks; c) a layer of carbon fiber rod is deposited on said first layer of plastic material; then d) a second layer of plastic is deposited on the layer of sticks; e) the sticks are impregnated with the two layers of plastic material in order to obtain a homogeneous distribution of the sticks in the thickness of the sheet. 3056 1/8