Method of forming an annular textile preform by needling a helical fiber sheet, and a machine for performing such a method

Abstract

A method of forming an annular textile preform by needling a helical fiber sheet includes in succession: unwinding a helical fiber sheet from a horizontal sheet-forming turntable driven at a constant and predefined speed of rotation N.sub.FS onto a horizontal intermediate unwinder driven at a speed of rotation N.sub.DI and positioned on a horizontal intermediate turntable driven at a speed of rotation N.sub.FI, unwinding the helical fiber sheet from the intermediate unwinder onto a final horizontal unwinder driven at a speed of rotation N.sub.DF, and unwinding the fiber sheet from the final unwinder onto a horizontal preform-forming turntable driven at a variable and predefined speed of rotation N.sub.FP so as to be subjected to needling thereon. The speeds N.sub.DI, N.sub.FI, and N.sub.DF are controlled in such a manner that N.sub.DF is proportional to N.sub.FP, N.sub.FI=(N.sub.FS−N.sub.DF)/2, and N.sub.DI=(N.sub.FS+N.sub.DF)/2.

Claims

1. A method of forming an annular textile preform by needling a helical fiber sheet, the method comprising in succession: unwinding the helical fiber sheet from a horizontal sheet-forming turntable driven at a constant and predefined speed of rotation N.sub.FS onto a horizontal intermediate unwinder driven at a speed of rotation N.sub.DI and positioned on a horizontal intermediate turntable driven at a speed of rotation N.sub.FI; unwinding the helical fiber sheet from the horizontal intermediate unwinder onto a final horizontal unwinder driven at a speed of rotation N.sub.DF; and unwinding the helical fiber sheet from the final horizontal unwinder onto a horizontal preform-forming turntable driven at a variable and predefined speed of rotation N.sub.FP so as to be subjected to needling thereon; the speeds N.sub.DI, N.sub.FI, and N.sub.DF being controlled in such a manner that: N.sub.DF is proportional to N.sub.FP; N.sub.FI=(N.sub.FS−N.sub.DF)/2; and N.sub.DI=(N.sub.FS+N.sub.DF)/2.

2. The method according to claim 1, wherein the horizontal sheet-forming turntable and the horizontal preform-forming turntable have respective mean speeds that are equal.

3. The method according to claim 1, further comprising counting a number of turns of helical fiber sheet unwound onto the horizontal intermediate unwinder.

4. The method according to claim 1, wherein needling of the helical fiber sheet is interrupted at an end of each cycle of forming an annular textile preform, in order to enable said annular textile preform to be removed.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) Other characteristics and advantages of the present invention appear from the following description made with reference to the accompanying drawing, which shows an implementation having no limiting character. In the figures:

(2) FIG. 1 is a diagrammatic view of a circular needling machine for performing the method of the invention for forming an annular textile preform; and

(3) FIG. 2 is an example of cyclical timing charts showing the speeds of the various elements of the FIG. 1 machine.

DETAILED DESCRIPTION OF THE INVENTION

(4) FIG. 1 shows in a highly diagrammatic manner a circular needling machine 2 of the invention for forming an annular preform from a helical fiber sheet (or strip).

(5) Typically, such a circular needling machine 2 comprises a sheet-forming table 4 that is to form a helical fiber sheet (e.g. by weaving). The sheet-forming table comprises in particular a horizontal sheet-forming turntable 6 having positioned thereon the fiber sheet 8 that is being formed.

(6) The sheet-forming turntable 6 is caused to move in rotation about a vertical axis 10. Since forming the sheet is an operation that can be performed continuously at a constant speed, the sheet-forming turntable 6 is more specifically caused to move in rotation at a speed of rotation N.sub.FS that is constant and predefined.

(7) The circular needling table 2 also has a final unwinder 12 situated under the sheet-forming table 4, the final unwinder typically serving to unwind the fiber sheet 8 as wound on the sheet-forming turntable 6 in order to take it to needling.

(8) As described in greater detail in publication EP 2 339 055, the final unwinder 12 comprises a circular conveyor 14 for causing the fiber sheet 8 to rotate about the vertical axis 10. The circular conveyor 14 may advantageously be made up of two curved conveyor portions 14a, 14b, each of which is in the form of half a disk, which portions are placed facing each other (the straight edges of these conveyor portions being parallel and face to face). These curved conveyor portions are caused to rotate in a direction so as to cause the fiber sheet 8 to perform one complete 360° turn about the vertical axis 10.

(9) The circular conveyor 14 of the final unwinder 12 is controlled so as to cause the fiber sheet 8 to rotate about the vertical axis at a speed of rotation N.sub.DF.

(10) A needling table 16 is positioned under the final unwinder 12 for the purpose of performing circular needling of the fiber sheet 8 as unwound from the final unwinder.

(11) The needling table 16 is known, e.g. from publication EP 2 339 055, and is therefore not described in detail. In brief, it comprises a horizontal preform-forming turntable 18 that receives the fiber sheet so as to move in rotation about the vertical axis 10 at a speed of rotation N.sub.FP, which speed is adjustable.

(12) During this rotation, the fiber sheet is subjected to needling by a needling head (not shown in FIG. 1) that extends over an angular sector of the sheet-forming turntable and that is driven relative thereto with reciprocating vertical motion.

(13) As described in publication EP 2 339 055, it should be observed that the fiber sheet 8 as unwound from the circular conveyor 14 of the final unwinder is conveyed towards the preform-forming turntable 18 via a regulator chute 20 for regulating the unwinding of the sheet, which chute extends vertically between the final unwinder and the preform-forming turntable. The combined presence of a circular conveyor and of such a chute serves to deliver the fiber sheet without tension, the sheet being guided vertically towards the preform-forming turntable by using the chute.

(14) By its very nature, the speed of rotation N.sub.FP of the preform-forming turntable 18 is not constant, since it is necessary, in particular at the end of each cycle of forming a preform by needling (after needling a predefined number of layers of fiber sheet), to stop the rotation of the turntable in order to remove the preform prior to beginning a new cycle. In particular, this speed of rotation N.sub.FP is a predefined value that is different from the speed of rotation N.sub.FS of the sheet-forming turntable 6.

(15) According to the invention, provision is made to position a horizontal intermediate turntable 22 under the sheet-forming turntable 6, the intermediate turntable 22 being driven at a speed of rotation N.sub.FI, and serving to provide temporary storage for a certain number of turns of fiber sheet 8 between the sheet-forming machine and the needling machine.

(16) Furthermore, still according to the invention, a horizontal intermediate unwinder 24 is positioned on the intermediate turntable 22 and is driven at a speed of rotation N.sub.DI. In the same manner as for the above-described final unwinder, the intermediate unwinder comprises a circular conveyor 26 that may be made up of two curved conveyor portions 26a and 26b, each of which is in the form of half a disk, which portions are arranged facing each other, with the direction of rotation of these curved portions being directed so as to cause the fiber sheet 8 to perform one complete 360° turn about the vertical axis 10.

(17) The control of the circular needling machine of the invention is performed as follows, in particular concerning the speeds of rotation of its various component elements.

(18) As mentioned above, the speeds N.sub.FS (of the sheet-forming turntable 6) and N.sub.FP (of the preform-forming turntable 18) are input variables that are known. Furthermore, these turntables 4 and 18 have respective mean speeds that are equal.

(19) The speeds N.sub.DI (intermediate unwinder 24), N.sub.FI (intermediate turntable 22), and N.sub.DF (final unwinder 12) are controlled so as to satisfy the following control equations: (a) N.sub.DF is proportional to N.sub.FP; (b) N.sub.FI=(N.sub.FS−N.sub.DF)/2; and (c) N.sub.DI=(N.sub.FS+N.sub.DF)/2.

(20) Control equation (a) is a consequence of the presence of the regulator chute 20 for regulating the unwinding of the sheet between the final unwinder and the preform-forming turntable. More precisely, this equation is equivalent to: N.sub.DF=k×N.sub.FP in which k is a predetermined constant or variable factor corresponding to regulating the servocontrol of the quantity of helical fiber sheet in the regulator chute.

(21) Control equations (b) and (c) serve in particular to store a plurality of turns of fiber sheet on the intermediate unwinder without stressing the fiber sheet between the intermediate unwinder and the final unwinder and without stressing the fiber sheet at the outlet from the sheet-forming turntable.

(22) FIG. 2 shows an example of controlling the speeds of the various elements of the circular needling machine of the invention.

(23) More precisely, this figure shows an example of cyclical timing charts for speeds N.sub.FP, N.sub.FS, N.sub.FI, and N.sub.DI that satisfy control equations (a) to (c) of the invention.

(24) In this example, the speed N.sub.FS of the sheet-forming turntable is programmed to be constant and equal to 6 revolutions per minute (rpm). Likewise, the speed N.sub.FP of the preform-forming turntable is programmed to vary cyclically over the range 0 rpm to 10 rpm.

(25) It should be observed that a zero speed N.sub.FP corresponds to time during which the preform-forming turntable is stopped in order to remove the preform once it has been finished and in order to reinitialize the machine before restarting for a new forming cycle. This stopping time is typically of the order of 50 seconds (s), approximately.

(26) Starting from these predefined speeds N.sub.FS and N.sub.FP, the operator controls the speeds N.sub.DF, N.sub.FI, and N.sub.DI so that they satisfy the above-mentioned equations (a) to (c). Cyclical timing charts for these speeds that satisfy these equations are shown in FIG. 2.

(27) FIG. 2 also shows the cyclical timing chart N.sub.TS representing the number of turns of fiber sheet that accumulate on the intermediate unwinder. In this example, controlling the speeds N.sub.DF, N.sub.FI, and N.sub.DI makes it possible for there always to exist an accumulation of 2 to 10 turns of fiber sheet on the intermediate unwinder.

(28) Thus, because of the presence of the intermediate unwinder, it is possible in particular to keep the speed N.sub.FS of the sheet-forming turntable constant in spite of the stops of the preform-forming turntable that are necessary for removing a preform at the end of each cycle and for restarting the turntable.