METHOD FOR BINDING A CYLINDRICAL PART BY THE TENSIONED WINDING OF FIBERS

Abstract

A method for binding a cylindrical part by the tensioned winding of fibers, the method including a preliminary step of passing the fibers around at least two braked tensioning cylinders in order to increase the tension in the fibers, wherein the method includes increasing the diameter of the cylinders as the tension in the fibers increases.

Claims

1-12. (canceled)

13. A method for binding a cylindrical part by the tensioned winding of fibers, comprising a preliminary step of said fibers passing around at least two braked tensioning cylinders (C.sub.1; C.sub.2) in order to increase the tension therein and consisting of increasing the diameter D of the cylinders as the tension in the fibers increases, wherein, n being an integer greater than or equal to 2 and m an integer strictly less than n, said method consists of maintaining a constant diameter for the first m cylinders (C.sub.1; C.sub.m) then increasing said diameter of the last (n−m) cylinders (C.sub.m+1; C.sub.n).

14. The method according to claim 13, wherein the diameter of the last (n−m) cylinders increases arithmetically.

15. The method according to claim 13, wherein it consists of increasing the peripheral velocity of the cylinders as the tension in the fibers increases.

16. The method according to claim 15, wherein, n being an integer greater than or equal to 2 and p an integer strictly less than n, said method consists of maintaining a constant peripheral velocity for the first p cylinders (C.sub.1; C.sub.p) then increasing said peripheral velocity of the last (n−p) cylinders (C.sub.p+1; C.sub.n).

17. The method according to claim 16, wherein the peripheral velocity of the last (n−p) cylinders increases arithmetically.

18. The method according to claim 13, wherein the diameter D.sub.n of the last cylinder C.sub.n is at least equal to 10% of the diameter of the cylindrical part to be bound.

19. The method according to claim 13, wherein all the cylinders are synchronized by gears, or by a chain, or by a toothed belt.

20. The method according to claim 19, wherein it consists of providing the brake of the cylinders with an electric motor synchronized with said cylinders, operating as a generator and supplying power to an electric motor of the cylindrical part to be bound.

21. The method according to claim 13, wherein the total number n of cylinders (C.sub.1; C.sub.n) is between 2 and 50, preferably between 10 and 30.

22. The method according to claim 13, wherein it causes the stress in the reinforcing fibers to increase from about 1 MPa to about 1000 MPa.

23. A method for manufacturing a flywheel, wherein the method comprises a step of manufacturing a concrete body by molding, then, after the hardening of the concrete, a step of binding the concrete body by winding tensioned fibers using the method according to claim 13.

24. A flywheel obtained using the method according to claim 23, wherein the flywheel comprises a cylindrical mass body of which the main component material has a compressive strength of at less 25 MPa, such as concrete, said body being enveloped, over at least part of its external surface, with fibers tensioned by means of a method for binding a cylindrical part by the tensioned winding of fibers and for which the winding tension around the body causes compression of said main material, wherein the method for binding a cylindrical part by the tensioned winding of fibers, comprises a preliminary step of said fibers passing around at least two braked tensioning cylinders (C.sub.1; C.sub.2) in order to increase the tension therein and consisting of increasing the diameter D of the cylinders as the tension in the fibers increases, wherein, n being an integer greater than or equal to 2 and m an integer strictly less than n, said method consists of maintaining a constant diameter for the first m cylinders (C.sub.1; C.sub.m) then increasing said diameter of the last (n−m) cylinders (C.sub.m+1; C.sub.n).

Description

PRESENTATION OF FIGURES

[0031] Other particular advantages, aims and features of the invention will become apparent from the following non-limiting description of at least one particular embodiment of said object of the invention, with reference to FIG. 1 which represents a method for reinforcing a solid flywheel using tensioned fibers.

[0032] Thus, FIG. 1 illustrates a flywheel 1 of cylindrical shape extending longitudinally between two distal ends 10 and 11 along an axis of revolution. This flywheel 1 comprises a mass 12 made of a component material such as concrete, and a casing 13 made of reinforcing fibers F wound under tension and inducing compressive forces on the mass 12. The concrete mass 12 is for example made by molding. The flywheel 1 incorporates a shaft 6 which protrudes from the end bases 10 and 11. This shaft 6 is made integral with the body of the flywheel 1 during manufacture by molding the mass 12, the shaft 6 having previously been placed in the mold into which the concrete was poured.

[0033] The casing/housing 13 is obtained by tensioned winding of the reinforcing fibers F, for example glass fibers, around the concrete mass 12 in order to generate compressive stress on said mass 12 when the latter is at rest, in other words with no rotation of the flywheel 1. The material of the mass 12 is thus prestressed.

[0034] For example, the main material is concrete having a compressive elastic limit of 100 MPa. The diameter of the cylinder forming the concrete core 12 is substantially equal to 0.6 m. It has a length (height) of 2 m. Its mass is approximately 1.4 t.

[0035] The thickness of the casing 13 of glass fibers is for example 12 mm. The mass of glass fibers is 0.11 t, which is much lower than the mass of the concrete core 12.

[0036] The method for obtaining the tensioned fibers F and then winding them around the cylinder 12 is described below.

[0037] Represented in this FIG. 1 are a series of braked tensioning cylinders numbered C.sub.1 to C.sub.11, and more generally C.sub.1 to C.sub.n with n>2.

[0038] The fibers F are stretched by having them pass successively over a portion of the outer surface of each of these cylinders which are rotated in a synchronized manner. More precisely, the odd-indexed cylinders rotate clockwise while the even-indexed cylinders rotate counterclockwise, so that the fibers F are successively tensioned between each pair of consecutive cylinders (between C.sub.1 and C.sub.2, then C.sub.2 and C.sub.3, etc. until C.sub.n).

[0039] As was presented above in the introductory part, the invention consists of increasing the diameter of the cylinders C.sub.1 to C.sub.n as the tension T increases in the fibers F, in order to follow their elongation and limit their sliding velocity on said cylinders.

[0040] Thus, as can be seen in FIG. 1 (the proportions, in particular those of the cylinders, are exaggerated in order to better understand the invention), the first m cylinders, m being an integer strictly less than n, m being equal for example to 5 in the present case, all have the same diameter D.sub.m such that D.sub.1=D.sub.2=D.sub.3=D.sub.4=D.sub.5.

[0041] On the other hand, the last (n−m) cylinders C.sub.m+1 to C.sub.n, meaning cylinders C.sub.6, C.sub.7, C.sub.8, C.sub.9, C.sub.10 and C.sub.11, have a diameter D.sub.n which gradually increases.

[0042] In practice, the variations in the diameter of the cylinders are extremely small: for a glass fiber increasing from a tensile stress at infeed of 1 MPa to a stress at outfeed of 1000 MPa and a determined elongation for example (non-limiting) of 1.4%, the difference in diameter between two cylinders starting from the cylinder of rank (m+1) averages 0.15%. For a cylinder C.sub.6 that is 50 mm in diameter, this makes a difference of 0.08 mm for each cylinder of higher tank, imperceptible to the naked eye but easily achievable mechanically by adjustment.

[0043] The corollary of this increase in the diameter D of the (last) cylinders is an increase in their peripheral velocity as the tension T in the fibers F increases.

[0044] Thus, if V.sub.n is the peripheral velocity of cylinder n, we therefore implement: V.sub.1<V.sub.2<V.sub.3<V.sub.4< . . . <V.sub.n.

[0045] It is possible to use cylinders of very different diameters, rotating at different speeds, provided the condition V.sub.1<V.sub.2<V.sub.3<V.sub.4< . . . <V.sub.n is respected. This can be of interest in reducing the contact pressure, which is proportional to the tension and inversely proportional to the diameter of the cylinder. It is therefore necessary to increase the diameter of the last cylinders, where the tension of the fiber is the highest.

[0046] Preferably, the diameter D.sub.n of the last cylinder C.sub.n is at least equal to 10% of the diameter of the cylindrical part to be bound.

[0047] Thus, the above relation is valid only starting from the cylinder of rank p+1, p being an integer strictly less than n, and this is true up to and including the last cylinder of rank n.

[0048] Consequently, if V.sub.n is the peripheral velocity of cylinder n, we therefore implement: V.sub.p+1<V.sub.p+2<V.sub.p+3<V.sub.p+4< . . . <V.sub.n. In this case, it means that V.sub.6<V.sub.7<V.sub.8<V.sub.9<V.sub.10<V.sub.11.

[0049] Preferably it will be arranged so that m=p.

[0050] From a mathematical point of view, if the first cylinder C.sub.1 has a diameter D.sub.1, and the tension in the fibers F increases from T.sub.0 to T.sub.1, the second cylinder will have a diameter D.sub.2 equal to:

D.sub.2=D.sub.1×(1+T.sub.1/(S×E))/(1+T.sub.0/(S×E)),

[0051] where S is the cross-sectional area of the fiber, and E its Young's modulus.

[0052] T.sub.0/(S×E) is the elongation of the fiber at the infeed to the first cylinder C.sub.1.

[0053] T.sub.1/(S×E) is the elongation of the fiber at the outfeed from the first cylinder C.sub.1.

[0054] In this manner, the fiber arrives on each cylinder with zero sliding: they are “synchronized”.

[0055] In practice, there is very little sliding on the first cylinders, but it increases exponentially as the tension T in the fibers F increases. When the sliding reaches a certain value (for example here the value of 0.1% is chosen arbitrarily and as a non-limiting example), it is possible to reduce the increase in the diameter of the cylinders. Advantageously, the peripheral velocity of the last (n−p) cylinders increases arithmetically, rather than exponentially.

[0056] With the invention, it is possible to choose the contribution of each cylinder to the total increase in tension in the fibers F. In practice, this means that it is not necessary to have sliding over the entire area of each cylinder C around which the fibers F pass.

[0057] The sliding angle is different from the winding angle. The winding angle is given by the geometry of the machine, and it remains constant. The sliding angle depends on the torque applied to the cylinder: it varies between 0 (zero torque) and the winding angle (maximum transmissible torque). We can therefore have winding over 180°, but sliding over only 40°.

[0058] It is thus possible to use the entire winding area at the start, when the tension is low, and only partially use it at the end, when the tension is high. It is thus possible to limit the maximum sliding velocity and protect the fiber. In return, it will be necessary to install more cylinders, their number able to vary from a few to about fifty and advantageously between about 10 and 30.

[0059] In order to further reduce the maximum sliding, it is possible to have an arithmetic progression of the diameter D of the last cylinders, and therefore also of their respective peripheral velocities.

[0060] To reduce the contact pressure between fibers and cylinders, which can reach 4 MPa (40 bar) and could damage the fibers which are sliding on the cylinder, the diameter D of the cylinders should be greatly increased so that the last one(s) is (are) fairly large compared to the flywheel 1. Here it is again possible to have an arithmetic progression of the diameter D of the last cylinders. Advantageously, the diameter D.sub.n of the last cylinder C.sub.n is at least equal to 10% of the diameter of the cylindrical part to be bound.

[0061] Gears make it possible to obtain the synchronization of the various speeds of rotation, then adjustment of the diameters makes it possible to obtain the desired sliding on each cylinder.

[0062] It is interesting to note that this increase in diameter in order to reduce the contact pressure is independent of the increase in the peripheral velocity in order to reduce sliding.

[0063] In practice, the following procedure is used: [0064] the approximate diameter of the cylinders is first calculated to limit the contact pressure; [0065] the gears are chosen so as to allow obtaining a substantially constant peripheral velocity (a pulley four times larger will turn four times slower); [0066] the exact diameter of the cylinders making it possible to obtain the anticipated peripheral velocity for limiting sliding is then recalculated.

[0067] It is also provided to equip the brake of the cylinders with an electric motor synchronized with said cylinders, operating as a generator and supplying power to an electric motor of the cylindrical part to be bound.

[0068] Once obtained, the glass fibers F are wound at an angle close to 90° relative to the longitudinal axis 6 of the concrete cylinder 12 of the flywheel 1, and under a tension which generates stress of about 1000 MPa. The initial prestressing (compression) in the concrete is 50 MPa. The flywheel 1 according to the invention can rotate up to 7700 revolutions/min, the speed at which the prestressing in the concrete becomes zero. The stored energy is then 23 MJ or 6.4 kWh.

[0069] As a result, due to the main material of the mass of the flywheel, which is prestressed via the tensioned winding of reinforcing fibers, the invention makes it possible to provide a compression of said material such that it is possible to achieve high speeds of rotation before reaching the point of rupture of the material, which very advantageously allows a large amount of energy to be stored.

[0070] It is of course understood that the detailed description of the object of the invention, provided solely for illustrative purposes, does not in any way constitute a limitation, the technical equivalents also being included within the scope of the invention.

[0071] The invention can be implemented with a two-cylinder system: it is sufficient to manufacture the braked cylinder (or cylinders) with stepped diameters D.sub.n satisfying the following rule: D.sub.1<D.sub.2<D.sub.3<D.sub.4< . . . <D.sub.n.

[0072] The gears can also be replaced with a chain or a toothed belt.