Technical Field

[0001] The present invention relates to manufacturing of anti-ballistic helmets using consolidated wound fibers. In particular, the invention relates to a novel method of winding filaments onto a mandrel.

Background Art

[0002] Producing anti-ballistic helmets with filament winding technique is well known. Fibers or filaments are wound onto a rotating mandrel such that a layer of fibers is produced. The fiber layer is then typically consolidated in a press at an elevated temperature, to consolidate a binder that binds the fibers together. This results in a helmet structure capable of withstanding ballistic projectiles.

[0003] As an example of a known process, publication EP2151312 presents a solution where fibers are spun onto a mandrel to create a semi-finished product. Before the semi-finished product is removed from the mandrel, the fibers are fixated at the area where the semi-finished product is cut. In this manner, the fibers remain in place when removing the mandrel. Also disclosed is a method for closing the aperture appearing in the semi-finished product, as a result of the rotating mandrel shaft.

[0004] Another solution is presented in publication US8850612. Here, fibers are wound onto a rotating mandrel for manufacturing of an anti-ballistic helmet. The mandrel shaft leaves an uncovered crown portion, which is filled with a plug material. Alternatively, the mandrel shaft itself is made of a material suitable for remaining as a part of the helmet.

[0005] Repairing the aperture resulting from the mandrel shaft in the wound product demands time and resources. Moreover, it may constitute a weakness in the anti- ballistic helmet since the wound fibers do not cover the aperture.

[0006] An object of the present invention may be to provide a solution for avoiding such problems. Summary of invention

[0007] According to a first aspect of the present invention, there is provided a method of producing helmets, comprising the following steps: a) providing a mandrel supported on a rotational shaft, wherein the mandrel comprises a first curved part and an opposite second curved part; b) winding a filament onto the mandrel during rotation of the mandrel, thus providing a first helmet preform on the first curved part and a second helmet preform on the second curved part, wherein a sacrificial preform is obtained between the first and second helmet preforms; c) separating the first helmet preform from the second helmet preform, wherein said separation comprises cutting through the sacrificial preform; d) consolidating the first and second helmet preforms with elevated temperature and elevated pressure into a first and second consolidated helmet product; and e) cooling the consolidated helmet products.

According to the invention, during step b), the rotational shaft is connected to the mandrel at the area of the sacrificial preform.

[0008] The helmets can advantageously be anti-ballistic helmets.

[0009] Step c) may comprise cutting through the sacrificial preform at a distance from the first and second helmet preforms. However, step c) may also comprise cutting along the interface between the sacrificial preform and the first and second helmet preforms.

[0010] The said elevated temperature and elevated pressure can be above 50 °C or even above 100 °C and above 10 bar. As the skilled person will appreciate, the selected temperature may be chosen based on the fiber used. For instance, a preferred fiber is an IIHMWPE fiber (ultra-high molecular weight polyethylene) that can withstand about 170 °C. As the skilled person will appreciate, the temperature and pressure may depend not only on properties of the filament but also the properties of a possible binder.

[0011] Filaments can preferably be made of highly crystalline polymeric fibers such as those made of ultrahigh molecular weight polyethylene and aromatic polyamide (aramid). However, other fibers of high strength, such as above 500 MPa, and stiffness, such as above 50 GPa, are applicable. Typical fibers are known in the art as certain types of Spectra, Dyneema og Kevlar fibers.

[0012] A rotational axis is aligned with the rotational shaft and extends along an axis distance between the opposite outer surfaces of the mandrel. Moreover, a center axis extends along a mandrel apex distance between an apex of the first curved part and an apex of the second curved part. In some embodiments, the mandrel apex distance is larger than the axis distance.

[0013] Step c) may comprise cutting through the sacrificial preform along a sacrificial preform cutting line, and the method may further comprise, after step e), cutting a consolidated sacrificial part off from the consolidated helmet product, along a helmet cut line (step f).

[0014] Step b) may include adding a securing agent onto the filament, wherein more securing agent is applied onto the filament at the position of the sacrificial preform than at the positions of the first and second helmet preforms.

[0015] The securing agent is applied to increase stability and integrity of the helmet preforms. In this manner, the helmet preforms will remain intact during handling before being consolidated in step d). In a typical embodiment, the securing agent can be applied only onto the sacrificial preform, thus not onto the first and second helmet preforms.

[0016] The securing agent can typically be a binder that will function as an adhesive or a glue that consolidates before the helmet preforms are separated in step c). Another form of binder is to use hotknife, wherein adjacent fibers or filaments are fixed to each other by welding (i.e. by melting and solidification).

[0017] The helmet cut lines can preferably include a curved cutout line, wherein the respective curved cutout lines of the two opposite, respective helmet cut lines are aligned, symmetric, and define a cutout portion where the rotational shaft is positioned during step b). The curved cutout lines are arranged directly opposite to each other.

[0018] The cut line can comprise a front cut line and a rear cut line arranged on respective sides of the curved cutout line. In some embodiments, the front cut line of one cut line is aligned with the rear cut line of the opposite cut line. [0019] In such embodiments, the shaft-produced aperture, or the rotational shaft, is located between the opposite curved cutout lines. In this manner the entire height (also referred to herein as a preform apex distance) of the filament layer can be made less than two times the height of one of the first or second helmet preforms.

[0020] Step d) may in some embodiments comprise placing the first and second helmet preforms inside respective moulds, sealing cut end portions of the first and second helmet preforms with a seal, thus preventing liquid ingress between the helmet preforms and the moulds, and then, with a hydroclave, elevating pressure and temperature to consolidate the helmet preforms. In such embodiments, the first and second preforms are compressed between the inner face of the moulds and the liquid pressure provided by the hydroclave. The moulds are then compressed between the helmet preforms and the liquid pressure.

[0021] As discussed above, a rotational axis extends through and along the rotational shaft, and a center axis extends through an apex of the first curved part and an apex of the second curved part. In some embodiments, the mandrel is symmetric about the center axis.

[0022] In other embodiments though, the mandrel can be asymmetric about the center axis. In such embodiments, the consolidated first and second preforms may have a shape that is substantially corresponding to the final shape of the consolidated helmet product.

[0023] The method may in some embodiments further comprise, between step b) and step d): covering the first and second helmet preforms with an elastic mould (step g).

[0024] According to a second aspect of the present invention, there is provided a mandrel configured for filament winding of helmet preforms. The mandrel comprises a first curved part, an opposite second curved part, and an intermediate mandrel part arranged between the first and second curved parts. It also comprises a rotational shaft that is connected to the intermediate mandrel part.

[0025] It will be appreciated that the first and second curved parts are configured for receiving filaments that will be part of produced helmets.

[0026] A rotational axis is aligned with the rotational shaft and extends along an axis distance between the opposite outer surfaces of the mandrel. Moreover, a center axis extends along a mandrel apex distance between an apex of the first curved part and an apex of the second curved part. In some embodiments, the mandrel apex distance is larger than the axis distance.

[0027] Moreover, in some embodiments, the mandrel may comprise a first mandrel part and a second mandrel part that is detachably connected to the first mandrel part. The rotational shaft can then comprise a locking means releasably maintaining the first and second mandrel parts in a connected state. Such a locking means can take various forms, for instance as securing screws or securing clamps.

Detailed description of the invention

[0028] While various features have been presented in general terms above, a more detailed and non-limiting example of embodiment will be presented in the following with reference to the drawings, in which

Fig. 1 is a schematic cross section view through a mandrel and a wound filament layer;

Fig. 2 is a schematic cross section of the parts shown in Fig. 1 , however with an elastic mould arranged onto the filament layer;

Fig. 3 is a schematic cross section view illustrating a consolidation step occurring inside an autoclave;

Fig. 4 is a perspective view of the mandrel and a rotational axis for rotation of the mandrel;

Fig. 5 is a schematic cross section view of the mandrel, for illustration of its shape;

Fig. 6 is a perspective view of the filament layer and its different parts;

Fig. 7 is a schematic side view of the filament layer shown in Fig. 6; and

Fig. 8 illustrates an alternative embodiment.

[0029] Fig. 1 to Fig. 3 illustrate a method of consolidating a layer of fibers that have been wound onto a mandrel. It will be appreciated that these illustrations are schematic, with an aim to briefly present the consolidation process. [0030] Fig. 1 depicts a cross section view through a mandrel 1 , onto which a filament layer 3, of wound fibers or filaments 4, is arranged. The filament 4 can typically be in form of towpreg, comprising a plurality of fibers in a bundle together with a polymer binder.

[0031] Between the filament layer 3 and the mandrel 1 , there is arranged a non-stick layer 5. The non-stick layer 5 facilitates later removal of the filament layer 3 from the mandrel 1. As will be appreciated by the skilled reader, the non-stick layer 5 is not compulsory, but can be applied according to need.

[0032] Fig. 2 shows the same parts as in Fig. 1 , however further with an elastic mould 7 attached to the outer face of the filament layer 3. The elastic mould 7 secures the filament layer 3, such that the fibers remain in the wound position when the mandrel 1 is removed.

[0033] Fig. 3 shows the filament layer 3, still together with the non-stick layer 5 and the elastic mould 7. In addition, these three layers have been cut through, to enable removal from the mandrel 1 .

[0034] The elastic mould 7 is not compulsory but is included in this example embodiment as an option.

[0035] After removal from the mandrel 1 , the two parts are placed in a metallic mould 9, as shown in Fig. 3. They are then exposed to elevated pressure and temperature inside a hydroclave (not shown), for consolidation of the filament layer 3.

[0036] A seal 11 is preferably provided at the cut face of parts, to prevent liquid from entering the filament layer 3 when using the hydroclave.

[0037] After consolidation in the hydroclave, the parts are removed from the metallic moulds 9, and the non-stick layer 5 and the elastic mould 7 (if present) are removed from the now consolidated filament layer 3.

[0038] Reference is now made to Fig. 4, for discussion of the filament winding method. The mandrel 1 comprises a first curved part 1a and an opposite second curved part 1 b. Between the first and second curved parts 1a, 1 b, the mandrel 1 has an intermediate mandrel part 1c. The first curved part 1a, the second curved part 1 b, and the intermediate mandrel part 1c together form a ball-shaped or spherical mandrel 1 . As indicated with the drawing of Fig. 4 (and with the schematic illustrations of Fig. 1 and Fig. 2), the radius of the ball-shape is not constant along its outer surface.

[0039] In some embodiments, the first and second curved parts 1 a, 1 b of the mandrel 1 can have a shape corresponding to a helmet. In such embodiments, one will not need to re-shape the preform before consolidation. In other embodiments, the first and second curved parts 1 a, 1 b can have an axis-symmetrical shape, such as a sphere or an ellipsoid. In such embodiments, the helmet preforms 3a, 3b need to be shaped into the desired helmet shape before consolidation.

[0040] A center axis A is indicated, extending through the first and second curved parts 1 a, 1 b. In some embodiments, the mandrel 1 can by symmetric about the center axis A. In other embodiments, however, the mandrel 1 can be non-symmetric about the center axis A. In the latter case, the shape of the mandrel 1 can be better fitted to the final shape of an anti-ballistic helmet.

[0041] A rotational shaft 13 connects to the mandrel 1 at the position of the intermediate mandrel part 1 c. During the filament winding step, the mandrel 1 is made to rotate by rotating the rotational shaft 13. A rotational axis R, about which the mandrel will rotate, is also indicated.

[0042] Fig. 5 is a schematic cross section view through the mandrel 1 . The center axis A and the rotational axis R are indicated, extending orthogonally with respect to each other. The center axis A extends through the apex of the first curved part 1 a and the apex of the second curved part 1 b of the mandrel 1 . The distance between these apexes is termed a mandrel apex distance Hm. Moreover, between the outer surface of the mandrel 1 , at the position of the rotational axis R, there is an axis distance a. As appears from Fig. 5, in this embodiment the mandrel apex distance Hm is larger than the axis distance a.

[0043] A radius n is indicated, extending from and orthogonally from the center axis A to the outer surface of the mandrel 1 . In some embodiments the radius n may vary about the circumference, rotated about the center axis A. In other embodiments it may be constant.

[0044] Fig. 6 depicts the filament layer 3 after the winding step. A filament has been wound onto the mandrel 1 . The filament layer 3 has a first helmet preform 3a, a second helmet preform 3b, and a sacrificial preform 3c. The sacrificial preform 3c is arranged between the first and second helmet preforms 3a, 3b. The sacrificial preform 3c is located on the intermediate mandrel part 1c of the mandrel 1 .

[0045] After the winding step, the rotational shaft 13 has been removed. As indicated in Fig. 6, cf. the shaft-produced aperture 13a, the sacrificial preform 3c is without filament at the position where the rotational shaft 13 was located.

[0046] Advantageously, a binder can be added to the sacrificial preform 3c during winding. This binder could in some embodiments be added to the filaments only at the area of the sacrificial preform 3c, while not to the first and second helmet preforms 3a, 3b. This contributes to maintaining the filaments in their wound position when cutting the filament layer 3 in two parts.

[0047] The said cutting takes place through the sacrificial preform 3c, such that the first and second helmet preforms 3a, 3b are maintained intact. A sacrificial preform cutting line 15, along which the said cutting step can take place, is indicated in Fig. 6.

[0048] Thus, during the consolidation step, typically taking place in an hydroclave (not shown), the first and second helmet preforms 3a, 3b are still attached to a part of the sacrificial preform 3c.

[0049] The consolidation step converts the first and second helmet preforms 3a, 3b into a first and second consolidated helmet product. The sacrificial preform 3c is also consolidated, into a consolidated sacrificial part. The consolidated sacrificial parts is cut off from the consolidated helmet products, along a helmet cut line 17, indicated in Fig. 6.

[0050] Anti-ballistic helmets typically comprise an ear cutout, i.e. a portion of the helmet edge that renders space for the user's ear. In Fig. 6, an ear cutout portion 19 is shown. By arranging the rotational shaft 13 at the ear cutout portion 19, cf. the shaft-produced aperture 13a, one obtains a significant distance between the helmet cut lines 17 and the rotational shaft 13. In this manner, the winding pattern on the first and second helmet preforms 3a, 3b are not excessively disturbed by the presence of the rotational shaft 13.

[0051] Fig. 7 is a schematic side view, showing the same items as in Fig. 6. The respective helmet cut lines 17 comprise a curved cutout line 17a. The curved cutout line 17a extends between a front cut line 17b and a rear cut line 17c. When used by a person, the front cut line 17b is configured to extend along the person's forehead, while the rear cut line 17c is configured to extend along the neck. In the embodiment shown in Fig. 7, the curved cutout lines 17a of the two opposite helmet cut lines 17 are aligned and symmetrical. In this manner, one obtains a large distance between the rotational shaft 13 and the helmet preforms 3a, 3b. [0052] Fig. 8 depicts an alternative embodiment. In this embodiment, the front cut line 17b of one cut line 17 is aligned with the rear cut line 17c of the opposite cut line 17. The shaft-produced aperture 13a is located between the opposite curved cutout lines 17a. In this manner, and as indicated in Fig. 8, an entire preform apex distance H _P of the filament layer 3 is less than two times the height of one of the first or second helmet preforms 3a, 3b. The said preform apex distance H _P corresponds to the mandrel apex distance Hm, except that the distance is measured from the outer surface of the preform 3 (not the mandrel 1 ). This solution saves waste filament material, since the sacrificial preform 3c is relatively small.