Abstract:
A method for producing a ballistic protective armour includes superimposing a certain number of textile layers ( 116 ) in such a way that a layer structure ( 114 ) is formed, in sewing the textile layers ( 116 ) of the layer structure to each other and in pressing the layer structure ( 114 ). Prior to a sewing process, the textile layers ( 116 ) of the layer structure ( 114 ) are pre-pressed by a pre-pressing process ( 30 ) in such a way that a preform ( 130 ), whose three-dimensional shape corresponds to a final product shape, is formed and subsequently, after the sewing process ( 50 ), the preform is exposed to a heat-pressing process ( 100 ) at a temperature greater than the temperature of the pre-pressing process ( 30 ).

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a method for producing a ballistic protective armour according to the premeable of claim  1 . 
   Ballistic protective armours are known as components of ballistic protective clothing in a number of different embodiments, as, for example, military helmets protecting against projectile impacts and shell splinters, as flak jackets and suchlike. For producing a protective armour of this kind, single textile layers made of highly durable fabrics are layered onto each other to form a layered structure. The textile layers of this layered structure are sewed together and subjected to a pressing step to form a laminate. A protective armour of this kind is known, for example, from the patent document U.S. Pat. No. 3,841,954 and serves in the case described in this document as a back-side reinforcement of another armouring layer, so that a high stability against the impact of a splinter is achieved. 
   The compactness and and rigidity of the layered structure can be improved by sewing so that the protective effect of the armouring is improved. Moreover it is known to form ballistic protective armours from laminated textile layers which absorb the energy of a striking projectile to a large extent. This is achieved by a deformation of the projectile which penetrates the outer layers of the laminate, the deformed projectile being intercepted by the remaining layers at the inner side of the armour which is to be protected, because the kinetic energy is already strongly reduced after destroying the outer layers. These remaining catching layers delaminate in parts from the penetrated outer layers so that an inward bulge is formed at the inner side of the protective armour, in which the projectile remains. Because an extensive bulging effect can lead to strong injuries of the wearer of the ballistic protective armour, for example, to severe head injuries of the wearer of a military protective helmet which is built that way, it is possible to delimit the peeling or delamination effect of the catching layers by providing seams. Thus it is possible to provide a protective armour made of a textile laminate which absorbs an impact sufficiently on one hand and keeps the person to be protected from suffering injuries on the other hand. 
   To ensure a wearing comfort which is as high as possible as well as an extensive protective effect, the ballistic protective armour should be adapted to the body form of its wearer. It is therefore desired to produce the armour in a large variety of different forms. This is not always achievable without problems because the inner structure of the relatively rigid textile laminate can be changed by a subsequent bending, bulging, deep drawing or the like in a way that the protective effect may be impaired all over the whole product or locally. In particular it is disadvantageous if a covering which is coated to the textile layers for forming the laminate penetrates too deep into the fibers, because the fabric of the textile layers and the yarn of the seams shall keep well-defined properties with respect to elasticity and tensile strength. For example, the protective armour disclosed by U.S. Pat. No. 3,841,954 is bendable to a certain extent after sewing and subsequent pressing, but it is not spherically deformable, for example, to a hemisphere. So it is not possible to form helmet shells by that way. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a method for producing a ballistic protective armour of the above kind which makes it possible to produce protective armours in a broader variety of forms as it used to be possible according to the state of the art, without imparing its protective properties. In particular it is an object of the present invention to permit the production of helmet shells made of a coated textile material comprising textile layers which are sewed and pressed together. 
   This object is achieved by a method according to claim  1 . 
   According to the present invention, the textile layers of the layered structure are pre-pressed to a preform before sewing, the shape of the preform corresponding to the end product to be produced, for example, the desired spherical form. Subsequently the textile layers of this pre-pressed preform are sewed with each other. The production process is finished by a hot pressing step at a higher temperature than during the pre-pressing step. While the pre-pressing step generally serves to bring the layered structure into the desired shape before sewing, the layers are densified to form the desired laminate with high rigidity. By this step the produced ballistic protective armour also obtains its stiffness. 
   One advantage of the method according to the present invention lies in the fact that the shape of the end product is already present before sewing, and the final hot pressing does not cause a considerable change of the shape of the product. The preform is not bent or bulged after sewing so that it keeps its structure during the hot pressing step. Therefore the structure of the fabric of the textile layers is obtained as well as the tensile properties of the yarn which is used for sewing, so that the tensile strength and elasticity are maintained sufficient for generally keeping the cohesion of the laminate at the impact of a projectile into the protective armour. 
   Preferred embodiments of the present invention are disclosed in the subclaims. Preferably a method for producing the helmet shell of a ballistic protective helmet is claimed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following a preferred embodiment of the present invention is explained with respect to the following drawings. 
       FIG. 1  is a flow diagram representing schematically a preferred embodiment of the method according to the present invention; 
       FIGS. 2 to 9  are schematic views of single method steps from  FIG. 1 ; 
       FIGS. 10   a  to  10   j  are plan views of examples of blanks of textile layers for forming the layered structure; and 
       FIG. 11  is a view of the end product produced by the method according to the present invention from below. 
   

   DETAILED DESCRIPTION  
   In the following the production of a spherically convex ballistic protective armour shall be described by way of example, which shall serve as the helmet shell of a ballistic protective helmet. As a basic material are textile layers being woven of a yarn with high strength or technical fibers like, for example, aramid, high molecular polyethylene or the like, said textile layers being covered on one side by a connecting agent like, for example, resin, plastic or an adhesive agent. This can be achieved by applying a resin coating which attaches to the surface of the fabric when heated without penetrating the fibers. During hot pressing, a laminate connection of the textile layers with each other is formed, wherein the connecting agent penetrates the textile layers partially but only as far as the elasticity and flexibility of the fibers of the fabric is maintained. Therefore, the textile layers can absorb the kinetic energy of an impacting projectile to a certain extent. 
   A preparation step of the method according to the present invention can be the preparation of single textile blanks by covering them with a connection agent like, for example, a resin, plastic or adhesive agent. The blanks of the textile layers, which are shown in  FIGS. 10   a  to  10   j  by way of example, are first layered in a predetermined order onto each other in a step marked by reference number  10  in  FIG. 1 . Some of the blanks are provided with radial insections which allow to give the layer a vaulted shape by overlapping of surface areas to allow further processing to an almost spherical shape. 
   Because the covered textile layers usually have a high rigidity, the step of layering  10  to form a layer structure can be carried out in a mold which also serves as a pre-heating mold. Because the number of used textile layers can be large, it may be helpful to fix the layer structure for example by fasteners at the rim of the pre-heating mold. In a pre-heating step  20 , the textile layers are heated and lay against each other and on top of the pre-heating mold  110 , which preferably has the general shape of the end product to be produced. 
   After the pre-heating step  20 , the layered structure is pre-pressed in a cold state in a pre-pressing step to produce a preform with a shape corresponding to the end product to be produced. The textile layers of this preform can be fixed to each other pointwise by fasteners or the like (step  40 ) after the pre-pressing step  30  to keep their coherence. In the following step  50  the textile layers of the preform are sewed together. The sewing step can be followed by an intermediate pressing step  60 , after which additional seams for reinforcing critical zones of the ballistic protective armour can be applied (step  70 ). After a second intermediate pressing step  80 , the completely sewed preform can be provided with a protective layer on its inner surface and/or on its outer surface (step  90 ). At last the sewed preform is pressed together with its protective layers in a hot pressing step  100  to connect its textile layers by the applied connecting agent to form a laminate. The ballistic protective helmet which is formed by this procedure is kept together by the cohesion of the laminate of the textile layers on one hand and additionally by the seams which are applied in the sewing steps  50  and  70  on the other hand. 
   The method steps shown in  FIG. 1  are explained in the following with respect to  FIGS. 2 to 9 . 
     FIG. 2  is a schematic section through a pre-heating mold  110 , the inner surface  112  of this pre-heating mold  110  being formed hemispherically for receiving a layered structure  114  of textile layers. Each of these textile layers, one of them being provided with the reference number  116  in  FIG. 2 , consists of yarns or fibers with high tensile strength like, for example, high molecular polyethylene, aramid or the like and is covered by a connecting agent like resin, plastics or adhesive agent on one of its sides in a preparation step. This textile layer material has usually a certain stiffness, so that it is preferably pre-heated within a pre-heating mold  110  before being further processed. To this purpose the step of layering the textile layers  116  marked by reference number  10  in  FIG. 1  can be carried out in the pre-heating mold  110  itself. Radial insections  118  in the layer blanks facilitate the matching to the pre-heating mold  110 . The layered structure  114  formed this way can temporarily be fixed in or at the mold to prevent the textile layers  116  from being shifted against each other. 
   When the pre-heating mold  110  or its inner surface  112  is heated in a suitable way, the textile layers  116  of the layered structure  114  lay against the hemispherical inner surface  112  because of the heating of the material of the textile layers and the coated connecting agent, making the layers flexible. The pre-heating is preferably carried out at a temperature of the pre-heating mold 110 of 60° C. In the ideal case the single textile layers  116  lie flat on each other after the pre-heating step  20  so that the layered structure  114  takes a hemispherical form.  FIG. 3  shows the pre-heating mold  110  in a lateral section from a perspective view, comprising the layered structure  114 . 
   After the pre-heating the hemispherical layered structure  114  is transferred into a cold press  120 , like it is shown in  FIG. 4 . The cold press  120  comprises a hemispherical lower mold half  122  on which the layered structure  114  is laid with its concave inner side, as well as a concave upper hemispherical mold half  124  which is provided to be lowered onto the lower mold half  122  in a way that it encloses the outside of the layered structure  114 , as shown in  FIG. 5 . In this state the layered structure  114  comprising the textile layers  116  is pre-pressed in a cold state (method step  30  in  FIG. 1 ). In this pressing step, pressure and temperature must be chosen to form an interstage product with a relatively compact packing of layers in which the layers do not dissolve from each other automatically. The pre-pressing can be carried out at room temperature with a pressure of 150 kg/cm 2 . 
   The preform  130  shown in  FIG. 6 , which is produced by the pre-pressing step  30 , already comprises the shape of the ballistic protective armour to be produced, which is the desired form of the helmet shell in the example described here. However, it acquires its final protective properties by further method steps which are explained in the following. 
   The single textile layers  116  of the preform  130  can be locally fixed against each other before further processing (method step  40  in  FIG. 1 ), like, for example, by pointwise attaching of connectors like cramps or the like, which are shot into the layered structure  114  at different positions. These connectors are not shown in  FIG. 6  for the sake of simplicity. The preform  130  from  FIG. 6  is subsequently sewed, like it is schematically shown in  FIG. 7  (method step  50  in  FIG. 1 ). For this purpose a preform  130 , which is pre-pressed and fixed pointwise, where necessary, is provided with seams by a sewing machine, keeping the single textile layers  116  of the layered structure  114  together.  FIG. 7  shows a meandering seam  132  running in portions on the inner side as well as on the outside of the preform  130 , and the portions  134  and  136  running on the inside, and on the outside are connected by portions  138  of the seam  132  extending radially with reference to the hemisphere of the preform  130 , i. e., in the layering direction, ensuring the cohesion of the textile layers  116 . The stitch pattern of the seam  132  is shown simplified in  FIG. 6  and can be more complex. The sewing method can be adapted arbitrarily to the desired protective properties of the ballistic protective helmet to be produced. The yarn of the seam  132  is chosen such that it comprises a high tensile strength as well as a certain elasticity, to prevent a large number of yarn portions  138  from being sheared in the layering direction to the inside. It is advantageous when the yarn  132  can absorbe a large part of the energy of the projectile and is stretched that way. A partial delamination of the inner textile layers  116  of the layers structure  114  is accepted in a certain extent. 
   The course of the seam  132  can be chosen in a way that the seam winds spirally from the center  140  of the area of the hemisphere of the preform  130  around this center  140  to the rim  142  of the hemisphere, like it is additionally shown in  FIG. 11 , showing a top view onto the inner surface  144  of the preform  130 . For the sake of simplicity, only a part of the spiral form of the course of the seam  132  is shown, and it goes without saying that the seam  132  continues its course to the rim. The spiral course of the seam  132  simplifies the processing because it is easy to hold the preform  130  in the sewing machine and to rotate it in this position. The radial pitch of the seam  132  can be varied. Generally speaking, the cohesion of the layered structure  114  is improved by a higher density of the seams. Considering the pitch of the seams, the elasticity and tensile strength of the yarn of the seam  132  and of the textile layers  116  and the proportion of the connection agent in the layered structure  114  (for example, the resin content), the protective properties of the end product can be varied to achieve a sufficient resistance against perforation and to permit a delamination of the inner textile layers of the layered structure  114  by a penetrating projectile only in a small extent. If, for example, the resin content of the layered structure  114  is low to decrease the weight of the protective armour, the delamination effect of the inner layers  116  is promoted. However, this can be balanced by decreasing the pitch of the seams. The seam  132  is an additional component which allows a decreasing of the resin content without impairing the protective effect. 
   In a circular area R around the surface center point  140  of the hemisphere of the preform  130 , the pitch of the seams in the radial direction may be 6 mm, for example, while it increases to 10 mm outside of this area R. In a strip-like rim portion A extending in the circumferential direction of the preform  130  along its rim  142  it can decrease again to be 6 mm. 
   After sewing  50  a preform  130  can be subjected to an intermediate pressing step (method step  60  in  FIG. 1 ) to give the layered structure  114  of the preform  130  an even stronger coherence. After this intermediate pressing step  60 , additional seams  146  can be attached in certain portions of the preform  130 , which cross the spiral seam  132  and reinforce areas of the ballistic protective helmet to be produced which are especially endangered, like, for example, the ear portions. After attaching these additional seams (method step  70 ), a second intermediate pressing step can be carried out (step  80 ). Consequently, an intermediate pressing step  60 , 80  can be carried out after each sewing step  50 , 70 . 
   After sewing the preform  130  completely, protective layers are applied on its inside and on its outside to fix the seams  132 , 146  at their portions  134 , 136  which are exposed on the surfaces, protecting these portions for being damaged. The outer protective layer is a textile layer being covered on both sides with the connection agent, which is resin, plastics or adhesive agent, said textile layer consisting of the same or a similar material like the layers  116  which have already been sewed together. This outer textile layer  150  is laminated layer-like onto the preform  130  while the opposed inner side  144  of the preform  130  is only coated with the connection agent covering also the textile layers  116  and  150 . This means that a layer  152  of resin, plastics or adhesive agent is applied to the hemispherical inside  144  of the preform  130  and protects and fixes the inner portions  136  of the yarn  132  so that the preform  130  is protected on both of its opposing surfaces, and when the textile layer structure  114  is damaged, the yarn  132  cannot slip partly out of the sewing channels. This method step of applying the protective layers  150 , 152  (step  90  in  FIG. 1 ) is shown in  FIG. 8 . 
   Finally, the preform  130  being provided with the protective layers  150  and  152  is subjected to a hot pressing step shown in  FIG. 9 . For this purpose the coated preform  130  is brought into a hot press  160  in a way that the preform  130  is put with its concave inside onto a corresponding lower mold half  162  while a hemispherical concave upper mold half  164  is provided to be lowered vertically onto the lower mold half  162 . The hot pressing (step  100  in  FIG. 1 ) is carried out preferably at a temperature between 150° C. and 175° C. and at a pressure of 200 kg/cm 2 , which are higher pressure and temperature values than at the pre-pressing and intermediate pressing steps  30 , 60 , 80 . During hot pressing, the coating of the connecting agent of the single textile layers  116  partially penetrates the fabric and forms a connection matrix by which the textile layers  116  are connected with each other to form a laminate. During this process the layered structure  114  of the preform  130  can be slightly compressed without changing the shape of the preform  130 . The outer protective textile layer  150  and the inner protective layer  152  become parts of this laminate as well and form a solid connection with the sewed layered structure  114  of the preform  130 . 
   The spherical shape of the preform  130  is not changed by the hot pressing step  100 . Consequently there is no danger that the configuration of the layer structure  114  already defined by the hot pressing  30  and the sewing  50 , 70  is deteriorated. This means that the final shape of the end product to be produced is already created by the pre-pressing  30  during the production of the preform  130 , and the sewing  50 , 70  is carried out at an intermediate product which has already the desired shape. This is an important advantage over known methods by which a layer structure is defined by sewing and subsequent pre-pressing in a plane, while the deformation of the laminate is carried out afterwards. 
   After the hot pressing step  100  in  FIG. 9 , the ballistic protective helmet can be taken out as the end product and can be subjected to final working steps, like, for example, polishing the rims, attaching rim protection elements, painting the upper side, adapting a suitable lining for the inner portion of the helmet shell and so forth.