Abstract:
A can of a drive motor is provided for a pump assembly, wherein the can ( 22 ) is manufactured at least partly of plastic ( 52 ). At least in a part of the can ( 22 ) the plastic ( 52 ) is reinforced by individual fibers ( 32 ) distributed in the plastic ( 52 ). The fibers ( 32 ) in at least one layer ( 35 ) of the can ( 32 ) are aligned in a defined manner in the peripheral direction with respect to the longitudinal axis (Z) of the can ( 22 ). A method for manufacturing such a can is also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of U.S. patent application Ser. No. 12/679,209, filed Jul. 15, 2010, which was a Section 371 of International Application No. PCT/EP2008/007507, filed Sep. 12, 2008, which was published in the German language on Apr. 2, 2009, under International Publication No. WO 2009/039967 A1 and the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a can of a drive motor for a pump assembly, as well as to a method for the manufacture of such a can. Such a pump assembly may for example be a heating circulation pump assembly. 
     The drive motors of such pump assemblies are designed as wet-runners, wherein a can is arranged between the stator space and the rotor space, and this separates the fluid filled rotor space from the dry stator space. Until now, such cans have mostly been manufactured of metal. This however has the disadvantage that they compromise the magnetic field between the stator and the rotor. For this reason, it is preferable to apply electrically non-conducting cans, for example cans of plastic. With the cans of plastic however, there exists the problem of ensuring the desired pressure strength, given larger pump pressures. For this, the can must have a certain minimum thickness. However, the distance between the rotor and the stator increases with an increasing thickness of the can in the radial direction, whereby the efficiency of the drive motor is worsened. 
     BRIEF SUMMARY OF THE INVENTION 
     It is therefore the object of the invention to improve a can of a drive motor, in a manner such that, on the one hand, it may be designed such that it influences the magnetic field between the rotor and stator as little as possible and, on the other hand, it may be designed more thinly, in order to be able to reduce the distance between the rotor and the stator. 
     This object is achieved by a can of a drive motor for a pump assembly, wherein the can is manufactured at least partly of plastic, characterized in that the plastic at least in a part of the can is reinforced by individual fibers distributed in the plastic, wherein the fibers in at least one layer of the can are aligned in a defined manner in the peripheral direction with respect to the longitudinal axis (Z) of the can. 
     This object is also achieved by a method for manufacturing a can of a drive motor for a pump assembly, characterized in that fluid plastic, to which individual fibers are admixed for reinforcement, is introduced into an injection molding tool which defines the shape of the can to be manufactured, wherein an inner mold part of the injection molding tool is rotated relative to an outer mold part of the injection molding tool, during the introduction and/or after the introduction of the plastic. 
     The stator according to the invention is manufactured at least partly of plastic. Thereby, the plastic preferably forms the supporting material, i.e. the material ensuring the mechanical strength of the can. Reinforcing elements, in particular fibers, may be provided in the plastic and these fibers may also be manufactured of plastic, but also of other suitable materials. Thus, a plastic composite material may be applied as the plastic. Furthermore, preferably a metallic layer may be attached on the inner side or outer side of the can, in order to design the can in a hermetically tight manner. 
     According to the invention, the plastic is reinforced by individual fibers distributed in the plastic, at least in a part of the can. With regard to these individual fibers, it is the case of fibers which are randomly distributed in the plastic and are not connected to one another into a fabric. These fibers may be admixed to the plastic before its processing, i.e. before the injection molding, so that a mixture of plastic and fibers is processed in the injection mold, i.e. is brought into the shape of the can. If the fibers are also randomly, preferably uniformly distributed in the whole plastic, then this does not mean that they are also directed in a random manner. Rather, according to the invention, the fibers are aligned in a defined manner in the peripheral direction with respect to the longitudinal axis of the stator, in at least one layer of the can. Thus in this layer, the individual fibers extend in the peripheral direction or tangentially to the longitudinal axis of the stator. This is particularly the case in a region of the can which is designed essentially cylindrically about the longitudinal axis of the can. In this region, the peripheral alignment of the fibers has the advantage that the can is reinforced by the fibers, thus particularly in the peripheral direction. In this direction, the fibers may counteract a pressure acting in the inside of the can, i.e. give the material the required tensile strength in this direction, in order to withstand such a pressure. It is possible for the fibers to be aligned in a defined manner in the peripheral direction in the described manner over the whole thickness of the can in the radial direction. However, it is also possible for the can to be designed in a multi-layered manner, seen in the radial direction, and for the alignment of the fibers in the described manner to only be given in one or a few of several layers. The fibers in the other layers may either be aligned in a defined manner in another direction, or however aligned in a random manner. 
     A greater strength of the can with a reduced wall thickness is achieved by the alignment of the fibers. 
     The fibers may for example be carbon fibers, glass fibers, metal fibers or aramide fibers, but also natural fibers, such as hemp, cotton or silk, for example. 
     The plastic of the can preferably comprises at least two layers which border one another, wherein the fibers are aligned in the peripheral direction in one layer, and the fibers are aligned in the axial direction with respect to the longitudinal axis of the can in the second adjacent layer. These two layers are formed lying over one another and bordering one another, seen in the radial direction. These layers in the cylindrical section of the can thus likewise extend lying over one another in a cylindrical shape. If the can is designed in a pot-like manner, i.e. with a closed base at one axial end, then there, according to the invention, the fibers may extend in the peripheral direction in at least one layer. In the case that several layers are provided, the fibers in the base may extend in the radial direction in at least one further layer. This is then the layer in which the fibers extend in the axial direction in the peripheral section of the can. A reinforcement of the can may be achieved in the axial as well as in the peripheral direction, or in the base in the peripheral direction as well as in the radial direction, on account of the crossed alignment of the fibers in two layers adjacent one another created by this. 
     Further preferably, the plastic comprises at least three layers, wherein the fibers in a middle layer are aligned in the peripheral direction, and the fibers in the adjacent outer layers are aligned in the axial direction in the previously described manner. In the case that the can has a base, then there, the fibers are accordingly aligned in the radial direction in two outer layers and the fibers are aligned in the peripheral direction in the layer lying therebetween. Thereby, the outer layers preferably form edge layers and have a smaller layer thickness than the middle layer. A greater reinforcement in the peripheral direction is achieved by this. 
     According to a further preferred embodiment, the can is designed in an open manner at at least one axial end, and there has a radially outwardly directed collar, wherein the fibers in the collar are aligned radially to the longitudinal axis in at least one layer of the plastic. The can may be fastened with this collar at a later stage in the stator housing or brought into sealing contact with the stator housing, in order to seal the stator space with respect to the rotor space. The collar is reinforced in the radial direction on account of the radial alignment of the fibers in this collar, so that forces may be transmitted or accommodated, in particular in this direction. Alternatively or additionally, it is possible to align the fibers tangentially or peripherally in a part or a layer of the collar. 
     According to a further particular embodiment of the invention, the can comprises an outer ply of a prestressed material, and an inner ply which is formed of the plastic which is reinforced by individual fibers distributed in the plastic, wherein the fibers, in the previously described manner, are aligned in a defined manner in the peripheral direction with respect to the longitudinal axis of the stator, in at least one layer of the inner ply. The outer ply of the prestressed material ensures an additional strength of the can, even with small wall thicknesses. A peripheral tensile stress, but, as the case may be, also an axial tensile stress, may be produced in particular in the cylindrical section of the can, by the outer ply, which leads to compressive stresses in the inner ply and to a radially inwardly directed pressure force acting on the inner ply. A detachment of the outer and inner ply from one another is prevented by this arrangement. Furthermore, this pressure force counteracts fluid pressure acting onto the can from the inside. Fractures in the inner ply may be prevented by the prestressing of the outer ply, and thus the sealing of the can may be improved. 
     The prestressing of the material may be achieved by it being the case of an elastically extendible material which is extended before, or when injecting the plastic of the inner ply. Since the material after the extension tends to assume the initial position again, on account of its elasticity, the desired stresses occur in the material after connection to the inner ply. With an adequately large extension, these stresses may also be maintained when the material of the inner ply shrinks due to cooling. For this, the extension of the material of the outer ply before or when injecting the plastic material of the inner ply, is selected such that the extension has a greater extent than the shrinkage of the plastic material of the inner ply when this plastic material solidifies. A prestressing of the material of the outer ply may also be maintained after the solidification of the plastic of the inner ply by this. 
     One may manufacture a particularly strong and simultaneously particularly thin can by a combination of the alignment of the fibers in the plastic of the inner ply in the described manner, and the arrangement of a prestressed outer ply. 
     According to a further preferred embodiment, a bearing which is provided for mounting a rotor, or a bearing holder which is provided for receiving a bearing for mounting the rotor, is cast in the plastic of the can. The assembly of a pump assembly may be simplified in this manner, since the bearing or a bearing holder for receiving the bearing, may be positioned and fixed in the can in a defined manner directly on manufacture of the can. 
     The bearing and the bearing holder are preferably manufactured of a material which has a greater hardness and/or stiffness than the plastic of the can, and in particular of metal. Thus the bearing and the bearing holder may have the required strength, in order to ensure a wear-free mounting. 
     Further preferably, the at least one surface of the bearing or of the bearing holder, which is in contact with the plastic of the can, is provided with a surface structuring, in particular with a macro-structuring or micro-structuring. This structuring permits an improved contact or engagement with the plastic. Ideally, a positive-fit connection between the plastic and the bearing or the bearing holder may be achieved by the plastic engaging into the structuring on the surface. A better adhesion of the plastic material on the surface may be achieved by a suitable roughening. The structuring may either be designed in a very small manner as a micro-structuring, or be designed larger as a macro-structuring. Such a macro-structuring may for example be achieved by a conical design of the bearing or in another manner by forming undercuts. Thus, parts of the bearing or the bearing holder are designed such that the plastic may engage behind them. 
     In particular, projections, recesses and/or holes may be incorporated into the surface. The structuring may be incorporated for example in a material-removing manner. It is also possible the treat the surface by laser beam or electron beam, in a manner such that recesses and raised parts are formed, which lead to a cramping with the surrounding plastic. 
     According to a preferred embodiment, grooves or channels are formed in the bearing or the bearing holder, and extend parallel to the longitudinal axis of the can over the axial length of the bearing or the bearing holder. These grooves serve the peripheral flushing of the bearing or bearing holder by the fluid in the inside of the can. By this, on the one hand one succeeds in all components being held at the same temperature level by the peripherally flowing fluid, in order to avoid thermal stresses. On the other hand, the bearing may be cooled by the peripherally flowing fluid. As the case may be, the fluid may also be used for the lubrication of the bearing. 
     The invention further relates to a method for the manufacture of a can of a drive motor for a pump assembly, in particular for manufacturing a can according to the preceding description. 
     According to the method according to the invention, at least one part of the can is manufactured of plastic with the injection molding method, wherein individual fibers for reinforcing, are admixed to the plastic before the injection molding. The fibers thereby are preferably uniformly distributed in the plastic material. Subsequently, the fluid plastic with the fibers distributed therein, is brought or injected into an injection molding tool. The injection molding tool defines the shape of the can to be manufactured. An inner mold part of the injection molding tool is rotated relative to an outer mold part of the injection molding tool during the introduction and/or after the introduction of the plastic. Thereby, the rotation takes place about the longitudinal axis of the can to be molded. It is possible to start the rotation already during the injection of the plastic. It is also possible to start the rotation not until after the injection of the plastic, i.e. preferably directly after the injection. The rotation between the outer and inner mold part thereby takes place in a time interval, in which the plastic has at least not yet fully solidified. A defined alignment of the fibers in the plastic may be achieved by the rotation of the inner and outer shape part relative to one another. Thereby, an alignment in the rotation direction, i.e. in the peripheral direction or tangentially with respect to the longitudinal axis of the can, is achieved by the rotation. An increased tensile strength of the plastic is effected in this direction on account of this alignment of the fibers. As a whole, a strong and simultaneously thin can may be designed by this. The previous description is referred to with regard to the advantages of this design. 
     Depending on the course and the control of the injection molding procedure and of the rotation between the outer and inner mold part, it is possible to orient the fibers in the plastic in a defined manner in the peripheral direction, and in the mentioned manner, over the whole radial thickness, but also to generate different layers in which the fibers are directed in different directions. This means that of the several layers which lie over one another in the radial direction, it is possible for the fibers to be aligned in the peripheral direction by the rotation in only one or individual layers. 
     The fluid plastic preferably flows in the axial direction parallel to the longitudinal axis of the can to be manufactured, into the part of the injection molding tool which shapes or defines the peripheral wall of the can. This may be achieved by the plastic being injected from the axial end. It is however also possible to inject the plastic in the middle of the can, so that it flows in the axial direction in opposite directions. First, a corresponding axial alignment of the individual fibers admixed to the plastic may be achieved on account of the axial inflow of the plastic. 
     On account of the described relative rotation from the inner to the outer mold part, one may subsequently succeed in a part or all fibers changing their orientation from the axial alignment into a peripheral or tangential alignment with respect to the longitudinal axis of the can. It is possible, depending on the setting of the method parameters, for several layers to be formed in the injected plastic on solidification, which differ with regard to the orientation of the fibers. In particular, it is possible to form at least one layer which bears on the wall of a mold part, and in which the fibers remain aligned in the axial direction when the plastic solidifies. This is effected in that the plastic solidifies first of all in the edge region of the gap between the inner and the outer mold part, i.e. adjacent a wall of a mold part. The plastic remains fluid or flowable longer in the regions of the mold which are spaced further from the walls of the mold part, so that here an alignment of the fibers in the peripheral direction may occur by the rotation of the mold parts to one another. In this manner, preferably a second layer solidifying later is formed, in which the fibers are aligned in the peripheral direction. A targeted reinforcement of the can may be achieved in several directions by the fibers on account of the different alignment of the fibers in the different layers. Thereby, in contrast to randomly aligned fibers, one achieves a targeted strengthening of the can, which in particular ensures a thin design of the can having a stability which remains the same or is increased. 
     According to one particular embodiment, a three-layered construction of the plastic material may be achieved, with which the axial alignment of the fibers is achieved by the injection procedure and is retained on solidification, in the two edge regions which are situated to the outside and face the two mold parts. A peripheral orientation of the fibers in the middle region lying therebetween is effected by the rotation of the mold parts to one another. The middle region thereby preferably has a larger thickness in the radial direction than the edge regions, so that the reinforcement in the peripheral region is larger than in the axial direction. The middle region preferably has a thickness of 40% or more, preferably more than 60% of the total thickness of the plastic in the radial direction. 
     According to a further preferred embodiment, a bearing or bearing holder is applied into the injection molding tool in a defined position, before the fluid plastic is introduced into the injection molding tool. With the subsequent injection of the plastic, this then flows around the bearing or bearing holder, so that the bearing or the bearing holder is cast firmly into the can. 
     Preferably, the bearing or the bearing holder is applied in a recess in the injection molding tool, in particular on the inner mold part of the injection molding tool. The recess thereby is arranged and designed, such that the bearing is held in the mold in a defined position, so that afterwards, it is enclosed and held in a defined position in the plastic in the cast can. 
     It is preferable for the bearing or the bearing holder to be inserted in a recess on the inner mold part, and there, to be held bearing on at least one surface of the mold part by the pressure of the plastic during the introduction of the fluid plastic. In this manner, it is ensured that the bearing may not be dislocated out of the defined position. Furthermore, a non-positive fit between the bearing and mold part may be achieved, so that on rotation of the mold part for example, the bearing or the bearing holder which is in a non-positive fit bearing with the mold part, is rotated about the longitudinal axis of the can to be manufactured. A further advantage of the bearing on the surface is that a sealing bearing may be achieved, whereby one prevents the plastic entering into the region between the bearing or bearing holder, and the surface of the mold part. 
     Usefully, before the insertion into the injection molding tool, a structuring, in particular a micro-structuring and/or macro-structuring is formed on at least one surface of the bearing or bearing holder, which is envisaged to come into contact with the plastic. This structuring may be effected in the manner described above with regard to the can. 
     According to a particular embodiment of the method according to the invention, a pre-manufactured material ply is applied into the injection molding tool before the introduction of the fluid plastic, wherein the fluid plastic is subsequently preferably introduced between the inner mold part of the injection molding tool and the pre-manufactured material ply. This means that the material ply is applied into the injection molding tool before the closure of the injection molding tool, so that the material ply is then firmly connected to the injected plastic material after the injection of the fluid plastic and its solidification. This material ply preferably forms the outer material ply of the can to be manufactured, which is why the plastic is injected into the space between the material ply and the inner mold part. This material ply may form an additional reinforcing element, for example of fibers. It is preferably the case of a fabric. Thermoplastic fibers, carbon fibers, metal fibers and/or aramide fibers or other suitable fibers may be applied as fibers for example. Moreover, natural fibers such as hemp, cotton or silk may be applied as fibers. 
     Particularly preferably, the pre-manufactured material ply is elastically extendible and is extended when introducing the plastic. In this manner, a prestressing of the outer material ply may be achieved in the solidified condition of the plastic. This stress in the outer material ply effects an inwardly directed pressure force, which keeps the outer ply in firm contact with the inner ply. This leads to an increased strength of the can. The above description is referred to with regard to further advantages. 
     The extension of the outer material ply on injection of the plastic is preferably so great, that the extension exceeds the later shrinkage of the plastic on its solidification. In this manner, an extension of the outer material ply is also maintained in the solidified condition of the can, whereby the mentioned prestressing results. 
     A part of the injection molding tool may be heated according to a further preferred embodiment. This may for example be the outer and/or inner mold part. The edge layers of the plastic which are adjacent to the respective mold part, may be heated or cooled more slowly by heating the mold parts, so that the solidification of these edge layers may be delayed. In this manner, it is possible to orientate the fibers in the peripheral direction by rotation of the form parts to one another, also in the edge sections. It is thus possible to orientate the fibers in the peripheral direction in the complete plastic material, seen in the radial thickness direction. It is also possible to merely form one edge layer, in which the fibers are orientated in the axial direction, as was described above. 
     According to further special embodiment of the method, the injection molding tool, in which the can is formed, comprises a gap which is designed for forming a radially extending collar at the open end of the can to be manufactured. During the solidification of the plastic, which is injected into the injection molding tool and thus is also injected into this gap, a pressure is exerted on at least one of the walls of the injection molding tool which defines this gap, wherein this pressure is directed towards the opposite wall of the gap. I.e. the gap is narrowed in its width by moving the walls apart. For this, the tool preferably has a base plate which lies opposite the outer mold part. This base plate is distanced to the outer mold part, in order to define the gap for forming the collar. The base plate during the solidification is moved onto the outer mold part, so that the gap is reduced in size. This method is particularly advantageous, if the gap has a larger width than the gap between the outer and inner mold part which defines the peripheral wall of the can to be manufactured. It is possible in this manner to manufacture a can with a very thin peripheral wall, which despite this has a collar of a larger material thickness at its open face-end. By applying a pressure force onto the wall of the gap forming the collar or by reducing the gap width during the solidification, one prevents bubbles (blowholes) or similar cavities from being able to form in this region on account of the shrinkage of the plastic on solidification. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
         FIGS. 1 a  to 1 d    are schematic diagrams of the injection molding procedure of a can, according to the invention; 
         FIGS. 2 a  to 2 c    se schematic views of an alignment of the fibers in a can according to the invention; 
         FIG. 3  is a schematic diagram of the arrangement of an outer fabric ply, on an injection molding tool; 
         FIG. 4  is a schematic cross-sectional view of a closed injection molding tool with an inserted fabric ply; 
         FIGS. 5 a  to 5 d    are schematic cross-sectional views of the injection molding procedure of a can, according to a second embodiment of the invention; 
         FIGS. 6 a  to 6 c    are diagrams showing the stress distribution in a can according to an embodiment of the invention; 
         FIG. 7  is schematic cross-sectional view of the injection molding procedure of a can, according to a further embodiment of the invention; 
         FIG. 8  is schematic cross-sectional view of an injection molding tool for a can, according to a further embodiment of the invention; 
         FIG. 9  is a sectional view of a can manufactured in the injection molding tool according to  FIG. 8 ; 
         FIGS. 10 a  and 10 b    are designs of a bearing holder with a bearing; 
         FIG. 11  is a sectional view of a can manufactured according to the invention; and 
         FIG. 12  is a sectional view of a can according to a further embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First, in a stepwise manner, the manufacture of a can according to the invention is explained by the  FIGS. 1 a  to 1 d   .  FIG. 1 a    schematically shows an inner mold part  2  or a core  2  of an injection molding tool for the manufacture of a can. The inner mold part  2  defines the shape of the inner space of the can to be manufactured. Thereby, a first axial end-side  4  defines the inner side of a base of a can to be manufactured. Such a can is designed closed by a base at one axial end, i.e. in a pot-like manner. The opposite axial end of the can is designed in an open manner and is the axial end which is later applied onto a pump housing. The inner mold part  2  at its end distant to the end-side  4  is attached on a base plate  6 , for forming this open axial end of the can. The base plate  6  extends radially outwards normally to the longitudinal axis Z of the can to be manufactured or the inner mold part  2 . A central recess  8  is formed on the axial end-side  4 , and serves for receiving a bearing  10  as is shown in  FIG. 1 d   . The bearing  10  in the can later serves for mounting a rotor shaft of the rotor to be arranged in the can. Even if it is only a bearing  10  which is described, it is however to be understood that a bearing holder may be inserted into the recess  8  in an identical manner, instead of the bearing  10 . A bearing is then assembled in the bearing holder. 
     After insertion of the bearing  10  into the recess  8 , the injection molding tool is closed by an outer mold part  12 . The outer mold part  12  in its inside comprises a recess  14  which defines the outer contour of the can to be manufactured. A gap  16  remains between the wall of the recess  14  in the outer mold part  12 , and the outer wall of the inner mold part  2  in the closed condition of the injection molding tool, and this gap  16  corresponds to the shape of the can to be manufactured. A gap  18  also remains between the base plate  6  and the outer mold part  12 , and extends annularly or in a collar-like manner, proceeding from the gap  16 , in the radial direction with respect to the longitudinal axis Z. This gap serves for forming a collar  20  at the open axial end of the can  22 , as is shown in  FIG. 1   d.    
     The inner mold part  2  is not firmly connected to the annular base plate  6 , but is arranged in a circular recess in the base plate  6 , so that an annular gap  24  remains between the base plate  6  and the inner mold part  2 . The annular gap  24  serves on the one hand for bleeding the gap  16 , and on the other hand for the inner mold part  2  to be able to rotate about the longitudinal axis Z in the direction of the arrow A relative to the outer mold part  12  and also the base plate  6 . 
     A fluid plastic material is injected into an injection channel  26  in the direction of the longitudinal axis Z for injection molding the can. The injection channel  26  runs into the gap  16  in a central manner with respect to the longitudinal axis Z, opposite the axial end-side  4  of the inner mold part  2 , i.e. opposite the recess  8 . By this, on injecting, the fluid plastic first presses directly against the inserted bearing  10  and fixes this in the recess  8  or holds the end-side of the bearing  10  which is distant to the injection channel  26 , in a sealed bearing with the base of the recess  8 . 
     The fluid plastic subsequently flows further through the gap  16  to the annular gap  24  and the radially extending gap  18 . 
     According to the invention, individual fibers are added to the plastic which is injected into the injection molding tool, and these fibers are preferably uniformly distributed in the plastic. The inner mold part  2  is rotated about the longitudinal axis Z in the direction of the arrow A during, or directly after the injection of the plastic, whilst the outer mold part  2  and the base plate  6  remain stationary. A special orientation of the fibers occurs due to this, as will be explained later by  FIG. 2 . 
       FIG. 1 d    shows the finished can  22  which is cast centrally in the base  27  of the bearing  10 . The bearing  10  thereby is surrounded by a ring  28  of plastic material which preferably engages into a structuring on the surface of the bearing  10 . The peripherally extending, i.e. radially outwardly extending collar  20  of the can is formed on the opposite open face-end  29 . 
     The alignment of the fibers of the plastic which is achieved by rotation of the inner mold part  2  is now explained in more detail by  FIGS. 2 a    to  2   c.    
       FIG. 2 a    schematically shows the plan view of the base  27  of the can  22 .  FIG. 2 b    shows a section of the transition region between the base  27  and peripheral wall  30  of the can  22 .  FIG. 2 c    shows a schematic cut-out of the peripheral wall  30 . Fibers  32  are arranged in a defined manner in the plastic of the wall. In the shown example, three layers  34 ,  35  and  36  lying over one another are formed in the plastic material seen in the radial direction with respect to the longitudinal axis Z. The layers accordingly lie over one another in the axial direction in the base  27 . The layers  34  and  36  form edge layers, which face the walls of the injection molding tool. This means that the layer  34  borders the inner wall of the recess  14  in the outer mold part  12 , and the layer  36  borders the outer side of the inner mold part  2 . In the two outer layers  34  and  36 , the fibers  32  are directed in the flow direction of the plastic material on injecting into the gap  16  in the injection molding tool. This means that proceeding from the injection channel  26 , the flow direction in the base  27  is first essentially in the radial direction and, in the peripheral wall  30 , in the axial direction with respect to the longitudinal axis Z. Since the edge zones  34  and  36  solidify first of all, there, the alignment of the fibers in the flow direction is retained. The solidification in the layer  35  which is distanced furthest to the walls of the inner mold part  2  and the outer mold part  12 , takes place later. One succeeds in the fibers  32  in the layer  35  being orientated in the peripheral direction with respect to the longitudinal axis Z, by the rotation of the inner mold part  2  relative to the outer mold part  12 . A great strength of the can may be achieved by the alignment of the fibers  32 . In particular, the middle layer may be designed particularly thickly, for example may take up more than 40%, preferably more than 60% of the total thickness, so that a large part of the fibers is orientated in the peripheral direction and ensures an increased strength of the can in this direction. The edge layers  34 ,  36  are designed relatively thickly in the embodiment represented schematically in  FIG. 2 b   , and the edge layers  34  and  36 , as previously explained, are designed in a thin manner so that a thicker middle layer  35  arises, as is shown in  FIG. 2   c.    
     In the shown example, two edge layers  34  and  36  are provided with axially directed fibers  32 . However, it is also possible to design only one or no such edge layers  34  and  36  by a suitable setting of the parameters, and in particular by heating the inner mold part  2  and/or the outer mold part  12 . For this, the plastic after the injection or during the injection must first be kept flowable also in the vicinity of the walls of the injection molding tool, so that a peripheral alignment of the fibers may be achieved by rotation of the inner mold part  2  and the outer mold part  12 . If for example the inner mold part  2  is heated on its surface, then a peripheral alignment of the fibers  32  may also be achieved in the layer  36 . Accordingly, a peripheral alignment of the fibers  32  may also be achieved in the layer  34 , if the outer mold part  12  is heated at its inner wall in the recess  14 . One may also possibly do away with the heating if the rotation already takes place during the injection of the plastic. 
     It was previously described that the inner mold part is rotated. Accordingly, it is also possible to rotate the outer mold part  12 . It is merely a question of the relative rotation of both parts. 
     One succeeds in the bearing  10  being rotated or turned together with the inner mold part  2  by the fact that the plastic presses against the bearing  10  on injection, and retains this with a firm bearing in the recess  8 . 
       FIG. 3  shows the inner mold part  2  with the inserted bearing  10  and the base plate  6 . It is shown in  FIG. 3  how first an outer ply  38  of a woven fiber material  40  is placed onto the inner mold part  2 . Thereby, the outer ply  38  already essentially has the shape of the can to be manufactured. This means that the outer ply  38  is designed in an essentially pot-like manner with a closed face-end  42 . An opening  44  through which the fluid plastic is injected into the injection molding tool as will be explained later by  FIG. 5 , is formed centrally in the base or closed face-end  42 . 
     The outer ply  38  at the opposite open axial end  46  comprises a radially outwardly extending collar  50  which comes to lie in the gap  18  of the injection molding tool, and later reinforces the collar  20  of the can  22 . The outer ply  38  of the fabric serves for an additional reinforcement of the can. Here for example, one may apply a thermoplastic fabric, a fabric of metal fibers, aramide fibers, carbon fibers or glass fibers. 
       FIG. 4  shows a sectioned view of an injection molding tool with the applied fabric ply  38  which defines the outer ply of the wall of the can. Otherwise, the injection molding tool corresponds to the injection molding tool shown in  FIG. 1 c   . In the example shown in  FIG. 4 , the outer ply  38  bears directly on the inner wall of the recess  14  of the outer mold part  12 . The plastic material is injected into the gap  16  between the inner mold part  2  and the outer ply  38 , as is explained hereinafter by  FIG. 5 . This may be effected in the axial direction either through a central opening in the inner mold part  2 , or also through an injection channel  26 , as is shown in  FIG. 1 , wherein this injection channel is not shown in  FIG. 4 . In the case that a central opening is formed in the inner mold part  2 , then the inner mold part is preferably designed of two parts, with a stationary middle part in which the opening is formed. The surrounding part of the inner mold part which faces the outer mold part  12 , is arranged in a rotatable manner about this stationary middle part, and may be rotated relative to the outer mold part  12  in the described manner. Thereby, it is ensured by the stationary middle part that the opening through which the plastic is injected, does not rotate. 
     A bearing holder  11  with a bearing  10  is inserted into the end-side recess  8  on the inner mold part  2 . One may recognize that a gap remains peripherally of the bearing holder  11  to the inner wall of the recess  8 , and this gap is later filled with plastic, so that the bearing holder  11  is peripherally closed by plastic. 
       FIG. 5 a    schematically shows the inner mold part  2  with the inserted bearing  10  corresponding to the representation in  FIG. 1 d   . The corresponding description is referred to. Furthermore, the outer ply  38  with the opening  44  is shown on the right in  FIG. 5 a   . This ply is placed onto the inner mold part  2 . Subsequently, the outer mold part  12  is placed onto the inner mold part  2 , as is shown in  FIG. 5 b   . The material of the outer ply  38  is an elastically extendible material. This may be achieved by a suitable elastic design of the individual fibers, from which the outer ply  38  is manufactured, or however also by a special design of the fabric of the outer ply  38 . As may be recognized, the thickness of the outer ply  38  is smaller than the width of the gap  16 . The ply  38  is applied into the gap  16 , in a manner such that it does not bear on the inner wall of the recess  14  in the outer mold part  12 , at least in sections, in particular in sections of the peripheral wall  30  of the can to be molded. Thus a gap  16   b  arises between the outer ply  38  and the outer mold part  12 . Simultaneously, the outer ply  38  in the region of the peripheral wall however also does not bear on the wall of the inner mold part  2 , so that a gap  16   a  is formed there. The outer ply  38 , surrounding the opening of the injection channel  26 , bears on the inner wall of the recess  14  only with the axial face-end, in which the opening  44  is arranged. 
     As may be further recognized in  FIG. 5 b   , the peripheral region of the outer ply  38  is not designed in a completely cylindrical manner, but widens proceeding from the end-side  42  by an angle α towards the opposite axial end. By this, one succeeds in the outer ply  38  at the axial end facing the base plate  6 , not bearing on the outer wall of the inner mold part  2 . A bleeding through the annular gap  24  may thus be effected. 
     As has already been explained by  FIG. 1 c   , subsequently, as represented in  FIG. 5 c   , fluid plastic is injected into the injection channel  26 , and there flows through the opening  44  in the outer ply  38  into the gap  16   a  between the outer ply  38  and the inner mold part  2 . The outer ply  38  is extended by this, whereby the gap  16   a  is increased in size, and the gap  16   b  disappears, i.e. the outer ply  38  comes to bear directly on the inner wall of the recess  14  in the outer mold part  12 . Thereby, the outer ply  38  is extended in particular in the peripheral direction with respect to the longitudinal axis Z. The collar  50  of the outer ply  38 , lies in the gap  18  between the base plate  6  and the outer mold part  2 . The inner mold part  2  is rotated relative to the outer mold part  12  in the direction A about the longitudinal axis Z, as has been described by  FIG. 1 , during and/or after the injection of the plastic  52 . The previously described alignment of the fibers  32  occurs by this, said fibers being admixed to the plastic  52 . The outer ply  38  thereby is rotationally fixed to the outer mold part  12 . Inasmuch as this is concerned, the inner mold part  2  also rotates relative to the outer ply  38 . Thereby, the outer edge layer  34  described by  FIG. 2  is preferably formed on the inner side of the outer ply  38 .  FIG. 5 d    shows the finished manufactured can  22  as described by  FIGS. 5 a  to  c   . A special stress distribution, as explained by  FIG. 6 , is given in this can  22 , in particular in the peripheral wall  30 . 
     As is shown in  FIG. 5 d   , the collar  20  comprises a collar part  53  which extends radially outwards in the radial direction beyond the extension of the outer ply  38  in the collar  20 . This part is only injection molded by the plastic  52  of the inner ply. In order to achieve an adequate density of the material in this part of the collar  20 , and in particular in order to avoid bubbles/blowholes on account of the shrinkage of the plastic  52  on solidification, a pressure in the direction of the outer mold part  12  is preferably exerted via the base plate  6 , whereby the gap  18  is reduced in size. 
     As is shown schematically in  FIG. 6 c   , the plastic  52  forms the inner ply  54  which bears on the inner wall of the outer ply  38 . Both plies  38 ,  54  together form the peripheral wall  30  of the can  22 . 
     A prestressing is achieved by the extending of the outer ply  38  on injecting the plastic  52 . First, the situation without the extending of the outer ply  38 , i.e. without prestressing, is observed by  FIG. 6 a   . The outer ply  38  and the inner ply  54  which is formed of the plastic  52 , are represented separately from one another at the top in  FIG. 6 a   . One may recognize that the inner ply  54  has shrunk with respect to the outer ply  38  on solidification. If the outer ply  38  and the inner ply  54  are firmly connected to one another, as is shown at the bottom in  FIG. 3 a , 6 a   , this leads to the fact that, on account of the shrinkage of the inner ply  54 , this ply is subjected to tensile stresses  56 , and the outer ply  38  is subjected to compressive stresses  58 . This leads to the fact that the outer  38  and the inner ply  54  connected to one another, tend to part or delaminate from one another. 
       FIG. 6 b    now shows the design according to the invention, according to which the outer ply  38  is designed in an elastically expansible manner. First, the outer ply  38  and the inner ply  54  in the condition of not being connected to one another, are shown first in a schematic manner in  FIG. 6 b   . The two plies  38 ,  54  are shown in the connected condition at the bottom in  FIG. 6 b   . On injecting the plastic  52 , the outer ply  38 , as described above, is first elastically stretched or extended. Thereby, it is extended to a greater extent than the plastic  52  shrinks later on solidification. If the plastic  52  now solidifies and shrinks, this leads to the fact that the outer ply  38  retains a certain extension and thus retains a certain prestressing. As a whole, by this, one succeeds in the outer ply  38  being subjected to tensile stresses  56  in the solidified condition, whilst the inner ply  54  is subjected to compression stresses  58  in the solidified condition. The effect of these stresses is that the outer ply  38  and the inner ply  54  are pressed against one another in the radial direction with respect to the longitudinal axis Z, and are held in the connected condition. Furthermore, the tensile stresses  56  in the outer ply  4  may counteract pressures occurring in the inside of the can  22 . An increased stability of the can  22  is achieved in this manner, whereby the wall thickness may be kept small. Furthermore, the tensile stresses  56  in the outer ply  38  counteract a fracture formation in the inner ply  54 , whereby one may achieve an increased sealing of the can. 
     In the example according to  FIG. 5 , the plastic was injected through the injection channel  52  which lies opposite the closed face-end or the base  27  of the can to be manufactured.  FIG. 7  now schematically shows an embodiment, with which the fluid plastic  52  is injected from the opposite end. In the representation according to  FIG. 7 , the outer ply  38  is inserted into the gap  16  between the outer mold part and the inner mold part  2  according to the description with regard to  FIG. 5 d   . The outer ply  38  however has no opening  44 , and the plastic is injected through openings  59  from the axial end, i.e. proceeding from the open face-end  29  of the can  22  which is to be cast. Thereby, the plastic flows in the axial direction, i.e. parallel to the longitudinal axis Z through the gap  16  to the base of the can to be molded, i.e. towards the base of the recess  14  of the outer mold part  12 . The outer ply  38  also undergoes an extension in the axial direction, i.e. in the direction of the longitudinal axis Z by this. For this, the outer ply  38  in its initial position is arranged in the gap  16  such that it does not bear on the wall of the recess  14 , also at the base of the recess  14 , i.e. opposite the axial end-side  4  of the inner mold part  2 . The outer ply  38  is then also extended in the axial direction by the inflowing plastic  52 , so that this ply also comes to bear on the base of the recess  14 . A prestressing may also be achieved in the axial direction in this manner. The inner mold part  2  is rotated for orientating the fibers in the plastic  52 , in the manner described by the other Figs. 
       FIG. 8  shows an injection molding tool consisting of an inner mold part  2  and an outer mold part  12  with plastic  52  already injected, which forms a can  22 . The embodiment corresponds essentially to that embodiment described by  FIGS. 1 c  and  d   , as well as  FIG. 4 , so that the description with respect to this is omitted. In contrast to the embodiment according to  FIG. 4 , no outer ply  38  is provided with the embodiment according to  FIG. 8 . Inasmuch as this is concerned, here the method corresponds to that explained by  FIG. 1 . In contrast to  FIG. 1  however, here the bearing  10  is not arranged directly in the plastic  52 , but in a surrounding bearing holder  11 , around which the plastic  52  flows. When the bearing holder  11  with the bearing  10  is inserted into the recess  8  of the inner mold part  2 , a gap which defines the ring  28  of plastic remains between the peripheral wall of the recess  8  and the outer wall of the bearing  10  or the bearing holder  11 , in order to form this ring  28  of plastic, as has been described by  FIG. 1   d.    
       FIG. 9  shows the can manufactured according to  FIG. 8 . This can  22  corresponds essentially to that can shown in  FIG. 1 , with the difference that the bearing  10  is not cast in a direct manner, but is surrounded by a bearing holder  11 . Grooves  60  extending axially parallel to the longitudinal axis Z are distributed over the periphery in the bearing holder  11 , and these ensure that the bearing  10  may be peripherally flushed by the fluid in the inside of the can  22  through the grooves  60 . Thus, the fluid may later penetrate into the free space between the bearing  10  and the bearing holder  11 . This ensures an improved cooling of the bearing, and further that the bearing  10  and bearing holder  11  are kept where possible at the same temperature level, in order to avoid thermal stresses. 
     The design of these grooves is explained in more detail by  FIG. 10 a   . With the embodiment according to  FIG. 10 a   , the bearing holder  11  which is designed in an essentially annular manner, comprises three protuberances  62 , by which the three grooves  60  are formed on its outer periphery. The inserted bearing  10  is formed in a cylindrical manner on its outer contour, so that free spaces between the bearing holder and the bearing  10  arise at the grooves  60 . 
       FIG. 10 b    shows a second embodiment with which the grooves  60  are not formed on the inner periphery of the bearing holder  11 , but on the outer periphery of the bearing  10 . 
       FIG. 11  shows a sectioned view of a can designed according to the invention. The can  22  according to  FIG. 11 , with respect to the previously described orientation of the fibers  32  in its inside, corresponds to the preceding description. The can according to  FIG. 11  is not designed with a constant diameter, in contrast to the previously described cans. It comprises two sections  30   a  and  30   b  of the peripheral wall which are arranged lying behind one another in the direction of the longitudinal axis Z. The diameter as well as the wall thickness are designed smaller in the section  30   a  than in the section  30   b . This is achieved by designing the gap  16  between the inner mold part  2  and the outer mold part  12  accordingly differently wide, or in a stepped manner. 
       FIG. 12  shows a further embodiment example of a can  22  according to the invention, wherein, here too, the orientation of the fibers corresponds to the preceding description. The can shown in  FIG. 12  does not comprise a bearing which is cast in. Projections  64  extending parallel to the longitudinal axis Z, distributed over the inner periphery, are formed in the can  22  in the section which is distant to the open end  29 , and later come to bear on the outer wall of the bearing  10 . This means that the bearing is fixed and centred between the projections  64 , preferably with a non-positive fit. Thereby, free spaces  65  remain in the peripheral direction between the projections  64 , and these have the same function as the previously described grooves  60 . 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.