Abstract:
The invention relates to a device and a method for altering the characteristics of a three-dimensional molded part by means of electrons, including at least one electron accelerator for generating accelerated electrons and two electron exit windows, wherein the two electron exit windows are arranged opposite one another, wherein the two electron exit windows and at least one reflector delimit a process chamber in which the surface or an edge layer of the molded part are bombarded with electrons, wherein an energy density distribution inside the process chamber can be detected at least over one spatial dimension by means of a sensor system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national phase of international application PCT/EP2007/002458, which international application was filed on Apr. 4, 2007. 
         [0002]    In addition, this application claims priority under 35 U.S.C. § 119 of German Patent Application No. 10 2006 012 668.8-54, filed on Mar. 20, 2006. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The invention relates to a device and a method for modifying material characteristics on the surface and in the edge area of three-dimensional molded parts using the energy of electrons. Furthermore, uses of the method are shown. 
         [0005]    2. Background Information 
         [0006]    Using electrons, energy can be fed into materials in a spatially and chronologically determinate manner in order to alter their material characteristics on the surface, in the edge layer or in the volume. The electrons required to this end are generated, formed and accelerated in electron accelerators before they are guided via a usually flat electron exit window out of the high vacuum to a higher pressure level in the process chamber. A constant electron density over the entire extent of the electron exit window is usually desirable thereby. After the penetration of the gas layer (for example, air) in the distance between electron exit window and product, the electrons reach the product surface to be treated. 
         [0007]    Shaped beam generators, also called band emitters, or axial-beam generators are used as electron accelerators. An electron accelerator according to the prior art embodied as an axial-beam generator comprises in addition an electron beam deflection chamber with a beam deflection system, by means of which a generated electron beam is periodically deflected over the entire electron exit window and with virtually the same dwell time on time average in all partial areas of the window. 
         [0008]    Three-dimensional molded parts, such as, e.g., packaging, medical implants, surgical instruments, prostheses of different materials (e.g., plastic, paper, metal, ceramics) are used in various fields (for example, the packaging industry, pharmaceuticals, medical engineering, plastics industry). For certain uses, an alteration of properties (for example, sterilization, surface functionalizing, cross-linking, hardening) of the entire surface and the edge area of the molded part is necessary. 
         [0009]    3. Prior Art 
         [0010]    It is known to influence characteristics of the entire surface of three-dimensional molded parts by means of electron energy, in that a molded part is guided past an electron exit window in several passes (DE 199 42 142 A1) and in an altered position. Known devices for generating electrons for the modification of molded part characteristics are embodied such that a virtually identical electron energy density is generated and emitted over the entire electron exit window. 
         [0011]    The alteration of the position of a molded part ensures that the entire molded part surface is bombarded with electron energy. One disadvantage of devices of this kind is that a multiple pass is associated with a relatively high expenditure of time. Altering the position of the molded part between the individual passes cannot be carried out in an arbitrary manner, either, but must be coordinated such that individual surface areas in total are not bombarded with different electron energy densities, which would lead to different characteristics. 
         [0012]    According to the prior art, the entire surface of a three-dimensional molded part is modified during only one pass by means of electron energy, in that several (at least two or three) electron exit windows are arranged such that they surround the cross section of a molded part, wherein the molded part is guided through between these electron exit windows and thus the entire three-dimensional surface is bombarded with electrons. 
         [0013]    A device for sterilizing the surface of molded parts by means of electron energy is known from LINAC Technologies (technical description “ELECTRON BEAM SURFACE STERILISATION SYSTEM 200 KeV—The Ke VAC S”), in which three electron accelerators are arranged such that their associated electron exit windows surround a volume with the cross section of an isosceles triangle, through which the molded parts to be sterilized are guided through in one pass. Although with devices of this type the time expenditure is reduced with respect to known solutions in which a molded part is bombarded with electrons in several passes, the technical expenditure is very great due to the use of three electron accelerators. 
         [0014]    Similar arrangements of three electron exit windows are known in which the electrons are generated, however, only by means of one electron accelerator and are distributed among the three electron exit windows with the aid of a deflection system. 
         [0015]    All known solutions with three electron exit windows utilize the advantage that through their triangular arrangement the electron accelerators do not influence one another reciprocally or do so only to a negligible extent, that is, that the accelerated electrons of an electron accelerator do not emit substantial energy fractions to the respectively other electron accelerators. This is necessary in order to limit the energy fraction absorbed in the electron exit window and thus its operating temperature to a subcritical level. If the material application temperature is exceeded, the sensitive material of the window covering would otherwise be destroyed by the mechanical stress of the atmospheric pressure applied from outside, relative to the high vacuum in the interior of the beam generator. A maximum temperature of approximately 400° C. must not be exceeded on any account for the titanium film conventionally used in electron exit windows. A maximum of 200-250° C. is assumed for continuous operation. 
         [0016]    The arrangement of only two opposite electron exit windows is likewise known. With the technologically necessary small distance between the electron exit windows, a considerable energy fraction is thereby inserted into the opposite electron exit window, which results in a temperature increase by a factor of 2 to 5, depending on the construction. The necessary limitation of the maximum temperature can be achieved only by proportional limitation of the beam current. However, this limits the effectiveness of the total system. 
         [0017]    Another possibility for limiting the temperature of two opposite electron exit windows is the arrangement of an additional absorber such as, e.g., an (at least partially transparent) transport belt between the electron exit windows (U.S. Pat. No. 2,741,704). A substantial energy fraction is then allocated to the absorber, which limits the irradiation of additional energy on the opposite electron exit window. 
         [0018]    The solution is likewise known of arranging two electron exit windows opposite one another and laterally offset in the product transport direction. The radiation of power into the respectively opposite electron accelerator and thus its overheating are thus prevented. 
         [0019]    With the known devices, in which two and more electron exit windows surround a molded part and in which a virtually identical electron energy density is emitted over an entire electron exit window and a molded part is bombarded with electrons in only one pass, individual surface partial areas of the molded part, depending on the geometry thereof and the resulting differing distance of the surface partial areas from an electron exit window, can be bombarded with a different dose (energy per unit surface area or energy per mass unit) of electron energy. 
         [0020]    In order to realize a certain characteristic on a molded part, a certain dose of electron energy is necessary. Expediently, the output of the electron generator is adjusted such that on those surface areas at which the lowest dose arrives, the dose arriving there corresponds exactly or corresponds at least to the dose that is necessary for the modification of the characteristic. All other surface areas of the molded part are inevitably bombarded with an increased dose. This increased dose of energy is also called an overdose. The higher the overdose in individual areas of a molded part, the more marked the deviation of the characteristics in these areas from the target parameters. However, an overdose of electron energy not only has a negative impact on the characteristics to be modified of a molded part, but can also lead to undesirable side effects that may even be damaging to the process through the formation of undesirable by-products (for example, ozone) in the process gas (for example, air). 
         [0021]    A parameter described as an overdose factor indicates the factor by which a necessary dose for adjusting a desired characteristic is exceeded. With the known devices, depending on the geometry of molded parts to be modified, overdose factors are reached in individual surface areas that are not acceptable for many uses in order to realize sufficiently uniform characteristics over the entire surface and which also entails the already cited undesirable side effects. 
         [0022]    To achieve high productivities, an adjusted high transport speed of the molded parts is necessary. Due to the proportionality of transport speed and beam current, the achievement of a technologically predetermined minimum dose (for the application area of sterilization, this is, e.g., 25 kGy) necessitates an increase of the beam current proportional to the speed, which leads to the disproportionate increase of the operating temperature of the electron exit windows. In the case of the arrangement of two electron accelerators opposite one another without additional absorbers or lateral displacement of the systems, no solution suitable for practical use currently exists. 
       SUMMARY OF THE INVENTION 
       [0023]    The invention is therefore based on the technical problem of creating a device and a method by means of which the disadvantages of the prior art are overcome. In particular, the device and method should be suitable for modifying characteristics of three-dimensional molded parts with a low expenditure in terms of time and technology such that a sufficiently uniform modification of the entire surface or of an edge layer of the molded parts is carried out and nevertheless have none of the disadvantages limiting productivity from the overall arrangement of the electron accelerators. The overdose factor should be so low thereby that it corresponds to the technical/technological requirements of the molded parts. 
         [0024]    According to the prior art, it was hitherto assumed that at least two electron exit windows with lateral displacement or with an absorber located between them or with limited beam current or three electron exit windows are necessary in order to be able to bombard the cross-sectional circumference of a three-dimensional molded part in one pass completely with electrons and to produce the desired changes in characteristics. It is shown according to the invention that a limitation of the beam current resulting from an arrangement of electron exit windows opposite one another is not necessary and in addition a bombardment of a molded part surface with a virtually uniformly distributed energy dose is possible. 
         [0025]    A device according to the invention for altering characteristics of a three-dimensional molded part using electrons comprises at least one electron accelerator for generating accelerated electrons and two electron exit windows, wherein the two electron exit windows are arranged opposite one another. Jointly with at least one reflector, the two electron exit windows delimit a process chamber in which the molded part is bombarded with electrons. The electron exit windows are thereby arranged so far apart from one another that an influence of an electron exit window by the emitted energy of the electron exit window lying opposite is negligible. The distance necessary for this is essentially dependent on the acceleration voltage of the electrons, the thickness and density of the film of an electron exit window and the density of the gas between the electron exit windows. 
         [0026]    The disadvantage that all surface areas (in particular the areas that run largely perpendicular to the surface of the electron exit windows) of the molded part to be modified are no longer bombarded sufficiently with electrons with a distance of this type, is offset in that the reflector is shaped and arranged such that electrons (in particular from the edge areas of the electron exit windows) which would not strike the molded part, are reflected by the reflector onto the surface areas of the molded part that exhibit a deficit in the bombardment with electrons. 
         [0027]    Furthermore, a device according to the invention comprises a sensor system by means of which the energy density distribution in the process chamber can be detected over at least one spatial dimension. Depending on the data detected hereby, the energy density emitted via the electron exit windows can then be controlled such that a uniform bombardment with electrons on the molded part surface takes place within the dimension in which the energy density distribution was detected. 
         [0028]    A device of this type is particularly suitable for molded parts that have a largely round, oval or trapezoidal cross section. However, molded parts with a differently shaped cross section can also be modified therewith. 
         [0029]    To generate the accelerated electrons, an electron accelerator can be used by which the electrons are distributed among the two electron exit windows with a corresponding deflection control. Alternatively, however, a separate electron accelerator can also be assigned to each electron exit window. Area accelerators, also called band emitters, as well as axial beam generators are suitable as electron accelerators. 
         [0030]    With a parallel alignment of two opposite electron exit windows embodied in a flat manner with optimum spacing and arrangement according to the invention of a reflector system, it was possible to realize overdose factors below the value 4 during the electron treatment of molded parts with largely trapezoidal cross section, whereas with the treatment of identical molded parts in devices according to the prior art with three electron exit windows or with two electron exit windows lying opposite one another and an absorber lying between them, overdose factors of far more than 4 had to be accepted. Compared with known solutions, thus with high productivity on the one hand energy is saved and on the other hand the surface of the three-dimensional product is protected from radiation-chemical damage and side effects damaging to the process are reduced due to the lower discharge of ozone. 
         [0031]    One embodiment of the invention comprises two reflectors that delimit the process chamber and are arranged opposite one another in a mirror symmetrical manner. Each of the two reflectors can thereby comprise a plurality of partial reflectors. 
         [0032]    In a particular embodiment, the reflectors are at the same time a component part of the sensor system for detecting an energy density distribution. Hereby, for example, a number of reflectors or partial reflectors that, in such an embodiment, can comprise a material with high atomic number (for example, gold, tungsten or molybdenum) can be connected electrically via a resistor with the electric mass or another electric potential. Electrons that are not reflected by a reflector/partial reflector then form a beam current so that a voltage can be detected via a resistor belonging to the reflector/partial reflector. A corresponding statement can then also be made using the values of the detected voltage at the individual reflectors/partial reflectors regarding the energy density of the electrons reflected by a reflector and corresponding control steps can be taken regarding a uniform energy density distribution. 
         [0033]    It is particularly advantageous if the energy density distributions are detected and correspondingly evaluated in this manner in the x, y and z direction of a Cartesian coordinate system. 
         [0034]    With the aid of a combination of this type of reflectors and sensor system, for example, it can also be detected whether a molded part is located in the process chamber. The generation of electrons can be controlled depending thereon, so that the output of the electron accelerators is adjusted to a process-specific value, for example, when a molded part is located in the process chamber, and otherwise is lowered or reduced to zero. 
         [0035]    With a device according to the invention the maximum occurring overdose factor or a uniform bombardment with electrons of the molded part surface can be further optimized in that the two electron exit windows are aligned to one another at an angle depending on the geometry of a molded part to be treated such that as many surface sections of the molded part as possible are spaced apart with virtually the same measurement from the respectively energy-emitting electron exit window. 
         [0036]    In addition to flat shaped electron exit windows, these can also be embodied, for example, in a concave manner towards the molded part or also adapted to the geometry of the molded part, which likewise causes as many surface sections of the molded part as possible to be spaced apart by virtually the same measurement from the respective energy-emitting electron exit window, whereby lower overdose factors can be achieved. 
         [0037]    With one embodiment an electron generator comprises a device by means of which the electron energy density emitted over the area of at least one electron exit window is controllable such that different electron energy densities are emitted over individual partial areas of the electron exit window. Thus, for example, in the partial areas of the window in which surface areas of a molded part lie opposite the window at a great distance, the electron energy density can be increased with respect to partial areas of the window in which surface areas of the molded part lie opposite the window at a small distance, so that as far as possible all the surface areas of the molded part absorb the same dose and thus uniform characteristics are formed over the entire surface in the processing depth to be modified (surface or edge layer). Constructive systems lying within a shaped beam generator (without electromagnetic beam deflection), engaging in the electron optics, such as apertures, compensation electrodes or components influencing the temperature of the cathodes, which systems influence the distribution of the electron current, can be used as a means of modifying the electron energy density over individual partial areas of an electron exit window 
         [0038]    Another possibility lies in the arrangement of means outside the electron accelerator, in particular of magnetic and/or electric systems that influence the direction of the accelerated electrons. 
         [0039]    Another embodiment of the invention is characterized in that at least one electron exit window is arranged in a movable manner. For example, at the beginning when a molded part is inserted in the process chamber between two windows, this electron exit window can thus be tilted toward the front face of the molded part in order to improve the bombardment with electrons at the front face. During the further transport of the molded part through the process chamber, the window can then be tilted in the direction of parallel alignment to the opposite window and when leaving the process chamber in the direction of the rear of the molded part. However, it is also possible for other movement forms to be carried out with the window. For example, the window thus can be carried along for a time in the movement direction of the molded part. 
         [0040]    Another optimization in the object of modifying the characteristics uniformly over the entire surface of a molded part, is possible by means of a device that controls via magnetic and/or electric deflection systems not only the point at which an electron leaves an electron exit window, but also the exit direction of the electron at this point. Certain surface areas of the molded part can thus be bombarded with electrons in an even more targeted manner. 
         [0041]    In a particular embodiment, at least one electron exit window is embodied as a vacuum-tight film and thus as a pressure barrier between beam guide chamber and process chamber. Alternatively, an electron exit window can also be embodied as a gas-permeable pressure stage arrangement between the electron generator and process chamber. 
         [0042]    A method according to the invention for altering characteristics of a three-dimensional molded part by means of electrons is characterized in that electrons are generated, accelerated and emitted over the surface of two electron exit windows lying opposite one another by means of at least one electron accelerator, wherein the two electron exit windows and at least one electron reflector delimit a process chamber in which the surface or an edge layer of the molded part is bombarded with electrons, wherein an energy density distribution within the process chamber is detected over at least one spatial dimension by means of a sensor system and the spacing of the electron exit windows is adjusted such that an influence of an electron exit window by the emitted energy of the electron exit window lying opposite is negligible. 
         [0043]    Advantageously, the spacing of the electron exit windows is adjusted depending on the acceleration voltage of the electrons and the thickness and the density of the electron exit windows. 
         [0044]    With one embodiment, the spacing a of the electron exit windows is adjusted in a range that results from the formula: 
         [0000]    
       
         
           
             a 
             = 
             
               f 
               * 
               
                 
                   
                     6 
                     , 
                     67 
                     * 
                     
                       10 
                       
                         - 
                         7 
                       
                     
                      
                     
                       
                         
                           ( 
                           
                             Ub 
                             * 
                             
                               k 
                               1 
                             
                           
                           ) 
                         
                         
                           5 
                           / 
                           3 
                         
                       
                       
                         ρ 
                         W 
                       
                     
                     * 
                     
                       k 
                       2 
                     
                   
                   - 
                   
                     
                       ρ 
                       F 
                     
                     * 
                     
                       d 
                       F 
                     
                   
                 
                 
                   ρ 
                   G 
                 
               
             
           
         
       
     
         [0000]    whereby, 
         [0045]    a=spacing of the electron accelerators 
         [0046]    Ub=acceleration voltage 
         [0047]    ρ w =density of water 
         [0048]    ρ G =density of the medium between the electron exit windows 
         [0049]    ρ F =density of the window film 
         [0050]    d F =thickness of the window film 
         [0051]    k 1 =1*V −1    
         [0052]    k 2 =1*(g/m 2 ) −1    
         [0053]    f=spacing factor (0.5&lt;f&lt;1.5). 
         [0054]    The range for the spacing a results hereby from the value range of the spacing factor f, wherein an optimum computing value for the spacing a results from a spacing factor with a value of 1. 
         [0055]    Different alternative possibilities are available for the irradiation of a molded part inside the process chamber between the two electron exit windows. 
         [0056]    Thus, a molded part can be guided through the process chamber at constant speed and during this can be bombarded with electrons. 
         [0057]    Alternatively, there is also the possibility that a molded part is guided into the process chamber and there in the stationary state is bombarded with electrons by a one-time or multiple irradiation operation. 
         [0058]    In a further alternative embodiment a molded part is bombarded with electrons in the so-called step-and-repeat mode. This means that the molded part is guided into the process chamber such that at least one piece of the molded part projects into the process chamber. In the stationary state the molded part is then bombarded with electrons from the electron exit windows. This is followed by another transport step in which the molded part is moved another distance into or through the process chamber. In the stationary state an irradiation step is then again carried out in which the molded part is again bombarded with electrons. Transport and irradiation steps thus alternate until the molded part has been moved completely through the process area. A respective transport step can be carried out thereby such that the individual surface areas that are bombarded with electrons after the respective transport steps are adjacent to one another or overlap one another with an alternative variant. 
         [0059]    Finally, a modification of a molded part can also be carried out in that the molded part in the process chamber rotates around an axis extending between the two electron exit windows and during this is bombarded with electrons through a one-time or multiple irradiation operation. 
         [0060]    Methods according to the invention can be used, for example, for sterilizing packaging and products of the pharmaceutical industry and medical engineering, for the sterilization/disinfecting or degerming of products such as fruits, eggs or other natural products, for the modification of plastics, hardening of coatings or for sterilizing/disinfecting objects. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0061]    The invention is described in more detail below based on an exemplary embodiment. The drawings show: 
           [0062]      FIG. 1  A diagrammatic cross-sectional representation of a device according to the invention; 
           [0063]      FIG. 2  A graphic representation of the depth dose distribution of the electrons emitted from the electron exit windows  5   a  and  5   b  from  FIG. 1  lying opposite one another; 
           [0064]      FIG. 3  A diagrammatic representation of a sensor system, comprising the reflectors  7   a   1  and  7   b   1  from  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0065]    In  FIG. 1  a device  1  for electron treatment for the purpose of sterilizing the surface of a molded part  2  is shown diagrammatically in cross section. Molded part  2  is an elongated object with a trapezoidal cross section. Device  1  comprises two electron accelerators  3   a ,  3   b  embodied as shaped beam generators  3   a ,  3   b  that respectively comprise an electron acceleration chamber  4   a ,  4   b  and an electron exit window  5   a ,  5   b . The electron exit windows are hereby embodied as a titanium film 11 μm thick. The electron accelerators  3   a ,  3   b  are arranged such that the flat shaped electron exit windows  5   a ,  5   b  are aligned parallel opposite one another. Molded part  2  is guided continuously through between the two electron exit windows  5   a ,  5   b  on a conveyor belt system  6  interrupted in the area of the electron exit window  5   b  and shown by a dotted line in  FIG. 1  and the entire surface thereof is thereby bombarded with electron energy. Respectively, the lowest energy dose is thereby transferred to the oblique lateral surfaces of the molded part  2  at the points furthest distant from the electron exit windows, which is compensated by the arrangement of electron reflectors  7   a   1 ,  7   b   1 ,  7   a   2 ,  7   b   2  of gold. This is carried out in that the unused edge beams  8   a   1 ,  8   a   2 ,  8   b   1 ,  8   b   2  of the respective electron beam of the two electron accelerators  3   a ,  3   b  strike the respectively closest electron reflector, are reflected there and guided to the molded part through the angled arrangement of the reflectors in the range of the lowest dose. An overall arrangement of this type results in an energy dose on the entire surface or else in an edge layer of the molded part with a minimum overdose factor, a maximum utilization of the electron current and a minimum of the reactive ozone occurring in the air gap. 
         [0066]    The spacing of the two electron exit windows  5   a  and  5   b  selected in the arrangement corresponds largely to the following context: 
         [0000]    
       
         
           
             a 
             = 
             
               f 
               * 
               
                 
                   
                     6 
                     , 
                     67 
                     * 
                     
                       10 
                       
                         - 
                         7 
                       
                     
                      
                     
                       
                         
                           ( 
                           
                             Ub 
                             * 
                             
                               k 
                               1 
                             
                           
                           ) 
                         
                         
                           5 
                           / 
                           3 
                         
                       
                       
                         ρ 
                         W 
                       
                     
                     * 
                     
                       k 
                       2 
                     
                   
                   - 
                   
                     
                       ρ 
                       F 
                     
                     * 
                     
                       d 
                       F 
                     
                   
                 
                 
                   ρ 
                   G 
                 
               
             
           
         
       
     
         [0000]    whereby, 
         [0067]    a=spacing of the electron accelerators 
         [0068]    Ub=acceleration voltage 
         [0069]    ρ W =density of water 
         [0070]    ρ G =density of the medium between the electron exit windows 
         [0071]    ρ F =density of the window film 
         [0072]    d F =thickness of the window film 
         [0073]    k 1 =1*V −1    
         [0074]    k 2 =1*(g/m 2 ) −1    
         [0075]    f=spacing factor (0.5&lt;f&lt;1.5), wherein f=1 defines an optimum spacing. 
         [0076]    With titanium films 11 μm thick as electron exit windows  5   a ,  5   b  and the medium air (here assumed 1188 g/m 3 ) between these electron exit windows an optimal spacing results of 196 mm. 
         [0077]      FIG. 2  shows by way of example the depth dose distribution of the arrangement according to the invention of two electron accelerators according to  FIG. 1  with a thickness of the electron exit window films (titanium) of 11 μm with an acceleration voltage of 150 kV and an optimum spacing of the electron exit windows of 196 mm. Curve  10  represents the distribution of the energy dose generated by electron accelerator  3   a  over the penetration depth of the electrons. The energy of the electrons has dropped to zero at point  11  with a weight per unit area of 280 g/m 2  (with a density of 1000 g/m 3  corresponding to a penetration depth in mm compliant with the numerical value—in the given case therefore 280 mm). Only at this distance is the electron exit window  5   b  located, the weight per unit area of which is shown as a shaded area in  FIG. 2 . The same conditions result for the electron accelerator  3   b , the generated energy dose of which shown as curve  13  is reduced to zero at point  14  (in the representation  FIG. 2  at approximately 50 g/m 2 ). The distance of the points  11  and  14  represents the distance between the two electron exit windows  5   a  and  5   b  and corresponds to the weight per unit area of approximately 230 g/m 2 , which multiplied by the density of air (here assumed at 1188 g/m 3 ) corresponds to approximately 196 mm. According to the invention under the assumed conditions an optimal spacing of 196 mm therefore results, at which no power is absorbed in the respectively opposite electron exit window. The distance can be varied according to the spacing factor. 
         [0078]      FIG. 2  also shows the point  16  with the highest energy dose that is generated at approximately 100 g/m 2  by electron accelerator  3   a . The electron reflectors  7   a   1  and  7   a   2  are arranged at approximately this point. Taking into account the weight per unit area shown as shaded area  15  of the electron exit window  5   a  of approximately 50 g/m 2 , in air the optimal distance of the reflectors  7   a   1  and  7   a   2  from the electron exit window  5   a  results of approximately 42 mm. The same ratios apply for the electron accelerator  3   b  with reflectors  7   b   1  and  7   b   2 . 
         [0079]      FIG. 3  shows a detailed view of a reflector system, comprising the reflectors  7   a   1  and  7   b   1  from  FIG. 1 , which at the same time are embodied as component parts of a sensor system. It can be seen from  FIG. 3  that the reflectors  7   a   1  and  7   b   1  are subdivided in the y direction, that is in the direction of movement of the molded part  2 , into partial reflectors  7   a   1 . 1  and  7   a   1 . 2  or  7   b   1 . 1  and  7   b   1 . 2 . Each partial reflector is thereby arranged electrically insulated with respect to all of the other partial reflectors. Thus as a measuring device  9   a   1 . 1  is assigned to the partial reflector  7   a   1 . 1 , a measuring device is also assigned to every other partial reflector, by means of which measuring device the electron currents striking the assigned partial reflector can be detected. 
         [0080]    As described above with respect to reflectors  7   a   1  and  7   b   1 , the reflectors  7   a   2  and  7   b   2  arranged in a mirror symmetrical manner to the reflectors  7   a   1  and  7   b   1  are also subdivided into partial reflectors, which at the same time with associated measuring devices are component parts of a sensor system. 
         [0081]    In this manner there are at least two measuring points with corresponding measurement results respectively in the x, y and z direction, by means of which results a statement is thus possible regarding the electron current density distribution in the x, y and z direction. It should be discernible thereby that a more precise statement can be made regarding the electron current density distribution, the higher the number of the partial reflectors embodied in the x, y and/or z direction. 
         [0082]    Depending on the electron current density distributions determined in this manner, device  1  is therefore suitable for the continuous process control by monitoring and optionally controlling the beam current density distribution of the two electron accelerators  3   a  and  3   b  lying opposite one another. By means of the device  1  according to the invention it is therefore possible on the one hand to bombard with electrons in a surface-covering manner the entire surface of a molded part  2  despite only two electron exit windows  5   a ,  5   b , on the other hand, the operation can be controlled thereby such that all of the surface sections are bombarded with a largely uniform energy dose. 
         [0083]    Through the combination of reflector system and sensor system it is furthermore possible to monitor the stay of the molded parts  2  in the process zone it terms of space and time. With the absence of a molded part  2 , the edge beams  8  strike the respectively opposite reflector (e.g., edge beam  8   a   1  strikes reflector  7   a   1  and then reflector  7   a   2 ) and are registered in the sensor system as an ascending electron current value. With the presence of a molded part  2  in the process zone, the molded part  2  however absorbs the reflected edge beams and the registered signal is reduced. In addition the proportion is reduced of other scatter electrons that strike the sensor system. A statement can thus be made on whether a molded part  2  is located in the process chamber.