Abstract:
An electron beam emitter comprises a housing enclosing a cathode capable of emitting electrons within the housing and a window for allowing the emitted electrons to exit the housing, wherein the housing has an opening adapted to be at least partly engaged with a high voltage connector assembly, the assembly being adapted to connect the cathode to a power supply, the electron beam emitter further comprising a cooling flange surrounding the opening and having an interior channel extending between an inlet port and an outlet port for receiving cooling fluid for cooling the high voltage connector assembly. The invention further relates to a method of cooling an electron beam device.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an electron beam emitter. More particularly, the present invention relates to an electron beam emitter having a cooling flange for reducing the temperature of the electron beam emitter. The invention further relates to a method of cooling an electron beam device. 
       BACKGROUND ART 
       [0002]    Electron beam emitters have been known for a long time and different applications are continuously arising due to the number of advantages over other techniques. 
         [0003]    In e.g. liquid food packaging electron beam irradiation has been considered as a promising alternative for sterilizing purposes, for which wet chemistry involving hydrogen peroxide has been the traditional technical platform. However electron beam emitters may be utilized to provide sufficient sterilization of the packaging material thus eliminating the negative consequences of wet chemistry within the packaging machine. 
         [0004]    Different issues need to be considered when dealing with electron beam emitters, of which excessive heat is one important aspect. The electron beam emitter, commonly including a main body enclosing an electrically powered cathode and an exit window, will provide a cloud or beam of emitted electrons when activated. As a result of the scattered electrons, and a high temperature electron-generating filament inside the electron beam emitter, the heat dissipated within the main body of the electron beam emitter will be high and so will the temperature within the main body. 
         [0005]    The exit window may for this reason be provided with external cooling for improving the stability and operating life time of the exit window. 
         [0006]    However, there is also a need for reducing the temperature at the connector area, i.e. at the location where the cathode is connected to the power supply. This is due to the fact that excessive heat is transferred from the main body towards the connector area. At this position, the temperature should not exceed 70° C. and preferably stay below 50° C. in order to provide optimal performance of the connector area. To provide the necessary cooling a simple, low-cost cooling solution is needed. 
         [0007]    There is thus a need for an improved electron beam emitter which is capable of providing efficient cooling of the connector area. Further, there is also a need for an electron beam emitter for which the connector area cooling is provided by means of a less complex and more cost effective solution. 
       SUMMARY OF THE INVENTION 
       [0008]    Therefore, an object of the invention has been to provide a device for electron beam irradiation in which the above mentioned considerations have been taken into account and solved. 
         [0009]    In an embodiment of the invention an electron beam emitter comprises a housing enclosing a cathode which is capable of emitting electrons within said housing and a window for allowing said emitted electrons to exit said housing. Said housing has an opening adapted to be at least partly engaged with a high voltage connector assembly, said assembly being adapted to connect said cathode to a power supply. Said electron beam emitter further comprising a cooling flange surrounding said opening and having an interior channel extending between an inlet port and an outlet port for receiving cooling fluid for cooling said high voltage connector assembly. 
         [0010]    The interior channel of said cooling flange may be a circular loop which is advantageous in that the cooling flange may provide improved cooling of the connecting area of the electron beam emitter. 
         [0011]    The cross section of said cooling flange is essentially U-shaped such that said interior channel of said cooling flange is sealed by the outer surface of the housing. Hence, efficient cooling is provided since the wall of the housing is in direct contact with the cooling fluid flowing within said cooling flange. 
         [0012]    The cooling flange may comprise scalings for providing a fluid tight seal between said cooling flange and the outer surface of the housing. Hence, possible leakage of cooling fluid is prevented. 
         [0013]    The inlet port and the outlet port may be arranged on opposite sides of said cooling flange, which is advantageous in that cooling fluid is allowed to flow evenly in both directions from the inlet port to the outlet port. 
         [0014]    The opening may have a circular shape, and the cooling flange may have a ring shape. Hence there will be no sharp corners in the interior channel of the cooling flange which is advantageous in that there will be no undesired turbulence in the flow of the cooling fluid. 
         [0015]    The opening may be arranged on an axial edge of said housing, which facilitates the mounting and connecting procedure of the power supply to the electron beam emitter housing. 
         [0016]    An electrical insulator may be arranged between said housing and said cathode at said opening, wherein the electrical insulator may be made of a ceramic material. 
         [0017]    The invention further relates to a filling machine capable of providing carton-based packages enclosing liquid food, comprising an electron beam emitter as described above. 
         [0018]    The invention further relates to a method for cooling an electron beam emitter comprising a housing enclosing a cathode capable of emitting electrons within said housing and a window for allowing said emitted electrons to exit said housing. Said housing has an opening adapted to be at least partly engaged with a high voltage connector assembly, said assembly being adapted to connect said cathode to a power supply. The method comprises the steps of providing a cooling flange surrounding said opening and having an interior channel extending between an inlet port and an outlet port, and supplying cooling fluid to said inlet port for cooling said high voltage connector assembly. 
         [0019]    The invention further relates to a method for sterilizing a carton-based packaging material in a filling machine by means of an electron beam emitter comprising said method. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Hereinafter, the invention will be described with reference to the appended drawings, wherein: 
           [0021]      FIG. 1  is an isometric view of an electron beam emitter according to an embodiment; 
           [0022]      FIG. 2  is an isometric view of a cathode of an electron beam emitter according to an embodiment; 
           [0023]      FIG. 3  is an exploded isometric cross sectional view of a connector assembly of an electron beam emitter according to an embodiment together with a portion of the housing; 
           [0024]      FIG. 4  is an isometric view of portions of the connector assembly and the housing shown in  FIG. 3  in an assembled state; 
           [0025]      FIG. 5  is an isometric view of a cooling flange according to an embodiment; and 
           [0026]      FIG. 6  is a side view of a filling machine including an electron beam emitter according to an embodiment. The drawing is not according to scale. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]    With reference to  FIG. 1  an electron beam emitter  10  is shown. The electron beam emitter has a housing  12  extending between a first end  14  and a second end  16 . The housing  12 , having a tubular shape and forming a main body of the electron beam emitter  10 , is provided with an electron exit window  18  extending along the longitudinal axis of the housing  12 . 
         [0028]    The first end  14  of the housing  12  has an opening  20  through which a cathode  22  (shown in  FIG. 2 ) may be inserted and aligned laterally with the electron exit window  18 . The opening  20  is adapted to be engaged with a high voltage connector assembly of which an electrically insulating disc  24  is inserted into the opening  20  and positioned between the periphery of the housing  12  and a male connector part  26  of the connector assembly. The male connector part  26  is in one end connected to the cathode  22  and in the other end connected to a female connector part  38  (shown in  FIG. 3 ), said female connector part  38  being connected to a power supply. The insulating disc  24  electrically insulates the cathode  22 . 
         [0029]    With reference to  FIG. 2 , the cathode  22  and some parts of the high voltage connector assembly is shown in further detail. The electrically insulating material  24 , having a ring shape, surrounds the male connector part  26 . The cathode  22  is extending within the housing  12  and has a length which corresponds to the length of the exit window  18  of the housing  12 . The cathode  22  includes a number of components which are well known in the art, such as a filament, a control grid, etc. 
         [0030]    Now referring to  FIG. 3  and  FIG. 4 , the high voltage connector assembly  30  of an electron beam emitter is shown. The connector assembly  30  is provided to the first end  14  of the electron beam emitter  10  shown in  FIG. 1  and includes a number of components which form the first end  14 . 
         [0031]    The male connector part  26  is surrounded by the ring shaped disc  24  of electrically insulating material, and attached to the wall  32  of the housing  12  by means of a circular flange  34 . Preferably, a ring  36  made of stainless steel is provided to hold the flange  34  in place on the housing  12 . In fact, the ring  36  cooperates with a groove  68  in the housing  12  to form an end stop for the flange  34 . The ring shaped disc  24  is preferably made of a ceramic material, for example comprising Al 2 O 3 . The housing  12  is made of stainless steel, but has an end portion  70  preferably made of an alloy comprising iron (Fe), nickel (Ni) and copper (Co), which has a thermal coefficient between the ceramic material and the stainless steel. 
         [0032]    The female connector part  38  is adapted to be electrically connected to the male connector part  26  and may include different connectors  39   a,    39   b,    39   c,  for connecting to different parts of the cathode  22 . The female connector part  38  is connected to a power supply (not shown) through a cable (not shown). For example, a first connector  39   a  may provide a voltage to a filament (not shown), a second connector  39   b  may provide a voltage to a control grid (not shown), and a third connector  39   c  may provide a voltage to the cathode body (not shown). However different connector configurations may also be utilized in order to provide adequate functionality of the cathode. 
         [0033]    A spacer  40  is further arranged between the female connector part  38  and the ceramic disc  24 . 
         [0034]    A cooling flange  50  is provided at the exterior surface of the wall  32  of the portion  70  of the housing  12 , preferably being axially aligned with the interface of the male connector part  26  and the connectors  39   a,    39   b,    39   c  as well as with the ceramic disc  24 . The cooling flange  50  has a circular ring shape and is sealed against the wall  32  by means of two O-rings  52   a,    52   b.    
         [0035]    The cooling flange  50  has an angular U-shaped cross section such that a rectangular interior channel  54  is formed between the interior walls of the cooling flange  50  and the wall  32  of the portion  70  of the housing  12 . The cooling flange  50  is further provided with an inlet port  56  and an outlet port  58 . The inlet port  56  and the outlet port  58  are preferably arranged on opposite sides of the cooling flange  50  such that cooling fluid, e.g. water, may enter the interior channel  54  of the cooling flange  50  and flow in opposite directions towards the outlet port  58  where the cooling fluid is allowed to exit the cooling flange  50 . Preferably the inlet port  56  and the outlet port  58  are connected by means of a closed circulation system, including e.g. fluid line, a pump, a heat exchanger, etc. The circulation system may thus be arranged remote of the electron beam emitter and may consequently form a part of already existing cooling systems depending on the particular application and implementation of the electron beam emitter. 
         [0036]    The cooling flange  50  has a number of receiving bores  60 , extending axially through the cooling flange  50  outside the interior channel  54 . The receiving bores  60  are configured to receive bolts  62  or other fasteners for securing the cooling flange  50  to threaded bores in flange  34 . The female connector part  38  is provided with bolts  66  for securing it to the threaded bores in flange  34 , and consequently securing it also to the housing  12 . The bolts  66  of the female connector part  38  are extending through some of the bores  60  in the flange  34 , which bores are provided without threading. 
         [0037]    With reference to  FIG. 5  the cooling flange  50  is shown in further detail. Here, the cooling flange  50  has a circular ring shape such that is may be fitted with a cylindrical housing of an electron beam emitter. Other shapes may also be used, e.g. rectangular etc, as long as the inner dimensions of the cooling flange  50  corresponds to the outer dimensions of the first end  14  of the housing  12 . The cooling flange  50  may be made of various materials, such as for example stainless steel or for example aluminium with a corrosion protection coating. Further, two grooves  64 ,  65  are provided adjacent to the interior channel  54  for receiving the O-rings  52   a,    52   b  shown in  FIG. 3  in order to prevent cooling fluid to leak out. 
         [0038]    With reference to  FIG. 6  a filling machine  100  is shown, utilizing two oppositely directed electron beam emitters  110 . The electron beam emitters  110  are constructed according to what has been described with reference to  FIGS. 1 to 5 . When electron beam emitters  110  are employed for sterilizing packaging material in automatic packaging machines, they can, for instance, be arranged in the manner illustrated in  FIG. 6  which illustrates a sterile chamber  112  into which a packaging material web  114  which is unwound from a magazine reel  116  is fed through a passage  118 . In the sterile chamber  112 , a sterile atmosphere is maintained and, in order that no infected air can penetrate in through the passage  118 , a slight excess pressure may be maintained within the sterile chamber  112 . The web  114  introduced into the sterile chamber  112  is caused to pass, in this case, the electron beam emitters  110  whose exit window  120  are aimed towards the inside and outside surfaces of the packaging material web  114 . The electron beam emitters  110  are shielded off from the environment by an essentially S-formed x-ray shield  111 . On passage of the packaging material web  114  past the electron beam emitters  110 , the surfaces of the web  114  is affected by electron beams of energy-enriched electrons from the emitters  110 , whereupon the interior and exterior sides of the web is sterilized. The web is thereafter led into a tubeforming section, whereby the web is passed over a bending roller  122  and formed into a tube in that the longitudinal edges of the web  114  are united to one another and sealed by means of a longitudinal sealing device  124 . The tube  126  of sterilized packaging material is filled with sterile contents through the supply conduit  128 , whereafter the tube  126  is discharged out of the sterile chamber  112  and is divided by means of sealing devices  130  into individual packaging containers  132  by repeated transverse seals transversely of the longitudinal direction of the tube  126 . The formed packaging units  132  can then be separated into individual packaging containers by means of incisions in the sealing zones, and possibly be formed by folding or other means into parallelepipedic packages or packages of other configuration. 
         [0039]    Although specific embodiments have been described it should be appreciated that various modifications may be made to the electron beam emitter without departing from the scope as defined in the accompanying claims.