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(21)  Application Number: Kll/P/1999/000157

(22) Filing Date: 0611011999

(30) Priority data: 98830588.4  07/10/1998  EP

(73)0wner: TETRA LAVAL HOLDINGS & FINANCE SA of  70, Avenue GenCrni-Guisan CH-1009 Pully, Switzerland

(72) Inventors: BENEDETII, Paolo  ofViaMnlntesta, 21,1-41100 Modena,  Italy and SELBERG, Hans of Algskyttev 7 S-222 53 Lund,  Sweden

(74) Agent/address for correspondence: Waruingc & Waruingc Advocates, P, 0, BOX 72384-00200 NAIROBI

(54}  Title: METHOD OF PRODUCING SEALED PACKAGES CONTAINING POURABLE FOOD PRODUCTS FROM A TUBE OF PACKING MATERIAL, AND PACKING UNIT IMPLEMENTING SUCH A METHOD

(57) Abstraet: A method of producing scaled packages (2) containing pourable food products from n tube {3) of heat sent sheet packing material fed 11iong a vertical path (A) and filled continuously with the food product; the method including the steps of pressure gripping equally spaced cross sections of the tube (3) by means of two pairs of jaws (8, 9) acting cyclically and successively on the tube (3); cutting the tube (3), ot eoch of the cross sections, along a respective parting line (L); and then heat sealing the packing material of the tube (3) on opposite sides of the parting line (L).
 
METHOD OF PRODUCING SEALED PACKAGES CONTAINING POURABLE FOOD PRODUCTS FROM A TUBE OF PACKING MATERIAL, AND PACKING UNIT IMPLEMENTING SUCH A METHOD

TECHNICAL  FIELD

The present invention relates to a method of producing sealed packages containing pourable food products from a tube of packing material, and a packing

15    unit  implementing  such  a  method.

BACKGROUND  ART

Many  pourable  food  products,   such  as   fruit   juice,

pasteurized or UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of

20    sterilized  packing  material.

A typical example of such a package is the parallelepiped packing container for liquid or pourable food products known by the name of Tetra Brik Aseptic (registered trademark) , which is formed by folding and

25    sealing a strip-rolled packing material. The rolled packing material comprises layers of fibrous material, e.g. paper, covered on both sides with heat seal plastic material, e.g. polyethylene.
 

For aseptic packing of long-storage products, such as UHT milk, the packing material comprises a layer of barrier material, e.g. an aluminium sheet, which is

superimposed  on  the  layer  of  heat  seal  plastic  material

and is in turn covered with another layer of heat seal plastic material forming the inner face of the package actually contacting the food product.

As is Jmown, packages of the above type are produced on fully automatic packing machines, on which a

10    continuous tube is formed from the packing material supplied in strip form. The strip of packing material is sterilized on the packing machine, e.g. by applying a

chemical sterilizing agent, such as a hydrogen peroxide solution; following sterilization, the sterilizing a~ent

15    is removed, e.g. vaporized by •heating, from the surfaces of the packing material; and the strip of packing material so sterilized is kept in a closed sterile environment, and is folded and sealed longitudinally to

form  a  tube.

20 The tube is filled with the sterilized or sterile-processed food product, and is gripped at equally spaced cross sections by two pairs of jaws, which operate cyclically and successively on the tube to heat seal the packing material of the tube and form a continuous strip


25    of pillow packs connected to one another by respective transverse sealing bands.

The pillow packs are separated by cutting the respective sealing bands, and are transferred to a final


folding station where they are folded mechanically into the final parallelepiped shape.

Packing units of the above type are known in which the reciprocating movement of the jaws is controlled by a cam system comprising an electric motor, the output shaft of which is fitted, for each pair of jaws, with two cams with appropriately differing profiles. By means of respective lever mechanisms, the cams control the up and down movement of a supporting slide to which a respective
10    pair of jaws is hinged, and the reciprocating opening and closing movement of the j awe.

Two facing forming tabs are hinged respectively to the j awe in each Pair, and are moved between an open position, into which they are pushed bY elastic means,

15    and a closed position in which they mate to define a space defining the shape and volume of the package to be formed in between. The forming tabs are closed by cams

fixed to the structure of the unit, and which interact with respective rollers carried by the tabs.

20 The portion of the tube gripped between each pair of jaws is simultaneously heat sealed transversely by induction heating mean~ on the jaws.

More specifically 1 one of the jaws in each pair comprises a main body made of nonconducting material 1 and
25    an inductor housed in a front seat on the main body. The inductor is normally supplied by a high-frequency generator 1 and comprises a bar made of electrically

conducting material and which interacts with the tube material to heat it to the required sealing temperature.

The other jaw in each pair comprises pressure pads made of elastic material and which cooperate with the inductor to heat seal the tube along a respective sealing

band.

Once  the  sealing  operation  is  completed,  a  knife  on one  of  the  jaws  in  the  pair  interacting  with  the  tube  of packing  material  is  activated  to  cut  the  tube. along  the 10    center  of  the  sealing  band  and  so  detach  a   pillow  pack from  the  bottom  end  of  the  tube  of  packing  material.  As the   bottom   end   is   sealed   transversely,    the   jaws,    on reaching  the  bottom  dead  center  position,   can  be  opened to   prevent   interfering   with   the   upper   portion   of   the


IS tube. At the same time, the other pair of jaws, operating in exactly the same way, moves down from the top dead center position to repeat the above gripping/fanning, sealing and cutting operations.

As    stated,   the   tube   of  packing  material   is   heat

20    sealed by inducing electric loss current in the aluminium sheet, which current melts the plastic heat seal material

locally when the respect•ive pair of jaws grips the tube, so as to seal a cross section of the tube by heat sealing the plastic coating.

25 From analysis of the packing material during the heat seal operation, the loss current induced in the cross section of the tube of packing material gripped between each pair of jaws has been found to follow a
 

closed path, which ia linear along the two longitudinal sides of the region in which tbe inductor interacts with the tube, and is roughly semicircular close to the edges

of  the  cross  section.  That  is,  tbe  current  flows  linearly

s in opposite directions along the two longitudinal oides of the region in which the inductor interacts with the tube, and is deflected towardo the center of the cross section gripped between the jaws close to the edges of the cross section ("bending-off effect"), sa that the

10 oealing band is narrower at the ends than at the central portion. On the other hand, when packing pourable food products containing small solid particles, such as scedo in tomato products, which may get trapped between the nonsealed portions of the two contacting sheets of

IS packing material, tbe sealing band should be ao wide as possible to reduce the likelihood of channels forming through the sealed portion.

DISCLOSURE  OF  INVENTION

It  is  an  object  of  the  present  invention  to  provide 20    a   method   of   producing   sealed   pourable   food   product packages   from   a   tube  of  packing   material,   designed   to eliminate     the     aforementioned     drawbacks     tYPically

associated  with  known  methods.

According    to   the   present".   invention,    there   are

'2S provided a method of producing sealed packages containing pourable. food products from a tube of heat seal sheet packing material, as claimed in Claim lam! packing unit implementing such a method and as claimed in Claim 2.


BR:IEF  DESCRIPTION  OF  THE  DRAWINGS

A  preferred,  non-limiting  embodiment  of  the  present

S    invention will be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a view in perspective, with parts removed for clarity, of a packing unit for producing aseptic sealed packages containing pourable food products

10    from a tube of packing material and according to the method of the present invention;

Figure  2  shows  a  side  view,   with  parts  removed  for

clarity,  of  the  Figure  J.  unitr

Figure  3  shows  a  aide  view  of  the  Figure  2  unil:.  in

IS    a  different  operating  configuratiOn;

Figures 4 to 6 show_ larger-scale side viewa of two forming asaemblieo of the Figure 1 unit at various stages in the processing of the tube of packing material:

Figure    7    shows    a    larger-scale    section    of    an

20    induction heating element. of t.he Figure 4-6 forming assemblies;

Figure 8    shows    a larger-scale section of a

variation  of  the  Figure  7  induction  heating  element..

BEST  MODE  FOR  CARRYING  OIJT  THE  INVENTION

2S Number 1 in Figures 1 to 3 indicates ao a whole a packing unit for producing, from a tube 3 of packing material, aseptic sealed packages 2 (Figures 4 to 6)

containing  a  pourable  food  product,   such  as  pasteurized

or  UHT  milk,   fruit  juice,  wine,  etc.

The    packing   material   has   a   multilayer   structure

{not    shown} ,   and  comprises  a   layer  of  fibrous  material,

normally    paper,   covered   on   both   sides   with   respective

layers  of  heat  seal  plastic  material,   e.g.  polyethylene.

The    side   of   the  packing  material   eventually  contacting

the    food  product  in  package  2  also  comprises  a  layer  of

electrically  conductive  barrier  material,  e.g.  aluminium,

10    in turn covered with one or more layers of heat seal plastic material.

Tube  3  is  formed  in  known  manner  upstream  from  unit

~ by  longitudinally  folding  and  sealing  a   strip  of  heat

seal    strip   material,   is   filled   with  the   sterilized  or

15    sterile-processed food product for packaging, and is fed by known devices {not shown) along a vertical path defined by an axis A.

Unit ~ comprises a supporting structure 4 defining a pair of cylindrical vertical guides 5 1 5 1 located

20    symmetrically with respect to the longitudinal vertical mid-plane a of unit ~ through axis A {Figure ~) .

With reference to Figures ~ to 6 1 unit l. comprises in known manner a pair of forming assemblies 6 1 6 1 movable vertically along respective guides 5, 5 1 and

25    which interact cyclically and successively with tube of packing material to grip equally spaced cross sections of the tube and perform cutting and heat seal operations on tube 3 as described in detail later on.

As assemblies 6, 6 1 are known and symmetrical with respect to plane a, only one (assembly 6} will be described, and only as regards the parts pertinent to the present invention. The corr~sponding parts of assemblies 6, 6 1 are indicated in the drawings using the same

numbering  system.

Assembly 6 substantially comprises a slide movable along respective guide 5; and a pair of j awe B, defined, in the example shown 1 by substantially L-shaped

10    plates,   which  are  hinged  at  the  bottom  to  slide  7  about

respective    horizontal   axes  B,   C  perpendicular  to  plane

a., and are movable between a closed position (Figures 2, 4, 5} and a fully-open position (Figure 3).
More    specifically,    each   jaw   8,    comprises   a

15    substantially quadrangular base portion 10 hinged at the bottom end to a bottom portion of slide 7; and an arm 11

for interacting with tube 3 1 and which is fixed to the top end of portion ~0 and projects from portion 10 in a direction perpendicular tO plane ct • ArmS 1~ Of jaws 8 I

20    extend towards and beyond plane a; on opposite sides of tube 3.

At respective portions 10, jaws a, 9 comprise respective integral transmission members 12 in the form of sector gears, which mesh with each other so that the

25    rotation of one of j awe B 1 9 about respective axis B 1 C is transmitted in the opposite direction to the other jaw

Assembly 6 also comprises a first hook element 13 integral with portion 10 of one (9} of the jaws; a second hook element 14 hinged to portion l.O of the other jaw (8) about an axis D parallel to axes B, C; and a hydraulic cylinder 15 for engaging hook elements 13 and 14 tightly in an engaged position corresponding to the closed

position  of  jaws  B,   9  about  tube  3.

More specifically, hook elements 13 and 14 are mutually engaged by means of respective teeth 16 and 17.

10    Cylinder 15 comprises a piston 19 extending integrally from hook element 14 at the opposite end to hook element 13, and which slides in sealed manner inside an outer

jacket  20  and  is  normally  pushed  towards  hook  element  13 by  a   spring   21  housed  inside   jacket   20 1      so   that,•  when 15    disconnecting    hook    elements    13    and    14,     a    minimum clearance  is  maintained  between  and  to  disengage  teeth  16 and  17   (Figures  4  and  5  relative  to  assembly  6 1  )   •     When oil  under  pressure  is  fed  into  jacket  20  through  an  inlet in  cylinder  15,   spring  21  is  compressed  to  engage  teeth


20    16 and 17 tightly (Figures 4 and 5 relative to assembly 6, and Figure relative to assembly 6 1 ) .

Jaws B, are therefore movable vertically by slide 7 moving along guide 5, and also perform an opening and closing movement about tube 3 of packing material by

25    rotating about respective hinge axes B, C between the jaws and slide 7. The opening and closing movement is superimposed on the up and down vertical movement of slide 7.

The vertical movement and the opening and closing movement are controlled respectively by a first and second known cam actuating device 25, 26.

With  reference  to  Figures  ~ to  3,   actuating  device

25    comprises  a  cam  27  rotating  about  a  respective  axis  E

parallel  to  axes  B,   c,   D;   a  substantially  vertical  lever

28 hinged at the bottom to a top portion of slide 7 ,• and a substantially horizontal rocker arm lever 29, which is located over cam 27, is hinged at opposite ends to lever

10    28 and to structure 4, and cooperates with the outer profile of cam 27 by means of a respective intermediate idle roller 30.

Rocker  arm  levers  29  of  assemblies  6,   6'   are  also

connected •to   each  other  and  to   structure   4   by  a   lever

15    mechanism 3~, so that rollers 30 of rocker arm levers 29 are kept contacting respective cams 27 at all times. Lever mechanism 3~ comprises a pair of substantially vertical rods 32 hinged at the top to respective rocker arm levers 29, and at the bottom to a transverse lever 33

20    in turn hinged centrally to structure 4 about an axis perpendicular to axes A, B, c, D. More specifically, each rod 32 is hinged to respective rocker arm lever 29 in an intermediate position between respective roller 30 and respective lever 2 8 .


25 Actuating device 26 comprises a cam 35 having an axis E and defining, on the outer face, a first and second annular groove 36, 37 having appropriately differing profiles, and which, by means of respective

lever mechanisms 38, 39, respectively control the rotation of jaws 8, 9 about axes B, C and the engagement

and  release  movement  of  teeth  16  and  17  of  hook  elements

Band  H .

More specifically, lever mechanism 38 comprises a substantially vertical first rod 40 hinged at the top end to structure 4 and supporting a projecting idle roller 41 engaging in rolling manner groove 3 6 of cam 35 i and a second rod 42 extending parallel to plane a. and

10 crosswise to axis A, and hinged at opposite ends to jaw 8 about axis D, and to the bottom end of rod 40.

Lever mechanism 39 comprises a substantially vertical first rod 43 hinged at the top end to structure 4 and supporting a projecting idl-e roller 44 engaging in

15 rolling manner groove 3 7 of cam 35; and a tubular second rod 45 fitted in ax.ially-slidin§J manner on rod 42 and hinged at opposite ends, by means of respective connecting rods 46, 47, to the bottom end of rod 43 and to hook element 14, at a point below axis D.

20    Since,   as  stated  previously,   the  vertical  movement

of slide 7 and the opening and closing movement of jaws 8, 9 are superimposed, •lever 28 moves reciprocatingly, while rods 42 and 45 perform a periodic movement resulting from the combination of the reciprocating

25    movement of lever 28 and a further component of periodic motion for opening and closing jaws 8, 9.

With reference to Figures 2 to 6 1 assembly 6 also comprises two mutually facing forming tabs SO hinged to

respective jaws 8, 9 and movable between an open position {Figure 2), into which they are pushed by elastic means (not shown) , and a closed position (Figures 4 and 5} in which they mate to define a space defining the shape and

volume  of  the  package  2  to  be  formed  in  between.  Tabs  SO

are closed by known cams (not shown) fixed to structure 4 of uhit 1, and which interact with respective rollers

(not  shown)   on  tabs  SO.

With  reference  to  Figures  4   to  7,   assembly  6  also

10    comprises a sealing device 51 and a cutting device 52, which, for each cross section of tube 3 of packing

material gripped between respective jaws 8 and 9, provide respectively for heat sealing the cross section and cutting along a respective middle "parting line L.

IS With reference to Figures 4 and 7 in particular, device 51 comprises a substantially U-shaped induction heating element 53 housed in a similarly shaped front groove 54 formed in arm 11 of jaw 8 .

Heating  element  53  has  a   substantially  ring-shaped 20    cross    section;    an    inner   cavity   for    the   passage   of coolant;    and    a    pair    of    straight,    elongated    active surfaces   55,   which  interact  with   tube   3   and   extend   on opposite  sides  of  and  parallel  to  an  intermediate  plane  1t perpendicular   to   axis   A   and   coinciding,   in   use,   with 2S    parting  line  L  of   the  cross   section  of   tube   3   gripped


between  jaws  8  and  9.

Heating element 53 also comprises a pair of straight longitudinal projections 56 projecting from

respective    active   surfaces   55   towards   jaw   9,   extending

substantially the whole length of active surfaces 55, and which, during heat sealing, provide for increasing the gripping pressure on tube 3.

Heating element 53 is supplied in known manner by an electric current generator 57 shown schematically in

Figures  4  to  6.

Device  51  also  comprises  a  pair  of  pressure  pads  58

(Figure  4},   which  are  normally  made  of  elastic  material, 10    are   fitted   to   the   front   of   jaw   9,   and   cooperate   with respective  active   surfaces   55   of  heating  element   53   to
grip  and  heat  seal  tube  3  on  opposite  sides  of  plane  1t.

With   reference    to    Figures    4    to    6,    device    52 comprises  a   substantially  flat  cutting  element  59  hOused 15    in  sliding  manner  in  a  front  seat  60  on  jaw  9  and  movable in  a  direction  perpendicular  to  plane  a;   and  a  hydr~ulic cylinder  61   for  activating  cutting  element  59  and  built

into  jaw  9.

More    specifically,   cylinder   61   comprises   a   piston

20    62 integral with cutting element 59 and movable inside a chamber 63 formed in the body of jaw 9 and communicating on one side with seat 60" and on the opposite side with a pressurized oil inlet. cutting element 59 is normally maintained in a withdrawn idle position, fully housed

25    inside seat 60 (Figures 5 and 6) , by a spring 64 housed inside chamber 63 and interposed between piston 62 and a wall separating chamber 63 from seat 60, and is moved by pressurized oil into a forward cutting position (Figure

4)    projecting frontwards from jaw 9 and cooperating with a cavity• in jaw 8.

Unit 1 also comprises a central control unit 70 (Figures 4 to 6) connected to generator 57 and to cylinders l.S, 61 via the interposition of respective known solenoid valves 71, 72 shown schematically with no indication of the supply, discharge or drive ports.

According to the present invention, central control unit 70 provides, when tube 3 is gripped by each pair of

10    jaws a, 9, for controlling respective generator 57 and the control cylinder 61 of respective cutting element 59 according to a predetermined program memorized in unit 70 itself, so as to first cut the cross section of tube 3 gripped between jaws a and 9 along the parting line L,

15    and then heat seal the packing material of tube 3 on opposite sides of parting line L o

Operation    of unit l., which is    partly self-

explanatory  from  the  above  description,  is  as  follows o

As    each  assembly  6,   6'   travels  downwards,   jaws   8

20    and 9 of assembly 6, 6 1 move into the closed position to grip tube 3 with a downward vertical component of motion equal to the traveling speed of tube 3 o As they travel downwards, jaws 8 and 9 are kept closed and grip tube 3

tightly    by  central   control  unit   70   activating   cylinder

25    l.S, and in particular by the movement of piston 1.9 engaging teeth 1.6 and l. 7 of hook elements 1.3 and 14 and so gripping jaws 8 and 9.

At    this   stage,   central   control   unit   70   activates

cylinder  6~ to  move  cutting  element  59  from  the  withdrawn

to  the  forward  position  to  cut  the  cross  section  of  tube

3 of packing material g:r:ipped between jaws 8 and 9 along parting line L (Figure 4) .

Once cylinder 61 is deactivated, and hence cutting element 59 restored to the withdrawn position by spring 64, central control nnit 70 activates generator 57 to supply electric current to heating element 53 and so heat

10    seal tube 3 of packing material on opposite sides of parting line L (Figure 5) .

During   this   stage,   heating   element   53   melts   the

plastic  heat  seal  layer  of  the  packing  material  locally; and  the  electric  current  supply  to  heating  element  53  is lS     cut  off  while  maximum  pressure  is  still  being  exerted  by jaws  B   and  9   on  tube  3,   so  that  cooling  and  consequent setting,   on  which  the  seal  depends 1      of  the  plastic  layer commence   nnder   pressure   to   ensure   pe:r:~ect  sealing   of

packages  2.

20 Close to the bottom dead center position, central control unit 70 deactivates cylinder 15 to release hook elements 13 and 14 and sO open jaws 8 and 9 - which are opened fully as they travel upwards - and release tube 3

(Figure  6).

25 The movement of assemblies 6, 6 1 is obviously offset by half a cycle : assembly 6 with jaws 8 1 9 open t:r:aveled upwards at the same time assettlbly 6 1 with jaws 8, 9 closed travels downwards, so that arms J.l of
 
assembly    6 1    pass  between  arms  22   of  assembly  6  with  no

interference.

Inverting  the  cutting  and  heat  sealing  of  tube  3  of

packing    material   as   compared   with   the   known   methods

described  previously  alters  the  path  of  the  loss  currents

induced  in  the  packing  material  by  heating  element  53 .

That    is,    as   parting   line   L   formed   by   cutting

element    59   in   tube   3   of   packing   material   produces   an

interruption  in  the  electric  continuity  of  the  aluminium

10    sheet 1 the electric loss currents induced in the packing material by the two active surfaces 55 of heating element

53  are  confined  on  opposite  sides  of  parting  line  L.   In

other    words,   the   electric   loss   current   induced   in   the

packing  material  by  one  of  active  suifaces  55  of  heating

15    element 53 on one side of parting line L tends to move towards the other active surface 55 of heating element 53, but, on account of the interruption produced in the packing material, is forced to close its path on the same

side  of  parting  line  L.

20 As a result, the sealing area on both sides of parting line L is more or less constant, by eliminating the bending-off effect of the electric loss current close to the edges of the cross section gripped between jaws a and 9.


25 The Figure 8 variation relates to an induction heating element 75 similar to heating element 53, but comprising two straight active surfaces 76a, 76b in lieu of each active surface 55.

More    specifically,   heating  element   75   comprises   a

substantially  U-shaped  first  body  77,   which  is  housed  in

a    similarly  shaped  front   groove  78   formed  in  arm  1.1.   of

jaw  B,  has  a  substantially  ring-shaped  cross  section,  and

defines, externally, two active surfaces 76a on opposite sides of plane 7t.

Heating element 75 also comprises a second body 79, which is defined by a straight bar having a u-shaped
cross  section  and  housed  in  an  intermediate  recess  80  in

10    jaw 8, and defines two active surfaces 76b on opposite sides of mid-plane 1t and interposed between active

surfaces  76a.

Like    heating    element    53,    heating    element    75

comprises    four   straight   longitudinal   projections   Bla,

15    Blb, Blc, Bld projecting towards jaw 9 from respective active surfaces 76a, 76b.

Using heating element 75, the electric loss current induced in the packing material has been found to follow substantially symmetrical closed paths on opposite sides

20    of parting line L. More specifically, on each side of parting line L, the electric loss current travels linearly along each acti-ve surface 76a, 76b of heating

element 75, with only a minimum amount of deflection close to the edges of the packing material, and which,

25    involving only a very small part of the sealing region, is practically negligible. The method according to the present invention has been found by the Applicant to produce sealed pourable food product packages 2 in which

the full height of the transverse sealing region is completely sealed.

As stated above, in known techniques, two contiguous packages are usually sealed transversely along two parallel lines before being separated along line L.

The Applicant, on the other hand, has found it more advantageous to separate the packages unsealed and simply compressed between the sealing and elastic contrasting elements, which provides for expelling the small amount

10    of product compressed between the two projections, and so bringing the two layers of heat seal material even closer
together  to  improve  the  seal.

Using    heating  element  53  with  two  active  surfaces

55,    the   two   edges   cut  by  cutting  element   59  but   still

15    close tOgether may possibly be traversed by currents in opposite directions, thus resulting in short circuiting - also aided by the presence of the usually conductive product - with the surrormding metal masses, and in less than perfectly reliable operation of the packing unit.

20 Using heating element 75 with four active surfaces 76a, 76b, on the other hand, the problem is eliminated entirely, by the whole of the central conductor (76b, 79) being at the same potential, and by the cutting element 59 penetrating along a line of symmetry of the currents

25 with no possibility of affecting the amplitude or direction of the currents, thus enabling the product to be expelled and improving both sealing and the reliability of the packing rmit itself.

Tests    conducted  by  the   Applicant   have   also   shown

that    using  heating  element  75  with  four  active  surfaces

76a,    76b  and  at  least  two  projections  Bla,   8~,  Slc,   Sld

provides for greatly reducing product leakage from tube 3 of packing material cut prior to heat sealing. Projections 81, Blb, Bl.c, Bld may be either continuous or

segmented.

Clearly, changes may be made to unit 1 as described herein without, however, departing from the scope of the

10    accompanying  Claims.

Though particularly advantageous for sealing packing material by induction of electric current, the method described also applies to other sealing processes.

CLAIMS

1)    A   method   of   producing   sealed   packages (2}

containing a pourable food product from a tube (3) of heat seal sheet packing material fed along a vertical path(A} and filled with said food product; said method comprising the steps of:

- pressure gripping equally spaced cross sections of said tube (3) by means of at least two pairs of jaws (8, 9) acting cyclically and successively on the tube

(3);

-    cutting   said   tube   (3),   at   each   of   said   cross

sections,    along  a  respective  parting  line  {L);  and  then

- heat sealing the packing material of said tube (3} on opposite sides of said parting line (L);

characterized in that said cutting and sealing steps are performed while the tube (3) is continuously filled with said food product, and in that said sealing step is performed by inducing, on opposite sides of said parting line (L) of said tube {3) of packing material, electric loss currents travelling along substantially symmetrical paths with respect to the parting line (L) .


2)    A packing  unit  (1)   for  producing  sealed  packages

(2)    containing  pourable  food  products  from  a   tube   (3•)   of

heat    seal   sheet   packing  material   fed   along  a   vertical

path    (A)  and  filled  with  said  food  product,  said  unit   (1)

comprising:

-    a  fixed  structure  (4);
 



-    21  -

-    at least two pairs of jaws (8, 9) movable with respect to said structure (4) and acting cyclically and successively on said tube {3} to pressure grip equally spaced cross sections of the tube;

-    sealing means (51) and cutting means (52) carried by each said pair of jaws (8, 9) to respectively perform, on each said cross section of said tube (3) of packing material gripped between the jaws (8, 9), a heat seal operation and a cutting operation along a respective parting line (L) ; and


-    control means (70) for controlling said jaws (8, 9), said sealing means (51) and said cutting means (52)' to perform, on said tube (3) of packing material, first said cutting operation along said parting •line (L) and then said heat seal operation;


characterized in that said cutting and sealing means (52, 51) are activated while the tube (3) is continuously filled with said food product, and in that said sealing means (51) comprise electric-current-induction heating means (53, 75} for inducing, on opposite sides of said parting line (L) of said tube (3) of packing material, electric loss currents travelling along substantially symmetrical paths with respect to the parting line (L) .



3) A unit as claimed in Claim 2, characterized in that said heating means {53, 75) compriser for each pair of said jaws {8, 9}, at least two elongated active surfaces (55, 76a, 76b) interacting with each said cross
 

section of said tube (3) gripped between the jaws (8 1 9) 1 and located on opposite sides of the respective said parting line {L) .

4) A unit as claimed in claim 2 or 3 1 characterized in that said heating means (53, 75) are carried by one

(B)    of  said  jaws   (8 1      9)   in  each  pair;   contrasting  means

(58) carried by the other (9) of said jaws (8 1 9) in said pair and cooperating with said heating means (53, 75); and electric current generating means (57) for supplying said heating means (53, 75).

5)    A unit as claimed in Claim 3 or 4, characterized in that said heating means (75) comprise, for each pair of said jaws ( B 1 9) , four elongated said active surfaces (76a, 76b) interacting with each said cross section of said tube (3) gripped between the jaws (8, 9), and located in pairs on opposite sides of the respective said parting line (L) .


6)    A unit as claimed in any one of Claims 3 to 5, characterized in that said heating means {53, 75) comprise, for each said active surface (55, 76a 1 76b} 1 a projection (56, 81) projecting frontwards from the active surface (55, 76a 1 7Gb) and extending substantially the whole length of the active surface.


7)    A  unit  as  claimed  in  any  one  of  Claims  2  to  6 1

characterized in that said cutting means (52) comprise at least one cutting element (5.9) carried by one (9) of said jaws (8, 9) in each pair and movable, with respect to the jaws (8, 9) 1 crosswise to said tube (3) of packing

material; and first actuating means (61) for moving said cutting element (59) between an idle position, and a cutting position in which the cutting element projects frontwards from the respective said jaw (9).

8)    A unit as claimed in any one of Claims 2 to 7, characterized by comprising first and second hook means (13, 14) carried by respective said jaws (9, 8) in each pair; and second actuating means ( 15) for pressure engaging said first and second hook means (13, 14) in an engaged position corresponding to a closed position of the jaws (8, 9) on said tube (3} of packing material.


9)    A unit as claimed in Claim 8, characterized in that said control means comprise a central control unit

(70)    connected to said first and second actuating means (61, 15) and to said electric current generator (57).

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