Induction sealing device and method which may be used for producing packages of pourable food products

• US 7,538,302 B2
• Filed: 03/26/2004
• Issued: 05/26/2009
• Est. Priority Date: 03/28/2003
• Status: Active Grant

• Current Assignee: Tetra Laval Holdings & Finance SA (Tetra Laval Holdings BV)
• Original Assignee: Tetra Laval Holdings & Finance SA (Tetra Laval Holdings BV)
• Inventors: Galavotti, Giorgio, Javed, Saquib, Ferrari, Claudio, Melandri, Antonio
• Primary Examiner(s): ROBINSON, DANIEL LEON
• Application Number:
  US10/551,206
• Publication Number:
  US 20060242928A1
• Time in Patent Office: 1,887 Days
• Field of Search: 219618-633
• US Class Current: 219/633
• CPC Class Codes: B29C 65/00 Joining or sealing of preformed parts , e.g. welding of plastics materials; Apparatus therefor general aspects of processes or apparatus for joining preformed parts B29C66/00; using porous material formed by internal pressure generated therein for joining preformed parts B29C44/1228, B29C44/326
• CPC Class Codes: B29C 65/3656 being a layer of a multilayer part to be joined, e.g. for joining plastic-metal laminates
• CPC Class Codes: B29C 65/368 with a polymer coating
• CPC Class Codes: B29C 66/1122 Single lap to lap joints, i.e. overlap joints B29C66/45, B29C66/472, B29C66/52272 take precedence
• CPC Class Codes: B29C 66/43121 Closing the ends of tubular or hollow single articles, e.g. closing the ends of bags closing tube ends B29C57/10
• CPC Class Codes: B29C 66/71 characterised by the composition of the plastics material of the parts to be joined welding bar compositions B29C65/125
• CPC Class Codes: B29C 66/72321 consisting of metals or their alloys
• CPC Class Codes: B29C 66/849 Packaging machines
• CPC Class Codes: B29C 66/9131 by measuring the heat or the thermal flux, i.e. the heat flux
• CPC Class Codes: B29C 66/91651 by controlling or regulating the heat generated by Joule heating or induction heating
• CPC Class Codes: B29C 66/934 by controlling or regulating the speed
• CPC Class Codes: B29C 66/961 involving a feedback loop mechanism, e.g. comparison with a desired value
• CPC Class Codes: B29K 2023/06 PE, i.e. polyethylene
• CPC Class Codes: B29K 2023/086 EVOH, i.e. ethylene vinyl alcohol copolymer
• CPC Class Codes: B65B 51/227 by induction welding
• CPC Class Codes: H03H 7/40 Automatic matching of load impedance to source impedance
• CPC Class Codes: H03J 2200/10 Tuning of a resonator by means of digitally controlled capacitor bank
• CPC Class Codes: H03J 5/246 using electronic means H03J5/244 takes precedence

Abstract

An induction sealing device which may be used for producing packages of pourable food products by transversely sealing a tube of sheet packaging material having at least one layer of induction heatable material covered with plastic material. The sealing device has: a generator for generating an alternating power signal; an inductor receiving the alternating power signal to induce a parasitic electric current in the layer and locally melt the plastic material to form a transverse seal; and a matching circuit for achieving optimum power transfer between the generator and the inductor. The matching circuit includes an inductive-capacitive circuit, in which the capacitance of a variable capacitance capacitive element is adjustable so that the current-voltage phase angle is close to zero.

Claims

1. An induction sealing device for producing packages of pourable food products by transversely sealing a tube of sheet packaging material comprising at least one layer of induction heatable material covered with plastic material, said sealing device comprising:

generating means for generating an alternating power signal, said alternating power signal having a current-voltage phase angle;

at least one inductor receiving the alternating power signal to induce a parasitic electric current in said layer and locally melt said plastic material to form a transverse seal; and

a matching circuit for achieving optimum power transfer between said generating means and said inductor;

wherein said matching circuit comprises an inductive-capacitive circuit, in which at least one inductive element is connected to at least one variable-capacitance capacitive element;

the capacitance of the capacitive element being adjustable so that the current-voltage phase angle is close to zero.

2. A sealing device as claimed in claim 1, wherein said inductive element and said capacitive element are parallel to each other.

3. A sealing device as claimed in claim 1, wherein said capacitive element comprises at least one main capacitor, and a number of auxiliary capacitors selectively connectable/disconnectable parallel to said main capacitor.

4. A sealing device as claimed in claim 3, wherein switching devices are connected to respective auxiliary capacitors to switch respective auxiliary capacitors on/off.

5. A sealing device as claimed in claim 4, wherein each switching device comprises a first and a second IGBT transistor having emitters connected to each other, and collectors communicating respectively with an electric line communicating with the main capacitor, and with an end terminal of a respective auxiliary capacitor;

the gates of said IGBT transistors being connected to each other, and receiving a voltage command V_da to turn said IGBT transistors on/off.

6. A sealing device as claimed in claim 5, wherein at least one resistor is interposed between the gates and the emitters of the IGBT transistors;

said resistor ensuring discharge of the current stored in the internal capacitors of the IGBT transistors when these are off.

7. A sealing device as claimed in claim 5, wherein at least one Zener diode is interposed between the gate and the emitter of each IGBT transistor;

said Zener diode limiting the voltage V_ga of the IGBT transistor to a predetermined maximum value.

8. A sealing device as claimed in claim 1, wherein said inductive element has a variable inductance value;

said inductance value being regulated so that the impedance of said matching circuit assumes a value close to an optimum impedance value Z_ott, to maximize power transfer from said generating means to said inductor.

9. A sealing device as claimed in claim 8, wherein said inductive element comprises a transformer having a primary winding with a number of inputs associated with respective turns and so producing, when selected, different transformation ratios of the transformer.

12. A sealing device as claimed in claim 2, wherein said capacitive element comprises at least one main capacitor, and a number of auxiliary capacitors selectively connectable/disconnectable parallel to said main capacitor.

13. A sealing device as claimed in claim 8, wherein the optimum impedance value Z_ott is 50 ohms.

10. An induction sealing method for producing packages of pourable food products by transversely sealing a tube of sheet packaging material comprising at least one layer of induction-heatable material covered with plastic material said method comprising the steps of:

generating an alternating power signal by means of a generator, said alternating power signal having a current-voltage phase angle;

supplying said alternating power signal to at least one inductor to induce a parasitic electric current in said layer and locally melt said plastic material to form a transverse seal; and

optimizing power transfer between said generator and said inductor by means of a matching circuit;

wherein said optimizing step comprises adjusting the capacitance of at least one capacitive element connected to at least one inductive element so that the current-voltage phase angle is close to zero.

11. A sealing method as claimed in claim 10, and comprising the step of regulating the inductance value of said inductive element so that the impedance seen by said generator assumes a value close to an optimum impedance value Z_ott, to maximize power transfer from said generator to said inductor.

14. A sealing method as claimed in claim 11, wherein the optimum impedance value Z_ott is 50 ohms.