Apparatus and method of making containers

1. An apparatus for making containers made of sheet material, said apparatus comprising:

a supply station configured to supply a film, the film having at least one folded portion having three or more film flaps folded and superimposed with respect to each other,

a welding station configured to receive the film from the supply station, wherein the welding station comprises at least one welding head configured to contact the film and weld at least the folded portion of said film to form a container having a housing compartment, wherein the welding head comprises at least one heater made of electrically conductive material having an electrical resistivity which, at least in a predetermined temperature range, decreases upon the increase of temperature of the electrically conductive material; and

at least one power supplier connected to the welding head and configured to provide electric power to the heater so as to enable the passage of an electric current flow within the heater, the apparatus further comprises a control unit active on the power supplier and configured to command the power supplier and control the supply of electric power to the heater, said control unit being further configured to command to the power supplier a heating cycle comprising:

applying an electric voltage to the conductive strip of the heater to generate a temperature increase of an exposed surface of the welding head so to take it to a first temperature;

controlling said electric voltage to maintain the exposed surface of the welding head at the first temperature for a first discrete time interval; and

reducing or eliminating the voltage applied to the conductive strip of the heater to reduce the temperature of the welding head below said first temperature.

2. The apparatus of claim 1 , wherein the welding head is movable between:

a rest position where it is spaced from the film, and

a welding position wherein the welding head contacts the film;

wherein the control unit is configured to control the welding head so that, during each heating cycle, said head maintains the welding position at least during said first discrete time interval.

3. The apparatus of claim 1 , wherein the control unit is active in command on the supply station and the welding station, said control unit being configured to command to the supply station an advancement cycle comprising:

moving the film along the advancement path for a predetermined time interval;

stopping the film for a respective predetermined time interval;

wherein the control unit is configured to interval movement steps with stop steps so as to generate a discontinuous advancement of the film,

said control unit being configured to command to the welding station the welding of the film during the film stop step,

wherein the control unit is configured to command the first and the second operative condition of the first and second tools of the welding head, the control unit being configured to:

synchronize the first operative condition of the first and second tools with the moving the film,

synchronize the second operative condition of the first and second tools with the stopping the film.

4. A method, comprising:

using the apparatus of claim 1 to make folded film containers.

5. A method of making containers using the apparatus of claim 1 , said method comprising:

arranging a continuous film having at least one folded portion comprising a number of superimposed flaps equal to or greater than three,

positioning the continuous film at the welding head of the welding station,

welding the continuous film by the welding head in order to define at least one container.

6. The method of claim 5 , wherein the arranging of the film comprises:

unwinding a continuous film from a reel according to a flat configuration,

folding said flat film to define the folded portion having a number of superimposed film flaps equal to or greater than three,

wherein, following the folding step, the folded portion is substantially W-shaped,

wherein the welding step comprises at least one step of placing the welding head in contact with the film, optionally at least with the folded portion of the film,

wherein the welding comprises at least:

placing the first and the second tool of the welding head in the first operative condition in which the tools are spaced from each other,

arranging the film between said first and second tools placed in the first operative condition,

placing the first and second tools of the welding head in the second operative condition so that said tools can act by pressing on the film arranged interposed between the tools,

at least during the step in which said first and second tools are in the second operative condition, applying an electric voltage to the conductive strip of the at least one heater of at least one among the first and second tools in order to generate a temperature increase of an exposed surface of the welding head so to take it to a first temperature such to enable the welding of the film and make said container,

following the welding of the film, placing the first and the second tool in the first operative condition,

moving said container together with the continuous film along the advancement path exiting from the welding head.

7. The method of claim 5 , wherein the welding of the film to make said container occurs in a single step of contact of the welding head with the film.

8. The method of claim 5 , further comprising at least cutting the continuous film exiting from the welding station so as to define discrete containers.