INDUCTOR FOR ELECTROMAGNETIC INDUCTION HEATING FOR PLASTICIZING CYLINDERS

Abstract

Disclosed is an inductor for electromagnetic induction heating of a plasticizing cylinder, including at least one coil, made of an electric conductor, arranged on an internal support element of thermal insulation towards the cylinder, made of non-magnetic and non-conductive material. The device provides an even number of two or more identical coils, each having an internal terminal and an external terminal, wherein: the winding direction is the same for all coils; the winding axis of the coils is perpendicular to the axis of the cylinder to be heated; the coils are mounted symmetrically to the cylinder axis to be heated and angularly equidistant; and the adjaent external or internal terminals of the coils are connected to each other and the internal or external terminals are electrically powered, so as to generate an electromagnetic field transverse to the cylinder.

Claims

1-7. (canceled)

8. An inductor for electromagnetic induction heating (300) of a plasticizing cylinder (5), comprising an even number of two or more identical coils (6), made of an electric conductor, arranged on an internal support element (4) of thermal insulation towards the cylinder (5), and made of non-magnetic and non-conductive material, said coils (6), each having an internal terminal (A) and an external terminal (B), wherein the winding direction is the same for all coils, the winding axis of the coils (6) is perpendicular to the axis of the cylinder (5) to be heated, the coils are mounted symmetrically to the cylinder axis to be heated and angularly equidistant, the adjacent external (B) or internal (A) terminals of the coils (6) are connected to each other and the internal (A) or external (B) terminals are electrically powered, so as to generate an electromagnetic field transverse to the cylinder (5), wherein: said coils (6) have a spiral structure conformed to the surface of the cylinder (5), such as to leave a free area inside the coil; said supporting element (4) consists of an internal support element (4.2), made of non-magnetic and electrically non-conductive material, disposed towards the cylinder (5) to be heated, of an intermediate thermal insulation element (4.3) made of non-magnetic and electrically non-conductive material, and of an external element (4.1) for supporting the coils in non-magnetic and electrically non-conductive material; all the elements constituting the inductor are flexible and open on a generatrix line of the plasticizing cylinder (5).

9. The inductor for electromagnetic induction heating (300) according to claim 8, wherein a ferrite shield (9) is placed outside the coils (6).

10. The inductor for electromagnetic induction heating (300) according to claim 9, wherein said ferrite screen (9) is made of sufficiently small ferrite elements contained in a flexible non-conductive and non-magnetic material structure and is open on a generatrix line of the plasticizing cylinder.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0037] Further characteristics of the invention will be made clearer by the detailed description that follows, referring to purely exemplary and therefore non-limiting embodiments thereof, illustrated in the appended drawings, in which:

[0038] FIG. 1 is an axonometric side view of a plasticizing cylinder for plastic material processing machines according to the prior art, equipped with resistive heaters;

[0039] FIG. 2 is an axonometric view of a plasticizing cylinder for plastic material processing machines according to the prior art, provided with inductors with solenoid-type coils for inductive heating;

[0040] FIG. 3 is a view of an inductor according to the invention;

[0041] FIG. 4 is a view of the basic configuration of the inductor coils according to the invention;

[0042] FIG. 5 is a cross-sectional view of the inductor according to the invention;

[0043] FIG. 6 is a representation of the magnetic induction field pattern produced by an inductor with two coils according to the invention;

[0044] FIG. 7 is a view of the configuration with four coils of an inductor according to the invention;

[0045] FIG. 8 is a representation of the magnetic induction field produced by the inductor with four coils according to the invention;

[0046] FIG. 9 is a sectional view of the inductor according to the invention with an external ferrite shield;

[0047] FIG. 10 is a representation of an alternative solution for the inductor in which the elements which constitute it, with the exception of the coils, are divided into two parts by a plane passing through the axis of the inductor.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0048] With reference to the accompanying figures, and for now in particular to FIG. 3 an inductor for electromagnetic induction heating according to the present invention is shown, in its basic structure common to all the different configurations, globally indicated by the reference number (300), without closing cover.

[0049] The inductor for electromagnetic induction heating consists substantially of an internal support and insulation element 4, made of non-magnetic and electrically non-conductive material, to be placed on the plasticizing cylinder, of two or more coils 6, made with an electric conductor, in an even number, arranged symmetrically with respect to the cylinder, with axis perpendicular to the axis of the cylinder to be heated, so as to generate an electromagnetic field transverse to the cylinder, two protection elements 7 at the two ends of the assembly.

[0050] FIG. 4 is a schematic representation of the basic configuration of the two identical spiral wound coils 6 and their spatial positioning. The coils 6 have a flat spiral structure conformed to the surface of the cylinder, such as to leave a free area inside the coil as large as possible, compatible with the dimensions thereof and the number of turns for the passage of the magnetic field lines. In this way the field lines avoid cutting the coil conductor reducing the self-heating phenomenon.

[0051] In the figure, the terminals of the coils are indicated with: A internal terminal, B external terminal for the first coil and A and B for the second coil. The coil 6 is curved in such a way as to adapt to the support 4 placed on the plasticizing cylinder.

[0052] FIG. 5 is a sectional representation of the inductor assembly (300) and of the plasticizing cylinder 5. The structure of the support element 4 is constituted by an external cylindrical element 4.1 made of non-magnetic and electrically non-conductive insulating material, whose function is to support the coils 6, an intermediate cylindrical element 4.3 made of non-magnetic and electrically non-conductive insulating material, whose function is thermal insulation, and an internal cylindrical element 4.2 made of non-magnetic and electrically non-conductive insulating material, the function of which is support for the whole assembly.

[0053] With reference to FIG. 4, connecting the external terminals B and B to each other, of two identical coils (6), and supplying the coils with a suitable generator between the internal terminals A and A a magnetic induction field is generated transversely crossing the plasticizing cylinder, of which FIG. 6 provides a schematic representation.

[0054] The generation of a magnetic induction field 8, in figure 6, which passes through the cylinder and tends to concentrate on the internal diameter causes the parasitic currents to be distributed inside the cylinder and that the generation of heat takes place mainly in the area around the internal diameter.

[0055] FIG. 7 provides a schematic representation of a four-coil configuration for the case of a larger outer diameter cylinder. In this case connecting each other the terminals B and B of the first two coils and the terminals B and B of the other two coils and feeding the coils thus coupled between the terminals A and A and between A, A, a pattern of the magnetic induction field lines 8 in the plasticizing cylinder 5 is obtained, a representation of which is given in FIG. 8.

[0056] In a similar way, internal terminals A can be connected to each other and the external terminals B can be supplied.

[0057] Similar configurations of magnetic induction field lines are possible with an even number of coils greater than four.

[0058] FIG. 9 provides a sectional representation of the inductor assembly (300), consisting of two coils 6 internally supported by the electrically insulating and non-magnetic element 4 and completed externally by a ferrite casing 9. The purpose of the outer ferrite cylinder 9 is to create a low reluctance path for the magnetic induction field outside the inductor (300). This configuration allows to effectively shield the inductor (300) avoiding field dispersion with very low efficiency losses since the ferrite is non-conductive.

[0059] To simplify the construction, the screen 9 can be made by assembling several parallelepiped or semi-cylinder ferrite elements contained in a structure of non-conductive and non-magnetic material.

[0060] FIG. 10 provides a representation of an alternative solution for the inductor (300); in this solution all the elements constituting the inductor with the exception of the coils are divided by a median plane so as to form two partially separable elements 300 and 300, except for the conductor connecting the two coils. With this solution a direct mounting on the plasticizing cylinder is allowed without having to fit the inductor from one end of the plasticizing cylinder, as in the case of the solenoid inductor.

[0061] A further version of the inductor (300) provides that all the elements which constitute the internal support element 4 are flexible and open on a generatrix of the inductor cylinder.

[0062] Advantageously, in this case, the ferrite screen 9 is constructed with sufficiently small ferrite elements contained in a flexible non-magnetic and non-conductive material structure and is open on a generatrix line of the inductor cylinder. With this solution, direct mounting on the plasticizing cylinder is allowed by wrapping the inductor on the cylinder.

[0063] Naturally, the invention is not limited to the particular embodiments previously described and illustrated in the accompanying drawings, but numerous detail modifications can be made to it, within the reach of a person skilled in the art, falling within the scope of the invention defined by the attached claims.