EP0715140A1 - Process for heating metallic can bodies, and apparatus for carrying out the method - Google Patents

Abstract

The heating system has the metal tubes (1) transported along a conveyor (2), with the inductive heating effective along a limited area extending in a line along the tube mantle surface during the passage of each tube past an inductor (3) extending parallel to the tube axis. Pref. the tubes are moved past the inductor at a rate of 3 m/s, with the relative spacing between the inductor and the tube axis being variable. Pref. the inductor is provided by a hollow waveguide.

Description

The invention relates to a method and an arrangement for carrying out the method for heating sheet metal packaging, preferably by means of an induction device, for thermally influencing materials applied to frames, which serve to form a coating on the longitudinal seam of the frame. Depending on the type of materials applied, they must be melted, dried, cured, crosslinked, vulcanized or thermally influenced in a similar way.

Methods and arrangements for inductive heating for sheet metal frames are known, inter alia, from EP 0 202 869 and from US Pat. Nos. 468 0871, 469 4586 and 505 0315. In these solutions, the induction devices are designed in the form of a coil in such a way that the sheet metal frame is either stationary for heating in the interior of the induction coil or is guided through the interior of the coil by means of a transport device. The entire sheet metal frame is heated.

The disadvantage of these solutions is that only the entire frame can be heated in these devices. Furthermore, complicated frame transport devices are necessary, which are also located inside the induction coil, which results in high demands on the material selection, z. B. the use of non-conductive materials.

Further disadvantages are spatial problems with very small frames and unfavorable coupling conditions between the inductor coil and the frame.

The object of the present invention is to avoid the disadvantages mentioned above and to provide a method and an arrangement which make it possible to heat inductively only individual regions of the sheet metal frame.

According to the invention this is achieved in that the heat input is partially in a limited area along a surface line, for. B. along the frame weld, while the frame is moving past the inductor. The frames are transported at a speed of up to 3 m / s, the frames being moved past an inductor and the heating process can thus take place online in the manufacturing process of the frames. Only narrow, axial segments of the frame are heated along a surface line.

As a result of the heating, the materials applied to coat the frame weld seam are either melted, dried, hardened, crosslinked or vulcanized.

The temperature of the segments to be heated can be adjusted continuously by varying the inductor current I and / or the frequency f.

The temperature gradient of the heating phase is also infinitely adjustable by varying the induction current I and / or the frequency f.

This makes it possible to simplify the arrangement structurally and to arrange it immediately after a frame welding machine and the seam coating device. With this arrangement, the already existing frame transport device, for. B. the magnetic tape can be used.

The arrangement according to the invention consists of an induction device which is designed as a longitudinal inductor and is arranged at an adjustable distance approximately parallel to the frame transport device. The forward and return conductors of the inductor are arranged approximately one behind the other in the radial direction or at the same distance from the frame surface. The longitudinal inductor can consist of two individual inductors, the first inductor serving to heat the sheet metal frames and the second inductor to maintain an approximately constant end temperature.

In a further embodiment, the induction device is also designed as a longitudinal inductor and is arranged at an adjustable distance approximately parallel to the frame transport device, the forward and return conductors of the inductor being designed such that the connecting line of the forward and return conductors with the surface normal passing through the center the heating zone goes, forms an angle α and this angle is in the range 0 ° <α <90 °.

The longitudinal inductor is preferably designed as a round or rectangular waveguide and a cooling liquid flows through it for cooling. For The inductor is preferably supplied with a sinusoidal current with a frequency between 16 and 500 kHz. The series inductor can be coupled with a capacitor to form a resonant circuit and, together with an electronic circuit, can form a resonant circuit inverter.

The heat input occurs partially in a limited area along a surface line, e.g. B. along the frame weld, while moving the frame past the inductor.

The frames are transported at a speed of up to 3 m / s, the frames being moved past an inductor and the heating process can thus take place online in the manufacturing process of the frames. Only narrow, axial segments of the frame are heated along a surface line.

As a result of the heating, the materials applied to coat the frame weld seam are either melted, dried, hardened, crosslinked or vulcanized.

This makes it possible to simplify the arrangement structurally and to arrange it immediately after a frame welding machine and the seam coating device. With this arrangement, the already existing frame transport device, for. B. the magnetic tape can be used.

An embodiment will be explained below with reference to the drawings.

Fig. 1

eine schematische Erwärmungseinrichtung in Seitenansicht

Fig. 2

eine partiell zu erwärmende Zarge mit Erwärmungszone

Fig. 3

eine Erwärmungseinrichtung im Querschnitt

Fig. 4

eine Erwärmungseinrichtung im Querschnitt

Fig. 5

eine Erwärmungseinrichtung im Querschnitt

Fig. 6

vereinfachte Darstellung der magnetischen Feldverläufe

Fig. 7

eine Variante der Erwärmungseinrichtung mit Teilinduktoren

Anhand der Figuren 1 bis 7 soll nachfolgend die Erfindung beschrieben werden. Es wird dabei von vorzugsweise kreiszylinderförmigen Zargen ausgegangen, jedoch gelten die gemachten Aussagen auch für davon abweichende Querschnittsformen.Show it

Fig. 1

a schematic heating device in side view

Fig. 2

a frame to be partially heated with a heating zone

Fig. 3

a heating device in cross section

Fig. 4

a heating device in cross section

Fig. 5

a heating device in cross section

Fig. 6

simplified representation of the magnetic field profiles

Fig. 7

a variant of the heating device with partial inductors

The invention will be described below with reference to FIGS. 1 to 7. It is assumed that the frames are preferably circular-cylindrical, but the statements made also apply to cross-sectional shapes that deviate therefrom.

Fig. 1 shows a schematic representation of a heating device according to the invention. The frames 1 to be partially heated are moved by means of a transport mechanism 2 at the speed v below the inductor 3. In the case shown, it is a conveyor belt 2. However, other means such as driven rollers, chains with driving fingers and the like are also. Arrangements possible. Due to the inductor arranged completely outside the frame, very simple mechanical constructions of the heating device result.

Fig. 2 shows a partially heated frame 1 with the axial heating zone 5 of width b. Only in the hatched area is an essential one Heat input. The energy saving compared to conventional induction systems becomes clear.

3, 4 and 5 show different inductor designs.

Diese Formel dient in Verbindung mit den allgemeinen Maxwellschen Gleichungen für quasistationäre elektromagnetische Felder als Basis für die weitere Dimensionierung der Induktionseinrichtung.3 there are forward and return conductors 3 one behind the other in the radial direction. This arrangement is advantageous for very narrow heating zones and represents the standard version. Below the inductor 3 there is the maximum of the tangential component of the magnetic field strength on the frame surface. If the surface curvature of the frame 1 is neglected and if an idealized, linear inductor is assumed, the simplified, quantitative relationship is obtained as the basis for the rough dimensioning of the inductor $${\text{H}}_{\text{O}}{\text{(x) = (I / 2π) {-h / (x}}^{\text{2nd}}{\text{+ h}}^{\text{2nd}}{\text{) + (h + a) / [x}}^{\text{2nd}}{\text{+ (h + a)}}^{\text{2nd}}\text{]}}$$

In conjunction with the general Maxwell equations for quasi-stationary electromagnetic fields, this formula serves as the basis for the further dimensioning of the induction device.

Über eine Variation der Induktorparameter a und h ergeben sich gute Anpassungsmöglichkeiten an den technologischen Gesamtprozeß.Fig. 4 shows an inductor version in which the forward and return conductors of the inductor 3 have the same distance from the frame surface. This inductor version can be used for wider heating zones. This results in two local maxima of the tangential component of the magnetic field strength H and thus also two current density maxima on the frame surface. Under the same assumptions as for the first inductor variant, a simplified, quantitative relationship between the geometric dimensions can also be derive the current intensity I and the surface field strength for a rough dimensioning of the inductor. $${\text{H}}_{\text{O}}{\text{(x) = (Ih / 2π) {[(xa / 2)}}^{\text{2nd}}{\text{+ h}}^{\text{2nd}}{\text{]}}^{\text{-1}}{\text{- [(x + a / 2)}}^{\text{2nd}}{\text{+ h}}^{\text{2nd}}{\text{]}}^{\text{-1}}\text{}}$$

By varying the inductor parameters a and h, there are good possibilities for adaptation to the overall technological process.

5 shows a further inductor version. The forward and return conductors 3 are arranged at an angle α from one another to the heating zone 5. The frame 1 is moved at a speed v below the inductor by means of a transport mechanism, not shown. The rollers 4 take over the upper management. The arrangement of the inductor shown with respect to the frame surface is characterized in that both the inner and the outer field of the inductor contribute to the heating.
Since the inductor has an inner and an outer field, which are very different in their mode of operation, there are different effects on the heating. The effect of the inner and outer fields against one another can be influenced by a suitable choice of the angle α. For example, it is possible to avoid edge overheating at the beginning and end of the frame 1 and to achieve an approximately constant temperature profile along the heating zone 5.

6 shows the course of the magnetic field lines and the eddy currents caused thereby in a simplified manner. The variable designated as variable x in the formulas is also shown.

The coupling of the inductor to the frame can be influenced by varying the dimensions a and h. Small values of h and large values of a increase the coupling factor and vice versa. The coupling factor establishes the relationship between inductor current and surface field strength. This makes it possible to cover a wide range of applications with a uniform basic mechanical concept by varying parameters a, h.

kann von der magnetischen Feldstärke $\overrightarrow{\text{H}}$

auf die Wirbelstromdichte $\overrightarrow{\text{G}}$

geschlossen werden. $\overrightarrow{\text{H}}$

stellt hierbei den Vektor der magnetischen Feldstärke innerhalb der gesamten Blechdicke d dar und ist über geeignete Randbedingungen zu berechnen. $\overrightarrow{\text{G}}$

ist der Stromdichtevektor.Using the first Maxwell equation for quasi-stationary electromagnetic fields $$\text{red}\overrightarrow{\text{H}}\text{=}\overrightarrow{\text{G}}$$

can depend on the magnetic field strength $\overrightarrow{\text{H}}$

on the eddy current density $\overrightarrow{\text{G}}$

getting closed. $\overrightarrow{\text{H}}$

represents the vector of the magnetic field strength within the entire sheet thickness d and is to be calculated using suitable boundary conditions. $\overrightarrow{\text{G}}$

is the current density vector.

By adding the electrical conductivity of the sheet, it is possible to draw conclusions about the power input given the specific temperature conditions.
Since the permeability µ in the sheet is a function of the field strength H, there are non-linear relationships. However, the exact mathematical evaluation of the overall relationships can be understood by a specialist using iterative calculation.

An advantageous embodiment of the invention consists in dividing the inductor 3 into two different partial inductors.

Fig. 7 shows a variant, which is characterized in that the inductors 3.1, 3.2 are connected to each other in such a way that the same current I flows through both. Zone I serves as a heating zone, characterized by a high coupling factor with high heat input. Zone II serves to maintain a desired temperature and has a lower coupling factor combined with a lower heat input. Another advantage of the arrangement in Fig. 7 is that both inductor parts are flowed through by the same current and thus both are powered by an energy source. In addition to different coupling factors and heat inputs, different values for a and h also result in different inductor inductivities for the two sections I and II Individual inductors.

This results in simple, manageable load conditions for the feeding source.

• Parallelkompensation des Induktors und Anordnung als Wechselrichter mit Parallelschwingkreis
• Reihenkompensation des Induktors und Anordnung als Wechselrichter mit Reihenschwingkreis
• gemischte Kompensation des Induktors (Parallel- und Reihenkapazität) und entsprechender Wechselrichterbetrieb.

Both the heating temperature and the temperature gradient can be set during the heating phase via the inductor current I and / or frequency f. This possibility is given by using suitable electronic circuits. The inductor can be supplemented with a capacitor to form an oscillating circuit and forms an oscillating circuit inverter with an electronic circuit. Different solutions are possible:

• Parallel compensation of the inductor and arrangement as an inverter with parallel resonant circuit
• Series compensation of the inductor and arrangement as an inverter with a series resonant circuit
• mixed compensation of the inductor (parallel and series capacitance) and corresponding inverter operation.

The use of modern semiconductor components that can be switched off, such as IGBTs, results in a wide range of possible solutions for the concrete implementation of the feeding source. Since the specific electronic circuit for the feeding source is not the subject of the invention, it will not be discussed further here.

A sinusoidal inductor current with a frequency of 16 to 500 kHz is used to supply the inductor. The influence of current displacement can no longer be neglected in this frequency range. If copper is used as the inductor material, penetration depths of 0.3 ... 0.5 mm result. The current density in the inner part of a solid inductor would be almost zero. The inductor can therefore advantageously be implemented as a waveguide and a cooling liquid can flow through it.

In the plants for the production of sheet metal frames, especially in the packaging industry, there are usually always cooling water circuits. This usually results in favorable conditions for connecting the inductor cooling within the overall process.

With modern inverter circuits, internal efficiencies greater than 90% can be achieved. Even taking into account the losses of the inductor of around 50% of the power fed in, the active power consumption is only 25 ... 50% compared to the known solutions.

Claims (10)

Process for heating metallic frames by means of an induction device for thermally influencing materials applied to frames,
characterized in that
the heat input occurs partially in a limited area along a surface line as the frame moves past the inductor. Method according to claim 1,
characterized in that
the frames are moved past the inductor at a speed of up to 3 m / s. Arrangement for carrying out the method according to claims 1 and 2, consisting of an induction device and a frame transport device,
characterized in that
the induction device is designed as a longitudinal inductor and is arranged at an adjustable distance approximately parallel to the frame transport device. Arrangement according to claim 3,
characterized in that
The forward and return conductors of the longitudinal inductor are arranged approximately one behind the other in the radial direction. Arrangement according to claim 3,
characterized in that
The forward and return conductors of the longitudinal inductor are arranged at approximately the same distance from the frame surface. Arrangement according to claim 3,
characterized in that
the line connecting the forward and return conductors of the longitudinal inductor with the surface normal, which passes through the center of the heating zone, forms an angle α, and this angle is in the range 0 ° <α <90 °. Arrangement according to claim 3 to 6,
characterized in that
the longitudinal inductor consists of two inductors, the first inductor being designed for heating and the second inductor for maintaining an approximately constant end temperature along the surface line of the frame. Arrangement according to claim 3 to 7,
characterized in that
the longitudinal inductor is designed as a waveguide (wherein the waveguide has a round or rectangular cross section and a cooling liquid flows through it). Arrangement according to claim 3 to 8,
characterized in that
a sinusoidal current is preferably passed through the inductor, the frequency of the inductor current being in the range from 16 to 500 kHz. Arrangement according to claim 3 to 9,
characterized in that
the series inductor is coupled to a capacitor and is designed as an oscillating circuit inverter with an electronic circuit.

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