WO2017013285A1 - System and method for induction tempering of metal parts - Google Patents

Abstract

The invention relates to a system (1) and a method developed for induction tempering of metal parts (4) which are closed over the entire cross-section thereof, preferably large ball bearings. The diameter of said ball bearings is between 1.5 and 10 metres approximately. The system (1) is designed to inject current through a primary coil (3) generating a magnetic flux in a transformer nucleus (3) which induces a current that heats a metal part (4) acting as a secondary coil. The method using the system comprises opening the transformer nucleus (2), placing the part (4) inside and closing the nucleus, injecting current through the primary coil (3) and inducing a current into the metal part (4) in order to heat same, activating a PID controller in order to obtain a homogeneous temperature throughout the entire metal part (4), opening the transformer nucleus (2) in order to demagnetise same, removing the metal part (4) and subsequently cooling the metal part (4).

Description

 SYSTEM AND METHOD FOR THE REVENUE BY INDUCTION OF PARTS

 METALS

DESCRIPTION

OBJECT OF THE INVENTION

 The object of the present invention relates to a system and method developed to perform the induction tempering of closed metal parts throughout its section. These pieces, which are preferably made of steel and must be closed on themselves to close a magnetic circuit, are large bearings, specifically wind bearings. The diameter of these bearings is between 1.5 and 10 meters approximately.

Find special application in the field of aerospace, automotive, medicine, forging, rail, shipbuilding, etc.

TECHNICAL PROBLEM TO BE RESOLVED AND BACKGROUND OF THE INVENTION

 The tempering treatment consists of heating a piece of steel, after tempering, at a temperature below the critical point, followed by controlled cooling to reduce the great fragility of steels after tempering.

Tempering not only improves the effects of tempering by taking the steel part to a point of minimum fragility, but also reduces the internal transformation stresses that originate in the hardening, reducing tensile tear strength, the elastic limit and the hardness and raising the characteristics of ductility and toughness.

At present the tempering of parts once tempered is carried out in conventional furnaces or pit furnaces, this type of furnaces are normally buried in the ground. These ovens have capacity for more than one piece, however this tempering method entails multiple disadvantages such as: several pieces accumulated in the process; the tempering, it is necessary to do it before two hours after tempering, so many times they come back one at a time even if the oven has capacity for more pieces (low efficiency); The oven must be turned on before the tempering process, the processing time is usually about 2 hours, etc. Therefore, the present invention solves the problems of the prior art mentioned above, providing a system and a method that have the following advantages:

 - With this new method the tempering is done instantly, since it is done by induction, so it is not necessary to have to turn on an oven in advance, with this new method the processing time is much shorter, going from 2 hours about 15 minutes in an oven,

 With this new method you save energy,

 - With this new method, the problem of cracks is avoided by reducing the time between tempering and tempering.

DESCRIPTION OF THE INVENTION

 The present invention relates to a system for induction tempering of closed metal parts throughout its entire section comprising at least: an oscillating circuit that sets a working frequency of the system, connected to a primary winding wound on a transformer core, where The transformer core comprises two lateral columns, an upper cylinder head and a lower cylinder head, such that the transformer core is configured to insert and support the metal part, separated from the primary winding, so that said metal part acts as a secondary winding, where The system is configured to inject current through the primary winding generating a magnetic flux in the transformer core that induces a current that heats the metal part. The metal parts are large steel bearings, specifically wind bearings.

Additionally, the system for induction tempering comprises a turning system formed by rollers mounted on refrigerated bearings, which makes the metal part can rotate to distribute the heating evenly throughout the piece.

The transformer core comprises opening and closing means, which are selected between a cylinder coupled to the core and a servo-controlled motor, and also includes guides for moving the upper cylinder head and one of the columns lateral with respect to the lower stock and the lateral column with the primary winding.

The system for induction tempering also comprises a pyrometer to measure the temperature of the metal part and a PID regulator to homogenize the temperature of the metal part.

Another object of the invention is the method that makes use of the previous system, wherein said method comprises the following phases: i) open the transformer core and place the metal part inside, resting on the lower cylinder head of said transformer core and on the rollers of the turning system, and separated from the primary winding,

 ii) close the transformer core once the metal part is placed inside, iii) inject current with a determined working frequency through the oscillating circuit through the primary winding to generate a magnetic flux in the transformer core and induce a current in the metal part to heat it,

 iv) activate a PID controller for a preset time to homogenize the temperature in the entire metal part once the tempering temperature required for said metal part has been reached,

 v) measure the temperature of the metal part by means of a pyrometer to avoid overheating,

 vi) open the transformer core to demagnetize it and remove the metal part, vii) cool the metal part by air or water.

The working frequency is inversely proportional to the section of the metal part. BRIEF DESCRIPTION OF THE FIGURES

 In order to complete the description and in order to help a better understanding of the features of the invention, this descriptive report is attached, as an integral part thereof, a set of drawings where, for illustrative and non-limiting purposes, it has been represented the next:

Figure 1.- Shows the system of the invention where it is observed how once the core is opened, and the bearing introduced, it is supported on the lower cylinder head of the core and on the rollers of the rotation system, separated from the primary winding.

Figure 2.- Shows the core once closed, so that by circulating current through the primary winding a magnetic flux is generated in the transformer core and a current is induced in the part by heating it.

Below is a list of the different elements represented in the figures that make up the invention: 1. Tempering system.

 2. Core of a transformer.

 3. Primary winding.

 4. Metal part (bearing).

 5. Rollers

 6. Upper stock.

 7. Bottom stock.

 8. Side columns.

 9. Base.

 10. Guides.

DETAILED DESCRIPTION

 The object of the present invention relates to a system (1) and a method developed for induction tempering of closed metal parts (4) throughout its section. As described above, these pieces (4) are made of steel and must be closed on themselves to close the magnetic circuit. These parts (4) are large bearings, specifically wind bearings. The diameter of these bearings is between 1.5 and 10 meters approximately.

The principle of operation of this new method is based on the operation of a transformer, which as is known, the transformers are composed of a core

(2), a primary winding (3) and a secondary winding. However, instead of having a secondary winding as usual, in this case, the large metal part (4) is closed throughout its section. The system (1) to be able to carry out the tempering method comprises: - a current generator: which converts the energy obtained from the conventional electrical network into a medium or high frequency signal suitable for feeding the induction tempering system (1);

 - an oscillating circuit: that provides the necessary capacity to establish a resonant circuit together with the inductance of a coil. The oscillating circuit sets the working frequency of the induction tempering system (1), which will allow the heating to have characteristics consistent with the process to be achieved, essentially, the oscillating circuit is composed of one or more capacitors whose number and type depends of the electrical characteristics of the oscillating circuit to be established;

 - a transformer core (2): closed of ferromagnetic material, consisting of two lateral columns (8), an upper cylinder head (6) and a lower cylinder head (7) as a frame and in the middle of said frame comprises a gap to introduce the piece (4) to be heated. This transformer core (2) is common to the primary winding (3) and the part (4), and is responsible for conducting the magnetic flux through it (keeping it confined within it) to generate the current in the part (4) . It is sized to work in the voltage range and working frequency determined for the part (4);

 - a primary winding (3): composed of copper wire wound on one of the columns (8) of the transformer core (2) and covered by an insulating layer, which is usually varnish. Defines the multiplication factor of the current delivered by the generator, and together with the capacitors sets the working frequency of the oscillating circuit;

 - a system of rotation of the piece (4): the heating of the piece (4) in the area where the transformer core (2) is located is greater than in the rest of the piece (4), due to the dispersion flow of the core (2) transformer. Therefore, it is necessary to have a turning system to be able to move and thus distribute this greater heating throughout the perimeter of the piece (4). This system of rotation of the piece (4) consists of rollers (5), which are mounted on refrigerated bearings (not shown in the figures) to ensure that the rollers (5) are not burned by energy transfer.

When the transformer core (2) is opened to be able to place the part (4) inside, the lateral column (8) of the primary winding (3) together with the lower cylinder head (7) remain fixed, while the lateral column (8) free together with the upper stock (6) move horizontally through guides (10) incorporated in the transformer core (2). Subsequently, once the part (4) is supported on the lower stock (7) and on the rollers (5) of the rotation system, the transformer core (2) is closed again to close the magnetic circuit. Figure 1 shows the open transformer core (2) and the part (4) (bearing) resting on the lower cylinder head (7) and on the rollers (5) of the turning system. A base (9) allows the fastening of the transformer core (2). It can also be seen how guiding means, specifically guides (10), incorporated in said transformer core (2) allow to move and separate the upper cylinder head (6) and one of the lateral columns (8) with respect to the lower cylinder head (7 ) and the side column (8) with the primary winding (3) to be able to introduce the part (4).

 Although the oscillating circuit is not shown in the figures, it would be connected to the primary winding (3). Another object of the invention is the method for induction tempering of metal parts (4).

According to the invention, the primary winding (3) is wound on one of the side columns (8) of the core (2), separated from the part (4) and connected to the current generator, which is responsible for passing a current through said primary winding (3) with a determined working frequency. This working frequency depends on the section of the piece (4) to be heated, the larger the section of the piece (4) to be heated, the lower the frequency used and the smaller the section of the part (4) to be heated. It will be the frequency used.

The only connection between the primary winding (3) and the part (4) is the common magnetic flux established in the core (2). The core (2) is generally made of iron or stacked sheets of electric steel, an appropriate alloy to optimize the magnetic flux.

The current passing through the primary winding (3) must be high enough to be able to transmit the required power to the part (4) (heat the part), obviously, said necessary current will depend on the dimensions of the part (4) and the desired heating time. As explained, the power in the piece (4) is achieved because it acts as a secondary winding of the core (2) transformer, then a current proportional to the current of the primary winding (3) multiplied by the number of turns of said primary winding (3) will circulate through the part (4).

12 (Item) = II (i primary winding) ^■ Nl (No. of turns primary winding)

The power delivered to the part (4) will depend on the losses due to Joule effect that occur due to the conductive material of said part (4) when circulating current through it. This is:

P (Piece power) = I2 ² (i piece) ^■ R (Equivalent part resistance)

Once the primary winding (3) is connected to the current generator, the method comprises the following steps:

 i) open the transformer core (2) and place the part (4) inside, resting on the lower cylinder head (7) of said transformer core (2) and on the rollers (5) of the turning system, and separated from the primary winding

(3) ,

 ii) close the transformer core (2) once the part (4) has been placed inside to close the magnetic circuit,

 iii) inject current with a working frequency determined by the oscillating circuit through the primary winding (3) to generate a magnetic flux in the transformer core (2) and induce a current in the metal part (4) to heat it,

 iv) activate a PID controller for a preset time to achieve temperature homogeneity throughout the metal part

(4) once the tempering temperature required for said metal part (4) has been reached,

 v) measure the temperature of the metal part (4) by means of a pyrometer to avoid overheating,

 vi) open the core (2) transformer to demagnetize it and remove the metal part (4),

 vii) cool the metal part (4) by air or water.

The opening and closing means of the transformer core (2) are selected between a cylinder coupled to the core (2) and a servo-controlled motor. The tempering temperature required for each piece (4) will depend on its dimensions, while the homogenization time carried out by the PID regulator is approximately 5 minutes.

The opening of the transformer core (2) allows the demagnetization of said core (2), that is, when opened, the established magnetic circuit is broken and this prevents a certain amount of magnetic flux from being trapped in the core (2). The remaining magnetism can cause several problems such as an erroneous diagnosis based on the measurements in the transformer, a sudden increase in the starting current of the transformer, etc.

The present invention should not be limited to the embodiment described herein. Other configurations can be made by those skilled in the art in view of the present description. Accordingly, the scope of the invention is defined by the following claims.

Claims

1. System (1) for the induction tempering of closed metal parts throughout its section comprising at least:  - an oscillating circuit that sets a working frequency of the system (1), connected to - a primary winding (3) wound on a transformer core (2),  where the transformer core (2) comprises two lateral columns (8), an upper stock (6) and a lower stock (7), characterized in that the transformer core (2) is configured to insert and support the metal part (4), separated from the primary winding (3), so that said metal part (4) acts as a secondary winding, where the system ( 1) is configured to inject current through the primary winding (3) generating a magnetic flux in the transformer core (2) that induces a current that heats the metal part (4). 2. System (1) for induction tempering of closed metal parts throughout its section according to claim 1, characterized in that it comprises a turning system for distributing the heating throughout the piece (4). 3. System (1) for induction tempering of closed metal parts throughout its section according to claim 2, characterized in that the turning system comprises rollers (5) mounted on refrigerated bearings. 4. System (1) for induction tempering of closed metal parts throughout its section according to any one of the preceding claims, characterized in that the metal parts (4) are steel bearings. 5. System (1) for induction tempering of closed metal parts throughout its section according to any one of the preceding claims, characterized in that the transformer core (2) comprises opening and closing means. 6. System (1) for induction tempering of closed metal parts throughout its section according to claim 5, characterized in that the opening and closing means of the transformer core (2) are selected from a cylinder coupled to the core (2) and a servo-controlled motor. 7. System (1) for induction tempering of closed metal parts throughout its section according to any one of the preceding claims, characterized in that the transformer core (2) comprises guides (10) to move the upper cylinder head (6) and one of the lateral columns (8) with respect to the lower stock (7) and the lateral column (8) with the primary winding (3). 8. System (1) for induction tempering of closed metal parts throughout its section according to any one of the preceding claims, characterized in that it comprises a pyrometer for measuring the temperature of the metal part (4). 9. System (1) for induction tempering of closed metal parts throughout its section according to any one of the preceding claims, characterized in that it comprises a PI D regulator to homogenize the temperature of the metal part (4). 10. Method for induction tempering of closed metal parts throughout its section that makes use of the system (1) defined in claims 1 to 9, characterized in that it comprises the following phases: i) opening the transformer core (2) and placing the metal part (4) inside, resting on the lower cylinder head (7) of said transformer core (2) and separated from the primary winding (3),  ii) close the core (2) transformer once the metal part (4) is placed inside,  iii) inject current with a determined working frequency through the oscillating circuit through the primary winding (3) to generate a magnetic flux in the transformer core (2) and induce a current in the metal part (4) to heat it. eleven . Method for induction tempering of closed metal parts throughout its section according to claim 10, characterized in that it comprises the following additional phases: iv) activating a PI D regulator for a preset time for homogenize the temperature in the entire metal part (4) once the tempering temperature required for said metal part (4) has been reached, v) measure the temperature of the metal part (4) by means of a pyrometer to avoid overheating. 12. Method for induction tempering of closed metal parts throughout its section according to claim 1, characterized in that it comprises the following additional phases:  vi) open the core (2) transformer to demagnetize it and remove the metal part (4),  vii) cool the metal part (4). 13. Method for induction tempering of closed metal parts throughout its section according to claim 12, characterized in that in step vii) the metal part (4) is cooled by air or water. 14. Method for induction tempering of closed metal parts throughout its section according to claim 10, characterized in that in step i) the metal part (4) additionally rests on the rollers (5) of the rotation system. 15. Method for induction tempering of closed metal parts throughout its section according to any one of the preceding claims, characterized in that the working frequency is inversely proportional to the section of the metal part (4).