Induction heating device

Abstract

An induction heating device (1) for heating a metal product (3), comprising a support plate (2) having an upper surface for receiving the metal product (3) and a plurality of induction coils (7, 8, 9, 10, 11, 12), the support plate (2) having an upper surface for receiving the metal product (3), the plurality of induction coils (7, 8, 9, 10, 11, 12) being arranged concentrically around an axis (XX') and arranged at the lower side of the support plate, each induction coil being connected to a generator and selectively powered by the generator, wherein the device further comprises at least one temperature probe (5, 13), which is placed on the metal product during heating to monitor and control the heating of the product.

Description

Technical Field

[0001] The present invention relates to an induction heating device comprising a plate and a concentrically arranged induction coil for heating a metal product, such as a rolling element bearing, a ring or a gear, by inducing eddy currents in the metal product.

[0002] The invention also relates to a method of heating a metal product using an induction heating device comprising a plate and a concentrically arranged induction coil. Background Art

[0003] EP 2728965A1 describes a known type of bearing induction heater, which comprises a closed magnetic core closed by a removable closed yoke and around which the bearing to be heated is placed. In addition, two temperature probes are used during the heating cycle; one temperature probe monitors the temperature of the inner ring of the bearing and the other temperature probe monitors the temperature of the outer ring of the bearing. The difference between the two temperatures triggers the switch between a first part of the heating cycle and a second part of the heating cycle. The heating rate during the second part is less than the heating rate during the first part.

[0004] US 2018 / 0279421A1 describes another known type of bearing induction heater. The heater comprises a plate having an upper surface for receiving the side of the bearing to be heated. A plurality of concentrically arranged induction coils are arranged on the underside of the support plate. A plurality of temperature sensors are arranged on the upper surface of the support plate at different radial distances from the central axis of the coils, each coil being associated with one or more temperature sensors.

[0005] When a bearing comprising an inner ring and an outer ring is heated due to an induction heater, it is important that the temperature difference between the inner ring and the outer ring does not exceed a predetermined value in order to avoid damaging the bearing.

[0006] Furthermore, it is very important not to exceed ( / overshoot) the target temperature, otherwise there is a high risk of damaging certain components (such as lubricants or seals of bearings) which cannot withstand high temperatures as well as metal components (such as rings or rolling elements).

[0007] In the induction heating devices known today, it is more difficult to avoid this temperature overshooting problem in the case where the metal product is heated most rapidly.

[0008] So improvements can still be made. Summary of the invention

[0009] Therefore, an object of the present invention is to provide an induction heating device for heating a metal product having a side surface, in particular, a bearing having an inner ring and an outer ring.

[0010] According to the present invention, the induction heating device comprises a support plate having an upper surface for receiving the side of the metal product. A plurality of concentrically arranged induction coils are arranged at the lower side of the support plate, and each induction coil is connected to a generator and selectively powered by the generator.

[0011] The device further comprises at least one temperature probe which is placed on the metal product during heating to monitor and control the heating of the (metal) product.

[0012] According to other advantageous but non-mandatory aspects of the invention, the induction heating device may include one or more of the following features:

[0013] - there is only one temperature probe;

[0014] – The presence of two temperature probes;

[0015] - the metal product is a bearing having an inner ring and an outer ring;

[0016] - there is only one temperature probe and this temperature probe is placed on the upper side of the bearing;

[0017] - there are two temperature probes, one temperature probe is placed on the upper side of the inner ring, and the other temperature probe is placed on the upper side of the outer ring;

[0018] Another aspect of the present invention provides a method for heating a metal product using the induction heating device according to the present invention, the method comprising the following steps:

[0019] - placing a metal product on the upper surface of the plate and placing at least one temperature probe on said product; then

[0020] - estimating ( / estimating / assessing) the position of the metal product on the upper surface of the plate and estimating some dimensional characteristics of the product, such as the center of the product, the height of the product and the mass of the product; and then

[0021] - based on these estimates, determine the initial heating strategy to be applied, i.e. which coils to power and at what power level; then

[0022] - starting heating according to said initial heating strategy; then

[0023] - using the measurements of at least one temperature probe to better estimate the dimensional characteristics of the article, to measure the delay of the temperature change measured by the at least one temperature probe; analyzing the speed of change (average acceleration of temperature) to determine how much the temperature of the article will continue to rise once the heating process is stopped; and then

[0024] - optionally, adjusting the parameters of said initial heating strategy based on the results obtained during the preceding steps; then

[0025] - Running a heating cycle to bring the article to the desired temperature.

[0026] According to other advantageous but non-mandatory aspects of the invention, the method may include one or more of the following features:

[0027] - The heating cycle comprises the following consecutive steps:

[0028] a) a determination step during which the allowed full power curve is used until the temperature rate stabilizes and during which the estimated final temperature is continuously calculated; then

[0029] b) a main step during which heating is continued in an attempt to maintain a maximum heating rate, but during which the temperature rate is held constant; and then

[0030] c) an approach step during which the heating power is gradually reduced until a predetermined minimum temperature velocity is reached or the target temperature becomes very close, thereby limiting the maximum absolute temperature on the bottom of the article and reducing the temperature difference between the top and bottom surfaces for each turn; and then

[0031] d) An equalization step during which heating is stopped and the measured temperature and the estimated temperature converge to the target temperature until the measured temperature and the estimated temperature reach the target temperature.

[0032] -The method also includes a continuous ( / sequential) standby step, during which the heating is still stopped and the temperature and temperature changes of the bearing are kept monitored until the operator stops the working session or the bearing has cooled by 10% from its target temperature. The method also includes another continuous ( / sequential) reheating step, during which the heating is first started again using full power until a significant temperature increase is reached, and then a reduced amount of power is used until the target temperature is reached again.

[0033] The method further comprises the step of maintaining the bearing at the target temperature, once it has been reached at the end of the equalization step, for a given period of time or until the user stops heating the working section, and during this time generating a minimum amount of heat to compensate for heat losses in the environment.

[0034] - During heating, more energy is concentrated towards the center of the article.

[0035] Thanks to the invention, the metal product can be heated quickly without exceeding the (target) temperature to be reached and without damaging the product.

[0036] Thanks to the invention, when a bearing having an inner ring and an outer ring is heated, the temperature difference between the inner ring and the outer ring remains below a safe value. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The invention and its advantages will be better understood by studying the detailed description of a particular embodiment given by way of non-limiting example and illustrated by the accompanying drawings, in which:

[0038] - Figure 1 A first preferred embodiment of the induction heating device according to the present invention is shown;

[0039] - Figure 2 Shows Figure 1 An induction heating device and an induction coil transparent through a support plate;

[0040] - Figure 3 A second preferred embodiment of the induction heating device according to the present invention is shown;

[0041] - Figure 4 Shows Figure 3 An induction heating device and an induction coil transparent through a support plate;

[0042] - Figure 5 shows the different steps of the heating process according to the invention; and

[0043] - Figure 6 An example of a heating cycle according to the invention is shown.

[0044] XX' axis

[0045] 1 Induction heating device

[0046] 2 Support plate

[0047] 3 Metal products, bearings

[0048] 4 Temperature indicator

[0049] 5.13 Temperature probe

[0050] 6.14 Wire

[0051] 7, 8, 9, 10, 11, 12 Induction coil DETAILED DESCRIPTION

[0052] Figure 1 and Figure 2 An induction heating device 1 is shown, comprising a support plate 2 having an upper surface for receiving the side of a metal product ( / metal article) 3. A plurality of concentrically arranged induction coils 7, 8, 9, 10, 11, 12 are arranged concentrically around an axis XX' and are provided on the underside of the support plate. Each induction coil is connected to a generator and selectively powered by the generator. The induction coils are of different sizes and can provide different maximum powers.

[0053] The temperature probe 5 is placed on the metal product and is electrically connected to the heating device via a wire 6 .

[0054] Temperature probes are used to monitor ( / monitor) the heating of metal products.

[0055] The heating device also includes a temperature indicator 4 which can selectively display the temperature measured by the probe or a desired temperature target desired for the heated article.

[0056] The metal product may be a bearing, a ring or a gear.

[0057] If the product is a bearing having an inner ring and an outer ring, the temperature probe is preferably placed on the upper side of the inner ring.

[0058] The heating device further comprises an alternator (not shown) to which each coil is connected. The alternator is controlled by a control unit (not shown) configured to selectively energize the coils and to determine the load on the coils when energizing the coils.

[0059] The control unit is programmed to perform a heating cycle that will raise the temperature of the bearing inner ring to a value that enables the bearing to be shrink-fit onto the shaft through thermal expansion and contraction. Typically, the inner ring is heated to a temperature of approximately 110°C. The heating cycle includes inductive heating of both the inner and outer rings to prevent excessive temperature differences between the bearing rings that could damage the bearing.

[0060] The measurements from the temperature probe are fed to a control unit and used to control the heating of the metal product.

[0061] Figure 3 and Figure 4 A second preferred embodiment of the induction heating device is shown. Figure 3 and Figure 4Shown with Figure 1 The induction heating device in FIG. 1 is the same as the induction heating device in FIG. 2 , but has two temperature probes 5 , 13 , each of which is electrically connected to the induction device via a wire 6 , 14 .

[0062] The temperature probe is placed on the metal product.

[0063] In the case of a bearing having an inner ring and an outer ring, the first temperature probe 5 is placed on the upper side surface of the inner ring, and the second temperature probe 13 is placed on the upper side surface of the outer ring.

[0064] The heating device also includes a temperature indicator 4 which can selectively display the temperature measured by each probe or a desired temperature target of the heated product.

[0065] During the heating cycle, the induction heating device continuously monitors the temperature reading(s).

[0066] We will now describe a method of heating a metal product to a target temperature using the induction heating device according to the present invention.

[0067] Figure 5 The various steps of the method are summarized.

[0068] First, a metal product is placed on the upper surface of the plate, and at least one temperature probe is placed on the upper surface of the product.

[0069] Then, an estimate is made of the position of the article on the upper surface of the plate, and an estimate is made of some dimensional characteristics of the article.

[0070] This characterization is done by mapping the energy required by each coil. When the metalwork is on the board, the coils require a different amount of current than when the metalwork is not present due to electromagnetic interactions. For greater accuracy, the energy or current readings with the metalwork in place are compared to calibration readings taken when there is no metalwork on the board. This comparison results in a normalized reading, eliminating internal losses and correcting for differences in coil size.

[0071] These normalized readings are further processed to correct for hardware limitations that detect odd situations, such as when the metal article is a bearing that includes a metal enclosure that blocks the magnetic field, or when the article is very large or very small to be properly read by the innermost or outermost coils.

[0072] Processing of these data (also called fingerprint analysis) results in the determination of an extended fingerprint of the article, from which a number of dimensional features of the metal article can be estimated, such as the center of the article, the height of the article and the mass of the article. This is based on statistical analysis using a large number of different metal articles.

[0073] Based on these estimates, an initial heating strategy is determined to be used at the start of a heating cycle. The initial heating strategy defines which coil or coils need to be powered and at which power level or levels.

[0074] In a subsequent step of the method, the heating of the product is started according to an initial heating strategy and the measurements of at least one temperature probe are used to improve the estimation of the dimensional characteristics of the product and to heat the product in a fast and accurate manner. When the heating starts, the delay of the temperature change measured by the temperature probe located on the upper surface of the product is measured. This delay allows to correct the height estimation of the product if necessary.

[0075] In addition, by analyzing the rate of change (average acceleration of the temperature), it is determined how much the temperature of the product will continue to rise due to thermal inertia caused by internal heat conduction once the heating process is stopped. For example, if the average acceleration is high, it means that the power supply to the induction coil should be stopped very early, because after that, the temperature will continue to rise at a very high rate for a considerable period of time.

[0076] Based on these measurements, parameters for the initial heating strategy are optionally adjusted, if necessary, and stored in a heating strategy.

[0077] Then, a heating cycle according to the heating strategy is performed. As will now be explained, the heating cycle comprises a plurality of steps in succession.

[0078] Figure 6 An example of a heating cycle with these consecutive steps for heating a bearing using an induction heating device comprising two temperature probes is shown. The bearing comprises an inner ring and an outer ring, each ring having two side surfaces. The side of the inner ring in contact with the upper surface of the support plate and the side of the outer ring in contact with the upper surface of the support plate are called bottom surfaces. The other side surfaces of the inner ring and the outer ring are called top surfaces.

[0079] like Figure 4 As shown, one temperature probe is located on the top surface of the inner ring and the other temperature probe is located on the top surface of the outer ring.

[0080] In addition, the temperatures of the bottom surfaces of the inner and outer rings are estimated.

[0081] During the first step, called the determination step, the allowed full power curve as determined by the fingerprint analysis is used. The actual heating delay is established and gradually adjusted until the transition point is found. In addition, the total acceleration is measured until the temperature velocity stabilization point is reached. These measurements are then used together with the current temperature velocity to continuously calculate the estimated final temperature for when the heating process needs to be stopped due to reaching the target temperature.

[0082] for Figure 6 In the example shown above, for each circle, the temperature difference between the bottom surface and the top surface rises rapidly at first, but gradually begins to stabilize. Similarly, the temperature change increases almost linearly until the stable point.

[0083] Then, when the temperature rate has stabilized and reached a stable point, the second step (called the main step) begins. Heating continues in an attempt to maintain the maximum heating rate, which may only be corrected if the ring bottom temperature is estimated to be too high. This is done by using the ring bottom temperature estimated using the bearing characteristics and the average power applied.

[0084] During the main phase, the temperature rate remains generally constant and the temperature difference between the top and bottom sides is almost constant due to the constant applied power. The greater the temperature difference between the bearing and the environment, the greater the temperature losses become. Especially bearings with low mass can show this effect, but this is almost negligible when compared to the heating rate that can be achieved during the heating cycle.

[0085] Using the average acceleration from the determined phase, the established heating delay and the current temperature velocity, a final temperature estimate is continuously calculated. This final temperature estimate is used not only as a heating stop, but also to determine when to proceed to the next step (called an approach step).

[0086] When the heating approaches its final target, the heating enters a ramp down phase or approach phase, during which the heating power is gradually reduced until a predetermined minimum temperature rate is reached or the target temperature becomes very close. This approach phase has two goals, the first is to limit the maximum absolute temperature on the bottom of the bearing ring. For each ring, the ramp down method is designed to maintain a stable bottom temperature and slowly reduce the temperature difference between the top and bottom surfaces. In addition to limiting the maximum temperature in the bearing, this has another purpose.

[0087] Figure 6 It shows how the temperature rate starts to decline in an almost linear manner. The temperature difference between the top and bottom surfaces of the two rings starts to decrease, so the maximum temperature in the bearing workpiece remains relatively constant and stops rising. The top temperature starts to stabilize towards the desired target temperature.

[0088] When the estimates of the bearing and heating performance are sufficiently accurate, the bearing will reach its target near the end of the ramp down, and heating will be stopped. The next step, called the equalization step, will then begin.

[0089] During the equalization step, the measured temperature and the estimated temperature converge to the same temperature, the target temperature. Even though the heating has been stopped, the bottom temperature drops, while the top temperature rises. When the temperatures are all stable at the target temperature, the equalization step stops.

[0090] At this point, the bearing is ready for safe mounting. In fact, when the bearing reaches the target temperature, the temperature is evenly distributed throughout the bearing, which will facilitate mounting the bearing on the shaft and will limit any mechanical stresses that occur. This reduces the internal relaxation of the inner and outer rings and any balls or rollers between them.

[0091] In an optional continuous step, called the standby step, the bearing temperature and temperature changes are monitored. Transitions are made only when the user stops the session or when the bearing has cooled 10% from its target temperature.

[0092] Then, in another optional sequential step, called the reheating step, heating is started again, still using all the measured temperature characteristics of the bearing, to maintain the target temperature for the operator-operated heating device. During this step, full power is used until a significant temperature increase is reached again, then switching to a minimum heating phase until the target temperature is reached again.

[0093] As an option, and also optionally, once the target temperature has been reached at the end of the equalization step, the method comprises a further step during which the bearing is kept at the target temperature for a given period of time or until the user stops heating the working section. During this step, a minimum amount of heat is generated to compensate for heat losses in the environment.

[0094] exist Figure 6 In the example shown above, the target temperature has been set to 110°C and the maximum temperature of the bearing bottom has been limited to a maximum value of 150°C in order not to damage the bearing.

[0095] In the worst case, the temperature difference from bottom to top is about 90 degrees.

[0096] Furthermore, the maximum temperature reached in the bearing remains at an acceptable value and it can be clearly seen that the temperatures have equalized when the target temperature has been reached.

[0097] If the heating is maximized until the target temperature is reached, it may reach 200 degrees on the bottom of the bearing and there will be a large overshoot in temperature.

[0098] Advantageously, a temperature analysis is performed during the complete heating process to improve the estimate.

[0099] Advantageously, during heating, more energy is focused towards the inner ring of the bearing or the center of the article. This allows for faster heating.

[0100] Advantageously, when the article is a bearing with a cage, rolling elements or a sealing cage, and when multiple coils are powered during heating, the power to the central coil(s) is reduced to avoid overheating of the cage, cage, rolling elements.

[0101] If one coil is not powerful enough (despite being estimated to be the best choice for heating the article), then the other coil (which can provide higher power due to better electromagnetic coupling) is chosen to be powered.

[0102] When the article is a bearing having an inner ring, an outer ring and rolling elements between the rings, the amount of energy transferred to the inner and outer rings is such that the inner ring heats faster than the outer ring. However, the temperature of the inner ring never exceeds the temperature of the outer ring by a predetermined value (usually between 20°C and 40°C) to ensure tension-free heating, in other words, to ensure that the rolling elements are not compressed to the extent that they are plastically deformed in the raceways of the rings.

[0103] Thanks to the invention, the metal product can be heated in a rapid manner and without damaging it.There is no target temperature exceeded which the metal product is to be heated.

Claims

1. An induction heating device (1) for heating a metal product (3), comprising a support plate (2) having an upper surface for receiving the side of the metal product (3) and a plurality of induction coils (7, 8, 9, 10, 11, 12), wherein the support plate (2) has an upper surface for receiving the side of the metal product (3), wherein the plurality of induction coils (7, 8, 9, 10, 11, 12) are arranged concentrically around an axis (XX') and are arranged at the lower side of the support plate, wherein each induction coil is connected to a generator and selectively powered by the generator, wherein: The induction heating device further comprises at least one temperature probe (5, 13) to be placed on the metal product during heating to monitor and control the heating of the product, wherein measurements of the at least one temperature probe (5, 13) are used to improve an estimate of a dimensional characteristic of the metal product, wherein the estimate of the dimensional characteristic of the metal product is used to control the heating of the metal product.

2. The induction heating device according to claim 1, characterized in that: The induction heating device comprises only one temperature probe.

3. The induction heating device according to claim 1, characterized in that: The induction heating device comprises two temperature probes.

4. The induction heating device according to claim 2, characterized in that: The metal product is a bearing having an inner ring and an outer ring, and the temperature probe is placed on an upper side surface of the bearing.

5. The induction heating device according to claim 3, characterized in that: The metal product is a bearing having an inner ring and an outer ring, and one temperature probe is placed on the upper side of the inner ring, and the other temperature probe is placed on the upper side of the outer ring.

6. A method of heating a metal product using an induction heating device according to any one of the preceding claims, the method comprising the steps of: - placing the metal product on the upper surface of the support plate, and placing at least one temperature probe on the metal product; Then - estimating the position of the metal article on the upper surface of the plate and estimating some dimensional characteristics of the article; Then - based on these estimates, determine the initial heating strategy to be applied, i.e. which coils will be powered and at what power level; then - starting heating according to said initial heating strategy; Then - using measurements from at least one temperature probe to improve said estimate of the dimensional characteristic of said article, to measure the delay of a temperature change measured by said at least one temperature probe; analyzing the rate of change to determine how much the temperature of said article will continue to rise once the heating process is stopped; and then - A heating cycle is performed to bring the article to the desired temperature.

7. The method according to claim 6, characterized in that The dimensional characteristic of the article includes at least one of a center of the article, a height of the article, and a mass of the article.

8. The method according to claim 6, characterized in that The step of analyzing the rate of change includes analyzing the average acceleration of the temperature.

9. The method according to claim 6, characterized in that The method further comprises adjusting parameters of the initial heating strategy based on the results obtained during the preceding steps.

10. The method according to claim 6, characterized in that The heating cycle comprises the following consecutive steps: - a determination step during which the allowed full power curve is used until the temperature rate stabilizes and during which the estimated final temperature is continuously calculated; then - a main step during which heating is continued in an attempt to maintain a maximum heating rate, but during which the temperature rate is kept constant; then - an approach step during which the heating power is gradually reduced until a predetermined minimum temperature velocity is reached or the target temperature becomes very close, so as to limit the maximum absolute temperature on the bottom of the article and, for each turn, reduce the temperature difference between the top and bottom surfaces; Then - an equalization step during which the heating is stopped and the measured temperature and the estimated temperature converge to the target temperature until the measured temperature and the estimated temperature reach the target temperature.

11. The method according to claim 10, characterized in that The method further comprises the following consecutive steps: a standby step during which the heating is still stopped and the temperature and temperature changes of the bearing are kept monitored until the operator stops the working section or the bearing has cooled by 10% from its target temperature, and - a reheating step during which heating is started again first using full power until a noticeable temperature increase is reached and then using a power of reduced magnitude until the target temperature is reached again.

12. The method according to claim 10, characterized in that The method further comprises the following consecutive steps: - Maintaining the bearing at the target temperature during a given period of time or until the user stops heating the working section, so that during this phase a minimum of heat is generated so as to compensate for heat losses to the environment.

13. The method according to any one of claims 6 to 12, characterized in that During heating, more energy is concentrated towards the center of the article.

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