JP2011161458A - Method of measuring gap between molds - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of measuring a gap between molds, which prevents a scale from adhering and improves the measurement sensitivity in measuring a gap between molds. <P>SOLUTION: The invention relates to the method of measuring a gap between molds for measuring a vertical gap of a forging mold having an upper mold 3 and a lower mold 6. The gap between the mold 3 and mold 6 is measured by using an electromagnet 2a which is embedded in one of the mold 3 and the mold 6 and by using a magnetic-field detector 2b which is embedded in a section of the other one of the mold 3 and the mold 6, the section facing the electromagnet 2a, and detects a magnetic field generated by turning on electricity to the electromagnet 2a. The method controls turning on and off electricity to the electromagnet 2a in accordance with the open and close operation of the mold 3 and mold 6. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a forging die gap measuring method for measuring the upper and lower die gaps (distance between dies) of a forging die.

  In the hot forging press, the work itself is heated to form in order to reduce the deformation resistance of the work, so that the periphery of the mold is in a considerably high temperature state. Therefore, in the die of a press machine having an upper die and a lower die, the bottom dead center of the upper die is displaced due to the influence of temperature, and the distance between the upper and lower die is changed. In particular, a hot forging press performs molding in a harsh environment as described above, and it is extremely difficult to directly measure the distance between molds by installing a measuring device such as a displacement sensor in the mold. Have difficulty.

  As a die distance measuring device of a forging press machine that can directly measure the die distance at the time of such forging, Patent Document 1 discloses a non-contact displacement meter such as an eddy current sensor as a die. Disclosed is a configuration that measures the distance between molds while cooling the sensor and removing the scale (the workpiece surface is oxidized and peeled off, also referred to as oxidized scale) by embedding and flowing air. Has been.

JP 2009-156698 A

  However, when an eddy current sensor is used as a non-contact displacement meter as described in Patent Document 1, since the signal due to the eddy current is weak, the influence of the scale that cannot be removed even with the air for removing the scale. As a result, an error may occur in the measurement distance between molds, and stable measurement cannot be performed.

  Therefore, in order to increase the sensitivity of measurement signals when measuring between molds, a non-contact displacement meter other than the eddy current sensor is embedded with a magnet (permanent magnet) in the upper mold and a sensor for detecting the magnetic field of the magnet in the lower mold. It is also possible to measure the distance between the molds using a non-contact displacement meter that converts the magnetic field strength of the magnet into a displacement distance. In this case, the scale is attracted by the magnet, and the scale with air for removing the scale is used. Removal becomes difficult. In addition, when a magnet having a strong magnetic field strength is applied to the upper mold in order to improve the sensitivity of the measurement signal, the scale is further attracted.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a forging die gap measuring method for improving measurement sensitivity while suppressing adhesion of scale when measuring a forging die gap.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

That is, in claim 1,
A forging die gap measuring method for measuring an upper and lower die gap of a forging die having an upper die and a lower die,
An electromagnet embedded in one of the upper and lower molds;
A magnetic field detecting means embedded in a position facing the electromagnet in the other mold of the upper and lower molds, and detecting the magnetic field generated when the electromagnet is energized to measure the upper and lower mold gaps. Measure the gap
The ON / OFF of energization to the electromagnet is controlled in accordance with the opening / closing behavior of the upper and lower molds.

In claim 2,
When the upper and lower mold gaps become the narrowest in the opening and closing behavior of the upper and lower molds, energization to the electromagnet is turned on.

In claim 3,
When energization of the electromagnet is turned on, scale removing air is blown onto the electromagnet.

  By controlling ON / OFF of the energization of the electromagnet according to the opening / closing behavior of the upper and lower molds, it is possible to generate a magnetic field only when measuring the upper and lower mold gaps, while suppressing the adhesion of scale due to the magnetic field, and the electromagnet Thus, the measurement sensitivity of the upper and lower mold gaps can be improved.

It is a schematic diagram which shows the whole structure of the forge die gap measuring device to which the forge die gap measuring method according to the present invention is applied. It is a schematic cross section which shows the up-and-down type | mold which embedded the detection means. It is a figure which shows the time chart of an upper mold | type behavior and the excitation timing of an electromagnet. It is explanatory drawing which shows the relationship between upper mold | type behavior and ON / OFF of the electricity supply to an electromagnet, (a) is explanatory drawing which shows the state in which the upper mold | type is a position of a top dead center and an electromagnet is OFF, (b) is lower It is a figure which shows the state where a type | mold is a position of a bottom dead center and an electromagnet ON. It is a figure which shows the example of an upper mold | type bottom dead center detection and record storage, (a) is a figure which shows raw waveform data and a hold output value, (b) is a time chart which shows the signal from a control means, (c) Is a time chart showing a hold signal, and (d) is a time chart showing a data output signal.

Next, embodiments of the invention will be described.
In this embodiment, an example in which the forging die gap measuring method according to the present invention is applied to a hot forging press machine will be described. However, the present invention is not particularly limited, and the press machine has a die composed of upper and lower molds. Can be widely applied.

First, an overall configuration of a forging die gap measuring apparatus 1 to which the forging die gap measuring method according to the present invention is applied will be described with reference to FIGS. 1 and 2.
The forging die gap measuring device 1 is a distance between upper and lower dies of a forging die having an upper die 3 and a lower die 6 provided in a hot forging press (a gap between the upper die 3 and the lower die 6 shown in FIG. Device (referred to as mold gap), which is detection means 2 (see FIG. 2), energization means 7, amplifier 14, data display 16 as display means, server 25 as recording apparatus, and control means. 23 mainly.
In addition, in the upper mold | type 3 and the lower mold | type 6 which concern on this embodiment, the lower mold | type 6 is fixed and the upper mold | type 3 can be moved up and down. The upper mold moves up and down between the top dead center and the bottom dead center.

The detection means 2 is a non-contact displacement meter that can detect the intensity of a magnetic field generated by an electromagnet and convert it into a displacement distance. As shown in FIG. 2, one of the upper and lower molds 3 and 6 is used. The electromagnet 2a embedded in the upper mold 3 in this embodiment and the electromagnet embedded in a position facing the electromagnet 2a of the other mold of the upper and lower molds 3 and 6 (lower mold 6 in the present embodiment) It comprises a detection coil 2b which is a magnetic field detection means for detecting a magnetic field generated when energizing 2a and measuring a mold gap. The electromagnet 2a is obtained by winding a coil around an iron core, and the upper die 3 is in a state where the electromagnet 2a is accommodated in the central portion of the non-magnetic electromagnet accommodating portion 5 (the electromagnet 2a is not directly exposed on the lower surface of the upper die 3). Embedded in a predetermined position. The electromagnet 2a is connected to energizing means 7 for energizing a predetermined current to the coil of the electromagnet 2a. The energization means 7 is connected to the control means 23.
On the other hand, the detection coil 2b is obtained by winding a coil around an iron core, and is housed in the center of a non-magnetic sensor housing 4 embedded in the lower mold 6 (the detection coil 2b is Embedded in a predetermined position of the lower mold 6 in a state where it is not directly exposed on the upper surface of the mold 6. The detection coil 2b is connected to the control means 23 via the amplifier 14, and the control means 23 gives the detection coil 2b the strength of the magnetic field generated when the energized electromagnet 2a approaches. It can be detected as a flowing induced current and converted into a displacement distance (mold gap).

Further, as shown in FIG. 1, the detection coil 2b housed in the sensor housing part 4 having a rectangular parallelepiped shape has four locations in the vicinity of the forging part 8 which is a part for setting the forging target product (workpiece) of the lower die 6. It is buried in. In the upper mold 3, electromagnets 2 a stored in the electromagnet storage section 5 are embedded at positions facing the respective detection coils 2 b embedded in the lower mold 6.
That is, a plurality of pairs of the detection coils 2b and the electromagnets 2a detected by the detection coils 2b are arranged.

One end of the detection coil 2b is connected to a cable 11 having heat resistance. That is, the four detection coils 2b housed in each sensor housing section 4 are embedded in the lower mold 6 via each of the four cables 11 connected to one end of each detection coil 2b. Are connected to one cable relay box 10. The cable relay box 10 is connected to a plurality of amplifiers 14, 14, 14, 14 (four in this embodiment) disposed in one amplifier box 13 via a cable 12 having heat resistance. Yes. That is, each of the four detection coils 2b, 2b, 2b, and 2b is connected to the amplifiers 14, 14, 14, and 14 via the cable 11, the cable relay box 10, and the cable 12, respectively. And each amplifier 14,14,14,14 is connected to the data display 16 mentioned later via the data transmission cable 15 which has heat resistance, or the wireless transmission apparatus which is not shown in figure. The amplifiers 14, 14, 14, 14 are connected to the control means 23 via a hold signal controller 24 described later. Further, the detection coil 2b can energize the amplifier 14 with a measurement output signal (induced current value due to the magnetic field of the electromagnet 2a) corresponding to the mold gap.
In this embodiment, the electromagnet 2a is embedded in the upper mold 3 and the detection coil 2b is embedded in the lower mold 6. However, the present invention is not particularly limited, and the detection coil 2b is embedded in the upper mold 3. The electromagnet 2a may be embedded in the lower mold 6.
In addition, a thermocouple or the like is provided as a temperature sensor in the vicinity of each electromagnet 2a and each detection coil 2b to measure the temperature at the time of mold gap measurement, and the temperature and reference data for temperature correction obtained in advance are used. Based on this, it is also possible to perform a temperature correction (temperature drift correction) of the measurement output value sent from the detection coil 2b so as to obtain an accurate measurement value of the mold gap.

As shown in FIG. 1, the sensor storage portion 4 has a box shape (a rectangular parallelepiped box in this embodiment), and is formed of a heat-resistant nonmagnetic material. The plurality of sensor storage portions 4 (four in this embodiment) are configured so that the detection coils 2b are stored in the respective interiors so that the detection coils 2b are not directly exposed on the upper surface of the lower mold 6. The die 6 is buried in the vicinity of the four forged portions 8. The sensor storage unit 4 includes a foreign matter accumulation prevention mechanism 9 that removes foreign matters such as the scale S deposited on the detection coil 2b and the scale S adhering to the vicinity of the electromagnet storage unit 5 (electromagnet 2a) by air purge. The foreign matter accumulation preventing mechanism 9 includes a plurality of air purge holes 18 (see FIG. 2, two in each sensor storage portion 4 in the present embodiment) opened at the upper part of each sensor storage portion 4, and the air purge holes 18. The air guide pipe 19 guides the air for jetting from the air, and the air supply means (not shown) connected to the air guide pipe 19 and capable of supplying a predetermined amount of air. The air supply means is connected to the control means 23, and the control means 23 can control the air flow rate supplied from the air purge hole 18 by controlling the air flow rate supplied by the air supply means. It is.
In the present embodiment, the sensor storage unit 4 and the electromagnet storage unit 5 are formed in a box (cuboid) shape, but are not particularly limited, and the shape of the mold, the size of the mold, or the detection used. The shape may be appropriately changed according to the shape and size of the coil body or electromagnet body. For example, the sensor storage portion can be formed in a cylindrical shape according to the shape of the detection coil, and can be configured to be embedded in the mold with a smaller volume.
Further, the electromagnet and the detection coil are not limited to the configuration embedded in the mold as in this embodiment, and can be installed in a bolster around the mold.

The foreign matter accumulation prevention mechanism 9 blows off foreign matter such as the lubricating mist and scale S that accumulates and adheres in the vicinity of the electromagnet 2a and the detection coil 2b by injecting the air supplied from the air supply means from the air purge hole 18. It is configured to be able to be removed. That is, by injecting air from the upper end of the sensor housing 4 through the air purge hole 18 (an arrow portion pointing upward from the air purge hole 18 shown in FIG. 2), the lubrication mist, scale S, etc. that affect the measured value of the mold gap It is possible to prevent foreign matter from accumulating and adhering and to remove foreign matter in the vicinity of the electromagnet 2a above the detection coil 2b.
The air purge hole 18 is not limited to the position shown in the figure, and can be appropriately disposed at a position where the scale S is easily deposited.
Further, the air injected from the air purge hole 18 may be configured to be used as cooling air for the detection coil 2 b before being injected from the air purge hole 18. That is, the air supplied from the air supply means is first supplied to the periphery of the detection coil 2b in the sensor housing 4 so that the detection coil 2b body is cooled by air cooling and then injected from the air purge hole 18. It is also possible to configure as described above. When air is used for cooling the detection coil 2b, the air flow rate is appropriately determined in consideration of the cooling performance.

The data display 16 includes four display units 16a, 16a, 16a, and 16a, a digital data output terminal 21, and an analog data output terminal 22. The display sections 16a, 16a, 16a, and 16a are used to measure mold gaps (bottom dead center of the upper mold 3) for each molding shot respectively measured by the four detection means 2 provided in the vicinity of the forging section 8 of the lower mold 6. The value can be displayed in real time.
Note that the data display 16 and the amplifier box 13 can be integrally configured by incorporating the above-described amplifier box 13 in the data display 16.

  As shown in FIG. 1, the server 25 is a server connected to the digital data output terminal 21 or the analog data output terminal 22 (such as a personal computer, which is connected to the digital data output terminal 21 in this embodiment). . By connecting to the server 25, the measured value of the measured mold gap for each molding shot is collectively managed in the server 25 (the measured value of the measured mold gap for each molding shot is stored as a production record). And data processing using the measured value).

  The control means 23 is a control means for controlling the opening and closing of the upper and lower molds 3 and 6 included in the press machine, and signals from each molding shot (see FIG. 5B). Is sent to a hold signal controller 24 described later. The control means 23 can control ON / OFF of energization to the electromagnet 2a by the energization means 7 in accordance with the opening / closing behavior of the upper and lower molds 3 and 6. When the energization of the electromagnet 2a is turned on, the control means 23 excites the electromagnet 2a to generate a magnetic field having a predetermined intensity (see FIG. 4B. The dotted line portion that radiates downward from the lower end of the electromagnet 2a is a magnetic field. Showing). When the control means 23 turns off the energization of the electromagnet 2a, the excitation of the electromagnet 2a is stopped and the magnetic field disappears. Moreover, the control means 23 can be controlled to generate a magnetic field having a desired intensity from the electromagnet 2a by controlling the energization amount to the electromagnet 2a by the energization means 7.

  The hold signal controller 24 receives a signal of each molding shot from the control means 23 and sends an ON or OFF hold signal to each of the amplifiers 14, 14, 14, and 14 as shown in FIG. is there.

Next, a mold gap measuring method applied to the forging mold gap measuring apparatus 1 described above will be described.
When measuring the mold gap when forging a workpiece heated at a high temperature by a hot forging press using the forging mold gap measuring device 1, the control means 23 has the upper mold behavior shown in FIG. When the upper die 3 reaches the bottom dead center according to the excitation timing (A) of the electromagnet 2a shown in the time chart and FIG. 3B, each electromagnet 2a is energized by turning on the power to each electromagnet 2a. An induced current flows through each detection coil 2b according to the generated magnetic field, and the mold gap is measured by measuring the induced current value. That is, in the mold closing operation that shifts from the case where the upper mold 3 is located at the top dead center (state shown in FIG. 4A) to the case where it is located at the bottom dead center (state shown in FIG. 4B), When the upper mold 3 reaches the bottom dead center, the control means 23 energizes each electromagnet 2a according to the time chart shown in FIGS. 3A and 3B, and excites each electromagnet 2a to remove the mold gap. Measurement is performed. More specifically, the control means 23 starts excitation of each electromagnet 2a immediately before the upper die 3 reaches the bottom dead center (T1 shown in FIG. 3), and the upper die 3 holds the bottom dead center position. The excitation is continued while the upper die 3 is away from the bottom dead center (T2 shown in FIG. 3), while the excitation is stopped (T1 and T2). ) To measure the mold gap. Thus, by controlling ON / OFF of the energization to the electromagnet 2a in accordance with the opening and closing behavior of the upper and lower molds 3 and 6, a magnetic field can be generated only when measuring the mold gap of the upper and lower molds 3 and 6. It becomes possible, and scale adhesion by a magnetic field can be suppressed. In addition, when the upper and lower molds 3 and 6 have the narrowest mold gap in the opening and closing behavior of the upper and lower molds 3 and 6, the energization to the electromagnet 2a is turned on, thereby the molds of the upper and lower molds 3 and 6 are turned on. Since the magnetic field is generated only at the time of measuring the mold gap when the gap is the narrowest, the adhesion of the scale due to the magnetic field can be suppressed, and the generation of the measurement error due to the scale can be prevented. That is, the scale magnet is prevented from adhering by turning off the energization to the electromagnet 2a except when measuring the mold gap. Furthermore, as shown in FIG. 4B, when energizing the electromagnet 2a is turned on, air for scale removal is blown toward the electromagnet 2a. That is, in a state where the upper mold 3 reaches the bottom dead center and the mold gap is narrowed, air is injected from the plurality of air purge holes 18 in the upper part of the sensor housing portion 4 so as to be accumulated in the vicinity of the detection coil 2b. The lubricant mist and scale S, which are foreign matters that affect the sensor measurement value, are blown off to prevent the foreign matter from accumulating, and the scale S attracted to the electromagnet 2a having a magnetic field by energization (excitation) is blown off. As a result, even during measurement, measurement can be performed stably without error without being affected by the scale. As described above, the scale S can be prevented from adhering to the periphery of the detecting means 2 and the scale S can be efficiently removed by air, so that the sensitivity of the measurement signal is improved without worrying about the influence of the scale S. Therefore, a strong magnetic field strength can be generated from the electromagnet 2a, and the sensitivity of mold gap measurement can be improved.
In addition, as the air injection amount, when the energization to the electromagnet 2a is turned off, the scale S is removed by air injection that does not affect the work temperature, and the energization to the electromagnet 2a is turned on (vertical type) When the gap becomes narrow), the air injection amount may be set in advance so as to perform air injection to the extent that the scale S attracted around the electromagnet 2a is blown off by the magnetic force of the electromagnet 2a.
Further, the interval at which the excitation timing shown in FIG. 3 is ON may be any time as long as the upper mold 3 is located at the bottom dead center. For example, as shown in the excitation timing (B) shown in FIG. It is not necessary to continuously excite while the upper die 3 is located at the bottom dead center, and it is possible to end the excitation as soon as the die gap measurement by the forging die gap measuring device 1 is finished.

  Further, the timing for removing the scale by air only needs to consider the excitation timing (mold measurement timing), and since the excitation timing in this embodiment is the position where the electromagnet 2a is closest to the air purge hole 18, air to be blown is used. There is an advantage that the scale S can be blown away without making the flow rate excessive.

Next, the case where the mold gap is continuously measured for each molding shot of the hot forging press will be specifically described with reference to FIG.
In this embodiment, the lower mold 6 is fixed, and the displacement of the bottom dead center of the upper mold 3 (displacement from the lower mold 6 at the bottom dead center of the upper mold 3) is measured as the mold gap. In particular, the measurement conditions of the mold gap are not limited.
In the graph shown in FIG. 5A, the vertical axis obtained by converting the output value (voltage V) at the time of measuring the mold gap by the detecting means 2 into displacement (mm), the output 1V corresponds to the displacement 1 mm, and the horizontal axis This is time (s), and on this graph, raw waveform data (solid line) which is a measured output value corresponding to the mold gap of the detecting means 2 is shown. In this graph, the displacement is plotted on the graph from when the upper mold 3 descends and the displacement of the vertical axis of the graph becomes 10 mm or less. That is, when the bottom dead center of the upper mold 3 is larger than 10 mm, a constant value is maintained in the vicinity of 10 mm on the graph.

A control unit (not shown) in each of the amplifiers 14, 14, 14, 14 has a measured output value (shown in FIG. Raw waveform data) is sampled and input. As a timing when the upper mold 3 starts to descend (a portion indicated by an arrow A in FIG. 5), a signal indicating that the upper mold 3 is lowered from the control means 23 (an arrow D portion in the time chart in FIG. 5B) is used as a trigger to hold a signal. The hold signal controller 24 sends a hold signal to each amplifier 14 in the amplifier box 13 using that as a base point. Each amplifier 14 determines the minimum value of the measured output value (displacement of the upper die 3) input to the amplifier 14 for a certain period of time based on the hold signal (ON signal indicated by an arrow E in FIG. 5C). When the mold gap between the upper mold 3 and the lower mold 6 is the smallest, that is, when the upper mold 3 comes to the bottom dead center, the measured output value is output as a hold output value (FIG. 5A). Arrow B portion). Then, the bottom hold value (the part indicated by the arrow C in FIG. 5A), which is the measurement output value when the upper mold 3 becomes the bottom dead center, is detected as the measured value of the mold gap (displacement 6 mm in this embodiment). To do. Then, in order to transmit this measurement value to the data display 16, a data output signal shown in FIG. 5D is transmitted to the data display 16. The measured values (bottom hold values) of the four mold gaps are displayed on the display sections 16a, 16a, 16a, and 16a of the data display 16 for each molding shot by the transmitted data output signal, and connected to the data display 16 The bottom hold value data of each molding shot is recorded and stored in the server 25. In addition, the measured value of the mold gap for each molding shot of the upper and lower molds 3 and 6 displayed on the data display 16 can be confirmed in real time by the operator, so that it is immediately reflected in the molding conditions of the press machine. Thus, the molding conditions can be adjusted. Moreover, it is possible to link the product (forged product) and the measured value data of the mold gap at the time of molding the product using the server 25, and when the product is produced from a single product. It is possible to easily trace all the transitions of the mold gap during the molding process. Further, as a trigger when the upper mold 3 is lowered, it is also possible to use an output signal of the detection means 2 (detection coil 2b). In other words, the production record storage function of the forging die gap measuring device 1 of the present invention is that the bottom dead center of the upper die 3 of each molding shot is triggered by the signal of the control means 23 or the output signal of the detection coil 2b itself. The value can be detected and stored as a production record in the server 25 which is a recording device, and the product and manufacturing conditions can be linked.
Further, the lower surface of the upper die 3 (the surface facing the upper surface of the lower die 6) with respect to the upper surface of the lower die 6 from each measured value of the die gap measured by the detecting means 2 in the vicinity of the four forged portions 8 It is also possible to calculate the inclination angle.

  In this way, the signal of the control means 23 that controls the opening and closing of the upper and lower molds 3 and 6 or the measurement output signal of the detection coil 2b is used as a trigger for each molding shot based on the measurement output obtained from the detection means 2. A server 25 that is a recording device that acquires the measured value of the mold gap via the amplifier 14 and stores the measured value, and a data display 16 that is a display unit that displays the measured value of the mold gap for each molding shot. The value of the bottom dead center (die gap) of the upper die 3 of each molding shot can be stored in the server 25 as a production record, and the product and manufacturing conditions can be linked. That is, quality control based on 100% inspection of products can be easily performed instead of quality control based on sampling inspection.

  The present invention can measure a mold gap during forging with higher sensitivity than a method using a conventional overcurrent displacement sensor without being affected by scale.

  The present invention uses a forging die clearance measuring device in which an electromagnet is embedded in an upper die and a detection sensor is embedded in a lower die in order to increase signal sensitivity compared to an eddy current displacement meter, and the magnetic field strength of the electromagnet is increased. This is a method of measuring the upper and lower mold gaps by a non-contact displacement measuring method that converts to a displacement distance, and controls ON / OFF of the electromagnet in accordance with the behavior of the upper and lower molds. Since the electromagnet is turned on at the timing required for measurement, it is possible to suppress the adhesion of extra scale, and it is possible to improve the magnetic field strength without worrying about the influence of the scale, thereby improving the measurement sensitivity.

  The present invention can be utilized for mold inclination and mold deformation measurement by arranging a plurality of detection means on the upper and lower molds. Moreover, since measurement during forging can be performed, storage as a production record is also possible.

2 detection means 2a electromagnet 2b detection coil 3 upper mold 6 lower mold

Claims (3)

A forging die gap measuring method for measuring an upper and lower die gap of a forging die having an upper die and a lower die,
An electromagnet embedded in one of the upper and lower molds;
A magnetic field detecting means embedded in a position facing the electromagnet in the other mold of the upper and lower molds, and detecting the magnetic field generated when the electromagnet is energized to measure the upper and lower mold gaps. Measure the gap
A forging die gap measuring method, wherein ON / OFF of energization to the electromagnet is controlled in accordance with the opening / closing behavior of the upper and lower dies.   2. The forging die gap measuring method according to claim 1, wherein energization of the electromagnet is turned ON when the upper and lower die gaps become the narrowest in the opening and closing behavior of the upper and lower dies.   The forging die clearance measuring method according to claim 1 or 2, wherein scale removing air is blown onto the electromagnet when the electromagnet is energized.

Images