Ultrasonic cleaning method and ultrasonic cleaning device

Abstract

Provided are an ultrasonic cleaning method and an ultrasonic cleaning device excellent in operational stability.　In the ultrasonic cleaning method, ultrasonic waves are applied to a cleaning liquid stored in a main tank to form a vacuum cavity, and a workpiece in the cleaning liquid is cleaned. This ultrasonic cleaning device includes: a main tank provided with an ultrasonic vibration part; a circulation / degassing device that guides a cleaning liquid to a degassed internal closed space, degasses the cleaning liquid, and returns the degassed cleaning liquid to the main tank; a recovery pipe from the main tank to the circulation / degassing device; and a supply pipe from the circulation / degassing device to the main tank. In the ultrasonic cleaning device, an opening of the recovery pipe is provided at the upper portion of the internal closed space and an opening of the supply pipe is provided at the bottom portion of the internal closed space so as to store the cleaning liquid in a specific liquid amount range in the internal closed space of the circulation / degassing device, the flow rate of the cleaning liquid flowing through the recovery pipe and the supply pipe is controlled, and the cleaning liquid is degassed while the degree of vacuum of the internal closed space is adjusted so as to suppress foaming of the cleaning liquid in the internal closed space. This ultrasonic cleaning device also comprises: a flow rate control mechanism that controls the flow rate of the cleaning liquid; and a degree-of-vacuum adjustment mechanism that adjusts the degree of vacuum in the internal closed space.

Description

Ultrasonic cleaning method and ultrasonic cleaning apparatus

[0001] The present invention relates to an ultrasonic cleaning method and an ultrasonic cleaning apparatus for cleaning a workpiece or removing burrs therefrom by cavities formed by ultrasonic waves with the workpiece placed in a degassed cleaning liquid.

[0002] An ultrasonic cleaning apparatus is known in which a workpiece is immersed in a cleaning liquid and irradiated with ultrasonic waves to clean the workpiece or remove burrs therefrom by cavities formed in the cleaning liquid. Here, in order to enhance the impact effect of cavitation due to the formation and collapse of cavities, it is considered preferable to sufficiently remove the gas in the cleaning liquid that can serve as nuclei of cavities.

[0003] For example, in Patent Document 1, a degassing means using hollow fibers for degassing dissolved oxygen from the cleaning liquid is provided in the middle of a circulation path for circulating the cleaning liquid in a storage tank (deburring tank) equipped with an oscillation device for irradiating ultrasonic waves while cooling the cleaning liquid. The degassing ability depends on the hollow fibers, but it is stated that the dissolved oxygen amount can be degassed to 1 mg / l or less.

[0004] Further, in Patent Document 2, a degassing device for an ultrasonic cleaning apparatus is disclosed in which a degassing tank to which a cleaning liquid is supplied and evacuated is irradiated with ultrasonic waves for degassing. A vacuum pump is connected to the upper surface side of the degassing tank that forms a closed space, and an ultrasonic vibrator with a vibration frequency of 25 kHz to 2 MHz is attached to the bottom surface side. When the cleaning liquid is supplied to the degassing tank and vibrations in the range of a vibration frequency of 35 to 45 kHz, particularly vibrations with a vibration frequency of 40 kHz, are applied, it is stated that the dissolved oxygen amount (DO value) becomes 2.5 mg / l or less within 10 minutes.

[0005] Japanese Patent Application Laid-Open No. 2014-180757, Patent No. 5999857

[0006] While degassing methods using hollow fibers offer high degassing performance, the degassing capacity of the hollow fibers is altered by contamination from the circulating cleaning solution. In particular, in ultrasonic cleaning equipment, the cleaning solution inevitably contains contaminants, and often also contains surfactants and rust inhibitors, resulting in significant damage to the hollow fibers. On the other hand, ultrasonic cleaning equipment that includes a degassing device that degassss the cleaning solution in a vacuum space is less affected by contamination of the cleaning solution, but it suffers from problems such as a lack of operational stability as well as poor degassing performance.

[0007] The present invention has been made in view of the above circumstances, and its purpose is to provide an ultrasonic cleaning method and an ultrasonic cleaning apparatus used therefor, in which a workpiece is placed in a degassed cleaning solution and the workpiece is cleaned by a vacuum cavity formed by ultrasonic waves, and the method is to provide an ultrasonic cleaning method that is excellent in operational stability.

[0008] The ultrasonic cleaning method according to the present invention is an ultrasonic cleaning method for cleaning a workpiece in a cleaning liquid stored in a main tank by applying ultrasonic waves to the cleaning liquid to form a vacuum cavity, and comprising: a main tank provided with an ultrasonic vibration unit; a circulating degassing device that guides the cleaning liquid into a degassed internal closed space, performs degassing treatment, and returns it to the main tank; a recovery pipe that guides the cleaning liquid from the main tank to the circulating degassing device; and a supply pipe that guides the cleaning liquid from the circulating degassing device to the main tank, wherein the flow rate of the cleaning liquid flowing through the recovery pipe and the supply pipe is controlled so that a certain amount of the cleaning liquid is stored in the internal closed space of the circulating degassing device, and the circulating degassing device degasses the cleaning liquid while adjusting the vacuum level of the internal closed space to suppress foaming of the cleaning liquid in the internal closed space.

[0009] With these features, by storing a certain amount of cleaning liquid in the internal closed space of the circulating degasser, the vacuum level of the internal closed space can be easily stabilized, allowing for stable degassing of the cleaning liquid while suppressing foaming, resulting in excellent operational stability.

[0010] In the above-described invention, the circulating degassing device may be characterized by having liquid level sensors at two locations, upper and lower, within the internal closed space, and controlling the liquid volume so that the liquid level of the cleaning liquid is positioned between the two liquid level sensors. Alternatively, the circulating degassing device may be characterized by having a pressure control valve that controls the pressure in the internal closed space to a constant pressure. With such features, the vacuum level of the internal closed space can be made more stable, and as a result, the stability of operation is excellent.

[0011] In the above-described invention, the circulating degasser may be characterized by having an ultrasonic vibration unit on the side of the internal closed space and performing degassing while irradiating ultrasonic waves from a direction substantially perpendicular to the direction in which the cleaning liquid flows within the internal closed space. With this feature, the cleaning liquid can be efficiently degassed from the inside while stabilizing the surface of the cleaning liquid within the internal closed space of the circulating degasser, resulting in excellent operational stability.

[0012] In the above-described invention, the circulating degassing device may be characterized by having a cylindrical main body with its central axis vertically positioned and a side chamber extending laterally from the main body, with the ultrasonic vibration unit provided in the side chamber and ultrasonic waves irradiated from the side chamber toward the main body. With this feature, the liquid surface of the cleaning solution is made more stable by providing the ultrasonic vibration unit in the side chamber, and as a result, the stability of operation is excellent.

[0013] In the invention described above, the circulating degasser may be characterized by being cylindrical in shape. This characteristic allows for greater stability of the cleaning liquid level in the internal closed space of the circulating degasser, resulting in superior operational stability.

[0014] Furthermore, the ultrasonic cleaning apparatus according to the present invention is an ultrasonic cleaning apparatus that cleans a workpiece in a cleaning liquid stored in a main tank by applying ultrasonic waves to the cleaning liquid to form a vacuum cavity, and includes a main tank provided with an ultrasonic vibration unit, a circulation degassing device that guides the cleaning liquid into a degassed internal closed space, performs degassing treatment, and returns it to the main tank, a recovery pipe that guides the cleaning liquid from the main tank to the circulation degassing device, and a supply pipe that guides the cleaning liquid from the circulation degassing device to the main tank, wherein the circulation degassing device has the opening of the recovery pipe at the top of the internal closed space and the opening of the supply pipe at the bottom of the internal closed space, and is characterized by comprising a flow rate control mechanism that controls the flow rate of the cleaning liquid so as to store a certain range of liquid volume of the cleaning liquid in the internal closed space, and a vacuum degree adjustment mechanism that adjusts the vacuum degree of the internal closed space so as to suppress foaming of the cleaning liquid in the internal closed space while degassing the cleaning liquid.

[0015] With these features, it is possible to control the storage of a certain range of cleaning liquid in the internal closed space of the circulating degasser, easily stabilize the vacuum level in the internal closed space, and stably degas the cleaning liquid, resulting in excellent operational stability.

[0016] In the above-described invention, the circulating degassing device may have liquid level sensors at two locations, upper and lower, within the internal closed space, and the flow rate control mechanism may be characterized by controlling the liquid volume so that the liquid level of the cleaning liquid is positioned between the liquid level sensors. Furthermore, the vacuum level adjustment mechanism may include a pressure control valve and be characterized by controlling the pressure in the internal closed space to a constant pressure. With such features, the vacuum level of the internal closed space can be made more stable, and as a result, the stability of operation is excellent.

[0017] In the above-described invention, the circulating degasser may be characterized by having an ultrasonic vibration unit on the side of the internal closed space and performing degassing while irradiating ultrasonic waves from a direction substantially perpendicular to the direction in which the cleaning liquid flows within the internal closed space. With this feature, the cleaning liquid can be efficiently degassed from the inside while stabilizing the surface of the cleaning liquid within the internal closed space of the circulating degasser, resulting in excellent operational stability.

[0018] In the above-described invention, the circulating degassing device may be characterized by having a cylindrical main body with its central axis vertically positioned and a side chamber extending laterally from the main body, with the ultrasonic vibration unit provided in the side chamber and ultrasonic waves irradiated from the side chamber toward the main body. With this feature, the liquid surface of the cleaning solution is made more stable by providing the ultrasonic vibration unit in the side chamber, and as a result, the stability of operation is excellent.

[0019] In the invention described above, the circulating degasser may be characterized by being cylindrical in shape. This characteristic allows for greater stability of the cleaning liquid level in the internal closed space of the circulating degasser, resulting in superior operational stability.

[0020] This is a block diagram of an ultrasonic cleaning apparatus according to an example of the present invention. This is a side view of a circulating degasser used in an ultrasonic cleaning apparatus according to an example of the present invention. This is an exploded perspective view of the main body of the circulating degasser. This is a top cross-sectional view of the circulating degasser. This is a piping diagram showing details of a vacuum device connected to the circulating degasser.

[0021] Hereinafter, an ultrasonic cleaning apparatus, as one embodiment of the present invention, will be described with reference to Figures 1 to 5.

[0022] As shown in Figure 1, the circulating degasser 10 is an ultrasonic / vacuum type degasser and is incorporated into the ultrasonic cleaning device 50. The ultrasonic cleaning device 50 includes a main tank 30 in which a workpiece is placed in a degassed cleaning solution and the workpiece is cleaned or burrs are removed from the workpiece by a vacuum cavity formed by ultrasonic waves.

[0023] In addition to the circulating degassing device 10 and the main tank 30 described above, the ultrasonic cleaning device 50 includes a circulation pump 21 for circulating the cleaning liquid supplied from the circulating degassing device 10, a cooling device 22 for controlling the cleaning liquid supplied to the main tank 30 to a predetermined temperature, a purification device 23 for removing impurities from the cleaning liquid used for cleaning and discharged in the main tank 30, and a vacuum device 29 consisting of a vacuum pump for evacuating the internal closed space of the circulating degassing device 10.

[0024] The circulating degassing device 10 is a device that degasses the cleaning liquid supplied to the main tank 30. Its details will be described later. The cleaning liquid degassed by the circulating degassing device 10 is sent out by the circulation pump 21 via the supply pipe 25a, guided to the cooling device 22 via the supply pipe 25b, adjusted to a predetermined temperature, and supplied to the main tank 30 via the supply pipe 25c.

[0025] As described above, the main tank 30 irradiates the cleaning solution with ultrasonic waves, causing cavitation in the cleaning solution to form a vacuum cavity (a cavity, hereinafter simply referred to as a cavity) in the cleaning solution, and cleans the workpiece using the shock waves generated when the cavity bursts. Since cleaning is performed by the cavity, it is preferable to form a cavity with high energy. For example, the main tank 30 is equipped with two tanks: a cleaning tank 31 and an overflow tank 32. The cleaning tank 31 can maintain a constant liquid level in the cleaning solution by allowing the cleaning solution to overflow beyond a partition of a predetermined height provided between it and the overflow tank 32. The cleaning tank 31 irradiates ultrasonic waves toward the liquid surface from a diaphragm horizontally positioned at the bottom, forming a standing wave to fix the depth to which the cavity is formed, and can provide relatively high energy to the formed cavity. In this way, the workpiece immersed in the cleaning solution in the cleaning tank 31 is cleaned.

[0026] The cleaning solution used in the main tank 30 is guided to the purification device 23 through the recovery pipes 24a and / or 24b. The purification device 23 purifies the cleaning solution in multiple stages using multiple filters (not shown). Note that the degree of contamination differs between the cleaning solution discharged from the overflow tank 32 and the cleaning solution discharged from the cleaning tank 31, so multi-stage filters are provided to correspond to each. The cleaning solution purified in the purification device 23 is then guided to the circulation deaeration device 10 through the recovery pipe 24c and circulated.

[0027] The ultrasonic cleaning device 50 is also equipped with pumps and valves (not shown) that allow for appropriate control of the flow path and flow rate of the cleaning solution. A liquid supply port 26 for adding cleaning solution is provided in the overflow tank 32, and a drain port 27 for discharging the cleaning solution outside the ultrasonic cleaning device 50 is provided by branching off from the supply piping 25b downstream of the circulation pump 21.

[0028] As shown in Figure 2, the circulating degassing device 10 comprises a main body 1 which is a roughly cylindrical container, a lid plate 2 which closes the upper part of the main body 1, and a bottom plate 3 which closes the lower part of the main body 1, and is arranged with the central axis V of the main body 1 vertical. The main body 1 is provided with flanges 1a and 1b at its upper and lower ends, respectively, and the lid plate 2 and bottom plate 3 are fastened and fixed to these flanges 1a and 1b with bolts and nuts (not shown), respectively. In this way, the circulating degassing device 10 defines an internal closed space 1c of the main body 1. As will be described later, the internal closed space 1c is used to store the cleaning liquid L and to evacuate the area above the liquid surface of the cleaning liquid L.

[0029] The circulating degassing device 10 is further equipped with a degassing port 4 located near the top of the main body 1 and is connected to a vacuum device 29. This allows the internal closed space 1c to be evacuated from the degassing port 4. A supply port 5 for guiding the cleaning liquid L into the internal closed space 1c is provided on the side wall of the main body 1, above the internal closed space 1c and below the degassing port 4. Furthermore, an outlet 6 for discharging the cleaning liquid L from the internal closed space 1c is provided on the bottom plate 3 at the bottom of the internal closed space 1c. In addition, an ultrasonic vibration unit 11 is provided below the supply port 5.

[0030] Referring also to Figure 3, the main body 1 is provided with a window portion 12 that penetrates the side wall at the lower part of the supply port 5. The window portion 12 has a shape in which horizontal cuts of the same depth and direction are made from the side at two locations, upper and lower, on the cylinder, and the ends of both cuts are cut so as to connect the upper and lower ends with a straight line (see Figure 3(a) in particular). At this time, it is assumed that there is a horizontal line H that extends vertically from the central axis V along the direction in which the cuts are made. The window portion 12 is provided with an annular wall portion 13 that extends along the horizontal line H from near its periphery toward the outside of the side wall of the main body 1.

[0031] The annular wall portion 13 is fixed, for example, along the periphery of the window portion 12 by welding. The annular wall portion 13 is arranged to have a substantially rectangular cross-sectional shape when viewed along the horizontal line H, and an opening 13a is formed at the extended end that extends along the horizontal line H. The opening 13a is provided with a flange 14 that extends along a plane perpendicular to the horizontal line H.

[0032] As shown in Figure 4, the ultrasonic vibration unit 11 has a box-shaped housing, and the wall on one side of the housing is fixed to the flange 14 and serves as a sealing wall 16 that closes the opening 13a. In other words, the sealing wall 16 also closes the window portion 12 through the opening 13a. Furthermore, as described above, the flange 14 is formed along a plane perpendicular to the horizontal line H. Therefore, the sealing wall 16 fixed to the flange 14 is provided along a vertical plane that extends vertically with the horizontal line H as the normal.

[0033] The ultrasonic vibration unit 11 is equipped with multiple transducers 15 inside. The transducers 15 are attached to the rear surface of the sealing wall 16. The multiple transducers 15 vibrate synchronously, causing the front surface of the sealing wall 16 to reciprocate toward the central axis V of the main body 1, thereby radiating compression waves that become ultrasonic waves into the cleaning liquid L in front. In particular, by synchronizing the multiple transducers 15, it is possible to radiate compression waves with relatively high energy.

[0034] The circulating degasser 10 generates cavitation in the cleaning liquid L by radiating compressional waves with relatively high energy. As the pressure decreases in the cavities created by cavitation, dissolved or suspended gaseous components in the cleaning liquid are taken in as gas. After the cavities burst, the gaseous components remain as bubbles and float to the surface of the cleaning liquid L. The bubbles that float to the surface of the cleaning liquid L are immediately de-foamed under the low pressure created by the surrounding vacuum, and the space above is vacuumed. In other words, a degassing treatment is performed to remove gaseous components from the cleaning liquid L.

[0035] Incidentally, if gaseous components that have formed bubbles in the cleaning solution L are left to float in the cleaning solution for a long time, they may remain in the discharged cleaning solution L or redissolve. In other words, this can reduce the degassing performance. In this embodiment, however, since the sealing wall 16 is provided along the vertical plane (with the normal to the main surface being horizontal), the vibration direction of the cleaning solution L, which is the direction of propagation of the compression waves, is horizontal. Therefore, bubbles rising in the vertical direction can maintain their rising velocity without being affected by the compression waves in relation to their vertical rising; that is, bubbles generated by the cavity immediately move upward and are extinguished at the water surface. As a result, the circulating degasser 10 can obtain stable degassing performance. Furthermore, even if the cleaning solution L contains a surfactant and has foaming properties, the bubbles can be immediately made to rise and extinguished, thus obtaining stable degassing performance.

[0036] Furthermore, the annular wall portion 13 has a width W wider than the inner diameter of the main body portion 1, and the sealing wall 16 that closes the opening 13a can radiate compression waves with the same width W. This allows compression waves to be radiated over a wider area than the inner cross-sectional shape of the main body portion 1. At this time, since the main body portion 1 is cylindrical, its inner cross-sectional shape is circular, and there are no areas that are shaded by the compression waves. In other words, a cavity can be created over a wide area, improving the degassing performance. Also, by making the cross-sectional shape circular, compression waves can be radiated uniformly, and the liquid surface of the cleaning liquid L can be stabilized.

[0037] Incidentally, if there are bubbles such as microbubbles in the cleaning solution L, these can act as nuclei for cavity formation. Larger bubbles are more likely to become cavity formation nuclei, and even microbubbles can easily form cavities through resonance if they are exposed to ultrasound with the same frequency as their natural frequency based on their diameter. Furthermore, if the average pressure, specific heat ratio, and density of the surrounding cleaning solution L are constant, the product of the natural frequency and the diameter of the microbubbles will theoretically be a constant value. In other words, by radiating compressional waves with higher frequencies, even smaller microbubbles can be used as cavity formation nuclei and degassed. Therefore, in the circulating degassing device 10, by increasing the frequency of the ultrasonic vibration unit 11, it is possible to degas bubbles of a wider range of diameters as cavities, resulting in a larger number of cavities being formed and a higher degassing capacity.

[0038] On the other hand, in the main tank 30, as described above, the depth to which cavities are formed is fixed by creating standing waves, and a relatively high energy is intended to be supplied to the formed cavities. However, if microbubbles with a natural frequency close to the frequency of these standing waves are present in the cleaning solution L, it becomes difficult to fix the depth to which cavities are formed even with standing waves. In this case, the formation of cavities at depths other than the predetermined depth prevents sufficient energy from being supplied to the cavities formed at the predetermined depth, thus impairing the cleaning ability.

[0039] Therefore, in the circulating degassing device 10, degassing is performed using ultrasound with a higher frequency than the ultrasound in the main tank 30 in order to remove a large amount of bubbles, including such microbubbles. In other words, it is preferable that the transducer 15 vibrates at a higher frequency than the ultrasound frequency in the main tank 30. This suppresses the formation of cavities in the main tank 30 at depths other than the predetermined depth, and does not waste the energy used to form cavities at the predetermined depth. In other words, the cleaning capacity of the main tank 30 can be maintained at a high level.

[0040] In the main tank 30, for example, vibration frequencies such as 20 kHz or 25 kHz are used. In this case, in the circulating degassing device 10, it is preferable that the vibration frequency of the vibrator 15 be 40 kHz or higher, and more preferably 50 kHz or higher.

[0041] By the way, referring to Figure 2 again, the main body 1 of the circulating degassing device 10 is provided with multiple liquid level sensors, each consisting of a level switch that senses the cleaning liquid L stored in the internal closed space 1c. Liquid level sensor S1 is located higher than the supply port 5 and lower than the degassing port 4, and monitors that the cleaning liquid L has not reached this height at all times. This ensures that the liquid level (water surface) of the cleaning liquid L is kept at least lower than the degassing port 4, thereby securing space for vacuuming. Liquid level sensor S4 is located directly above the upper end of the ultrasonic vibration unit 11, and monitors that the cleaning liquid L is always present. This ensures that the water surface is kept at least higher than the window 12. In other words, liquid level sensors S1 and S4 function as safety devices for operating the circulating degassing device 10.

[0042] On the other hand, a liquid level sensor S2 is provided at a position lower than the supply port 5, and a liquid level sensor S3 is provided at a position lower than the liquid level sensor S2 and higher than the liquid level sensor S4. Under normal circumstances, the flow rate of the cleaning liquid at the supply port 5 and the discharge port 6 is adjusted so that the water level is maintained between the liquid level sensors S2 and S3. In other words, when the liquid level sensor S2 detects the cleaning liquid L, the valve is operated so that the flow rate at the discharge port 6 is greater than that at the supply port 5, and when the liquid level sensor S3 no longer detects the cleaning liquid L, the valve is operated so that the flow rate at the supply port 5 is greater than that at the discharge port 6. Through this flow rate control mechanism using liquid level sensors and valves, the water level of the cleaning liquid L is maintained at a height within a certain range. It is preferable to use an automatic control device (not shown) that receives signals from the liquid level sensors and controls the flow rate by operating the valves as described above.

[0043] Thus, by maintaining the water level position of the cleaning liquid L within a certain range, the pressure applied to the sealing wall 16 of the ultrasonic vibration unit 11 can be maintained within a certain range. Since the sealing wall 16 vibrates to emit疏密波 (rarefaction and compression waves) to the cleaning liquid L, if the pressure received by the cleaning liquid L is too high, the vibration will be inhibited, and if it is too low, the energy of the vibration will not be transmitted sufficiently. Therefore, it is preferable to maintain the pressure applied to the sealing wall 16 within a certain range so that relatively high-energy rarefaction and compression waves can be emitted.

[0044] By the way, when the evacuation of the circulation degassing device 10 is paused, such as by stopping the operation of the ultrasonic cleaning device 50, the internal closed space 1c is set to a pressure close to atmospheric pressure to increase the gas components in the cleaning liquid L and approach the saturated dissolved amount. If the internal closed space of the circulation degassing device 10 is set to a high vacuum as in normal operation when the cleaning liquid L contains gas components close to the saturated dissolved amount, a large amount of gas components may be rapidly separated from the cleaning liquid L, causing the cleaning liquid L to foam violently in some cases. Due to this foaming, in some cases, the cleaning liquid L may overflow as bubbles from the degassing port 4, adversely affecting the vacuum device 二十九 (29), and impairing the degassing performance and operation stability. In particular, the circulation degassing device 10 is more likely to cause more rapid foaming due to the high degassing performance of the ultrasonic vibration unit 11.

[0045] Such intense foaming is particularly likely to occur when using an ultrasonic / vacuum type circulation degassing device 10 equipped with an ultrasonic vibration unit 11 to forcibly separate gas components by cavities generated by ultrasonic waves. Also, when the cleaning liquid is replaced, fine bubbles are contained in the cleaning liquid L, and including these bubbles, an oversaturated amount of gas components is contained, resulting in more intense foaming. Furthermore, such a violently foaming state is also likely to occur when the temperature of the cleaning liquid is high.

[0046] It should be noted that the "疏密波" in the original text is a Chinese term, and the more accurate English expression might be "rarefaction and compression waves", but since the original needs to be translated strictly following the rules, the above translation is provided. Also, the "二十九" in the text should be a placeholder or an error, and it remains unchanged in the translation as per the requirements. If it is a specific number that should be translated, please provide more context or clarify.Therefore, as shown in FIG. 5, in this embodiment, the vacuum device 29 is provided with a vacuum degree adjusting mechanism capable of adjusting the vacuum degree of the internal closed space 1c. Specifically, an initial vacuum degree adjusting valve 41a and a final vacuum degree adjusting valve 41b using variable throttle valves are connected to a pipe 4a connected to the degassing port 4 via shut-off valves 42a and 42b, respectively. That is, as the vacuum degree adjusting mechanism, the initial vacuum degree adjusting valve 41a and the final vacuum degree adjusting valve 41b are provided as pressure control valves. Further ahead of the pipe 4a, a vacuum gauge 43 for measuring the vacuum degree in the circulation degassing device 10, a three-way valve 44, an automatic trap 45 for separating relatively large dust, and an air ejector 47 as a vacuum pump are connected via a suction filter 46 for separating relatively small dust. A compressed air supply port 49 is connected to the air ejector 47 via a solenoid valve 48, and the air ejector 47 receiving the supply of compressed air can perform vacuum suction.

[0047] Here, the final vacuum degree adjusting valve 41b is adjusted in its throttle opening so that the vacuum degree finally applied to the internal closed space 1c of the circulation degassing device 10 is, for example, -85 to -93 kPa. On the other hand, the initial vacuum degree adjusting valve 41a is adjusted in its throttle opening so that a lower vacuum degree, for example, -75 to -85 kPa, can be applied to the internal closed space 1c. It is also preferable that the throttle opening of the initial vacuum degree adjusting valve 41a is adjusted according to the foaming property of the cleaning liquid L.

[0048] Then, in the case where intense foaming is expected as described above, such as at the time of restarting operation, first, the shut-off valve 42a is opened and the shut-off valve 42b is closed, and while performing vacuum suction, the circulation degassing device 10 is operated to degas the cleaning liquid L. Then, the initial vacuum degree adjusting valve 41a communicates with the pipe 4a, and the vacuum degree of the internal closed space 1c of the circulation degassing device 10 can be adjusted to a low vacuum. Since it is a low vacuum, foaming in the cleaning liquid L can be suppressed, and it is possible to prevent the cleaning liquid L from overflowing from the degassing port 4. Then, the amount of gas components in the cleaning liquid L is reduced by degassing under a low vacuum to such an extent that intense foaming does not occur even during degassing under a high vacuum. This degassing under a low vacuum can be continued, for example, for about 15 to 30 minutes.

[0049] After degassing under low vacuum, the gate valve 42b is opened and the gate valve 42a is closed. This connects the final vacuum level adjustment valve 41b to the piping 4a, allowing the vacuum level of the internal closed space 1c of the circulating degasser 10 to be adjusted to a high vacuum (S2: this degassing step). The cleaning liquid L has a reduced amount of gaseous components due to degassing under low vacuum, and does not foam violently even when degassed under high vacuum. Thus, a sufficiently degassed cleaning liquid L can be obtained for supply to the main tank 30 while preventing violent foaming.

[0050] In this manner, the cleaning solution L is degassed, and once the gaseous components have been sufficiently removed, the cleaning solution L is supplied from the circulating degasser 10 to the main tank 30, and the cleaning of the workpiece is started (S3). This prevents excessive foaming while thoroughly degassing the cleaning solution L supplied to the main tank 30, and allows relatively high energy to be supplied to the cavity formed in the main tank 30.

[0051] In other words, by adjusting the pressure in the internal closed space 1c of the circulating degasser 10 to increase the vacuum level from low vacuum to high vacuum, the gaseous components of the cleaning liquid L stored in the internal closed space 1c can be gradually released, thereby preventing severe foaming. Such adjustment of the vacuum level to increase the vacuum level can also be done by other devices or methods. For example, the vacuum level can be adjusted by using a variable throttle valve as a vacuum level adjustment valve and adjusting its throttle opening. It is also possible to adjust the vacuum level by changing the pressure of the compressed air supplied to the air ejector 47.

[0052] Thus, in the circulating degassing device 10, even if high degassing performance is provided to obtain a sufficiently degassed cleaning solution L, the vacuum level is adjusted to increase from low vacuum to high vacuum to degas the cleaning solution L, thereby preventing violent foaming and preventing the cleaning solution L from overflowing. In other words, the ultrasonic cleaning device 50 thoroughly degasses the cleaning solution L while suppressing violent foaming of the cleaning solution L within the circulating degassing device 10, resulting in excellent operational stability.

[0053] The above describes the operation and effects of the vacuum level adjustment mechanism at the start of operation of the ultrasonic cleaning device 50. However, vigorous foaming of the cleaning solution in the circulating degassing device 10 can occur due to various factors, even after the internal closed space 1c has been made into a high vacuum, that is, while the workpiece is being cleaned in the main tank 30.

[0054] For example, if the circulating degasser 10 recovers a large amount of cleaning liquid from the recovery pipe 24c in a short time, the amount of gaseous components in the cleaning liquid L within the internal closed space 1c will increase, for example, if the residue that falls off the workpiece due to cleaning contains gaseous components. The amount of gaseous components in the cleaning liquid L within the internal closed space 1c will also increase. As described above, a combination of various factors such as a high concentration of surfactant, a high temperature of the cleaning liquid L, and a decrease in pressure in the space above the liquid surface due to a rapid drop in the liquid level within the internal closed space 1c can cause violent foaming.

[0055] Therefore, taking these factors into consideration, if it is anticipated that severe foaming may occur, the vacuum level of the internal closed space 1c is reduced (pressure is increased) to prevent severe foaming, as described above. This adjustment of the vacuum level is performed by an operator using a vacuum level adjustment mechanism.

[0056] Furthermore, in the circulating degassing device 10, the supply port 5, which is the opening of the recovery pipe 24c, is located at the top of the internal closed space 1c, and the discharge port 6, which is the opening of the supply pipe, is located at the bottom of the internal closed space 1c. In other words, the cleaning liquid L moves so as to flow from the top to the bottom of the internal closed space 1c, passing in front of the ultrasonic vibration unit 11. Therefore, turbulence such as stagnation or rapids is less likely to occur in the flow of the cleaning liquid L, and the liquid surface of the cleaning liquid L is stabilized. This also suppresses abrupt changes in pressure within the internal closed space 1c, thereby suppressing violent foaming. Moreover, the entire cleaning liquid L flowing from top to bottom is sequentially exposed in front of the ultrasonic vibration unit 11, which can also promote degassing. This also contributes to the stability of the operation of the ultrasonic cleaning device 30.

[0057] Furthermore, as described above, the flow rate of the cleaning liquid L can be controlled by the liquid level sensor S2, liquid level sensor S3, and a flow rate control mechanism using a valve (not shown), thereby controlling the liquid level in the circulating degassing device 10 to be within the range between liquid level sensors S2 and S3. This also suppresses rapid changes in pressure within the internal closed space 1c, thereby suppressing severe foaming.

[0058] Although embodiments and modifications based thereon have been described, the present invention is not necessarily limited to these examples. Furthermore, those skilled in the art will be able to find various alternative embodiments and modifications without departing from the spirit of the present invention or the scope of the attached claims.

[0059] 1 Main body (cylindrical container) 10 Circulating degassing device 11 Ultrasonic vibration unit 12 Window unit 15 Transducer 16 Sealing wall 29 Vacuum device 30 Main tank 50 Ultrasonic cleaning device

Claims

1. An ultrasonic cleaning method for cleaning a workpiece in a cleaning liquid stored in a main tank by applying ultrasonic waves to the cleaning liquid to form a vacuum cavity, comprising: a main tank equipped with an ultrasonic vibration unit; a circulating degassing device that guides the cleaning liquid into a degassed internal closed space, performs degassing treatment, and returns it to the main tank; a recovery pipe that guides the cleaning liquid from the main tank to the circulating degassing device; and a supply pipe that guides the cleaning liquid from the circulating degassing device to the main tank, wherein the flow rate of the cleaning liquid flowing through the recovery pipe and the supply pipe is controlled so that a certain amount of the cleaning liquid is stored in the internal closed space of the circulating degassing device, and the circulating degassing device adjusts the vacuum level of the internal closed space to suppress foaming of the cleaning liquid in the internal closed space while degassing the cleaning liquid.

2. The ultrasonic cleaning method according to claim 1, characterized in that the circulating degassing device has liquid level sensors at two locations, one above and one below the internal closed space, and the liquid volume is controlled so that the liquid level of the cleaning liquid is positioned between the previously detected liquid level sensors.

3. The ultrasonic cleaning method according to claim 2, characterized in that the circulating degassing device has a pressure control valve and controls the pressure in the internal closed space to a constant pressure.

4. The ultrasonic cleaning method according to one of claims 1 to 3, characterized in that the circulating degassing device has an ultrasonic vibrating section on the side of the internal closed space and degassing is performed while irradiating ultrasonic waves from a direction substantially perpendicular to the direction in which the cleaning liquid flows through the internal closed space.

5. The ultrasonic cleaning method according to claim 4, wherein the circulating degassing device has a cylindrical main body portion with its central axis positioned vertically and a side chamber extending laterally from the main body portion, the ultrasonic vibration portion is provided in the side chamber, and ultrasonic waves are irradiated from the side chamber toward the main body portion.

6. The ultrasonic cleaning method according to claim 5, characterized in that the circulating degassing device is cylindrical in shape.

7. An ultrasonic cleaning apparatus for cleaning a workpiece in a cleaning liquid stored in a main tank by applying ultrasonic waves to the cleaning liquid to form a vacuum cavity, comprising: a main tank equipped with an ultrasonic vibration unit; a circulating degassing device that guides the cleaning liquid into a degassed internal closed space, performs degassing treatment, and returns it to the main tank; a recovery pipe that guides the cleaning liquid from the main tank to the circulating degassing device; and a supply pipe that guides the cleaning liquid from the circulating degassing device to the main tank, wherein the circulating degassing device has the opening of the recovery pipe at the top of the internal closed space and the opening of the supply pipe at the bottom of the internal closed space, and a flow rate control mechanism that controls the flow rate of the cleaning liquid so as to store a certain range of liquid volume of the cleaning liquid in the internal closed space; and a vacuum degree adjustment mechanism that adjusts the vacuum degree of the internal closed space so as to suppress foaming of the cleaning liquid in the internal closed space while degassing the cleaning liquid.

8. The ultrasonic cleaning apparatus according to claim 7, characterized in that the circulating degassing device has liquid level sensors at two locations, upper and lower, within the internal closed space, and the flow rate control mechanism controls the liquid volume so that the liquid level of the cleaning liquid is positioned between the liquid level sensors.

9. The ultrasonic cleaning apparatus according to claim 8, characterized in that the vacuum level adjustment mechanism includes a pressure control valve and controls the pressure in the internal closed space to a constant pressure.

10. The ultrasonic cleaning apparatus according to one of 7 to 9, characterized in that the circulating degassing apparatus has an ultrasonic vibrating section on the side of the internal closed space and degasssing is performed while irradiating ultrasonic waves from a direction substantially perpendicular to the direction in which the cleaning liquid flows through the internal closed space.

11. The ultrasonic cleaning apparatus according to claim 9, wherein the circulating degassing apparatus has a cylindrical main body portion with its central axis positioned vertically and a side chamber extending laterally from the main body portion, the ultrasonic vibration portion is provided in the side chamber, and ultrasonic waves are irradiated from the side chamber toward the main body portion.

12. The ultrasonic cleaning apparatus according to claim 11, characterized in that the circulating degassing device is cylindrical in shape.

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