Continuous and vacuum pre-treatment moulds, valve body deburring and casting sand removal equipment

The truth about vacuum [pre-treatment] ultrasonic cleaning technology.

  • How can we best achieve the desired performance with a correct understanding of the intention for which it was developed – As a developer – I would like to seek to ensure that it is used correctly and not in a customer-focused term [vacuum].

Introduction.

When asked what ultrasonic cleaning equipment we are proud of, I immediately think of our SIRIUS series of ultrasonic oscillators and transducers, which have recently begun to attract attention in the electronic components, liquid crystal and semiconductor industries.Even I, who have grown up in this industry for many years, am deeply impressed when I see the oscillation state of the 50KHz and 800KHz types in this series (they blow up more than 20 cm over almost the entire vibrating surface).I am deeply impressed by the depth of ultrasonic waves and the new age of ultrasonic waves to come (I have been in the industry for many years).Every time I see how powerful and precise it is, I realise the depth of ultrasound and the new era of ultrasound (I call it the fourth generation) that is coming.Slowly but surely, the era of super-powerful 50KHz and 80KHz applications will come.Ultrasonic engineers should be able to understand what this means by looking at the oscillation situation.However, since we are talking about equipment here, we would like to focus on valve body deburring and aluminium die-cast casting sand removal equipment from among the continuous and vacuum [reduced pressure] ultrasonic cleaning equipment that is rapidly becoming popular.

More than ten years ago, a presentation was made at the Industrial Research Institute in Okaya (originally proposed as a cleaning technology for the adhesive part of printed circuit boards as a countermeasure against CFC-113) that placed the object to be cleaned once in a vacuum to remove air from the gaps and surface of the object to be cleaned, thereby improving the effectiveness of ultrasonic cleaning.Of course, a patent application was filed.However, a similar system was subsequently put on the market under the catchphrase “vacuum ultrasonic cleaning”, and since the content differs considerably from the original intent, the word “vacuum” is added in brackets after “decompression” to eliminate misunderstandings.We would like to report on the latest situation with this system.


Water and oscillation conditions at 50 KHz 2400 W2W/cm2

Principle of continuous and vacuum [pre-treatment] ultrasonic cleaning systems.

1.significance of general vacuum [pre-treatment] ultrasonic cleaning

If the shape of the object is complex and air cannot easily escape when placed in the liquid, it must be vacuumed before immersion in the cleaning solution.Air curtains and bubbles in the stop-holes of the cleaned object or surface layers, such as sintered metal, are generated by ultrasound in the vicinity.Not only do they have a significant effect on the shape of the cavity, but they also efficiently reflect the ultrasonic waves themselves and absorb changes in sound pressure, causing the cavity, or its positive and negative shock waves, to be absorbed and mitigated.In other words, it reduces the cleaning effect.Therefore, the majority of precision cleaning with complex geometry essentially falls into the category of this cleaning system.However, as ultrasonic cleaning is still the same in this case, it is almost impossible to control cavitation in a circular cleaning tank.The shape of the cleaning tank, the flow of the liquid and the depth of the liquid must be optimised to enable cavity control, which is a natural basic design condition.The basic conditions for cavity control and tank design are omitted here, as they are not the main topic of this article.Of course, the introduced liquid must be kept stable at the desired dissolved air content, even when exposed to the atmosphere.Ultrasonic cleaning under reduced pressure (vacuum) should only be carried out in limited cases.During ultrasonic oscillation, the pressure must be returned to atmospheric pressure to stabilise the amount of dissolved gas (air) and ultrasonic cleaning must be carried out.Otherwise, the cleaning power of the cavity will be significantly reduced.If they are done correctly, the effect of air can be eliminated and ultrasonic cleaning can be carried out.However, they still have the following drawbacks

2.drawbacks of general vacuum [pre-treatment] ultrasonic cleaning.

As a matter of course, vacuum [reduced pressure] ultrasonic cleaning involves (1) placing the cleaning materials, (2) covering the lid, (3) vacuuming, (4) introducing the degassing liquid, (5) adjusting the liquid depth, (6) returning to atmospheric pressure, (7) ultrasonic cleaning, circulation filtration, continuous degassing and opening the lid.(8) Control ultrasonic waves (9) Drain liquid after cleaning (10) Move cleaned material to the next tank…This is the main basic cycle.In other words, compared to general multi-tank batch washing systems, there are many processes (2), (3), (4), (5), (6) and part (7), (9).The large number of processes makes it time-consuming and appears unsuitable for today’s high-speed continuous cleaning.Even more basic, the cleaned material is released into the atmosphere when it is transferred to the next tank.Vacuum drying is understandable, if costs can be ignored, but vacuum [reduced pressure] washing repeated more than once is unacceptable.Rinsing is as important a process as cleaning and sometimes requires more ultrasonic cleaning power than the cleaning process.An example is the deburring of workpieces contaminated with machine oil.In this case, degreasing cleaning is relatively weak and deburring (rinsing) cleaning requires powerful ultrasonic waves.In other words, vacuum [reduced pressure] ultrasonic cleaning has the disadvantage of not being able to keep up with the high speed of modern technology when trying to make use of its excellent features.Therefore, in November 2003, with the cooperation of the production engineering department of a major automobile parts manufacturer, the author started to develop a continuous vacuum [pre-treatment] ultrasonic cleaning and deburring system that performs high-speed processing while utilising the features of vacuum [reduced pressure].

An overview is given below.

3.successful development of continuous and vacuum [reduced pressure] ultrasonic cleaning equipment and its principles.

The target workpieces of the development are precision-processed aluminium products, such as valve bodies, etc., for cleaning and deburring.The cassette is approximately 750 mm long, 200 mm wide and 200 mm high, weighing approximately 20 kg, with a processing time of 70 seconds per cassette.The process is approximately as follows.

  1. Vacuum [decompression] treatment

    Cassettes fed by a conveyor at a height of 750 mm are taken into the vacuum [reduced pressure] processing tank.There is an opening/closing shutter on the side of the processing tank, and when the cassette is in position, the vacuum shutter on the side opens, the cassette is taken into the tank, and as soon as it is taken in, the vacuum shutter closes to start vacuuming to achieve the desired degree of vacuum.When the desired vacuum is reached, degassing liquid is introduced, and when the liquid depth is the same as that of the next tank, introduction is stopped and atmospheric pressure is returned.This is done in approximately 50 seconds.The vacuum shutters at the boundary between this tank and the next tank are then opened and the cassette is introduced into the next tank through the shutters.This processing tank is called the vacuum [pre-processing] processing tank.

  2. Ultrasonic cleaning tanks (ultrasonic deburring tanks)

    This tank has ultrasonic transducers on both sides of the tank parallel to the direction of movement of the cassette.The cassettes, as well as the target precision-machined parts, come to this ultrasonic tank from the previous vacuum treatment tank by moving through a cleaning solution (e.g. water) without being exposed to air.Once introduced into the ultrasonic chamber, the shutters between the vacuum chamber and the ultrasonic chamber are immediately closed.The ultrasonic transducers located on both sides are generally wide-area simultaneous multiplexed waves with a fundamental frequency of 25 KHz and multiplexed frequencies up to 535 KHz.The fundamental frequency is used to synchronise circuits and phases, to cause simultaneous oscillation and resonance from both sides, to increase the sound pressure of the ultrasonic waves and to increase the shape, size and number of cavities.The sound pressure is set between 15 and 65 V, depending on the target workpiece and frequency.The ultrasonic sound pressure varies depending on the temperature of the liquid, the amount of dissolved oxygen and the fine-tuning of the frequency, which is monitored by our ultrasonic cleaning power meter [U-sonic Tester].Naturally, effective circulating filtration is a must for both cleaning and deburring.After a set ultrasonic time, the cassettes are sent to the next tank.Between the ultrasonic cleaning (or deburring) tank and the next tank there is the same shutter as before, which is opened after the ultrasonic time and the cassette is introduced through it into the next tank.Naturally, the depth of liquid must be the same in the next tank as in the ultrasonic tank.(Although it is the liquid level rather than the liquid depth.)

  3. Rinse, shower tank.

    As soon as the cassette is introduced into the rinse or shower tank, the shutters close.If rinsing ultrasound is required again, the same process as in 2. is repeated.In the case of shower cleaning, the liquid is collected in the storage tank immediately after the shutter is closed, the drainage system is switched and shower cleaning is carried out.This idea is repeated below and will be omitted.One feature of this system is that the height of the cleaning equipment is 1.2 m to 1.5 mm, which is very low despite being automatic, and greatly helps with machine layout and plant safety management.Of course, during cleaning and deburring, if the lid is made of transparent acrylic or similar material, it is possible to look down and observe the inside of the machine.

  4. Significance of continuous and vacuum [pre-treatment] ultrasonic cleaning and deburring equipment.

    Vacuum pre-treatment is essential for future ultrasonic cleaning.In such cases, a shutter is installed on the side of the cleaning tank to separate the vacuuming time from the ultrasonic irradiation time, which is not available in general cleaning, to meet the demand for higher speeds.At the same time, the vertical lifting and lowering mechanism for automated ultrasonic cleaning was eliminated, reducing costs and maintenance points significantly, and automation was achieved through lateral movement, vacuum opening/closing shutters and management of the upper and lower limit movement of the liquid level.The height of the automatic cleaning system has been halved, which is significant.After more than a year of testing, the system is now used in a wide variety of applications as well as in valve body deburring and cleaning equipment.Continuous vacuum [pre-treatment] mould and ultrasonic casting sand removal system.

Continuous vacuum [pre-treatment] mould and ultrasonic casting sand removal equipment.

Powerful ultrasonic waves are irradiated from the outside on aluminium casting parts such as blocks, heads, etc. of automobile engines to remove casting sand from internal cooling water pipes, etc.The cleaning liquid is water.The internal cleaning technology for high-speed circuit (F1) engines and the high-speed deburring technology for valve bodies, etc. described above have been combined to create a new device for removing casting sand from die-cast aluminium such as automobile engines.Casting sand is a mass of air and ultrasonic waves cannot be powerful as it is.Therefore, it is necessary to vacuum the casting sand once to remove the air.Furthermore, engine blocks, for example, have a complex labyrinthine structure inside, and simply immersing them in the sand does not allow all the air to escape.Therefore, vacuum [pre-treatment] treatment is inevitably necessary.The principle is the same as for other continuous types, but the ultrasound is different.The ultrasound is described below.

  1. Ultrasonic oscillator for cast sand removal, transducer 7200Wx2=14,400W 8W/cm2

    After vacuum treatment, the engine blocks and other components are introduced into the ultrasonic cleaning tank, one or two in a row.The ultrasonic transducers are arranged parallel and opposite each other on both sides.One side has 7200 W 4 W/cm2.The distance between the diaphragms is set to the design value and a resonance synchronisation circuit is set up.The frequency is a simultaneous wide-area multiplexed wave that synergises high frequencies up to 535 KHz, based on a frequency of 25 KHz.The tank width, liquid depth, liquid flow and temperature distribution are designed so that cavitation can be generated stably and easily controlled.When oscillated, the system produces a powerful cavitation distribution of 7200 W x 2 units = 14,000 W 8 W/cm2.This ultrasonic wave is not affected by air and causes powerful vibrations in the engine block and also reaches the inside, creating a large spherical cavity (spherical nebula) and removing hard, stuck and embedded casting sand in a short time.Removal time is approximately 2 minutes for two 2000 cc class machines.

  2. Processing of casting sand
    The casting sand is heavy and mostly settles to the bottom of the tank.With the help of ultrasonic vibrations, it is collected in the casting sand storage tank through the drain opening.At regular intervals, the casting sand storage tank is disconnected from the pipework by closing the valve and the casting sand is removed.Depending on the shape, a shower tank is installed in the tank next to the ultrasonic casting sand removal tank and a shower is used to wash away the casting sand that has accumulated relatively low in the wash.

Future of continuous vacuum [pre-treatment] type ultrasonic and casting sand removal equipment.

At present, enquiries and orders for precision aluminium die-casting and casting sand removal equipment are received from home and abroad, and the company is busy with deliveries.Many have been delivered to China, and maintenance is also carried out in cooperation with local suppliers.Unlike conventional high-pressure sprays, even invisible parts can be removed.This continuous vacuum [decompression] type, ultrasonic casting sand removal system is just one example of our powerful ultrasonic applications, but we believe it also shows a new direction for future ultrasonic development.

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