The evolution of ultrasound for metal cleaning

In Italy we find ultrasounds from the beginning of the late 50s, they were imported from United States.

The generator was built with the technology of that time, using thermionic valves both for control circuits that for power circuit.

The box that contained the generator was very big and very heavy. That generator stoked a magnetostrictive transducer built of treated nickel foils blocks, welded at about 700°C  on an stainless steel foil in 6.35 mm (1/4”) in thickness.

Bendix owned this technology and  Italy had a licence to product of it.

At that time it was used for the pieces cleaning , above all in the galvanic industry.

It was so successful that other operators imported from USA other ultrasonic systems whose transducer, even if it was built in a different way, used nickel to exploit its magnetostrictive characteristics.

Bendix evolved introducing, in the late 60s, a controlled diode (SCR) generator and transistors circuits of control. The transducer kept the previous technology. The number of installations kept growing and found application in many industry sectors.

Nothing changed until the late 70s, when piezoelectric transducers appeared, they were cheaper and more productive. New generators, combined with piezoelectric transducers, could realize  ultrasonic cleaning tanks even very big.

Many firms, thanks to the huge number of applications, entered the market with  ultrasonic groups (generators and piezoelectric transducers) very similar between them, installed on metal cleaning plants and in the cleaning tanks of the galvanic industry.

We lived ultrasonic evolution directly, from the late 60s.

We could check on the field advantages and disadvantages of the existing products and we wanted to produce something innovative concerning both the cost of the equipment and the efficacy.

We set up an applied research program to realize ultrasonic equipment at low price and high performance.

At first it was necessary to measure the efficacy of  ultrasounds in the cleaning tanks; in lack of measures it is impossible to control any physical size, even the cavitation developed in ultrasonic tanks.

The check method is empirical and it avails itself of an aluminium sheet as check object; if the sheet is broken into from the cavitation it means that it works.

Nevertheless this system, where sure parameters, such as material ( aluminium or its alloys),  sheet thickness, position of the sheet into the tank, time of exposition, temperature of the solution in the tank, number of the holes on the sheet after the exposition to the cavitation, dimension of the holes, etc. etc., miss has never provide sufficient results. 

After a long work we produced the measure instrument of the cavitation and we called it cavitometro.

Thanks to the cavitometro we started measuring the cavitation intensity present in the ultrasonic tanks to verify which was the right power of ultrasounds according the tank volume.

The ultrasonic sizing has always been made in Watt/litre ,convinced that there was a direct relation between the applied power, the cavitation intensity and the tank volume.

This concept has blocked the possibility of installing the ultrasounds in very big tanks, because it would have been very expensive.

Let’s imagine a 10,000 litres tanks where, to obtain a good cavitation, are necessary 8 Watt per litre of water; 80KW of ultrasounds should be necessary and it  would imply a huge buying cost and a big electric energy use. Even the noise of the installation would be unacceptable.

Thanks to the cavitometro we started working on the transducers and on the generator to check if it was possible to size in a different way  the ultrasounds power.

In the end we did it. We do not size the ultrasounds in Watt/litre, but in an other and more technologic method.

Equally we can say that for big tanks  our sizing can be  made in about 2/3 Watt/litre even if, we want to point it out , it is not a value comparing to what our competitors affirm.

Our technology enable us to obtain the same cavitation in tanks of little volume (10/15 litres) as in tanks of big volume (5,000 litres and more).

The advantage of this result is immediately evident; it is possible to carry out experimental tests of washing on tanks of little volume ( measuring the intension of cavitation) to realize after the real plant, checking that there is the same intensity of cavitation of the tank used for the test.

Thanks to our technology it is possible to face the problem of metal cleaning in a technically rigorous way and sure.

Our ultrasonic groups

Our generator, produced in double version ,one is a microprocessor, has the digital control of the resonance of the transducers and it allow us to stoke the transducer always in the better conditions, keeping it “normally on”, while that of our concourse , in some chances, keep the transducer “normally off”.

That’s one of the reasons why we can avoid the sizing in Watt for litre of water.

Further on the generator does not create a low frequency noise which takes, if persisting, to an increase of about 3 dBA of acoustic pollution produced (every 3 dBa the noise level doubles).

The microprocessor version can be associated to the cavitometro and it obtains unimaginable results with other systems.

The equipment automatically  provides to show when the liquid is de-gassing, to furnish alarms, to modify the working parameters in function of the noticed cavitation, to stoke the transducer on multi frequency; it also allow the operator to plan out the modulation parameters, frequency gaps etc. The generator and the cavitometro can be connected to a management system which check the operation of the generator .It can also modify its parameters.

Even our transducer is very particular and it is characterised of an high efficiency.

This result as been obtained operating on the piezoelectric baked clay choice, on the mechanical precision during the construction of metallic parts, in the calibration of every block using an instrument that we realized.

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