Ultrasonic cleaning in industrial parts cleaning applications

Using ultrasonic waves is a mechanical cleaning that is very efficient while also being very kind to the surface getting cleaned.  An ultrasonic transducer creates an ultrasonic field (a field of areas with periodically alternating over- and low-pressure).  The pressure changes caused by the presence of this field have a significant impact on the cleaning procedure.

During the low-pressure period, so-called cavitation bubbles get formed; these bubbles collapse rapidly once the pressure returns to its nominal level.  These microscopic high-energy implosions occur immediately at the surface of the workpieces, even in regions that are difficult to access.  As a result, the contamination gets blasted away.  The resulting collision pressure is around 1000 bar.

Many manufacturers of parts cleaning equipment use a rod or tube-type transducers.  These are quick and easy solutions for parts cleaning machine producers but do not always represent the most effective and efficient ultrasonic cleaning method.  Unfortunately, the tube-type transducers radiate energy around a full 360° putting energy into areas like the wall of the process chamber.  This undirected energy can ultimately lead to weld fractures and leaks in poorly designed or constructed chambers, as seen in this image taken from outside a process chamber.

Compared to the typical rod-type push-pull transducers, the single elements that Karl Roll prefers to use in their single-chamber plants offer the benefit of an optimal alignment of the ultrasonic field on the workpieces and longer service life.  Karl Roll attributed this advantage to the construction of the single elements from a single piece of material.  The typical ultrasonic frequencies used in part cleaning are 25 – 40 kHz, though special applications may require different frequencies.

Karl Roll took the time to understand ultrasonic cleaning technically and then developed a design suitable for operating in a vacuum.  The Karl Roll design ensures ultrasonic energy gets directed into the middle of the process chamber and not in the body of the chamber.  In doing this, lower energy levels can get deployed whilst still achieving the same cleaning effect.  Known in-house as the hockey puck design, the ultrasonic elements are a round Ø50mm dia disk, around 15mm thick, as seen in this image.

The advantages of individual ultrasonic elements are as follows:

  • Uniform radiation directly towards to parts to be cleaned provides maximum efficiency
  • No reflection sheets are required to guide sound back, leading to possible rotary-directed radiation resulting in wear, loss of efficiency and potential weld fractures.
  • Ultrasonic power per element is only approx. 70 W by this low mechanical power of the transducer (lifetime)
  • in the event of a defective US element, systems only lose 70W rather than 1000-3000W of a single tube type transducer resulting in minimal impact on the overall cleaning capacity of the parts cleaning machine.