Ultrasonic Solvent Cleaning Machinery

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On the left: an example of Ultrasonic Cleaning Machine

These cleaning machines, made by a number of manufacturers for film cleaning world wide, work on the principle of "cavitation" similar to low pressure boiling induced by ultrasonic generators. The ultrasonic emissions in warm solvent create large quantities of minute bubbles that contain vaporised liquid. The bubbles are unstable and collapse, releasing energy in the form of shock waves that shock the immersed film and the attached dirt providing an intense surface scrubbing action.

Most modern cleaners run at 50-350 ft per minute, the emersion time is only a few seconds and the subsequent drying time even less. The solvent, now Perchlorethylene, lost to the atmosphere during drying is sometimes recovered from the extracted air. Eventually the solvent bath is so contaminated that it no longer cleans and before this point [in a well run establishment!] the solvent is changed, and in most cases reclaimed by evaporation and redistillation or other recovery methods, and used again.

 There are several manufacturers’ of Ultrasonic Film Cleaners, including RTI in USA, CTM in France, and Lipsner Smith in UK. Some units use a rotary buffer of camel hair brushes or plush, after the film has been immersed in the solvent to lightly scrub the film, to remove loosened dirt and grease, in combination with the ultrasonic generator, and these undoubtedly are more effective without causing any surface damage to the film. However, damaged film even well repaired can be further damaged if sharp projecting edges catch on the buffers and most specialist laboratories have a cleaner without the buffers.

Buffers on a solvent cleaning machine.
Solvent tank is retired to allow access to the buffers

Drying of the film after solvent cleaning is usually carried out by air knives in an enclosed drying tower directed across the film soon after the film leaves the cleaning solution. The knives produce an even drying across the two surfaces of the film and produce no streaking. Air knives are slotted tubes through which emit a stream of clean air and are usually of a designed to extract solvent from the surface by the Venturi effect, a mechanism that reduces the air pressure locally at the surface of the film by the action of an air jet.