Ultrasound turns clothes 'ultraclean'

Tokyo—In the never-ending effort to improve the performance of appliances, two Japanese companies have hit on the idea of applying ultrasound to washing machines, though they came up with very different applications of the technology.

Sanyo Electric Co. recently put on sale a washing machine that doesn't require detergent to clean lightly soiled clothes. The machine is fitted with electrodes on the side of the tub that electrolyze the water, and an ultrasonic wave generator at the base of the machine. The ultrasonic waves, which are essentially millions of tiny air bubbles, help loosen grime and grit on clothes in a purely mechanical action.

Electrolyzing the water produces active oxygen, or forms of oxygen such as hydrogen peroxide and ozone, and hypochlorous acid, a mild bleaching agent. Hypochlorous acid kills bacteria while active oxygen dissolves such dirt as the residue of body sweat. Sanyo claims this is enough for cleaning shirts, underwear, and towels soiled primarily by perspiration. Detergent can be used in the machine to clean clothes heavily stained with dirt or grease.

Sanyo claims users can halve the cost of doing normal laundry. Reducing the amount of detergent sent into waste water streams is also environmentally friendly. Currently, the 8kg load capacity washer is only available in Japan.

Rather than applying ultrasound waves on the entire wash, Sharp Corp. chose to use the technology in a spot washer intended to remove rings of dirt from collars and other stains. The Sharp washer features a small ultrasound generator that mounts in an arm positioned over a tray above the washer tub. Users position the stained part of the fabric between the washing head on the arm and a small trough on the tray, something like positioning fabric under a sewing machine needle.

With the trough filled with water, the fabric is saturated. The washer head oscillates up and down 34,000 times per second. On the downstroke, water molecules are pushed away; on the upstroke, cavitation results in cavities in the water. As these cavities combine and explode within the fabric fiber, stain-causing particles are blown away. After treating the stains, the garment is washed normally. The ultrasound arm and tray can be folded away.

"This same principle has been used in washing machines for commercial laundries and for jewelers," says Kazuo Tajima, general manager of engineering for laundry systems for Sharp.

Like Sanyo, the company currently has no plans to offer the 8 kg capacity machine outside Japan.