Ultrasound turns clothes "ultraclean"

In the effort to improve the performance of appliances, two Japanese companies have hit upon 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. Instead, electrodes on the side of the tub electrolyze the water. An ultrasonic wave generator at the base of the machine uses sonic waves to generate millions of tiny air bubbles to 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 things like shirts, underwear, pajamas, and towels. 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. The 8-kg load capacity washer sells for about $1,100. Currently it is only available in Japan, but Sanyo may consider overseas sales in the future.

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 above 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 bubbles 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 Sharp. Tajima says the company spent three years adapting the technology for a home washing machine.

Sharp's 8-kg capacity washer with the ultrasonic spot washer will be put on the market in November at a list price of $1,125. The company currently has no plans to offer the machine outside Japan.