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Ultrasonics Sound technology for textiles and nonwovens

Ultrasonic technologies have developed rapidly, with manufacturing, mixing, slitting, guiding and wet processing options available.

The term ‘ultrasonic’ refers to sound vibrations with frequencies beyond the human hearing range - above 18,000 cycles per second. Everything that makes a sound vibrates, and everything that vibrates makes a sound. But not all sounds are audible. Ultrasound encompasses sound above the human audible spectrum.

The Pinsonic unit uses a heat-producing sonic horn and pin-covered drum to quilt fabric.

Modern ultrasonic generators can produce frequencies as high as several gigahertz (GHz) by transforming alternating electrical currents into mechanical oscillations. Researchers have produced ultrasound with frequencies up to 10 GHz. The upper limit of usable ultrasound frequencies is not yet known. Higher frequencies have shorter wavelengths, which allow them to reflect more readily from objects and to provide information about these objects. Extremely high frequencies are difficult to generate and to measure.

Detection and measurement of ultrasonic waves are accomplished by piezoelectric receivers or by optical means. The latter is possible because ultrasonic waves are rendered visible by the diffraction of light.

Ultrasonics is used in a wide range of industrial and medical applications. These include industrial part washers such as vapour degreasers, jewellery cleaners and non-destructive testing of bolted joints. Ultrasonic energy has been used for mixing of products, such as the homogenisation of milk. Some medical applications include checking blood circulation and heart valves, and fetus examination in pregnant women.

Ultrasonic energy has found extensive use in textiles, nonwovens and their downstream processing. Many of these uses are based on the ability to use ultrasonic energy to induce heat and pressure by vibratory action to join thermoplastic materials. Major uses of these principles for textiles and related products include the following:

• Quilting effects without the use of thread;
• Slitting at speeds of up to 400 feet per minute (ft/min); and
• Seamless sealing at speeds of up to 600 ft/min.

Morrison Berkshire’s Pinsonic machine uses ultrasonic energy to impress a quilted pattern on thermoplastic materials.

Products, suitable fibres

Major textile products produced by these techniques include quilted bedspreads and mattress pads, window shades, vertical blinds, curtains, bias binding and ribbons, protective clothing, disposable diapers, filtration units and woven industrial belting. Consumer products companies like The Procter & Gamble Co., Cincinnati, and Kimberly-Clark Co., Neenah, Wis., use the technology in a wide range of products, including disposable diapers.

According to Dukane Corp, St. Charles, Ill, the fabrics and films best suited to ultrasonic processing contain thermoplastic materials with similar melting temperatures and compatible molecular structures. Other important fabric/film characteristics include a broad melting range, high coefficient of friction, uniform thickness, a minimum of 65 per cent thermoplastic content, and sufficient rigidity and thickness to accept energy at the material interface. Polyester, nylon and polyolefins are considered good materials for ultrasonic applications.

Pinsonic quilting and thermal joining machine

This product was developed by the Textile Machinery Group of Crompton & Knowles Corp (now known as Crompton Corp) in the early 1970s. At that time, Crompton & Knowles was still a producer of weaving machines. Early work on the Pinsonic ultrasonic quilting machine was conducted under the direction of Delmar D Long, director of new product development. He worked very closely with Branson Sonic Power Co of Danbury, Conn, which supplied the ultrasonic components for the early units. The initial trials were made at Springs Mills and Cannon Mills for their quilted bedspread products.

The Pinsonic unit uses a heat-producing sonic horn and pin-covered drum to quilt fabric. Crompton & Knowles transferred the Pinsonic quilting technology to James Hunter Machine Co, North Adams, Mass. James Hunter modified the ultrasonic quilting system by replacing the small patterned disc with a full-width pin-covered roll. The fabric is brought to bear on the pinned roll and vibrated by the sonic horn, producing heat and impressing the quilting pattern on the fabric.

In 1984, Morrison Berkshire Inc, North Adams, Mass, purchased certain assets, including the Pinsonic technology, from James Hunter, which was in bankruptcy.

Jim White, president, Morrison Berkshire, said, "The Pinsonic machine is more than 30 years old, and we are still finding new applications for it. Initially, the units were used only for quilted products for home furnishings, but they are now also used extensively for industrial products. Ultrasonic bonding technology is valuable for making composites of films, fabrics and foams for hospital/medical and filtration products. A major advantage of using the Pinsonic units is that no additional adhesive products have to be incorporated in the product."

Ultrasonic bonding assembles two or more layers of material by passing them between a vibrating horn and a rotary drum, which is often referred to as an anvil. The rotary drum is usually made from hardened steel and has a pattern of raised areas machined into it. Ultrasonic bonding facilitates assembling materials with different melting points without adding any adhesive materials. Morrison Berkshire often uses ultrasonic units made by Dukane for its Pinsonic units.

Ultrasonic Slitting

An advantage of ultrasonic slitting of fabrics and films is a smooth, clean, durable edge produced without discolouration. The sealed edge is tapered without a bead. The geometry of the cutting wheel (anvil), the material and the material’s weight and thickness are factors that influence the speed of ultrasonic slitting.

Mixing of fibre and textile finishes

Sonic Corp of Stratford, Conn, sells its Sonolator high-pressure, ultrasonic homogenising device to emulsify, disperse, blend and de-agglomerate a wide range of materials. Benefits of Sonolator technology include:

• Increased efficiency
• Pressure is 30 to 50 per cent lower than conventional homogenisers;
• Reduced processing cycles
• Process times are reduced and throughput is increased;
• Reduced operating costs - lower horsepower motors reduce energy costs;
• Direct scale-up - scale-up from bench or pilot level is seamless;
• Multi-feed processing - systems can be customised for multiple-stream feeds to create a single emulsion; and
• In-line processing - in-line processing approach means no recirculation.

Sonic has worked closely with fibre lubricants supplier Goulston Technologies Inc, Monroe, NC, to help the company deliver in-line blending systems to the textile industry. Customers include carpet and fibre manufacturers.

Ultrasonic edge detection system

Web and edge guiding systems are used extensively in processing and converting all types of fabrics and films. The earliest systems used vacuum pneumatic sensors, but these systems were troublesome because of process dust and contamination. Incandescent bulb and LED sensors are improvements over the vacuum pneumatic systems, but they require periodic cleaning and replacement due to dirt and dust build-up.

In 1988, AccuWeb Inc of Madison, Wis, patented the digital, dynamically compensated ultrasonic edge detection system. This system uses a process in which the detection signal is monitored by a micro-controller that automatically compensates the guide point for changes in process temperature, humidity, air turbulence and build-up of dust and other contaminating materials. The AccuWeb ultrasonic sensor component is a rugged piezoelectric crystal that is pulsed to create a mini-displacement of air. A similar sensor is used to detect the resultant air signal, converting it to an electrical signal proportional to the lateral web edge position. The signal is amplified and becomes the linear actuator controller input. Ultrasonic edge detectors are available for use in hazardous locations and for temperatures of up to 500øF. The latest AccuWeb Ultrasonic Array Edge Detector, patented in 1999, provides web width monitoring and web width changes of up to 36 inches. Changes can be made without moving the edge detector.

AccuWeb’s edge detectors feature two pairs of ultrasonic sensors for added reliability.

Ultrasonic array edge detectors from AccuWeb Rotary Ring Welder: Using ultrasonics for filter bags

Chase Machine & Engineering Inc, West Warwick, RI, sells a Rotary Ring Welder for the manufacture of liquid filter bags. The material for these filter bags typically is needle-punched polypropylene or polyester fabric. The unit can produce different-sized filter bags. The ultrasonic welding replaces sewing and provides low-cost changeovers in a minimum amount of time with reduced tooling costs.

The Rotary Ring Welder is available in two models. The single-position ultrasonic rotary ring model uses a sonic rotary horn. The filter bag and the plastic ring are mounted on a mandrel. The sonic horn and the mandrel are engaged under pressure, and the sonic horn rotates while the mandrel counter-rotates, thus welding the bag to the ring.

The three-position turret-style system uses the same sonic rotary horn technology. The filter material and plastic ring are unloaded and preloaded in the ready positions. Using a turret system, the rings are then indexed into place for the sonic welding process as described for the single position system. The cycle time for the three-position system is less than 12 seconds for most filter media. Chase uses a single rotary horn developed by Branson Ultrasonics Corp, Danbury, Conn.

Ultrasonics for wet processing of textiles

Investigations have been made into using ultrasonic energy in the dyeing process to seek benefits such as energy savings and reduced processing times, environmental improvements, process enhancements and lower overall processing costs.

Much of this work was undertaken under the auspices of the National Textile Center (NTC) in the mid-1990s at North Carolina State University, Raleigh, NC, and at the Atlanta-based Georgia Institute of Technology. Laboratory work showed that the following phenomena were observed during ultrasonification of a dyebath:

• Localised heating;
• Decreasing aggregation of particles in solution;
• Destruction of the diffusion layer at dye/fibre interfaces;
• Generation of free radicals; and
• Dilation of polymeric amorphous regions.

A major difficulty in commercialising the use of ultrasonic technology in dyeing is that the required high intensities of ultrasonic energy are difficult to produce uniformly in large dyeing vessels.

The most promising areas to further pursue this technology might be in applications where the dyeing is to take place in a compact unit involving relatively small amounts of dye solution, such as continuous dyeing of tow, narrow fabrics, or possibly single ends of yarn. Morko Co, Korea, is pursuing the use of ultrasonic technology for dyeing processing, including jet-dyeing equipment. The components of its Ultrasonic M/C unit for dyeing equipment include a generator, transducer and electronic wire.