A new weapon is being developed to help in waste management. It is designed into a product from the start but not called on until its dying moments. Eric Russell discusses active disassembly
AD enables a product to be dismantled into its constituent parts very quickly and easily at the end of its life. An early illustration showed mobile phones being dropped into a tumble drier. The heat and vibration released the fastenings within a few minutes and the sub-assemblies were simply taken out and placed into different containers depending on the way they had to be recycled. In practice, a number of dismantling technologies are suggested for AD.
Dr Joe Chiodo, director of Active Disassembly Research, says smart fasteners could bend back and open under controlled activation as one example, while screw bosses could expand and release a holding screw.
Polymer screws could retract their threads under heat and fall out of their holes. Activation would be triggered by an external stimulus such as microwaves, electromagnetic induction, infrared radiation, vibration, flash heating, chemical application and supercooling. These stimuli change the nature of the target materials, making them do the opposite of what they were originally asked to do. Various smart materials can be used for this non-destructive self-disassembling process, including shape memory alloys (SMA) for actuator devices and shape memory polymers (SMP) for releasable fastener devices. This technique is known as active disassembly using smart materials (ADSM). Dr Chiodo says the company is working on numerous projects in Europe, North America, Japan and China which are confidential. These range from cost-effective working prototypes to negotiations for technology package development and sale. It is also just coming to the end of an EU project investigating the recycling of liquid crystal displays, called ReLCD. It has been calculated that more than 2.5B LCDs are coming up for disposal.
Currently the only methods used to deal with redundant LCD units are incineration and dumping in landfills. Both are expensive and create emissions into the atmosphere. Consequently, the European Commission requests the disassembly of LCDs with an area bigger than 100cm2 in Directive 2002/96/EC.
Other techniques for AD include hot-wire adhesive release, where a thin wire is embedded inside a hot melt adhesive joint. Passing current through the wire heats it, releasing the joint; and polymer coated joining, where components are coated with a thin layer of thermoplastic polymer before polymer welding. Upon heat triggering, the coating melts, releasing the joint.
AD using biodegradable layers and components is based on biodegradable components made of gelatine or starch which melt in the presence of high humidity or water. De-polymerisable polymeric components need high-temperature triggering to unzip the chains of molecules. And smart, or thermally reversible, adhesives are softened by heat, lowering their adhesive strength. Thermally reversible polymers and thermoplastic hot-melt adhesives are also softened by heat. Interposed or interstitial layers use a thin layer or coating sprayed on each component before adhesive or silicon bonding. Upon heating and, optionally, vibration, the layer degrades and loses its strength.
In practice, companies are still investigating ways to incorporate AD into products. But Kodak, for example, has redesigned its single-use camera to facilitate the recycling and reuse of its parts. Cameras are collected at photo development booths and returned to a collection facility that removes packaging, the front and back covers, and any batteries. They have been designed to be recycled at least ten times. Plastic is reground into flake and reused in new products. If batteries are still live, they are used internally for employees' pagers, donated to organisations as gifts-in-kind or sold as recycled batteries. The camera frame, metering system and flash circuit board are reused after testing and cleaning in an ionised-air vacuum system. Old viewfinders and lenses are replaced but many small parts such as wind-on thumb wheels and gears are reused. Well over a billion one-time use cameras have now been collected under the company's worldwide recycling programme.
ADSM has been investigated at Brunel University since the mid 1990s. Last year, researchers achieved disassembly times of 1-2sec using SMP thread-loosening devices on a prototype Nokia 6110 cellular phone. Afterwards, the screws returned to their originally trained shapes without any evidence of having been put through the ADSM procedure. Ideas are being develop by a spin-off company, Active Fasteners.
The prototype phone was disassembled into four sections: printed circuit board, liquid crystal display, covers, and battery. The sub-assemblies would be treated with different technologies for secondary disassembly.
Shape Memory Alloy actuators bend back to open the snap-fits that hold the cover, display and display window in place. The disassembly mechanism is an integrated part of the actual fastening mechanism between the upper and lower covers of the product and acts as a lock. A deforming pin releases a snap fastener, utilising the movement of a programmed SMA. It is activated by heating a stud with a laser, which ensures fast and precise action without any mechanical contact.
An SMA wire is partly coil shaped and connected to the heating stud while a straight section of the wire holds the two covers of the terminal together. The upper cover has a slot where the pin is situated. The lower cover has a snap extension in which the SMA-pin fits in order to lock the upper and lower covers together. When the wire reaches the reaction temperature, the coil shaped area deforms. The straight section of the wire slides off from the snap fastener, releasing the covers.
The special coil form enables creation of a relatively long movement even though the part is small. It is also possible to leave the battery inside the casing without fear of damage because the heat of the disassembly process is both small and localised.
Brunel University and Nokia are part of a larger consortium participating in the EU Framework V Active Disassembly using Smart Materials programme. Nokia says the project identified some limitations and uncertainties that need further development. These include material-related issues such as long-term stability, reliability, availability and release temperature requirements.
Japanese companies are actively is working on ADSM according to a DTI Global Watch Mission of last September. These missions enable small groups of UK experts to visit and learn from leading overseas technology organisations. It found that Sharp has in production one of the first electronic devices featuring ADSM based on shape memory polymer components. The concept is also being implemented by a number of other companies.
Sharp's development is being implemented on a screw fixing for a battery casing.
A shape-memory alloy split-c washer expands when immersed in boiling water
and releases the screw fixing. The technique also appears to be used by the company in some of its LCD screen manufacturing.
Toshiba is also probably carrying out sensitive R&D into active disassembly. These companies obviously regard AD as a technology that will enhance their competitive edge because they are generally unwilling to discuss the subject in any depth. TWI is one of the world's largest independent research and technology organisations and says design for disassembly is still evolving as companies decide how best to meet recycling legislation in the WEEE Directive. The company has invented several AD technologies including a biodegradable circuit board and a reversible adhesive.
Another European project developing AD is Sustainable Electrical and Electronic Systems (SEES) for the automotive sector. Its main objective is to develop sustainable and efficient prototypes and dismantling processes to increase vehicle component reuse rate. The SEES consortium involves ten partners covering car design and manufacture; dismantling and recycling; and research organisations. It has a broad brief that covers software management tools, design guidelines and new recycling technologies as well as the demonstration and application of ADSM.
For more information on active disassembly techniques, visit www.activedisassembly.com, www.activefasteners.co.uk and www.brunel.ac.uk