Guidelines for designing for disassembly and recycling

Transcription

1 1 de 10 Guidelines for designing for disassembly and recycling Tracy Dowie & Matthew Simon Design for Environment Research Group Department of Mechanical Engineering, Design and Manufacture Manchester Metropolitan University DDR/TR18 September 1994 Abstract: Future legislation may make it important for products to be designed to facilitate recycling in some form when they reach the end of their lives. The types of recycling which may take place are product or part reuse, product repair, product or part recycling (through disassembly) and material recycling (by shredding the product). Different organisations will instruct their designers in different ways to enable them to successfully carry out this task and maximise the amount of the product which is effectively and economically recycled. One design tool which could be employed in such a situation is a set of design guidelines. This paper illustrates those guidelines developed by Manchester Metropolitan University and design examples are given for a number of them. The importance of these types of guidelines is shown and ways in which they can be applied is given. Future design scenarios are also discussed. Index 1. Introduction 2. Guidelines 3. "Make subassemblies and inseparably connected parts from the same or a compatible material" 4. "Minimise the amount and number of wires" 5. "Locate parts with the highest value in easily accessible places" 6. "Eliminate incompatible labels on plastic parts" 7. Discussion 8. Conclusions

2 2 de References 1. Introduction The research at Manchester Metropolitan University in the Department of Mechanical Engineering, Design and Manufacture has been concerned with the design of products to facilitate disassembly and recycling when they reach the end of their lives. Areas which have been examined include the way in which products can be rapidly disassembled and the materials and parts reused, repaired or recycled as appropriate. Ways have also been considered to assess product designs for their ease of disassembly and ability to be recycled. The other main area of the research has been to establish a set of guidelines which could be used by designers to ensure that products are designed to meet the requirements for disassembly and recycling. It is these guidelines, and the product development environment in which they are used, which are discussed in the paper. 2. Guidelines As designing for disassembly and recycling has gained more recognition so a number of organisations have devised their own sets of suitable guidelines to design practice. A comprehensive examination of designing for ease of recycling has come from the German Standards organisation VDI, in the form of VDI 2243 [Ref 1]. This is a standard on the design of technical products for ease of recycling and was published in October In this document the guidelines are classified into three distinct stages of recycling: recycling during production, recycling during the use of the product and recycling after the use of the product. The main aim of recycling during production is to minimise waste and enable material to be recycled without any adverse effects on the environment. Recycling during the use of the product is defined as reconditioning a product in order to extend its life in service and is further divided up into; dismantling; cleaning; inspecting and sorting; component reconditioning and assembly. Recycling after product use aims to recycle as much of the material as possible and also to maximise the value which can be gained when the product is recycled. Other organisations have produced their own guidelines such as ICER (Industry Council for Electronic Equipment Recycling) in the UK [Ref 2] who

3 3 de 10 are trying to promote recycling of electronics goods. The guidelines developed at Manchester Metropolitan University have also been classified according to three areas of the product design: materials, fasteners and connections and product structure. This table lists 25 guidelines divided between the three areas. The guidelines are not all distinct; many are actually dependent on each other. The following table gives the classified guidelines. A. Materials Reason for guideline 1. Minimise the number of different Simplify the recycling process. types of material. 2. Make subassemblies and Reduce the need for disassembly and inseparably connected parts from the sorting. same or a compatible material. 3. Mark all plastic and similar parts Many materials' value is increased by for ease of identification. accurate identification and sorting. 4. Use materials which can be Minimise waste; Increase the end-oflife value of the product. recycled. 5. Use recycled materials. Stimulate the market for recyclates. 6. Ensure compatibility of ink where Maintain maximum value of printing is required on plastic parts. recovered material. 7. Eliminate incompatible labels on Avoid costly label removal or sorting plastic parts. operations. 8. Hazardous parts should be clearly Rapidly eliminate parts of negative marked and easily removed. value. B. Fasteners & Connections 9. Minimise the number of fasteners. Most disassembly time is fastener removal. 10. Minimise the number of fastener Tool changing costs time. removal tools needed. 11. Fasteners should be easy to Save time in disassembly. remove. 12. Fastening points should be easy to access. Awkward movements slow down manual disassembly.

4 4 de Snap-fits should be obviously located and able to be disassembled using standard tools. 14. Try to use fasteners of material compatible with the parts connected. 15. If two parts cannot be compatible make them easy to separate. 16. Eliminate adhesives unless compatible with both parts joined. 17. Minimise the number and length of interconnecting wires or cables used. 18. Connections can be designed to break as an alternative to removing fasteners. Special tools may not be identified or available. Enables disassembly operations to be avoided. Many adhesives cause contamination of materials. Flexible elements slow to remove; copper contaminates steel, etc. Fracture is a fast disassembly operation. C. Product Structure 19. Minimise the number of parts. Reduce disassembly. 20. Make designs as modular as Allows options of service, upgrade or possible, with separation of functions. recycle. 21. Locate unrecyclable parts in one Speeds disassembly - see no.8. area which can be quickly removed and discarded. 22. Locate parts with the highest value Enables partial disassembly for in easily accessible places. optimum return. 23. Design parts for stability during Manual disassembly is faster with a disassembly. firm working base. 24. Avoid moulded-in metal inserts or Creates the need for shredding and reinforcements in plastic parts. separation. 25. Access and break points should be Logical structure speeds disassembly made obvious. and training. Table 1: Design guidelines for disassembly and recycling Few designers would find these guidelines unreasonable and many have commented that they would work to such rules if only the product

5 5 de 10 specification allowed them enough freedom. The difficulty of using such a table is in prioritising the conflicting issues. It is necessary to have some idea of the likely fate of a component, and even of the whole product, before a decision can be made. However, few companies have a product development strategy that feeds this type of information into the product specification. Some life cycle analysis (or at least awareness) will be needed, for example, before the environmental costs of reprocessing material can be judged against the benefits of recovery. We will return to this issue after some further examples. We have selected four examples to illustrate the application of the guidelines and the conflicts that arise. 3. "Make subassemblies and inseparably connected parts from the same or a compatible material" Most complex products have a mixture of different materials which often cannot be recycled together. This invariably results in a large amount of disassembly being needed in order to separate the materials and facilitate recycling. However often the quantities of separated materials are too small to be economically recycled and so costly disassembly does not result in all the product being recovered. This needs to change if the profit gained from a product is to be maximised and disassembly and recycling is to be made more attractive to companies. An example of one product where the mixture of materials has caused problems for recycling is an upright vacuum cleaner. The main body of the vacuum cleaner was made from ABS whilst the hose hook on the body was made from "Triax", an ABS/Nylon blend, which contaminates the ABS and so prevents its recycling. The hook was made from this material because the hose is covered in PVC, from which the plasticiser will migrate into ABS and make it brittle. Unfortunately removal of the hook was difficult and so the value of the body part was reduced. The solution in this case is to redesign the hose in a material such as flexible polyethylene. The same material incompatibility problem arose in this product with the co-moulding of a PVC bumper onto an ABS part. This was done for valid designfor assembly reasons: flexible parts are slow to assemble.

6 6 de 10 However, a new design maintains function but allows the co-moulded assembly to be recycled as one material. 4. "Minimise the amount and number of wires" Often products which contain large number of electrical and electronic parts also contain large quantities of wiring to connect all these components. This is due to part arrangement by mechanical function or shape rather than electrical connectivity. If the chassis of a product such as a photocopier is made from steel, it is preferable to remove as much of the copper wiring as possible if the steel is to be recycled as the highest possible grade. This is because there are maximum quantities of copper allowed in all grades of steel. The copper wire removed from the steel can be sold for recycling but the proce is low because of the PE/PVC coating and quantities are not large enough to offset the cost of disassembling. It is therefore necessary to design products which have as little traditional wiring as possible. One way this can be done is to locate parts close together that need to be connected with a wire; more adventurous solutions include using pre-wired assemblies, printed flexible wiring elements and other methods which simplify the loom. If wires are carrying signal voltages only they may be replaced with other communication techniques such as optical fibres. 5. "Locate parts with the highest value in easily accessible places" One of the aims of disassembly is to carry out the optimum amount of disassembly in order that the revenue gained from recycling the parts is greater than the cost of carrying out the operations. Often the costs exceed the revenue; this is because of the low value many materials have when they are recycled and also because disassembly is often awkward or difficult. However, many products do have particularly valuable parts such as transformer or electric motors, these types of parts offer a great incentive to disassemble and recycle a product at the end of its life. Unfortunately these types of valuable parts are often buried deep within a product and access to them is not easy. In many cases, once the parts have been removed any recycling value that they may have has been cancelled out by the costly disassembly which was needed to access them.

7 7 de 10 The following table gives typical disassembly times, costs and revenues in the UK scrap market for selected products. Note that the revenue from sale of materials is very variable. Market prices change; currently polymer prices are low. An increase in these (at the time of writing, ABS prices are rising) will improve the profitability of many of the products illustrated. Product Disassembly Time Cost* (min) ( ) Materials Revenue ( ) Computer keyboard (soldered) (membrane) DDR concept study Telephone: BT ** Viscount BT Relate U.S. GEC Featurephone Vacuum cleaner cylinder - upright Car heater fan unit Car air-con heater/cooler Gas cooker *** Photocopier (partial dis.) (full disassembly) n/a An example of a product which suffers from having some high value parts in inaccessible places is a desktop photocopier. The product contains electric motors and transformers which are valuable but access to them is difficult and time consuming, since they are non-maintainable items placed deep in the product structure. There is also an counter-example. A cylinder cleaner which contains an electric motor is an example of good design for disassembly practice. The

8 8 de 10 valuable motor can be accessed by simply opening a catch and then removing five screws. The total time for these disassembly operations is approximately 50 seconds, enabling partial disassembly of this cleaner to be more profitable than full disassembly. This then opens up the option of incinerating the (possibly dirty) polymer fraction for its energy content after recovery of the copper-containing motor. 6. "Eliminate incompatible labels on plastic parts" Labelling of products is often desirable for consumer information, batch differentiation or it may be required by legislation. The first choice for polymer casings is to use either moulded-in legends and/or compatible ink printing or paper labels with compatible adhesive, since they can be separated on an air table after granulation. However, a snap-in panel, or (cheaper) a thin section of casing that can be knocked out is an alternative. The knock-out would incur a disassembly time of a couple of seconds (the same as an average screw) since it would be one operation with a tool. Of course, it will work better in some polymers than others: there may be difficulties with PP or PVC in obtaining a clean break. It is a recognised DFD technique and can be used to eliminate a welded-in threaded insert, for example. A recent initiative by ICER in the UK has led to an agreement by BABT, the telecommunications equipment approval board, to relax its requirements on labelling of telephones and similar equipment. Previously, labels specified by BABT were of PVC-coated paper and incompatible with typical phone casings of ABS. A UK recycling company will in future be spared the cost of manually scraping labels off old telephones! 7. Discussion If future products are to be easier to disassemble and recycle designers must consider these problems early enough in design. It will not be possible for one product to conform totally to all guidelines as there are always other criteria which have to be considered in the design process, such as design for assembly and manufacture as well as cost considerations.

9 9 de Conclusions Although it is believed that these guidelines cover the majority of design problems that may prevent a product from being disassembled and recycled it is important that observations continue to be made during practical disassembly work to ensure that there are no further guidelines that must be included. The work on these guidelines is continuing but is now concentrating on developing them into a design assessment tool. The tool aims to enable a design to be assessed in the terms covered by the guidelines and result in it being given some overall score for its ease of disassembly and ability to be recycled. The assessment should also highlight those areas of the design that do not conform to guidelines listed above. In the future if products are to be recycled quickly and effectively disassembly will be needed, however, this can only be achieved if disassembly and recycling is considered early in the design process either in the form of applying appropriate guidelines as outlined earlier or a similar design tool. 9. References 1. VDI, Design of Technical Products for Ease of Recycling, VDI 2243, May ICER, Guidelines:Design for Recycling:General Principles, November Simon, M & Dowie, T "Objective assessment of designs for recycling", WKD ICED 93, The Hague, The Netherlands, August See, for an introduction, Turner, R K, Pearce, D & Bateman, I "Environmental Economics", Harvester/Wheatsheaf 1994, or the original "Blueprint for a Green Economy", D Pearce, Earthscan, London, Baraf L, "Expert system for DFE", in "Design for environment workshop", ETH, Zurich, 31/10/94. Back to top About People Courses Projects Publications Links Home

10 10 de 10 Design for the Environment Research Group Department of Mechanical Engineering, Design and Manufacture Manchester Metropolitan University John Dalton Building, Chester Street, Manchester M1 5GD, UK URL: Last updated 26 September, 1997