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9.2 Guidelines

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• Use screws made of materials compatible with joint components, to avoid their separation before recycling (Example 9.8) • Use self-tapping screws for polymers to avoid using metallic inserts

Examples 9.7 Brunel University, UK, has developed special screws made of polyurethane-Shape Memory Polymer (SMP). Its elasticity is very modular and is subject to differentiated temperature (Tg); consequently, these screws can be easily disassembled when exposed to critical temperatures. Example 9.7 Fastening screws made of polyurethane SMP

9.8 Metal screws in plastic materials pose serious recycling problems. If normal depreciation (which effectuates frequent disassembly and re-assembly) does not interfere it is recommended to use thermoplastic screws made of polymers that are compatible with the components.

9.2.3 Engaging Permanent Joining Systems that Can Be Easily Opened It has been said that reversible systems are generally better; if the permanent systems are more convenient, then according to the chosen system the following indications should be taken into account: Rivets: leaves behind contamination marks, when the components are incompatible with each other. Hot riveting: preferable to nailing, because it is less intrusive, being integrated with one of the connecting components. Providing necessary fastening force requires comparatively little material, just using raw force is sufficient for fast separation. Pressurising systems: can pose serious problems for disassembly; separable with physical force. Welding; separable with physical force, though it often occurs that welded components are compatible and in the case of recycling there will be no need for separation.

Design for Environmental Sustainability  

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Design for Environmental Sustainability  

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