Guanghong Duan

A review of mechanochemistry applications in waste management

Mechanochemistry is defined to describe the chemical and physicochemical transformation of substances during the aggregation caused by the mechanical energy. Mechanochemical technology has several advantages, such as simple process, ecological safety and the possibility of obtaining a product in the metastable state. It potentially has a prospective application in pollution remediation and waste management. Therefore, this paper aims to give an overall review of the mechanochemistry applications in waste management and the related mechanisms. Based on our study, the modification of fly ash and asbestos-containing wastes (ACWs) can be achieved by mechanochemical technology. Waste metal oxides can be transformed into easily recyclable sulfide by mechanochemical sulfidization. Besides, the waste plastics and rubbers, which are usually very difficult to be recycled, can also be recycled by mechanochemical technology.

Subassembly identification based on grey clustering

Nowadays discarded electromechanical products are more and more common, and have done much harm to the ecological environment, human health and natural resources. In order to recycle discarded products effectively, it is necessary to disassemble them properly in an integrated consideration of economic returns and environmental protection. Therefore Disassembly Process Planning has become a key part in Environmentally Conscious Design. Because there may be a combination explosion when the disassembly process of a product with a large number of parts is planned, subassembly identification is often adopted to divide the product into some reasonable subassemblies. This paper uses a method of grey clustering based on grey system theory to perform subassembly identification. The clustered objects are part pairs with adjacency relation in a product, and the clustering indices consist of energy consumption of disassembly, disassembly time, disassemblable direction and diameter of part pair. The indices can be obtained by detailed estimate or direct input from a CAD system via secondary development. After five grey clusters are set up, their whitening weight functions are presented in detail. Several other key problems in subassembly identification based on grey clustering are also expounded, such as obtaining the nondimensional matrix of sample values, determining the weight of clustering index relative to grey cluster. A heat-sealing machine with 80 components is selected as an example to validate the method of subassembly identification based on grey clustering. The identification result of the example is feasible according to experiences, and at the same time it satisfies the requirement of Disassembly Process Planning.

Disassembly AND/OR graph model for "disassembly for recycling"

There exists combination explosion during the course of modeling of AND/OR graph for disassembly planning for recycling, which makes it nearly impossible to handle a product with numerous parts. To conquer the difficulty, set AND/OR graph (SAOG) is defined, and with the mapping from SAOG to product, complete disassembly AND/OR graph (DAOG) is presented. In order to ensure the validity and applicability of DAOG, several sieves are designed to delete most of the vertexes and edges. These sieves are successively applied to DAOG, and finally the complete DAOG becomes sieved DAOG which is the model used for disassembly planning. DAOG contains all possible disassembly actions, thus it provides a suitable basis for generation and evaluation of all possible disassembly sequences of an end-of-life product.

The Recycle Model of Printed Circuit Board and Its Economy Evaluation

The rational reclamation of the waste printed circuit board (PCB) plays the key portion in the solution of electronic waste. The evaluation of the feasibility and rationality of the reclamation mostly consists of technicality and economical efficiency. Current research inclines to the former factor. And the study on the economical efficiency of the reclamation is insufficient. Thus, this paper presents a new technique of waste PCB recycle, based on which an economical model of the recycle is elaborated. Aiming at the specific conditional of a Hong Kong plant, we perfect the economical model, and make the evaluation of the economical efficiency and feasibility of the waste PCB recycle process conducted by that plant. Finally, we offer quantitative analysis for the rational production of that plant.

Mathematical and Simulation Modelling of Moisture Diffusion Mechanism during Plastic IC Packages Disassembly

Reuse of plastic IC packages disassembled from printed circuit boards (PCBs) has significant environmental benefits and economic value. The interface delamination caused by moisture diffusion is the main failure mode of IC packages during the disassembling process, which greatly reduces the reusability and reliability of disassembled IC packages. Exploring moisture diffusion mechanism is a prerequisite to optimize prebaking processes before disassembling that is an effective way to avoid the interface delamination. To this end, a computational model with variable boundary conditions is developed based on the different combination state of water in IC packages. The distribution characteristics and mechanism of moisture diffusion behavior are analyzed including the humidity distribution field and the relation among baking temperature, water loss rate, and baking time during baking process, and then the results are validated by FEA simulation based on the improved definition of relative moisture concentration. Baking under variable temperature is proposed and compared with the baking process and baking efficiency under constant temperature to find out the optimized baking parameters. Finally, a set of curves which indicate the relation between baking energy consumption and temperature are determined under actual industrial baking experiments, which could be used as references to develop industrial standards for PCB disassembling process.