Pedro V. Vasconcelos

Permeability of diatomite layers processed by different colloidal techniques

Abstract Recently, efforts have been directed towards the development of ceramic filters for water treatment systems in which the microstructure is tailored to the application, is well characterised and is reproducible. This work reports on the use of slip and tape casting techniques, as well as a new “direct consolidation technique”, to obtain porous diatomite layers for filtration purposes. Diatomite has been chosen because of its low price, abundance, and intrinsic properties such as high porosity and small grain size. Layers prepared by tape casting and lamination, with a bending strength of 57 MPa, were almost 3 times stronger but less permeable than those produced by slip casting, due to the presence of binders and to the lamination step that promoted particle rearrangement. However, both forming techniques gave relatively low permeable layers due to fine (0.25–0.6 μm) and monomodal pore size distributions. The use of starch granules (30–50 wt%) as pore former and consolidator agents enabled to increase the permeability of sintered bodies for almost one order of magnitude as a result of the increasing amount and average size of pores. As expected, porosity and average pore size values show a direct dependence on the starch content.

Porosity development of diatomite layers processed by tape casting

Abstract The processing from colloidal suspensions is a good method to obtain bodies with low microstructural heterogeneities, by careful control of the interfacial stresses. In previous papers we described the use of slip and tape casting techniques to obtain diatomite porous layers, having controlled morphology such as the amount and size of pores. The present work reports the use of tape casting bodies for filtration purposes. As the maximum thickness of the layers produced by tape casting is about 0.3 mm, their mechanical resistance is very low. It was necessary to produce thicker compacts made by several single layers (up to 20), obtained by thermocompression at different temperatures between 20 and 90 °C followed by sintering at 1200 °C. By selecting a careful heating programme, final bodies with 0.6–1.3 mm thickness were obtained, having porosity levels of about 44% and pore sizes between 0.1 and 1μm. High bending strength values (57 MPa) were obtained, enough to support mechanical stresses in use as a membrane. Permeability to an air flux was evaluated as a function of relevant morphological parameters (porosity, thickness, etc.).

The Importance of Rapid Tooling in Product Development

Rapid Prototyping emerged in 1987 with stereolithography. After a medium growth rate of 22%, it began to decrease in the final years of the 20 th century, in parallel with a growing interest in Rapid Tooling (RT) systems. In fact, the idea behind RT responds better to the growing interest of the industry in reducing the time to market of new products and respective cost. The rapid production of a tool prototype allows the manufacturer to have a better overall control of the new product development process, not only of the product itself visual aids for engineering, ergonomics, and fit but also of the processing technology by having a prototype tool at an early stage of the process. The RT concept is not clearly defined yet, since there are two investigation and development perspectives. One of them is centralized in completely original technologies of directly manufacturing of prototype tools. The other one deals with indirect technologies based on a model manufactured by a RP (Rapid Prototyping) technology. This communication intends to better clarify the classification of the different RT systems and their respective stage of development at the moment.

Mathematical Models for Particulate Filled and Milled Fibre Reinforced Composites

Due to the low price, low density, good dimensional stability and accuracy, ease and speed of processing, and good workability, liquid epoxy resins are frequently considered ideal materials for manufacturing models and prototype tools of certain complexity. The good mixture capacity with other reinforced materials, in particulate or fibre form, leads to composite materials with intermediate properties that result from the combined action of the constituents. Starting from epoxy based systems suited for high temperatures, different dispersed materials, like aluminium particles, milled carbon and glass fibres were added to the polymeric matrix for Rapid Tooling applications. Aluminium is intended to increase the thermal conductivity of the tool, while the milled fibres improve the wear resistance of the composite tool. In this communication mathematical models for mechanical behaviour of these epoxy matrix composites are discussed. The research is essentially focused on the elastic modulus, because the properties related with the material failure are difficult to analyse due to the complexity of the mechanism that controls the failure of polymer based composite materials. Halpin-Tsai-Nielsen and Halpin-Tsai models were applied to the particulate filled and fibre reinforced epoxy systems, respectively. A critical analysis of the mismatches detected between the experimental and the theoretical values allowed us to propose a semi-empirical model more suited to the results obtained. Parameters related with the particle-matrix and fibre-matrix interface influence the mechanical behaviour of the particulate and milled fibre reinforced composites.

Contribution of the Phase-Matrix Interface to the Behaviour of Aluminium Filled Epoxies

Polymeric materials present mechanical and thermal limitations that disable their use in the mould manufacturing. Nevertheless, an adequate selection of the polymeric matrix and the dispersed materials allows the possibility to achieve performances closer to the metals and their alloys. These new materials are attractive solutions for applications that have less demanding mechanical properties, as is the case of the rapid tooling applications where a small number of parts are required. The composites were obtained from a mixture of an epoxy resin with fine and coarse aluminium particles. One can state that besides the dispersed phase resistance overcome the matrix one, its contribution to the global resistance of the composite is restricted, because the fracture surface lies basically in the matrix and interfaces. As the matrix section under load is reduced, with the increment of the dispersed phase, the composite properties turn out to be dependent on the interfaces quality and resistance. This is particularly true when fine aluminium particles are used. The interface contribution to the global composite properties depends basically on two parameters, the binding quality between the matrix and the dispersed phase, and the interface extension per unit volume. This paper studies the main contribution of the phase-matrix interface in the mechanical behaviour of aluminium filled epoxy. Introduction Aluminium filled resins are frequently employed in the area of Rapid Prototyping (RP) and Rapid Tooling (RT) to manufacture moulds for production of small series of plastic parts [1-3]. The strength of these composites is very sensitive to the different phase properties and to the respective concentrations. Furthermore, as shown in this study, the interface also seems to be an important parameter in the composite mechanical behaviour. The adhesive resistance through the interface depends essentially on the extension and quality of the adhesive bonding. The chemical complexity of the epoxy systems and the respective interfacial interactions with the aluminium surfaces represents an extra difficulty in the interpretation of the adhesive bonding mechanism. Different theories are under development to explain the adhesion mechanism, and how it affects the interface resistance [4, 5]. Experimental Two epoxy systems for high (A) and medium (B) temperature (see Table 1) were mixed with aluminium particles of two different classes, fine (F) and coarse (C), with an average equivalent diameter of 45.5 μm (PD 200 grade) and 1400 μm (size distribution from 500 to 2000 μm), respectively (Fig. 1). Eight composites were manufactured, A1 to A4 and B1 to B4. The matrix epoxy system is represented by a letter and the aluminium class by a number (Table 2). The flexural strength and Charpy impact tests were performed according to ASTM D790-02 and D5942-98 standards, respectively. The ASTM D1002-94 standard was used to determine the shear strength of the aluminium-resin interface adhesive bonding. Materials Science Forum Online: 2004-05-15 ISSN: 1662-9752, Vols. 455-456, pp 635-638 doi:10.4028/www.scientific.net/MSF.455-456.635

Stereolitography, the Front Edge of Rapid Prototyping

Based on the annual sales volume, stereolitography (SLA) can be considered a Rapid Prototyping (RP) technology with a promising future. Besides being the pioneering equipment, when RP took the first steps in 1988, this technology has been developed with interesting and fast innovations, and a great activity in patents registration. One can assist to a strong research seeking the enlargement of the system capacity to produce large and micro-size parts, and simultaneously impose the technology as a mass production process that is evolving towards a true Rapid Manufacturing (RM) technology. SLA is an excellent tool to materialize concepts and ideas due to the high-resolution capacity, transparency and fine details of the models and prototypes that can be produced. In this study, the state of art of SLA is analyzed and the recent innovations are presented, and considering that the authors have a considerable experience in supervising design students, from different universities, some of the more emblematic projects that were developed at INEGI – Institute of Mechanical Engineering and Industrial Management, are presented. SLA and direct conversion processes were combined to produce new products in materials such as glass, ceramics and metals, for different industrial sectors.