Molded Body Research Articles

Aetiology of Defects in Large Ceramic Moldings

This study is an attempt to identify the causes of defects that appear in large ceramic injection molded bodies after sintering. It asks the question: are such defects established at the injection molding stage or are they caused by the debinding process or by sintering? Moldings with ascending thickness were prepared using a mold cavity with replaceable tool faceplates. Control over pressure during solidification was compared by using conventional molding and a novel molding technique that uses an insulated sprue. The organic vehicle is polyoxymethylene, which can be displaced by catalytic degradation in the solid state. This is a shrinking unreacted core process with a clearly defined reaction boundary in which there is no provision for particle movement in the liquid state. This study tracks the development of defects at each stage and concludes that the defects apparent after sintering have their origin in injection molding, even though they do not mature until a later stage.

Panel for constituting sound insulating wall

A panel for constituting sound insulating wall is provided with a front plate, a rear plate, and a sound absorbing material put between the plates. The sound absorbing material contains reduced plastic products coated with magnetic material such as magnetic tape and magnetic sheet. The front plate is provided on the sound source side and constituted of a plate having numerous holes. The sound absorbing material is composed of a permeable bag and the reduced plastic products in the bag so that the apparent specific gravity and permeation resistance can be 0.05-0.4 and 3-90 dyn.S/cm4, respectively. The reduced plastic products may be reduced plastic products alone not subjected to other processings, or may be a mixture of reduced plastic products and molded bodies of reduced plastic products. Alternatively, only molded bodies of reduced plastic products can be put in the permeable bag. Therefore, an inexpensive panel for constituting sound isolating wall which has an excellent sound absorbing characteristic, a moisture resistance, a water resistance, and a light weight can be fabricated by utilizing plastic products coated with magnetic material such as magnetic tape and magnetic sheet, and particularly scrap of plastic products.

Chemistry of removal of ethylene vinyl acetate binders

The research presented herein has focused on debinding of an ethylene copolymer from a SiC based moulded ceramic green body within an inert atmosphere. Upon heating, the pure polymer undergoes a two-stage thermal degradation process. In the first stage, acetic acid is the only degradation product formed. The effect of the introduction of high surface area powder on the chemistry and kinetics of this first stage reaction was examined. The effluents were captured and analysed in a gas chromatograph/mass spectrometer. The product of the reaction was not altered by introduction of the ceramic powder. However, the kinetics of the reaction were altered. The kinetics of the reaction were determined with the use of thermogravi metric analysis (TGA). The mechanism of mass transport during binder removal was determined by monitoring dimensional changes during binder removal. It was found that one unit volume of shrinkage corresponded with one unit volume of binder removed, indicating that no porosity developed. The escaping acetic acid effluents must diffuse through the liquid polymer filled pores to escape. Bloating was observed in certain conditions and was attributed to the concentration of acetic acid exceeding a critical value, resulting in bubbling.

Numerical Analysis of Residual Stress in Resin-Molded Products. 1st Report. Visco-Elastic Analysis of Stress and Deformation caused by Cooling after the Curing Process.

A computer program to analyze residual stress and deformation, which occur by cooling after the curing process of resin-molded products, is developed. Visco-elastic behavior of the resin is simulated in this program. This program enables simple analysis of the molded body of a complicated three-dimensional shape because (1) it uses approximation with exponential function of the relaxation modulus, (2) it applies this approximation to the creep finite-element method, (3) it uses the effective stress function method. Comparative experiments, using test pieces of molded metals to confirm the performance of this program, showed that the deformation of the test pieces during cooling after curing agreed well with the calculated results.

Structure of PP Structural foam Moldings Made by the Gas-Counterpressure Process

An experimental study was carried out to investigate the gas-counterpressure process by egression of a part of the polymer melt from the core of the molded body towards the accumulator. A systematic study of bubble morphology development and structural parameters of structural foam moldings is reported. The structural foam samples were produced on a two-stage molding machine (SIEMAG Structomat 2000/70) with passively transporting accumulator and on an in-line injection molding machine (KuASY 800/250) with FIFO-type accumulator, the melt temperature being varied in the range 473 to 533 K. The polymer used was isotactic polypropylene into which chemical blowing agent (azodicarbonamide) was added. The structural properties studied were overall density, local density, and density distribution. It was found that the distance from the sprue to the extreme of flow and the melt temperature have a profound influence on the bubble sizes and their distribution. It was established that the use of the two types of accumulator causes remarkable differences in the structural organization of the structural foam moldings.

断熱材用シリカバルーン回収のための温水浮選によるアラゴナイトの除去

Among nearly thirty types of calcium silicate hydrates, hydrothermally synthesized porous xonotlite is being used as fire resistant building material and heat resister. The molded body can be synthesized to have the necessary bulk density, strength and low thermal conductivity. When the porous amorphous silica (silica balloon) is synthesized through the removal of calcium from calcium silicate, the volume of ultrafine pores increases and the heat conductivity is further reduced. But, during the above process beside silica balloon, the needle shaped aragonite is also obtained. Since the aragonite not porous, the thermal conductivity of the slurry becomes five times that of silica glass. Therefore, to improve the thermal insulation aragonite has to dissolved using hydrochloric acid, a method that is costly and also the reuse of aragonite becomes impossible. In this study, we have examined the viability of separating aragonite and silica balloon using flotation and have arrived at the following conclusions.(1) When silica balloon and aragonite were floated separately with sodium oleate as collector, the floatability of aragonite was low and silica balloon did not float at all. But, in the flotation of aragonite-silica ballon mixture increment in floatability was observed in the case of aragonite due to large average diameter of the particle and the floatability of silica ballon also increased due to calcium ion activated surface and consequently the separation became difficult.(2) In the flotation of aragonite only, beside the collector sodium oleate, frother alcohol also was added. The floatability improved when the number of carbon atoms in the alkyl group was more than three. But, in the case of aragonite-silica mixture, silica balloon also floated due to the presence of dissolved calcium ions and the separation was difficult.(3) At the elevated temperatures the solubility of aragonite decreases leading to a decrease in the calcium ion concentration in the suspension. As a result the separation of aragonite and silica balloon becomes possible at temperatures higher than 353 K using sodium oleate as collector.

Interfacial Delamination in Plastic Encapsulated Integrated Circuits (Pics)

AbstractThe reliability of plastic packaged integrated circuits was assessed from the point of view of interfacial mechanical integrity. It is shown that the effect of structural weaknesses caused by poor bonding, voids, microcracks or delamination may not be evident in the electrical performance characteristics, but may cause premature failure. Acoustic microscopy (C-SAM) was selected for nondestructive failure analysis of the plastic integrated circuit (IC) packages. Integrated circuits in plastic dual in line packages were initially subjected to temperature (25 °C to 85 °C) and humidity cycling (50 to 85 %) where each cycle was of one hour duration and for over 100 cycles and then analyzed. Delamination at the interfaces between the different materials within the package, which is a major cause of moisture ingress and subsequent premature package failure, was measured. The principal areas of delamination were found along the leads extending from the chip to the edge of the molded body and along the die surface itself. Images of the 3-D internal structure were produced that were used to determine the mechanism for a package failure. The evidence of corrosion and stress corrosion cracks in the regions of delamination was identified.

金属射出成形で作製したＮｄ‐Ｆｅ‐Ｂ磁石の磁気特性

The Nd-Fe-B alloy powder was kneaded at 283K with the binder of methylcellulose dissolved in water. The mixture was injected at temperature 293K in a die of 353K, which is slightly above the sol-gel transformation temperature of methylcellulose. The magnetic field of 1.35 (MA/m) was applied to produce the alignment of easy magnetization direction of alloy powder in a molded body. The molded body was dehydrated by the vacuum-drying method to suppress the oxidation of alloy powder. By heating it in H2 at 573K for 0.5H, about 80% of carbon in binder was removed, although the oxygen in binder remained unremoved. With the molded body added 2wt% methylcellulose, these treatments can allow to suppress the residual contents of oxygen and carbon in the resulted sintered Nd-Fe-B alloy within less than 9000ppm and 800ppm, respectively. The highest coercive force (iHc) and maximum energy product (BH) m ?? x for a sintered anisotropic magnet prepared by the above mentioned process are 1.10(MA/m) and 287.2(kJ/m3), respectively.

Destruction of Asbestos Fibres by Sintering Asbestos-Volcanic Tuff Mixtures

A new method for the disposal of hazardous asbestos bearing wastes is described; it is based on low temperature sintering of asbestos fibres-unzeolitized tuffs quarry dusts mixtures. Ceramic products similar to grès employable as floor covering both in public and industrial installations, have been produced. Mixtures containing up to 50 wt% asbestos fibres were prepared and moulded by dry grinding and pressing. In spite of the low moisture content, the presence of the fibres produces high strength moulded green bodies which were, without drying, fired at temperatures ranging from 1060 to 1180°C.

The use of overpressure in thermolytic debinding of moulded ceramic bodies

A furnace within a pressure vessel capable of with-standing 0–1 MPa and temperatures up to 600 °C is described. The furnace allows the pyrolysis of injection moulded ceramics to take place at higher heating rates than is possible at atmospheric pressure without defects caused by bloating or cracking. The effectiveness of the method is described for a commercial injection-moulding composition pyrolysed in nitrogen. The various effects of gas pressure on the process are listed and the main beneficial effect is considered to be the increase in boiling point of the polymer-degradation product solution which forms the continuous phase. In the early stages of heat treatment, this allows more rapid mass transport both by diffusion and fluid flow.

Modelling the removal of organic vehicle from ceramic or metal mouldings: The effect of gas permeation on the incidence of defects

A shrinking undegraded core and a porous outer layer result, if the organic vehicle used for shaping ceramic or metal powder mouldings recedes in the interparticle space of the moulded body during pyrolysis. In the present work, a numerical model has been used which simulates the undegraded shrinking core situation and quantifies degradation of the organic vehicle and the diffusion of the resulting products in solution in the organic phase during pyrolysis of a ceramic moulding. This model is extended to include gaseous mass transport in the porous outer layer for a moulding in the shape of an infinite cylinder. The effect of resistance to gaseous mass transport in the porous outer region on defects originating in inner regions was estimated. It is shown that the greatest obstruction to mass transport is diffusion of degradation products in solution in the organic phase. However, the permeability coefficient for gas transport in the outer region begins to affect the critical heating rate required for avoidance of defects only when it is less than 10−15m2.

Microwave debinding of a ceramic injection moulded body

Microwave debinding of a ceramic injection moulded body

Solvent debinding of injection moulded bodies : I. Nanjo et al (Sumitomo Metal Mining Co, Tokyo, Japan)

Solvent debinding of injection moulded bodies : I. Nanjo et al (Sumitomo Metal Mining Co, Tokyo, Japan)

Predicted Bow of Plastic Packages of Integrated Circuit (IC) Devices

In this study, we develop analytical stress models for the evaluation of thermally induced bows in the following two types of plastic packages: thin elongated packages with large chips, known as thin small outline packages (TSOPs), and high lead count large square packages with relatively small chips, known as plastic quad flat packages (PQFPs). In the case of TSOP packages, we consider the package warpage caused by the thermal contraction mismatch of the constituent materials: silicon chip, metal leadframe, and molding compound. The temperature change is assumed to be the same throughout the package. In the case of PQFP packages, we evaluate the bow due to the temperature gradient (non-uniform distribution of temperature) in the through-thickness direction of the molded body The developed models enable one to evaluate the effect of the package geometry and materials properties on its bow, and more importantly, to design a plastic package with a sufficiently low residual warpage.

Shrinkage during removal of organic vehicle from injection moulded aluminum bodies: M.J. Bevis et al, (Brunel University, Uxbridge, UK), Powder Metallurgy, Vol 35, No 2, 1992, 113–116

Shrinkage during removal of organic vehicle from injection moulded aluminum bodies: M.J. Bevis et al, (Brunel University, Uxbridge, UK), Powder Metallurgy, Vol 35, No 2, 1992, 113–116

Relaxation effects in large injection moulded ceramic bodies

Abstract Small cubic samples were cut from various positions within large unfired injection moulded ceramic bodies and thermal expansion in different directions was measured by dilatometry. Dramatic heterogeneities and anisotropies in apparent thermal expansion were observed. Negative apparent expansions were noted in some cases. The results have implications for the way in which local deformation occurs during reheating such mouldings to remove the organic vehicle. Small organised displacements of particles resulting from the relaxation of the organic phase during binder removal may contribute to the defects which appear at that stage.

Calculation of Temperature Distributions during the Solidification Stage in Ceramic Injection Molding

A finite difference procedure for calculating unsteady‐state temperatures in a molded ceramic–polymer suspension during solidification is described. The method incorporates temperature‐dependent thermal diffusivity and enthalpy of fusion of the polymer. An experimental method is used to assess the surface heat transfer coefficient h at the mold wall. It is found that at low injection pressures h varies with time as the molded body shrinks from the wall, but at high injection pressures h can be treated as constant throughout the solidification stage. Using an analytical method, graphical charts are produced for dimensionless temperature as a function of dimensionless time for values of Biot's modulus in the region relevant to ceramic injection molding.

Fibre-reinforced polymer moulded body: Yagi, K. and Mantoku, H. (Mitsui Petrochemical Industries, Ltd, Tokyo, Japan) US Pat 4 894 281 (16 January 1990)

Fibre-reinforced polymer moulded body: Yagi, K. and Mantoku, H. (Mitsui Petrochemical Industries, Ltd, Tokyo, Japan) US Pat 4 894 281 (16 January 1990)

On the removal of organic vehicle from moulded ceramic bodies

The origin of defects in moulded ceramic bodies during pyrolytic removal of the organic vehicle is predicted. The kinetics of thermal degradation of the polymer are combined with a nonlinear, numerical model for the unsteady-state diffusion of degradation products in solution in the parent polymer. The resulting centre concentration of monomer in an infinite cylinder is used to predict the incidence of boiling which results in the formation of internal defects in the ceramic body. The calculation, which incorporates the concentration dependence of the diffusion coefficient based on free volume theory, reveals the outcome of the competition between degradation and diffusion and thus allows the influence of material, geometric and process variables to be explored.

Particle Packing in Ceramic Injection Molding

The shrinkage of ceramic injection molding suspensions caused by pyrolytic removal of the organic vehicle was measured for initial ceramic volume fractions from 0.48 to 0.64. Shrinkage was inversely related to initial ceramic volume fraction V, and maximum volume fraction after pyrolysis V*,max was 0.65. The factors which restrict shrinkage are discussed. The maximum volume fraction, obtained from semiempirical equations relating the viscosity of suspensions to volume fraction of powder (Vmax) was 0.73 to 0.76. Both the viscosity of the suspensions and the shrinkage on removal of the organic vehicle can be interpreted in terms of a free volume of fluid over and above that needed to fill interstices between contacting particles. Thermomechanical measurements also show that the free‐volume concept helps to interpret the transition from fluid to quasi‐solid properties as the organic vehicle is removed by pyrolysis from a molded body.