Capillary Flow of Hard-Metal Carbide Powder Compounds

Experimental data relating to capillary flow of hard-metal carbide powders compounded with various polymeric binders are presented. Such powder—binder mixtures are used for the production of sintered hard-metal carbide components, mainly by injection moulding. In addition to measurements of their rheological behaviour in a capillary rheometer, the compounds were also subjected to thermo-gravimetric analysis in order to assess the ability of the binder to debind properly. The binder composition was varied from paraffin wax and its combinations with polyethyleneglycols to multi-component binders consisting of polyethyleneglycol, polyethylene, ethylene/vinyl acetate copolymer, and paraffin wax. Two kinds of hard-metal carbide powders differing in particle size distribution (uni-modal, bi-modal) were used. Although the compounds containing the simpler binder types had acceptable flow properties, their debinding behaviour was unsatisfactory. The multi-component compounds exhibited considerably better debinding; their flow was stable within a wide range of shear rates. Flow instabilities appearing at high solids loadings can limit the processability of the compounds used.

Viscoelastic Properties of Flexible Organic Fiber Composites

In this paper, molten high density polyethylene (HDPE) was compounded with four kinds of high performance organic fibers: two types of aramid (KF29 and KF49), liquid crystalline polymer (LCP) and poly(vinyl alcohol) (VF), differing in their chemical structure and fiber lengths. From the SEM pictures, it is observed that shape and size of these organic fibers maintained almost the same even after cutting in pellets, following the mixing process. VF/HDPE and LCP/HDPE systems show generally lower rates of increase of both storage modulus and dynamic viscosity with fiber content than KF/HDPE composites. Comparison of these functions at the fixed fiber content has shown that the most effective parameter, affecting the viscoelastic behaviour of organic fiber filled systems, seems to be their rigidity/flexibility in the molten state. The influence of fiber rigidity/flexibility becomes gradually lower with the increase of both strain amplitude and angular frequency. The parameters of the equations describing relationship between relative values of viscoelastic functions and fiber content were found to be largely dependent on fiber content. Such finding remarkably differs from behaviour of short inorganic fiber filled systems, where these variables maintained constant values.

Rheological and Thermal Properties of a Model System for PIM

Powder injection moulding (PIM) is an important and accepted industrial technique for net shaping of precision components which can have a rather complex geometry. In order to meet the imposed, often rather strict, requirements with regard to dimensional accuracy, it is important to have an adequate knowledge and control of the rheological behaviour and the related processing properties of the powder/polymer melt (feedstock). Such a knowledge is furthermore of crucial importance in numerical simulations of the PIM-process. In the present work, a model system, consisting of steel powder, poly(ethylene glycol) and wax, is used in order to illustrate how the viscometric properties as well as thermal properties, such as the conductivity and the specific heat, of the system can be related to the corresponding properties of the polymeric binder system. In a similar way, the pvT (pressure-volume-temperature)-behaviour of the model system is analysed and discussed. The pvT-behaviour, which has not been extensively reported on for PIM-feedstocks, is considered to be of significant relevance for controlling the outcome of the injection moulding process.