EVA/beeswax binder

This chapter focuses on the apphcation of polymers in the formulation of binder blends for MIM. A brief summary of the different classifications of binder blends is presented. The rheological, thermal and mechanical properties of a feedstock with EVA/beeswax binder is discussed to highlight the influence of binder-powder interactions on these properties. 

Figure 7 shows a plot of viscosity versus shear rate for a MIM feedstock (58 vol. % carbonyl iron powder with EVA/beeswax binder) for 130, 150 and 170 °C. It can be observed that within the range of shear rate investigated, the feedstock exhibited shear thinning behavior. 

Figure 12 shows the shear stress versus shear rate plot of a feedstock (58 vol% carbonyl iron powder with EVA/beeswax binder) at various temperatures. As the slope of the curves represents the viscosity of the feedstock, it can be observed that the viscosity decreases with temperature. 

Figure 13. Arrhenius plot for feedstock (58 vol. % carbonyl iron powder with EVA/beeswax binder) at 0. Is shear rate.

Figure 30. SEM micrograph of tensile fractured surfece of carbonyl iron powder feedstock with EVA/beeswax binder. (X 4,000)...

Foong et ai [23] showed that yield stress is dependent on temperature. Figure 14 shows the variation of yield stress with temperature for three carbonyl iron powder feedstocks. Feedstocks No. 2, 3 and 4 contained binder with EVA/beeswax ratio of 40/60, 60/40 and 70/30 respectively. It can be observed that yield stress decreases non-linearly with increasing temperature. This observation contrasted the views of Malkin [50]. He proposed that the yield stress of a filled polymer melt is independent of temperature. However, as there were neither actual experimental data nor references nuoted the nrono-sal was difficult to be verified. 

Figure 16 shows a plot of viscosity versus shear rate data for carbonyl iron powder feedstocks with different binder composition. The binders are composed of EVA/beeswax in proportions of 40/60, 60/40 and 70/30. It can be observed that as the EVA content in the binder is increased, the viscosity is increased accordingly. 

Figure 23. DSC output for binder containing 40/60 ratio of EVA/beeswax.

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