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2 µm - eTheses Repository - University of Birmingham

2 µm - eTheses Repository - University of Birmingham

The plunger velocity

The plunger velocity of the die casting machine was varied within the range from 0.4 m/s to 4.5 m/s in order to investigate its influence on preform compression behaviour and infiltration quality. At a given velocity, the flow rate was calculated assuming that the melt covered the whole are of the plunger in the shot sleeve. The gate velocity vgate was calculated as: Apl v gate = v pl Equation 44 A gate Where Apl is the surface area of the plunger, Agate the gate cross-sectional area and vpl the velocity of the plunger. In the present system, the preform was infiltrated isostatically from all outer surfaces. Thus the sum of the outer surface areas was used as the infiltration area for calculation of v0 which is defined in 2.3.2. The outer surface area was calculated to be 7.6x10 -3 m² for the standard geometry of 61 mm x 42 mm x 8 mm. The Weber number was calculated using Equation 37, with the surface tension calculated using Equation 1 at a temperature of 700°C, which was the temperature of the melt at the gate during infiltration as predicted by computer simulations (158) . The plunger velocity and the calculated velocities, flow rate and calculated Weber numbers are given in Table 3.8. Table 3.8 Designation and preform infiltration parameters using direct (DSQC), indirect squeeze casting (ISQC) and high pressure die casting (HPDC) at different velocities. DSQC 05 10 20 40 04 09 18 36 Plunger velocity v pl (m/s) 0.017 0.5 1.0 2.0 4.0 0.4 0.9 1.8 3.6 Flow rate dV/dt (10 -3 m³/s) 5·10 -5 1.4 2.8 5.7 11.3 0.6 1.4 2.8 5.7 Gate velocity v gate (m/s) n.a. 1.6 3.1 6.3 12.6 6.0 15.4 30.8 61.6 Superficial velocity v o (m/s) 0.02 0.18 0.36 0.72 1.44 0.07 0.18 0.36 0.72 Weber number We () n.a. 63 252 1008 4030 76 504 2015 8061 85 ISQC HPDC

A graphic presentation of the relationship between the plunger velocity, vpl , and the Weber number, We, is given in Figure 3.12 a). Weber Number number We We() a) b) 10000 8000 6000 4000 2000 HPDC ISQC 0 0 1 2 3 4 86 Superficial velocity v (m/s) 0 0 / m/s 2.0 1.6 1.2 0.8 0.4 Plunger velocity v (m/s) pl pl / m/s 0.0 0 1 2 3 4 Figure 3.12 Weber number and superficial velocity as a function of plunger velocity in ISQC and HPDC infiltration mode: a) relation between Weber number and plunger velocity b) relation between superficial velocity and plunger velocity. Corresponding superficial velocities are marked with arrows. The superficial velocity was adapted in such a way that it would be equal in both infiltration modes, ISQC and HPDC. As the plunger velocities were limited, this target could be reached with only three plunger velocities in the different infiltration modes, as shown in Figure 3.12 b), namely ISQC05 and HPDC09, ISQC10 and HPDC18, and ISQC20 and HPDC36. 3.5. MMC characterisation 3.5.1. Differential thermal analysis Reactions of the final MMC materials after infiltration with alloy IS was investigated by qualifying the calorimetric thermal characteristics using simultaneous thermal differential method (SDTA) (DSC 12E of Mettler-Toledo, Switzerland). In SDTA measurements, the

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