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It is numerically studied the influence of the angular velocity, the molten metal viscosity, and the mold wall roughness on the molten metal distribution in the mold of a horizontal centrifugal casting process. The undesirable raining phenomenon sometimes arises in horizontal centrifugal casting. It occurs when the molten metal rains or falls from the top of the mold to the bottom while the mold is rotating. Using Computational Fluid Dynamics simulations, the conditions for the emergence of the raining phenomenon were explored in this work. For the system considered, angular velocities less than 77 rad/s cause the emergence of the raining phenomenon and accumulation of the molten metal in the lower part of the mold, whereas angular velocities greater than 77 rad/s produce a constant thickness of the molten metal and prevent raining.

Centrifugal casting accounts for 15% of the total casting output of the world in terms of tonnage [

Equiaxed grains are formed during solidification. These grains oscillate with a frequency and amplitude which depend on the rotation rate. The amplitude of oscillation of equiaxed grains decreases with increasing rotation rate and these grains travel backwards with respect to the rotation direction [

Related to numerical modeling, in [

The raining phenomenon sometimes arises in horizontal centrifugal casting. It occurs when the molten metal rains or falls from the top of the mold to the bottom while the mold is rotating [

The influence of the angular velocity, the molten metal viscosity, and the mold wall roughness on the molten metal distribution inside the mold of a horizontal centrifugal casting process is analyzed here. Using the Computational Fluid Dynamics technique, momentum, mass, turbulence, and multiphase model equations were numerically solved. Numerical transient two-phase isothermal simulations were carried out considering axial symmetry in the system. Besides the molten metal and velocity distributions, it were explored the conditions for the emergence of the raining phenomenon.

The Computational Fluid Dynamics (CFD) technique [

In the horizontal centrifugal casting two main forces are involved in the molten metal flow: the centrifugal forces, and the gravity forces [_{c}) and the gravity forces (F_{g}) is a dimensionless parameter commonly known as G-factor (G_{F}) [

G F = F c F g = v 2 R g = R ω 2 g (1)

where v is the peripheral speed (m/s), R is the mold internal radius (m), ω is the angular velocity (rad/s), and g is the gravity acceleration (m/s^{2}). Manipulation of Equation (1) yields an expression to determine the rotational speed:

N = 29.91 G F R (2)

where N is the rotational speed (rev/min). For horizontal centrifugal casting, it has been empirically determined that G_{F} must have a value between 60 and 80 in order to obtain the same thickness of the molten and solidified layers around the mold circumference [

Numerical transient two-phase isothermal simulations were carried out considering axial symmetry in the system. As the work is mainly focused in the molten metal distribution in the mold, to reduce the computer time no heat transfer and no solidification were considered. Time step of 0.001 s was employed in the geometrical system with a mesh consisting of 7300 trilateral elements. Run time of the computer simulations was 10 s. Non-slip condition and rotational motion were assumed as boundary conditions at the mold wall.

Given that axial symmetry is assumed, a two-dimensional slice was considered, as is shown in _{F}. Then,

δ = R − R i (3)

where R_{i} is the internal radius of the molten layer. A mass balance of molten metal inside the mold slice of _{i}:

R i = R 2 − ( α R 2 180 − 2 a ( R − h ) π ) (4)

where the meaning of the angle α (in degrees), the length a, and the molten depth h are clearly indicated in

α = cos − 1 ( R − h R ) (5)

a = R 2 − ( R − h ) 2 (6)

In the numerical simulations it was assumed that value of the mold radius was R = 0.1 m. and the mold rotates counterclockwise. Besides, three values of the angular velocity, the molten metal viscosity, and the mold wall roughness (Ra) were considered, as follows: ω = 50, 60, and 77 rad/s; μ = 0.002, 0.0067, and 0.01 kg/(m.s); Ra = 0, 0.001, and 0.005 m, respectively. The cases considered are shown in

On the other hand, viscosity measures the internal friction forces in a fluid, and in this way represents the opposition of a fluid to flow. Besides, it is well known that the viscosity of a liquid depends inversely, in a non-linear fashion, on the liquid temperature through an Arrhenius-like behavior [

Case | ω, rad/s | μ, kg/(m·s) | Ra, m | v, m/s | N, rpm | G |
---|---|---|---|---|---|---|

1 | 77 | 0.0067 | 0 | 7.7 | 735.1 | 60.4 |

2 | 77 | 0.0067 | 0.001 | 7.7 | 735.1 | 60.4 |

3 | 77 | 0.0067 | 0.005 | 7.7 | 735.1 | 60.4 |

4 | 60 | 0.0067 | 0 | 6.0 | 573.0 | 36.7 |

5 | 50 | 0.0067 | 0 | 5.0 | 477.6 | 25.5 |

6 | 77 | 0.010 | 0 | 7.7 | 735.1 | 60.4 |

7 | 77 | 0.002 | 0 | 7.7 | 735.1 | 60.4 |

Parameter | Value |
---|---|

Molten metal density | 7100 kg/m^{3 } |

Molten metal viscosity | 0.002, 0.0067, 0.01 kg/(m∙s) |

Molten metal surface tension | 1.69 N/m |

Air density | 1.225 kg/m^{3 } |

Air viscosity | 1.7894 × 10^{−5} kg/(m∙s) |

Roughness of the mold wall increases the friction between the molten metal and the mold wall. The most important effects of roughness are the change of the mean velocity profile near the wall and the increment of the adherence of the molten metal to the mold wall [

Phase distribution inside of the centrifugal casting mold was obtained using the cases of _{F} values are, in accordance to [

The effect of the molten metal viscosity on the melt distribution is shown in

In

Finally, ^{−3} m.

Through the CFD technique, the distribution of molten metal and air phases in a horizontal centrifugal casting process was studied. Based on the results of computer simulations, the following conclusions can be drawn:

1) For the system considered, angular velocities less than 77 rad/s, or G-factor less than 60, cause the emergence of the raining phenomenon and accumulation of the molten metal in the lower part of the mold.

2) On the contrary, angular velocities greater than 77 rad/s produces a constant value of the molten metal layer around the mold wall and prevent the emergence of the raining phenomenon.

3) During the initial stage of the process the molten metal viscosity contributes to homogenize the distribution of the molten metal in the centrifugal casting mold.

4) The roughness of the mold wall enhances the uniformity of the molten layer thickness just during the initial stage of the process.

Future work must be done given that heat transfer and solidification were not considered here.

The authors declare no conflicts of interest regarding the publication of this paper.

Barron, M.A., Medina, D.Y. and Reyes, J. (2020) Analysis of Molten Metal Distribution in the Mold of a Horizontal Centrifugal Casting. Open Journal of Applied Sciences, 10, 444-454. https://doi.org/10.4236/ojapps.2020.107031