This set of Phase Transformation MCQs focuses on “Solidification – Case Studies of Practical Casting and Weld”.
1. The process in which molten metal flows by gravity or other force into a mold where it solidifies in the shape of the mold cavity is known as_____
Explanation: The above mentioned process is known as casting. Part made from casting process is also termed as CASTING this process is carried out in foundry. It can be used to create complex parts, very large parts can be manufactured.
2. Upper half of a mold is known as ______
Explanation: Upper and lower half of a mold is known as Drag and Cope respectively. Gating system in a casting mold is the channel or network of channels by which molten metal flows into the cavity from outside the mold and the riser is a reservoir.
3. Which among the following is not a challenge in determining heat input?
a) Specific may be different for solid and liquid
b) Alloy melt over a range of temperature
c) Significant heat loss to environment
Explanation: The general problems encountered are as follows. Specific heat and other thermal properties of a solid metal vary with temperature, especially if the metal undergoes a change of phase during heating. Specific heat may be different for solid and liquid state. Alloys melt over range of temperatures. Values in eq. for typical alloys are not easily available. There are significant heat losses to the environment during heating.
4. One cubic meter of some alloy is heated in a crucible from room temperature to 100 degree Celsius above its melting point for casting. The alloy density = 7.5 g/cm3, melting point = 800 0C, specific heat = 0.33 J/gC in the solid state and 0.29 J/gC in liquid state and heat of fusion = 160 J/g. How much heat energy must be added to accomplish the heating, assuming no losses? Ambient temp = 25 °C. Density of solid and liquid are same.
a) 4535 * 106J
b) 8735 * 106J
c) 9135 * 106J
d) 7835 * 106J
Explanation: Here the heat energy that should be added is given as = density*V*[Cs(Tm-T] + Hf +Cl*[Tp – Tm]. Cs represents weight specific heat for solid metal, Tm represents the melting temperature of metal, T represents the ambient temperature, and Hf represents the heat of fusion. Tp represents the pouring temperature.
5. A mold sprue is 20 cm long and the cross sectional area at its base is 2.5cm2. The velocity of the flowing metal is given as 198cm/sec. Volume rate of flow?
Explanation: According to the continuity rule the volume flow rate is given as the product of area and velocity, thus the increase in area will result in a decrease in the velocity so in this case substituting the values will give the required answer.
6. A mold sprue is 20 cm long and the cross sectional area at its base is 2.5cm2. Calculate the velocity of the flowing metal at the base of the sprue?
Explanation: The velocity of the flowing metal at the base of the sprue is given as square root of 2*g*H and substituting the respective values will give √2gh = 198.1cm/s.
7. The sprue feeds a horizontal runner leading into mold cavity whose volume is 1560cm3.Find the time required to fill the mold if the volumetric flow rate is given as 495cm2/sec?
Explanation: Here we assume the runner from the sprue base to the mold cavity to be horizontal so that the volume flow rate through the gate into the mold cavity remains equal to v*A at the base. So in this case the time required is given as Volume / Volumetric rate = 1560/495= 3.2sec.
8. In the casting of steel under certain mold condition the mold constant in Chvorinov’s rule is known to be 4 min/cm2.The volume and the surface area of the casting plate is known to be 600cm3 and 760cm2 respectively. Calculate the solidification time?
Explanation: Higher Volume to surface area ratio will cool and solidify slowly than with lower ration. Solidification time for riser must be more than the solidification time for casting. Riser with higher volume to area ratio can lead to solidification of casting prior to riser. Here in this case the solidification time is given as C(V/A)2 = 4(600/760)2.
9. Metal forming can be done in the cold working process. Which among the following is a disadvantage of this process compared to hot working?
a) Surface oxidation
b) Shorter tool life
c) Poor finish
d) Higher forces or power required
Explanation: Here in this case the cold working process gives good surface finish, better tool life and the chance of surface oxidation is very less but the power required or the force required for this process is bit high compared to the hot working process.
10. Which among the following is a property of warm working process?
a) Enhanced plastic deformation
b) Working temperature is more than the melting temperature
c) Higher forces are required
d) Work piece is not ductile
Explanation: In this case, forming is performed at temperatures just above room temperature but below the recrystallization temperature. The working temperature is taken to be 0.3 Tm where Tm is the melting point of the work piece. Enhanced plastic deformation properties (2) lower forces required are some of the major advantages of this form of working.
11. Which among the process is used to create objects of a fixed cross sectional profile?
Explanation: Extrusion is the process that is used to create objects of a fixed cross sectional profile. Extrusion is a compression process in which the work metal is forced to flow through a die opening to produce a desired cross sectional shape.
12. In the case of arc welding find the arc time, if the time for which the arc is switched on is given as 4hrs and the hours worked with that is given as 2hr?
Explanation: It is often measured as arc time (also called arc-on time), that is the proportion of hours worked that arc welding is being accomplished. Arc time = Time arc is on/ hours worked. Productivity is also an issue. So in this case 4/2 = 2hrs.
13. Which among the following is not a part of electrode composition of stainless steel?
Explanation: The electrode composition of stainless steel contains nickel, chromium, carbon, silicon and magnesium, even the phosphorus and Sulphur is present in minor traces.
14. Permanent Mold casting uses two molds that are designed for easy precise opening and closing. The materials behind the making the mold are_____________
a) Nickel and calcium
b) Cast iron or steel
c) Tungsten and steel
d) Plastic material
Explanation: Permanent Mold casting uses two molds made up of steel or cast iron that are designed for easy precise opening and closing. Cavity and gating system is machined in two halves for good accuracy and surface finish.
15. Which among the following is not an example of permanent mold casting?
d) Sand casting
Explanation: Option d is an example of expandable mold casting. Expendable mold casting requires new mold for every casting and permanent mold casting mold can be reused. Permanent Mold casting uses two mold made up of steel or cast iron that are designed for easy precise opening and closing.
Sanfoundry Global Education & Learning Series – Phase Transformation.
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