50 MCQs on Manufacturing Processes
(Dry & Green Sand Casting, Casting Defects, Die Casting, Continuous Casting, Centrifugal Casting, Gas Welding)
Each question has four options. The correct answer is indicated, followed by a detailed explanation.
Green Sand & Dry Sand Casting
1. Green sand is so named because:
A) It contains green pigments
B) It is used in the green (moist) state
C) It is environmentally friendly
D) It is made from green moulding sand
Answer: B
Green sand contains moisture (usually 2–8%) and is used in the damp/moist condition without baking or drying. The term “green” refers to the unbaked, moist state of the sand.
**2.** The main binder in green sand is:
A) Resin
B) Clay (bentonite)
C) Sodium silicate
D) Cement
**Answer: B**
Bentonite clay (montmorillonite) acts as the primary binder. When mixed with water it develops plasticity and strength, holding the sand grains together.
**3.** Typical moisture content in green sand is:
A) 0.5–1%
B) 2–8%
C) 10–15%
D) 15–20%
**Answer: B**
Optimum moisture is generally 2–8%. Too little moisture reduces strength; excess moisture causes steam defects and reduced permeability.
**4.** Dry sand moulds are prepared by:
A) Using only dry sand without binder
B) Baking green sand moulds to remove moisture
C) Using oil-bonded sand
D) Using CO₂ process
**Answer: B**
Dry sand moulds start as green sand moulds that are subsequently dried/baked (typically 150–300 °C) to remove free moisture, giving higher strength and better dimensional accuracy.
**5.** Compared with green sand, dry sand moulds have:
A) Lower strength and higher permeability
B) Higher strength and better surface finish
C) Lower cost and faster production
D) Higher moisture content
**Answer: B**
Baking removes moisture, increases mould strength, reduces gas defects, and generally improves surface finish and dimensional accuracy, though at higher cost and longer cycle time.
**6.** The primary advantage of green sand casting is:
A) Highest dimensional accuracy
B) Lowest cost and high production rate for small–medium castings
C) Ability to cast very large components only
D) No need for pattern
**Answer: B**
Green sand is inexpensive, reusable, and allows rapid mould making, making it the most widely used process for ferrous and non-ferrous castings of moderate size.
**7.** Facing sand is used:
A) To fill the entire flask
B) Only next to the pattern to improve surface finish
C) As a core material
D) For venting
**Answer: B**
Facing sand (finer, higher-quality mixture) is placed against the pattern surface to obtain better surface finish; backing sand fills the rest of the mould.
**8.** Permeability of moulding sand is important to:
A) Increase mould hardness
B) Allow escape of gases generated during pouring
C) Improve collapsibility
D) Increase green strength
**Answer: B**
During pouring, steam and other gases form. Adequate permeability prevents gas porosity and blowholes by allowing gases to escape through the mould wall.
**9.** Which property is higher in dry sand moulds than in green sand moulds?
A) Collapsibility
B) Dry strength
C) Moisture content
D) Flowability
**Answer: B**
Drying significantly increases dry compressive strength, enabling the mould to withstand the metallostatic pressure of heavier castings.
**10.** Green sand moulds are most suitable for:
A) Very large castings requiring high strength
B) Mass production of small to medium castings
C) Precision investment casting
D) Titanium alloys only
**Answer: B**
The process is economical and fast for high-volume production of components in the small-to-medium size range.
**11.** The main disadvantage of dry sand moulds is:
A) Poor surface finish
B) Higher cost and longer production time
C) Low strength
D) High gas evolution
**Answer: B**
Extra drying/baking step increases energy cost, cycle time, and labour, making the process less economical for high-volume production.
**12.** Which of the following is NOT a constituent of green sand?
A) Silica sand
B) Clay
C) Water
D) Phenolic resin
**Answer: D**
Phenolic resins are used in shell moulding or cold-box processes, not in conventional green sand.
### Casting Defects (Questions 13–24)
**13.** Blowholes are caused mainly by:
A) Low pouring temperature
B) Entrapment of gases in the molten metal
C) Incorrect gating system design only
D) Excessive ramming
**Answer: B**
Gases (steam from moisture, air, or reaction gases) trapped during solidification form round or irregular cavities known as blowholes.
**14.** Shrinkage cavity is a defect resulting from:
A) Gas evolution
B) Volume contraction during solidification without adequate feeding
C) Sand expansion
D) High moisture
**Answer: B**
Most metals contract on solidification. If liquid metal is not supplied to compensate, an internal or external shrinkage cavity forms.
**15.** Cold shuts occur when:
A) Two streams of molten metal meet but do not fuse properly
B) Mould collapses
C) Excess gas is present
D) Pouring temperature is too high
**Answer: A**
If the metal streams cool below the fusion temperature before meeting, they fail to weld together, producing a discontinuity called a cold shut.
**16.** Scab defect is associated with:
A) Expansion of moulding sand
B) Gas porosity
C) Misrun
D) Hot tear
**Answer: A**
When the mould face expands (due to silica phase change or heating) and breaks away, a thin layer of sand is pushed into the casting, forming a scab.
**17.** Hot tears (hot cracks) are caused by:
A) Low mould strength
B) Restricted contraction of the solidifying metal
C) Excess moisture
D) High pouring rate
**Answer: B**
As the casting cools and contracts, if the mould or cores offer high resistance, tensile stresses develop and produce intergranular cracks (hot tears) while the metal is still weak.
**18.** Misrun defect occurs when:
A) Metal solidifies before completely filling the mould cavity
B) Excess metal is poured
C) Mould is overheated
D) Core shifts
**Answer: A**
Insufficient fluidity (low temperature, long thin sections, or slow pouring) causes the metal to freeze before the cavity is completely filled.
**19.** Rat tails and buckles are surface defects caused by:
A) Gas
B) Expansion of the sand surface
C) Shrinkage
D) Core movement
**Answer: B**
Uneven expansion of the mould face produces irregular ridges (rat tails) or larger raised areas (buckles) on the casting surface.
**20.** Inclusion defects are primarily caused by:
A) Foreign materials (slag, sand, oxide) entrapped in the metal
B) High cooling rate
C) Low carbon content
D) Correct gating
**Answer: A**
Non-metallic particles from slag, eroded mould material, or oxides become trapped, forming inclusions that act as stress raisers.
**21.** Which defect is minimised by proper riser design?
A) Blowholes
B) Shrinkage cavities
C) Cold shuts
D) Scabs
**Answer: B**
Risers act as reservoirs of liquid metal that feed the casting during solidification, compensating for shrinkage.
**22.** Pinholes are a type of:
A) Shrinkage defect
B) Gas porosity (small, widely distributed)
C) Sand expansion defect
D) Hot tear
**Answer: B**
Pinholes are very small gas pores, often caused by dissolved gases (especially hydrogen in aluminium) coming out of solution during solidification.
**23.** Shift or mismatch defect is caused by:
A) Improper alignment of cope and drag
B) Excess moisture
C) Low permeability
D) High pouring temperature
**Answer: A**
If the two halves of the mould (cope and drag) are not properly aligned, the casting shows a step or offset at the parting line.
**24.** Which of the following helps reduce gas porosity?
A) High moisture content
B) Good permeability and proper venting
C) Low pouring temperature only
D) No risers
**Answer: B**
Adequate permeability and vents allow generated gases to escape, reducing the chance of gas entrapment.
### Die Casting, Continuous Casting & Centrifugal Casting (Questions 25–37)
**25.** Die casting is primarily used for:
A) Large ferrous castings
B) High-volume production of non-ferrous alloys with high dimensional accuracy
C) One-off prototype castings
D) Sand-moulded steel castings
**Answer: B**
Die casting forces molten metal under high pressure into reusable metal dies, ideal for aluminium, zinc, magnesium, and copper alloys in large quantities with excellent surface finish and tolerances.
**26.** In hot-chamber die casting, the injection system is:
A) Completely outside the furnace
B) Immersed in the molten metal bath
C) Operated only with steel alloys
D) Used for very large castings
**Answer: B**
In the hot-chamber process the gooseneck and plunger are submerged in the molten metal, allowing rapid cycling; it is suitable for low-melting alloys (Zn, Mg, Pb).
**27.** Cold-chamber die casting is preferred for:
A) Zinc alloys
B) Aluminium and copper alloys (higher melting points)
C) Only pure metals
D) Very small components
**Answer: B**
Higher-melting alloys would attack the submerged components of a hot-chamber machine; therefore metal is ladled into a cold shot sleeve for each cycle.
**28.** Continuous casting is widely used for producing:
A) Complex shaped engine blocks
B) Long lengths of billets, blooms, and slabs
C) Artistic sculptures
D) Thin-walled pressure die castings
**Answer: B**
Molten metal is poured into a water-cooled mould and continuously withdrawn as a solidifying strand, which is then cut into desired lengths of semi-finished products.
**29.** The main advantage of continuous casting over ingot casting is:
A) Lower productivity
B) Higher yield, better quality, and reduced energy consumption
C) Ability to cast only pure metals
D) No need for cooling
**Answer: B**
Continuous casting eliminates intermediate soaking and primary rolling steps, gives higher metal yield, more uniform structure, and lower energy use.
**30.** In centrifugal casting, the mould is rotated about:
A) A horizontal, vertical, or inclined axis
B) Only a fixed axis at 10 rpm
C) No rotation is involved
D) Only vertical axis at very low speed
**Answer: A**
Depending on the component (pipes, rings, rolls), the mould may rotate about a horizontal, vertical, or inclined axis; centrifugal force distributes the metal.
**31.** True centrifugal casting is mainly used to produce:
A) Solid castings of complex shape
B) Hollow cylindrical components such as pipes and tubes
C) Flat plates
D) Gears with teeth
**Answer: B**
Metal is poured into a rotating cylindrical mould; centrifugal force throws the metal against the mould wall, forming a hollow cylinder without a core.
**32.** Semi-centrifugal casting is suitable for:
A) Long pipes
B) Symmetrical objects such as wheels and pulleys where density variation is desired
C) Thin sheets
D) Only ferrous alloys
**Answer: B**
The mould is rotated about a vertical axis; denser metal moves outward, producing sound outer sections while the centre can be machined away if needed.
**33.** Centrifuging (centrifuge casting) is used for:
A) Large single castings
B) Multiple small castings arranged around a central sprue
C) Continuous slabs
D) Sand moulds only
**Answer: B**
Several mould cavities are placed radially around a central sprue on a rotating table; centrifugal force assists filling of the cavities.
**34.** Die casting produces castings with:
A) Poor surface finish
B) Excellent surface finish and close dimensional tolerances
C) High porosity always
D) No need for draft
**Answer: B**
Metal dies and high pressure result in fine detail, smooth surfaces, and tight tolerances (often ±0.05 mm or better).
**35.** Which process is best suited for producing long seamless pipes?
A) Green sand casting
B) True centrifugal casting
C) Investment casting
D) Gravity die casting
**Answer: B**
True centrifugal casting is the standard industrial method for cast iron and steel pipes.
**36.** In continuous casting, the mould is usually made of:
A) Sand
B) Water-cooled copper
C) Ceramic only
D) Graphite only
**Answer: B**
High-conductivity copper moulds with intensive water cooling extract heat rapidly so that a solid shell forms quickly.
**37.** A major limitation of die casting is:
A) Low production rate
B) Restricted to relatively low-melting-point non-ferrous alloys and high tooling cost
C) Poor dimensional accuracy
D) Inability to produce thin walls
**Answer: B**
Steel dies are expensive and have limited life with high-melting alloys; therefore the process is mainly used for Zn, Al, Mg, and some Cu alloys.
### Gas Welding (Questions 38–50)
**38.** The most common fuel gas used in oxy-fuel gas welding is:
A) Hydrogen
B) Acetylene
C) Propane
D) Natural gas
**Answer: B**
Acetylene produces the highest flame temperature (~3100–3200 °C) when burned with oxygen, making it ideal for welding steel and many other metals.
**39.** The neutral flame in oxy-acetylene welding has the ratio of oxygen to acetylene approximately:
A) 1 : 1
B) 2 : 1
C) 1 : 2
D) 3 : 1
**Answer: A**
A neutral flame (equal volumes) has an inner cone with a rounded tip and is used for most welding because it neither oxidises nor carburises the metal.
**40.** An oxidising flame is obtained when:
A) Acetylene is in excess
B) Oxygen is in excess
C) Equal volumes are used
D) No oxygen is supplied
**Answer: B**
Excess oxygen produces a shorter, pointed inner cone and is used for welding brass, bronze, and some non-ferrous metals where a slight oxide film is beneficial.
**41.** A carburising (reducing) flame is characterised by:
A) Excess oxygen
B) Excess acetylene (feathery outer cone)
C) Equal volumes
D) Pure acetylene only
**Answer: B**
Excess acetylene produces a luminous feather around the inner cone; it is used for welding high-carbon steels and for hard-facing.
**42.** The temperature of a neutral oxy-acetylene flame is approximately:
A) 1500 °C
B) 2500 °C
C) 3100–3200 °C
D) 4000 °C
**Answer: C**
The hottest part of the neutral flame (just beyond the inner cone tip) reaches about 3100–3200 °C.
**43.** Filler metal in gas welding is usually in the form of:
A) Powder
B) Rod or wire of similar composition to the base metal
C) Electrode with flux coating
D) Solid bar only
**Answer: B**
Bare or lightly coated rods matching the base metal composition are melted by the flame and added to the joint.
**44.** Flux is required in gas welding mainly when welding:
A) Mild steel
B) Cast iron, brass, bronze, and aluminium
C) Only pure copper
D) Never required
**Answer: B**
Flux removes oxides and protects the molten pool when welding metals that form refractory oxides (cast iron, non-ferrous alloys).
**45.** Leftward (forehand) welding technique is generally used for:
A) Thick plates (>6 mm)
B) Thin sheets and plates up to about 6 mm
C) Only vertical welding
D) Only overhead positions
**Answer: B**
In leftward welding the torch moves ahead of the filler rod; it gives good control on thin sections and is the most common technique for sheet metal.
**46.** Rightward (backhand) welding is preferred for:
A) Thin sheets
B) Thicker sections (>6 mm) because it provides better penetration and slower cooling
C) Only aluminium
D) Spot welding
**Answer: B**
The torch follows the filler rod, preheating the joint and allowing higher welding speeds and better fusion on thicker material.
**47.** The maximum thickness that can be conveniently welded by oxy-acetylene gas welding in a single pass is approximately:
A) 1 mm
B) 5–6 mm (beyond this multi-pass or other processes are preferred)
C) 25 mm
D) 50 mm
**Answer: B**
Gas welding is most efficient on thin to medium thicknesses; for thicker plates arc welding processes are generally more economical.
**48.** Flashback in gas welding is:
A) A desirable phenomenon
B) The burning of the flame back into the torch or hoses
C) Formation of slag
D) Excess filler metal
**Answer: B**
Flashback is a dangerous reverse travel of the flame into the torch or supply lines; it is prevented by flashback arrestors and correct operating procedures.
**49.** The inner cone of a neutral oxy-acetylene flame consists mainly of:
A) Carbon dioxide
B) Carbon monoxide and hydrogen (primary combustion zone)
C) Pure oxygen
D) Water vapour only
**Answer: B**
Primary combustion of acetylene with oxygen produces CO and H₂ in the inner cone; secondary combustion with atmospheric oxygen completes the reaction outside.
**50.** Which safety device is essential on both oxygen and acetylene lines?
A) Only pressure gauges
B) Flashback arrestors and non-return valves
C) Only regulators
D) No special devices needed
**Answer: B**
Flashback arrestors stop the flame from travelling back into the hoses or cylinders; non-return (check) valves prevent reverse gas flow, both being critical safety features.
These 50 questions cover the requested topics with accurate technical detail suitable for engineering students and competitive examinations.