Riser Design MCQ Quiz in తెలుగు - Objective Question with Answer for Riser Design - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

Concept:

For optimum cylindrical side riser (h) = 2r

The time of solidification should be higher in riser than in casting.

\(\Rightarrow {\left( {\frac{V}{A}} \right)_{riser}} \ge {\left( {\frac{V}{A}} \right)_{casting}}\)

Calculation:

Given side of cube = 10 cm;

⇒ Volume of cube = 10³ cm³;

Shrinkage volume = 5 % of volume 

Riser volume = 3 × shrinkage volume;

⇒ Riser volume = 3 × 0.05 × 10³

Riser volume = 150 cm³ = πr²h        -----(1)

Now,

\({\left( {\frac{V}{A}} \right)_{casting}} = \frac{{{{10}^3}}}{{6\left( {{{10}^2}} \right)}} = \frac{{10}}{6} = 1.66\)

\({\left( {\frac{V}{A}} \right)_{riser}} = \frac{{\pi {r^2}h}}{{2\pi rh + 2\pi {r^2}}} = \frac{{\pi {r^2}\left( {2r} \right)}}{{2\pi r\left( {2r} \right) + 2\pi {r^2}}}\)

\({\left( {\frac{V}{A}} \right)_{riser}} = \frac{r}{3}\)      ---(2)

Now,

From equation (1)

150 = πr² (2r)

∴ r = 2.879 cm

Now,

\({\left( {\frac{V}{A}} \right)_{riser}} = 0.959\)

Which is less than \({\rm{\;}}{\left( {\frac{V}{A}} \right)_{casting}}\)

But, \({\left( {\frac{V}{A}} \right)_{riser}} \ge {\left( {\frac{V}{A}} \right)_{casting}}\)

\(\frac{r}{3} \ge 1.66\)

r ≥ 4.98

∴ r ≃ 5 cm

∴ h ≃ 10 cm.  

Shape factor \(\left( {SF} \right) = \frac{{L + W}}{T}\)

For hollow cylinder L = h = 10 mm

Width \(\left( W \right) = \frac{{\pi \left( {{D_o} + {D_i}} \right)}}{2}\)

\(\begin{array}{l} = \frac{{\pi \left( {16+ 8} \right)}}{2} = 12\pi \\ T = \frac{{{D_o} - {D_i}}}{2} = \frac{{16 - 8}}{2} = 4\;mm \end{array}\)  

\(SF = \frac{{10 + 12\pi }}{4}\)

Concept:

Casting modulus is defined as the ratio of the volume to the cooling surface area of the casting (or a part of the casting). For complicated shapes, the casting is subdivided into smaller basic shapes and modulus is calculated for each section.

Explanation:

According to Modulus Method,

Modulus of riser = 1.2 × Modulus of casting

⇒ M_r = 1.2 M_c

\(\Rightarrow \frac{D}{6} \propto {M_c}\)

∴ D ∝ M_C

The diameter will increase by 60%.

Explanation:

Riser

• A riser in casting serves as a reservoir of molten metal and ensures that shrinkage cavities and voids do not form in the casting due to metal contraction during solidification. Its primary purpose is to feed the casting with molten metal until the solidification process is complete, ensuring the final casting is free from defects such as shrinkage porosity

Shrinkage in a mold, from the time of pouring to final casting, occurs in three stages

• During the liquid state
• During the transformation from liquid to solid
• During the solid-state
• The first type of shrinkage is being compensated by the feeders or the gating system
• For the second type of shrinkage, risers are required. Risers are normally placed at that position of the casting which is last to freeze
• A riser must stay in a liquid state at least as long as the casting and must be able to feed the casting during this time

Concept:

Caine's Method is given by the following relation:

\(x=\frac{a}{y-b}-c\)

where x = freezing ratio, y = volume ratio and a,b and c are constants.

Volume ratio is the ratio of riser volume to casting volume.

Calculation:

Given:

Side of casting = 100 mm

Freezing constant, a = 0.1, b = 0.03, c = 1

Freezing ratio = 1.25 = x

\(x=\frac{a}{y-b}-c\)

\(1.25=\frac{0.1}{y-0.03}-1\)

∴ y = 0.0744

Volume of casting = (100)³ = 10⁶ mm³

For side riser:

height = diameter

Volume = \(\frac{\pi}{4}d^2h=\frac{\pi}{4}d^3\)

y is the volume ratio

\(y =\frac{V_{riser}}{V_{casting}}=\frac{V_r}{V_c}\)

\(0.0744 =\frac{V_r}{10^6}\)

Volume of riser = 0.0744 × 10⁶ mm³

\(\frac{\pi}{4}d^3=0.0744\times10^6\)

d = 45.59 mm

According to Caine’s Method

Freezing ration \(\left( {FR} \right) = \frac{{{{\left( {\frac{{SA}}{V}} \right)}_{casting}}}}{{{{\left( {\frac{{SA}}{V}} \right)}_{riser}}}}\)

(SA)_casting = 2(20 × 20) + 4(20 × 5) = 1200 cm²

V_casting = 20 × 20 × 5 = 2000 cm³

\({V_{riser}} = \frac{\pi }{4}{d^2}h = \frac{\pi }{4}{d^3} = \frac{\pi }{4}{\left( {10} \right)^3} = 785.35\;c{m^3}\)

\(S{A_{riser}} = \frac{\pi }{4}{D^2} + \pi Dh\)

\(= 2\times \frac{\pi }{4}{D^2} + \pi {D^2} = \frac{3}{2}\pi {D^2} = \frac{3}{2} \times \pi \times {\left( {10} \right)^2}\)

= 471.23 cm²

Explanation:

Riser:

• The riser is a reservoir of molten metal provided in the casting so that hot metal can flow back into the mould cavity when there is a reduction in the volume of metal due to solidification.
• A riser must stay in a liquid state at least as long as the casting and must be able to feed the casting during this time.
• In Casting process there are mainly two types of raisers are used;
  • Open riser (Top Riser)
  • Blind riser (Side Riser)
• The top riser is placed at the topmost point of the casting so that molten can rise up to the highest point of the casting. The top surface of the riser will be open to the atmosphere hence we can visually check filling up of mould cavity in the top riser.
• Blind Riser is completely enclosed in the mould and not exposed to the atmosphere. Blind risers maintain heat longer than open risers.

Chills:

• Chills are metallic objects, which are placed in the mould to increase the cooling rate of castings to provide uniform or desired cooling rate.
• Chills are provided to improve directional solidification.
• The material of the chills should be the same as the casting material.

Concept:

\({\rm{Using\;caines\;equation}},{\rm{\;}}x = \frac{a}{{y - b}} + c\)

a = freezing constant, b = contraction ratio, c = 1 / relative freezing = 1, assuming same mold material for casting and riser)

\(x = \frac{{{{\left( {\frac{A}{V}} \right)}_c}}}{{{{\left( {\frac{A}{V}} \right)}_r}}} = freezing\;ratio\)

Calculation:

\(x = \frac{{0.2}}{{y - 0.03}} + 1\)

x = 1.44

Now,

\(0.44 = \frac{{0.2}}{{y - 0.03}} \Rightarrow y = 0.4845\)

\(y = \frac{{{V_r}}}{{{V_c}}}\)

For side riser, h = d

V_r = πd³/4

V_c = (20)³

\( \Rightarrow \frac{{\pi {d^3}}}{4} = 0.4845 \times {20^3}\)

∴ d = 17.0260 cm

Concept:

\(Freezing\;ratio,\;FR = \frac{{{{\left( {\frac{A}{V}} \right)}_{casting}}}}{{{{\left( {\frac{A}{V}} \right)}_{riser}}}}\)

Calculation:

Volume of casting = 30 × 20 × 10 = 6000 cm³

Surface area of casting = 2[(30 × 20) + (20 × 10) + (10 × 30)] = 2200 cm²

\({\left( {\frac{A}{V}} \right)_{casting}} = \frac{{2200}}{{6000}} = 0.367\)

For Cylindrical riser, D = H = 15 cm

\({\left( {\frac{A}{V}} \right)_{riser}} = \frac{{2.\frac{\pi }{4}{D^2} + \pi DH}}{{\frac{\pi }{4}{D^2}H}} = \frac{6}{D} = \frac{6}{{25}} = 0.24\)

\(FR = \frac{{{{\left( {\frac{A}{V}} \right)}_{casting}}}}{{{{\left( {\frac{A}{V}} \right)}_{riser}}}} = \frac{{0.367}}{{0.24}} = 1.529\)

Volume of casting = 300 × 150 × 50 = 225 × 10⁴ mm³

Shrinkage volume = 3% of costing volume

= 0.03 × 225 × 10⁴ mm³

= 67.5 × 10³ mm³

According to shrinkage volume method the minimum volume of riser is equal to three times the shrinkage volume.

Minimum volume riser = 202.5 × 10³ mm³

= 202.5 cm³