1) The document discusses design considerations for cast iron components, including keeping stressed areas in compression, rounding external corners, avoiding abrupt changes in cross-section thickness, and avoiding thin sections. 2) It recommends consulting the foundryman and patternmaker when designing castings and provides general principles such as keeping sections uniform, avoiding metal concentration at junctions, and using draft angles on patterns. 3) Some ways to improve casting strength are inserting studs, using cored holes, and providing minimum section thicknesses depending on the casting process.

1. GUJRAT
POWER
ENGINEERING
&
RESEARCH
INSTITUTE
NAME :- THAKKAR VIJAYKUMAR B.
ENROLLMENT NO:- 161043119012
SUB:- DESIGN COSIDERATION OF CASTING
GUIDED BY:-
PARIN PATEL SIR

2. Complex parts, which are otherwise difficult to
Machine, are made by casting process using sand mould. Almost any
metal can be melted and cast. Most of the sand cast parts are made of
cast iron, aluminum alloys and brass. The size of the sand casting can be
as small as 10 g and as large as 200 *103 kg. Sand castings have irregular
and grainy surfaces and machining is required if the part is moving with
respect to some other part or structure. Cast components are stable,
rigid and strong compared with machined or forged parts. Typical
examples of cast components are machine tool beds and structures,
cylinder blocks of internal combustion engines, pumps and gear box
housings.
Poor shaping of a cast iron component can
adversely affect its strength more than the composition of the material.
Before designing castings, the designer should consult the foundry
man and the patternmaker, whose cooperation essential for a successful
design. The general principles for the design of casting.
are as follows:

3. Always Keep the Stressed Areas of the Part in
Compression Cast iron has more compressive strength than its tensile
strength. The balanced sections with equal areas in tension and
compression are not suitable for cast iron components. The castings
should be placed in such a way that they are subjected to compressive
rather than tensile stresses as illustrated in Fig. 3.1. When tensile
stresses are unavoidable, a clamping device such as a tie rod or a
bearing cap as illustrated in Fig. 3.2 should be considered. The clamping
device relieves the cast iron components from tensile stresses.

5. Round All External Corners It has two
advantages—it increases the endurance limit of the component and
reduces the formation of brittle chilled edges. When the metal in the
corner cools faster than the metal adjacent to the corner, brittle chilled
edges are formed due to iron carbide.
Appropriate fi llet radius, as illustrated in Fig. 3.3
reduces the stress concentration. The values of the corner radii for
different section thickness are give in Table 3.1.

6. Wherever Possible, the Section Thickness
throughout should be Held as Uniform as Compatible with Overall
Design Considerations Abrupt changes in the cross-section result in high
stress concentration. If the thickness is to be varied at all, the change
should be gradual as illustrated in Fig. 3.4.
Avoid Concentration of Metal at the Junctions At
the junction as shown in Fig. 3.5, there is a concentration of metal. Even
after the metal on the surface solidifi es, the central portion still remains
in the molten stage, with the result that a shrinkage cavity or blowhole
may appear at the centre.

7. There are two ways to avoid the concentration of
metal. One is to provide a cored opening in webs and ribs, as illustrated
in Fig. 3.6. Alternatively, one can stagger the ribs and webs, as shown in
Fig. 3.7.
Avoid Very Thin Sections In general, if the
thickness of a cast iron component is calculated from strength
considerations, it is often too small. In such cases, the thickness should
be increased to certain practical proportions. The minimum section
thickness depends upon the process of casting, such as sand casting,
permanent mould casting or die.

8. casting. The minimum thickness for a grey cast iron component is about
7 mm for parts up to 500 mm long, which gradually increases to 20 mm
for large and heavy castings.
Shot Blast the Parts wherever Possible The shot
blasting process improves the endurance limit of the component,
particularly in case of thin sections.
Some ways to improve the strength of castings are
illustrated in Figs 3.8 to 3.11. In Fig. 3.8, the inserted stud will not
restore the strength of the original thickness. The wall adjacent to the
drilled hole should have a thickness equivalent to the thickness of the
main body. Figure 3.9 shows cored holes in webs or ribs. Oval-shaped
holes are preferred with larger dimensions along the direction of forces.
Patterns without a draft make a mould diffi cult and costly. A minimum
draft of 3° should be provided, as illustrated in Fig. 3.10. Outside bosses
should be omitted to facilitate a straight pattern draft as shown in Fig.
3.11.