2. Title of slide
Lesson Objectives
In this chapter we shall discuss the following:
Learning Activities
1. Look up
Keywords
2. View Slides;
3. Read Notes,
4. Listen to
lecture
Keywords:
9. Casting Cleaning :
•The casting is separated from the mold
and transported to the cleaning
department.
•Burned-on sand and scale are removed.
•Excess metal is removed (Fins, wires,
parting line fins, and gates).
•Subsequently the casting can be
upgraded using welding or other such as
procedures.
•Final testing and inspection to check for
any defects
Advantages:
•Improves the surface appearance and finish of casting
•Improves overall quality and functionality by removing impurities,
such as sand, scale and excess metal
Finally the sand from the mold is separated and processed through a
reclamation system for further use.
10. • Defects may occur due to one or more of the following
reasons: Fault in design of casting pattern
• Fault in design on mold and core
• Fault in design of gating system and riser
• Improper choice of molding sand
• Improper metal composition
• Inadequate melting temperature and rate of pouring
11. • Classification of Casting Defects
• Surface Defects Blow, Scar, Blister, Drop,
Scab, Penetration, Buckle
• Internal Defects Blow holes, Porosity, Pin
holes, Inclusions, Dross
• Visible Defects Wash, Rat tail, Swell, Mis run,
Cold shut, Hot tear, Shrinkage/Shift
12. • Discontinuities in
castings that exhibit a
size, shape,
orientation, or location
that makes them
detrimental to the
useful service life of
the casting
• Some casting defects
are remedied by minor
repair or refurbishing
techniques, such as
welding
• Other casting defects
are cause for rejection
of the casting
Casting Defects
13. • Metallic Projections: fins (flash), swells,
and scabs
– Fins are excessive amounts of metal created by
solidification into the parting line of the mold
Fins are removed by grinding or sandblasting
– Swells are excessive amounts of metal in the
vicinity of gates or beneath the sprue
– Scabs are surface slivers caused by splashing and
rapid solidification of the metal when it is first
poured and strikes the mold wall
Casting Defects — Metallic Projections
14. • Blowholes, pinholes, shrinkage cavities, & porosity
– Blowholes and pinholes are holes formed by gas
entrapped during solidification
– Shrinkage cavities are cavities that have a rougher
shape and sometimes penetrate deep into the casting
Shrinkage cavities are caused by lack of proper
feeding or non-progressive solidification
– Porosity is pockets of gas inside the metal caused by
micro-shrinkage, e.g. dendritic shrinkage during
solidification.
Casting Defects — Cavities
15. • Cracks in casting and are caused by hot tearing, hot
cracking, and lack of fusion (cold shut)
– A hot tear is a fracture formed during solidification
because of hindered contraction
– A hot crack is a crack formed during cooling after
solidification because of internal stresses developed in
the casting
– Lack of fusion is a discontinuity caused when two streams
of liquid in the solidifying casting meet but fail to unite
Rounded edges indicate poor contact between various
metal streams during filling of the mold
Casting Defects — Discontinuities
16. • Casting surface irregularities that are
caused by incipient freezing from too
low a casting temperature
• Wrinkles, depressions and adhering
sand particles
Casting Defects — Defective Surfaces
17. • Particles of foreign material in the
metal matrix
• The particles are usually nonmetallic
compounds but may be any substance
that is not soluble in the matrix
– Slag, dross, and flux inclusions arise from
melting slags, products of metal treatment, or
fluxes
They are often deep within the casting
– Mold or core inclusions come from sand or mold
dressings and are usually found close to the
surface
Casting Defects — Inclusions
30. Shell molding
• Advantages
•
• Better surface finish
• Better dimensional tolerances.
• Reduced Machining.
• Less foundry space required.
• Semi skilled operators can handle the process.
• The process can be mechanized.
Disadvantages
The raw materials are relatively expensive.
•The process generates noxious fumes which must
be removed.
•The size and weight range of castings is limited.
32. Manufacturing,
Engineering &
Hot Tears in Castings
Figure 10.12 Examples of hot tears in castings. These defects occur because the casting
cannot shrink freely during cooling, owing to constraints in various portions of the molds
and cores. Exothermic (heat-producing) compounds may be used (as exothermic padding)
to control cooling at critical sections to avoid hot tearing
33. Manufacturing,
Engineering &
Common Casting Defects
Figure 10.13 Examples of common defects in castings. These defects can be minimized or
eliminated by proper design and preparation of molds and control of pouring procedures.
Source: After J. Datsko.
