Sand Inclusion

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Al Alagarsamy, Citation Corporation, Birmingham, AL. 1

HOT TOPICSIssue #9-2003

Casting Defect: Inclusions – Sand

1. Defect code G131-CI-GS (Cast iron in green sand)

2. Name: Sand inclusions

3. Description: Non metallic materials (molding or core sand) present in the casting surface.

Some times these materials are removed from the casting during shot blastingleaving a void on the surface of the casting. If the graphite shape is not affected

near the defective areas, it is good chance that the defect is caused by sandinclusions. If the defect is at the bottom most parts of the casting, it is probably

sand.

4. Pictures of this defect are located at the end of this document.

5. Mechanism of defect formationThere are two ways sand defects occur in the casting.

A) Sand already present prior to pouring: Sand that falls into the cavity duringcore setting, mold closing, and/or mold handling rests at the lowest levels of the

cavity. When blowing loose sand out of the mold after core setting, loose sand can be moved around and not expelled from the mold will accumulate at shadow

areas.

b) Sand washed into the casting during pouring. During pouring, sand from

gating systems and cavity areas may be eroded and washes into the casting cavity.Disturbed mold surface may be washed by flowing metal or may separate from

the rest of the mold and fall into the cavity prior or during mold filling.

6. All possible causes

Ø Design

• Very high pouring rates, metal stream impacting the mold

• Very long pouring times

• Sharp corners on runner systems

• Too much metal flowing through one gate

• Very long pouring times

• Not adequate crush strips on parting banks

• Narrow and deep pockets near metal flow areas

Ø Equipment

• Pattern equipment worn, negative drafts, not enough draft, fillets loose etc.

• Uneven mold stripping, closing and core setting equipment




• Rough mold handling equipment, shots on rails

• Worn pins and bushings resulting in erratic closure

• Machines not aligned properly for smooth traveling (Vertically partedmolds)

• Uneven mold compaction

Ø Process• Thin sand ridges formed by cracks in the tooling

• Rough pouring cups cut by sprue cutters

• Mismatched pouring cup and sprue

• Not blowing off loose sand after core setting

• Worn out core prints and core boxes resulting in too big a core and toosmall a print causing crush during core setting

• Cores too soft, uncured that can be eroded easily

• Dirty area causing loose sand to fall in

• Contaminants in molding sand (core lumps etc.)

• Hydraulic oil spill resulting in weak mold

• Hot sand drying too fast

• Sand friability too high

• Compactability too low

• Too low clay and fines

• Sand not mulled well

• Green sand having too low dry strength

7. Most probable causes

• Sand not blown from cavities

• Mold to mold crush

• Core to old crush• Sand too dry (hot sand, low compactability)

• Too low moisture (low clay and or fines)

• Worn out pins and bushing resulting in shifts and crushes

• Worn out tooling

8. Process variables that should be controlled to avoid defect

• Use metal gating components in tooling

• Provide adequate draft for the type of molding equipment

• Use adequate crush strips, especially for offset parting planes

• Maintain adequate clay, fines and moisture in the greensand system

• Maintain adequate western bentonite for good plasticity and dry strength

• Keep the sand system clean, free of core lumps and other contaminants

• Keep the sand system full (return sand silo should hold at least 2 hours ofsand consumption)

• Return sand should be cooled below 1250F, with around 2% moisture

• Compactability at the molding machines should as high as the machineswill allow for good mold production.




Figure 1. at top showing a micrograph of a section through the sand inclusion on

the casting surface.

Figure 2. Molding edges were very friable due to hot sand and low clay.




Figure 3. Erosion scabs resulting in sand inclusions. Hot sand and poor mulling and low

amount of sand in return sand silo were the main reasons for this defect.

Figure 4. Casting surface with erosion of molding sand where the metal

impinged on the mold cavity. Too low total clay and low compactability

resulted in low moisture sand with low dry strength causing erosion




Fig-5 Erosion of molding sand at the junction of sprue and runner as well as

on the runner side. Low dry strength of molding sand due to sand mix

containing low western bentonite in the mix contributed to this defect

Figure 6. Sand falling down from parting line crush

Sand Inclusion

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