Question

Statement (I): Sand with grains of uniform round shape is preferred for preparing moulds.

Statement (II): If gains are large and regular in shape, the air-venting property of the mould prepared with them would be better.

1. Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I)
2. Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I)
3. Statement (I) is true but Statement (II) is false
4. Statement (I) is false but Statement (II) is true

Answer 1

Correct Answer - Option 4 : Statement (I) is false but Statement (II) is true

Concept:

Refractoriness of the sand is the property that ensures resistance to high temperature. Refractoriness depends upon the composition of the sand.  If the fusion point of the sand is high the sand still may fuse to the casting if grain shape, grain size and grain distribution are not uniform. Therefore precautions are taken while selecting the moulding sand.

The grain should be of uniform size but the roundness of sand is not the limitation of choosing the sand for preparing the mould.

Therefore statement I) is not correct.

Permeability is the property of the sand that permits the gasses and air to pass through the sand. This permeability is the opening between the grains that permit passage of gases.

Permeability depends upon four factors

• Shape of sand grains

• Fineness of the sand grains

• Type of the binder used and

• The moisture content

If grains are coarse it has high permeability because of the greater proportion of large size grains and the larger void between them.

Therefore statement II) is correct.