Properties of moulding sand

• The following are the properties of mould sanding.

  1. Strength

  2. Permeability

  3. Grain size & shape

  4. Thermal stability

  5. Refractoriness

  6. Collapsibility

  7. Adhesiveness

  8. Reusability

  9. Easy of preparation and control

  10. Conductivity

STRENGTH :

• The sand ought to have adequate strength in its green, dry and hot states. Green is that the strength of sand in the wet state and it’s needed for making the mould.

• If the metal is poured into a green mould the sand adjacent to the metal dries and therefore the dry state ought to have strength to resist erosion.

• The strength of the sand that has been dried is termed dry strength. At the time of Pouring the molten metal should be able to withstand the flow and pressure of the Metal at high temperature otherwise the mould might enlarge, crack, get washed or break.

• Strength of the moulding sand depends on,

  • Grain size and shape

  • Moisture content

  • Density of sand when ramming

PERMEABILITY :

• The moulding sand should be sufficiently porous to permit the dissolved gases, that are evolved when the metal freezes or moisture present or generated within the moulds to be removed freely when the moulds are poured. This property of sand is termed porosity or permeability.

GRAIN SIZE AND SHAPE :

• The size and shape of the grains in the sand determine the application in various types of manufacturing plant. These are 3 sizes of sand grains.

  • Fine

  • Medium

  • Coarse

• Fine sand is used for little and complex castings. Medium sand is used for benchmark and light-weight floor works. Coarse sand is used for larger casting.

THERMAL STABILITY :

• The sand adjacent to the metal is suddenly heated and undergoes expansion. If the mould wall isn’t dimensionally stable beneath rapid heating, cracks, buckling and flacking off sand might occur.

REFRACTORINESS :

• Refractoriness is that the property of withstanding the high temperature condition moulding sand.

• It is the ability of the moulding material to resist the temperature of the liquid metal to be poured so it doesn’t get fused with the metal. The refractoriness of the Silica sand is highest.

COLLAPSIBILITY :

• The moulding sand ought to collapse during the contraction of the solidified casting it doesn’t offer any resistance, which can result in cracks in the castings.

• Besides these specific properties the moulding material ought to be low cost, reusable and will have good thermal conductivity.

ADHESIVENESS :

• It is defined as the sand particles should be capable of adhering to another body, then only the sand ought to be easily attach itself with the sides of the moulding box and give easy lifting and turning the box when filled with the stand.

REUSABILITY :

• Since large quantities of sand are used in a manufacturing plant it’s important that the sand be reusable otherwise apart from cost it will produce disposal issues.

EASY OF PREPARATION AND CONTROL :

• Sand ought to lend itself to easy preparation and control by mechanical equipment.

CONDUCTIVITY:

• Sand ought to have enough conductivity to permit removal of heat from the castings.