The Properties of molding sand are adhesiveness, cohesiveness, flowability, collapsibility, refractoriness, permeability, reusability, Grain size, grain shape, dry strength, Porosity etc..
Before looking at the properties of molding sand or Characteristics , we look into the definition of sand casting.
It is a process in which the liquid molten metal is poured into the casting cavity whose shape is the same as that of the shape of the casting to be produced, allowing to solidify and after solidification, the casting will be taken out by breaking the mold called as Sand Casting Process.
The properties of molding sand are as follows.
The ability of the bond formation of sand particles with other materials is called as adhesive property and that testing is done by means of Universal testing machine.
Ability to form bond between same material particles is called as cohesiveness property or shear strength. It is determined by a universal testing machine and the name of the test is interlaminar shear strength test.
The ability of flowing of molding sand into each and every corner of the mold is called as flowability and it can be measured using orifice meter.
The ability of the mold with a little amount of force application is called as collapsibility. It is measured using vibration machine. By slowly increasing the vibration, it is possible to determine at what vibration the mold can be broken.
As the force required for breaking the mould is reducing, the collapsibility property of mould is increasing.
The ability of withstanding higher temperatures without losing its strength and hardness is called as Refractoriness.
The testing can be done a universal testing machine with the temperature control chamber.
The permeability test is used for determining the porosity property of molding sand.
The molding sand with which already the components are cast, can be reused for the preparation of new components.
The higher the grain size of silica sand particle, higher the porosity property i.e. as the grain size increases the gaps between the particles becomes larger.
This property evaluates the shape of the individual grains of molding sand based on how round they are.
The strength i.e. tensile strength, compressive strength, shear strength can be used for determining the strength of a component and that can be tested by means of Universal testing machine.
The ability of escaping the air or gases through the molding sand is called as the porosity.
The porosity property of molding sand is required for escaping the air/gases present in casting cavity during filling of molten metal into the cavity. i.e. If the air/gases are present in the cavity, it will affect the strength of casted object as blowholes will be formed.
The factors affecting the porosity are as follows.
Percentage of clay sand:
The higher the percentage of the clay, the porosity will be less. It reduces the porosity of molding sand.
The clay will fill gaps existing between the sand particles and the porosity decreases.
vent holes: with this, the porosity can be increased.
Ramming force/Compressive Force:
It is applied during the mold preparation. The higher compressive force, the lower the porosity property.
Adding saw dust and wood powder, the porosity property can be improved.
This is the detailed explanation of properties of molding sand. If you have any doubt, you can feel free to contact us and we will reply you in within 24 hrs.
More Resources:Casting Process-Overview
Machine Molding and Hand Molding Operations
Sand Casting Process