explanation:-a pattern is basically a duplicate of the object that we intend to cast. patterns can be made up of wood, plastics or metals. a pattern is generally made up of two or three pieces, whereas it is casting which is in one piece.
explanation:-patterns are duplicates of the objects we desire to cast. these patterns can be made up of plastics, metals or wood. a pattern is slightly larger in size as compared to casting because a pattern carries various allowances and the core prints.
3. A pattern carries which allowance for internal and external surfaces?
explanation:-draft allowance is also known by the name of tapering allowance, as the diameter of the cast goes on increasing in a trapezoidal shape from the bottom. a pattern has a draft allowance of an order of 1 and 3 degrees for external and internal surfaces respectively.
explanation:-in distortion allowance, the amount goes on to vary from 2mm to 20mm. this allowance depends on the shape of the casting that is being used. it also depends on the size of the cast and the material that is being employed for the casting.
7. Ferrous metals need more allowance than non-ferrous metals.
explanation:-in rapping or shake allowance, the pattern is taken out of the mould and it is rapped or shaken, so as to free it from the adjoining sand. due to this, there may be a little increase in the size of the mould cavity.
explanation:-the coal is a material which is not used in the formation of the molding sand as the particle size of the coal is high and there are chances that it will react with the possible gases that are produced during the pouring of the metal and result in casting defects.
11. The size of the sand particles in the molding sand is the biggest.
explanation:-molding sand is added with chemicals to enhance properties such as permeability, compressive strength etc., however, the chemical reactions happening is not viable for the formation of the casting as it might cause explosion or severe fatal effects in the casting.
14. The property ensures the removal of excess sand in the mould box.
explanation:-the adhesiveness is a property of molding sand to get the stick or adhere to foreign material such as sticking of molding sand with an inner wall of the molding box. hence, as the sand sticks to the box and the excess sand is removed.
15. Binding property of the sand increases because of the property.
explanation:-after the molten metal in the mould gets solidified, the sand mould must be collapsible so that free contraction of the metal occurs and this would naturally avoid the tearing or cracking of the contracting metal. in absence of collapsibility property, the contraction of the metal is hindered by the mold and thus results in tears and cracks in
17. The adhesiveness and cohesiveness are the same properties of the molding sand.
explanation:-iron is the metal having a melting point of about 1537oc and latent heat of fusion of 65.0 cal/g. it has a mean specific heat of 0.141 cal/g-oc and heat required for melting 1 kg of iron is 1168 kj.