Casting Defects & Remedies 01. Shrinkage 02. Cold Shut 03. Mismatch 04. Blow holes 05. Pin Holes 06. Fin 07. Drop 08. Swell 09. Metal

Penetration 10. Hot Tears 11. Porosity 12. Scabs 13. Hard Spots 14. Buckles\Rat Tails 15. Misrun

SHRINKAGE 

Shrinkage cavity is a void on the surface of the casting caused mainly by uncontrolled and haphazard solidification of the metal.

SHRINKAGE Causes:  Inadequate and improper gating.  Poor design of casting involving abrupt changes in thickness.  Too high pouring temperature.

SHRINKAGE Remedies:  Use the suitable composition that is adjusted silicon and (1.80 to 2.10) or carbon equivalent (3.9 to 4.1).  Carry out proper ramming and maintain optimum pouring temperature and time.

Cold Shut 

When two streams of molten metal approach each other in the mould cavity from opposite directions but fail to fuse properly, with the result of discontinuity between them, it is called a cold shut.

Cold Shut Causes:  Low temperature of molten metal  Improper gating system  Too thin casting sections  Slow and intermitted pouring  Improper alloy composition  Use of damaged pattern

Cold Shut Remedies:  Smooth pouring with the help of monorail.  Properly transport mould during pouring.  Provide proper clamping arrangement.  Providing appropriate pouring temperature.

Mismatch 

It is a shift /misalignment between two mating surfaces or the top and bottom parts of the casting at the mould t.

Mismatch Causes:  Worn dowel in patterns made in halves.  Improper alignment of mould boxes due to worn out/ill fitting mould boxes. Remedies:  Properly arrange box warpage.  Properly move boxes with pins.  Properly clamp the boxes.

Blow Holes 

Balloon-shaped gas cavities caused by release of mould gases during pouring are known as blow holes.

Blow Holes Causes:  Ramming is too hard.  Permeability is insufficient.  Venting is insufficient.

Blow Holes Remedies:  Moisture content of moulding sand should be controlled  Sand of appropriate grain size should be used.  Ramming should not be too hard.  Moulds should be adequately vented.

Pin Holes 

Pin holes are tiny blow holes appearing just below the casting surface.

Pin Holes Causes:  Sand with high moisture content.  Absorption of hydrogen / carbon monoxide gas in the metal.  Alloy not being properly degassed.  Steel is poured from wet ladles.  Sand containing gas producing ingredients.

Pin Holes Remedies:  Reducing the moisture content of moulding sand.  Increasing its permeability.  Employing good melting and fluxing practices.  Improving a rapid rate of solidification.

Fin 

Fins are excessive amounts of metal created by solidification into the parting line of the mold

Fin Causes:  Inadequately weighted sand as well as incorrectly assembled moulds and cores.  Over flexible bottom boards.  Loose plates and improper clamping of flasks. Remedies:  Correct assembly of the mouldand cores used for casting.

Drop 

Drop is an irregularly-shaped projection on the cope surface caused by dropping of sand.

Drop Causes:  Low green strength of the moulding sand.  Low mould hardness.  Insufficient reinforcement of sand projections in the cope. Remedies:  Moulding sand should have sufficient green strength.  Ramming should not be too soft.

Swell 

Swells are excessive amounts of metal in the vicinity of gates or beneath the sprue

Swell Causes:  Insufficient or soft ramming.  Low mould strength.  Mould not being adequately ed.

Remedies:  Sand should be rammed evenly and properly.

Metal Penetration 

Penetration occurs when the molten metal flows between the sand particles in the mould. These defects are due to inadequate strength of the mold and high temperature of the molten metal adds on it.

Metal Penetration Causes:  Low strength of moulding sand.  Large size of moulding sand.  High permeability of sand.  Soft ramming. Remedies:  Use of fine grain with low permeability.  Appropriate ramming.

Hot Tears 

A hot tear is a fracture formed during solidification because of hindered contraction.

Hot Tears Causes:  Faulty casting design leading to excessive stresses at certain portions in the casting.  Very hard ramming.  Too much shrinkage of molten metal.  Incorrect pouring temperature.  Improper gates and risers.  Low flowability of molten metal.  High sulphur content in molten metal.

Hot Tears Remedies:  Ramming should not be too hard.  Modification in pattern to take care of residual stresses.

Porosity 

Porosity is pockets of gas inside the metal caused by micro-shrinkage during solidification.

Porosity Causes:  Dissolved hydrogen and sulphur dioxide in molten metal.  Excessive poring temperature.  Slow rate of solidification.  High moisture content of the mould.

Porosity Remedies:  Maintenance of proper melting temperature.  Casting should be made to solidify quickly by using proper gating and risering.  Permeability of the mould should be increased.  Moisture content of mould should be kept low.

Scabs 

Scabs are surface slivers caused by splashing and rapid solidification of the metal when it is first poured and strikes the mold wall

Scabs Causes:  insufficient strength of mould and core.  uneven mould ramming.  lack of binding material in facing as well as core sand.  Faulty gating.  intense local heating due to slow running of molten metal over sand surface.

Scabs Remedies:  appropriate ramming.  improved gating system.  addition of sufficient binders in facing and core sands.

Hard Spots 

These spots are formed due to the local chilling by moulding sand which leads to the formation of white cast iron at those places, rendering them hard.

Hard Spots Causes:  Faulty metal composition.  Faulty casting design resulting in relatively more rapid cooling of certain spots. Remedies:  Modification of casting design.  Modification of casting composition.

Buckles/Rat Tails 

Rat tail or a buckle is a long, shallow, angular depression caused by expansion of the sand.

Buckles/Rat Tails Causes:  Excessive mould hardness.  Lack of combustible additives in the moulding sand.  Continuous large surfaces on the casting.

Buckles/Rat Tails Remedies:  Suitable addition of combustible additives to moulding sand.  Reduction in mould hardness.  Modifications in casting design.

Misrun 

When the molten metal fails to fill the entire mould cavity before the metal starts solidifying, resulting in an incomplete casting, the defect is known as misrun.

Misrun Causes:  Low temperature of molten metal  Improper gating system  Too thin casting sections  Slow and intermitted pouring  Improper alloy composition  Use of damaged pattern

Misrun Remedies:  Smooth pouring with the help of monorail.  Properly transport mould during pouring.  Arrange proper clamping arrangement.  Providing appropriate pouring temperature.