To Know And Identify Casting Defects

A proper casting, well prepared mould and correctly melted metal must result in a flawless casting. However, if proper control is not taken care for several defects might result in a casting.

These defects could be for several reasons:

(a) Improper design pattern

(b) Improper construction of mould and core

(c) Improper melting

(d) Improper pouring

(e) Improper gating system

(f) Improper composition of metal

(g) Insufficient melting temp and rate of pouring

Defects mainly fall into 3 categories. They are:

(1) Severe defects

(2) Intermediate defects

(3) Minor defects

Surface defects:

Owing to design and quality of sand moulds.

Blow:

A larger cavity produced by gases when molten metal is displaced

Blow casting defect

Scar:

Owing to improper permeability or venting, a scar is a shallow blow. Occurs on flat surface; whereas a blow occurs on a convex casting surface.

Scab:

This defect happens when a portion of the face of a mould lifts or breaks down and the gap thus made is filled by metal.

Drop:

It is an irregularly shaped projection on the surface of the casting. This is caused by broken part of mould sand and results in a weak packing of the mould, low strength of the moulding sand, multifunctionality of moulding device, high jolts and strikes at the flask while assembling the mould.

Buckle:

It’s a shallow, broad, depression that occurs in the surface of flat castings due to sand expansion caused by heat of metal, when the sand has insufficient hot deformation

Internal defects:

Blow holes:

Blow holes are rounded cavities with a clean and smooth surface. They appear either on the casting surface or body of a casting.

They are caused by:

i) Excess content of moisture or organic content of sand, chaplets or metal inserts

ii) Inadequate gas permeability of moulded sand

iii) Poor venting of mould, it’s insufficient drying and cores, higher gas content of the molten metal

Pin holes:

They are small gas holes either on the surface or just below. This occurs due to gas dissolved in an alloy and the alloy not well degassed.

Visible defects: There are some defects which could be seen. They include wash, rat tail, hot tear, swell, shrinkage and shift.

With this we conclude. Keep visiting our space to know more.

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