Casting defects · training

Identifying casting defects

Defects are usually misnamed not through carelessness but because two different defects can look much alike. Working from family to defect, and knowing the handful of tells that separate the confusable pairs, takes a new inspector most of the way.

By Versatile Equipments Pvt Ltd · equipment manufacturer & calibration provider · updated 2026-09-07

Start with the family, not the name

New inspectors often try to jump straight to a defect name and end up choosing between twenty possibilities. It is quicker and more reliable to place the defect in a family first, because that decision is usually obvious, and then to separate within the family, where only two or three candidates remain.

Is metal missing, or is something extra there? A void, a cavity or an unfilled section is one branch; an inclusion, a fin or adhering sand is the other.
If metal is missing, is it a cavity inside or an incomplete shape? Cavities are gas or shrinkage. Incomplete shapes are misrun, cold shut or poured short.
If something extra is there, is it from the mould or from the melt? Sand, coating and mould material on one side; slag, dross and refractory on the other.
Is the surface itself damaged? Expansion defects, penetration and burn-on sit here.
Is it a crack? Then the only real question is whether it formed hot or cold.

The full list of families and the pages behind them are set out in the casting defects guide.

The tells that separate confusable pairs

Most misnaming happens inside a handful of pairs. In each case there is one feature that does the work.

Commonly confused	The tell	Usually found
Blowhole vs shrinkage cavity	The wall. Gas pushed the metal aside, so a blowhole is smooth and rounded. Metal pulled away as it fed, so shrinkage is rough, jagged and dendritic.	Blowhole near the cope or over cores; shrinkage at thermal centres and junctions, under feeders
Gas porosity vs shrinkage porosity	Pore shape and spread. Gas gives dispersed rounded pores; shrinkage gives spongy, interconnected voiding between dendrites.	Gas through the section; shrinkage at the last place to freeze
Sand inclusion vs slag inclusion	What the material is. Sand is gritty with visible grains; slag and dross look glassy, dark or filmy.	Both often near the ingate or on upper surfaces, so judge the material, not the position
Cold shut vs crack	The edges. A cold shut has rounded, smooth edges where two fronts met and did not fuse. A crack has a broken face.	Cold shut where two streams meet, often mid-wall or opposite the ingate
Hot tear vs cold crack	Appearance of the break. A hot tear is ragged, follows grain boundaries and is often discoloured or oxidised because it opened while hot. A cold crack is straighter and cleaner.	Hot tear at hindered contraction, at junctions and corners; cold crack after knockout or handling
Misrun vs poured short	Where the metal stopped. A misrun leaves thin sections missing with rounded edges. Poured short leaves the top of the casting missing at a level line.	Misrun in thin and far sections; poured short at the highest part
Penetration vs burn-on vs fusion	Degree. Penetration is metal forced between grains giving a knobbly metal-and-sand mass; burn-on is sand adhering tightly; fusion is sand actually melted and glazed on.	Hot spots, heavy sections, re-entrant corners
Scab vs buckle vs rat tail	Severity of the same expansion problem. A rat tail is a shallow line, a buckle an indentation or ridge, a scab a rough metal crust over a lifted sand face.	Large flat cope surfaces
Mismatch vs core shift	What has moved. Mismatch offsets the whole casting at the parting line. Core shift changes wall thickness while the outside stays true.	Mismatch at the parting line; core shift felt as uneven wall

Where you find it is evidence

Position on the casting narrows the answer before you look closely at anything.

Cope surface. Gas rises and dirt floats, so blowholes, slag and sand tend to collect on upper surfaces.
Over a core. Points toward core gas and core venting.
Thermal centres and junctions. The last metal to freeze, so shrinkage and hot tears.
Near the ingate. Erosion, cold shot and washed sand.
Thin and far sections. Filling problems: misrun and cold shut.
Parting line. Flash, mismatch and crush.

When it appears matters

Record the stage at which the defect was found, because it changes what you are looking at.

As cast. Surface and filling defects show first, sometimes under adhering sand.
After shot blast. The surface reads honestly for the first time; scabs, penetration and cold shuts become much clearer.
After machining. Subsurface blowholes and shrinkage appear here, often for the first time. A defect found at the machine still belongs to the heat, the pattern and the cavity that made it, which is why those details are worth carrying on the record.

What to do when you are not sure

This is the part that matters most for a new inspector, and it is the opposite of what people expect.

An honest "unknown" is worth more than a confident guess. A guessed name does not simply fail to help; it adds a wrong entry to the count, shifts the ranking, and can send a corrective action toward the wrong process. An unknown, with a good photograph, costs the plant nothing and can be settled by a supervisor or metallurgist in a few seconds.

Photograph it before the casting moves, with enough light to show the wall or edge of the defect.
Record what you can be certain of: the part, the cavity, the heat and where on the casting it sits.
Mark the defect as unknown rather than choosing the nearest-sounding name.
Let it be reviewed, and then look at what it turned out to be. That is how the next one becomes obvious.

A register that makes unknown an easy, respectable answer will be more accurate than one that quietly pressures everybody to pick something. This is covered further in the defect register guide.

Building the eye

Defect identification is learned by seeing many examples with the answer attached, and the most useful examples are your own plant's castings rather than photographs from a book. Your alloys, your sand, your patterns and your surface finish are what an inspector will actually meet.

Where each entry keeps both the first call and the corrected one, the plant slowly builds its own teaching set: this is what an inspector said, this is what it turned out to be, and here is the photograph. Reviewing a few of those each week is a faster way to bring a new inspector on than any amount of classroom description, and it keeps the knowledge in the plant rather than in one or two people.

Frequently asked questions

How do I tell a blowhole from a shrinkage cavity?

Look at the wall of the cavity. A blowhole is smooth and rounded because trapped gas pushed the metal aside. A shrinkage cavity is rough, jagged and dendritic because metal pulled away as it solidified. Position helps too: blowholes sit near the cope or over cores, shrinkage sits at thermal centres and junctions.

What should I do if I cannot tell which defect it is?

Record it as unknown, photograph it clearly, and note the part, cavity, heat and where on the casting it is. A guessed name adds a wrong entry to the count and can send corrective action after the wrong cause, whereas an unknown can be settled by a supervisor or metallurgist in seconds and becomes a training example afterwards.

Do all defects show on the as-cast surface?

No. Surface and filling defects usually show as cast or after shot blast, but subsurface blowholes and shrinkage often appear only at machining. A defect found at the machine still traces back to the heat, pattern and cavity that produced it, so those details are worth recording at inspection.

How long does it take to train a new casting inspector?

It varies with the range of castings and how often the trainee sees each defect. What shortens it reliably is reviewing real examples from your own plant with the agreed classification attached, rather than learning from general descriptions alone.

Log defects on the floor, free

CaRe 101 is a free shop-floor app from Versatile: your team photographs the casting, marks the defect and taps its name - no typing, works offline. The rejection register builds itself, so you can see which defects hit which parts and act on the pattern.

Open CaRe 101 - free See how it works