Casting Defect Analysis

SURFACE BLOW HOLECharacteristic featuresIndividual or• Groups of cavities Mostly large with smooth walls.

Incidence of the defect•

Gases entrapped by solidifying metal on the surface .• which result in a rounded or oval blow hole as a cavity.

• The defects are nearly always located in the cope part of the mould

• The formation of blow holes is more intense with grey iron castings than with SG iron.

SURFACE BLOW HOLE

Formation of a large gas bubble in the top of a grey cast iron

 

SURFACE BLOW HOLE

Low alloyed grey iron casting. Formation of surface bubbles in the top part

SURFACE BLOW HOLE• POSSIBLE CAUSES• Clay-bonded sand

Moisture content of sand too high, or water released too quicklyGas permeability of the sand too lowSand temperature too highBentonite content too highToo much gas released from lustrous carbon producer

• Moulding plantCompaction of the mould too high

• Gating and pouring practiceCasting temperature too lowMetallostatic pressure too low when pouring

SURFACE BLOW HOLE• REMIDIES

• Clay-bonded sandReduce moisture content of sand.

• Reduce inert dust content.Improve gas permeability.

• Endeavour to use coarser sand.• Reduce bentonite and carbon carrier content.

Reduce sand temperature. • .

Use slow-reacting lustrous carbon producer or

SURFACE BLOW HOLE

• Moulding plantReduce compaction of the molds. Ensure more uniform mold compaction through better sand distribution.

• Gating and pouring practiceIncrease pouring temperature, if necessary increase pouring speed.Increase metallostatic pressure by changing the gating systems.

SURFACE BLOW HOLEFeature Control

Water content Decrease

Compactability Decrease

Permeability Increase

Fines content Decrease

Bentonite content Decrease

Inert dust Decrease

Active carbon Decrease

Loss on ignition Decrease

PENETRATION

• Characteristic featuresDegree of roughness which is greater than the size of sand grains, at hot spots or under-compacted sections.

• Incidence of the defectPenetration particularly occurs at positions where parts of the mold have been heated to a greater degree (edges, thick walled castings, near to the gate), and at sections where the sand has been poorly compacted.

PENETRATION

Grey iron casting. Penetration at the hottest spot adjacent to the ingate

PENETRATION

Micrograph of the metal/sand interface in a grey iron casting. Purely physical penetration of the liquid iron

PENETRATION

• Possible causes

Clay-bonded sandSand too coarseInsufficient carbon carriersInsufficient finesToo high compactability

• Moulding plantInsufficient and non-uniform mould compaction

• Gating and pouring practiceMould and core sections overheated

PENETRATION• Remedies Clay-bonded sand

Make the sand finer by using finer inflowing core sand, or by adding finer sand to the circulating sand. Increase quantity of carbon carrier.

Increasing the lustrous carbon producing capacity reduces the wetting of the surface of the sand.Increase coke content.Increase quantities of fines.

Reduce the compatibility of the sand. This increases its flow ability. Better compaction is also possible.

PENETRATION

• Moulding plantImprove mould compaction.

• Increase the compacting pressure. • Achieve more uniform mould compaction

through better sand distribution.Products containing graphite improve compaction and increase packing density.

PENETRATION

• Gating and pouring practiceImprove gating. Avoid too high quantities of inflowing metal and thus local overheating.Increase spacing of patterns. Under certain circumstances this leads to reduction of overheated areas.Reduce casting temperature.

PENETRATION Feature Control

Water content Decrease

Compactability Decrease

Permeability Decrease

Fines content increase

Bentonite content Increase

Inert dust Increase

Active carbon increase

PIN HOLE• Pinhole porosity - surface blowholes

Differentiation is made between hydrogen pinholes, hydrogen-nitrogen pinholes and pinholes due to CO-slag reactions.

• Characteristic featuresPores or small blowholes with a smooth surface.

• Sub-surface blowholes often contain a thin graphite film. • There is no differentiation between hydrogen and

hydrogen-nitrogen pin holes.• Pinholes due to CO-slag reaction also have smooth

surfaces.

PIN HOLE

Large areas of surface bubbles on a grey iron casting

PIN HOLE

Bubbles over the complete surface of a grey iron casting.

Section through the surface of a grey iron casting in the area of pinhole formation. Pinhole formation is promoted by surface oxidation,

 

PIN HOLE

Section through a surface bubble in a grey iron casting, hydrogen/nitrogen defect

PIN HOLE

Microstructure of a slag/gas defect in a grey iron casting

PIN HOLE

• Incidence of the defectPin holes can appear individually or over an area. All areas of the casting can be affected. However, pin holes are more common in areas of the casting located away from the gate. Hydrogen and hydrogen-nitrogen pin holes occur in both grey and SG iron castings. Pin holes due to CO-slag reaction only occur in grey iron castings

PIN HOLE• Possible causes• Metallurgical

Ferrous metals Nitrogen content in the melt too high due to the charge composition.Proportion of oxides, hydroxides (rust) and other impurities in the charge materials too highAluminium content in the melt too highManganese and sulphur contents in the melt too high

PIN HOLE

• Clay-bonded sandNitrogen content in the sand too high Moisture content in the sand too highLustrous carbon production in the moulding sand too low

• Gating and pouring practicePouring passages too longToo much turbulence and slag formation during pouring

PIN HOLE

• Remedies• Metallurgical

Use charge components with low nitrogen content, e.g. reduce the quantity of steel scrap.Use scrap and return material free of rust, water and oil impurities. Use return material free of adhering sand and feeder aids.Use charge materials and, above all inoculants and circulating materials, with low aluminium and titanium contents.Deoxidize melts as well as possible. Avoid excessive supply of titanium or aluminium.Reduce the formation of slag and, above all the formation of slags containing manganese sulphide, by adjusting the manganese and sulphur content

PIN HOLE• Resin-bonded sand

Reduce the amount of binder. Use binder with lower nitrogen content.Improve core venting, dress core if necessary.Add iron oxides to the core sand mixture.

• Gating and pouring practiceIncrease pouring temperatureShorten flow routes into the mouldAvoid turbulence when pouring

PIN HOLE CONTROLLING PROPERTIES

• Feature control water Decrease

Compactability Decrease Permeability IncreaseGrain size IncreaseFines content Reduce Bentonite addition Reduce

SURFACE ROUGHNESS• Characteristic features

The casting surface is rough if the maximum size of the penetration of the metal into the sand mould is in the order of that of the sand grains.

• Incidence of the defectThe defect primarily occurs near the gate and in very hot areas and is frequently to be regarded as an early stage of penetration. The defect is also found at positions where mould compaction is poor.

SURFACE ROUGHNESS

Very rough surface of a grey iron casting caused by adherence of sand grainsto the pattern during moulding

Surface roughness primarily equivalent to the sand grain size. Coarser roughness is caused by breaking loose of sand and its adhesion to the pattern plate

SURFACE ROUGHNESS• Clay-bonded sand

Sand grains too coarseToo little lustrous carbon producer in the moulding sandToo few fines in the sand.

• Moulding plantToo low compactionToo much adhesion of sand grains to the patternToo little bonding of the sand grains in the mould surface

• Gating and pouring practiceToo high pouring temperatureToo high metallostatic pressure

SURFACE ROUGHNESS

• Remedies• Clay-bonded sand

Use fine-grain sand. If necessary, refine core sand that determines the fineness of the recirculating sand.Increase production of lustrous carbon in the moulding sand. Adjust "active carbon content" to 0.35% - 0.45%Use carbon carrier that produces more lustrous carbon.Increase fines content. Increase coke formation in moulding sand, if necessary increase return of dust in order to increase fines content.

SURFACE ROUGHNESS

• Moulding plantImprove mould compaction. Increase compacting pressure. Improve sand distribution to achieve more uniform mould compaction.Reduce adhesion of sand grains to the pattern. Use a release agent or use it more frequently. Sufficiently heat patternImprove bonding of sand grains at the mould surface. Avoid rapid drying out of the surface by means of better development

SURFACE ROUGHNESS

• Gating and pouring practiceReduce pouring temperatureImprove gates. Avoid local overheating

SURFACE INCLUSION

• Characteristic featuresIrregularly formed sand inclusions, close to the casting surface, combined with metallic protuberances at other points.

SURFACE INCLUSION

Inclusions of large areas of sand and individual sand grains in a grey iron casting.

SURFACE INCLUSION

Micrograph of an inclusion defect in a grey iron casting. The enclosed sandgrains are clearly recognizable

SURFACE INCLUSION

• Possible causes• Moulding plant

Break-up of mould sections during stripping of patterns, core setting or assembling moulding flasksUneven compaction of moulds, partially too high compaction.

• Clay-bonded sandToo low compactabilityBentonite content too low or poorly developed bentoniteToo high inert material contentToo high lump content

SURFACE INCLUSION

»Too low core strengthToo much core mismatching

»Gating and pouring practicePouring rate too high, with heavy impact against mould wall surface resulting in erosionLadle too far above pouring basinPouring time too long

SURFACE INCLUSION

• Remedies• Moulding plant

Check moulds for pressure marks and, if necessary, insert pressure padsCarefully blow out mould cavitiesImprove pattern plates, increase pattern tapers and radii. Heat pattern plates and, if necessary, use release agent.Check the moulding plant for uniform flask stripping and overhaul moulding plant as necessary.Automate core setting. Check and, if necessary, modify core prints before start of production.Ensure uniform mould compaction, avoid over-compacted sections

SURFACE INCLUSION• Clay-bonded sand

Raise compactibility and thus plasticity of the sandIncrease bentonite content. Use bentonite with high specific binding capacity. Improve bentonite development by extending mixing time or by prewetting used sand.Reduce inert dust content. Reducing the dust content reduces lumps in the sand.Reduce content of lustrous carbon producer.

Gating and pouring practiceAvoid high pouring rates and impact of metal stream against mould wallsShorten pouring times, improve distribution of gates

SURFACE INCLUSION INCLUSION CONTROL PROPERTIES

Feature Control Water content IncreaseCompactability Increase Permeability = Fines content increase

LOI Decrease Inert dust Decrease Active carbon =

SLAG INCLUSION

• Characteristic featuresIrregular shape non-metallic inclusions, frequently on upper casting surfaces, which may occur in association with gas blow holes

SLAG INCLUSION

Slag in the top part of a grey iron casting, in some cases still there, in others already removed by shot blasting.

 

SLAG INCLUSION

Slag inclusions defects of a grey iron casting. Inclusions caused by turbulence

SLAG INCLUSION

Microstructure of a slag inclusions in an SG iron casting.

SLAG INCLUSION• Possible causes• Metallurgical

Oxide content of the charge too high.Too high impurity levels of oxides and hydroxides in charge materials.Poor or too slow dissolution of inoculants.Ladle lining too highly reactive.Poor de-slagging of the molten metal.

• Gating and pouring practiceCasting temperature too low and pouring rate too slowToo much turbulence when pouring and poor slag precipitation

• Clay-bonded sandProportion of inert dust too high.Proportion of bentonite too low, bentonite poorly developed or has poor binding capacity.Oxygen contents in mould cavity too high.Proportion of low melting-point compounds too high.

SLAG INCLUSION

• Remedies• Metallurgical

Keep elements which strongly react with oxygen as low as possible, e.g. aluminium, magnesium, manganese, if necessary reduce them; use materials without impurities.Optimize the use of inoculants; avoid slagging; in case of failure to dissolve, reduce grain size or do not inoculate.Dry ladle prior to use; hold molten metal in the ladle for shortest possible time; avoid alloying in the ladle; skim ladles carefully, use slag binders; if necessary use teapot ladles.

SLAG INCLUSION• Gating and pouring practice

Increase pouring temperature and shorten pouring timesImprove gating, keep pouring basin full, use slay traps. Avoid turbulence when pouring. Install strainer core.

• Clay-bonded sandReduce proportion of inert dust, if necessary add new sand and reduce dust recirculation.Use bentonites with increased binding capacity and high montmorillonite content, if necessary increase proportion; improve development of bentonite.Increase lustrous carbon production in the moulding sand or use carbon carriers with higher lustrous carbon producing capacity.

Burnt-on sand

• Characteristic featuresThin sand crusts firmly adhering to the casting. The defect occurs to a greater extent in the case of thick-walled castings and at high casting temperatures.

Burnt-on sand

Thin wall grey iron casting with closely adhering sand layer.

Burnt-on sand

• Possible causes• Clay-bonded sand

Lustrous carbon content too lowProportion of low melting substances too highMoulding plantUneven mould compaction

• Gating and pouring practiceUneven distribution of inflowing metal with resultant local overheatingTemperature of liquid metal too high

Burnt-on sand• Remedies• Clay-bonded sand

Increase proportion of lustrous carbon producer. This increases the amount of coke as well as the amount of lustrous carbon, which then results in positive separation between mould and metal.Use purer silica sands or, if necessary, add new sand. Reduce dust content. If necessary reduce the amount of bentonite.Reduce oolitization by adding new sand.

Burnt-on sand

• Moulding planEnsure uniform compaction. If necessary, increase heat removal from the moulds.

Gating and pouring practiceEven out incoming metal flowReduce pouring rateReduce liquid metal temperature

SURFACE INCLUSION SAND BURNT 0N CONTROL PROPERTIES

Feature Control Water content Decrease Compactability Decrease Permeability = Fines content Decrease

LOI Decrease Inert dust Decrease Bentonite addition Decrease

EROSION

• Characteristic featuresSand erosion principally occurs in the proximity of the gate and is frequently combined with slag inclusion. Thickening of the casting occurs in this area.

EROSION• Explanations

Erosion defects occur as a result of moisture loss where moulds have been standing for long periods without pouring. The defect has arisen with increasing frequency since the introduction of high-pressure moulding plants, as sands of lower compactibility are used. The binder is not able to hold the silica grains in the mould surface. They are flushed out and dispersed to remote regions of the casting.

EROSION• Possible causes Content of active bentonite too low.

Insufficient cohesion of the bentonite. Can be caused by inadequate bentonite quality or insufficient development of the bentoniteToo high proportion of inert dust to be bonded in the sand.Sand temperature too high. The sand dries out and loses its cohesion.Sand too coarse, therefore too small contact surface. Bonding of the grains in the mould surface is insufficient.Lustrous carbon content in the moulding sand too low. Molten metal wets the sand grains and parts them from the mould surface.Salt content in moulding sand too high. The binding capability of the bentonite is reduced.

EROSION

• Moulding plantToo low compaction of mould parts.

Gating and pouring practicePouring rate too high. Parts of mould become too hot and eroded.Volume of metal flowing through too great. Severe local overheating of the mould takes place.

EROSION• Remedies• Clay-bonded sand

Increase the amount of bentonite.Check that quality of the bentonite is in accordance with VDG (Verein Deutscher Giessereifachleute) Sheet P 69. If possible, use bentonite with lower proportion of inert material.Improve development of bentonite. Increase moisture, increase mixing times. If necessary, introduce moisturization of used sand.Lustrous carbon producers with graphite and, above all, specially prepared bentonite/graphite systems such as Quickbond, improve development of the sand.Reduce sand temperature to below 40 oC. Improve cooling of sand. If necessary, improve moisturization of used sand.Use finer sandIncrease lustrous carbon carrier in moulding sand or change over to more active materials.Increase addition of new sand when the salt content in the sand is too high. If necessary, introduce partial desalination of water.

EROSION• Moulding plant

Improve and homogenize compaction in mould. Endeavour to achieve more homogeneous mould filling. Carbon carriers containing graphite and bentonite improve the flowability during compaction.

Gating and pouring practiceReduce pouring rate.Modify the gating system to achieve uniform distribution of heat in the sand.

EROSION EROSION SAND CONTROL PROPERTIES

Feature Control Water content Increase Compactability Increase Permeability Decrease Fines content Increase

LOI Increase Inert dust Decrease Bentonite addition Increase Active clay Increase

PENETRATION

• Characteristic featuresLarge-area penetration occurs in regions of the mould which have been filled with metal too quickly.

PENETRATION

Large area penetration in regions of fast inflowing metal. Grey iron casting

 

PENETRATION

Grey iron casting. Heavy penetration all over the lower part.

 

PENETRATION• Possible causes• Clay-bonded sand

Moisture levels too high, above all "free" water in the moulding sand.Insuffficient mulling of the moulding sand. The water is quickly released.Proportion of inert dust too high, thereby binding in too much water.Amounts of binder too high and thus too much water.Sand grains too coarse. Slight pressure increase through evaporating water leads to penetration.Too much water bound in due to lustrous carbon producer and its residues.

• Moulding plantMoulds too highly compacted.Unevenly compacted moulds with over-compacted areas.

• Gating and pouring practicePouring rate too high. Metal flowing over areas with condensed water. Metal streams running together too quickly.Incomplete venting of mould and core gases from the mould cavity.

PENETRATION

• Remedies

Clay-bonded sandReduce water content by using high-quality bentonite with high thermal stability and high montmorillonite content.Reduce compactability.Improve degree of mulling by premoisturizing used sand, by accelerating water absorption of bentonite, by increasing mixing times.Reduce inert dust content through use of high-quality bentonite. If necessary restrict dust recirculation.Reduce bentonite content. Use more highly active bentonite with higher montmorillonite content.Reduce sand grain size. Use finer core sands or from time to time add fine new sand to circulating sand.Use more active lustrous carbon producer. Reduce amount of lustrous carbon producers and coke.

PENETRATION• Mouldingplant

Homogenize mould compaction and reduce compacting pressures.Endeavour to achieve more uniform sand filling.

• Gating and pouring practiceReduce pouring rate by modifying gating system. Reduce rate of mould filling.Spray oil into sections at risk, thereby avoiding water condensation at these points.Provide vents to improve removal of gases containing water vapour.

PENETRATION PENETRATION SAND CONTROL PROPERTIES

Feature Control Water content Decrease Compactability Decrease Permeability Decrease Fines content Decrease

LOI Increase Inert dust Decrease Bentonite addition Decrease Active clay =

SWELLING• Characteristic features

Solid thickening on internal and external surfaces as well as edges of castings. Frequently appearing in association with rough casting surface.

• Incidence of the defectThe defect may appear principally in areas which have not been optimally compacted. Also, it can often appear in lower sections of the mould. In the case of grey cast iron expansion may occur as a result of expansion pressure. The defect frequently appears in conjunction with "roughness" and "penetration" defects

SWELLING

Large grey iron casting. Thickening at undercompacted positions adjacent to the flask wall

SWELLING• Possible causes• Moulding plant

Uneven or poor compacting• Clay-bonded sand

Compactibility too highPoor flowability of the sand

• Resin-bonded sandInsufficient compaction

• MetallurgicalIn the case of grey cast iron expansion pressure too high

SWELLING

• Remedies • Moulding plant

Improve distribution of sand prior to compaction, if necessary, increase pressure; increase tapers on patterns

• Clay-bonded sandReduce sand compactibilityImprove flowability of the sand during compaction by using products containing graphite.

SWELLILNG SWELLING SAND CONTROL PROPERTIES

Feature Control

Water content Decrease

Compactability Decrease

Permeability =

Fines content =

LOI =

Inert dust Increase

Bentonite addition =

Active clay =

SCABBING

• Characteristic featuresIrregular small to large-area solid metallic thickening, frequently several millimeters thick.

• They often run parallel to the casting surface, their surfaces being rough. The edges frequently exhibit so-called "undercuts". Castings with solid scabbing often exhibit sand crust inclusions

SCABBING

Scabs on the top part of a large surface grey iron casting

SCABBING

Start of a scab "rats-tail" in the upper part of a grey iron casting adjacent to the ingate

SCABBING• Incidence of the defect

Scabs may appear on all casting surfaces when pouring into green sand moulds.

• They appear more frequently on the top and bottom areas of the mould cavity, highly compacted parts of the mould cavity also being at risk.

• Scabs can be created when the mould wall is heated by radiant heat.

SCABBING• Possible causes• Clay-bonded sand

Too little bentonite or poor bentonite quality in the moulding sand.Proportion of fine quartz in the sand too highMoulding sand too fine.Insufficient conditioning of bentoniteDegree of chamottization of the sand too low .Too much salt in the sand.

• Moulding plantToo high or irregular compaction

• Gating and pouring practiceSand heated up too severely by inflowing metal and too long exposure to radiated heat.

SCABBING• Remedies

Clay-bonded sandIncrease bentonite content in the moulding sandUse bentonite with a higher specific binding power.Reduce proportion of fine quartz in moulding sand.Reduce recirculation of dust, if necessary use bentonites with higher montmorillonite content.Use coarser moulding sand.Improve conditioning of bentonite; prolong mixing times; wet used sand.If practical, reduce amount of new sand to increase the degree of chamottezation.Improve water quality; switch from well water to public supplies; perform partial desalinization.

SCABBING

• Molding plantReduce compaction; reduce compacting pressure.Ensure even distribution of sand and more uniform compaction of the mould.

• Gating and pouring practiceImprove gates to avoid local overheating through excessive amounts of metal.Aim for shorter pouring times and therefore shorter exposure to radiated heat.

SCABBING SCABBING- SAND CONTROL PROPERTIES

Feature Control Water content Decrease Compactability Decrease Permeability Increase Fines content Increase

LOI Increase Inert dust Decrease Bentonite addition Increase

Hot Tears• Material partition in liquid /solid state, which occurred as the

stresses, which occurred in the casting in the area of the elastic deformations, were larger than the strength of the material.

• Stresses can occur in case of uneven cooling conditions (differences in wall thicknesses). Special design of the casting can prevent contraction. –shrinkage onto the core -Hot cracks primarily occur in steel castings.

• preferred defect locations:- at sudden, steep transitions in wall thicknesses.- at wall thickness transitions with too small radiiRemedial measures:- Design suitable for stresses, balance out cross-sections with large wall thicknesses

Core damage• Unintentional protruding core parts.• Typical characteristics:

Parts of the core are displaced relative to each other.• Preferred defect locations:

At parting lines of the cores. • Remedial measures:

Check core box guides - Check core boxes (is there a defect in the core box?)

Dimensional variation• The casting has larger or smaller dimensions compared to the

dimensionally checked initial pattern released by the customer and the drawing.

• Typical characteristics:This defect can conceal a range of casting defects, starting with pattern wear, so that it is not always possible to quickly narrow down the defect.

• Remedial measures:- Check the pattern equipment and core boxes - Core print clearance- Check the mould making, mould box guides- Compact the mould

Dross• Irregularly shaped interruption in the material

Typical characteristics: Dark scars, foamy dark surfaces, very finely distributed. Dross worsens the mechanical properties, Dross mainly consists of magnesium oxy-silicates and magnesium sulphides, and is a product of the reaction of magnesium with oxygen, sulphur and silicon.

Preferred defect locations: In the upper casting surface or beneath cores. Mostly in cast iron with nodular graphite, often only visible after the casting skin has been removed.

• Remedial measures: Dross cannot be prevented, only reduced.

• Melts:- High temperature - Low residual Mg contents- Clean melting of pure raw materials- Highly concentrated Mg master alloys or pure Mg- Gas purging- Refining slags (melt cleaner)

In the work pieces:- Draw off and restrain treatment slags (large pouring basin, optimum casting system)- Filters are very effective - Dry, closed moulds- HOT casting

Elephant skin• Irregularly scared and/or creased surface with net

shaped notches

Typical characteristics: Parchment like appearance

Preferred defect locations: Normally in the top part of thick-walled castings on horizontal surfaces. The defect can effectively always be identified in unmachined casting.

• Remedial measures:

- Use pure, base iron with low sulphur and oxygen contents - Use a teapot ladle- Adjust the degree of saturation of the melt according to the casting temperature - Possible extension of the dead-melting time after the magnesium treatment- Use refining slags- Use filter

Inclusion of foreign metal• Manifestation:

Material not homogeneously formed.

Typical characteristics: Visible irregularities in the microstructure.

Preferred defect locations: On the inside of the casting, partly extending out to the surface too. during machining, the inclusions are worn down by the machining tool.

• Remedial measures:

- Adequately high temperature- Clean melting of pure raw materials- Gas purging- Draw off treatment slags and hold back (large pouring basin, optimum casting systems)- Mould fill rising, gently and fast - Filters are very effective - HOT casting

Mismatch in mold• Manifestation:

Unintentional protruding casting parts.

Typical characteristics: Parts of the casting are displaced relative to each other.

Preferred defect location: On dividing planes.

• Remedial measures:

- Check box guides, mould assembly and closure equipment- Check models

Fillet• Manifestation:

Fillets in castings, especially in wall thickness transitions do not often occur according to the drawings, or they contain defects.

Typical characteristics:- Radii at the fillets are considerably smaller in the casting than in the patters. - The surface of the fillets is maculate.

Preferred defect locations:Fillets at wall thickness transitions with large agglomerations of mass. At these places the mould material is subjected to extreme thermal stresses .

Remedial measures:- Make radii larger than those given in the drawing. - Check addition of new sand

Mould damage• Manifestation:

Irregular, widespread thickening of the outside or inside of the casting. After the pattern has been stripped, areas of the subsequent cast contour are broken off in the mould material area of the mould cavity.

Typical characteristics:Enlargement of the wall thicknesses or change in contour, the broken off areas of the mould material are then found in the casting as mould material inclusions, if the defect is caused when the mould is assembled and closed by pressing core prints or in the mould joint.

Preferred defect locations:Joint face or core prints

• Remedial measures:-Re-open the mould after assembling and closing and check for pressure points and broken off edges.-Check pattern and core box, core print allowance

Rough casting surface / Roughness • Manifestation:

Roughness must be assessed relative to the grain size of the casting selected. Under certain circumstances a workpiece cast in coarse sand with fully uniform surface must be assessed as being smooth, although it is rougher than a “rough area” on a workpiece cast in fine grained sand.

• Preferred defect locations: Close to gate, parts deep in the mould, zones with inadequate compaction

• Remedial measures:

- Use finer sand - Reduce water content - Increase compaction pressure - Reduce casting temperature

Internal Shrinkage cavities

• Defect is almost always identifiable during machining. Zones of visibly "loose" microstructure, occasionally sponge-like structure or an agglomeration of numerous small pores.

• Remedial measures:- Check the gate and feeder system - Increase the degree of saturation - Reduce the casting temperature- Carry out a solidification simulation

Dispersed shrinkage• Accumulation of small, crack-like cavities. Only visible after

machining. Cross-sections up to around 8 mm long and 1-2 mm wide, up

• All cavities are the same size and always oriented perpendicular to the surface, arranged at the outer edges of the lines bisecting the angles. to 2 cm deep.

• Remedial measures: - Minimise core sand intake - Reduce water content - Extend mixing time - Increase casting temperature

Fusion• Manifestation:

Surface defect.Thin sand crusts, which firmly adhere to the casting.

Typical characteristics: Rough cast surface.Sand sintered on the casting, which can only be removed by grinding.

Preferred defect locations: Possible on all parts of the casting.Especially in thick-walled castings.Near to the gate.

• Remedial measures:

- Add more new sand- Reduce dust fractions in sand - Uniform compaction - Check the use of blacking

• Reduce pouring temeprature

Runout• Manifestation:

During the casting, metal runs out of the box at the parting.

Typical characteristics: Casting is incomplete or fully missing

Preferred defect locations: The upper part of a casting is mostly missing

• Remedial measures:

- Clamp the two halves of the box - Place weights on mould

Rattails• Manifestation:

The defect involves a sand expansion defect, which can frequently occur in highly compacted parts of the mould.

Typical characteristics:Scratches appear on the surface of the casting, which can be partly arranged in parallel.

Preferred defect locations:On areas of the mould cavity covers but primarily on the bases. Can be mostly identified on the surface in the cast condition.Remedial measures:- Optimise mould material preparation with the aim of increasing the wet tensile strength - Fast mould filling- Reduce the casting temperature

Swell• Manifestation:

Irregular, widespread thickening of the casting on the outside or inside.

Typical characteristics: Gradual, unwanted increase in wall thickness.

Preferred defect locations: Possible in all areas of the casting, however mostly in the lower part of the mould.

Remedial measures:

- Higher binder content- More uniform compaction- Reduce casting /sprue height

Washout/Erosion• Manifestation:

Thickening of the casting at one place.

Typical characteristics: Sand washout, combined with sand and /or slag inclusions.

Preferred defect locations: Mostly close to the gate or on edges, which tend to heat up

• Remedial measures: - Choose binder with good properties at high temperatures - Greater compaction of the mould sand - Avoid high flow speeds and long pouring times

Pouring Metal Defects

Mis Runs and Cold shuts

• Metal unable to fill the mold cavity completely• Cold shut is caused when two metal streams while

meeting in the mold cavity do not fuse together properly, thus causing a discontinuity or weak spot.

• Remedial measures:- Increase casting temperature - Increase casting speed and make gates larger

Cold shot inclusion/ spray bead• Spray beads are pearl or bead shaped inclusions, which are

only loosely bonded with the metal. They are partly already visible at the surface, they are often not exposed until the machining.

• The beads are created by turbulences during casting or by the effect of spray in the mould, metal particles prematurely solidify in drip or spherical form. These splashes oxidise very easily and the oxide skin prevents the spray beads from being re-incorporated by the subsequent melt flow.

Spray bead in micro-section (etched)      unetched:

                                             

Sand Drop

Fin