Sand Casting Core Defects Series – Part 2

Part 2

Core showing thin walls

Melt point too high (above 218 degrees)
Lack of heat (below 450 degrees)
Invest time too short
Sand temperature too cold (below 60 degrees)

Core showing parting line shift

Worn locators
Missing locators
Box made improperly

Poorly drained cores

Melt point of sand too low (below 205)
Hot spots in core box near blow end
Invest time too long
Drain time too short
Blow hole too small for sand to drain out
Sand temperature too hot (above 90 degrees)

Core showing thick walls

Melt point too low (below 205 degrees)
Heat too high (above 550 degrees)
Invest too long
Sand temperature too hot (above 90 degrees)

Core showing cracks

Core walls are too thin
Core is under cured
Core is over cured in areas
Core box is opening uneven
Bushings or locators are worn
Missing locators
Back draft in core box
Sand has low hot strength (too weak)

Common Core Defects

Core sticking in box

Sand too cold – should be between 60 to 80 degrees
Box too cold – below 450 degrees (450-550 degrees)
Box too hot – above 550 degrees (450-550 degrees)
Free resin in sand due to vibration or fracturing of sand grains
Blow pressure too high – average blow pressure 30-50 lbs (blasting on)
Blow hole in blow plate larger than blow hole in core box (blasting on)
Blow hole in blow plate off center of blow hole in core box (blasting on)
Blow time too long
Box has just been cleaned – no film left on surface of core box
Box is dirty causing back drafts
Lack of wax in sand (release agent)
Lack of venting in core box – causing operator to raise air pressure or lengthen blow time (blasting on)
Cure cycle is too short – core is yellow – resin sticking
Core cycle is too long – core is black – resin is burning on
Core box has back draft

Core is showing peel back (voids under skin)

Very high melt point of sand (above 220 degrees)
Cold areas in core box (more heat-more burners)
Burners out in some areas
Core box temperature below 450 degrees
Vibrator too strong during rock and drain cycle
Low density (sand will not stick together)
Blow pressure too low (creating low density)
Blow pressure too short (causing low density)
Too high of blow pressure – and long blow timer (together they cause chilling in the box in vent areas)
Cold sand (below 60 degrees)
Moisture in blow lines (poor flow ability causing poor density and chilling of the box)
Vents plugged (air not getting out)
Lack of vents (air not getting out)
Lack of seal between core box and blow plate (blowing out which causes low density)
Sand may be to coarse
Dirty box (excessive build-up from resin and release agent causing poor heat transfer)

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