In this two-part foundry series, we explore the most common core defects and provide the most probably casuses. If you run into these core defects, use this troubleshooting guide to check your system. Minimizing the amount of defects in the core making room will boost overall production.
Common Core Defects
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)
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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