Cracks in casting are the most costly defects in metal production. They ruin parts, waste materials, and delay production schedules.
The key to preventing cracks is understanding their three main types: hot tears form during solidification, cold cracks appear after cooling, and shrinkage cracks develop from uneven contraction.
Each type requires specific prevention strategies. By controlling temperature, adjusting alloy composition, and optimizing mold design, manufacturers can eliminate most casting cracks before they start.
Hot Tears
Hot tears are jagged cracks that form when metal is partially solid—between liquid and solid states. They occur because different sections cool at different speeds, creating stress that tears the weak, mushy metal apart.
These cracks typically appear at sharp corners, thick-to-thin transitions, and constrained areas where the metal cannot move freely during cooling.
Prevention strategies for hot tears:
- Reduce sharp corners – Round all internal corners with generous radii to distribute stress evenly during solidification
- Control cooling rates – Use chills in thick sections and insulation in thin areas to achieve uniform solidification throughout the casting
- Modify alloy composition – Add grain refiners like titanium or boron to create smaller, stronger grain structures that resist tearing
- Improve mold design – Create collapsible cores and flexible mold sections that move with the shrinking metal instead of restraining it
- Optimize pouring temperature – Pour at the lowest practical temperature to minimize thermal gradients and reduce solidification time
Cold Cracks
Cold cracks form after the casting has completely solidified and cooled below 400°F. Unlike hot tears, these cracks have smooth surfaces and often follow grain boundaries.
They result from residual stresses that exceed the metal’s strength at lower temperatures.
Cold crack prevention methods:
- Control cooling speed – Cool castings slowly through critical temperature ranges, especially for high-carbon steels and brittle alloys
- Heat treat properly – Apply stress-relief annealing immediately after casting to eliminate internal stresses before they cause cracking
- Avoid rapid temperature changes – Never quench hot castings in cold water or expose them to drafts during cooling
- Design for uniform thickness – Maintain consistent wall thickness to prevent stress concentration from differential cooling rates
- Use proper alloy selection – Choose ductile alloys with good low-temperature toughness for parts subject to thermal cycling
Shrinkage Cracks
Shrinkage cracks develop when liquid metal cannot feed areas that are solidifying and contracting. These cracks often appear as irregular voids or linear defects in the last areas to solidify.
They’re most common in heavy sections and isolated hot spots.
Effective shrinkage crack prevention:
- Design adequate risers – Size risers 1.5 times larger than the sections they feed and position them at the highest, thickest points
- Create directional solidification – Engineer cooling patterns so metal solidifies progressively toward the risers, maintaining liquid feed paths
- Reduce section thickness – Replace solid sections with ribbed or cored designs that cool uniformly without creating isolated hot spots
- Add feeding aids – Use exothermic sleeves and insulating materials on risers to keep them liquid longer than the casting
- Calculate shrinkage allowance – Account for typical 5-7% volumetric shrinkage in pattern design and riser sizing
- Improve gating systems – Design runners and gates that maintain metal temperature and promote smooth, turbulence-free filling
