Heat-checking crack
Heat checks are fine network cracks on the surface of die-casting molds. They are caused by constant thermal shock: hot metal expands the surface, cooling contracts it again – until the material at the surface cracks.
What Heat Checks Are
Heat checks are fine, network-like cracks that form on the surface of die-casting molds. They look like a fine pattern of hairline cracks and are not caused by a single overload, but by thousands of repetitions.
Why They Form
Thermal shock is the cause: liquid aluminum at over 600 °C hits the mold surface and expands it, and the subsequent cooling contracts it again. This constant change fatigues the material at the surface until it cracks.
Where They Occur
Heat checks appear preferentially at hot spots of the mold – at gate areas, thin ribs, and edges, where the temperature change is greatest.
When Welding
Heat checks must be completely ground or milled out before welding, otherwise they will continue under the repair. Then weld hot and temper to restore the hot strength of the mold.