Shoe sole defects: cracks, scratches and deformation
The sole takes the weight, the flexing and the wear. Sole defects can come from the supplier, from storage or from assembly, and some only show when the shoe bends.
Cracked soles
What it is. Splits in the sole, on the surface or deeper, often where the shoe flexes.
Where it starts. Compound or curing problems, a bad batch from the supplier, storage that's too cold or too hot, or excessive strain during assembly.
Why inspection misses it. A hairline crack closes when the sole is flat and only opens when the shoe bends, and in the tread grooves it hides in the pattern.
How to prevent it. Check sole batches on arrival, run flex tests, store soles as the supplier specifies and record the batch of every sole.
Sole scratches
What it is. Marks on the sole surface, especially on the sidewalls that stay visible.
Where it starts. Handling, contact with conveyors and work surfaces, or roughing that went past the bonding area.
Why inspection misses it. On the sidewall a fine scratch blends into the texture, and over-roughing stays hidden until the shoe is assembled.
How to prevent it. Protect soles between operations, keep roughing within the marked area and keep work surfaces clean.
Deformed soles
What it is. Warped soles, uneven thickness, or soles that don't sit evenly on a flat surface.
Where it starts. Uneven cooling during injection or vulcanisation, storage under weight or heat, or uneven pressing during assembly.
Why inspection misses it. Deformation is subtle on a single shoe and shows when the pair sits side by side on a flat surface.
How to prevent it. Check soles on arrival, store them free of weight and heat, set the press evenly and stand the pair on a flat surface at inspection.
How TreadlyAI helps
Photographing the shoe right after the stage where these defects start helps catch them before they move down the line. TreadlyAI highlights the defect area, records every inspection and alerts you when defects pass the limit you set, so you can fix the cause and not just the pair.
Other areas of the shoe
- Upper: Scratches, stains, creases and holes in the leather or upper material. Many come from the raw material or from handling between operations.
- Stitching: Loose or skipped stitches, thread ends on show and uneven seams. Cosmetic defects that can open up with wear.
- Bonding: Glue past the bonding line and soles that come apart. A multi-step process where every step counts.
- Finishing: Mould marks, uneven paint and dirt. The last chance to catch a defect before the box.
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