Grade sorting happens at the end of the line, after the kiln and any polishing or rectifying. Tiles pass through measuring equipment and visual checks, and each tile is assigned a grade, a shade and a calibre. The packing machine then puts each group into its own boxes and prints the codes.
The equipment is similar across modern plants. What differs is how strictly it is set and how carefully the people beside it work.
The steps on the sorting line
- Size measurement checks each tile's length, width and squareness, and groups tiles into calibres.
- Flatness measurement checks warpage at the centre, edges and corners.
- Surface inspection looks for chips, cracks, pinholes, glaze faults and print defects, by camera, by trained sorters under lights, or both.
- Shade sorting groups tiles whose colour matches closely, either by machine or by eye.
- The line sends each tile to a stacker for its grade, shade and calibre, and rejects go to a separate stack.
- The packing machine boxes each stack and prints design, grade, shade, calibre and batch on the carton.
Where the judgement comes in
Machines measure size and flatness well, but they work to limits the factory sets. Tighten the limits and more tiles fall to a lower grade. Loosen them and more tiles pass. So the settings are a business decision as well as a technical one.
Surface faults and shade still involve human judgement in many plants. A sorter looking at thousands of tiles a shift will tire. Lighting, line speed and training all affect what gets through. A borderline tile can end up in either grade depending on who is sorting.
Shade sorting is the most sensitive step. Our guide to shade variation explains why colour varies between firings and how it is controlled.
What this means for your order
A good sorting line does not guarantee a good shipment. Problems usually come from what happens around it:
- Sorting limits are relaxed when a run has a lot of borderline tiles.
- Tiles from different runs or days are packed under the same shade code.
- Lower-grade boxes are added to a container to make up quantity.
- Re-sorted stock from the warehouse is mixed with fresh production.
The controls that stop it
Each of these is covered by contract terms and inspection. Our article on avoiding mixed grades in a tile shipment explains the controls.
What to look at on a factory visit
If you visit, spend time at the end of the line, not only in the showroom. Check the lighting at the sorting stations, the line speed, and how many sorters work each shift. Ask what limits the size and flatness machines are set to for each grade, and who can change them.
Look at the reject and lower-grade stacks too. If they are nearly empty on a busy line, the sorting may be loose. Then follow a stack to packing and check that the box codes match what was sorted.
Afterwards, check the packed result against your grade definition. Our article on checking tile grade at the factory sets out the method.
Next step
We look at sorting lines during factory audits and inspect your packed lot before it loads. To see how a plant sorts your product, book a free sourcing review.