Three in the afternoon at a seal plant. A sorter has been bent over a black tray under a ring-light since lunch, rolling small O-rings between her fingers and flicking rejects into a cup. Early in the shift she caught a hairline nick on a ring no thicker than a bootlace. Now her eyes ache and the rings blur. A ring with a short non-fill on its inner face goes into the good pile. It ends up in a customer's valve, and the whole lot comes back.
The first strain on our seal and O-ring makers page is exactly this: sorting under a lamp tires the eyes, and one missed fault can sink a lot. Machines help, but in most seal plants the final word on each ring still rests with a person at a bench.
What the sorter is looking for
- Parting line flash left after cryogenic tumbling or hand trimming.
- Non-fill, a short patch where compound did not reach the cavity edge.
- Flow lines and knit marks, faint streaks where compound met but did not bond well.
- Nicks and cuts from trimming, tumbling or rough handling.
- Trapped air and blisters, small bumps or pits on the surface.
- Backrinding, a torn, ragged zone along the parting line.
- Foreign specks, dust or fibre moulded into the surface.
Many of these are smaller than a grain of rice and only visible when the ring is rolled under the right light. Seeing them reliably for hours is a skill, and it fades with fatigue.
Why faults get missed late in the shift
Sustained close attention drops after a long unbroken spell. Glare from a badly placed lamp, a chair at the wrong height and a tray with poor contrast all speed the decline. Sorters often go hours without a break because the lot must ship. Pay adds to it. Where sorters earn by the count, a careful pace costs money. Where they earn helper wages, the best ones leave for better-paid work, and the bench fills with newcomers.
Few plants can say how accurate each sorter is. Rejects are counted, but missed faults only appear at the customer. Without that information, a tired sorter and a sharp one look the same on paper.
What one missed ring costs
A seal customer who finds one bad ring often rejects or re-inspects the whole lot. The plant pays for re-sorting, freight and a debit note. Worse, the customer may ask for extra inspection records on every delivery, which adds work for months. Batch tracing then points at a sorter, and if that feels like blame, the whole bench learns to say less about doubtful rings.
Six fixes that keep the bench sharp
- 1
Cap continuous sorting spells
Fix a maximum spell at the lamp, followed by gauging, packing or a short rest. Put the rotation on the rota board. The shift and attendance process for seal makers can hold it.
- 2
Set up every bench properly
A ring-light or diffused lamp placed to avoid glare, a contrast tray in black or white to suit the compound, a chair and footrest at the right height, and the magnifier at a comfortable distance.
- 3
Use seeded trays to coach
Mix known faulty rings into a sample tray and see which ones each sorter finds. Use the result to coach and adjust spells, never to punish. Performance practice for seal makers covers how to keep it fair.
- 4
Write the sorter's job properly
List the defects, the master samples, the gauges and the rotation in a job description. Role design for seal makers shows the format.
- 5
Grade sorting as a skilled trade
Two or three sorter grades, each with a seeded-tray test and a pay step. Compare those rates with nearby work through compensation benchmarking for seal plants.
- 6
Offer an eye check
At joining and from time to time after, arranged through a local optician. A sorter who needs reading glasses and does not have them is working blind to the smallest faults.
Checks for the owner this week
- Time how long sorters sit at the lamp without a break.
- Sit at a sorting bench for ten minutes. Is there glare? Is the chair right?
- Sort last month's rejects by hour and see when misses happen.
- Compare sorter pay with helper pay, and ask the sorters how that feels.
- Ask whether any sorter has had an eye check since joining.
Further reading
The full people picture for the trade sits on our rubber products hub. For setting rates for finishing and sorting work, read paying finishing teams fairly, and for tracking sorters' skills, the skill matrix template for rubber plants includes a lamp sorting column.
