Sampling and Acceptance Rules for Incoming Electrode Inspection

Electrodes are often racked straight after arrival, and by the time a furnace is started and a wrong dimension or a crack at the end face is discovered, the loss is no longer just the cost of the material. Acceptance exists to keep batch risk outside the warehouse at a finite inspection cost. Sampling ratios, inspection sequence and acceptance rules should be written into the contract at the signing stage, not negotiated on the spot after the goods arrive.

Sampling Ratios Follow Batch Risk

Sampling is not a fixed percentage. For electrodes of the same specification, batch and heat number, the number of pieces to be inspected can be set according to the lot size; for first deliveries, new suppliers, long-distance transport or batches with a history of packaging damage, the number inspected should be increased. Custom parts with high unit weight and many machining operations usually require piece-by-piece inspection of appearance and key dimensions.

When the sample inspection finds a nonconforming item, the handling method must also be agreed in advance: double the sample, or return the whole batch. Only when the rule is written into the contract do the people on site have a basis for executing it.

Inspection Sequence for Appearance and Dimensions

1. Packaging and marking first: check the crate for damage or signs of damp, and whether the grade, batch number and quantity on the label match the delivery note.
2. Surface next: cracks, pits, inclusions, scratches and oxidized discoloration, with particular attention to the ends and the threaded sections.
3. Dimensions after that: diameter, length, straightness, go/no-go thread gauges, measured at the positions marked on the drawing.
4. Weighing last: a large deviation between unit weight and theoretical value may indicate abnormal density or internal defects.

The sequence runs from outside to inside, performing the non-destructive items first and then deciding whether destructive testing is needed. Molybdenum is noticeably brittle at room temperature, so avoid impact and dropping during handling and measurement, or a conforming part will be turned into scrap.

What to Verify in the Quality Certificate

The certificate should correspond to the physical batch and cover grade, heat or batch number, chemical composition, dimensions and inspection conclusion. The buyer must check that the batch number on the certificate matches the label on the goods, and that the test methods and acceptance limits for each element conform to what was agreed. Where the contract requires third-party testing, the report number and the sampling method should also be filed.

The quality and inspection section of this site describes how routine inspection items are selected and can serve as a reference for building an acceptance form. Where composition or density is in doubt, ask the supplier for a retained sample from the same batch for re-testing.

Checking the certificate should not be a formality only. The measured diameter of the batch can be compared with the value recorded on the certificate; if the deviations point in the same direction, the records are credible; if the two differ substantially, ask where and with what instrument the measurement was taken. When the documents are filed, build the index by batch number so that they can be retrieved quickly if a problem arises later.

Disposition Flow for Nonconforming Items

Once an item is judged nonconforming, isolate it and attach a label so that it is not mixed with conforming material. Then send the supplier written notification within the agreed time limit, with photographs, measurement records and the sampling plan. Disposition usually covers return, replacement, concession acceptance and rework, and which one applies depends on how much the defect affects use.

Concession acceptance requires sign-off by the technical department and a record of the conditions and period of downgraded use. When the same defect recurs, it should enter supplier evaluation rather than be handled separately each time. For the relationship between purchasing specifications and acceptance parameters, see the notes on the product specification page.

Making acceptance a documented, traceable process reduces disputes and builds a basis for later material selection.