The cheapest place to catch a quality problem is the receiving bay. A deviation found in an incoming sample costs one test; the same deviation found after the material is mixed costs a batch, and after it is fired, a campaign.
Documents, and their limit
Ask for the certificate of analysis for that specific batch, the technical datasheet, and the origin of the material. Then treat the certificate as the supplier’s claim rather than as verification. File it, but base acceptance on your own sample — a disagreement between the two is itself useful information.
Representative sampling
The commonest mistake is a sample that represents nothing. Take increments from several random points of the consignment — top, middle and bottom of several bags or big-bags — combine them, and reduce by quartering to a laboratory sample. Keep a retained sample from every delivery; if a dispute arises later, it is the only neutral evidence.
What to test, by material
| Material | Critical parameters | Risk if out of spec |
|---|---|---|
| Bauxite / alumina | Al₂O₃, Fe₂O₃, SiO₂, LOI | Iron and silica lower refractoriness |
| Dead burned magnesite | MgO, CaO, SiO₂, C/S ratio, density | Lime and silica cut slag resistance |
| Calcined alumina | Al₂O₃, Na₂O, surface area | Soda forms beta-alumina |
| Graphite | Fixed carbon, ash, moisture | Ash brings impurities, hurts non-wetting |
| Clays and kaolin | Al₂O₃, Fe₂O₃, LOI, plasticity | Iron stains and lowers refractoriness |
Three impurities deserve watching almost everywhere: iron oxide, alkalis (Na₂O, K₂O) and free silica. Each forms low-melting phases, and a small percentage moves the service temperature more than buyers expect.
Physical checks
- Moisture — weigh before and after drying; you are otherwise buying water.
- Grain size — sieve and compare against the ordered range.
- Visible contamination — metal, wood, plastic, soil, or mixing with another grade.
- Colour uniformity between bags, which often reveals blending of two sources.
Red flags
A certificate with no batch number or reused across shipments; visible variation between bags; unusual moisture or caking; no stated mine or origin; and a price notably below market, which usually means lower purity or a blend. None is proof on its own, but each earns a closer look.