Resin sand loss on ignition (LOI) is the percentage of mass lost after high-temperature ignition, mainly reflecting the content of resin binder, moisture, crystal water and carbonate decomposition volatiles. It is the core indicator for foundry sand reclamation and molding-sand performance control.
1. Standard basis
The primary reference is GB/T 2684 'Testing method for foundry sand and mixtures' (current 2009 edition; the 2021 edition also lists the same item), with JB/T 8583 'Technical conditions for reclaimed resin sand' as a supplement. Samples are usually taken from multiple points of the sand stream or heap, reduced to about 500 g, and dried at 105±5°C to constant weight before the LOI test.
2. Procedure
Weigh about 1–5 g (commonly 5 g or 1 g) of sample into an ignited-to-constant-weight crucible and place it in a muffle furnace. The reclaimed-sand method commonly ignites at 1000°C for 1 h, while the coated-/resin-sand method commonly uses 850±20°C to constant weight. Cool in a desiccator, weigh, then re-ignite, cool and weigh, repeating until two masses meet the constant-weight requirement.
3. Calculation
LOI (%) = (W1 − W2) / W1 × 100%, where W1 is the sample mass before ignition and W2 the constant-weight mass after ignition and cooling. Subtract the empty-crucible mass in the calculation and report the result to two decimal places.
4. Control range and significance
Reclaimed resin sand is generally controlled at 2.0%–3.5% LOI; above 4.0% it indicates poor reclamation or excess binder and reclamation must be intensified (higher attrition, air-classification velocity, or 15%–25% new sand addition). Coated sand for non-ferrous casting is often held at 1.8%–2.5%; excessive LOI raises casting gas evolution and the risk of blowhole defects.
5. Relation to constant weight
Accurate LOI depends on the 'ignite to constant weight' judgement. If constant weight is not truly reached, residual volatiles underestimate LOI and overestimate sand cleanliness. Automated instruments replace manual repeated weighing by reaching a prescribed constant-weight precision (e.g. 0.3 mg) within two cycles, greatly improving repeatability and throughput.
6. LabStone solution
The LabStone IRT-A Ignition Residue & Ash Tester covers 500–1000°C and automatically performs resin-sand/coated-sand LOI: automatic heating, holding, cooling, weighing and constant-weight judgement, reaching 0.3 mg within two cycles with no manual handling of hot crucibles, fitting the GB/T 2684 LOI item.
