For a chemically bonded foundry core, a clean, well-graded sand can still perform poorly if its surface chemistry interferes with the binder. Qualification should therefore connect grading, grain shape, moisture, pH, acid demand value (ADV), loss on ignition and contaminants to the resin/catalyst system actually used [1–5].
In Morocco, this logic is relevant to an industrial base in which metallurgy and metalworking supply transport, construction, energy and other manufacturing chains [6]. This reference establishes industrial context; it proves neither the use of a particular core-making process nor a Moroccan sand specification.
1. Why core making requires more than an AFS number
Particle-size distribution remains fundamental. Finer sand provides more specific surface to coat and can increase binder demand, while coarser sand can alter casting surface finish. SAMSA specifically highlights this trade-off for foundry sands [7].
In a chemically bonded system, however, core strength also depends on binder polymerization. A recent industrial review shows that sand size, shape, chemistry, moisture and reactive minerals can alter cure and strength, sometimes enough to make a previously stable binder setting unsuitable for a new sand source [4].
Procurement takeaway: do not approve a new sand only because its AFS index resembles the previous lot. Validate its interaction with the binder system as well.
2. pH and acid demand: two complementary measurements
SAMSA measures pH on 50 g of sand with 50 ml of prepared water after stirring and a stabilized reading [2]. This protocol shows why a pH result is meaningful only when the method is defined: solid-to-water ratio, water quality, stirring, calibration and stabilization time affect comparability.
Most importantly, SAMSA warns that pH alone can be misleading. Sparingly soluble carbonates may appear inconspicuous in an aqueous measurement and then react strongly in an acidic environment. pH + ADV is therefore recommended when investigating a new material [2].
ADV is a titration intended to characterize the sand’s acid consumption. It is particularly relevant to systems in which curing depends on an acid catalyst: a basic or carbonate-bearing fraction can consume part of the acid and alter polymerization [1,4].
| Control | What it indicates | What it does not prove by itself |
|---|---|---|
| pH | Suspension response under a defined method | Full compatibility with a binder |
| ADV | Sand acid consumption in the protocol | Final core strength |
| Particle size | Size distribution and surface to coat | Surface chemistry |
| Moisture | Free water that can affect dosing and cure | Nature of contaminants |
| Loss on ignition | Mass change on heating under the method | A unique cause of that loss |
3. Why ADV is not a universal threshold
The SAMSA protocol uses defined quantities of sand and hydrochloric acid followed by sodium-hydroxide titration to several pH points [1]. It also states an important limitation: sands containing more than 0.25% free calcium carbonate cannot be satisfactorily evaluated by this technique. That value belongs to the applicability limit of the SAMSA method, not to a universal foundry-core sand specification.
The 2026 review in the International Journal of Metalcasting reinforces this caution: sands with similar ADV values can show different curing behavior because ADV does not describe every chemical species or interaction mechanism [4].
ADV should therefore be used as an indicator of interaction risk, followed by binder testing: work time, strip time, early strength, strength after storage and casting behavior as required by the foundry.
4. Loss on ignition: especially useful for tracking residues and reclamation
Loss on ignition (LOI) is often tracked when a system reuses reclaimed sand. It can reflect organic residues or other constituents that lose mass during the test. It should not, however, be interpreted as a specific measurement of remaining binder.
Work on core-making systems shows that reclaimed-sand properties can evolve as residues, fines and mineral species accumulate. Control should therefore track trends across several parameters rather than one isolated number [4–5].
For new sand, low LOI can be a useful cleanliness indicator in a defined specification, but no universal limit is proposed here. Method, temperature, duration and calculation basis should be contractually defined.
5. Grading, shape and fines: the surface to coat matters
Particle-size distribution affects specific surface, packing, permeability and surface finish. SAMSA notes that relatively coarse sand generally requires less binder than finer sand, potentially at the cost of a coarser casting surface [7].
This does not mean buying “the coarsest sand.” For thin or complex cores, geometry, required strength and the mixture’s ability to fill tooling can push the decision the other way. An excessively narrow distribution can also change the core’s mechanical behavior.
The useful specification is therefore a particle-size curve with tolerances, not only an AFS number. Add grain shape and a process-defined fines limit where needed.
6. Moisture: a small variable with a large effect on some cures
Organic binder systems are sensitive to reaction conditions. The 2026 review identifies moisture, temperature, binder/catalyst dosage and sand chemistry among the variables that can alter polymerization [4].
Moisture should be controlled for two reasons: it changes the dry mass actually dosed and can directly affect system chemistry or kinetics. The acceptable tolerance depends on binder, equipment and shop conditions; it should be validated rather than copied from a foreign supplier datasheet.
7. The binder changes how results should be read
An acid-catalyzed furan system does not necessarily respond to a sand in the same way as a phenolic-urethane system or an inorganic binder. Experimental work on no-bake cores shows that acid-hardener quantity changes strength and hot behavior, while storage time and resin type also matter [5].
A material certificate therefore cannot meaningfully declare a sand “compatible with all binders.” Compatibility must be demonstrated within a defined process window.
8. Seven-step supplier qualification plan
- Describe the process: core type, alloy, binder, catalyst, equipment, cycle time and storage conditions.
- Set particle size: curve, AFS if used, fines, grain shape and tolerances.
- Characterize chemistry: pH and ADV where relevant, plus chemical/mineralogical analyses when risk justifies them.
- Control moisture and LOI: with explicitly defined methods.
- Make test specimens: same dosage, mixing, temperature and protocol when comparing sources.
- Validate in production: work time, stripping, strength, breakage, defects, binder consumption and stability.
- Lock incoming control: lot certificate, sampling, test frequency, tolerances and deviation procedure.
9. What a buyer in Morocco should request
For initial qualification, request at minimum product and lot identification, the particle-size curve, moisture and the methods used. Add pH, ADV, LOI, chemistry or mineralogy when the binder, sand history or observed defects make them relevant.
The Moroccan context supports a serious industrial approach: the ministry describes metallurgical and mechanical industries as an important link in the national manufacturing chain [6]. But none of the sources reviewed justifies turning that sector context into a single Moroccan specification for core sand.
Conclusion: qualify the sand–binder pair, not the sand alone
The right core sand is not defined by a magic AFS, pH, ADV or LOI number. A robust decision combines sand characteristics, test method, binder system and results on test specimens and then in production.
pH and ADV are particularly useful for detecting potential chemical interactions, but they should be read together and within the limits of their methods. Grading, fines, moisture and LOI complete the control plan. To secure supply in Morocco, the best specification is one that links each tolerance to a measurable process risk and a reproducible incoming-inspection method.