Sand Reclamation Unit

What is a Sand Reclamation Unit

A sand reclamation unit is an assembly of foundry equipment that takes spent molding sand from the shakeout, processes it through lump reduction, binder removal, classification, and cooling, and delivers grain clean enough to remix with fresh binder. It sits between the shakeout station and the sand mixer in the foundry sand loop, and in a no-bake plant it is the single largest determinant of sand running cost. The goal is not merely to return as much mass as possible, but to return grain whose surface and size distribution are close enough to new sand that the casting quality does not degrade.

The need for reclamation comes from what binders leave behind. After pouring, a resin residue remains on the grains of chemically bonded sand, and the presence of that spent binder makes the sand unusable without first removing the residue. In green sand, repeated heating cycles convert active bentonite to inactive dead clay, and the fines fraction climbs. In both cases, simply re-screening and re-cooling, which is properly called reuse or recycling rather than reclamation, leaves the contaminating film in place and steadily degrades the working sand. Reclamation removes that film.

It is worth fixing the vocabulary, because the three terms are often used loosely and the difference drives equipment choice. Recycling returns sand to the muller with only lump breaking, magnetic separation of metallics, screening, and cooling. Attrition adds the mechanical scrubbing that abrades the binder film off the grain. Reclamation is the complete restoration: attrition combined with classification to remove the liberated fines, and, where the binder is organic, a thermal stage that combusts the residual film. A reclamation unit is therefore a system, not a single machine.

Foundry sand reclamation is a mature discipline. Continuous mixers and the first dedicated reclamation plant for the furan no-bake process appeared in the early 1970s, and the field has since split into well-defined mechanical, thermal, and wet branches, each matched to a binder family and a target reclamation depth. Modern plants integrate shakeout, attrition, dust extraction, classification, and cooling into a controlled line, often with sand temperature and dust loading instrumented and trended.

Three engineering metrics anchor any reclamation discussion: reclamation yield (the fraction of spent sand returned to service), reclaimed sand quality (loss on ignition, grain fineness number, acid demand value), and energy plus consumables cost per tonne reclaimed. These three trade against each other. Pushing yield toward 90 to 95 percent on organic sand usually requires a thermal stage, which raises energy cost; accepting 70 to 80 percent yield from mechanical attrition alone is cheaper but leaves more residual binder. The selection task is to place your plant at the right point on that curve for your castings.

Reclamation Methods and Types

There are three primary reclamation methods, distinguished by the physical mechanism used to detach the spent binder: mechanical (attrition), thermal, and wet. Each suits a different binder chemistry and a different target reclamation depth, and large plants frequently combine them, for example mechanical pre-treatment ahead of thermal finishing. The table below compares the three methods on the dimensions that matter at selection.

Mechanical reclamation, also called attrition or dry reclamation, abrades the spent binder film off each grain and then classifies out the liberated fines with an upward air flow. It is the workhorse for cured organic no-bake sand because the brittle resin film fractures and rubs away cleanly. Within mechanical reclamation, three sub-types dominate: pneumatic attrition, where grains are accelerated against a target plate or against each other; vibratory attrition, where a vibrating chamber rubs grains together; and impact scrubbing. Vibratory technology has largely displaced impact scrubbers for routine attrition, because a vibrating mill efficiently scrubs the binder off the grains without aggressively damaging grain shape.

Thermal reclamation heats the sand to combust the organic binder completely, typically in a fluidized bed at roughly 700 to 800 degrees Celsius, with some industrial systems running the combustion zone hotter still. At that temperature the resin film burns off and loss on ignition drops below 0.5 percent, recovering grain close to new-sand cleanliness. Thermal plants are the route to high reuse fractions and to controlling residual nitrogen, but they carry the highest energy cost and require a downstream cooler before the sand can return to the mixer. They are well matched to oil-bonded sands and organic no-bake systems that contain no clay.

Wet reclamation uses water scrubbing to detach and wash away soluble binders, and is the classic route for sodium silicate (water glass) bonded sand, whose residue is water sensitive. It partially removes coatings and organic matter and produces a wet product that must be dried before reuse, which is why wet plant is less common than mechanical and thermal in modern Western foundries. It remains relevant where the chemistry specifically favors aqueous removal. The three methods are not mutually exclusive: a plant may mechanically pre-treat sand to break lumps and remove the bulk of the binder, then pass it through a thermal stage to finish the cleanup to near new-sand quality.

Process Stages and Equipment

A reclamation unit is best understood as a sequence of stages, each performed by a recognizable machine. Spent sand does not go straight from shakeout into the mixer; it passes through lump reduction, metallics removal, attrition, classification, cooling, and storage, with thermal foundries inserting a calcining stage. Understanding the sequence is what lets a buyer judge whether a quoted package is complete or whether key stages have been omitted. The table below maps the stages, their function, and the typical equipment.

Lump reduction and metallics removal come first because oversize lumps would jam attrition machinery and stray metal would damage it. A vibrating shakeout deck breaks the bulk of the mold, and a rotary lump breaker or screen reduces the remainder to grain size. A magnetic separator then strips shot, gates, flash, and tramp iron. Before sand can be processed in a thermal system in particular, lumps must be reduced in a mechanical stage first, so attrition mills are part of the typical sequence even in thermal plants.

Attrition is the heart of mechanical reclamation. Primary attrition removes the bulk of the binder, and a secondary attrition unit polishes the residual film. Secondary attrition units are designed to remove a substantial share of the remaining binder without damaging the grain, which is critical because over-aggressive scrubbing rounds or fractures grains and raises the fines content, shifting the grain fineness number and increasing binder demand on the next cycle. Grain preservation is therefore a design objective, not just an efficiency metric.

Classification and cooling finish the line. An upward air flow in a fluidized bed lifts the liberated fines and dead clay, which are lighter than the sand grains, and carries them to the dust collector, while clean grain stays in the bed. The same fluidized-bed cooler-classifier cools the sand, in some designs to within a few degrees of the cooling-water inlet temperature, so the grain reaches the mixer at a controlled temperature. Because binder cure rate is temperature sensitive, this cooling stage is integral to reclamation rather than optional. Dust extraction here is also an environmental requirement, not merely housekeeping, since the captured fines are the contamination being removed from the loop.

Binder Systems and Quality Criteria

The binder system decides which reclamation method applies and how the reclaimed sand must be tested. The two broad families are clay-bonded green sand, which uses bentonite and water, and chemically bonded sand, which uses an organic or inorganic resin cured at room temperature or by gas. Within chemically bonded sand sit furan no-bake, phenolic ester no-bake, phenolic urethane no-bake, phenolic urethane cold-box, and sodium silicate systems, each leaving a different residue. In a typical phenolic ester no-bake mix the resin content is on the order of 1 to 1.5 percent of sand mass, which sets the scale of the film the reclamation unit must remove.

Green sand is bonded with clay and water and contains no organic resin to combust, so its reclamation is mechanical: attrition liberates the inactive dead clay and fines, and air classification removes them. A widely used and economical strategy is to mechanically reclaim spent green sand and feed the cleaned grain into the core room as core sand, capturing value without a thermal stage. Mixing green sand and chemically bonded sand in one loop without separating clay from resin is avoided, because the two residues impose unpredictable and conflicting binder demand.

Chemically bonded no-bake sand carries a cured organic film that abrades mechanically but is fully eliminated only by thermal combustion. Acid-cured furan and alkaline phenolic films are brittle and reclaim well mechanically; phenolic urethane cold-box cores carry more nitrogen, which pushes foundries toward thermal reclamation to control nitrogen-related gas defects. Sodium silicate sand, being inorganic and water sensitive, is the classic candidate for wet reclamation. The reclamation method must be chosen against the specific chemistry, not the generic label no-bake.

Reclaimed sand is accepted or rejected on a small set of standardized tests, summarized below. These follow American Foundry Society (AFS) mold and core test procedures and national standard sieve and binder methods, but the pass-fail limits are set by the foundry against its own binder supplier requirements. A single number, such as a low loss on ignition, is never read alone, because a clean ignition result can still hide a contaminated grain surface that raises binder demand.

Representative published figures give a sense of scale. Mechanically reclaimed no-bake sand commonly lands near 1.5 to 3 percent loss on ignition, while thermal reclamation drives loss on ignition below 0.5 percent, close to new sand. One study of reclaimed sand reported loosely bound clay content around 1.5 percent, loss on ignition near 1.9 percent, and an acid demand value of about 1.5 mL per 100 g of sand. New silica sand typically carries a grain fineness number in the range of about 53 to 60. These are reference points; the binding requirement is the foundry's own specification.

Key Specification Parameters

When comparing reclamation plant quotes, a handful of parameters carry the decision. Different manufacturers list capacities and efficiencies in non-identical ways, so a buyer must normalize them before comparing. The seven parameters below are the ones that drive both capital cost and running cost, and each is decoded for what it actually constrains.

Throughput (capacity) is stated in tonnes per hour (TPH) of reclaimed sand. Commercial mechanical and vibratory lines span from about 1 TPH up to 50 TPH or more, with vibratory reclamation rated above 50 TPH for large plants, while gas-fired thermal reclaimers commonly run from roughly 0.25 up to about 12 TPH because combustion residence time limits throughput. Combination shakeout-and-reclamation machines fall in between, in the order of 15 to 20 TPH for mid-size units. Throughput must be matched to the molding line sand demand, not to the casting weight, which Chapter 6 addresses.

Reclamation yield is the fraction of spent sand returned to service, and is the headline of the cost case. Mechanical attrition on organic no-bake sand commonly returns 70 to 80 percent; adding a thermal stage pushes reuse toward 90 to 95 percent. Tested reclamation systems have reported sand recovery coefficients in the 92 to 94 percent range. Read yield together with the resulting reclaimed sand quality, because a high yield at a poor loss on ignition is a false economy.

Reclaimed sand quality is the bundle of loss on ignition, grain fineness number, and acid demand value described in Chapter 4. A reclamation unit should be specified against the loss on ignition and acid demand value it must achieve for your castings, not against yield alone. Sand temperature out is the delivery temperature to the mixer, with a practical target commonly in the 20 to 30 degrees Celsius band; fluidized-bed cooler-classifiers can hold the sand to within a few degrees of the cooling-water inlet temperature.

The remaining parameters round out the comparison:

• Energy and consumables per tonne: Mechanical attrition is low-cost; thermal reclamation carries the highest energy bill because of fuel for the burner. Quote energy per tonne reclaimed, not just installed power.
• Dust extraction rate: The volume and capture efficiency of the dust collector, since the captured fines are the contamination removed. Undersized extraction leaves fines in the loop.
• Grain preservation: How aggressively attrition acts on grain shape. Over-aggressive scrubbing rounds grains and raises fines, shifting grain fineness number on every cycle.
• Footprint and integration: Floor area, height, and how cleanly the unit ties into the existing shakeout, conveying, and mixer line.

Selection Decision Factors

To convert the preceding five chapters into a specific machine, follow the decision sequence below. Most selection errors come not from a single wrong parameter but from deciding capacity or method before the binder system and casting requirements are pinned down. These steps double as an RFQ template.

1. Binder system first: Identify the exact chemistry (green sand, furan no-bake, phenolic urethane no-bake, cold-box, sodium silicate). The binder decides whether mechanical attrition suffices or a thermal stage is required, and whether wet reclamation applies.
2. Target reclaimed quality: Set the loss on ignition, grain fineness number, and acid demand value the reclaimed sand must meet for your castings. Thin-section or high-integrity work needs lower loss on ignition, which often forces a thermal stage; backing sand tolerates more.
3. Throughput from sand demand: Compute hourly sand demand from metal poured times the sand-to-metal ratio, commonly about 4:1 up to 10:1 or higher for no-bake work, then add surge margin so the day's sand clears within the shift. Size the unit to that, not to casting weight.
4. Method and stages: Choose mechanical, thermal, wet, or a mechanical-plus-thermal combination, and confirm the quoted package includes every required stage: lump reduction, metallics removal, attrition, classification, and cooling.
5. Cooling and temperature control: Specify the sand-out temperature to the mixer (commonly 20 to 30 degrees Celsius) and confirm a cooler-classifier is included, because warm sand shortens no-bake work time and wastes resin.
6. Dust extraction and environment: Size the dust collector to the fines load, and confirm compliance with local emission limits. The fines captured here are the contamination being removed from the loop, so under-extraction defeats the reclamation.
7. Quality testing and acceptance: Agree the AFS and national standard test methods and the pass-fail limits with the binder supplier before purchase, and require the manufacturer to demonstrate them on your actual spent sand, not a generic sample.
8. Total cost of ownership: Sum capital, energy and fuel, consumables, new-sand top-up still required, spent-sand disposal avoided, and maintenance. A thermal stage raises energy cost but can pay back through higher reuse and lower disposal levies; the right point depends on your sand volume and disposal cost.

One dimension is routinely underweighted at purchase: manufacturer serviceability and binder fit. A reclamation unit tuned for green sand is not interchangeable with one tuned for furan no-bake, so the supplier must match the unit to your chemistry and prove it on your sand. For chemically bonded no-bake sand, Omega Sinto (Omega Foundry Machinery) offers a full mechanical attrition and gas-fired thermal range, and Sinto and Heinrich Wagner Sinto supply mechanical reclamation including green-sand-to-core-sand systems. General Kinematics builds the VIBRA-MILL vibratory attrition family, and European builders such as Klein, Künkel Wagner, Webac, and Fata, along with numerous Chinese foundry-equipment makers, complete the field. Confirm local spare-part availability, service response, and a documented acceptance test before committing.