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Green Sand Metalcasting Foundry News

Advances in Green Sand Reclamation

Posted by Hill and Griffith Company on Mar 16, 2021 5:15:34 PM

Excerpt from the Foundry Management & Technology January 2021 article by Jack Palmer

Now is the time to be look at newer sand reclamation technologies, to reduce cost and environmental impacts, and to enhance casting quality.

Most everyone realizes that sand reclamation is necessary for cost reducing and environmental requirements. While the popularity of sand reclamation certainly resulted from increasing sand prices (caused primarily by the demand for fracking), there are few processes that provide as many immediate benefits as sand reclamation.

Reducing the cost of sand is by far the most attractive consideration for sand reclamation, though lowering disposal and transportation costs are equally attractive. Couple these with reducing your environmental footprint and you realize that reclaiming sand is just good business.

One of the most overlooked benefits from sand reclamation is quality assurance. Controlling your materials through an in-house system will enhance the quality of your castings; because better sand makes better castings.

Green Sand Reclamation

 

Higher casting quality

One of the main advantages of thermally reclaimed sand is that it helps foundries lessen expansion defects. This is especially critical for cast surfaces of impellers, volutes, etc., and so it is common for foundries to run all-new sand through the thermal system for this reason.

Thermally reclaimed sand also requires substantially less binder to achieve acceptable strengths compared to new sand, which produces stronger molds and cores. With less binder needed, there is the additional benefit of less smoke and odor. Fewer chemical additives also mean better sand grain, fewer defects, less grinding/welding, and better surface finishes.

With all of these advantages, the question emerges: Why aren't all foundries reclaiming spent sand? The easy answer is that the cost of entry can be quite high, seemingly out of reach. However, now there are many different levels of entry, as well as newer technologies to meet ROI requirements for both jobbing and larger-volume production foundries, reclamation solutions that are both bottom-line friendly and quality enhancing.

Sand reclamation systems

Sand reclamation involves physical, chemical, or thermal treatment of sand for reuse in molding and coremaking. There are two major types of systems: mechanical and thermal.

A mechanical system physically breaks down lumps of spent casting sand, into clean sand. A thermal reclamation system takes sand that has been broken down to grain size in a mechanical reclamation system and adds heat energy to burn off the remaining resins.

Before sand can be processed in a thermal system, lumps must be reduced in a mechanical system, with the following sequence of components: shakeout deck; attrition mill; elevating device; surge hopper; magnetic separator; agglomerate screener; fluid bed classifier (cooling optional); elevating or pneumatic transportation device; bulk storage silo for mechanically reclaimed sand; and dust collector.

Thermal reclamation system

A typical thermal reclamation system will include the following sequence of components: surge hopper for supply; magnetic separator (if not already included upstream); metered feed mechanism; heating zone; cooling zone; elevating or pneumatic transportation device; bulk storage silo for thermally reclaimed sand; and dust collector (likely high temperature.)

If a thermal reclamation system is included, some foundries will thermally reclaim all sand; others will thermally reclaim a portion of the sand and then blend it into the system in order to control their "loss on ignition" (LOI) readings. This choice also will affect the components included in a typical system, and exactly where the sand stream exits the mechanical reclaimer and enters the thermal reclaimer.


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Tags: Green Sand Casting Products, Green Sand Foundry Supply, Foundry Supply, Green Sand Coatings, Green Sand Release Agents, Green Sand Metal Casting, Green Sand Metalcasting, Core Binders, Green Sand Additive Products, Foundry Management & Technology magazine

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