Frac vs. Foundry Aggregate Expectations

frac foundry sand proppantSilica sand has been a hot commodity for more than a decade.  The two most demanding industries for this resource are arguably the two most important for our industrious world economy.

*(Not forgetting the glass industry, to keep this .short and sweet we will focus on the first two for now.)

Foundries have been using sand in metal casting since, well, forever.  Hydraulic fracturing, on the other hand, is relatively new in the silica sand world.  At times, it has proven difficult for mining operations to keep up with the high volume demands. Fulfilling the needs of both industries has caused some sand suppliers to attempt a difficult balance in product quality.

There are many similarities in the silica aggreagate products used by foundry and hydraulic fractuing industries.  Both Industries use aggregate mined from the same geologic formations. The manufacturing processes require the same type of equipment.  Conveyance, storage, and shipping methods are largely identical. Products need to be clean and preferably dust-free, stripped of all organic material, fall within the pre-set particle size distribution limits, meet or exceed high purity standards, etc…

However, the finished products are notably different and have specific requirements to meet or exceed before they can be defined as quality products for each industry.  The following sections highlight and compare a couple of the different expectations in product quality and performance standards.

The main job of a foundry aggregate (foundry sand), when mixed with a binding agent, is to form a quality mold.  Pore space between sand grains needs to allow gas to vent during ferrous/nonferrous metal casting.  The finished casting’s surface quality, strength, and structure are all affected by how effectively the gas escapes the mold.  Hydraulic fracturing uses silica aggregate (proppant) to “prop” open the induced micro-fractures of a shale layer.  The pore spaces between the sand grains allow gas and oil to flow into the proppant pack.  The aggregate performance is predicted mostly by using test data to calculate the American Petroleum Institute (API) % for proppant and the American Foundry Society Grain Fineness Number (AFS GFN) for foundry sand.

Individual grain strength plays a significant role in the overall aggregate life expectancy and performance for both industries.  Foundry sand needs to withstand constant extreme conditions including high heat exposure, continuous flow or pneumatic processing environments that cause increased surface abrasion, and a repeated chemical bonding process.  In the hydraulic fracturing process, proppant grains have similar requirements but need to meet or exceed specific crush pressure resistance typically measured in Pounds per Square Inch (PSI).

Both industries follow set standards and test methods specifically designed for the evaluation and quality assurance of silica aggregate.  Foundry Sand is tested to the methods outlined in the America Foundry Society (AFS) Mold and Core Handbook.  Hydraulic fracturing aggregate manufactureers test in accordance with the most current proppant testing standard, API-19-C Second Edition, August 2018.

It is an involved undertaking to thoroughly learn the ins and outs of quality control for either of these industries.  Material Spec Laboratories offers unbiased third party ISO 17025 accredited testing for those wishing to better evaluate and manage the quality of their substrate in both industries.