Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/440030
The ABCs of Blending OPERAT M ost aggregate op- erations realize the benefi ts of blending, as it is not new to the industry. Though the reasons for blending vary, all seem to focus on the ability to develop a desirable mix. Blending enables a producer to meet the gradation requirements for a customer's special needs, opens up new sales possibilities, and al- lows producers to use materials that might end up in a waste pile. "The reason we would typically blend is to meet a certain speci- fi cation," says Eric Bailey, general manager of aggregates, Oldcastle Materials – Texas. "You can meet specifi cations you wouldn't oth- erwise be able to meet, which allows you to win jobs you wouldn't normally get." Brian Rice, quality improvement manager for Lehigh Hanson, agrees. "A lot of plants can't make a specifi c specifi cation with their existing equipment," he says. "So the only good way to make them is to blend." Blending can be accomplished in several ways. The most rudimentary way is bucket blending. A loader operator gets a bucketful of material from one pile, adds a scoop from another pile, and maybe a scoop from a third pile or fourth pile, and then places them together and rolls them over to mix them. This type of blending is probably used at more than half of the aggregate opera- tions today, but it doesn't always produce a good blend. Bin blending, where you use any type of cold-feed bin or a pugmill to mix the materials together, allows an operator to be more accurate and get a better blend. "The nice thing about bins is that you can really dial them in," Bailey explains. "Depending on how the bins are set up, you can get a really uniform blend." Some operations are fortunate enough to have a fractionated plant, which makes blending much easier. Each size aggregate is separated into individual piles and then blend- ed back together to get the desired mix and gradation. Gates feed the different materials onto a conveyor belt that runs through the reclaim tunnel underneath the fraction- ated piles, allowing the aggregate to blend together as it runs up the conveyor to loadout. "We like to blend mechanically through the plant," Rice says. "That allows us to introduce each product separately and meter the propor- tions needed to get a fi nal product." Probably the most important part of blending is quality control (QC). The QC team should be involved with the blending process from the very beginning, both creating the blends and making sure they stay consistent. The only way a producer can know for sure that the blends being made are actually meeting specifi cations is through constant sampling and testing of the product. AGGREGATES MANAGER There are many reasons for an operation to blend. Blending allows an operation to meet the gradation requirements of a particular customer. A producer can meet specifi cations that might not otherwise be met, opening up new sales and job possibilities. It also al- lows producers to consume waste materials. If a par- ticular specifi cation has room in the mix, a material that might ordinarily be a waste product can be added, if the quality control team deems it appropriate. Bin blending is the next step up from bucket blending. It allows producers to have more control over the mix. Bin blending can be done with any type of cold-feed bin, or even a pugmill. The materials can be mixed together as they are fed into the bins or can be mixed as they are loaded into the customer truck or railcar. Depending on how the bins are set up at the plant, an operator can achieve a more uniform blend. 1 Why blend? 4 Bin blending