Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/708570
Sampling for Quality OPERATIONS Quality Control: "W hat you have to recognize is that sampling is critical to a plant's quality control. It's just as important as testing," says Tim Tipton, quality control director for Hinkle Contract- ing, a Summit Materials company. Tipton explains that production quality control has evolved over the years. Not only are producers more in control of testing their product quality than in the past, when the DOT agencies held all control, but the systems and methods for man- aging quality at aggregate facilities also have become more sophisti- cated. The fi rst step in testing material for quality is taking a sample of a product that will provide a true picture of the product's gradation for a customer's need. Tipton says valid concerns for the fi nal product also include contamination and segrega- tion, which can occur on conveyors and in stockpiles — both of which provide methods for sampling. Of course, there are pros and cons for each method. According to Tipton, Hinkle pre- fers to use the stockpile sampling method, acquiring the sample with a loader, which is safer than using a shovel and bucket to pull samples directly from the pile. "The loader operator takes material from three to fi ve locations in the stockpile, loading at a right angle to the fl ow of how the stockpile was built," he says. These samples are used to cre- ate a "mini" stockpile from which an- other sample is taken for testing. The method helps to address concerns of contamination and segregation, as long as an experienced operator is taking the sample. Conveyor belt cuts are another way to sample aggregate materials, and can be accurate for determining gradation. The traditional method for obtaining a belt cut sample requires the plant to stop production. A tem- plate that matches the curvature of the conveyor belt is used to manual- ly cut and separate a cross section of the material. The worker takes three to fi ve cuts, brushing the material into a bucket for testing. "This type of testing doesn't give you the full picture of your material. It relies on the employee taking a complete sample, including fi nes; it can affect your production rates, and it also creates safety concerns," Tipton says. Adam Orner, global product manager for wet and dry sampling at McLanahan Corp., agrees that the traditional belt cut method has its limitations and concerns. "This is why we promote the use of cross belt samplers," Orner says. Cross belt samplers are automated, enclosed machines mounted on the conveyor. They use a "bucket" with a counter- weight to swing and scoop samples from the moving conveyor, delivering them to a container. "With cross belt samplers, you have no downtime, and it eliminates safety concerns," he says. AGGREGATES MANAGER Conveyor belt cuts and falling stream samples provide a good picture of the products being made, especially addressing concerns with gradation. Belt cuts require shutting off the belt and taking samples from three to fi ve locations, using a template to cut out the samples. Manual sampling from the material fl ow falling from the head pulley leads to safety concerns. The belt cut method affects both production and safety. Sampling is a critical component of the entire quality control process — equally as important as testing. While there are a number of methods for sampling aggregates, two primary ways to obtain samples include stockpile sampling and conveyor belt sampling. With either pro- cedure, the producer must make sure to be consistent in how, when, and where the sample is obtained. Primary methods Belt cuts and falling stream samples 1 4