BCR - The Importance of Material Preparation
Within the past several years, the brick industry has experienced increasing upward pressure on costs. While labor accounts for a gradually shrinking fraction of overall costs due to the rapid advance of automation, the numerous new facilities that have been built in recent years have caused older plants to depreciate rapidly. Energy costs, which for a while remained stable and even declined, have now begun to skyrocket, and the cost of transportation is also becoming increasingly high.
While most of those factors are beyond our control, each plant does have the capability to reduce the cost of “WISMCBP”—or waste, ignorance, stops and missed chances through bad preparation.
Most structural clay plants can easily define waste. However, few know what percentage of the waste occurring in their plants in connection with extrusion, drying, handling or firing can be attributed to inadequate, uncontrolled preparation. It can also be difficult to determine how many of the stops, or how much of the downtime, occurring in connection with these production steps are a result of poor preparation.
And that is just the negative side of WISMCBP. There is also a positive side that has to do with unexploited potential. How much more could we produce—and how much better—at less cost in terms of energy, stops, waste and labor if we really had our preparation processes under control?
Reasons to Optimize Material PreparationMost heavy clay plants lose somewhere between 3 and 7% of their profits due to WISMCBP, and there have been cases in which plants have been able to increase output by more than 30% just by improving the preparation step—sometimes by simply adding a single piece of equipment. Even for “bread and butter” bricks with a simple raw material base, body preparation can be optimally tailored instead of off-the-rack, leading to a more sellable product.
Over the years, body preparation has gone through several stages. Until the middle of the 20th century, the “product” was extensively determined by the most readily available raw materials, and what we now refer to as “technology” was of rather minor importance. This was stage one in the evolution of the modern brick and tile industry—and this thinking can still be found in some countries.
Then came stage two, when technology came to equal the raw materials as a product determinant. In more than one case, “technology blindness” and the motto “there’s no other way!” caused certain heavy clay products to simply disappear from the market. Conversely, an exaggerated infatuation with technology sometimes went far beyond the real needs of the product.
Stage three began to emerge toward the end of the 20th century. Now, the product is the one and only target value. The product determines both the raw materials and the technology. For example, a roof tile plant built four years ago in Germany uses a river barge to obtain high quality raw materials from deposits located several hundred miles away. Consequently, the technology required for body preparation and downstream processes can be less complicated. Even more important is that the products’ properties and potentials with regard to customer value are dramatically higher, while the overall cost of production is no higher than that of other plants, despite the raw materials costing about 10 times as much. The extra attention given to raw material preparation has saved the company thousands of dollars in added equipment and downtime in the downstream production process.
Optimizing material preparation can also help structural clay manufacturers find solutions to specific problems. Palmetto Brick in Cheraw, S.C., for instance, was experiencing roots in its raw materials—a problem that was easily solved by installing a root selector. Other operations have installed simple pieces of equipment to deal with challenges such as quartzite rocks or soggy material during rainy periods.
Another reason material preparation is so important is that any brickyard, old or new, operates as a system. Any mistakes made at the body preparation stage are irreversible and will carry over into the rest of the process, becoming increasingly costly as they persist in the shaping, drying, handling and firing stages. Additionally, thermally optimized dryers and kilns can only work optimally in terms of output if the input—meaning the body—is time-constant. A sub-optimized kiln that takes 48 or 60 hours to fire the product allows a great deal of time to iron out many preparatory-stage glitches, but a kiln with a firing time of only six, 10, 12 or 16 hours demands a constant input and therefore an optimized body.
What Really Matters in Body Preparation?To obtain a good body mix, four parameters must be consistently achieved and monitored: accurate proportions of all components and additives; plasticity of the shaped body; particle size distribution of the shaped body; and quality of mixing and homogenization. All of these parameters and sub-parameters can be measured off-line, and new technology now allows proportioning accuracy and plasticity to be measured on-line as well.
The process selected to achieve these parameters simply depends on the application. Dry preparation is the most common method used in the structural clay industry, but wet preparation with filter presses has been used to remove fossil wood from a major material component for one roof tile manufacturer. In Europe, the prevailing combination of climatic conditions, products and available raw materials has made plastic preparation the dominant approach, with the core machines being pan mills, disintegrators, primary and fine roller mills, circular screen feeders, and, increasingly, machines to eliminate such foreign matter as roots, rocks and inorganics. And more and more frequently we are encountering combined methods involving plastic preparation for one or the other main component and wet or dry preparation for the rest.
The product should always be the first consideration. What do you want the end result to be? Define the parameters for your product, and then derive your preparation parameters from the product parameters. Armed with your preparation parameters and raw material data, you can then choose the best processing technology to meet your needs.