In picturesque Chattanooga, Tennessee, ASTEC Industries thinks about asphalt.
Not about the paving of highways, or even the machinery that builds roads; rather they think about the plants that make asphalt mixes.
With units as far afield as South Africa, Brazil, Germany and Australia, ASTEC
is a global enterprise with almost 4,000 employees and 21 factories.
ENGINEERING.com visited the home base in Chattanooga, where ASTEC develops new technology for global operations, as well as manufactures complete asphalt plants.
According to ASTEC Inc. president Malcolm Swanson, “At this factory, we have half a million square feet of production space with 660 employees. We’ll clear a billion dollars this year for the first time in our history. In North America, we have about an 80 percent market share.”
Those are big numbers because asphalt is big business.
93 percent of the 2.6 million miles of paved road in the US are asphalt covered. Every year, 500 million tons of asphalt is used to build and maintain these roads, representing a value of about 30 billion dollars. To top things off, some 4,000 asphalt plants in the US employ 300,000 people directly and indirectly.
Swanson notes that a public effort to support federally funded highways would pay off economically for the entire US economy, and recommends visiting www.dontletamericadeadend.com.
“I don’t know how many bridges have to fall down before the federal government understands the need for stable funding,” says Swanson.
Asphalt for roads, wood pellets for power
ASTEC is dominant in asphalt plant markets, but intends to diversify in order to reduce reliance on federal and state highway funding for market growth. As a result, the firm is expanding into wood pellet and thermal soil remediation plants.
“We feel wood pellets will be a climbing market,” says Swanson. “It displaces coal in power plants. The Europeans are using wood pellets as a means of achieving their Kyoto Protocol emissions targets,”
ASTEC’s second plant is under construction in Pine Bluff Arkansas, and will produce 600,000 tons of pellets annually, much of it for export to Europe.
Asphalt, however, is still the primary business for ASTEC, with competitive pressures driving new, industry-changing technologies, such as warm mix by water foaming.
In addition, making asphalt is now a continuous production process, unlike the older batch operations, and now includes recycling of old paving materials milled from roads.
Recycling is accelerating, declares Swanson: “It’s ideal to recycle at high rates, and we don’t know what the upper limit is for recycled content in a high quality road. 50 percent recycled mixes are high by DOT standards, but perform exceptionally even compared to 100 percent virgin asphalt mixes, particularly in crack resistance.
“We’re pushing 65-70 percent recycling right now, comfortably,” continues Swanson. “Some original recycled mixes didn’t perform well, but they’ve improved light-years since then. Some state DOT’s are aware, but some prohibit recycled asphalt entirely.”
ASTEC is a machinery maker, and as such, the firm engineers the critical drives and controls as carefully as the massive mechanical components of an asphalt or wood pellet plant.
Internally, issues are tracked with software, and documentation is handled with a computer-based technical service bulletin system that keeps service personnel up to date on running changes.
Daily support call logs record the action of the on-site support team, who feed information back to ASTEC controls engineering. If a problem develops into a pattern, the controls group can address it quickly.
Motors are the prime movers in ASTEC equipment, driving everything from fans to conveyors, and so motor controls are a major focus for energy and efficiency improvement.
Precise control of ingredient control isn’t easy in a continuous flow process that handles tons of material an hour, but advanced control improves product consistency and quality.
ASTEC uses Siemens control systems in their equipment, both for new build orders and retrofits. Modular CPU’s and advanced variable frequency drives make it work without excessive complexity. The latest project is migration to Siemens’ TIA Portal platform.
ASTEC’s system-wide control solution is called the DASH system, which allows real-time monitoring of multiple asphalt plants simultaneously.
Asphalt is a difficult manufacturing environment, not just because the product is hot and heavy, but because it needs to be made in close proximity to the paving project. This means multiple plants, spread out over a wide area.
The DASH project displays process performance from multiple plants in a graphical interface that looks like an automotive dashboard, making it easy to spot stoppages or production bottlenecks.
What’s coming in the future?
“Intelligent devices…the smart plant,” declares Mark Chambers, who manages ASTEC’s controls department. “More precise production data logging, fuel meter monitoring and an improved data logging mechanisms are part of the streamlined configuring process we’re working on. We want to reduce ‘behind the scenes’ configuration and provide wizards to guide users through the configuration process.”
ASTEC is also developing RFID technology with Siemens to create paperless, ticketless truck movement through their plants. RFID also allows significantly more information to follow a load of asphalt, including customer specifics, time and date of pickup and delivery as well as product specifications.
When monitoring the quality of multiple loads over a major paving project, paper tickets represent a major manual data entry problem which slows payment to contractors and complicates compliance with state and local DOT regulations.
In the future, a DOT inspector with a tablet may be able to make on-the-spot checks of individual loads, assuring quality and reducing or eliminating work stoppages on the construction site.
Simplified assembly, better reliability
Asphalt production isn’t a clean environment, making motor controls and drive configuration more complex than simple rack mounting.
ASTEC uses pressurized panels for some applications and extensively employs DIN rail mounting of control modules for ease of assembly and service. ASTEC also builds motor controls into stand-alone motor control centers for asphalt plants, incorporating the operators’ monitoring station.
A combined control and motor control center.
The philosophy is simple: if operators are comfortable, the control hardware will be too. Additionally, centralization reduces cost; cabling can cost as much as 70 dollars per foot.
ASTEC also supplies self-contained 20 and 40-foot motor control units for use where local safety codes require separation of personnel from controls and switchgear.
Advanced process control is paying off for ASTEC in terms of both energy efficiency and operational efficiency, declares Chambers: “Variable frequency drives give us better control and a significant energy reduction in multiple operations.”
For more information on Siemen's control systems, visit siemens.com.