Astec’s core business is the manufacture of hot mix asphalt plants. Malcolm Swanson, president, Astec in the US says most plants are built on skids and can be moved or shipped anywhere.
Swanson noted that continuous process production methods have become “the preferred method of production for asphalt,” with batch production largely “a thing of the past for this industry.”
Though the assembly of these asphalt plants is a very manual process, requiring 8-10 weeks, the operation of the plants is highly automated.
One of the key automation technologies in these asphalt plants are variable frequency drives (VFDs). “Siemens VFDs have enabled the development of many Astech technology ideas, especially in our MCC (motor control center) assembly,” said Swanson.
VFDs are important to the warm mix water-foaming method used by Astec that helps reduce the energy needed for making asphalt. For example, the VFD used with Astec’s variable speed drier drum is key to heat transfer in the drum as well as the overall energy efficiency of the burners used to provide the drying heat in the drums.
We need very precise control of ingredient flow and the ability to track historical data.
The drives also play an important role in asphalt pavement recycling. Highlighting the importance of asphalt recycling, Swanson pointed out that the “value of recycled pavement is same as what it replaces, plus it keeps materials out of the landfill.”
Though Astec will build its asphalt plants using whatever automation technology its customers specify, the company has largely standardized on the use of Siemens controllers, drives, and SCADA/HMI systems. “This reduces the opportunity for mistakes while speeding up our assembly process,” Swanson said.
Explaining Astec’s asphalt plant control centers in more detail, Mark Chambers, controls director at Astec, said the company’s hot mix asphalt blending control systems, such as the PMII, PMIII, and TCII, use Siemens Simatic ET 200 distributed I/O, WinCC SCADA systems, and Simocode solid state motor management.
“Our control systems use Profibus or Profinet for networking because of its ease of troubleshooting and fast connections,” said Chambers, who added that Astec is increasingly moving toward standard use of Profinet because of its greater bandwidth capabilities and speed.
Chambers said Astec is looking to start using more intelligent devices, such as real-time moisture probes and more precise data monitoring and logging using Siemens TIA portal. The company is looking to increase its use of automation technologies as it focuses on optimizing energy use in its asphalt plants and reducing waste. “We need very precise control of ingredient flow and the ability to track historical data,” said Chambers. “Moisture control, in particular, is a big issue in asphalt mixing, because moisture levels need to be consistent as materials are added to ensure the resulting batch meets regulated specs.”
Chambers also provided insight into some homebrewed automation projects Astec is working on, such as a “crawlerbot” that can be used to measure the density of asphalt silo walls. Using the crawlerbot eliminates the need for inspection scaffolding and sending workers up into the silo to take measurements manually.
The crawlerbot is a small, automated device-much like a remote controlled toy car-that uses brushless AC motors for propulsion and magnetized wheels to adhere to the walls of the silo. Outfitted with a camera, staff on the ground can review the images captured by the crawlerbot’s camera for density measurements.