Heatec has built equipment for asphalt emulsion facilities for several years, providing asphalt tanks, hot oil heaters, water heaters, and other equipment. According to Tom Wilkey, president of Heatec, Inc., building a new emulsion mill was a logical step in creation of a new product to meet the demands of the market.
"The heart and soul of any emulsion plant is the colloid mill," said Wilkey. "In conjunction with our sister company JCI, we developed a plan to produce an emulsion mill after complete due diligence of similar units; we integrated the best components into a JCI-Heatec design. After about one year of research and development, we have the Barracuda."
Wilkey continued: "We have a Barracuda mill in operation at Vance Brothers in Oklahoma City, Oklahoma. It's a prototype that was placed last November for testing. Our goal was to get the mill in operation and make various types of emulsion. To date, approximately 150,000 gal (567.81 l) have been produced; it's all good product, passing the specifications required."
Products made through the mill so far include:
Vance Brothers in Oklahoma City, Oklahoma, currently has the Barracuda mill prototype in operation. According to Bryan Midgett, manager of operations at Vance Brothers, the new mill is robust.
"We've been very satisfied with the mill so far, especially the ability to change the mill gap," says Midgett. "The emulsion produced thus far has been of good quality and production has increased."
According to Wilkey, the key concerns center on longevity and maintenance, and how long between rebuilds.
"The mill will be thoroughly tested as more gallons (liters) are run through the unit at Vance Brothers," said Wilkey. "This will provide us with data in the coming months to determine how well the mill is functioning with respect to the different asphalt emulsions."
The Colloid Mill
The Barracuda mill mixes virgin asphalt with a water/chemical solution to produce a stable, homogenous material, either cationic or anionic. The end product, or emulsion, is a maintenance product for use on rural and secondary roads as a surface treatment for pavement preservation.
Mixing in the mill takes place in the gap between the two mill plates. One plate is mounted on the stator and remains fixed during operation. The other plate is mounted on the rotor and spins at 3600 rpm. The liquids are combined by the action of the plates. The gap between the plates can be adjusted to produce the optimum mixture. The plates have 100-percent machined surfaces and are precisely made from stainless steel.
The gap between the mill plates is controlled by the position of the stator. The stator is adjustable, unlike mills with adjustable rotors. The adjustable stator avoids inherent problems with seals on shafts of adjustable rotors. Adjustments can be made while the mill is running—a unique feature of this mill.
Adjustment of the stator is achieved using a self-locking worm drive. Manually rotating the worm moves the stator 0.002-in (0.005 cm) each turn. Total adjustment is 0.375-in (0.952 cm) or 187.5 turns.
The worm shaft is supported by precision bronze bushings that do not require lubrication. The worm shaft can be rotated with an ordinary wrench to adjust the position of the stator. A digital readout system using quadrature encoder technology indicates the gap between the mill plates for easy, precise adjustments of the gap.
Long Life Seals
The rotor shaft in the mill uses seals highly suitable for production of asphalt emulsions. Three seals are used. Two are lip seals used on the shaft in the rotor shaft frame. The third is a common, spring-loaded face seal used in the mill chamber. It is standard equipment. The seals are not adversely affected by recurring expansion and contraction. For example the shaft elongates as much as 0.015-in (0.038 cm) at the rotor seal due to thermal expansion.
Bearings and Lubrication
The rotor shaft frame houses and supports the rotor shaft. The shaft has bearings at each end of the frame. The bearings permit elongation of the shaft as it heats. Lubrication of the rotor shaft in the frame is critical for long bearing life. Lubrication is achieved by a simple, closed loop system with a 1/2 hp motor. The lubricating oil is filtered as it constantly circulates through the frame and is returned to its external reservoir by gravity. It is unaffected by temperatures in the mill housing and does not need water cooling used on some mills.
The Total Package
The typical emulsion plant has 15 to 20 different asphalt tanks and a processing building which contains the colloid mill. Wilkey explained the process: "The water is heated and the chemicals are added, and then the asphalt is injected into this solution in the colloid mill, and then pumped outside the building into an emulsion tank. The emulsion is now ready for sale to a DOT (Department of Transportation) or municipality for road maintenance treatments."
Heatec is looking forward to putting more emulsion mills into operation.BACK TO ISSUE
LOOKING FOR MORE ARTICLES LIKE THIS?
Astec Advanced Customer Schools provide training you won’t soon forget
Using your smartphone to avert problems at your asphalt plant
Astec’s latest plant controls—PMIII