Hot Mix GlossaryThere are 402 entries in this glossary.
|saddle chain drive||
A type of roller chain drive system commonly used to rotate a dryer or mixer drum. The entire chain runs under the drum and makes a loop around two sprockets, a drive sprocket and an idler sprocket. The upper half of the loop engages another sprocket, which encircles the drum.
A special type of valve that enables an operator to easily take samples of liquid from a tank. They are often used on liquid asphalt storage tanks. In a horizontal asphalt tank the valve is usually installed in one end, about 24 inches above the bottom. In a vertical asphalt tank it is installed in the side, about the same height above the bottom.
Sampling valves for use with asphalt tanks are usually manually operated and feature a screw stem operated by a hand crank. They are virtually clog-free because of the way the valve is designed and mounted in the tank. (They do not need a hot oil jacket.) Moreover, they are usually leak-free and provide free-flow.
Gate valves and other types of valves are sometimes used for taking asphalt samples, even though such valves are not designed for sampling. They often clog and require use of a torch to heat them and their connections to get the material to flow. But valves specifically designed for sampling virtually eliminate the hazards and difficulty associated with valves not designed for that purpose.
Styrene-butadiene-rubber. A polymer that is often mixed with asphalt cement to produce modified asphalt.
Styrene-butadiene-styrene. A polymer or common synthetic rubber that is capable of withstanding high temperatures and extreme tearing forces. It is often mixed with asphalt cement to produce modified asphalt.
A wire mesh screen, which passes material small enough to go through the spaces between the wires and withholds or separates material larger than the spaces between the wires. Screens with various mesh sizes are used in making HMA.
Usually, the coils in a direct-fired tank that scavenge heat from the heated asphalt. (See direct-fired tank.)
Silicon Controlled Rectifier. A solid-state electrical device that controls the amplitude of current or voltage in an alternating current circuit. In Astec HMA facilities, belt feeder drives have SCRs to control magnetic clutches. (See belt feeder.) The SCR is controlled by an independent control circuit.
Normally used on the head shaft of a conveyor to clean the belt. Sometimes a brush is used instead.
|screen mesh sizes||
(See mesh numbers.)
A conveyor with a helical screw (auger) that rotates in a tubular housing or trough. It is used mainly to convey dust, lime or other powder-like material.
Equipment used to remove dust particles from the gas stream of the aggregate drying process. Water spray is showered through the dust-laden gas stream thereby scrubbing it and removing most of the particles.
The resulting slurry of water and dust is pumped to a pond where the dust particles sink to the bottom of the pond and form a sediment. The sediment is not reused to make HMA.
In a modern HMA facility, scrubbers have largely been replaced by baghouses. Baghouses are more effective and more efficient. Depending upon the mix design, some or all of the baghouse dust or fines can be used in the mix, a significant economical advantage.
On an open-fired burner, it is that part of the combustion air that enters the dryer around the burner and not through it. This is air drawn into the combustion zone by the baghouse fan. Most of this air is needed to attain complete or stoichiometric combustion. (Compare primary air.)
A sprocket that is made in several pieces to facilitate replacement. The sprockets in drag conveyors are usually segmented sprockets, allowing replacement of worn segments while the drag chain remains in place
Segregation usually occurs as a result of moving mixed material from one place to another. When mixed material flows into a pile, the larger pieces tend to roll off the top of the pile to one side while the smaller pieces remain near its center. This, of course, segregates the material. Special techniques are used to avoid segregation.
A word often used in connection with building codes that apply to structures in a HMA plant to denote the amount of earthquake activity they can withstand without damage.