Aggregate(s) or soil(s) to be processed are fed into the rear 16 cubic yard material feed hopper, which is optionally lined with a kryptonics urethane to prevent material sticking and improve flow characteristics. The hopper may be split with the optional dividers so as to accommodate two types of soil or aggregate. The hopper may be fed one of three ways. First, a front-end loader can feed the hopper directly by building a ramp perpendicular to the hopper. Secondly, material may be conveyed into the hopper. Thirdly, a screen can process directly into the hopper. Experience has shown that screening directly into the hopper is a good method to limit the handling of material, but due to screen capacity, it is often the limiting factor concerning maximum production of the mixing plant.
Aggregate(s) or soil(s) are fed to the mixing chamber by means of a wide low speed belt feeder with a long hopper opening. This configuration prevents material bridging and provides a continuous and uniform flow. Flow sensors for each component are located at the feed point and will immediately shut down the mix if either material is empty or clogged. Feed belts are not the ideal place for inline weighing because changes in hopper levels and pressure from skirting will cause inaccuracies in the measurement. For this reason primary measurement of the aggregate takes place on the discharge belt, which allows for a long stable weigh platform with no variants to affect accuracy. A Ramsey Series 22, duel idler belt scale system coupled to their Micro-Tech 2101 Integrator, weighs discharge material. The maximum dry aggregate capacity is 600 tons per hour.
The rigid and rugged 10-22 duel idler weighbridge with no moving or wearing parts remains permanently aligned within the conveyor frame and provides a substantial 12 foot weigh span for maximum sample time. Weight is then provided to the integrator through its precision, strain-gage load cell applied in tension to guarantee load cell alignment and accuracy. The most reliable and accurate speed sensing device ever developed for scale service, the 60-12C digital belt speed sensor mounted on the tail pulley, provides true belt speed to the integrator. The advanced electronics of the Micro-Tech 2101 Integrator provides for automatic zero tracking, multiple machine directed calibration options and computes rate, total and speed information for the plant’s computer at better than ± 1/2 % accuracy (manufacturer’s specifications available upon request).
The Plant’s computer system then removes other mix ingredients plus aggregate stockpile moisture to arrive at a dry aggregate weight. Secondary measurement is derived volumetrically at the feed belt and is used to achieve the instantaneous rate required for mix proportioning. The computer continually verifies volumetric calibration while monitoring for variations between gravimetric and volumetric rates. This provides two measuring points for the aggregate, which the computer uses to identify scale problems or improbable failures.
Since the mix design is based on the dry material weight, it is crucial to know the materials’ moisture content. This will enable the control system to derive the proper proportions of dry materials and to add the correct amount of water for the desired mix moisture without affecting these proportions. The aggregate(s) moisture content can be entered manually, or computed by the optional Hydronix Hydro-Probe II microwave moisture sensor(s). Robust in construction and providing pin-point accuracy, Hydronix probes set the standard in moisture measurement. Built to a high specification to operate under the most arduous conditions without maintenance, the sensors use the unique Hydronix resonant microwave technique. This measures moisture deep into the material to better than ± 1/4 % accuracy that is not significantly affected by pollutants, temperature and particle size. (manufacturer’s specifications available upon request )