Screens & Feeders

Animal with a new sting to its tail

Pugmills are used for optimum moisture content (OMC), which is generally around eight per cent moisture, or making cement treated base (CTB) for use in higher road specification for increased stabilisation and longevity.
Precisionscreen has launched a new iteration of its longstanding mobile Scorpion pugmill ? and this is an animal with a new sting to its tail. 
Whereas the nominal capacity of a pugmill is around 250 tonnes per hour, this new model can pug roadbase with OMC at a rate of between 300 tph and 335 tph. 
It is capable of mixing three different products and cement powder simultaneously.
Complementing the Scorpion pugmill is a new cement transfer system – or CTS-50. The CTS-50 has a storing capacity of 50 tonnes (GP cement but Precisionscreen have the option to upgrade to 75 tonne and 100 tonne capacity silos). 
Both the Scorpion pugmill and CTS-50 have been manufactured at Precisionscreen?s Wacol facility.
The new Scorpion pugmill?s programmable logic controller (PLC) controls the mix of materials to achieve a homogenous product through the use of weighscales on the main product belt. 
The scales help to accurately work out the tonnage rate of the primary roadbase material. This is relayed back to the PLC that in turn regulates the percentage mix of each additional component, ie extra feed bin additives (eg clay/sand, etc), cement powder mix and water volume. 
The easy to use interface allows the user to change each product mix manually and store as pre-baked recipes for future use. For example, if there is a consistent mix recipe, the operator simply turns on the machine, selects ?Blend 1? or ?Blend 2? and hits auto-start. 
From there, the Pugmill starts each component separately, ensuring the correct belt speeds for accurate quantities.
The main roadbase product is added to the hopper bin on the pugmill and this discharge is controlled via belt speed onto the main inclined conveyor going to the pughead. 
Additional products can be added at this point via extra hopper bins located at right angles to the pugmill machine. The material travelling up the belt is layered like a cake (dry) before reaching the pug?s mixing chamber. Upon entry to the 3m long twin-shaft chamber, the correct dosage of cement powder is added via screw conveyor along with the regulated water flow. 
The cement powder is funnelled in from the top and directed to the sides of the chamber so it can be evenly blended with the layered product mix. Water is added through two spray bars at the same entry point. 
Once the material is in the chamber, the aggressive pugging nature blends the materials through the use of the 50 paddles and is discharged at the end to a stockpile or into the back of a haul truck.
Cement is transferred accurately to the pugmill thanks to the cement powder constant flow. This is achieved by an air slide to the discharge point. A pneumatically operated butterfly valve discharges the material to the screw conveyor. 
Cement powder is added to the pugmill by ratios of added quarry materials which in turn controls the variable electrical drive of the screw conveyor. A silo standing on four loadcells weighs the whole silo for verifying the discharge amount.
The Scorpion pugmill features a large hopper capacity of 10.5m3 (2.5m3 without extension), a 650mm wide belt variable feed belt, a 650mm wide main belt with weighing system and a 2.5? positive displacement water pump with variable feed drive and standard 100 psi wash down hose. 
The twin-shaft, two-speed action pughead is fitted inside a 3m long mixing chamber, complete with hydraulically variable angling. The pugmill is foldable for transport and ground level washout and servicing. It is also fitted with a drawbar and kingpin for site movement.
The CTS-50?s control station features a 87CFM, 2.45m3 meter per minute flow screw compressor, a reverse jet pulse filter, a 42kVA generator set (optional) and a ladder, safety cage and landing platform. ?
Source: Precisionscreen

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