Primary crusher and stockpile
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Primary crusher and stockpile |
The products we produce can be split into 3 main sections:
Roadstone
Surface Dressed
Chippings
Coated
ROADSTONE
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One of the secondary
crushers |
Once the basalt has been blasted from the quarry face it is transported to the primary crusher, by 40 and 50 tonne capacity dump trucks. This material is reduced down to approximately 200mm; it is then put onto the primary stockpile or sent straight to the secondary crushers.
There are 5 secondary crushers the first 2 reduce the aggregate down in stages, the final 3 crushers work together to produce the final size and shape of the range of material, which is 20mm, 14mm, 10mm, 6mm and Dust.
At this stage all these materials are a mixture and so are sent to the screen house which sorts the material into its various sizes by a process of passing or rejection over screens. The material now sorted according to size is then stored in bins under the screens. Doors under the bins allow loading onto lorries for dispatch or into a dumper, which will tip the material onto stockpiles for future use.
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Surface Dressing normally comes in sizes of 14mm, 10mm, and 6mm; this material can be taken from stock or direct from the storage bins by the dumper and introduced to the washing plant. The washing plant consists of a rotating drum, through which the aggregate passes; water is pumped though the drum washing the fine particles from the aggregate. The water is recycled via settling pits where the heavy particles fall to the bottom and the cleaner water from the top is used again. The then clean aggregate is stored in a new stockpile, which stands on a asphalt base until dispatch.
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Surface Dressing Chippings need to be clean in order to adhere to a layer of bitumen sprayed onto the road. Once the chippings have been rolled into the bitumen, this produces a new running surface for traffic and seals the old road surface against the elements. The general public does not always appreciate the process, however it is a very cost-effective way of maintaining and prolonging the life of a road and keeping the council tax bills down.
The generic term for all these types of materials is Asphalt. There can be many different recipes or mixes depending on the job. Binder Course, Base and Sub-Base materials are used on top of the Sub-Grade, these layers make up the majority of the road construction and they distribute the traffic load from the Surface Course.
| Surface Course | 40mm |
| Binder Course | 60mm |
| Base | 150-240mm |
| Sub-Base | 150-750mm |
| Sub-Grade | Starting Point |
The Surface Course is the part of the construction in which Wainwright's specialise because of the nature of our aggregate. This is known as Hardstone and has good wearing and resistance to skidding properties. The Surface Course is the part of the road in contact with the vehicle tyres, it must offer up skid resistance, be impervious and have a fine tolerance to produce a smooth running surface. The whole construction is known as a pavement.
To produce a coated material the process is the same but the amounts and types of material used will vary, we can for instance introduce imported aggregate to alter the skid resistance of the Surface Course.
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To achieve the mix specifications, production targets and the environmental criteria necessary a Benninghoven model TBA240U asphalt plant, equipped with a 4000 Kg mixer was installed in 2006. Capable of delivering a wide range of standard and specialised mixes, the plant has a production output of over 200 t/h of dense binder course and 120 t/h of Stone Mastic Asphalt.
The aggregate feed system consists of an in line unit of eleven cold feed hoppers, each of 14m³ capacity, each fitted with a frequency controlled belt feeder for accurate blending of the aggregates. Four of the hoppers are for sand and are supplied with hopper wall vibrators to ease material flow. All hoppers are sheeted on their sides, ends and roofs, with an extended canopy over the sand hoppers.
Aggregate feed
A full length concrete retaining wall supports the feed ramp, whilst the bulk of the aggregates are stored in large covered storage bays.
A 50m long collecting conveyor moves material onto an 19.5m long x 650 wide inclined dryer feed conveyor, which discharges onto a short 3.5m long reversible slinger conveyor from which material is fed directly into the dryer drum.
The aggregate dryer drum, which is 2.3m diameter x 9m long, is fully lagged with 70mm thick Rockwool insulation and aluminium clad for heat retention and noise reduction .The drum is friction driven by four support rollers through individual 15 kW geared motor units .The dryer is enclosed in a 2m high safety fence fitted with an electrical interlocked access gate.
Dryer drum
The burner is a Benninghoven Rax Jet 4-3EGOFU type, which burns both gas oil and natural gas. This is equipped with a full range of operating and safety devices to deliver high efficiency fuel usage. An air inlet silencer is connected to the burner to suppress noise levels. The burner and silencer are mounted on a track to allow the unit to slide back from the dryer for routine servicing.
The plants dust collection system, sized for the dryer unit and mixing section scavenging is rated at 52,000Nm³/h and achieves emission levels of less than 25mg/m³. A primary skimmer unit mounted alongside the dryer separates any coarse dust from the airstream, which passes to the hot stone elevator feed boot via a gravity flap valve and chute. A secondary cassette bag filter system collects any remaining dust and transfers it via two screw conveyors to a filler elevator. Dust is also collected from nuisance points at the screen, weigh hoppers and elevator. A dust monitor mounted on the exhaust stack provides a remote readout in the operator’s cabin. As a result the plant meets the most stringent dust control regulations.
Any excess dust collected can be discharged from the reclaimed dust silo through a rotary valve into a twin shaft paddle conditioner, where water is introduced so providing an environmentally friendly method of purging this reclaimed dust.
Hot aggregates are transported from the dryer up to the screen by a vertical bucket type elevator. This is totally enclosed and features a heavy duty double strand chain and wear resistant steel buckets with replaceable liner plates at impact points. Elevator drive is by a 37kw geared motor and toothed chain wheels at the elevator head .The elevator features outside located bearings and a safety backstop facility. A wide platform provides access for maintenance.
Material discharged from the elevator passes into a 6 deck screen which features twin shaft drive via two19 kW ‘bolt on’ low maintenance vibrating motors. These drive units are mounted outside the screen housing to allow the high temperature screening of materials. Wide access doors, together with a rollaway chute provides access to all screen decks. An extraction fan ensures negative pressure is maintained in the screen housing for optimum dust control.
The hot storage section has a total capacity of 160 tonnes and comprises six bins. The bins are all insulated and clad and each is fitted with continuous level indicators and overflow chute. Discharge is by a pneumatically operated radial door, which accurately regulates material flow to the aggregate weigh hopper, from where the aggregates are discharged direct into the mixer.
Accurate weighing out of ingredients is achieved by separate load cell mounted weigh hoppers, comprising a 4000kg capacity aggregate, 600kg filler weigh hopper, and a 400 litre capacity weigh vessel for bitumen. A 1400 Litres/min injection pump forces the bitumen into the mixer. Mixing takes place in an insulated 4000kg capacity, twin shaft paddle mixer, with drive provided by two 55kw geared motor units, through synchronised gears. A rapid and thorough mixing cycle is achieved by the mixers efficient paddle arrangement. A radiation pyrometer is situated at the mixer discharge to indicate mix temperature.
Mixed material discharged from the mixer falls into a 4000kg skip unit, which runs on horizontal tracks and distributes the material into 360 tonnes capacity silos, arranged in two rows of three 60 tonne compartments. All are fitted with high-level warning indicators and are insulated and fitted with electric trace heating around discharge doors. A direct load-out hopper is positioned beneath the mixer. All bins are mounted on load cells to ensure accurate material loading.
Mixed material discharge into lorries
Bitumen is stored adjacent to the plant in two vertical 150m³ and one 100m³ capacity tanks ,these are Benninghoven’s latest high thermal efficiency units, which give low running costs, due to their stepped heating system design. An in-built loading system with high-level probes offers fail-safe filling with no possibility of spillage.
Bitumen storage
Filler is stored in an external two compartment vertical silo holding approx. 85m3 reclaimed filler and 55m3 imported. Both silos are equipped with level indicators and shut off valves.
A gravimetric additive system is also incorporated in the plant to feed granulated material from a 30m³ silo. Each batch of granulate is accurately weighed in a load cell mounted weigh hopper before being discharged through a butterfly valve to the mixer. A similar specification silo for pigment is sited alongside.
Plant is controlled by a Benninghoven on-line Batcher 3000 computer system which displays all plant functions via colour graphics. The system, which is housed in an air-conditioned and heated control cabin overlooking the plant is modem linked, and provides storage for up to 500 asphalt mix recipes.
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