Hanson Frindsbury Wharf is based on River Medway in Kent, processing marine dredged sand and gravel. The operation produces 40mm, 20mm, 10mm and washed sand for use in concrete products, supply of ready mixed concrete plants and direct sand and aggregate sales.
The current static plant was commissioned in March 2009 to handle between 550 – 600 tph dependant on the variance in dredged material. This material is transported to site by ship of between 4500-5000 tonnes of product at a time, taking between 4 and 5 hours to discharge at high tide.
The Screening Process
Material is fed from the main stock pile to the fixed plant, where the first split takes place on a scalping screen +100mm is rejected from the top deck to an external storage bay, whilst the lower deck screens +40 to -100mm which is sent for crushing and the -40mm is sent to the wet screen house. The +40 to -100mm material is then crusher by one coarse and one fine closed circuit crushers, which products are then re-fed onto the main feed belt to the wet screen house.
In the wet screen house there are two double deck screens that select the 20mm and 10mm single size final products and govern the top end of the sand product which is then fed to the sand plant, whilst the +20mm is re-fed to the crusher circuit.
The Project
In the first half of the year it was identified by Hanson that one of the screens in the wet screen house required replacement and after consideration Hewitt Robins were selected to supply a replacement 2.2m x 6m double deck inclined screen. At the beginning of June SCS were also approached by Hanson directly to quote for supply and installation of new screen media to suit the replacement screen, Hanson specified the 85 system which is one of the most commonly used polyurethane modular systems in the industry.
After SCS was awarded the supply and installation of the screen media, a design for the system was developed. Taking into consideration a number of elements such as but not limited to;
· Screening duty
· Tonnage per hour (400 tph)
· Internal screen size dimensions
· Constraints of the 85 system (in terms of its design features)
· Minimal number of different parts (for simple reordering and stocking)
SCS was able to propose a design that satisfied all the criteria and with collaboration from Hewitt Robins a design that only required one size of module per deck and a total of seven different parts including modules for the entire screen media installation, of which only three are wear parts.
Screen Media Maintenance & Design
SCS believe that ease of maintenance is an important part of initial screen media design, as within the lifecycle of a screen the operator will spend a significant amount of money on screen media due to it being a replaceable wear part, therefore keeping the number of different wear parts to a minimum is key point. Not over complicating the design also simplifies maintenance so there are less chance of mistakes in the future causing issues with gradings.
Using the feed tonnage of the screen the bed depth of the material was calculated to be in excess of the height of standard modular system side bars, therefore to prevent wear to the side plates of the screen higher side bars have been installed. These are installed using a polyurethane wedge and angle cleat design, which reiterates the point about simple maintenance as the only tools required to remove and reinstall the modules and side bars are a hammer and a crow bar, eliminating the need for power tools and all the paraphernalia that comes with them.
Dave Blench – Heidelberg Cement AG, Head of Engineering commented “Time was of the essence with this project, SCS and Hewitt Robins ability to work together and design, manufacture and supply a complete screen and screen media in 6 weeks on time and in budget was of paramount importance”.
Liners – Steel Backed Rubber
Within this project SCS were also commissioned to supply liners for the feed tray and discharge lips manufactured from steel backed rubber. These liners are made from stocked 2m x 1m sheets that are then cut to size and drilled and cored to suit, the standard sheets are available in three different thickness 15+3, 25+5 and 45+5mm. If liners of other thickness combinations are required or are larger than the standard stock sheet sizes these can be made up from rubber sheeting cold bonded to backing plates.
For an individual discussion of your needs, please contact us on 01788 553300, or email us, sales@scsrugby.co.uk.
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