Hodge Clemco has completed the installation of a turn-key surface preparation and finishing facility in a new buoy maintenance unit opened by Trinity House at Harwich, Essex.
The £600,000 contract includes a blast room, a dry-filter combination spray and cure booth, a separate paint drying/curing booth, a hand paint booth, a compressed air package and a paint services and store booth.
Trinity House provides nearly 600 fixed and floating aids to navigation around the coast of the UK and Gibraltar and in the Thames Estuary, including 450 buoys for marking shipping lanes, hazards and other purposes. The buoys carry visual and audible warning systems chosen according to the situation where they are deployed. With the tail tube stabiliser fitted and other equipment in place, the largest models are over 15 metres high and weigh about 11 tonnes. All the buoys are periodically retrieved for repair and refurbishment, which requires the maintenance facility to complete two units a week.
The blast-room built by Hodge Clemco measures 7.6 metres wide x 6.2 metres long x 6.5 metres high and includes a 3.5 metre diameter powered turn-table set flush in the floor and a pneumatic access platform which together enable staff to work on all the structures easily and safely. In the past buoy were manufactured entirely from mild steel, but aluminium is now increasingly being used for the above-water superstructure. Staff generally use chilled iron abrasive on mild steel and medium-grade garnet on aluminium.
Blasting is performed by a high-output single chamber direct pressure unit with an RMS 2000 remote control system and dead-man handle which enables operators to turn the machine on and off from the nozzle. Abrasive is recovered continuously and automatically by a mechanical scraper system that feeds abrasive to a cleaner/separator. Clean abrasive of the correct specification is then delivered into a storage hopper above the blasting machine.
The dust extraction system has a total design volume of 16,000 cfm. Dust deposited on the filter cartridges is dislodged by a reverse pulse of air, activated automatically by an electro-pneumatic sequence controller, and falls into a collector for disposal. The pulsing rate on each cartridge can be adjusted individually, allowing cleaning cycles to be tailored to the dust loading.
The room has two folding doors at one end, each 4.8 metres wide x 5.5 metres high, that are fully interlocked to prevent blasting when they are open. Illumination is provided by multi-tube light modules at different levels to achieve optimum visibility, and emergency lighting has also been included.
The combination spray and cure booth is 7.6 metres wide x 8.5 metres long x 6.4 metres high and is similar in construction to the blast-room. Filtered clean air enters the booth at the front and is pulled horizontally at a constant velocity to the back, which provides optimum conditions for staff to achieve a high-quality finish. During the spray mode the air is pre-warmed to 18-20°C by a gas-fired burner. For curing, the temperature is raised to 30°C. Pressure balance is continuously maintained by automatic adjustment of exhaust fan speed as filters load with paint over-spray
A separate paint drying booth, 7 metres wide x 8.5 metres long x 6.4 metres high, stands next to the main spray/cure booth and provides additional drying capacity to prevent production bottle-necks. The construction of this booth is the same as that of the main spray-booth but without a turn-table and work platform.
The hand paint booth, 4.25 metres wide x 8.5 metres deep x 5.5 metres high, has a similar specification, including pressurised filtered air input and exhaust systems designed to ensure efficient particulate filtration by the intake and exhaust filters and optimise conditions for high-quality paint finishes.
The paint services booth and store has internal electrical supplies, sockets and lighting to Zone 1 standard, including a socket suitable for a solvent recovery unit. The design includes spillage containment and ventilation with high-level filtered input and floor level extract that maintain the concentration of hazardous substances below occupational exposure limits.