Thwaites green upgrade is picture of efficiency 05 October 2012

Yellow dump truck manufacturer Thwaites' paint line has been refurbished – and improved its efficiency and environmental sustainability on the way.

Steve Trotman, of Thwaites, explains that the line was installed 15 years ago at its Leamington Spa plant, but sections of the paint booth were corroded. And he adds that costs for cleaning and waste disposal were increasing.

So Birmingham-based Delta Process Systems was invited to survey the situation. It found two manual spray booths with pump-less water-washed exhaust systems for capturing paint over-spray – using high fan pressure to lift and atomise booth water for the washing action.

To maintain water level, the booths relied on pressure sensors, but too little water meant the efficiency of the scrubbing process would fall, while too much water led to the fan pressure struggling against the motor power, so dropping the booth exhaust air volume.

Meanwhile, chemical dosing was controlled and monitored using denaturant and flocculent to de-tack the paint and float the particles. However, removing floating paint waste was a manual operation, carried out several times per shift.

Finally, the scrubbing section was highly corroded with clearly visible signs of patchwork repairs.

All that has now been replaced with Delta's Aqua-Cleanse automated paint waste removal system, which separates booth water cleaning from the paint booth operation – transferring it from the two booths to a dedicated area.

Aqua-Cleanse relies on chemical dosing and utilises two stages of treatment: a denaturant fed into the booth water circulation system to convert the paint into non-sticky solid particles; and a flocculent fed into water being pumped from the booth into the system.

To ensure correct dosing, chemical feeds are automated and linked to the operation of the spray applicator so that dosing only occurs when the booth is painting.

The system controls flow of water through a holding tank, which provides a calm-zone that enables the flocculent to adhere to suspended paint solids, and allows solids to float.

With the addition of weirs, the surface flows gently towards a collection chute, with floating paint solids forming an increasingly dense raft of waste. A pneumatically driven scraper blade then removes and deposits the waste into a collection bag.

Separately, because the spray booth scrubbing systems were unfit for repair, the spray booths were converted to Delta's Aqua-Flow booth design, which works with the Aqua-Cleanse system so that the booths do not hold standing water when switched off.

Trotman explains that the modified booths have been arranged back-to-back with an intermediate corridor of 1.5 metres to allow access into the scrubbing chambers.
He also says that the existing large centrifugal exhaust fans were upgraded with new impellers, drives and bearings.

"It was vital that the refurbishment project was completed within the planned schedule, to ensure minimal disruption to production," states Trotman.

"Delta achieved this in a very professional manner and the result has made a significant contribution to maintaining Thwaites' reputation for quality and efficiency."

Brian Tinham

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