Thwaites green upgrade is picture of efficiency 16 August 2012

Yellow dump truck manufacturer Thwaites' paint line has been successfully refurbished to extend its working life, and improve its efficiency and environmental sustainability.

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 in poor condition.

And he adds that other concerns included increasing operational costs of cleaning and waste disposal.

So Birmingham-based Delta Process Systems was invited to survey the situation and offer solutions.

The two existing manual spray booths had pump-less water-washed exhaust systems for capturing paint over-spray – using high exhaust fan pressure to lift and atomise booth water for the washing action.

To work effectively, the booths relied on pressure sensors to maintain water level. Too little water and the efficiency of the scrubbing process falls; too much water and the fan pressure struggles against the motor power, dropping the booth exhaust air volume.

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

And finally, the scrubbing section of the booth was highly corroded with clearly visible signs of patchwork repairs. Inevitably, the area around the booth was awash with paint waste.

This process 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 is fed into the booth water circulation system to convert the paint into non-sticky solid particles; and a flocculent feeds 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 paint is used in the booth.

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

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

He also says that the re-design of the booth scrubbing chambers improved access for maintenance and cleaning. And he points out that the two 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 to support our many customers in the UK and around the world," 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

Related Companies
Delta Process Systems Ltd

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