William Hughes, the spring, bent wire form and assembly manufacturer, has installed a state-of-the-art, automated passivation plant at its UK headquarters in Stalbridge, Dorset.

According to the company, this will not only reduce the significant lead-time incurred by subcontracting this requirement, but will enable the company to provide another Nadcap process for aerospace customers.

“The decision to start thinking about passivation came about because one of our significant aerospace customers ceased this activity,” explains special processes manager, Shaun Tattershall. “As a result we began investigating various plant options and initiated a request for processing approval from our major aerospace customer.”

Tattershall sourced machinery that was designed and manufactured to William Hughes’ precise requirements and offered optimised control of the process in line with AMS 2700.

“This helped with our forward plan of gaining a Chemical Processing Nadcap accreditation,” he added. “We have also achieved Honeywell approval for passivation, and we appear on their approved processing supplier list.”

With the new passivation plant, there is no manual ‘dunking’ of component baskets from station-to-station, as with traditional systems. Instead, the plant performs ‘fluid transfer’, moving chemical solutions from holding tanks into the main processing unit as required. The entire process is automatic and PLC controlled. Typical treatments are nitric acid/sodium dichromate, and rinse cycles. These are followed by a final rinse in deionised water before a drying cycle.

Other plant functionality includes an ultrasonic passivation facility and a rotary option where parts can be rotated through the solution, thus filling air gaps in more complex and tubular-type components, for example.

“Ultimately the service will be offered to all customers – not just those in the aerospace sector – on a subcontract basis,” concludes Mr Tattershall. “There will be three service levels: standard five-day; express three-day; and super express 24 hours [subject to any testing requirements]. All services are designed to focus on the customer for high quality and fast turnaround. The working envelope size available is 520 x 300 x 200 mm.”

Since installing the passivation plant, William Hughes has relocated its Nadcap-accredited heat treatment and ultrasonic cleaning equipment into the same area, thus creating a brand new process department.