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Precision Controlled Bubbling for Colour Change Efficiency in Container Glass.

Grahame Stuart* discusses how careful application of bubbling can assist with colour change efficiency.

Many container glass manufacturers will agree that carrying out a colour change can present problems with prolonged glass defects as the old colour is gradually flushed out of the furnace, working end and forehearths. This is an issue particularly when going from a dark composition to a lighter one and can lead to defects as the colder, darker glass becomes entrained from areas such as the corners of the throat and any areas where there is a transition in depth or glass flow direction. The effects can last a number of days, coming and going as temperatures and pulls are changed.

A 7 Point Precision Control Bubbler Undergoing Final Testing in Electroglass Workshops.

A number of years ago Electroglass were asked to look at the possibility of installing their Precision Controlled Bubbler System (PCBS) in areas of the furnace, throat and working end where dark glasses may stagnate causing the problems already mentioned. At that time the Electroglass Precision Controlled Bubbler System (PCBS) had been employed by glass makers throughout the industry to help improve thermal and chemical homogeneity in many glass types by using single or multiple rows across the hot spot of the furnace. The systems simplicity of operation and proven reliability at slow bubbling rates had found favour with companies looking for ways to employ bubbling without the pitfalls found with conventional continuous and semi continuous systems, namely, increased refractory wear, parasitic bubble entrainment and premature bubbler failure due to blockage. The ability to effectively stop the bubblers for prolonged periods meant that the system could conceivably be employed for applications such as colour change bubbling, where bubbler operation may only be needed for 12-24 hours during the ‘off’ colour period.

Through a combination of physical model testing and experience, Electroglass engineers set about identifying areas where cold glass could accumulate and cause problems during and immediately after a colour change. The first colour change bubbler system was installed by Electroglass’ own in-house hot drilling team in the days leading up to a colour change on a furnace producing 250 tonnes per day of soda-lime glass in various colours for beer and wine bottle production.

Typical Throat Bubbler Installation for Colour Change Purposes.

Bubblers were placed in the throat entry and exit, forehearth entries from the working end and all four corners of the furnace. After installation the bubblers were left switched off in readiness for the ‘off’ colour period during which glass could not be used for production and was simply drained to waste. When ‘off’ colour was reached the furnace operators could switch on individual bubblers and adjust them independently thanks to a PLC control system which allows individual setting of bubble pressure, bubble duration and bubble frequency. Bubblers were then operated until the desired colour could be seen at the spouts, at which time the bubblers were shut down and effectively stopped until the next colour change, when by following an established bubbler start up procedure bubbling could recommence with ease.

The furnace in question runs around 6 colour changes each year and the customer reports that the colour change bubbler system has helped decrease colour change time and losses significantly.
In addition to the systems supplied for furnace colour change there is also scope for installing a similar systems in colouring feeders where the sweeping out of old colour could save many hours improving overall production yield, particularly where frequent colour changes are required.

The special, blockage resistant bubbler injectors designed and manufactured by Electroglass are the key to the system’s continued success. Having the ability to stop bubbling and a PLC control system that allows a start-up procedure to be implemented easily and quickly will no doubt continue to allow the use of bubblers to evolve and meet changing needs of glass makers for many years to come.

Grahame Stuart is Project Sales Engineer at Electroglass Ltd

T: +44 (0)1268 565577

F: +44 (0)1268 565594

4 Brunel Road, Manor Trading Estate,
Benfleet, Essex, SS7 4PS, England